dnv ship rules pt.4 ch.4 - rotating machinery, power transmission

RULES FORCLASSIFICATION OF

SHIPS / HIGH SPEED, LIGHT CRAFT ANDNAVAL SURFACE CRAFT

NEWBUILDINGS

MACHINERY AND SYSTEMSMAIN CLASS

PART 4 CHAPTER 4

ROTATING MACHINERY, POWER TRANSMISSIONJANUARY 2003

CONTENTS PAGE

Sec. 1 Shafting ...................................................................................................................................... 5Sec. 2 Gear Transmissions .................................................................................................................. 18Sec. 3 Clutches .................................................................................................................................... 29Sec. 4 Bending Compliant Couplings ................................................................................................. 31Sec. 5 Torsionally Elastic Couplings .................................................................................................. 33

DET NORSKE VERITAS

Veritasveien 1, N-1322 Høvik, Norway Tel.: +47 67 57 99 00 Fax: +47 67 57 99 11

CHANGES IN THE RULES

General

The present edition of the rules includes additions and amendmentsdecided by the Board in December 2002 and supersedes the January2001 edition of the same chapter.

The rule changes come into force on 1 July 2003.

This chapter is valid until superseded by a revised chapter.Supplements will not be issued except for an updated list ofminor amendments and corrections presented in Pt.0 Ch.1Sec.3. Pt.0 Ch.1 is normally revised in January and July eachyear.Revised chapters will be forwarded to all subscribers to therules. Buyers of reprints are advised to check the updated listof rule chapters printed Pt.0 Ch.1 Sec.1 to ensure that the chap-ter is current.

Main changes

• Sec.1 Shafting

— In items A402 and A403, the documentation requirements anddesign requirements for shaft alignment has been revised andclarified.

— In item B205, Table B1 has been amended with a new safety fac-tor for the reversed stress requirement for shafts.

— Item B306 introduces a calculation formula for minimum diam-eter of fitted bolts.

— Item B901, regarding shaft bearing dimensions, has been mademore specific concerning surface pressure.

— In item E301 TMON has been introduced as a class notation anddocumentation requirements have been updated.

— Sub-section F400, regarding shaft alignment, has been amendedand a new item F404 concerning acceptance criteria has beenadded.

— In item I201 acceptance criteria for vibration measurements onPTO-generators has been clarified.

• Sec.2 Gear Transmissions

— General: The material requirements for forgings have beenaligned with Pt.2 Ch.2 Sec.5.

— In item A201 a NDT-specification has been defined.— A new item B206 concerning expected level of cleanliness on

quenched and tempered steels has been introduced.— A new item B207 concerning expected level of cleanliness re-

garding gears made of special high grade materials has been in-troduced.

— A new item B208 concerning reduced fatigue strength for gearshas been introduced.

— Previous item B801 concerning stress relieving of welded gearcasings has been deleted, since the risk for distortion due to re-lease of residual stresses from welding is low. The remainingitems have been renumbered accordingly.

— In item C201 a flow chart concerning material requirements forgears has been introduced.

• Sec.4 Bending Compliant Couplings

— In item B205 the requirements for universal shafts with powertransmitting welds regarding combination of applied stresses andpermissible defects in the welds has been clarified.

— In item B205 a comment concerning lubrication oil film influ-ence has been removed.

• Sec.5 Torsionally Elastic Couplings

— A new item A203 introduces definitions of stiffness and damp-ing.

— Items B207 and B208 clarify that no interdependence is foreseenbetween permissible stresses for steady state and transient condi-tions.

— In item B305 type testing for determination of permissible powerloss to suit practice has been altered, and a core temperature limitfor silicone has been introduced.

— A new item G103 concerning coupling data with a guidance noteon applicable ambient temperatures has been introduced.

Corrections and Clarifications

In addition to the above stated rule requirements, a number of detect-ed errors, corrections and clarifications have been made in the exist-ing rule text.

Comments to the rules may be sent by e-mail to [email protected] subscription orders or information about subscription terms, please use [email protected] information about DNV and the Society's services is found at the Web site http://www.dnv.com

© Det Norske VeritasComputer Typesetting (FM+SGML) by Det Norske Veritas Printed in Norway

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Rules for Ships / High Speed, Light Craft and Naval Surface Craft, January 2003 Pt.4 Ch.4 Contents –

CONTENTS

SEC. 1 SHAFTING ........................................................... 5

A. General...................................................................................5A 100 Application........................................................................5A 200 Documentation of shafts and couplings ............................5A 300 Documentation of bearings and seals................................5A 400 Documentation of shafting system and dynamics.............6

B. Design .....................................................................................6B 100 General ..............................................................................6B 200 Criteria for shaft dimensions.............................................6B 300 Flange connections............................................................8B 400 Shrink fit connections .....................................................10B 500 Keyed connections ..........................................................11B 600 Clamp couplings .............................................................12B 700 Spline connections ..........................................................12B 800 Propeller shaft liners .......................................................13B 900 Shaft bearings, dimensions .............................................13B 1000 Bearing design details .....................................................13B 1100 Shaft oil seals ..................................................................13

C. Inspection and Testing........................................................13C 100 Certification ...................................................................13C 200 Assembling in workshop.................................................14

D. Workshop Testing ...............................................................14D 100 General ............................................................................14

E. Control, Alarm, Safety Functions and Indication............14E 100 General ............................................................................14E 200 Indications and alarms ....................................................14E 300 Tailshaft monitoring - TMON ........................................14

F. Arrangement........................................................................15F 100 Sealing and protection.....................................................15F 200 Shafting arrangement ......................................................15F 300 Shaft bending moments...................................................15F 400 Shaft alignment ...............................................................15

G. Vibration..............................................................................16G 100 Whirling vibration...........................................................16G 200 Rotor vibration ................................................................16G 300 Axial vibration ................................................................16G 400 Vibration measurements .................................................16

H. Installation Inspection ........................................................16H 100 Application......................................................................16H 200 Assembly.........................................................................16H 300 Shaft alignment ...............................................................17

I. Shipboard Testing ...............................................................17I 100 Bearings ..........................................................................17I 200 Measurements of vibration..............................................17

SEC. 2 GEAR TRANSMISSIONS ................................ 18

A. General.................................................................................18A 100 Application......................................................................18A 200 Documentation................................................................18

B. Design ...................................................................................20B 100 General ............................................................................20B 200 Gearing............................................................................20B 300 Welded gear designs .......................................................20B 400 Shrink fitted pinions and wheels.....................................21B 500 Bolted wheel bodies ........................................................22B 600 Shafts...............................................................................22B 700 Bearings ..........................................................................22B 800 Casing .............................................................................22B 900 Lubrication system..........................................................22

C. Inspection and Testing........................................................23C 100 Certification of parts .......................................................23C 200 Pinions and wheels..........................................................23C 300 Welded gear designs .......................................................26C 400 Ancillaries .......................................................................26C 500 Assembling .....................................................................26

D. Workshop Testing .............................................................. 27D 100 Gear mesh checking........................................................27D 200 Clutch operation..............................................................27D 300 Ancillary systems............................................................27

E. Control, Alarm, Safety Functions and Indication........... 27E 100 Summary .........................................................................27

F. Arrangement....................................................................... 27F 100 Installation and fastening ................................................27

G. Vibration ............................................................................. 28G 100 General ............................................................................28

H. Installation Inspection ....................................................... 28H 100 Application......................................................................28H 200 Inspections ......................................................................28

I. Shipboard Testing .............................................................. 28I 100 Gear teeth inspections .....................................................28I 200 Gear noise detection........................................................28I 300 Bearings and lubrication .................................................28

SEC. 3 CLUTCHES........................................................ 29

A. General ................................................................................ 29A 100 Application......................................................................29A 200 Documentation................................................................29

B. Design .................................................................................. 29B 100 Torque capacities ............................................................29B 200 Strength and wear resistance...........................................29B 300 Emergency operation ......................................................29B 400 Type testing.....................................................................29

C. Inspection and Testing ....................................................... 29C 100 Certification ....................................................................29C 200 Inspection and testing of parts ........................................29

D. Workshop Testing .............................................................. 30D 100 Function testing...............................................................30

E. Control, Alarm and Safety Functions and Indication .... 30E 100 Summary .........................................................................30

F. Arrangement....................................................................... 30F 100 Clutch arrangement.........................................................30

G. Vibration ............................................................................. 30G 100 Engaging operation .........................................................30

H. Installation Inspection ....................................................... 30H 100 Alignment .......................................................................30

I. Shipboard Testing .............................................................. 30I 100 Operating of clutches ......................................................30

SEC. 4 BENDING COMPLIANT COUPLINGS ........ 31

A. General ................................................................................ 31A 100 Application......................................................................31A 200 Documentation................................................................31

B. Design .................................................................................. 31B 100 General ............................................................................31B 200 Criteria for dimensioning................................................31


D. Workshop Testing .............................................................. 32D 100 Balancing ........................................................................32D 200 Stiffness verification .......................................................32

E. Control, Alarm, Safety Functions and Indication........... 32E 100 General ............................................................................32

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Rules for Ships / High Speed, Light Craft and Naval Surface Craft, January 2003Pt.4 Ch.4 Contents –

F. Arrangement ....................................................................... 32F 100 Coupling arrangement .....................................................32

G. Vibration.............................................................................. 32G 100 General ............................................................................32

H. Installation Inspection ........................................................32H 100 Alignment........................................................................32

I. Shipboard Testing............................................................... 32I 100 General ............................................................................32

SEC. 5 TORSIONALLY ELASTIC COUPLINGS ..... 33

A. General ................................................................................ 33A 100 Application......................................................................33A 200 Documentation ................................................................33

B. Design...................................................................................34B 100 General ............................................................................34B 200 Criteria for dimensioning ................................................34B 300 Type testing.....................................................................35


D. Workshop Testing...............................................................36D 100 Stiffness verification .......................................................36D 200 Bonding tests...................................................................36D 300 Balancing ........................................................................36

E. Control, Alarm, Safety Functions and Indication ........... 36E 100 Summary .........................................................................36

F. Arrangement .......................................................................36F 100 Coupling arrangement.....................................................36

G. Vibration..............................................................................36G 100 General ............................................................................36

H. Installation Inspection ........................................................ 37H 100 Alignment........................................................................37

I. Shipboard Testing...............................................................37I 100 Elastic elements...............................................................37

DET NORSKE VERITAS

Rules for Ships / High Speed, Light Craft and Naval Surface Craft, January 2003 Pt.4 Ch.4 Sec.1 –

SECTION 1SHAFTING

A. General

A 100 Application

101 Shafting is defined as the following elements:

— shafts— rigid couplings as flange couplings, shrink-fit couplings,

keyed connections, clamp couplings, splines, etc. (compli-ant elements as tooth couplings, universal shafts, rubbercouplings, etc. are dealt with in their respective sections)

— shaft bearings— shaft seals.

Shafts or couplings made of composite materials are subject tospecial consideration.

Sec.1 also deals with the fitting of the propeller (and impellerfor water jet), shaft alignment and whirling.

102 The rules in this section apply to shafting subject to cer-tification for the purposes listed in Ch.2 Sec.1 A200. However,they do not apply for generator shafts, except for single bearingtype generators, where documentation may be requested uponrequest in case of high torsional vibrations. Furthermore, theyonly apply to shafts made of forged or hot rolled steel. Shaftsmade of other materials will be considered on the basis ofequivalence with these rules.

103 Ch.2 describes all general requirements for rotating ma-chinery, and forms the basis for all sections in Ch.3, Ch.4 andCh.5.

104 Stern tube oil seals of standard design are to be type ap-proved.

A 200 Documentation of shafts and couplings

201 Drawings of the shafts, liners and couplings are to besubmitted. The drawings are to show clearly all details, such asfillets, keyways, radial holes, slots, surface roughness, shrink-age amounts, contact between tapered parts, pull up on taper,bolt pretension, protection against corrosion, welding detailsetc. as well as material types, mechanical properties, cleanli-ness (if required, see B203) and NDT specification, see Ch.2Sec.3 A202. For shafts with a maximum diameter > 250 mm(flanges not considered) that are to be quenched and tempered,a drawing of the forging, in its heat treatment shape, is to besubmitted upon request.

202 Applicable load data is to be given. The load data or theload limitations are to be sufficient to carry out design calcula-tions as described in B, see also Ch.2 Sec.3 A101. This meansas a minimum:

P = maximum continuous power (kW)

or T0 = maximum continuous torque (Nm)n0 = r.p.m. at maximum continuous power.

For plants with gear transmissions the relevant application fac-tors are to be given, otherwise upper limitations (see Ch.3Sec.1 G for diesel engine drives) will be used:

For direct coupled plants (i.e. plants with no elastic coupling orgearbox) the following data is to be given:

τv = nominal vibratory torsional stress for continuous oper-ation in the entire speed range. See torsional vibrationin Ch.3 Sec.1 G300

τvT = nominal vibratory torsional stress for transient opera-tion (e.g. passing through a barred speed range) and thecorresponding relevant number of cycles NC. See tor-sional vibration in Ch.3 Sec.1 G400.

Reversing torque if limited to a value less than T0.

For all kinds of plants the necessary parameters for calculationof relevant bending stresses are to be submitted, see F and G.

A 300 Documentation of bearings and seals

301 Drawings of separate thrust bearings, stern tube bearingsand oil seals are to be submitted. The drawings are to show alldetails as dimensions with tolerances, material types, and (forbearings) the lubrication system. (Drawings of ball and rollerbearings need not to be submitted.) For main thrust bearingsthe mechanical properties of the bearing housing and founda-tion bolts are to be submitted.

If the class notation TMON (tailshaft condition monitoringsurvey arrangement) is applicable, the following additional in-formation is required:

— lubrication oil diagram for the stern tube bearings withidentified oil sampling point and a description of the sam-pling procedure.

302 For all fluid film bearings the maximum permissibleload and maximum permissible operating temperatures with

KA = application factor for continuous

operation 1Tv

T0------+ 1

τv

τ0-----+= =

KAP = application factor for non-frequent peak loads (e.g. clutching-in shock loads or electric motors

KAice = application factor due to ice shock loads (applicable for ice classed vessels), see Pt.5 Ch.1 of the Rules for Classification of Ships

∆KA = Application factor, torque range (applicable to re-versing plants)

As a safe simplification it may be assumed that ∆KA = 2 KA or 2 KAP or 2 KAicewhichever is the highest.

Where:Tv = vibratory torque for continuous operation in

the full speed range (~ 90 - 100% of n0)τv = nominal vibratory torsional stress for continu-

ous operation in the full speed rangeτ0 = nominal mean torsional stress at maximum

continuous powerτmax reversed = maximum reversed torsional stress, which is

the maximum value of (τ + τv) in the entire speed range (for astern running), or τice rev (for astern running) whichever is the highest.

with star-delta switch)Tpeak

T0--------------

τpeak

τ0-------------= =

∆KA

KA P( ) ice( ) τ0 τmax reversed+

τ0------------------------------------------------------------------------=

DET NORSKE VERITAS

Rules for Ships / High Speed, Light Craft and Naval Surface Craft, January 2003Pt.4 Ch.4 Sec.1 –

regard to necessary oil film thickness if applicable is to bespecified.

303 The maximum permissible lateral movements for shaftoil seals are to be specified.

304 Documentation of the manufacturer’s quality controlwith regard to inspection and testing of materials and parts ofbearings and seals is to be submitted upon request.

305 For separate thrust bearings, calculation of smallest hy-drodynamic oil film thickness is to be submitted, see B901.

A 400 Documentation of shafting system and dynamics401 Drawings of the complete shafting arrangement are to besubmitted. Type designation of prime mover, gear, elastic cou-plings, driven unit, shaft seals etc. are to be stated on the draw-ings. The drawings are to show all main dimensions asdiameters and bearing spans, bearing supports and any sup-ported elements as e.g. oil distribution boxes.

If the class notation TMON (tailshaft condition monitoringsurvey arrangement) is applicable, the position of aft stern tubebearing temperature sensor(s) and position and way of electri-cal grounding has to be indicated.

402 Shaft alignment calculations are always to be submittedfor approval for propulsion plants with:

— intermediate shaft diameters of 400 mm or greater for sin-gle screw and 300 mm for twin screw

— gear transmissions with more than one pinion driving theoutput gear wheel, even if there is only one single inputshaft as for dual split paths

— shaft generator or electrical motor as an integral part of thelow speed shaft.

For geared plants, the calculation is only applicable for the lowspeed shaft line.

Upon request shaft alignment calculations may be requiredalso for other plants when considered sensitive to alignment,see also F400.

The shaft alignment calculations are to include the followingitems for all relevant operating conditions, see F402:

— equipment list, i.e. manufacturer and type designation ofprime mover or gear

— input data, including reference to relevant drawings— list of operating conditions data (torque, thrust, submerged

propeller, cold, warm, etc.)— bearing offsets from the defined reference line— calculated bearing loads— bearing reaction influence numbers— graphical view of the shaft deflections with respect to the

defined reference line— graphical view of the shaft bending stresses as a result of

the alignment— difference in slope between shaft and bearing centrelines

in aft sterntube bearing— appropriate acceptance criteria, see F404— verification data with tolerances (e.g. gap, sag and jacking

loads including jack correction factors)— mounting procedure.

403 For all propulsion plants other than listed in 402, only ashaft alignment specification is to be submitted for informa-tion. The shaft alignment specification is to include the follow-ing items:

— bearing offsets from the defined reference line— verification data with tolerances (e.g. gap and sag and

jacking loads including jack correction factors) and condi-tion (cold or hot, submerged propeller, etc.)

404 Calculations of whirling vibration or lateral rotor vibra-tion may be required upon request. Normally this means deter-

mination of natural frequencies.

