ad 2000-mb - s1 -02-2005

AD 2000-Merkblatt ICS 23.020.30 February 2005 edition

Special cases Simplified analysis for cyclic loading

AD 2000-Merkblatt

S 1

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 beexpected 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 ofthis 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 Hauptverband der gewerblichen Berufsgenossenschaften e.V., Sankt Augustin Verband der Chemischen Industrie e.V. (VCI), Frankfurt/Main Verband Deutscher Maschinen- und Anlagenbau e.V. (VDMA), Fachgemeinschaft Verfahrenstechnische Maschinen undApparate, Frankfurt/Main Stahlinstitut VDEh, DüsseldorfVGB PowerTech e.V., Essen Verband der Technischen Überwachungs-Vereine e.V. (VdTÜV), Berlin

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

Verband der Technischen Überwachungs-Vereine e.V., Friedrichstraße 136, 10117 Berlin

Contents

0 Foreword

1 Scope

2 General

3 Symbols and units

4 Determination of allowable number of

load cycles

5 Design

6 Manufacture

7 Testing

8 Consideration of special operating conditions

9 Measures to be taken when the design lifetime

has been reached

10 Additional details

Annex 1: Explanatory notes on AD 2000-Merkblatt S 1

Annex 2: Example of calculation

Annex 3: Simplified analysis for cyclic loading for spher-

oidal graphite cast iron

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 prob-

lems, 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 dif

ferent sectors of the law. Responsibility for testing is as

specified in the provisions of the relevant sector of the

law.

1 Scope

1.1 The following rules on simplified analysis for cyclic

loading1) apply to pressure-bearing parts of pressure ves-

sels made of

– ferritic and austenitic rolled and forged steels,

– spheroidal graphite cast iron grades as specified in

Annex 3

manufactured and tested according to the W and HP

series of the AD 2000-Merkblätter.

1.2 The calculation only applies for components dimen-

sioned on the basis of non-time-dependent design strength

values (see 6.2 and 6.3 of AD 2000-Merkblatt B 0) and sub-

jected to cyclic loads only in the form of pressure fluctuations.

Additional cyclic loadings, for example loads due to rapid

1) The term "cyclic loading" is meant here in a comprehensive sense as the variation

over time of a loading regardless of the magnitude and arithmetic sign of the mean

value.

Supersedes October 2004 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. Carl Heymanns Verlag has taken all reason-

able 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. ww

w. b

eut h

. de

© B

eut h

Ve r

lag

Gm

b H, D

-10 7

72 B

erlin

BA75E3EC9238321DFDAD9E8AEA77DB4BB3DF8BFFFF8CE3D73A9D38EFA8

AD

200

0 C

od

e -

Issu

e 20

11-0

1

AD 2000-Merkblatt AD-2000-Merkblatt S 1, 02. 2005 edition

changes in temperature during operation or from external

forces and moments, are to be assessed within the

framework of the calculation according to AD 2000-

Merkblatt S 2.

1.3 The analysis for cyclic loading shall only be consid-

ered a lifetime expectancy calculation to reasonably de-

termine test and inspection intervals so that fatigue crack-

ing which may occur can be detected in time.

The number of load cycles to be withstood may attain a

multiple of the design load cycle number if the scatter

band of the fatigue values is taken into account and in the

case of boundary conditions for design, manufacture and

loading that are more favourable than those on which

design approval is based.

1.4 If the following two conditions are satisfied, AD 2000-

Merkblatt S 1 need not be applied.

a) The number of load cycles with pressure fluctuations

between pressureless condition and allowable working

pressure p (start-ups and shutdowns) is N ≤ 1000 and

b) the range ( ) of any number of load fluctuations

does not exceed 10 % of p.

