ad 2000-mb - b7 -09-2010

AD 2000-Merkblatt

ICS 23.020.30 September 2010 edition

Design of

pressure vessels Boltings

AD 2000-Merkblatt

B 7

The AD 2000-Merkblätter are prepared by the seven associations listed below who together form the “Arbeitsgemeinschaft Druck-behälter” (AD). The structure and the application of the AD 2000 Code and the procedural guidelines are covered by AD 2000-Merk-blatt G 1.

The AD 2000-Merkblätter contain safety requirements to be met under normal operating conditions. If above-normal loadings are to be expected during the operation of the pressure vessel, this shall be taken into account by meeting special requirements.

If there are any divergences from the requirements of this AD 2000-Merkblatt, it shall be possible to prove that the standard of safety of this Code has been maintained by other means, e.g. by materials testing, tests, stress analysis, operating experience.

Fachverband Dampfkessel-, Behälter- und Rohrleitungsbau e.V. (FDBR), Düsseldorf

Deutsche Gesetzliche Unfallversicherung (DGUV), Berlin Verband der Chemischen Industrie e.V. (VCI), Frankfurt/Main

Verband Deutscher Maschinen- und Anlagenbau e.V. (VDMA), Fachgemeinschaft Verfahrenstechnische Maschinen und Apparate, Frankfurt/Main

Stahlinstitut VDEh, Düsseldorf

VGB PowerTech e.V., Essen

Verband der TÜV e.V. (VdTÜV), Berlin

The above associations continuously update the AD 2000-Merkblätter in line with technical progress. Please address any proposals for this to the publisher:

Verband der TÜV e.V., Friedrichstraße 136, 10117 Berlin.

Contents

Page

0 Foreword.................................................................................................... 2

1 Scope......................................................................................................... 2

2 General ...................................................................................................... 2

3 Symbols and units ..................................................................................... 3

4 Design temperature ................................................................................... 3

5 Safety factor............................................................................................... 3

6 Calculation ................................................................................................. 3

7 Allowances................................................................................................. 5

8 Minimum permissible bolt diameter ........................................................... 8

9 Literature.................................................................................................... 8

Supersedes August 2007 edition; | Amendments to previous edition

AD 2000-Merkblätter are protected by copyright. The rights of use, particularly of any translation, reproduction, extract of figures, transmission by photomechanical means and storage in data retrieval systems, even of extracts, are reserved to the author. Beuth Verlag has taken all reasonable measures to ensure the accuracy of this translation but regrets that no responsibility can be accepted for any error, omission or inaccuracy. In cases of doubt or dispute, the latest edition of the German text only is valid.

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AD 2000-Merkblatt B 7, 09.2010 edition

0 Foreword

The AD 2000 Code can be applied to satisfy the basic safety requirements of the Pressure Equipment Directive, principally for the conformity assessment in accordance with modules “G” and “B F”.

The AD 2000 Code is structured along the lines of a self-contained concept. If other technical rules are used in accordance with the state of the art to solve related problems, it is assumed that the overall concept has been taken into account.

The AD 2000 Code can be used as appropriate for other modules of the Pressure Equipment Directive or for different sectors of the law. Responsibility for testing is as specified in the provisions of the relevant sector of the law.

1 Scope

This AD 2000-Merkblatt applies to the design of bolting which as a non-positive connecting element is predominantly subjected to static tension. Additional loads due to thermal influences e.g. local or temporary thermal gradients, different thermal expansion coefficients and the like or external forces (e.g. from connecting pipe work) are not covered by this AD 2000-Merkblatt and should be considered separately1) if required.

2 General

2.1 This AD 2000-Merkblatt shall only be used in conjunction with AD 2000-Merkblatt B 0.

2.2 In order to make a bolted connection as elastic as possible, it is recommended to design it with necked-down bolts to DIN 2510. Necked-down bolts should be applied if the design temperature exceeds 300 °C or if the permissible operating pressure is higher than 40 bar. Care has to be taken that adequate effective bolt length is available which can be increased e.g. by sleeves to DIN 2510. The length of the bolt shank shall be at least twice the thread diameter.

2.3 Necked-down bolts are regarded to be bolts having a shank diameter ds 0,9 dK or having dimensions according to DIN 2510. Bolts with no reduced shank are regarded as being rigid as far as design is concerned.

2.4 Proof of the adequate load carrying capacity of bolted connections shall be provided either by calculation or by the application of a suitable standard, particularly when different pairs of materials are used or the geometries deviate from the relevant standards.

2.5 In the case of standardized pipe flanges the bolts are deemed to meet these requirements if number and diameter comply with the relevant pipe flange standard and the permissible service temperature for these flanges is not exceeded. For design temperatures higher than 120 °C and materials specified in the standards, the permissible operating pressure shall be reduced according to the decrease of the yield strength. This applies, however, to materials to AD 2000-Merkblatt W 7 only. Higher temperatures can also be considered by using materials with an accordingly higher yield point.