405 Axial vibration calculations may be required upon re-quest, see also Ch.3 Sec.1 A501 c).

B. Design

B 100 General

101 For design principles see Ch.2 Sec.3 A100. The shaftingis to be designed for all relevant load conditions such as ratedpower, reversing loads, foreseen overloads, transient condi-tions, etc. including all driving conditions under which theplant may be operated.

102 Determination of loads under the driving conditionsspecified in 101 is described in F and G as well as in Ch.3 Sec.1G.

B 200 Criteria for shaft dimensions

201 Shafts are to be designed to prevent fatigue failure andlocal deformation. Detailed criteria are given in ClassificationNote 41.4. Simplified criteria for the most common shaft ap-plications are given in 206, 207 and 208. For shaft sections notcovered by the assumption in 206, 207 and 208, such as shaftsections with high stress combinations in direct coupled plants,the detailed criteria have to be applied.

It is sufficient that either the detailed criteria or the simplifiedcriteria is fulfilled. In addition, the shafts are to be designed toprevent rust or detrimental fretting that may cause fatigue fail-ures, see also 402.

202 The major load conditions to be considered are:

— low cycle fatigue (103 to 104 cycles) due to load variationsfrom zero to full load, clutching-in shock loads, reversingtorques, etc. In special cases, such as short range ferrieshigher number of cycles (~105 cycles) may apply

— high cycle fatigue (>> 3·106 cycles) due to rotating bend-ing and torsional vibration

— ice shock loads (106 to 107 cycles), applicable to vesselswith ice class notations and ice breakers

— transient vibration as when passing through a barred speedrange (104 to 3·106 cycles).

203 For applications where it may be necessary to take theadvantage of tensile strength above 800 MPa and yieldstrength above 600 MPa, material cleanliness has an increasingimportance. Higher cleanliness than specified by materialstandards may be required (preferably to be specified accord-ing to ISO 4947). Furthermore, special protection against cor-rosion is required. Method of protection is to be approved, seeA201.

204 Stainless steel shafts are to be designed to avoid cavities(pockets) where the sea water may remain uncirculated (e.g. inkeyways). For other materials than stainless steel I, II and IIIas defined in Table B3, special consideration applies to fatigue

Table B1 Shaft safety factorsCriteria Safety factor, SLow cycle (NC < 104 stress cycles)

Peak stresses: 1.4Reversed stresses in notches: 1.25

High cycle (NC >> 3·106 stress cycles)

1.6

Transient vibration when passing through a barred speed range:(104 < NC < 3·106 stress cy-cles)

Linear interpolation (logτ-logN dia-gram) between the low cycle, peak stresses criterion with S = 1.4 and the high cycle criterion with S = 1.5. For propeller shafts in way of and aft of the aft stern tube bearing, the bend-ing influence is covered by an in-crease of S by 0.05.

DET NORSKE VERITAS


values and pitting corrosion resistance.

205 The shaft safety factors for the different applications andcriteria detailed in Classification Note 41.4 are to be, at least,in accordance with Table B1.

206 Simplified diameter formulae for plants with low tor-sional vibration such as geared plants or direct driven plantswith elastic coupling

The simplified method for direct evaluation of the minimumdiameters d for various design features are based on the follow-ing assumptions:

— σy limited to 0.7 σB (for calculation purpose only)— application factors KA and KAP ≤ 1.4, i.e. not valid for ice

classes with application factors, KAice above 1.4— vibratory torque Tv ≤ 0.35 T0 in all driving conditions— application factor, torque range ∆KA ≤ 2.7— inner diameters di ≤ 0.5 d except for the oil distribution

shaft with longitudinal slot where di ≤ 0.77 d— protection against corrosion (through oil, oil based coat-

ing, material selection or dry atmosphere).

If any of these assumptions are not fulfilled, the detailed meth-od in Classification Note 41.4 is to be used.

The simplified method results in larger diameters than the de-tailed method. It distinguishes between:

— low strength steels with σB ≤ 600 MPa which have a lownotch sensitivity, and

— high strength steels with σB > 600 MPa such as alloyedquenched and tempered steels and carbon steels with a

high carbon content that all are assumed to have a highnotch sensitivity.

A. Low cycle criterion:

k1 - Factor for different design features, see Table B2.σy - Yield strength or 0.2% proof stress limited to 600 MPa

for calculation purposes only

B. High cycle criterion:

Mb = Bending moment (Nm), due to hydrodynamic forceson propeller, propeller weight or other relevant sourcesfrom the list in F202.

For bending moments due to reactions from T0 as forgear shafts, Mb is to include the KA factor of 1.35.

k2, k3= Factors for different design features, see Table B2.

The higher value for d from A and B applies. However, forshafts loaded in torsion only, it is sufficient to calculate d ac-cording to A.

207 Simplified diameter formulae for stainless steel shaftssubjected to sea water and with low torsional vibration

This simplified method for direct evaluation of minimum di-ameters d for various design features are based on the sameconditions as in 206 except that the protection against corro-sion now is protection against crevice corrosion. This meansthat e.g. keyways are to be sealed in both ends and thus the cal-

culation in 206 applies for such design features. However, forcraft where the shaft is stationary for some considerable time,measures should be taken to avoid crevice corrosion in way ofthe bearings e.g. periodically rotation of shaft or flushing. It isdistinguished between 3 material types, see Table B3. The sim-plified method is only valid for shafts accumulating 109 to 1010

cycles.

d 29 k1 T0

σy------3=

d 17.5 k2 T0

0 32 σy 70+,--------------------------------3 1 k+ 3

Mb

T0-------

2

16---

=

Table B2 Factors k1, k2 and k3

Design feature Torsion only Combined torsion and bendingSpecified tensile strength σB (Mpa) ≤ 600 > 600 ≤ 600 > 600

k1 k1 k2 k2 k3Plain shaft or flange fillet with multiradii design, see B208, Ra ≤ 6.4 1.00 1.00 1.09 1.13 13Keyway (semicircular), bottom radius r ≥ 0.015 d, Ra ≤ 1.6 1.16 1.27 1.43 1.46 8Keyway (semicircular), bottom radius r ≥ 0.005 d, Ra ≤ 1.6 1.28 1.44 1.63 1.66 11Flange fillet r/d ≥ 0.05, t/d ≥ 0.20, Ra ≤ 3.2 1.05 1.10 1.23 1.26 19Flange fillet r/d ≥ 0.08 t/d ≥ 0.20, Ra ≤ 3.2 1.04 1.09 1.21 1.24 18Flange fillet r/d ≥ 0.16 t/d ≥ 0.20, Ra ≤ 3.2 1.00 1.04 1.16 1.18 16Flange fillet r/d ≥ 0.24 t/d ≥ 0.20, Ra ≤ 3.2 1.00 1.03 1.14 1.17 15Flange for propeller r/d ≥ 0.10, t/d ≥ 0.25, Ra ≤ 3.2 1.02 1.06 1.17 1.20 17Radial hole, dh ≤ 0.2 d, Ra ≤ 0.8 1.10 1.19 1.36 1.38 18Shrink fit edge, with one keyway 1.00 1.05 1.15 1.22 34Shrink fit edge, keyless 1.00 1.05 1.13 1.22 28Splines (involute type) 1) 1.00 1.00 1.05 1.10 15Shoulder fillet r/d ≥ 0.02, D/d ≤ 1.1, Ra ≤ 3.2 1.05 1.10 1.21 1.25 22Shoulder fillet r/d ≥ 0.1, D/d ≤ 1.1, Ra ≤ 3.2 1.00 1.03 1.14 1.17 16Shoulder fillet r/d ≥ 0.2, D/d ≤ 1.1, Ra ≤ 3.2 1.0 1.01 1.12 1.15 13Relief groove1), D/d = 1.1, D-d ≤ 2 r, Ra ≤ 1.6 1.00 1.04 1.15 1.17 16Groove1) for circlip, D-d ≤ 2 b, D-d ≤ 7.5 r, Ra ≤ 1.6 1.17 1.28 1.38 1.40 27Longitudinal slot 2) in oil distribution shaft, di ≤ 0.77 d, 0.05 d ≤ e ≤ 0.2 d, (1 − e) ≤ 0.5 d, Ra ≤ 1.6 1.54 1.73

1) applicable to root diameter of notch

2) applicable for slots with outlets each 180° and for outlets each 120°

DET NORSKE VERITAS


A. The low cycle criterion:

k1 - Factor for different design features, see Table B4.

For shafts with significant bending moments:

The formula is to be multiplied with:

B. The high cycle criterion:

Mb = Bending moment (Nm), e.g. due to propeller or impel-ler weight or other relevant sources mentioned in F202.However, the stochastic extreme moment in F301 item2) is not to be used for either low or high cycle criteria.

k3 = Factor for different design features, see Table B4.

The highest value for d from A and B applies.

208 Simplified diameter formulae for shafts in direct coupledplants

The simplified calculation method is limited to shafts with:

— flanges in shafts, of category k = 1.0 (see below), having aflange transition or any other stress raiser with a stressconcentration factor less than 1.05. This may be obtainedby means of a multiradii design such as e.g. starting withr1 = 2.5 d tangentially to the shaft over a sector of 5 de-grees, followed by r2 = 0.65 d over 20 degrees and finallyr3 = 0.09 d over 65 degrees (d = actual shaft diameter)

— inner diameters di < 0.4.d— keyless fitted propellers— keyless fitted shaft couplings— material of at least tensile strength σB of 560 MPa and

yield strength σy of 295 MPa (applicable only to shafts ofcategory k = 1.0)

— the use of carbon or carbon-manganese steel is limited toa specified tensile strength of 600 MPa

— no barred speed range above λ = 0.8 (λ = actual r.p.m./n0).

The shaft diameter d is not to be less than:

P = maximum continuous power (kW)k = factor for design feature:

1.0 for intermediate shafts and propeller shafts in frontof stern tube1.22 for propeller cone and aft stern tube bearing1.15 inside stern tube.

The shaft diameter is also to be designed to fulfil the followingcriteria for torsional vibration.

For continuous operation the vibratory torsional stresses arenot to exceed τ1:

ck = 1.0 for intermediate shafts and propeller shafts in frontof stern tube

0.8 for shafts at keyless shaft couplings

0.8 when k-factor = 1.15

0.55 when k-factor = 1.22

cd = 0.35 + 0.93 d(-0.2)

where d is the actual shaft diameter.

For transient torsional vibration (passing through a barredspeed range) the vibratory torsional stresses are not to exceedτ2:

However, as a simplification permissible transient torsionalstresses τ2 are to be compared with steady state torsional vibra-tion.

B 300 Flange connections

301 In 300 some relevant kinds of flange connections forshafts are described with regard to design criteria. Note that KAin this context means the highest value of the normal- or mis-firing KA and KAP and KAice.

302 Flanges (except those with significant bending such aspinion and wheel shafts and propeller- and impeller fitting) areto have a thickness, t at the outside of the transition to the (con-stant) fillet radius, r, which is not less than:

d = the required shaft diameterr = flange fillet radius.

Table B3 Stainless steel types

Material type Main structureMain alloy elements Mechanical properties

% Cr % Ni % Mo σB σy = σ0.2Stainless steel I Austenitic 16-18 10-14 ≥ 2 500-600 ≥ 0.45 σBStainless steel II Martensitic 15-17 4-6 ≥ 1 850-1000 ≥ 0.75 σBStainless steel III Ferritic-austenitic (duplex) 25-27 4-7 1-2 600-750 ≥ 0.65 σB

Table B4 Factors k1 and k3

A. Low cycle B. High cycle

Design feature2):Stainless Steel 1):

I II and III I, II and IIIk1 k1 k3

Plain shaft 1.00 1.04 14Propeller flange r/d ≥ 0.10 t/d ≥ 0.25 1.04 1.11 19

Shrink fit edge, keylessThe area under the edge is not subject to sea water, thus calcu-lated according to B206

1) According to Table B3

2) Surface roughness Ra < 1.6 applies for all design features

d 29 k1 T0

σy------3=

143---

Mb

T0-------

2+

16---

d 4 T03 1 k3

Mb

T0-------

2+

16---

=

d 100 k Pn0-----

560σB 160+----------------------

3=

τ1

σB 160+

18---------------------- ck cd 1.38 for λ 0.9≥=

τ1

σB 160+

18---------------------- ck cd 3 2 λ2

–( ) for λ 0.9<=

τ2 1.7 τ1

ck

---------=

td

4 1 2 rd---+

2-------------------------------=

DET NORSKE VERITAS


For multiradii fillets the flange thickness is not to be less than0.2 d.

In addition, the following applies:

— recesses for bolt holes are not to interfer with the flange fil-let, except where the flanges are reinforced corresponding-ly

— for flanges with shear bolts or shear pins:

db = diameter of shear bolt or pinσy,bolt = yield strength of shear bolt or pinσy,flange = yield strength of flange

303 Flanges with significant bending as pinion and wheelshafts, and propeller and impeller fittings are to have a mini-mum thickness of:

d = the required shaft diameterr = flange fillet radius.

For multiradii fillets the flange thickness is not to be less than0.25 d. In addition, the following applies:

— recesses for bolt holes are not to interfer with the flange fil-let, except where the flanges are reinforced corresponding-ly

— for flanges with shear bolts or shear pins:

db = diameter of shear bolt or pinσy,bolt = yield strength of shear bolt or pinσy,flange = yield strength of flange

304 Torque transmission based on combinations of ream-fit-ted shear pins or expansion devices and pre-stressed frictionbolts is to fulfil:

A. The friction torque TF is to be at least twice the repetitivevibratory torque Tv, i.e.:

µ = Coefficient of friction, see 307Tv = (KA − 1) T0 for geared plants (for continuous oper-

ation) (Nm)Tv = (KAice − 1) T0 for ice class notations (Nm)

Highest value of Tv in the entire speed range forcontinuous operation (i.e. not transient speed range)for direct coupled plants. See torsional vibration inCh.3 Sec.1 G300 and G400

D = Bolt pitch diameter (mm)Fbolts = The total bolt pre-stress force of all n bolts (N)

Bolt pre-stress limited as in 308.

B. Twice the peak torque Tpeak minus the friction torque (seeA. above) is not to result in shear stresses beyond the shearyield strength ( ) of the n ream fitted pins or expan-sion devices, i.e.:

Tpeak= Higher value of (Nm):

- KA T0 or

- KAice T0 or

- T + Tv in the entire speed range considering also nor-mal transient conditions

D = Bolt pitch diameter (mm)d = Bolt shear diameter (mm)

Guidance note:

Tv in normal transient conditions means with prescribed or pro-grammed way of passing through a barred speed range.

---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

305 Torque transmission based on n flange coupling boltsmounted with a slight clearance (e.g.< 0.1 mm) and tightenedto a specified pre-stress σpre is to fulfil the following require-ments:

— the friction torque is to be at least twice the repetitive vi-bratory torque (including normal transient conditions), see304 A.

— bolt pre-stress limited as in 308— the shear stress τ due to twice the peak torque minus the

friction torque combined with the pre-stress σpre is not toexceed the yield strength σy, i.e.:

τ = Shear stress in bolt,

σpre = Specified bolt pre-stress,

Tpeak= Peak torque, see 304 B.

306 Torque transmission based on ream fitted bolts only, isto fulfil the following requirements:

— the bolts are to have a light press fit— the bolt shear stress due to two times the peak torque, Tpeak

(see 304 B) minus the friction torque, TF is not to exceed0.58 σy

— the bolt shear stress due to the vibratory torque, TV forcontinuous operation is not to exceed σy/8.

This means that the diameter of the n fitted bolts are to fulfilthe following criteria:

and

Ream fitted bolts may be replaced by expansion devices pro-vided that the bolt holes in the flanges align properly.

t12--- db

σy bolt,σy flange,----------------------≥

td

3 1 2 rd---+

2-------------------------------=

t12--- db

σy bolt,σy flange,----------------------≥

TF

µ D Fbolts

2000-------------------------- 2 Tv (Nm)≥=

σy 3( )⁄

2 Tpeak TF

π n D d2 σy

8 103 3⋅

------------------------------- (Nm)≤–

σpre2

3 τ2+ σy≤

calculated as τ8 2 Tpeak TF–( )10

3

D π n d2

--------------------------------------------------=

calculated as σpre

4 Fbolts

π n d2

-------------------=

d 662Tpeak TF–

nDσy------------------------------≥

d 143TV

nDσy--------------≥

DET NORSKE VERITAS


Guidance note:Ream fitted bolts with a light press fit means that the bolts whenhaving a temperature equal to the flange, cannot be mounted byhand. A light pressing force or cooling should be necessary.


307 Torque transmission based on only friction betweenmating flange surfaces is to fulfil a minimum friction torque of2 T0 KA. The coefficient of friction, µ is to be 0.15 for steelagainst steel and 0.12 for steel against nodular cast iron. Othervalues may be considered for especially treated mating surfac-es. The bolt pre-stress is limited as given in 308.

D = Bolt pitch diameter (mm) Fbolts = The total bolt pre-stress force of all n bolts

308 Bolts may have a pre-stress up to 70% of the yieldstrength in the smallest section. However, when using 10.9 or12.9 bolts the thread lubrication procedure has to be especiallyevaluated, and only tightening by twist angle or better is ac-cepted (e.g. by elongation measurement). If rolled threads, thepre-stress in the threads may be increased up to 90% of theyield strength.

In corrosive environment the upper acceptable material tensilestrength is 1350 MPa.

These percentages are given on the condition that the peakservice stresses combined with the pre-stress do not exceed theyield strength. The bolts are to be designed under considera-tion of the full thrust and bending moments including revers-ing. For bending moments on water jet impeller flanges, seeF301 item 2.

The length of the female threads are to be at least

0.8 d σybolt/σyfemale

where d is the outside thread diameter and the ratio compen-sates for the difference in yield strength between the bolt andthe female threads.