The limit value for the pressure fluctuation range ( )

of 10 % may be increased to 20 % of p if the following

additional conditions are satisfied:

– the number of load cycles with pressure fluctuations

between pressureless condition and maximum allow-

able working pressure p (start-ups and shutdowns) is

N ≤ 1000

– steels with tensile strenghts ≤ 300 N/mm² at 20 °C, as

specified by the standards, are used

– wall thicknesses of up to 25 mm

– governing design temperature T* ≤ 200 °C

– geometries with a shape-dependent stress factor η ≤ 3

as shown in Table 3 of this AD 2000-Merkblatt.

1.5 With regard to an intended operational lifetime of

20 years (365 operational days) this AD 2000-Merkblatt

need not be applied either if the following conditions are

satisfied:

– the range of pressure fluctuations referred to

p does not exceed the values to Fig. 2

– steels with tensile strengths ≤ 300 N/mm² at 20 °C, as

specified by the standards, are used

The curves in Fig. 2 apply to

– N ≤ 1000 load cycles with pressure fluctuations be-

tween pressureless condition and allowable pressure

(start-ups and shutdowns)

– wall thicknesses of up to 25 mm

– governing design temperature T* ≤ 200 °C

– welded joints of weld class K 2 and geometries with a

shape-dependent stress factor η ≤ 3 as shown in Ta-

ble 3 of this AD 2000-Merkblatt.

For fillet welds for the connection of nozzles only 4/5 of the

referred pressure fluctuation range in Fig. 2 are beyond

the limits of application.

In the case of more than 1000 start-ups and shutdowns,

the ranges of pressure fluctuations as shown in Fig. 2

shall be reduced to obtain · Fp with Fp taken from

Fig. 3.

1.6 Instead of the maximum allowable pressure p the

ranges of pressure fluctuation ( ) may also be referred

to the design pressure pr (fictitious pressure).

1.7 If the number of pressure fluctuations to be expected

during operation exceeds the allowable number of load

cycles calculated according to this AD 2000-Merkblatt, it

is necessary to change the design or conduct a detailed

calculation according to AD 2000-Merkblatt S 2 to satisfy

the cyclic loading conditions.

1.8 This AD 2000-Merkblatt assumes that there are no

influences from the fluid which may reduce the fatigue life

(see clause 8).

1.9 A reduction in the permitted number of stress cycles

is not required at low operating temperatures within the

application limits of Stress Categories II and III in accor-

dance with AD 2000-Merkblatt W 10.

2 General 2.1 This AD 2000-Merkblatt shall only be applied in com-

bination with AD 2000-Merkblatt B 0.

2.2 The criterion for failure due to cyclic loading is an

incipient crack2).

2.3 A measure for cyclic loading in this AD 2000-

Merkblatt is the Auctation range (double the stress ampli-

tude) arising from the action of the repeatedly fluctuating

pressure (see Fig. 1).

2.4 The allowable number of load cycles calculated ac-

cording to AD 2000-Merkblatt S 1 is influenced by the

dimensioning and design of the pressure vessel. In the

case of frequent load cycles with considerable cyclic

loading, calculations according to AD 2000-Merkblatt S 2

are more practical, however, to assess appropriate modi-

fications measures. As a rule, this yields a greater allow-

able number of load cycles than the calculation to AD

2000-Merkblatt S 1.

2.5 Of special importance are fluctuations between the

unpressurised state and the maximum allowable pressure

p (start-ups and shutdowns). The pressure fluctuations

can also be superimposed, however, with low amplitude

on the working pressure (e.g. in surge or storage vessels)

or can arise with varying amplitude in the range between 0

and p with irregular sequence and differing frequency

(operational load regime). When the vessel is subjected to

external overpressure, the following procedure shall be

applied as appropriate: With pressure fluctuations be-

tween overpressure and vacuum in a pressure chamber,

in order to determine the pressure fluctuation amplitude,

the sum of the overpressure and vacuum values shall be

taken into account.

If different internal and external pressure load cycles fol-

low each other in a pressure chamber, the load cases

shall be considered separately and be evaluated in a uni-

versal load calculation.

If internal and external load cycles occur simultaneously at

a pressure-containing wall (e.g. between two pressure

chambers), the specific changes of pressure over time

shall be superposed and the resulting pressure fluctua-

tions of different amplitude and frequency shall be evalu-

ated by means of a universal load calculation.