2.6 For shell flanges to DIN 28032, DIN 28034, DIN 28036 and DIN 28038 the bolts are deemed to meet the requirements above if they comply with DIN 28030.

2.7 Bolted flange connections should have as many bolts as possible in order to obtain optimal tightening conditions and a pitch that is as small as possible (see AD 2000-Merkblatt B 8, Subclause 2.3).

2.8 The contact surfaces of bolts and nuts shall be at least of product grade B according to DIN EN ISO 4759-1. The thread shall be within the tolerance quality “medium” according to DIN ISO 965-2.

2.9 Consult also AD 2000-Merkblatt A 5, Clause 3 regarding bolting design. Bolt hooks subjected to unilateral loads shall not be used.

2.10 Flanges with slot and key or spigot and socket, or plain flanges with special gaskets (flanged gaskets, spiral asbestos gaskets with forced-in wire-mesh) shall not be used for inflammable or toxic gases.

2.11 Material combinations for bolts and nuts serving as pressure-containing elements for connection with the relevant flange materials can be evaluated in accordance with DIN EN 1515, Parts 1 to 4. In doing so, the specifications given in AD 2000-Merkblätter W 7 and W 9 shall be taken into consideration.

The suitability of non-metric thread types can be evaluated on the basis of the geometric comparison given in DIN EN 1759-1, Annex C.

1) E.g. on the lines of prestandard DIN 2505 (01.1986).


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3 Symbols and units

In addition to AD 2000-Merkblatt B 0 the following applies:

bD effective width of gasket in mm

c5 design allowance for rigidly connected bolts in mm

dK root diameter of bolt thread in mm

dS shaft diameter of a bolt in mm

n number of bolts –

AD area in compression in mm2

KD dimension stability of gasket material at the design temperature MPa UD mean gasket circumference in mm

X number of grooves –

in this context: auxiliary factor –

4 Design temperature

The design temperature depends on the type of bolted connection and the thermal insulation. If there is no extra proof of the bolt temperature or if the bolting is not in direct contact with the vessel content having a temperature higher than 50 °C then the design temperature of the bolting may be assumed to be lower than the maximum temperature of the vessel content by

a) 30 °C with two loose type flanges connected

b) 25 °C with one integral type and one loose type flange connected

c) 15 °C with two integral type flanges connected.

These temperature differences consider the decreased temperatures in the case of insulated bolted connections. Further reduction without extra proof of the bolt temperature is not acceptable even for bolted flange connections without insulation operating at lower temperatures which produce higher thermal stresses in the bolted connection though the bolt temperature is lower. For permissible service temperatures below 10 °C refer to AD 2000-Merkblatt W 10.

5 Safety factor

The safety factors for bolt materials shall be determined with a yield point/tensile strength ratio 0,8 according to Table 3.1; Table 3.2 applies for a yield point/tensile strength ratio 0,8. 0,75 shall be used for bolts with unmachined but parallel contact surfaces, eyebolts and hinged bolts; 1,0 for machined or equivalent contact surfaces. Non parallel contact surfaces are not permissible.

6 Calculation

6.1 Determination of the bolt load

6.1.1 General

The bolt load shall be determined for the bolting-up condition prior to pressurization and for service conditions. Where the test pressure is p 1,43 p, the bolt load shall also be determined for this load condition. For bolt materials with a yield point/tensile strength ratio 0,8, the bolt loads shall always be determined for the test condition.

6.1.2 Circular bolted flange connections with the gasket within the bolt-circle diameter

6.1.2.1 The minimum required bolt load is for the service condition

FSB FRB FFB FDB (1)

with the components

40

2i

RBdpF

(2)

40

2i

2D

FBddpF

(3)

FDB 10

p dD SD k1 (4)

where SD 1,2.

Equations (1) to (4) may be applied for the testing condition accordingly.


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6.1.2.2 The minimum required bolt load is for the bolting-up condition

FDV dD k0 KD (5)

If the setting load FDV is greater than FSB it may be replaced in the case of soft gaskets and metal coated soft gaskets by

F*DV 0,2 FDV 0,8 DVSB FF (6)

6.1.2.3 In order to keep the gasket load, bolt load and flange torsion as small as possible, it is recommended to design the gasket as narrow as possible (e.g. to DIN 28040) taking account of the permissible surface pressure (according to the gasket manufacturer’s data). For soft gaskets and metal coated soft gaskets permanent setting after first pressurization may occur. This is to be compensated by tightening the bolts.