B 400 Shrink fit connections401 Torque transmission based on shrink fitting (by oil in-jection or by heating) is to fulfil a minimum slippage safetyfactor S based on the peak torque Tpeak, in the entire speedrange i.e.:

Friction torque, TF ≥ S Tpeak

TF - Friction torque, see 405S - Safety factor, see Table B5Tpeak - Peak torque, see 304 B. However, in this context the

Tpeak is not to be assumed less than 1.4 T0. For thepurpose of calculating the slippage safety, the Tvwith malfunctioning speed control or erroneoushandling is to be considered. This means that thesteady state peak amplitude is to be considered.

If the shrunk-on part is subjected to high speeds (e.g. tip speed> 50 m/s), the influence of centrifugal expansion may have tobe considered.

If the connection is subjected to an axial force, the axial force

FA (N) is to be combined with the peak torque Tpeak (Nm) toan equivalent torque Teq for use in the criterion above as:

Friction torque, TF ≥ S Teq

FA - Axial forces, are to be considered as follows:

a) At full power:

— the thrust, may be calculated as 6 Tpeak/Hm(peak)— the axial force component due to shrinkage pres-

sure at the taper— the nut force may be disregarded.

b) At a barred resonance:

— the actual thrust, may be calculated as 6 T/Hm(res)— the axial force component due to shrinkage and the

nut force are considered to balance each other out,after the initial minor slippage

T - Mean torque at resonance (Nm)Hm - Mean propeller pitch (m)DS - shrinkage diameter (mm). For tapered connections the

average diameter is to be used.

The taper is normally not to be steeper than 1:20. However, ta-per of cone as steep as 1:15 is acceptable, provided that a morerefined mounting procedure and/or a higher safety factor thangiven in the Rules are applied.

The coefficient of friction for oil injection is to be taken as 0.14when steel-steel and 0.13 when steel-bronze. For hot shrinkageit is to be taken as 0.15 when steel-bronze and otherwise ac-cording to Table B2 in Sec.2. If glycerine replaces oil, and sur-faces are carefully degreased, the coefficient of friction may beincreased by 0.04.

402 Fretting under the ends of shrink fit connections has tobe avoided in general. However, very light fretting is account-ed for by notch factors see Classification Note 41.4 item 6.5.

In particular for a shrinkage connection with a high length todiameter ratio (>1.5) or if it is subjected to a bending moment,special requirements may apply in order to prevent fretting ofthe shaft under the edge of the outer member. This may be arelief groove or fillet, higher surface pressure, etc.

If the surface pressure at the torque end times coefficient offriction is higher than the principal stress variation at the sur-face, σ < p µ (see Fig.2 in Sec.2), fretting is not expected. Oth-er surface pressure criteria may also be considered. If suchsurface pressure or friction cannot be achieved, it may be nec-essary to use a relief or a groove.

Guidance note:The groove may be designed as indicated below:

A good choice is D = 1.1 d and r = 2 (D − d) and an axial over-shoot at near zero but not less than zero.

Other ways of preventing fretting under the edge of the hub are arelief groove in the hub or a tapered hub outer diameter. Howev-

Table B5 Safety factors for shrink fit connectionsApplication Safety factor, SInboard couplings 1.8Propeller mounting at sea water tem-perature of 35°C 1)

2.0 for normal operation1.8 for inadvertent operation

1) The safety factor is selected due to uncertainties in friction coefficient and pull up as well as in order to prevent fretting. Since inadvertent op-eration is considered rare, a lower safety factor than for normal condi-tions is required.

2 T0 KA

µ D Fbolts

2000-------------------------- (Nm)≤

Teq Tpeak2 FA DS

2000----------------

2+=

DET NORSKE VERITAS


er, these alternatives need to be documented by means of detailedanalysis as e.g. finite element method calculations.


403 For tapered connections where a slippage may cause arelative axial movement between the two members, the axialmovement is to be restricted by a nut secured to the shaft, orequivalent.

404 The permissible stress due to shrinking for the outermember (index “o”) depends on the nature of the applied load,coupling design and material. For ductile steels the equivalentstress (von Mises) may be in the range 70% to 80% of the yieldstrength σyo for demountable connections and 100% and evensome plastification for permanently fitted connections (see410). For propellers the limit is 70% and calculated for a tem-perature of 0°C.

The permissible stress due to shrinking at the outer diameter orat any other critical section (e.g. axial and radial bore intersec-tion) of the inner member (i.e. the shaft, index “i”) is not to ex-ceed 50% of the yield strength σyi.

405 The friction torque TF (Nm) is calculated as:

DS = see 401LS = length of shrinkage connection (mm)µ = coefficient of friction, see 401pmin = shrinkage pressure (MPa) due to minimum shrinkage

amount ∆Dmin (mm), see 407.

406 The shrinkage amounts are to be calculated under con-sideration of the surface roughness as follows:

∆Dmin = minimum shrinkage amount due to tolerances or pull-up distance minus

0.8 (Rzi + Rzo) ≈ 5 (Rai + Rao) (mm)

∆Dmax = maximum shrinkage amount due to tolerances orpull-up distance minus

0.8 (Rzi + Rzo) ≈ 5 (Rai + Rao) (mm).

The lower value is to be used for calculation of the requiredfriction torque. The upper value is to be used for calculation ofstresses in the inner and outer members. For tapered connec-tions the shrinkage amounts are to be converted to pull uplengths (Pull-up distance = ∆D . Taper of cone).

407 The following applies for shrinking within the elasticrange and both inner and outer member made of steel. Theminimum and maximum shrinkage pressures are:

pmin = (∆Dmin/DS) (E/K)

pmax = (∆Dmax/DS) (E/K)

E = 2.05 · 105 MPaK = (1 + Qi

2)/(1 − Qi2) + (1 + Qo

2)/(1 − Qo2)

Qi = inner diameter of inner member/DSQo = DS/outer diameter of outer member

The stress in the outer member is:

The stress calculation of the inner sleeve is to take any expan-sion sleeve or compression liner influence into account.

For permissible values see 404.

408 The minimum and maximum shrinkage amounts are tobe correlated to the measurement that is to be applied for veri-fication. For elements with constant external diameter, diamet-

rical expansion is preferred. Otherwise the pull up length (wetmounting) or the push up force (dry mounting) are to be spec-ified. The clearance of an intermediate sleeve is also to be con-sidered.

409 Tapered connections are to be made with an accuracysuitable to obtain the required contact between both members.For propeller mounting the minimum contact on the taper is70% when using toolmaker’s blue. There is to be a full contactband at the upper end. The same requirements also apply tocouplings unless otherwise approved.

410 The following applies to shrinking with a certain amountof plastification in the outer member applicable to parts that arenot intended to be disassembled. The simplified approach giv-en here is valid for both members being made of steel and solidinner member. If these conditions are not fulfilled, a more de-tailed analysis applies.

As specified in 404 the stresses in the inner member (shaft) dueto shrinking are not to exceed 50% of the yield strength σyi.Thus the shrinkage pressure is limited to:

pi lim = σyi /√3

In order to keep a safety factor of 1.25 versus full plastificationof the outer member the shrinkage pressure is limited to:

po lim = 1.6 σyo /√3 for Qo < 0.368

po lim = -1.6 ln(Qo) σyo /√3 for Qo > 0.368

The extent of permissible plastification ζp (i.e. the ratio be-tween the outer diameter of the plastified zone and DS) is lim-ited by 2 criteria:

1) 2 ln(ζp) − (Qo ζp)2 + 1 = √3 pp/σyo

where pp is the permissible shrinkage pressure and is the small-er value of po lim and pi lim.

2) ζp = (0.7 Qo2 + 0.3)1/2 / Qo in order to limit the plastified

cross section area to 30% of the full cross section.

The actual minimum and maximum extents of plastificationare calculated as:

ζmin, max = 0.931 (E/σyo)1/2 (∆Dmin, max/DS)1/2

ζmin is used to calculate the minimum shrinkage pressure as:

pmin = σyo (1 + 2 ln(ζmin) - (Qo ζmin)2)/√3

ζmax is not to exceed the permissible value ζp.

B 500 Keyed connections

501 Keyed connections are only suitable for unidirectionaltorque drives with low torque amplitudes and insignificantbending stresses. Conditionally, keyed connections may beused also for dual directional torque drives (see 503).

The following items are to be checked:

— shrinkage pressure to avoid detrimental fretting, see 502— shear stress in the key, see 503— surface pressure at shaft keyway side, hub keyway side

and key side, see 503— fatigue strength of the shaft, see 200— strength of hub, see 504— intersection with other notches, see 505.

Tapered connections are not to be steeper than 1:12. However,taper of cone as steep as 1:10 is acceptable, provided that amore refined mounting procedure and/or a higher safety factorthan given in the rules are applied.

502 In order to avoid detrimental fretting on the shaft underthe edge of the hub, there is to be a certain minimum interfer-ence fit between shaft and hub. For key connections subjectedto bending moments a rather tight fit is required. The criteriaare given in 402 and Classification Notes 41.4 item 6.5. Forkey connections transmitting torque only, there is to be a min-imum interference fit (friction torque) that corresponds to the

TF

π DS2 LS µ pmin

2000------------------------------------------- (Nm)=

3 Qo4

+ pmax

1 Qo2

–-------------------------------------

DET NORSKE VERITAS


applicable vibratory torque for continuous operation with asafety factor of 2.0. This means a friction torque:

TF ≥ 2.0 TV

that may be approximated as the highest value of:

— 2 (KA − 1) T0 for geared plants— 2 (KAice – 1) T0 for plants with ice class— 2 Tv for direct coupled plants.

When calculating shrink fit pressures between cylindricalmembers with one or two keyways, the real pressure is lessthan the calculated due to relief caused by the keyways. Thisinfluence may be approximated by a reduction factor of 0.8.With these assumptions and solid shaft with steel hub the nec-essary amount of shrinkage ∆d (mm) is:

∆d = TF/(128 d L µ (1 − (d/D)2))

∆d = shrinkage amount (mm) estimated as minimumamount due to specified tolerances or pull-up distanceminus 0.8 (Rz-shaft+ Rz-hub) ≈ 5 (Ra-shaft + Ra-hub)

d = shaft diameter (mm)D = outer diameter of hub (mm)L = hub length (mm)µ = coefficient of friction (0.15 may be used)Ra = surface roughness (mm) for shaft and hub, respective-

ly.

For tapered connections the minimum friction torque is to beprovided by means of either a specified push up force or aspecified pull up length. The latter is to be consistent with ∆dabove. However, if test pull-up is carried out, the subtractionof the surface roughness term may be omitted.

503 The key shear stress and the surface pressures in theshaft and hub keyways, respectively are calculated on the basisof the applied repetitive peak torque Tpeak (see 304 B) minusthe actual friction torque TF according to 502. Furthermore, theuneven distribution of the load along a key with a length be-yond Leff/d = 0.5 is considered empirically.

Shear stress in key:

τ = (Tpeak − TF/S) 2000 (1 + 0.25 (Leff/d − 0.5))/d Leff b i

Side pressure (for contact with shaft and hub):

σ = (Tpeak − TF/S) 2000 (1 + 0.25 (Leff/d − 0.5))/d Leff heff i

Leff = effective bearing length of the key (mm)b = width of key (mm)i = number of keys, if 2 keys use i = 1.5heff = effective height of key contact with shaft and hub, re-

spectively i.e. key chamfer and keyway edge roundingconsidered.

Permissible shear stress in key: 0.3 fd times the yield strengthof the key material.

Permissible side pressures: 1 fS fd times the respective yieldstrengths.

fd = torque direction factor.

For unidirectional torque fd = 1.

For dual directional torque with 103 to 104 reversals fd= 2/3.

For 106 or more reversals fd = 1/3.

fS = support factor.

fS = 1 for the key

fS = 1.2 for the shaft

fS = 1.5 for the hub

For plants with torque reversals the key is to have a tight side-

ways fit in both shaft and hub.

504 The tangential stresses in the hub when calculated as anideal cylindrical member with the maximum amount of shrink-age due to tolerances is not to exceed 35% of the yield strengthfor steel. For bronze or austenitic steel 45% are permitted.

For tapered connections the dimensions at the upper end are tobe used.

For calculation of stresses see 406 and 407.

505 If a keyway intersects with another notch such as a di-ameter step, the semicircular part of the end should be placedfully into the shaft part with the larger diameter. If the semicir-cular end coincides with the fillet in the diameter step, a com-bination of stress concentrations is to be considered.

506 For propeller fitting the contact between hub and shaft isto be at least 70% with a full contact band at the upper end,when using toolmaker’s blue.

For tapered couplings at least a full contact band at the upperend is required.

B 600 Clamp couplings

601 Clamp couplings are to be fitted with a key that fulfilsthe requirements in 500. For couplings transmitting thrust, anaxial locking device is to be provided.

602 The clamp coupling bolts are to be tightened so that thecoupling friction torque TF as specified in 502 is obtained.

603 The maximum bolt stress when the peak torque (see302) is applied is not to exceed 2/3 of the bolt yield strength.

604 The hub stress determined in a simplified way as the boltpre-stress divided by the hub length times minimum hub thick-ness at the keyway, is not to exceed 40% of the yield strengthof the hub material.

B 700 Spline connections

701 Spline connections are to be designed with regard toflank surface duration, shear strength and to avoid fretting (un-less life time requirements allow for some). Items 702 and 703only concern the splines, the shaft strength is dealt with in 200.

702 Spline connections are normally to be “fixed”, i.e. hav-ing no axial movements in service. “Working” splines (whichmove axially in service) will be especially considered. Splinesfor normal applications are to be flank-centred and withoutbacklash (light press fit). Tip centring and backlash is only ac-ceptable for connections which have no reversed torques inany operation mode.

703 The following calculation procedure may be used forspline connections provided:

— Involute “half depth” splines with 30° pressure angle.(“half depth” means common tooth height equal one mod-ule).

— Mainly torque transmission, i.e. no significant additionalsupport force. In the case of e.g. an external gear meshforce the outer member is to be supported at each end ofthe splines and the support is to be a tight fit. Otherwisespecial considerations shall be taken.

— The length to diameter ratio of the splines is to be so thattorsional deflections or bending (due to external forces)deflections corresponding to a misalignment beyond 1 mi-cron per mm spline length are avoided.

— Flank alignment tolerance is to be 0.5 micron per mmspline length for each of the male and female members.

Flank pressure criterion:

l d2 > 6000 KA T0 / HV

Shear stress criterion:

l d2 > 104 KA T0 / σy

DET NORSKE VERITAS


l = the spline length (mm)d = the pitch diameter (mm)HV = the flank hardness of the softer memberσy = the yield strength of the core material (minimum of the

two members)

B 800 Propeller shaft liners801 Bronze liners are to be free from porosities and other de-fects and are to be designed and produced to withstand a hy-draulic pressure of 2 bar without showing cracks or leakage.

802 The liner thickness in way of bearings is not to be lessthan:

t = (d + 230)/32 mm

Between bearings the thickness of a continuous liner is not tobe less than 0.75 t.

803 If a continuous liner is made of several lengths, the join-ing of the pieces is to be made by fusion through the wholethickness of the liner before shrinking. Such liners are not tocontain lead.

804 If a liner does not fit the shaft tightly between the bear-ing portions, the space between the shaft and the liner is to befilled with a plastic insoluble non-corrosive compound.

805 Liners are to be shrunk upon the shaft by heating or hy-draulic pressure, and they are not to be secured by pins.

806 Liners are to be designed to avoid water gaining accessto the shaft, between the end of the liner and the propeller hub.

B 900 Shaft bearings, dimensions901 Radial fluid bearings are to be designed with bearingpressures and hydrodynamic oil film thickness suitable for thebearing metals.

For aft stern tube bearings the nominal surface pressure (pro-jected area) is to be below 8 bar for all running conditions in-cluding on turning gear.

For other shaft bearings the nominal surface pressure is to bebelow 12 bar when running in the lower speed range includingon turning gear and 18 bar when running in the upper speedrange.

For shaft bearings with significant pressure (>12 bar) in plantsoperating at very low speeds (e.g. electric drives or long termrunning on turning gear), hydrostatic bearings may be re-quired.

These surface pressures apply to white metal lined bearings.For other lining metals or rubber, reinforced resins, etc., thepermissible surface pressures are to be especially considered,

but normally not to exceed those for white metal.

For separate thrust bearings the smallest hydrodynamic oilfilm thickness, taking into consideration the uneven load dis-tribution between the pads, is to be larger than the sum of theaverage surface roughness of the thrust collar and pad (Ra,collar+ Ra,pad).

902 The length of the aft stern tube bearing is to be chosen toprovide suitable damping of possible whirling vibration. Thismeans that the length is not only to be chosen with regard tothe nominal surface pressure, but also result in a certain lengthto diameter ratio.

903 Ball and roller bearings are to have a minimum L10a(ISO 281) life time that is suitable with regard to the specifiedoverhaul intervals. The influence of the lubrication oil filmmay be taken into account for L10a, provided that the necessaryconditions, in particular cleanliness, are fulfilled.

B 1000 Bearing design details

1001 Stern tube bearings are to be provided with grooves foroil, air and possible accumulation of dirt. Pipes and cocks forsupply and draining of oil and air are to be fitted.

1002 Water lubricated bearings are to be provided with lon-gitudinal grooves for water access.

B 1100 Shaft oil seals

1101 Shaft oil seals are considered on the basis of field expe-rience or alternatively, extrapolation of laboratory tests or pre-vious design.

C. Inspection and Testing

C 100 Certification

101 Regarding certification schemes, short terms, manufac-turing survey arrangement (MSA) and important conditions,see Ch.2 Sec.2.