2.6 The number and level of pressure fluctuations which

a pressure vessel can withstand during its probable life-

2) An incipient crack is a crack-type material discontinuity which can be detected by

optical means or non-destructive testing.

p∨∧ −p

p∨∧ −p

p∨∧ −p

pp–p

pp–p


AD

200

0 C

od

e -

Issu

e 20

11-0

1


time without damage to the pressure parts depend on a

large number of different influences, e.g.:

– Design,

e.g. configuration of component with regard to the

avoidance of high peak stresses;

– Manufacture,

e.g. avoidance of damaging residual stresses and weld

imperfections;

– Material,

softer steels are for example normally less notch-

sensitive than harder ones. With the notch-sensitive

steels it be noted that the probability of failure is

greater if a manufacturing defect is not noticed or the

operating conditions are unfavourable. The strength of

the weld metal should be equal to or just little higher

than that of the base metal;

– Surface condition,

design with minor surface roughness (machining, grind-

ing of welds) for high lifetime requirements;

– Wall thickness,

with equal stress range, an increase in the wall thick-

ness will reduce the component lifetime because of the

influence of size;

– Temperature,

higher temperatures reduce the cyclic strength of the

materials and hence the component's lifetime.

2.7 Corrosion arising during operation can reduce the

number of load cycles which can be withstood, especially

in notch-sensitive materials. Operational measures (see

8.1) and inspection during the operating period (see 7.3)

are of special importance here. Where a protective layer

forms, this shall be considered when dimensioning and

designing in order to prevent the protective layer from

tearing up.

2.8 For the calculation the following is defined as the

governing temperature during any load cycle under con-

sideration (see Fig. 1):

TTT(

·25,0+ˆ·75,0=* (1)

All temperature-related factors shall be related to this

governing temperature T* of the relevant load cycle.

2.9 To determine the allowable number of load cycles for

the whole vessel, the calculations according to clause 4

shall be performed for the various sections of the vessel.

The smallest value is the relevant one for the vessel.

3 Symbols and units The following symbols apply beyond the provisions of AD

2000-Merkblatt B 0 and as a deviation from it:

fT* temperature influence factor –

fN fatigue strength reduction factor for

welded joint classes –

fL load cycle increase (fatigue strength

extension) factor for pressure

fluctuations rp<pp (–ˆ

k number of intervals of differing pres-

sure fluctuation ranges which together

form the load regime –

pr pressure which can be calculated for

the whole vessel or also as ficticious

pressure only for sections with full utili-

sation of design stress K20/S and the

planned dimensioning according to B

series of the AD 2000-Merkblätter

(under certain circumstances, the for-

mulae shall be broken down to obtain p) in bar

)–ˆ( pp(

pressure fluctuation range (double

amplitude ; see also Fig. 1) in bar

Fd correction factor to take account of the

influence of the wall thickness –

N here: operational number of load cycles

Nzul here: allowable number of load cycles

with pressure fluctuation ranges )–ˆ( pp(

–

N100 allowable number of load cycles for

pressure fluctuation ranges (pr – 0) at

temperatures T* ≤ 100 °C –

T* governing calculation temperature

during one load cycle in °C

*a2σ fictitious pseudo-elastic stress range in N/mm²

2σaD fictitious endurance strength values in N/mm²

η stress factor (shape-dependent) –

Superscript = maximum value, e.g. p̂

Superscript = minimum value e.g. p(

Subscript k = number index e.g. Nk

4 Determination of allowable number ofload cycles

4.1 To determine the allowable number of load cycles the

fictitious pseudo-elastic stress amplitude 2σ shall be

calculated according to

SK

ppp

fF20

r*Td

*a ·)–ˆ(

··

=2

(ησ (2)

4.1.1 Here the fictitious pressure pr shall be determined

as allowable pressure with full utilisation of the design

stress K 20/S for a point under consideration on a pressure

vessel from the dimensioning formulae of the B series of

the AD 2000-Merkblätter. For this purpose, these dimen-

sioning formulae may have to be broken down to obtain p.