For metal gaskets the permissible load during service is

FD dD k0 KD (7)

or, where these are grooved

FD dD X k0 KD (8)

with KD to be taken from Table 2.

The bolted flange connection remains tight after several starts and stops only if

FD FSB (9)

If the permissible gasket load is exceeded it is recommended to shift to a more suitable gasket material or gasket type.

6.1.2.4 The gasket characteristics k1, k0 and KD or k0 KD are to be taken from Tables 1 and 2 taking into account that the characteristics for gases and vapours only apply for the service condition. Characteristics for other gasket types and shapes shall be determined by tests.

6.1.3 Circular bolted flange connection with full-face gasket

The bolt load shall be determined as in Equations (1) to (6). Here the gasket diameter dD is equal to the bolt-circle diameter dt and bD as in Table 1 is equal to half the effective width of the gasket.

6.1.4 Rectangular and other bolted flange connections having the gasket within the bolt-circle diameter

The minimum required bolt load for the service condition is for rectangular bolted flange connections

FSB 10

p e f 2 SD e f k1 (10)

and for other bolted flange connections

FSB 10

p AD SD UD k1 (11)

with SD 1,2.

Equations (10) and (11) may be applied for the test condition accordingly.

The minimum required bolt load for the bolting-up condition is for rectangular bolted flange connections

FDV 2 e f k0 KD (12)

and for other bolted flange connections

FDV UD k0 KD (13)

The values for e, f, AD and UD are referred to the mean contact line of the gasket.

Equation (6) may be applied accordingly.

6.1.5 Rectangular and other bolted flange connections with full-face gasket

The bolt load shall be determined as in Equations (10) to (13). The values for e, f, AD and UD are referred to the bolt hole centres and bD as in Table 1 is equal to half the effective width of the gasket. Equation (6) may be applied accordingly.


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6.2 Determination of bolt diameter

The required root diameter dK for rigid bolts or shank diameter dS for necked-down bolts of a bolted flange connection with n bolts is the greatest of the following

dK or dS Z nK

F

SB c5 (14)

for the service condition

dK or dS Z nK

F20

SP (15)

for the testing condition

dK or dS Z nK

F20

DV (16)

for the bolting-up condition with Z as in Table 3 or

Z S4

(17)

For necked-down bolts with bore, dS is to be replaced by 22S dd in Equations (14) to (16) where d is the bore diameter.

7 Allowances

For rigid bolts in the service condition the design allowance to Equation (14) is

c5 3 mm, if Z nK

F

SB 20 mm (18)

or

c5 1 mm, if Z nK

F

SB 50 mm (19)

Intermediate values are to be linearly interpolated according to

c5 15

65 SB

nKFZ

For necked-down bolts c5 0. Deviating from AD 2000-Merkblatt B 0 further allowances are not required.

Table 2 — Deformation resistance KD and KD of metallic gasket materials

KD KD in MPa Gasket material

MPa 100 °C 200 °C 300 °C 400 °C 500 °C

Soft aluminium 100 40 20 (5) – –

Copper 200 180 130 100 (40) –

Soft iron 350 310 260 210 170 (80)

Steel St 35 400 380 330 260 190 (120)

Alloy steel 13CrMo4-5 450 450 420 390 330 280

Austenitic steel 500 480 450 420 390 350

Intermediate values are to be interpolated.


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Table 1 — Gasket characteristics

Gasket characteristicsa

Liquids Gases and vapours

Settingb Service

conditionSettingb

Servicecondition

Group Type Designation Material

k0

mm

k0 KD

N/mm

k1

mm

k0

mm

k0 KD

N/mm

k1

mm

Board with suitable binder

– 20 bD bD – – –

Rubber – bD 0,5 bD – 2 bD 0,5 bD

Flat gaskets to DIN 2690

to DIN 2692

PTFEc – 20 bD 1,1 bD – 25 bD 1,1 bD

Expanded graphite without metal inlay

Graphite – –f –f – 25 bD 1,7 bD

Expanded graphite with metal inlay


Fibre material without asbestos

with a binder (hD 1 mm)

Fibre material – –f –f – 40 bD 2 bD

Soft gaskets

Fibre material without asbestos

with a binder (hD 1 mm)