102 All shafts, coupling hubs, bolts, keys and liners are to betested and documented as specified in Table C1 if not other-wise agreed in a MSA.

103 If the manufacturer’s quality control system (see A304)is approved without remarks, the bearings and oil seals are tobe delivered with the manufacturer’s certificates including ref-erence to the approval. If additions to the manufacturer’s in-spection and testing plans are required, the surveyor is to carryout those items as specified.

DET NORSKE VERITAS


C 200 Assembling in workshop

201 For shafts, hubs and liners that are assembled at the man-ufacturer’s premises, the following is to be verified in the pres-ence of a surveyor:

a) Liners mounted on the shaft with regard to tightness (ham-mer test) and that any specified space between shaft andliner is filled with a plastic insoluble non-corrosive com-pound.

b) Shrink fit couplings mounted on the shaft with regard tothe approved shrinkage amount (diametrical expansion,pull up length, etc.). For tapered connections the contactbetween the male and the female part is to be verified asspecified and approved.

c) Bolted connections with regard to bolt pretension.

d) Keyed connections with regard to key fit in shaft and hub.

202 Shafts for gas turbine applications, high speed side, areto be dynamically balanced.

D. Workshop Testing

D 100 General

101 Not required.

E. Control, Alarm, Safety Functions and Indica-tion

E 100 General

101 The requirements in E are a summary, applicable toshafting. For further details, see Ch.9.

E 200 Indications and alarms

201 Oil lubricated fluid film bearings are to be fitted with ei-ther local or remote oil temperature indication including indi-cation of the permissible maximum. For shafting transmitting10 MW or more, high temperature alarm is to be provided.

202 A low level alarm on stern tube lubricating oil gravitytank is to be provided. In case of forced lubrication, alarm forlow oil pressure or oil flow is to be provided and the lubricatingoil tank is to be provided with low level alarm.

E 300 Tailshaft monitoring - TMON

301 When the following design requirements are fulfilled,the class notation TMON (tailshaft condition monitoring sur-vey arrangement) may be obtained, see also Pt.7 Ch.2 Sec.4 ofthe Rules for Classification of Ships:

— the stern tube bearings are oil lubricated— high temperature alarm is fitted on aft stern tube bearing

(2 sensors or one easily interchangeable sensor located inthe bearing metal near the surface, in way of the area ofhighest load, which normally will be the bottom area (5 to7 o’clock) in the aft third of the bearing)

— where one interchangeable sensor is fitted one spare sen-sor is to be stored on board

— the setting of the stern tube high temperature alarm is nor-mally not to exceed 65°C. Higher alarm set point may beaccepted upon special consideration

— the sealing rings in the stern tube sealing box must be re-placeable without shaft withdrawal or removal of propel-ler

— arrangement for bearing wear down measurement is fitted— electrical grounding of the shafting is mandatory— the system must allow representative oil samples to be tak-

en for analysis of oil quality under running conditions. Lo-cation where samples are to be taken shall be clearlypointed out on system drawing and test cock to be fitted

Table C1 Requirements for documentation and testingPart Product

certificateChemical com-

position(ladle analysis)

Mechanical properties

Ultrasonic testing

Crack detection 1)

Hydraulic testing

Visual and dimensional

check 2)

Shafts 3) 7) for propul-sion when torque > 100 kNm

NV W NV W NV - NV

Other shafts 3) 7) for pro-pulsion

NV W W W W - NV

Shafts 3) in thrusters and gear transmissions

- W W W W - W

Rigid couplings for pro-pulsion when torque > 100 kNm

NV W NV W W - NV

Other rigid couplings and rigid couplings in thrusters and gear trans-mission

- W W W W - W

Keys, bolts and shear pins

- TR TR - - - W4)

Propeller shaft liners W - - W5) W6) -1) By means of magnetic particle inspection or dye penetrant. To be carried out in way of all stress raisers (fillets, keyways, radial holes, shrinkage surfaces

etc.), If especially required due to nominal stress levels, also the plain parts are to be crack detected. No cracks are acceptable, see Ch.2 Sec.3 A202.

2) The visual inspection by the surveyor is to include checking of all stress raisers (see above) with regard to radii and surface roughness, and for plain por-tions, the surface roughness. It is also to include the shaft’s protection against corrosion, if this is provided prior to installation onboard. Dimensional inspection to be done in way of shrinkage surfaces (actual shrinkage amount or individual dimensions are to be documented).

3) Any welds to be NDT checked in the presence of the surveyor and documented with NV certificate.

4) Can be omitted for keys, bolts and shear pins in reduction gears and thruster. Can also be omitted for friction bolts of standard type.

5) In way of fusion between pieces.

6) Test pressure 2 bar.

7) However, not applicable for rotor shafts in generators providing electric power for propulsion.

DET NORSKE VERITAS


with signboard. A written procedure for how to take oilsamples shall be submitted.

Guidance note:See also Classification Note 10.1 Appendix G. Guideline forstern tube lubrication oil analysis.


302 A test kit for monitoring of possible water content in thestern tube lubricating oil is to be provided on board. The testkit shall be able to detect water contents up to 15% by volume.However, the water content is normally not to exceed 2%.

303 Oil lubricated propeller shafts with roller bearings ar-ranged in the stern tube may be granted TMON see also Pt.7Ch.2 Sec.4 of the Rules for Classification of Ships. Additionalrequirements for such arrangements are:

a) The bearing temperature is to be monitored. Two sensors(or one sensor easily interchangeable at sea) are to be fit-ted. Temperature alarm level should normally not exceed90°C.

b) Vibration monitoring is required for roller bearings. Hand-held probes are not accepted; magnetic, glue, screwmountings or equivalent are compulsory.

c) Vibration signal is to be measured as velocity or accelera-tion. Integration from acceleration to velocity is allowed.

d) The vibration analysis equipment must be able to detectfault signatures in the entire frequency range for the mon-itored bearing. A reference level under clearly defined op-erational conditions is to be established. The referencelevel shall be used as basis for establishing an alarm level.

e) For podded propulsors (where the propeller shaft is a partof the electrical motor rotor) all roller bearings for the pro-peller shafting are to be monitored with both oil tempera-ture sensors and vibration monitoring.

f) The water contents is normally not to exceed 0.5%.

F. Arrangement

F 100 Sealing and protection101 A shaft sealing is to be provided in order to prevent wa-ter from gaining access to the internal spaces of the vessel.

102 A sealing is to be provided to prevent water from gainingaccess to steel shafts, unless approved corrosion resistant ma-terial is used.

103 Inboard shafts (inside the inner stern tube seal) are to beprotected against corrosion. Depending on the ambient condi-tions, this may be provided by oil based coating, paint, or sim-ilar.

F 200 Shafting arrangement201 The machinery and shafting are to be arranged so thatneither external nor internal (self generated) forces can causeharmful effects to the performance of the machinery and shaft-ing.

202 The shafting system is to be evaluated for the influenceof:

— thermal expansion — shaft alignment forces— universal joint forces— tooth coupling reaction forces— elastic coupling reaction forces (with particular attention

to unbalanced forces from segmented elements)— hydrodynamic forces on propellers— ice forces on propellers, see Pt.5 Ch.1 of the Rules for

Classification of Ships

— hydrodynamic forces on rotating shafts:

i) outboard inclined propeller shafts or unshielded im-peller shafts, see 301 1)

ii) mean thrust eccentricity caused by inclined waterflow to the propeller, see 301 1)

(Normally applicable to HS, LC and NSC)— thrust eccentricity in water jet impellers when partially air

filled or during cavitation, see 301 2)— forces due to movements of resiliently mounted machin-

ery (maximum possible movements to be considered)— forces due to distortion or sink-in of flexible pads.

F 300 Shaft bending moments

301 The shaft bending moments due to forces from sourcesas listed in 202 are either determined by shaft alignment calcu-lations, see 400, whirling vibration calculations, see G100, orby simple evaluations. However, two of the sources in 202need further explanations:

1) The hydrodynamic force F on an outboard shaft rotating ina general inclined water flow may be determined as

F = 0.87 · 10-4 η v n d2 sinα (N/m shaft length)

d = shaft diameter (mm)n = r.p.m. of the shaftv = speed of vessel (knots)α = angle (degrees) between shaft and general water

flow direction (normally to be taken as parallel tothe bottom of the vessel)

η = “efficiency” of the circulation around the shaft. Un-less substantiated by experience, it is not be takenless than 0.6.

In order to determine the bending moments along the shaftline of an outboard shaft (as well as at the front of the hub),the bending moment due to propeller thrust eccentricity isto be determined e.g. as:

Mb = 0.074 α D T/H (Nm)

D = propeller diameter (m)T = torque (Nm), which may be taken as the rated

torque if low torsional vibration levelH = propeller pitch (m) at 0.7 radius

The bending moment due to the (horizontal) eccentricthrust should be directed to add to the bending momentdue to the hydrodynamic force F in the first bearing span.

2) The stochastic bending moment due to thrust eccentricityin a water jet impeller during air suction or cavitation isbased on the worst possible scenario:50% of the normal impeller thrust (FTH in N) applied at thelower half of the impeller, resulting in a bending momentas:

Mb = 0.1 FTH D (Nm)D = the impeller diameter (m).

F 400 Shaft alignment

401 The shaft alignment is to evaluate bending moments andbearing reactions along the shaft line that is to be considered.For geared plants the shaft line is to include the output gearshaft radial bearings. For direct coupled plants the shaft line isto include at least 3 engine bearings (calculations will only re-flect the correct bearing reactions in the two aft of those). Thetolerances in the alignment specification have to correlate withthe tolerance ranges used in the calculations. Normally, theverification of the alignment is to be carried out afloat and maybe required to be carried out at several conditions. In specialcases also verification in running condition by means of straingauges and proximity transducers may be required.

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402 The shaft alignment has to reflect combinations of thefollowing conditions as applicable:

— alignment condition (during erection of shafting)— light ballast and full draught— cold, not running— hot, not running— hot running (MCR)— all relevant combinations of multi engine operation.

Note that e.g. a combination of hot running (MCR) with lightballast may influence the hydrodynamic propeller loads.

403 The shaft alignment has to take into consideration the ef-fects of the following items where appropriate:

— design principles defined in Pt.4 Ch.2 Sec.3 A100— hydrodynamic propeller loads (horizontal and vertical

force and bending moment)— hull and structure deflections (caused by e.g. tank fillings,

heated tanks in double bottom)— thermal rise of machinery components — angular working position in bearings (as a result of applied

forces in both horizontal and vertical plane)— sterntube bearing weardown— load distribution within sterntube bearings— bearing clearances— buoyancy of propeller.

For some of the effects listed above, the calculations are to bemade with certain tolerances in order to cover for their uncer-tainties.

404 The shaft alignment has to fulfil the following accept-ance criteria for all relevant operating conditions in F402:

— maximum bending stresses in shafts as limited by the shaftcriteria

— acceptance criteria defined by manufacturer of primemover, e.g. limits for bearing loads, bending moment andshear force at flange

— acceptance criteria defined by the manufacturer of thegearbox, e.g. limits for output bearing loads includingtheir maximum difference

— journal positions in gear output bearings (that influence onthe tooth faceload distribution)

— maximum and minimum bearing loads defined by bearingmanufacturer and B901 (zero or very low loads may havean influence on whirling)

— slope in aft sterntube bearing should normally not exceed50% of the bearing clearance (otherwise to be compensat-ed with slope bore)

— tolerances for gap and sag less than 5/100 mm are not ac-cepted

— angular working positions in bearings having longitudinaloil grooves.

G. Vibration

G 100 Whirling vibration101 Calculation of whirling vibration (when required, seeA404) is normally restricted to determination of natural fre-quencies. In special cases also forced whirling may be re-quired.

102 Calculations are normally to be made as parameter stud-ies. Important but uncertain parameters as stiffness of aft sterntube bearing, resulting bearing load position, bearing load dis-tribution over length (if calculating with distributed bearing re-action), entrained water on propeller, etc. are to be variedwithin their probable range and natural frequencies to be pre-sented as corresponding graphs.

103 Resonance in propeller blade frequencies near the upper

operating speed should be avoided. However, exceptions maybe made when the vibration mode and the bearing design is sothat a heavy damping is expected e.g. high bearing length to di-ameter ratio combined with a bouncing vibration mode.

104 Resonance with the shaft speed (1st order forward whirl)is to have a separation margin of at least 30% to the operatingspeed range.

G 200 Rotor vibration

201 Rotor means an assembly of a unit and the couplings andshafts, e.g. a power take off (PTO) driven shaft generator.

202 Resonance of the 1st order is normally to have a separa-tion margin of at least 30% to the operating speed range.

G 300 Axial vibration

301 Axial vibration calculations (when required) are to takethe thrust bearing stiffness into consideration, see also Ch.3Sec.1 A501 c) and G500.

G 400 Vibration measurements

401 If vibration measurements are required, the type of in-strumentation, location of pick ups, signal processing methodand the measurement program are to be agreed with the Soci-ety.

H. Installation Inspection

H 100 Application

101 The requirements in H apply to inspection of installationof shafts, couplings and bearings in propulsion plants. Regard-ing compliant couplings, see Sec.4 and Sec.5. Unless other-wise stated, a surveyor is to attend the inspections given in H.

H 200 Assembly

201 Flange connections are to be checked with regard to:

— ream fitted bolts, light press fit— friction bolts, pre-stress by bolt elongation.

202 Clamp couplings are to be checked with regard to tight-ening of the bolts. Unless otherwise approved, this is to bemade by measuring elongation (applicable for through bolts).

203 Keyed connections are to be checked with regard to:

— shrinkage amount between hub and shaft (applicable to cy-lindrical connections)

— contact between male and female tapered members, (fullcontact band at upper end required)

— push up force or pull up length of tapered connections— key tight fit in shaft and hub (applicable to reversing

plants).

204 For liners mounted at the yard, see C201.

205 Keyless shrink fit connections are to be checked with re-gard to:

— circumferential orientation (marking) between the parts(not applicable to sleeve couplings)

— contact1) between male and female tapered members (notapplicable for couplings certified as hub and sleeve togeth-er and contact checked at the manufacturer). As a mini-mum there is to be a full contact band at the big end

— shrinkage amount, verified by diametrical expansion orpull up length, whichever is approved

— draining and venting (by air).

1) For wet mounting, the contact may be improved by light grinding with asoft disc and emery paper in the hub (not the shaft). A test pull up mayalso be used to improve the contact.

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206 Bearing clearances (for fluid film bearings) are to be re-corded.

207 The protection against corrosion of inboard shafts is tobe checked, see F103.

208 Propeller fitting

a) For flange mounted propellers, the bolt tightening is to beverified.

b) For cone mounted propellers, the following is to be veri-fied:

— contact between propeller and shaft (e.g. by means oftoolmaker’s blue) to be at least 70% and with full con-tact band at the upper end, see also 205 footnote 1)

— pull up length, and for key mounting preferably pushup force

— key fit in both shaft and hub.

H 300 Shaft alignment301 The shaft alignment is to be within the tolerances givenin the shaft alignment specification.

302 When shaft alignment calculations are required (seeA403 and F400) the measured values as gap and sag, jackingloads with force-displacement diagrams, etc. are to be report-ed.

I. Shipboard Testing

I 100 Bearings101 During the sea trial, the temperatures in all fluid film

bearings (that are equipped with thermometers) are to bechecked.

I 200 Measurements of vibration

201 Measurements of vibration on power take off generatorsdriven from the engine driven reduction gear are to be carriedout at 90%, 100% and (at least) 105% of rated (generator)speed with unloaded generator and ship service speed understeady state operation. The measurements are to be made nearboth bearings in the vertical, horizontal and axial directions.Frequency analyses are to be made in the range of 2 to 100 Hz.

The vibration velocities are not to exceed the following:

For long-term continuous operation, i.e. 90% and 100% gener-ator speed:

— 4.5 mm/s r.m.s. per frequency component for vibrationcaused by internal sources.

— 7.1 mm/s r.m.s. per frequency component for vibrationcaused by external sources.

For operation in a limited time period, i.e. 105% generatorspeed:

— 7.1 mm/s r.m.s. per frequency component for vibrationcaused by internal or external sources.

For definitions, see ISO 10816-3.

Vibration caused by internal sources are defined as thosecaused by the generator rotor and the shaft couplings betweenthe generator and gearbox. This means the 1st and 2nd order ofthe generator speed as well as any coupling resonance to tor-sional and axial vibration.

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SECTION 2GEAR TRANSMISSIONS

A. General

A 100 Application101 The rules in this section apply to gear transmissions sub-ject to certification, see Ch.2 Sec.1 A200. The rules apply tothe gear transmission, it's integrated components, such as cool-ers and pumps, and the lubrication piping system. Gears forjacking machinery for self elevating offshore units, partiallydeviate from the rules in this section. This is specified in DNV-OS-D101 Sec.5 D. See Sec.1 regarding shafting and rigid cou-plings and Sec.3 for clutches.

102 Ch.2 describes all general requirements for rotating ma-chinery and forms the basis for all sections in Ch.3, Ch.4 andCh.5.

103 The complete gear transmission is to be delivered with aNV certificate that is based on the design approval in B, thecomponent certification in C and the workshop testing in D.

A 200 Documentation201 Plans to be submitted for approval:

a) Arrangement including part list(s)1):

— longitudinal section of the unit — transverse section (applicable to gears with more than

2 shafts).

b) Detail drawings2):

— pinion(s) and wheel(s) 3)

— shafts— hub(s)— clutch(es) and coupling(s)

— other power transmitting parts

c) Gear casing (unless the wall thickness and bearing sup-ports, including main thrust bearing support, are indicatedon the longitudinal section)

d) Gearbox fixation including chocking calculations, if appli-cable

e) Schematic lubrication oil system diagram including alarmset points with their delay times and indicator positions.