In this case, only 50 % of the minus tolerances (c1) and

wear allowances (c2) need be taken into account. In the

case of a pressure-containing wall being loaded by exter-

nal pressure, the fictitious pressure pr can de determined

from the design equations for the calculation against plas-

tic deformation according to AD 2000-Merkblatt B 6.

4.1.2 The stress factors η can be found in Table 3 as a

function of the component geometry3) 4). These stress

factors represent the upper limit of the stress factors for

dimensioning conditions of a certain component geometry

arising in practical situations.

Where lower stress factors η are selected, they shall be

verified.

4.1.3 To take account of the cyclic load strength-reduc-

ing influence of the component size a correction factor Fd

shall be taken for wall thicknesses se > 25 mm according

to

25,025=

ed s

F (3)

or from Figure 4. The factor Fd shall be limited to Fd = 0.64

with wall thicknesses of se ≥ 150 mm maximum. In the

case of forgings, the governing heat treatment diameter

3) See Annex 1 4) See also 5.2

*a

)(

<

<

AD 2000-Merkblatt AD-2000-Merkblatt S 1, 02. 2005 edition Page 3


AD

200

0 C

od

e -

Issu

e 20

11-0

1


according to DIN 17243 shall be taken as the wall thick-

ness.

4.1.4 With load cycle temperatures of T* > 100 °C up to

temperatures of non-time-dependent design strength

values, a temperature influencing factor fT* shall be con-

sidered. The correction factor fT* shall be determined for

ferritic material according to

fT* = 1,03 – 1,5 · 10–4 · T* – 1,5 · 10–6 · T*2 (4)

and for austenitic material according to

fT* = 1,043 – 4,3 · 10–4 · T* (5)

or shall be taken from Fig. 5.

4.2 The allowable number of load cycles shall be calcu-

lated within the scope 103 ≤ N ≤ 2 · 106 as a function of

the stress amplitude according to 4.1 from

m

*zul

2=

a

BN

σ (6)

where m = 3 for welded joints and m = 3.5 for unwelded

component areas with rolling skin surface, or shall be

taken from Figure 6. The notch effects from weld seams

or surface roughness and the greatest possible influence

of residual welding stresses or mean stresses from work-

ing pressure have already been taken into account here.

4.2.1 The values of the calculation constants B can be

found in Table 1. The class K 0 here applies to unwelded

component areas. The other classes relate to welded

joints allocated to classes K 1, K 2 and K 3 in Table 3 in

accordance with their notch effect.

Table 1. Calculation constants B

Class B [N/mm²]

103 ≤ N ≤ 2 · 106

K 0

K 1

K 2

K 3

7890

7940

6300

5040

4.2.2 The fictitious endurance limit is fixed as N = 2 · 106.

With stress ranges 2σ below the values 2σaD according

to Table 2, endurance may be assumed.

Table 2. Endurance limit values 2σaD

Class 2σaD [N/mm²]

N ≥ 2 · 106

K 0

K 1

K 2

K 3

125

63

50

40

4.3 For the special case of welded pressure vessels with

geometries to correspond to a stress factor η ≤ 3.0, at

temperatures T* ≤ 100 °C, wall thicknesses se ≤ 25 mm

and pressure fluctuations between 0 and pr, the allowable

number of load cycles within the range 1000 ≤ Nzul

≤ 2 · 106 can be determined by means of

Nzul = N100 · fN · fL (7)

with

320

10

100)/(

10·854,1=

SKN (8)

3rL

–ˆ=

ppp

f ( (9)

and

1,0 for K 1

fN = 0,5 for K 2 (10)

0,25 for K 3

The values N100 and fL can also be taken from Figs. 7

and 8.

The pressure fluctuation range related to pr, that can be

withstood under fatigue strength considerations by the

vessel, shall be taken from Fig. 9 as a function of K20/S.