Fibre material – –f –f – 35 bD 2 bD

Al – 8 bD 0,6 bD – 30 bD 0,6 bD

Cu, Ms – 9 bD 0,6 bD – 35 bD 0,7 bD Corrugated metal

Soft steel – 10 bD 0,6 bD – 45 bD 1 bD

Al – 10 bD bD – 50 bD 1,4 bD

Cu, Ms – 20 bD bD – 60 bD 1,6 bD

Metal coated gaskets

Flat metal jacketed asbestos

Soft steel – 40 bD bD – 70 bD 1,8 bD

Solid flat metal gasket

– 0,8 bD – bD 5 bD – bD 5

Diamond section ring gasket

– 0,8 – 5 1 – 5

Flat oval section ring gasket

– 1,6 – 6 2 – 6

O-section ring gasket

– 1,2 – 6 1,5 – 6

Ring joint gasket

– 1,6 – 6 2 – 6

Convex gasket to DIN 2696

– 1,6 – 6 2 – 6

X number of grooves

Grooved metal gasket to DIN 2697d

– 0,4 X – 9 0,2X 0,5 X – 9 0,2X

Flat metal weld gasket to DIN 2695

– 0 – 0 0 – 0

Metal gaskets

O-ringe

Rubber and rubber-like synthetic materials

0 – 0 0 – 0


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Table 1 — Gasket characteristics (continued)

Gasket characteristicsa

Liquids Gases and vapours

Settingb Service

condition Settingb

Servicecondition

Group Type Designation Material

k0

mm

k0 KD

N/mm

k1

mm

k0

mm

k0 KD

N/mm

k1

mm

PTFE coating on soft steel

PTFE – –f –f – 15 bD 1,1 bD

PTFE coating on stainless steel

PTFE – –f –f – 15 bD 1,1 bD

Graphite coating on soft steel


Graphite coating on low-alloy

high-temperature steel


Graphite coating on stainless steel


Grooved steel gaskets with soft covering on both sides

Silver coating on high-temperature

stainless steel Silver – –f –f – 125 bD 1,5 bD

PTFE filling on one side with

ring reinforcement PTFE – –f –f – 50 bD 1,4 bD

PTFE filling on both sides with

ring reinforcement PTFE – –f –f – 50 bD 1,4 bD

Graphite filling on one side with

ring reinforcement Graphite – –f –f – 40 bD 1,4 bD

Spiral gaskets with soft filling

Graphite filling on both sides withring reinforcement


a They apply to machined, flat and sound faces. Deviations are possible provided adequate proof has been furnished. The characteristics shall be regarded as minimum values. Higher gasket characteristics according to the manufacturer’s data sheet shall be noted.

b Where k0 cannot be given, the product of k0 KD is shown. c Polytetrafluoroethylene d The values do not apply to grooved metal gaskets with a covering. e The bolt load is to be increased by the ratio y1/y2 of the moment arms. f If there are no gasket characteristics for liquids, the gasket characteristic values for gases and vapours can be used.

Table 3.1 — Safety factor S, auxiliary factors Z and for a yield point/tensile strength ratio 0,8

Materials having a yield point and where the safety factor refers to the yield point or B/100000

Condition and quality factor Necked-down bolts e.g.

to DIN 2510 Bolts

Materials having no yield point and where

the safety factor refers to the tensile strength

Service conditions S 1,5 S 1,8 S 5,0

For 0,75 1,00

Z 1,60 Z 1,38

Z 1,75 Z 1,51

Z 2,91 Z 2,52

Bolting up and test condition S 1,05 S 1,26 S 3,0

For 0,75 1,00

Z 1,34 Z 1,16

Z 1,46 Z 1,27

Z 2,26 Z 1,95


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Table 3.2 — Safety factor S, auxiliary factors Z and for a yield point/tensile strength ratio 0,8

Materials having a yield point and where the safety factor refers to the yield point or B/100000

Condition and quality factor Necked-down bolts e.g.

to DIN 2510 Bolts

Service conditions S 1,5 S 1,8

For 0,75 1,00

Z 1,60 Z 1,38

Z 1,75 Z 1,51

Bolting up and test conditions S 1,1 S 1,3

For 0,75 1,00

Z 1,37 Z 1,18

Z 1,49 Z 1,29

8 Minimum permissible bolt diameter

Generally bolts smaller than M 10 or equivalent root diameter are not permissible. For special applications (e.g. bolts for fittings) smaller bolts may be used; however those shall not be smaller than M 6 or equivalent diameter.

9 Literature

[1] Trutnovsky, K.: Dichtungen; Werkstattbuch No. 92. Springer Verlag Berlin, Heidelberg, New York.

[2] Schwaigerer, S.: Festigkeitsberechnung im Dampfkessel-, Behälter- und Rohrleitungsbau. 4. Auflage (1983). Springer Verlag Berlin, Heidelberg, New York.

[3] Schwaigerer, S.: Die Berechnung der Flanschverbindungen im Behälter- und Rohrleitungsbau. VDI-Z. 96 (1954) No. 7.

Publisher: Source of supply:

Verband der TÜV e.V.

E-Mail: [email protected] http://www.vdtuev.de

Beuth Verlag GmbH 10772 Berlin Tel. 030 / 26 01-22 60 Fax 030 / 26 01-12 60 [email protected] www.beuth.de


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