202 Particulars to be submitted for approval:

a) Data according to Table A1 for each gear stage. The vari-ous data are explained in the Classification Note 41.2. anda special sheet, Data Sheet for Gear Calculations, FormNo. 71.10a, has been prepared for this.

1) The arrangement plans ought to contain as many details as prac-tically possible in order to reduce the total number of plans, e.g. if all details of other items as listed under b) above can be given on the arrangement plans, then separate plans of these items need not be submitted.

2) The plans are to show clearly all details as fillets, keyways and other stress raisers, shrinkage amounts (also for bearings), pull up on taper, surface roughness, bolt pre-tightening, etc. as well as types of material and mechanical properties, cleanliness (if re-quired, see B207) including NDT specification, see Ch.2 Sec.3 A202. “All details” means data that are necessary for evaluation according to the relevant criteria in B.

3) Pinions and wheels can normally be sufficiently described on the longitudinal section and with all particulars listed in 202 b) spec-ified on a data sheet (Form No.: 71.10a). However, if manufac-ture of the pinion and wheel set is subcontracted, separate sets of plans have also to be submitted.

Table A1 Gear dataItem Particulars Symbol Comments

Loads 1)

Maximum power (kW) on pinion P Alternatively, a load - time spectrum may be used. This is typical for gears designed for relatively short life time (less than for example a million cycles). See also Ch.2 Sec.3 A101.

R.p.m. of pinion n0Rated pinion torque corresponding to maxi-mum power and r.p.m.

T0

Application factors KA Both for normal operation and permissible diesel en-gine misfiring condition

Application factor for non-frequent peak loads KAP For example start-up of electric motor with star-delta shift or clutching-in shock

Application factor for ice condition KAice For vessels with ice class (see Pt.5 Ch.1 of the Rules for Classification of Ships)

Faceload distribution

Maximum permissible faceload distribution factor at rated load 2) 3)

KHβ For bevel gears with ordinary length crowning it is suf-ficient to specify the minimum permissible face width contact in %.

Dimensions 4)

Number of teeth zCentre distance a For gears with parallel axis onlyCommon face width at operating pitch diameter bFace widths at tooth roots b1,2Total face width including gap B For double helical gears onlyTip diameters daAddenda haMinimum and maximum backlash jAngle between shafts Σ For bevel gears only

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203 Documentation to be submitted for information only:

a) For power transmitting components of welded construc-tion full details of the joints, welding procedure, filler met-al particulars and heat treatment after welding are to bespecified.

b) The bearings are to be documented with:

— calculated life time of rolling bearings (L10a accordingto ISO 281)

— specification of material, nominal surface pressureand clearance tolerances for fluid film bearings.

Tool and gear geometry 4)

Normal module mn In mid section for bevel gears (mnm)Module of tool m0 For bevel gears onlyTransversal module at outer end mt For bevel gears onlyPressure angle in normal section at reference cylinder αn

Helix angle at reference cylinder βHelix angle in the midsection βm For bevel gears onlyAddendum of tool ha0 Referred to mnRadius at tip of tool ρa0 Referred to mnProtuberance pro Referred to mn and excluding grinding amountAddendum modification coefficient x Referred to mnIn mid section for bevel gears (xhm)Number of teeth of cutter zc If pinion type cutter is used

Addendum modification coefficient of cutter xcIf pinion type cutter is usedReferred to mn

Angle modification θk For Zyclo Palloid bevel gears onlyCutter radius re0 For Zyclo Palloid and Gleason bevel gears onlyTooth thickness modification coefficient (mid face) xsm

For bevel gears onlyReferred to mn

Material

Material specification including heat treatment method

See Ch.2 Sec.3, (e.g. EN 10084 18CrNiMo7-6, Case hardened)

Flank surface hardness, maximum and mini-mumMid face tooth root space hardness, minimum 5)

Tooth core hardness, minimum 5)

Core impact energy (KV) of coupon test at 20°C 5) If applicable, see C206 b)

Hardness depths after finishing process, appli-cable to surface hardened gears

t550, t400 and t300

Given as depth to 550HV, 400HV and 300HV as appli-cable, see Classification Note 41.2

Finishing process

Finishing method of flanksAcceptance level for root grinding notches Minimum radius and maximum depthShot peening parameters If applicableSurface roughness of flanks Rz Mean peak-to-valley roughnessSurface roughness of tooth root fillet Ry Maximum height of the profile

Tip and root relief Ca/CfAmount and extensionHeightwise crowning of tool for bevel gears

Lead modifications Amount and extension (end relief, crowning and/or he-lix correction)

Grade of accuracy according to ISO 1328, DIN 3962 or ANSI/AGMA 2015-A01 Q

Lubrication

Type of cooling Spray, dip, fully submerged, with additional cooling spray, etc.

Kinematic viscosity (mm2/s) ν At 40°C and 100°CFZG damage level (scuffing) According to ISO 14635-1Oil inlet temperature At normal operation

1) For gears that are subjected to negative torques both the negative torque level as well as the frequency of these occurrences are to be specified unless the following guidance is used:

The negative torque level is to be given in percent of the rated (forward) torque.

The frequency of occurrence may be classed as:

< 100 = rare

> 100 = frequent

where the numbers refer to torque reversals.

2) For specified faceload distribution factors that are considered as “optimistic” (see Classification Note 41.2) a contact pattern specification at 1 or 2 suitable part loads is to be submitted together with an explanation on how this leads to the specified faceload distribution at rated load, see 204 b).

3) Note that the rated load means normally the maximum rating with the application factor that is decisive for the scantlings. However, if this application factor differs much from the application factor at normal operation, it may be necessary to specify both faceload distribution factors.

4) The data is to be given for both pinion (index 1) and wheel (index 2), and for an idler or planet gear, where applicable.

5) Applicable to case hardened gears only.

Table A1 Gear data (Continued)Item Particulars Symbol Comments

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c) A brief summary of the manufacturer’s prescribed in-serv-ice inspection and maintenance routines.

d) For propulsion gears, acceptance criteria for shaft align-ment (where shaft alignment calculations are required ac-cording to Sec.1 A402).

204 Documentation to be submitted upon request:

a) If a manufacturer requests approval based on other meth-ods than those described in the rules and ClassificationNotes (e.g. special calculation methods or tests), addition-al documentation will be requested. For principles, seeCh.2 Sec.3 A100.

b) For gear stages where the approval is dependent upon ob-taining a certain optimistic faceload distribution, toothcontact pattern specifications at some selected part loadswill be requested (for approval) together with an explana-tion on how this leads to the specified faceload distributionat rated load.

c) Balancing specifications for high speed gears (e.g. turbinedriven) and for certain medium speed gears with non-ma-chined surfaces of rotating parts (for information only).

d) Calculation of thermal rating for gas turbine driven gears(for approval).

B. Design

B 100 General

101 For design principles see Ch.2 Sec.3 A100. All compo-nents in gear transmissions are to be designed for all relevantload conditions such as rated power or overloads, including alldriving conditions under which the plant may be operated. Re-garding dynamic loads, see Ch.3 Sec.1 G.

102 Details on calculation of gearing is given in Classifica-tion Note 41.2. It contains information on calculation of toothroot strength (fractures), flank surface durability (pitting,spalling and case crushing), and scuffing.

103 Requirements for shafting and rigid couplings are givenin Sec.1.

104 When considered necessary for completion of a type ap-proval process, type testing may be required. Details on thistype testing will be especially considered. For special gear de-signs a type approval may be pending satisfactory service ex-perience, as e.g. after 1000 to 3000 hours.

105 For gear transmissions used for vessels with ice class no-tations the criteria throughout this section apply with the use ofthe application factor KAice (see Pt.5 Ch.1 of the Rules forClassification of Ships) replacing KA and KAP provided thatKAice is greater.

106 Gear transmissions, and in particular power take off(PTO) branches, may be accepted for higher vibratory torquesin the low load range than given in Ch.3 Sec.1 G303 e). Thismay be accepted when gearing, shafts and in particular bear-ings are designed for such vibratory conditions.

107 For design requirements for components delivered as in-tegral parts of the lubrication, hydraulic operation and coolingsystems of the gearbox the following applies as found relevant:

— Electric motors, see Ch.8— Short lengths of flexible hoses may be used when neces-

sary to admit relative movements between components.The hoses with couplings are to be type approved.

B 200 Gearing

201 The gear teeth are to be designed with the minimum

safety factors as given in Table B1.

Due to the scatter of the FZG test results, the FZG level usedin the calculations is to be one level lower than the specified.Any gear utilising oils with specified FZG level above 12, thetest results for the actual oil are to be documented in a test re-port from a recognised laboratory, and/or oil supplier.

202 Gear designs may be limited by other criteria as thosementioned in 201. For example if service experience indicatesthat failure modes other than those in 201 become a problem(such as oblique fractures starting from the active flank, greystaining developing to pitting etc.), a gear design may be re-jected even though the criteria in 201 are fulfilled.

203 Gear designs are to take into account all relevant loadconditions such as dynamics described in Ch.3 Sec.1 (dieselengines) and in other relevant sections. If vibration or shockloads result in reversed torques, this influence is to be consid-ered.

204 Acceptance of gears may be based on approved tests.

205 For gearing designed to Baltic ice classes the calculationwith KAice is to assume a number of load cycles equal to 3 · 106. This is additional to the normal, open sea conditions.The stricter of these criteria are decisive.

206 Quenched and tempered steels and all surface hardenedsteels are to have a level of cleanliness that is suitable for thepermissible stress level for high cycle fatigue. A suitable levelin this context is e.g. chart diagram index 2 for all groups A -DS in ISO 4967.

207 Gears classed to "high grade" made of special high gradematerials, special high cleanliness will be required, see Ch.2Sec.3.

208 Pinions and wheels may be made from separate forg-ings, rolled bars or blanks cut out of a forged bar. Gears madefrom rolled bars will have tooth root stresses crosswise to thefibre direction of the material. Therefore, normally a 10% re-duction of the fatigue strength compared to gears made fromseparate forgings will be assumed. Correspondingly, gearsmade from blanks cut out of a forged bar are assumed to havea 20% reduction of the fatigue strength. However, such barsand blanks may be considered equivalent to separate forgingsprovided that either:

— they are further forged, or— the steel making process and forging process are specially

qualified. see Ch.2 Sec.3 A205.

B 300 Welded gear designs

301 If a pinion or wheel designed for high cycle (> 108) ismanufactured by welding, the permissible cyclic stress range

Table B1 Minimum safety factorsAuxiliary Propulsion

Tooth root fracture SF 1.43) 1.55Pitting, spalling and case crushing SH

1) 1.15 1.20Scuffing SS

1) 2) 1.4 1.51) These safety factors apply to medium and high speed gears designed

for long lifetimes (e.g. > 106 load cycles). For slow speed gears with short design life time (e.g. << 106 load cycles) and where a certain flank deterioration is acceptable, lower values may be considered.

2) For medium and high speed gears as mentioned above, a minimum dif-ference of 50°C between scuffing temperature and contact temperature applies in addition to the safety factor. However, if an oil inlet temper-ature alarm is installed, the minimum difference of 30°C between scuffing temperature and actual alarm level applies.

3) If an auxiliary gear stage is arranged as a power take off from a propul-sion gearbox, and a tooth fracture of the auxiliary gear stage may cause a consequential damage to the propulsion system, the tooth root safety factor is to be as for propulsion.

4) Safety factors for auxiliary gears may be applied for vessels with class notations NAVAL, PATROL, YACHT and CREW.

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(principal stresses) in the welds and HAZ is limited to 2/3 ofthe threshold value for crack propagation. This depends on thequality (i.e. NDT specification) of the weld with regard to ex-ternal and internal defects.

As a simplification the following may be used:

— for full penetration welds which are very smooth or ma-chined on all surfaces and 100% tested for surface defects(no linear indication > 1.5 mm) and according to ISO 5817level B for internal defects, the permissible stress range is50 MPa

— as above, but not very smooth or machined or ground sur-faces, 30 MPa

— for welds with inaccessible backside, 15 MPa.

For gears designed for a lower number of stress cycles (<< 108)higher permissible stress range values may be accepted, alter-natively less weld checking.

302 The calculation (usually by FEM) of the actual stressrange is to take the full load cycle of the pinion or wheel intoaccount as well as the stress concentration in the weld andHAZ due to fillet radii and or shape of the weld.

303 Welded pinions or wheels are to be stress relieved. If thestress relieving is not the final heat treatment process (as e.g.when followed by a case hardening), the permissible values in301 are to be reduced by 30%.

B 400 Shrink fitted pinions and wheels401 Shrunk on pinions or wheels are to be designed to pre-vent detrimental fretting, macro slippage and micromove-ments.

402 The criteria for macro slippage and fretting are given inSec.1 B400. The influence of axial forces and tilting momentsare to be considered.

403 Shrink fitted rims are to have a minimum safety of 2.0against micromovements based on the specified repetitivepeak torque. This means that the local shear stress τ between atoothed rim and the hub is to be less than half the local friction(p + σ) µ:

(p + σ) µ / τ > 2 = Flim/F

p = nominal shrink fit pressureσ = local radial stress due to the gear mesh force µ = coefficient of friction

The following method may be used:

The nominal tangential force per unit face width is:

Ft = 2000 T / (b d1)

T = the pinion torque (Nm)b = the face width of the shrink fit surface (mm)d1 = the reference diameter of the pinion (mm)

The force per unit face width to be used in the calculation is:

F = Ft KA

if the movement in the axial tooth force direction is preventedby e.g. a shoulder, or if there is a double helical gear rim madeof one body.

F = Ft KA / cos β in all other cases.

The shrinkage pressure p depends on the shrinkage amount,the equivalent rim thickness sv and the hub flexibility.

sv = s + mn (0.85 - 1.1 mn/s)

s = the rim thickness from tooth root to shrinkage diameterdf (mm).

(only valid for s > 2 mn )

Fig. 1Shrink fitted rim

The load limit per unit face width Flim when micromovementis expected to start is:

Flim = Fref Fcorr Froll

Fref = the reference load limit calculated as;

Fref = 5.65 p µ s (0.7 + 2 µ)

Fcorr = a correction factor which considers the influence of thehub flexibility (i.e. design and modulus of elasticity Ehub). It isunity for a solid steel hub. Otherwise calculated as:

Fcorr = 1.586 - 2.86 · 10-6 Ehub + f(b/bw),

where f(b/bw) considers the flexibility of a hub with webs. bwis the total face width of the webs.

f(b/bw) = 0.404 · 10-3 (b/bw)3 − 0.01 (b/bw)2 + 0.09 b/bw −0.081

(equal zero if b = bw )

Froll takes into account the rolling (tangential twist) load of anarrow rim (face width bhelix) due to an axial force component.The rolling moment causes a reduced surface pressure at anend of the face width. This is of particular importance for dou-ble helical gears with two separate rims. Froll applies even ifthere is an axial shoulder.

Froll is the minimum value of unityor (bhelix/df + 0.02) 4.8/tan βor (bhelix/(s + 1.3 mn) + 0.4) 0.2887/tan β

The coefficient of friction µ may be taken from Table B2.

Table B2 Coefficients of friction, µSurface condition Hub material

Steel Grey or nodular cast ironRim heated in oil 0.13 0.10Rim heated in gas furnace but not protected against oil penetration into the mating surface

0.15 0.12

Surfaces degreased and pro-tected against oil penetra-tion or with especially high surface pressure with local yielding (see Figure 2)

0.20 0.16

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Fig. 2Shrink fitted body with especially high surface pressure (only ap-plicable for shafts protruding on each end)

The safety against micromovements is:

S = (p + σ) µ / τ = Flim/F.

B 500 Bolted wheel bodies

501 Bolted wheel bodies (and pinions, if applicable) are tobe designed to avoid fatigue failure of the bolts due to pulsat-ing shear stresses when passing the gear mesh zone.

Fig. 3Bolted wheel body

Guidance note:The pulsating bolt forces will be reduced if the wheel body is ra-dially supported without radial clearance.


502 For gear rims that are flexible compared to the hub, thestresses in the bolts are to be calculated upon request (usuallyby means of FEM) for a mesh force corresponding to T0 KA.The shear stress range is not to exceed 0.25 σy.

503 Bolts used for flexible rims are to have a tight fit in theholes, i.e. any combination of the tolerances is not to result ina clearance, or the bolts are to be ream fitted with a slight pressfit.

B 600 Shafts

601 Shafts are to be designed to prevent fatigue. Detailed cri-teria are given in Classification Note 41.4. However, simpli-fied criteria for various common gear shaft designs are givenin Sec.1 B206.

When gear transmissions are designed for long life time (i.e.>> 106 cycles), the shafts are to be designed to prevent detri-mental fretting that may cause fatigue failures, see also Sec.1B402. Unless torsional vibration values are defined, the upper

permissible values for dynamics as given in Ch.3 Sec.1 G areto be used.

602 Shafts may be divided into 2 groups. These are shaftswith:

— significant bending stresses, e.g. pinion and wheel shaftswithin their bearing spans

— no significant bending stresses, e.g. quill shafts and shaftsoutside the bearing spans of pinions and wheels.

The major load conditions to be considered are:

— high cycle fatigue (>> 106 cycles) due to rotating bendingand torsional vibration, see Sec.1 B206 B and Classifica-tion Note 41.4 item 4

— low cycle fatigue (103 to 104 cycles) due to load variationsfrom zero to full load, clutching in or starting shock loads,reversing torques, etc., see Sec.1 B206 A and Classifica-tion Note 41.4 item 3.

Practically, shafts with significant bending stresses such aspinion and wheel shafts are dimensioned with regard to stiff-ness (gear mesh considerations) and high cycle fatigue, buthardly ever for low cycle fatigue because the two first will pre-vail.