The curves are described by

SKppp

/·3

2=

)–ˆ(

20

aD

r

D σ(

(11)

with 2σaD from Table 2.

4.4 If pressure fluctuations of differing range and fre-

quency occur (operational load regime), the allowable

fatigue life shall be determined using the linear damage

accumulation law.

0,1++=zulk

k

zul2

2

zul1

1

kzul

k

NN

NN

NN

NN

kL� (12)

4.4.1 N1, N2 ... Nk are the numbers of load cycles to be

expected in operation, with the load cycles with the same

pressure fluctuation range ( ) being comprised to

form one load regime. The related allowable number of

load cycles Nzul1, Nzul2 ... Nzulk shall be taken with the rele-

vant stress range 2σ according to equation (2) in the

corresponding load cycle curves to Fig. 6 or shall be cal-

culated according to equation (6).

4.4.2 If an operational load regime gives rise to stress

range 2σ aD

given in Table 2 for N > 2 · 106, the related allowable

numbers of load cycles Nzu6

damage portions of load regimes whose stress range

2σ is smaller than 50 % of the 2σaD values can be ne-

glected here.

5 Design

5.1 The fatigue life of cyclically loaded components

largely depends on the dimensioning and design. Special

care shall be taken here to ensure that designs with high

stress or strain concentration e.g. due to abrupt wall

thickness transitions, are avoided. Table 3 contains an

assessment of frequently used weld details in pressure

vessels. In the case of rigorous requirements regarding

component lifetime, the weld designs of class K 1 are

recommended. If necessary, more rigorous requirements

shall be imposed on the design than are given in AD 2000-

Merkblatt HP 1 (compare stress factors η in Table 3).

Suitable design shall make possible testing and inspection

as specified in clause 7.

5.2 To assess the life expectancy of designs not given in

Table 3, the anticipated η value shall be fixed by means of

corresponding estimates on the stress concentration fac-

tor (see clause 4 of AD 2000-Merkblatt S 2). In such

cases, however, it is practical to conduct a detailed calcu-

lation according to AD 2000-Merkblatt S 2. This generally

applies to cam closures and clasp-bolted joints, for ex-

ample.

*a2σ

*a

p∨∧ −p

*a

*a

*a

≤

AD 2000-Merkblatt Page 4 AD-2000-Merkblatt S 1, 02. 2005 edition

l = 2 · 10 shall be taken. The

which are smaller than the fatigue limits 2σ


AD

200

0 C

od

e -

Issu

e 20

11-0

1


5.3 The life expectancy can be increased within the fra-mework of design evaluation according to Table 3 by, for

example, the following design measures:

(1) Hemispherical or torispherical head instead of semi-ellipsoidal head;

(2) Conical shell with knuckle instead of cone with corner

joint;

(3) Avoidance of inclined nozzles and pad reinforce-

ments;

(4) Tapered transition between tubesheets, flanges etc.and the vessel shell;

(5) Avoidance of rectangular openings.

Over-dimensioning for predominantly static loading also

leads to a greater number of allowable load cycles. Simi-larly a greater number of load cycles can normally be

permitted by applying AD 2000-Merkblatt S 2 (see An-nex 2 of this AD 2000-Merkblatt).

6 Manufacture

For the manufacture of pressure vessels the HP series ofthe AD 2000-Merkblätter applies. For vessels calculated

according to this AD 2000-Merkblatt the following re-quirements shall additionally be met:

6.1 In the case of cyclic loading, defects arising duringproduction have a more unfavourable effect than with

static loading. The component lifetime can be considera-bly reduced by notches or unfavourable residual stresses.

6.2 For the components special requirements shall beimposed on the form of welds. The requirements shall be

imposed on the form of welds. The requirements of quality level B as specified in EN 25817 shall be met. With regardto heat control during welding and welding sequence,

special attention shall be paid to the welding residualstresses. All heat treatments shall be properly performed

to meet the material and wall thickness requirements.