603 For short shafts made by blanks cut from forged barswithout further forging, see Ch.2 Sec.3 A205.

B 700 Bearings

701 Fluid film bearings are to be designed with bearing pres-sures that are suitable for the bearing metals. The calculationof bearing pressures is to include the application factor KA.

702 Ball and roller bearings are to have a minimum L10a(ISO 281) life time that is suitable with regard to the specifiedoverhaul intervals. The influence of the lubrication oil filmmay be taken into account for L10a, provided that the necessaryconditions, in particular cleanliness, are fulfilled.

Guidance note:If no overhaul intervals are specified, a bearing life time of40,000 hours may be used for conventional ships and 10,000hours for yachts or ships and units that are not predominantlyused at full load for longer periods.


B 800 Casing

801 Inspection openings are to be provided in order to enableinspection of all pinions and wheels (measurements of back-lash and application of lacquer for contact pattern verification)as well as for access to clutch emergency bolts (if applicable).For special designs (e.g. some epicyclic gears) where inspec-tion openings cannot be provided without severely affectingthe strength of the design, holes for boroscope inspections maybe accepted as a substitute to openings. Such holes are to bepositioned to enable boroscope inspection of all gearing ele-ments.

802 Easy access to all inspection openings is to be provided.This means that no piping or coolers etc. are to be positionedto prevent access.

803 In order to prevent rust, the gear casing is to be providedwith proper ventilation.

B 900 Lubrication system901 The lubrication system is to be designed to provide allbearings, gear meshes and other parts requiring oil with ade-quate amount of oil for both lubrication and cooling purposes.This is to be obtained under all environmental conditions asstated in Ch.1 Sec.3 B200 of the Rules for Classification ofShips.

902 The lubrication system is to contain at least:

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— an oil pump to provide circulation— a filter of suitable fineness for gearing, hydraulics and

bearings (see B702). Normally 40 µm or less.— if necessary, a cooler to keep the oil temperature within the

specified maximum temperature when operating under theworst relevant environmental conditions, see 901.

903 For gear transmissions for propulsion where windmill-ing may be detrimental and considered as a normal workingcondition, there is to be either:

— a shaft brake designed to hold (statically) twice the highestexpected windmilling torque, or

— an extra oil pump which is not to be the same pump as re-quired as standby pump.

The chosen version is to be automatically activated within 30s after shutdown.

904 Gear transmissions for propulsion are normally to havean attached pump. For plants designed to normally operate atsuch low speeds that the attached pump cannot supply suffi-cient oil pressure (e.g. plants with frequency controlled electri-cal motor), the following will be accepted:

— either an extra electric oil pump that is activated at a givenpressure, or

— 2 electric main pumps of the same capacity, one of whichis arranged as a standby pump with immediate action.These 2 electric pumps are to be supplied from differentswitchboards.

905 For propulsion gears the lubrication system is to be ar-ranged so that the gear transmission can endure a run out of 5

minutes after a black out without jeopardising any bearings orgear teeth.

This may be provided by e.g.:

— an attached pump with an additional gravity tank (if nec-essary)

— electric pumps with a gravity tank with sufficient volumeand height for 5 minutes supply.

906 Gear transmissions in single propulsion plants are tohave a standby pump with immediate activation.

907 For gear transmissions in single propulsion plants thefiltering system is to be arranged to make it possible to cleanthe filters without interrupting the oil supply.

908 Filter casings made of aluminium are in general not ac-cepted.


C 100 Certification of parts

101 Regarding certification schemes, short terms, manufac-turing survey arrangement (MSA) and important conditions,see Ch.2 Sec.2.

102 The parts in a gear transmission are to be tested and doc-umented according to Table C1 and 200 through 400, if nototherwise agreed in a MSA, see Ch.2 Sec.2 C100. In 200through 400, the testing and inspection as required in Table C1are described in more detail.

C 200 Pinions and wheels201 The requirements in 200 apply to the toothed parts of

pinions and wheels. A flow chart and a summary of these re-quirements are presented in Fig.4 and Table C2, respectively.

Table C1 Requirements for documentation and testingPart Product

certificateChemical

compositionMechanical properties

X-Ray or Ultrasonic

testing

Crack detection 1)

Visual and dimensional

check 2)

Other 2)

Pinion and wheels NV See 200 - Table C2Built-in clutches, bend-ing compliant- and elastic couplings

NV See Sec.3 C, Sec.4 C and Sec.5 C, respectively

Shafts, rigid couplings and hubs See Sec.1 C

Welded gears W W 3) W 3) W 3) W 6)

Casing (welded) W W W 4) W 5)

Casing (cast) WBolts and keys TR TRAncillaries See C4001) By means of magnetic particle inspection or dye penetrant.

2) For details and extent, see relevant paragraph.

3) After final heat treatment (e.g. case hardening).

4) For thickness > 100 mm.

5) Of welds near bearings (at least 10% of the welds to be tested).

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Fig. 4Flow chart showing the applicable certification rules

202 The incoming material is to be documented with a Workcertificate (W) to be within the approved specification as fol-lows:

— chemical composition (ladle analyses)— ultrasonic testing in suitably machined condition.

For gears classed to “high grade”, the requirement for addi-tional documentation as specified in the approval, applies:

— cleanliness according to ISO 4967— oxygen content— grain size according to ISO 643— forging or rolling according to an agreed process.

See also Pt.2 Ch.2 Sec.5 A.

For materials that are delivered in their final core heat treat-ment condition, such as quenched and tempered steels for laternitriding, induction hardening or no further treatment, the ad-ditional requirement for documentation in 203 applies.

203 For quenched and tempered steels (QT) and normalisedsteels (N) the mechanical testing is to be documented by Workcertificate (W) in accordance with Pt.2 Ch.2 Sec.5 E.

Documentation of mechanical properties may be replaced bysurface hardness (HB) for QT steels with controlling sections(see ISO 6336-5 Annex A) below 200 mm and for normalisedsteels of all sizes.

204 For case hardening the gear manufacturer or the heattreatment subcontractor is to have a quality control system1)

acceptable to the Society. This quality control system is to pro-

vide that:

— suitable heat treatment is made prior to machining in orderto avoid excessive distortions during quenching

— carburising is made in a controlled furnace atmosphere.The furnace is to be equipped with temperature and carbonpotential controls and continuously recorded

— the entire case hardening process is checked by means ofcoupons2) at regular and agreed intervals with regard tosurface microstructure and core microstructure. For detailssee 205

— the gears are shot cleaned after the heat treatment.

1) If this requirement is not fulfilled or only partly fulfilled, the non fulfilledelements in this paragraph as well as in 205 and 206 are to be inspectedin the presence of a surveyor.

2) The coupon is to be representative for the quenching rate of the typicalgear sizes. The hardness and microstructure at the centre of the couponwill then be representative for the core of a typical gear. The coupon is tobe of the same type of material as the typical gears. The approximate sizeis minimum diameter 6 modules and length 12 modules. This module isto be either the module of the actual gear to be certified or from the upperrange of the production with that material. The coupon is to follow theentire heat treatment and shot cleaning processes and be quenched to-gether with the pinions and wheels in such a way that its quenching rateis as representative as possible.

205 With reference to 204 the requirements for the surface(i.e. polished depth of less than 0.03 mm) microstructure are:

a) Reduction of surface hardness in the outer 0.1 mm of thecase is not to be more than 2 HRC.

All incomingmaterials:

C202

Casehardening:

C204, C205,C206, C211

Further heat treatment?

Quenchedand

tempered:

C203

Induction orflame

hardening:

C203, C208

Nitriding:

C203, C207

Surface hardened steels:

C209

All:

C210, C212, C213

No Yes

C203

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b) Carbide precipitation at surface and at 0.2 mm depthchecked at approximately 400 times magnification. Onlyfine dispersed carbides are permitted, see ISO 6336-5.

c) Retained austenite at surface and at 0.2 mm depth not toexceed 25%. To be checked by comparison with referencepictures or by a calibrated magnetoelastic method.

d) Depth of intergranular oxidation (IGO) from unpolishedsurface is not to exceed 10 + 6 t550 (µm). t550 should begiven in mm.

Requirement for the core in the middle of the coupon:

— to be martensitic or bainitic with no blocky ferrite— hardness according to approved specification.

If these requirements are not fulfilled, the permissible valuesfor tooth root stresses and contact stresses and contact temper-atures (for scuffing) will be reduced according to special con-sideration.

206 For case hardening the following applies in addition tothe requirements in 204 and 205.

Each hardening batch and each material type is to be docu-mented (W) regarding:

a) Hardness profile1) with emphasis on depth to 550 HV and400 HV. For core hardness below 300 HV the depth to 300HV is also to be checked.

b) Core impact energy2) (KV).

c) Tooth root hardness3) at mid face of each pinion andwheel. To be made in the presence of a surveyor.

1) The case depths are to be checked on a coupon that follows the entire heattreatment process. The coupons are to be of the same type of material asthe actual gears to be certified and may be of a standard size. The corre-lation between these small coupons and the representative coupons men-tioned in 204 is to be documented by means of comparisonmeasurements.

2) The core impact energy has the objective of detecting unacceptable graingrowth and is to be verified by means of at least 2 test pieces taken fromthe centre of a coupon that has followed the entire heat treatment process.The coupon is to have a diameter of at least 2 modules. The coupon maybe taken from any of the positions in Fig.5 to Fig.8 in Pt.2 Ch.2 Sec.5 E,as well as from material near the surface.

The impact energy is to be at least 30 J, unless otherwise approved. If the cou-pon is taken longitudinally in a body with longitudinal grain flow, the mini-mum value is 40 J.

The core impact energy testing may be waived if all of the following condi-tions are fulfilled:

— carburising temperature below 940°C— maximum specified case depth to 550 HV below 3.0 mm— chemical composition contains grain growth preventing elements

(e.g. Al)— implemented manufacturing survey arrangement for heat treatment.

3) For modules 10 mm and above the surface hardness in the tooth rootspace in the middle of the face width is to be checked. A small spot is tobe polished (No grinding. Polishing depth less than 0.03 mm) and thehardness measured by means of a low force tester. Unless otherwise ap-proved, the minimum hardness is to be 58 HRC. The manufacturer maycarry out approved procedure tests in order to establish limit sizes for var-ious material types. Below these limit sizes the hardness will with a highprobability turn out to 58 HRC or more, and no such hardness testing isrequired for the individual gears. The procedure tests are to include var-ious designs and quenching baths.

207 Nitrided gears are to be documented with Work certifi-cates (W) for each heat treatment batch by means of a couponfollowing the entire nitriding process with regard to:

— case depth (to 400 HV)— white layer thickness (to be < 0.025 mm)

The coupon is to be of the same material type as the gears. Thecore properties are to be documented as described in 203.

208 Induction or flame hardened gears are to be documentedwith a NV certificate with regard to:

— hardness contour— hardness depth at pitch diameter— hardness depth at tooth root— surface structure, random inspection (to be mainly fine ac-

icular martensite).

The hardness pattern is to be checked at a representative testpiece with the same geometry (profile and root shape) and typeof material as the actual gears (except for face width whichmay be smaller). For batch production this testing is to be madeat least before and after each batch.

The hardness pattern checking applies to both ends and the midsection of the test piece. All three sections are to have valueswithin the approved minimum to maximum range. Each gearto be visually inspected at both ends and the contour is to beconsistent with the test piece.

For small gears with spin type hardening (see ISO 6336-5)only the surface structure (random) and external contour needto be checked. The core properties are to be documented as de-scribed in 203.

209 For all surface hardened teeth the final flank hardness isto be measured and documented with a Work certificate (W).The hardness is to be measured directly on the flanks near bothends and in the middle and at each 90 degrees. Low force test-ers are preferred provided suitable surface finish. For batchproduction a less frequent checking may be approved.

210 All teeth are to be crack detected, no cracks are accepted,see Ch.2 Sec.3 A202. This is to be documented with a Workcertificate (W). Normally gears are to be checked by means ofthe wet fluorescent magnetic particle method. However, nitrid-ed or not surface hardened gears may be checked by the liquidpenetrant method. For batch production a reduced extent ofcrack detection may be approved. The crack detection is to bemade prior to any shot peening process.

211 For case hardened gears grind temper inspection is to becarried out randomly and be documented by a test report (TR).

This inspection may be done by:

— nital etching per ISO 14104 or ANSI and or AGMA 2007-B92 (grade B temper permitted on 10% of functional area(FB1))

or

— a calibrated magnetoelastic method (acceptance criteriasubject to special consideration)

212 The tooth accuracy of pinions and wheels according toISO 1328 is to be documented with a Work certificate (W) asfollows:

— for specified grade 4 or better, all pinions and wheels areto be measured

— for specified grade 5 1) at least 50% are to be measured— for specified grade 6 1) at least 20% are to be measured— for specified grade 7 or coarser at least 5% are to be meas-

ured.

1) When a wheel cannot be measured due to its size or weight, at least everymating pinion is to be measured.

If other standards (e.g. DIN 3962 or ANSI/AGMA 2015-A01)are specified, measurement program equivalent to the aboveapplies (with respect to pitch, profile and lead errors).

Bevel gears (that are not covered by ISO 1328) are to be meas-ured regarding pitch and profile errors if required in connec-tion with the approval. Generally, all bevel gear sets are to bechecked for accuracy in a meshing test without load. The un-loaded contact pattern is to be consistent with the specified,and documentation thereof is to follow the gear set to the as-sembly shop.

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213 The surveyor is to review all required documentationand carry out visual inspection of the pinions and wheels withspecial attention to:

— surface roughness of the flanks— tooth root fillet radius

— surface roughness of tooth root fillet area— possible grinding notches in the root fillet area. Any grind-

ing (or any other machining) of the root area is not accept-ed unless this has been especially approved.

C 300 Welded gear designs

301 Welded gears are to be documented with Work certifi-cates (W) as follows:

— chemical composition and mechanical properties of all thematerials

— stress relieving (time - temperature diagram)— 100% weld quality control according to ISO 5817. To

meet level B for internal defects unless otherwise ap-proved.

— 100% surface crack detection by MPI or dye penetrant. Nolinear indication > 1.5 mm unless approved.

— visual inspection by a surveyor with special emphasis onthe shape of the outer weld contour (stress concentrations)at the root.

The 3 last items refer to the gear after the final heat treatment(e.g. after case hardening).

C 400 Ancillaries

401 Pumps, electric motors, coolers, piping, filters, valves,etc. that are delivered as integral parts of the lubrication, hy-draulic operation and cooling systems of the gearbox, are to bechecked by the gear manufacturer’s quality system as foundrelevant.

C 500 Assembling

501 Balancing of rotating parts and subassemblies of rotorsis to be documented with Work certificates (W) and shall bewithin the approved specification.

502 Cylindrical shrink fitting of pinions, wheels, hubs,clutches, etc. is to be documented with Work certificates (W)with regard to shrinkage amount. The diameters (and therewiththe shrinkage amounts) are to be checked at various positionsalong the length of the shrinkage surface. If conicity or ovalityin a connection with length to diameter ratio > 1 result in:

— a shrinkage amount near the minimum tolerance value atthe torque transmission end

and

— an amount near the maximum tolerance value at the oppo-site end,

the shrinkage specification is to be reconsidered with respectto possible fretting near the torque transmission end. (If thenon-torque end is subjected to bending stresses, possible fret-ting must be considered here too.)

503 Tapered shrink fit connections are to be documentedwith Work certificates (W) with regard to contact area and pullup distance or push up force or diametrical expansion (which-ever is the approved specification).

The contact between the male and female parts is to be checkedwith a thin layer of contact marking compound (e.g. toolmak-er’s blue). There is to be full contact at the end with torquetransmission (which is normally the upper end). If this is notobtained, light correction grinding with a soft disc and emerypaper may be done in the female part only (if wet mounting).Alternatively a test pull up may deform small irregularities andresult in an improved contact.

504 Keyed connections are to be checked with regard to:

— key fit in shaft and hub (for connections where the torquemay be reversed the key is to have a tight fit in both shaftand hub)

— shrinkage amount, see 502— push up force, see 503.

505 Spline connections are to be checked with regard to:

— tight fit if of the “fixed” type— lubrication if of “working” type.

506 Bolted connections such as bolted wheel bodies or

Table C2 Summary of certification requirementsTest Case hardening Nitriding Induction and

flame hardeningThrough

hardening (QT)No hardening

(N)Chem. composition 1) W W W W WUltrasonic 2) W W W W WMechanical properties 3) W W W WCase hardness profile 4) W W NVCore impact energy (KV) WTooth root hardness 5) NVWhite layer thickness WFinal flank hardness W W WCrack detection of all teeth 6) W W W W WRandom grind temper inspection TRTooth accuracy 7) W W W W WVisual inspection 8) NV NV NV NV NV1) Applicable to the incoming material

2) In suitably machined condition, i.e. after forging prior to surface hardening

3) For hardened gears with “controlling section” size ≤ 200 mm (see ISO 6336-5 Annex A) and all not hardened gears (N), surface hardness (HB) is sufficient

4) For relevant test parameters, see 206, 207 or 208

5) For modules ≥ 10 mm, at mid face

6) Prior to any shot peening process

7) See 212 for extent of documentation

8) See 213 for extent of inspection

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flange connections are to be checked with regard to:

— tightness of fitted bolts or pins— pre-stress as specified.

507 Access through inspection openings to gearing andclutch emergency bolts (if applicable) is to be verified, see alsoB801, B802 and Sec.3 B302.

D. Workshop Testing

D 100 Gear mesh checking

101 The accuracy of the meshing is to be verified for allmeshes by means of a thin layer of contact compound (e.g.toolmaker’s blue). This is to be done in the workshop in thepresence of a surveyor.

When turning through the mesh, the journals are to be in theirexpected working positions in the bearings. This is particularlyimportant for journals which will assume a position in the up-per part of the bearings (and the bearing clearances are differ-ent), and when external weights (such as clutches) may causea pinion to tilt in its bearings.

For small and medium gears with ground or skived flanks onboth pinion and wheel it is sufficient to check this at one posi-tion of the circumference.

For large gears (wheel diameter > 2 m) and for all gears wherean inspection after part or full load (in the workshop or on-board) cannot be made, the contact checking is to be made inseveral (3 or more) positions around the circumference of thewheel.

For bevel gears the contact marking is to be consistent with thedocumented contact marking from the production, see C212.

For highly loaded gears it may be required to carry out such amesh contact test under full or high part load by slow turningthrough a full tooth mesh at 3 or more circumferential posi-tions.

The result of the contact marking is to be consistent with thatwhich would result in the required faceload distribution at rat-ed load.

For propulsion gears connected to shafts in excess of 200 mmdiameter, the contact marking of the final stage is to be docu-mented by tape on paper or photography and is to be forwardedto the client as a reference for further checking onboard.

The backlash is to be documented for all gear meshes.

102 All gear transmissions are to be spin tested in presenceof a surveyor.

Prior to the spin test some teeth at different positions aroundthe circumference of all gear meshes are to be painted with anoil resistant but low wear resistant test lacquer. For multi-meshgears the lacquer is to be applied to the flanks that mesh withonly one other member.

After the spin test the initial contact patterns are to be docu-mented by sketches. The position of the initial contact is to beconsistent with that which would result in an acceptable loaddistribution at rated torque.

103 For gears that are workshop tested with a part load suf-ficient to verify the load distribution at rated torque, the testingin 101 and 102 may be waived, except for backlash measure-ments.

Such part load testing will only be representative for the fullload condition on board if the in- and out-put shafts are con-nected to systems that will not impose significant bending mo-ments or forces. Furthermore, the part load is to be so high(normally 40% torque or more) that reliable extrapolation torated torque can be made. Therefore, this part load testing is

subject to approval, see A200. If such part load testing is suc-cessfully carried out, the gear transmission certificate mayhave a remark stating that contact pattern testing onboard maybe waived.

104 During the running test the gearbox is to be inspected forleakage.

D 200 Clutch operation201 For clutches delivered integral with the gear box theclutching-in function is to be tested in the presence of a survey-or. For oil operated clutches the testing is to be made with theoil at normal service temperature.

The pressure - time function is to be within the approved spec-ification and the end pressure at the specified level. No pres-sure peaks beyond the nominal pressure are allowed. Theclutch operation pressure is to be measured as closely as pos-sible to the clutch inlet.

D 300 Ancillary systems301 The manufacturer is to demonstrate to the surveyor thatthe lubrication oil intake is placed to be well submerged underall environmental operation conditions for the actual type ofvessel. Furthermore, it is to be checked that the oil sprays forlubrication and cooling function properly. After the runningtest the filters are to be inspected.

302 All equipment delivered with the gearbox regarding in-dication, alarm and safety systems is to be function tested.


E 100 Summary101 The requirements in E are additional to those given inCh.9.

102 Lubrication oil pressure at bearings and spray pressurelevel is to be locally and remotely indicated and an alarm forlow pressure is to be provided. If individual local pressure in-dicators are not fitted, quick connectors for a portable instru-ment are to be provided in order to do local readings and setpoint verification of switches. The corresponding portable in-strument is to be provided on board. For gears fitted withstand-by pump, this is to be automatically activated.

103 The oil temperature at inlet to bearings and spray as wellas in the sump is to be locally and remotely indicated.

104 For gears with a total transmitted power of 5 MW ormore, all axial and radial fluid film bearings are to be providedwith remote bearing metal (or for thrust pads, oil outlet) tem-perature indication and alarm for high level.

105 Alarms (level 1) and start of standby pump are to bewithout delay, other than those necessary to filter normal pa-rameter fluctuations, if not otherwise approved.

F. Arrangement

F 100 Installation and fastening101 The gearbox is to be arranged so that appropriate align-ment and running conditions are maintained during all operat-ing conditions. For shaft alignment, see Sec.1 F400.

102 Gearboxes are to be mounted on chocks or epoxy resin.The bolts are to be designed for all relevant operating condi-tions (in particular when ice classes apply). Flexibly mountedgearboxes will be especially considered.

103 Gearboxes that are or may be subjected to external forc-es such as thrust, are to have end stoppers.

DET NORSKE VERITAS


104 Piping etc. is not to be arranged to obstruct access to in-spection openings.

G. Vibration

G 100 General

101 Regarding torsional vibration, see the section for the rel-evant prime mover, e.g. diesel engines Ch.3 Sec.1 G and B105.

102 The vibration of the gearbox foundation (except whenflexibly mounted) is normally not to contain gear alien fre-quency components with amplitudes exceeding 10 mm/s. Al-ien frequencies are those that are not rotational frequencies ofany gear internal parts.

Higher amplitudes may be accepted if considered in the geardesign.


H 100 Application

101 H applies to inspections in connection with installationof complete gearboxes. Regarding external couplings andshafts, and internal clutches, see respective sections.

Unless otherwise stated, a surveyor is to attend the inspectionsgiven in H and I.

H 200 Inspections

201 The following inspections are to be carried out:

— shaft alignment, see Sec.1 H300— fastening of propulsion gearboxes (stoppers and bolt tight-

ening)— flushing, applicable if the system is opened during instal-

lation. Preferably with the foreseen gear oil. If flushing oilis used, residual flushing oil is to be avoided.

— lubrication oil is to be as specified (viscosity and FZGclass) on maker’s list

— pressure tests to nominal pressure (for leakage) wherecooler, filters or piping is mounted onboard

— clutch operation, see Sec.3 H— tooth contact pattern, see 202.

202 A tooth contact pattern inspection as described in D101is to be made for gears where the installation on board can alterthe initial tooth contact pattern. This means e.g. all gear trans-missions with more than one pinion driving the output gearwheel, even if there is only one single input shaft as for dualsplit paths, and propulsion gears connected to shafts in excessof about 200 mm diameter. The result of the contact patterncheck is to be consistent with the result from the workshop.


I 100 Gear teeth inspections101 To prevent initial damage on the tooth flanks (scuffing)and bearings, the gear is to be carefully run in according to thegear manufacturers specification.

102 All inboard gears are to be checked with regard to con-tact pattern under load.

Exceptions are accepted when:

— this is mentioned in the design approval (due to low stresslevels)

— the design makes an inspection impossible without dis-as-sembling such as certain epicyclic gears (this does not ex-empt ordinary gears from having suitable inspectionopenings)

— the contact pattern under load is accepted in the workshoptest, see D103.

103 The contact patterns (all gear stages) are to be checkedby a suitable lacquer applied to some teeth (normally 2 each120 degrees) prior to the checking under load. The lacquer isto be applied to flanks that have only one mesh (in order toavoid accumulated patterns). When part load contact patternchecking applies, the lacquer is to be of a kind that quicklyshows the final pattern.

104 The gear is to be operated at the specified load level(s)without exceeding that particular level(s). After each specifiedlevel the contact patterns are to be checked in the presence ofa surveyor. The results, in both height and length directions,are to be within the approved specification.

105 After the full load test, or after the sea trial, all teeth areto be checked for possible failures as scuffing, scratches, greystaining, pits, etc. Shrunk-on rims are to be checked for possi-ble movements relative to the hub.

I 200 Gear noise detection201 Gears are to be checked for noise in the full speed range(high frequencies as gear mesh frequencies) and in the lowerspeed range (gear hammer).

202 If the high frequent noise is higher than expected, meas-urements may be required.

203 Gear hammer is to be detected in the lower speed rangeand also during diesel engine misfiring tests (see Ch.3 Sec.1I500). Speed ranges or operating conditions resulting in gearhammer are to be restricted for continuous operation.

I 300 Bearings and lubrication301 Lubricating oil and bearing temperatures (as far as indi-cation is provided) are to be checked during the full load test.All temperatures are to reach stable values (no slow gradual in-crease) without exceeding the approved maximum values.

302 After the sea trial all oil filters are to be checked for par-ticles.

DET NORSKE VERITAS


SECTION 3CLUTCHES

A. General

A 100 Application

101 This section applies to clutches, both for use in shaft-lines and in gearboxes that are subject to certification, see Ch.2Sec.1 A200.

102 Clutches of standard design are to be type approved.

103 Ch.2 describes general requirements for rotating ma-chinery. Attention is to be paid to Ch.2 Sec.3 A100 and in par-ticular A102.

104 Clutches are to be delivered with a NV certificate.

A 200 Documentation201 At least a sectional drawing of the clutch is to be submit-ted for approval.

The drawing is to show all details such as:

— connection to external shafts— type of material— mechanical properties — heat treatment of splines etc. — stress raisers — activation system.

202 The following particulars are to be submitted for eachclutch:

— static friction torque (with corresponding working pres-sure)

— dynamic friction torque (with corresponding workingpressure)

— maximum working pressure— minimum working pressure— pressure for compressing return springs— permissible heat development and flash power when

clutching-in (upon request when case-by-case approval)— alarm set points and delay times, see E.

203 For each application the clutching-in characteristicswith tolerances (pressure as function of time) including max.engaging speed, is to be submitted for approval.

204 Upon request the documentation (simulation calcula-tion) of the engaging process may be required, see Ch.3 Sec.1A501 b)c).

B. Design

B 100 Torque capacities101 The torque capacities of clutches for auxiliary purposesas well as propulsion are to be:

— static friction torque at least 1.8 T0 and preferably notabove 2.5 T0

1)

— dynamic friction torque at least 1.3 T0

Both requirements referring to nominal operating pressure andno ice class notation.

102 The torque requirements in 101 may have to be in-creased for plants with ice class notation, see Pt.5 Ch.1 of theRules for Classification of Ships. If the ice class application

factor KAice > 1.4, the torque capacities are to be increased bythe ratio:

KAice/ 1.4.

103 For clutches used in plants with high vibratory torques(beyond 0.4 T0) or intermittent overloads, the torque capacityrequirements will be especially considered.

B 200 Strength and wear resistance

201 The relevant parts such as flange connections, shrinkfits, splines, key connections, etc. are to meet the requirementsgiven in Sec.1 B300 to B700.

202 If a disc clutch is arranged so that radial movements oc-cur under load, the possible wear of the teeth and splines is tobe considered. This may be relevant for clutches in gearboxeswhere a radial reaction force may act on the discs. Such radialforces may occur due to bearing clearances in either an inte-grated pinion and clutch design or shafts that are moved offcentre due to tooth forces.

203 Trolling clutches are subject to special consideration.

B 300 Emergency operation

301 Clutches for single propulsion plants are to be of a de-sign that enables sufficient torque transmission to be arrangedin the event of loss of hydraulic or pneumatic pressure. Thismeans that for plants on board vessels without ice class or re-inforcement due to high torsional vibration level at least half ofthe rated engine torque is to be transmitted.

302 If the requirement in 301 is fulfilled by means of bolts,easy access to all bolts should be provided. For built-in clutch-es, this means normally that all the bolts are to be on the partof the clutch that is connected to the engine. This in order togain access to all bolts by using the engine turning gear. Suchbolts are to be fitted in place and secured to the clutch. Alter-native arrangements are subject to special consideration and inany case it should be possible to carry out the emergency oper-ation within 1 hour. The emergency operation procedureshould be given in the operating manual.

B 400 Type testing

401 Type testing in order to verify friction torques as speci-fied in 101 may be required.


C 100 Certification

101 Regarding certification schemes, short terms, manufac-turing survey arrangement and important conditions, see Ch.2Sec.2.

C 200 Inspection and testing of parts

201 Power transmitting parts as hubs, flanges and outer partsare to be documented with Work certificates (W) regardingchemical composition of the material and mechanical proper-ties.

202 Surface hardened (> 400 HV) zones with stress raiserssuch as keyways, radial holes, splines, etc. as well as shrinkagesurfaces are to be crack detected by means of magnetic particleinspection or dye penetrant. This is to be documented with aWork certificate (W).Unless otherwise approved on basis of experience, this appliesto 100%. Non-surface hardened zones with stress raisers are to

1) When above 2.5 T0 the documentation in A204 is obligatory.

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be crack detected if specified in the design approval.

D. Workshop Testing

D 100 Function testing

101 The clutch is to be function tested before certification.

102 If the clutch is delivered with the activation control, thepressure - time function for clutching-in is to be verified in thepresence of a surveyor. If the clutch is oil operated this is to bemade with a representative oil viscosity.

E. Control, Alarm and Safety Functions and Indication

E 100 Summary

101 Clutches are to be provided with:

— local and remote pressure indication, If individual localpressure indicators are not fitted, quick connectors for aportable instrument are to be provided in order to do localreadings and set point verification of switches. The corre-sponding portable instrument is to be provided on board.

— low pressure alarm (level 1) with automatic start of stand-by pump (if applicable) and load reduction with alarm(level 2).

F. Arrangement

F 100 Clutch arrangement

101 Clutches are to be arranged to minimise radial supportforces, see B202.

102 Easy access to the emergency operation device is to beprovided, see B300.

G. Vibration

G 100 Engaging operation

101 The calculation of the engaging process is to be based onthe particulars specified in A202 and A203. The calculation isto result in torque, flash power and heat development as func-tions of time, and are not to exceed the permissible values forthe clutch or any other element in the system. See also Ch.3Sec.1 G403.


H 100 Alignment

101 Clutches not integrated in a gearbox or thruster, are to bechecked for axial and radial alignment in the presence of a sur-veyor.


I 100 Operating of clutches

101 The following are to be checked in the presence of a sur-veyor:

— when engaged, the operating pressure to be within the ap-proved tolerance

— access to the emergency operation device (see B300), ifapplicable

— during engaging, the operating pressure as a function oftime to be according to the approved characteristics.

102 The clutch engaging as mentioned above, is to be madeat the maximum permissible engaging speed. The pressure in-dication is to be representative for the operating pressure, i.e.measured close to the rotating seal and without throttling be-tween the instrument and operating pressure pipe. No pressurepeaks beyond the specified maximum pressure are accepted.

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SECTION 4BENDING COMPLIANT COUPLINGS

A. General

A 100 Application

101 This section applies to couplings used in machinery thatis subject to certification, see Ch.2 Sec.1 A200.

Bending compliant couplings are membrane couplings, toothcouplings, link couplings, universal shafts, etc., i.e. all cou-plings that have a low bending rigidity, but high torsional ri-gidity. Couplings combining both low bending and lowtorsional rigidity are to fulfil the requirements in both Sec.4and Sec.5.

102 Couplings of standard design are to be type approved.


104 Couplings are to be delivered with a NV certificate.

A 200 Documentation

201 Drawings showing the couplings in longitudinal section(for link couplings also transverse section) are to be submittedfor approval.

The drawings are to specify:

— the type of material and mechanical properties — surface hardening (if applicable)— shot peening (if applicable)— design details as keyways, bolt connections, or any other

stress concentration.

For power transmitting welds a full NDT specification includ-ing acceptance criteria is to be submitted. For tooth couplingsthe tooth accuracy (ISO 1328) is to be specified.

202 For high speed couplings (for connection to gas tur-bines) the maximum residual unbalance is to be specified.

203 The following particulars are to be submitted:

— the permissible mean torque— the permissible maximum torque (impact torque)— the permissible vibratory torque for continuous operation— the permissible angular tilt for continuous operation— the permissible radial misalignment or reaction force (if

applicable) for continuous operation— the permissible axial misalignment for continuous opera-

tion— the angular (tilt), radial and axial stiffness (as far as appli-

cable)— the maximum permissible r.p.m.

204 Calculations to substantiate the relevant particulars giv-en in 203 are to be submitted upon request.

B. Design

B 100 General

101 For design principles see Ch.2 Sec.3 A100.

102 Couplings for turbine machinery (high speed side) con-taining high energy rotating parts that may be ejected in theevent of a remote failure are to have special guards or designprecautions.

B 200 Criteria for dimensioning

201 The couplings are to be designed with suitable safetyfactors against fatigue (“suitable safety factors” will depend onthe method applied, but typically be about 1.5).

202 For connections as flanges, shrink fits, splines, key con-nections, etc. see the requirements in Sec.1 B300 to B700 re-spectively.

203 For membrane, link or disc couplings the safety againstfatigue is to be documented:

— All relevant combinations of permissible loads (A203) areto be considered

— The calculations may be combined with results from ma-terial fatigue tests

— The safety against fatigue may also be documented by fa-tigue testing of the complete coupling. If so, the load andthe kind of loading (or combinations thereof) is to be se-lected to document the safety when all permissible loadsare combined.

204 Tooth couplings are to be designed to prevent tooth frac-ture, flank pitting and abrasive wear.

The maximum permissible radial reaction force, the permissi-ble mean and vibratory torque, the angular misalignment andthe lubrication conditions are to be combined in the calcula-tions.

205 Universal shafts with power transmitting welds are to bedesigned for a high safety against fatigue in the weld. The cal-culation is to consider the maximum permissible loads and thespecified weld quality.

The stresses in the welds combined with the maximum permis-sible defects according to the NDT specification are not tocause a stress intensity of more than .

Ball and roller bearings are to have a minimum L10a (ISO 281)life time that is suitable with respect to the specified overhaulintervals.


C 100 Certification

101 Regarding certification schemes, short terms, manufac-turing survey arrangement and important conditions, see Ch.2Sec.2.

C 200 Inspection and testing of parts

201 Power transmitting parts as hubs, sleeves, shaft tubes,flanges and flexible elements are to be documented with Workcertificates (W) regarding chemical composition of the materi-al, mechanical properties and surface hardness (if surface hard-ened).