Annealing temperatures, holding time and cooling condi-

tions shall be fixed as far as possible such that consider-able elongation and notched bar impact toughness are

ensured. In many cases the yield point and tensilestrength will set in at the lower limit of the allowable range.

Stress relief shall be performed such that the residual stresses are reduced to a low level and the above material properties are maintained (see the corresponding stan-

dards and material data sheets).

Stamping shall not be performed at locations subject to

high loading.

7 Testing

For the testing and inspection prior to, during and aftermanufacture, the following sections shall be observed in

addition to AD 2000-Merkblätter of the HP series :

7.1 Design examination

Within the context of the design examination as described

in AD 2000-Merkblatt HP 511, the relevant third party shallestablish the locations which shall be tested in particularwith regard to cyclic loading in the tests described in 7.2

and 7.3.

7.2 Tests during production and final test

7.2.1 The tests to be performed during production by themanufacturer or within the final test by the relevant third

party shall ensure that there are no defects present in thepressure vessel or pressure vessel component which may

grow rapidly in size under cyclic loading and which may result in failure of the pressure parts before the allowablenumber of load cycles has been reached (see AD 2000-

Merkblatt HP 5/1).

7.2.2 For the non-destructive test, the provisions of AD

2000-Merkblatt HP 5/3 in conjunction with the generaltable for HP 0 shall be observed. If according to this, the

method of non-destructive examination is left open, theultrasonic examination should be given preference. Loca-

tions subject to high loadings during operation such as welded-in nozzles, hole edges or cross sectional transi-

tions, shall as far as practicable be subjected completely to non-destructive testing. The visual examination forsurface defects and external visible welding defects shall

be performed with appropriate care.

7.3 Inspections during operation

7.3.1 Each pressure vessel for which the number ofallowable load cycles (cycle number N) has been fixed

shall undergo an internal inspection at the latest when half

of the load cycles fixed has been reached.

As a result of the type of operation, the intervals betweeninternal tests may be shorter in accordance with national

regulations.

The user is obliged to record the number of load cycles

arising by suitable means and, if necessary, to arrange forthe internal inspections.

7.3.2 If the operating conditions assumed in the calcula-tion under clause 4 deviate in terms of a greater cyclic

loading or if damage to the pressure-bearing wall is to beexpected before the end of the inspection intervals owing

to other operational influences, they shall be reduced inaccordance with national regulations.

Longer inspection intervals will possibly result from calcu-

lations according to AD 2000-Merkblatt S 2.

7.3.3 In the case of pressure vessels subject to cyclic

loading, in-service inspections are of particular impor-tance; they-permit early detection of incipient damage.

For this purpose, the internal inspections shall be supple-mented by non-destructive tests on highly loaded loca-

tions. Surface crack tests and ultrasonic tests are themethods to be considered here. For the examination of

readly accessible areas, the outside surface of the vessel can also be subjected to ultrasonic testing.

7.3.4 If no cracks are detected during an internal inspec-

tion, the next internal inspection shall be performed fol-lowing special agreement, and be within the shortest

interval specified in applicable national regulations. How-ever, the inspection shall be performed no later than when

half the number of load cycles has been reached. Thisalso applies if the allowable number of load cycles is ex-

ceeded.

7.3.5 The inspections described in 7.3.1 to 7.3.4 for

cyclic loading during operation may be waived if the com-ponent is designed to withstand an operational load cycle

number of 2 ⋅ 106.

7.3.6 At low permissible temperatures below –200 °C,

the intervals for carrying out internal inspections shall again be halved, i.e. internal inspections carried out in

accordance with 7.3.1 and 7.3.4 shall be carried out whena quarter of the specified number of stress cycles have

been completed.


AD

200

0 C

od

e -

Issu

e 20

11-0

1


8 Consideration of special operating conditions

In the case of corrosion-induced crack formation (fatigue

crack corrosion, strain-induced crack corrosion), hydro-gen-induced crack formation in compressed hydrogen, or

the presence of a magnetite protective layer, the provi-sions of AD 2000-Merkblatt S 2, shall be applied accord-

ingly.