202 Zones with stress raisers such as keyways, holes, teeth,splines, etc. as well as shrinkage surfaces are to be crack de-tected by means of magnetic particle inspection or dye pene-trant. This applies to 100% for surface hardened (>400 HV)zones. For not surface hardened zones with stress raisers, crackdetection may be required in connection with design approval.

203 Welds are to be documented in accordance with the ap-proved specification.

2MPa m

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D. Workshop Testing

D 100 Balancing101 The couplings are to be balanced in accordance with theapproved specification.

D 200 Stiffness verification201 For membrane, link and disc couplings verification ofthe specified stiffness in angular and axial directions is to becarried out by means of static measurements in the presence ofa surveyor. This applies to:

— one coupling of a series for which type approval is request-ed

— every case by case approved non-standard coupling.


E 100 General101 Control, alarm, safety functions and indication are notrequired.

F. Arrangement

F 100 Coupling arrangement101 Couplings are to be arranged to avoid the limitations

given in A203 to be exceeded. Furthermore, the reaction forcesfrom couplings on the adjacent elements are to be taken intoaccount. All permissible operating conditions are to be consid-ered.

G. Vibration

G 100 General101 Not required.


H 100 Alignment101 The coupling alignment (axial, radial and angular) is tobe checked in the presence of a surveyor. The alignment is tobe within the approved tolerances for the coupling as well asany other limitation specified in the shafting arrangementdrawings (in particular for the high speed side of gas turbineplants).

102 The alignment is to be made under consideration of alladjacent machinery such as resiliently mounted engines, etc.


I 100 General101 Not required.

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SECTION 5TORSIONALLY ELASTIC COUPLINGS

A. General

A 100 Application

101 This section applies to couplings used in machinery sub-jected to certification, see Ch.2 Sec.1 A200.

Torsional elastic couplings mean steel, rubber and siliconecouplings designed for a low torsional rigidity. Couplingscombining both low torsional rigidity and bending flexible el-ements as membranes or links are to fulfil the requirements inboth Sec.4 and Sec.5.

102 Couplings of standard design are to be type approved.


104 Couplings are to have a NV certificate.

A 200 Documentation

201 Drawings showing the couplings in longitudinal sectionare to be submitted. For elements that are non-symmetricalaround the axis of rotation, a transverse section is also needed.

The drawings are to specify:

— type of material and mechanical properties— surface hardening (if applicable) — shot peening (if applicable)— design details as keyways, splines or any other stress con-

centration

For power transmitting welds a full NDT specification includ-ing acceptance criteria is to be submitted.

202 The following particulars are to be submitted:

— rubber shore hardness H (laboratory test on rubber plates)— permissible mean torque TKN with the corresponding

highest nominal shear stress in the elastomer and the bond-ing stress

— permissible maximum torque TKmax1 for repetitive loadsas transient vibration, typically during clutching in etc.,see Fig. 1

— permissible maximum torque range ∆Tmax for repetitiveloads as transient vibration, typically as passing through amajor resonance during start and stop etc., see Fig. 2

— permissible maximum torque TKmax2 for rare occasionalpeak loads, e.g. short circuits in generators

— permissible vibratory torque1) for continuous operationTKV , see Fig. 3

— permissible power loss1) (heat dissipation) PKV— permissible angular tilt, radial and axial misalignment for

continuous operation— angular (tilt), radial and axial stiffness1)

— permissible permanent twist of rubber element (applicableto progressive couplings)

— maximum permissible r.p.m.— quasi-static torsional stiffness1)

— dynamic torsional stiffness1) including production toler-ance

— damping characteristics1) including production tolerance.

1) as a function of the main parameters.

These particulars are to be documented by means of relevanttests and calculations. See B100 and B200.

Fig. 1TKmax1 at transient vibration

Fig. 2∆Tmax at transient vibration

Fig. 3TKV at continuous operation

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203 Definitions of stiffness and damping are:

A) For linear couplings

Fig. 4Linear couplings

The stiffness K ( ) is the gradient of a line drawn

between the extreme points of the twist as indicated in Fig.4.

For hysteresis plots that deviate from the ellipse (pure viscousdamping) the line that determines K shall be drawn throughpoints determined as midpoints between the upper and lowerpart of the hysteresis curve, see Fig.5.

Fig. 5Hysteresis curve

The damping is the ratio between the area described by thehysteresis loop AD and the elastic work Ael,

For couplings with typical elliptical hysteresis curves, otherdefinitions may be considered.

B) For non-linear couplings

Fig. 6Non-linear couplings

Plants with non-linear couplings may be calculated by eithersimulation (numeric time integration) in the time domain or inthe frequency domain by linear differential equations.

In the first case the torque – twist plots can be used directly.

In the second case (more common method) representative lin-earised coupling properties must be used in the calculation. Forthis purpose the following applies.

The (linearised) stiffness K is the gradient between the extremepoints of the twist as indicated above.

For determination of the damping ψ the elastic work Ael mustbe determined so that the above indicated areas of Ael are equal(A1 = A2). Then the same definition as for linear couplings ap-plies.

B. Design

B 100 General101 For design principles see Ch.2 Sec.3 A100.

102 See E101 for emergency claw devices.

B 200 Criteria for dimensioning201 The couplings are to be designed with suitable safetyfactors (depending on the method applied, see B300) againstfatigue and overheating (rubber).

202 For connections as flanges, shrink fits, splines, key con-nections, etc. see the requirements in Sec.1 B300 to B700 re-spectively.

203 For steel spring couplings the safety against fatigue is tobe documented. All relevant combinations of permissibleloads (A202) are to be considered. The calculations may becombined with results from material fatigue tests. The safetyagainst fatigue may also be documented by fatigue testing ofthe complete coupling. If so, the load and the kind of loading(or combinations thereof) are to be selected to document thesafety when all permissible loads are combined.

The design is to be so as to prevent fretting on vital elements.

204 Couplings are not to have rigid torsional deflection lim-iters (buffers) within the permissible TKmax2. Furthermore,TKmax2 is not to be less than 1.4 TKN.

205 For ice class notations the couplings are to be designedso that:

TKV > T0 (KAice – 1) and

TKmax1 > T0 KAice.

206 For elements that are not designed to avoid local strainconcentrations, stricter values for the criteria given in 207 and208 may apply.

For silicone couplings special considerations apply.

207 For rubber couplings with shear loaded rubber elementsthe shear stress (MPa) due to TKN is not to exceed the smallervalue of:

— 1% of the shore hardness value

or

— 0.65 MPa

The corresponding shear stress in the steel-rubber bonding sur-faces is normally not to exceed 0.45 MPa.

The shear stress due to the permissible vibratory torque forcontinuous operation is not to exceed 0.25% of the shore hard-ness. This shear stress is superimposed to the shear stress dueto TKN. The corresponding peak value is not limited by TKmax1in 208.

Torque,TA

A el

D

∆Tel

∆ϕ ϕtwist

K∆Te1

∆ϕ------------=

twist

Torque,T A

Ael

D

••

••

ϕ∆ ϕ

•

∆Tel

ψAD

Ae1---------=

twist ϕ

Torque,TAA el

D

∆Tel

∆ϕ

A2

A1

= A = A2 1

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208 When not substantiated by means of an approved fatiguetesting combined with FE analyses, the following applies:Permissible torque ∆Tmax and TKmax1 for transient operation(50.000 cycles) are limited to:

a) A nominal shear stress ∆τmax not to exceed ∆τmax < 0.24 · 10-3 H2

b) A nominal shear stress τmax1 not to exceed in any directionτmax1 < 0.2 · 10-3 H2 and limited to TKmax1 ≤ 1.5 TKNNote that TKmax1 is not limiting the shear stress due toTKN + TKV.

209 The strength of the emergency claw device (if required,see 102) is to be documented by calculations. This device is tobe designed for a minimum lifetime of 24 hours and combinedwith all permissible misalignments.

210 Couplings of natural rubber are not to be subjected toambient temperatures above 70°C.

B 300 Type testing

301 Type testing applies to all rubber and silicone couplings,but also for special kinds of steel spring couplings.

302 Steel spring couplings that are designed such that thedamping properties are essentially non-viscous (e.g. mainlyfriction damping), are to be dynamically tested in order to es-tablish the dynamic characteristics (stiffness and damping) asfunctions of their main parameters.

303 Rubber and silicone couplings are to be documentedwith regard to compatibility with the characteristics and per-missible loads given in A202. This is to be made with both cal-culation and testing:

— As a minimum the dynamic torsional stiffness and thedamping are to be verified by testing, see 304. A reducedextent may apply for couplings that are approved for veryrestricted applications as e.g. in electric motor driventhrusters.

— Couplings used in plants with reciprocating machinery arealso to be tested for determination of permissible powerloss. Exemptions may only be made if the value for PKV isassessed very much to the safe side.

— The necessity for test documentation of the angular (tilt),radial and axial stiffness depends on the correspondingvalues for permissible misalignment.

— For case by case approval of a non-standard coupling thedocumentation (i.e. testing) applies to the necessity for theactual coupling application.

— For type approval of a coupling series where the couplingsizes only differ by a scale factor, the documentation test-ing for stiffness and damping of only one size (per rubbertype) may be sufficient. However, if power loss testing ap-plies, this testing is to be made with at least two differentcoupling sizes in order to extrapolate for inclusion of thewhole series.

— Quasi-static tests such as described in D200 are to be madewith the same elements as used for the dynamic testing,and prior to it. The purpose is to establish reference valuesfor certification testing.

304 The purpose for the testing of stiffness and damping isto establish the relations between the quasi-static tests men-tioned above and the dynamic behaviour of the coupling. Fur-thermore, the type testing is to establish the dynamic torsionalstiffness and damping (for the relevant rubber qualities of rel-evant element sizes) as functions of the main parameters suchas:

— Mean torque TM, normally at steps as

— Vibratory torque TV, normally at steps as

(* for the purpose of transient vibrations)— Vibration frequency, normally at steps as

and for elements loaded in compression, also at 40 Hz

— Temperature of the element. This is for the purpose of es-tablishing representative stiffness and damping values un-der various ambient temperatures as well as under highpower losses.Normally at:

reference condition, e.g. 30°C25% of permissible PKV *

100% of permissible PKV *

For couplings not to be used in diesel engine plants the tests atreference condition will be sufficient.

* PKV as for rotating or non-rotating coupling, whichever isrelevant for the laboratory.

It is not required to test all the possible combinations of theconditions mentioned above. Normally reference conditions ase.g. the bold values above, are kept constant when one param-eter dependency is tested. However, for typically progressivecouplings (stiffness increasing with torque) all permissiblecombinations of mean and vibratory torques are to be tested.

The test results are to be presented as torque-twist plots, to-gether with the details of the evaluation method.

305 The testing of the permissible power loss is to be madeby means of at least one temperature sensor in the rubber coreat the expected (calculated) position of maximum temperature(position to be approved prior to the testing).

The core temperature during pulsating of the element is to beplotted as a function of time until the end temperature is stabi-lised. The maximum permissible core temperature is 110°C fornatural rubber and 150°C for silicone.

The permissible power loss PKV is defined as the power lossthat results in the maximum permissible core temperature. PKVis normally tested at an ambient temperature of 20°C and is tobe linearly interpolated to zero at maximum permissible coretemperature as a function of operating ambient temperature.For coupling series where the sizes only differ by a scale fac-tor, interpolation and extrapolation may be done by the follow-ing formula:

PKV = a TKNb

where the constants a and b can be determined by testing twoor more different sizes of couplings in a series.

The power loss is normally to be measured by means of torque-twist plots and applied frequency. Alternative methods may beconsidered if their relevance can be documented and the resultsare estimated to the safe side.

When a steady state condition is reached, e.g. not more than1°C increase per hour, the actual power loss is determinedfrom a torque-twist plot as PKVtest = AD · f (Hz).

If the core temperature during this test ϑ test is different fromthe permissible value ϑ p, the PKV is determined as:

ϑ A = ambient temperature during testϑ Aref = reference temperature in catalogue.

Alternative methods to torque-twist pulsating may only be ac-TM/TKN = 0 0.25 0.50 0.75 1

TV/TKV = 0.50 1.0 2.0 *

2 Hz 10 Hz 20 Hz

PKV PKVtest

ϑp ϑAref–

ϑtest ϑA–--------------------------⋅=

DET NORSKE VERITAS


cepted if the evaluation of PKV is made conservatively (to thesafe side). If rotating with radial or angular misalignment isused, the assessment of the actual power loss in the elementsmust consider all possible increase of other losses (e.g. in bear-ings).

Further, the different temperature field versus the real one intorque-twist must be taken into consideration by e.g. finite el-ement analyses or preferably by comparison measurements inorder to arrive at a correlation factor between the applied meth-od and the real torque-twist condition.


C 100 Certification101 Regarding certification schemes, short terms, manufac-turing Survey Arrangement and important conditions, see Ch.2Sec.2.

C 200 Inspection and testing of parts201 Power transmitting parts as hubs, sleeves, shaft tubes,flanges etc. are to be documented with Work certificates (W)regarding chemical composition of the material, mechanicalproperties and surface hardness.

202 Surface hardened (> 400 HV) zones with stress raiserssuch as keyways, holes, splines, etc. as well as shrinkage sur-faces are to be crack detected by means of magnetic particle in-spection or dye penetrant. Unless otherwise approved on basisof statistics, this applies to 100%. Non-surface hardened zoneswith stress raisers are to be crack detected if specified in con-nection with the design approval. This is to be documentedwith a Work certificate (W).

203 Welds are to be documented with a Work certificate (W)in accordance with the approved specification.

D. Workshop Testing

D 100 Stiffness verification101 Each rubber or silicone coupling or elastic element is tobe verified with regard to quasi-static torsional stiffness in thepresence of a surveyor. This is to be done by twisting the cou-pling or by subjecting the elastic elements to a load which isequivalent to the coupling twist. The test torque is to be at least1.5 TKN. The resulting deflection is to be within the approvedtolerance and the deviation is to be specified in the certificate.

102 For couplings that are not approved for use in plantswith reciprocating machinery a reduced extent of testing maybe accepted.

103 For segmented couplings the assembling of a couplingwith segments from different charges (possibly different stiff-ness) is to be within the approved tolerance range for segmentdifferences.

D 200 Bonding tests201 For couplings with bonded rubber or silicone elementsthe bonding is to be checked in the presence of a surveyor. Thecoupling or elastic element is to be loaded in at least one direc-tion to the 1.5 TKN. At this load the element is to be inspectedfor any signs of slippage in the bonding surface. Additionallythe corresponding torque-deflection curve is to be smooth andshow no signs of slippage in the bonding.

202 The bonding may also be documented by alternativetests as e.g. tension where the tensile stress is to be at least ashigh as the shear stress under 1.5 TKN.

203 For couplings that have a limitation of the permanenttwist (all progressive couplings) are to be marked so that the

actual permanent twist and the limit twist are legible duringservice inspections.

D 300 Balancing301 Couplings for PTO/PTI branches are to be single planebalanced when:

— tip speed > 30 m/s— unmachined surfaces and tip speed > 10 m/s

E. Control, Alarm, Safety Functions and Indication

E 100 Summary

101 Elastic couplings for propulsion of single diesel engineplants are to be equipped with monitoring and alarm for:

— high angular twist amplitudes— high mean twist angle.

The alarm levels are subject to approval..

This applies to couplings when failure of the elastic elementmeans loss of torque transmission. Exemption may be accept-ed for couplings that are of a design that enables the full torqueto be transmitted in the event of failure of the elastic elements.Such emergency claw devices are not “getting home” devices,but only meant for temporary emergency in order to preventloss of manoeuvrability in harbours, rivers, etc

102 For couplings where twist amplitude alarm is chosen formonitoring of torsional vibration, see Ch.3 Sec.1 G302 j) andG303 d), the alarm levels and time delays are subject to specialconsideration.

F. Arrangement

F 100 Coupling arrangement

101 Couplings are to be arranged to avoid that the limitationsgiven in A202 are exceeded. Furthermore, the reaction forcesfrom couplings on the adjacent elements are to be taken intoaccount. All permissible operating conditions are to be consid-ered.

G. Vibration

G 100 General

101 Torsional vibration is covered by the relevant section forthe prime mover, e.g. diesel engines in Ch.3 Sec.1 G. Lateralvibration is covered by Sec.1 G100 and G200.

102 Lateral vibration calculations of arrangements with seg-mented couplings may be required. The calculations are toconsider the rotating forces due to possible unbalanced tangen-tial forces (1.0 order) at full torque as well as correspondingforces due to torsional vibration. Stiffness variations, in ac-cordance with the approved tolerance for the segmented cou-pling, are to be assumed.

103 The coupling data as stiffness and damping used for tor-sional vibration analysis are to be representative for the actualambient temperature as well as the temperature rise due topower loss. Further, the specified production tolerances are tobe considered.

Guidance note:Typical ambient temperature are:

— bell housing (with ventilation openings) 70°C

DET NORSKE VERITAS


— free standing at flywheel of diesel engine up to 50°C— free standing PTO branch from a gearbox 30°C— outside main engine room, special consideration.



H 100 Alignment101 The coupling alignment (axial, radial and angular) is tobe checked in the presence of a surveyor. The alignment is tobe within the approved tolerances for the coupling as well as

any other limitation specified in the shafting arrangementdrawings.

102 The alignment is to be made under consideration of alladjacent machinery such as resiliently mounted engines, etc.


I 100 Elastic elements

101 After the sea trial all rubber elements in propulsionplants and power take off branches are to be visually checkedby a surveyor. No cracks or deterioration are acceptable.

DET NORSKE VERITAS

dnv ship rules pt.4 ch.4 - rotating machinery, power transmission

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