In cases of doubt a calculation according to AD 2000-

Merkblatt S 2 shall be conducted.

9 Measures to be taken when the design lifetime has been reached

9.1 If the allowable number of load cycles for a compo-nent or the allowable value for cumulative damage ac-

cording to clause 4 has been reached, non-destructivetests according to 7.3 shall be performed as completely

as possible at a certain number of highly loaded locationsto be laid down with the relevant third party.

9.2 If no cracks are found in the tests conducted as

described in 9.1, continued operation is permitted. Theprerequisite for this is that no fatigue damage is found in

the non-destructive tests conducted in the inspectionintervals which correspond to 50 % of the operating time

specified in 9.1. After this operating time has beenreached, further measures shall be agreed for each indi-

vidual case in accordance with national regulations.

At low permissible temperatures below –200 °C, the inter-

vals for carrying out non-destructive tests shall be re-duced from 50 % to 25 % of the operating time in accor-dance with 9.1.

9.3 Should cracks or crack-type defects within themeaning of 5.2 and 5.4 of AD 2000-Merkblatt HP 5/3 or

other more extensive damage established in the tests carried out as described in 9.1 or 9.2, the component or

the structural element concerned shall be replaced, unless continued operation is deemed to be permitted by virtue

of appropriate measures to be agreed in accordance withnational regulations.

9.4 The following design, manufacturing and process-related measures can be considered to allow continuedoperation:

(1) Removal of cracks by grinding. If as a result of grind-ing too thin a wall thickness is obtained repair welding

shall only be carried out in cooperation with themanufacturer within the context of the national regula-tions;

(2) Grinding the welds to remove all notches;

(3) Removal of restraints to expansion: e.g. replacement

of cracked rigid stiffeners by joints not restraining ex-pansion;

(4) Change in mode of operation.

10 Additional details

10.1 In all cases where the conditions for waiving appli-cation of this Merkblatt as described in 1.4 an 1.5 are notmet, this shall be indicated to the manufacturer and for

the design examination of the relevant third party. In suchcases, measures adapted to operational needs shall be

provided for and, if necessary, agreed between the manu-facturer, customer/user and relevant third party. These

measures shall be included in the design-approved draw-ing and in the certificate of the final test, making reference

to AD 2000-Merkblatt S 1.

10.2 The following items shall be indicated in conformity

with the scope given in clause 1 (internal pressure fluctua-tions only):

– Number of pressure fluctuations between unpressur-

ised state and maximum allowable pressure (start-upsand shutdowns);

– Pressure fluctuations of constant amplitude which aresuperimposed on the working pressure, and their num-

ber of operational load cycles;

– Pressure fluctuations of various load cycle groups and

their number of operational load cycles for a specified operational load regime;

– Minimum and maximum temperature during a load cycle or, in the case of load regime, in the individual load cycle groups.


AD

200

0 C

od

e -

Issu

e 20

11-0

1



AD

200

0 C

od

e -

Issu

e 20

11-0

1


Table 3. Examples of structural forms and welded joints with the corresponding classes (K 0, K 1, K 2 and K 3) and

corresponding stress factors η (cracks drawn in as examples)

Serial

No.Illustration Description Requirements Class η

5.9

partial

penetration

welded head

welded from one side K 3 5,0

5.10

flange head, connecting weld knuckle radius and flange depth acc. to AD 2000-Merkblatt B 5,

Table 1, type a, weld design and

class assignment as serial

no. 1.1 – 1.3

K1/K2 1,5

5.11

flanged head, knuckle unwelded K 0 2,0

5.12

forged or extruded head,connecting weld

knuckle radius and flange depthacc. to AD 2000-Merkblatt B 5,

Table 1, type b, weld design and

class assignment as serial

no. 1.1 – 1.3

K1/K2 1,5

5.13

forged or extruded head, knuckle unwelded K 0 4,0

6. Jacketed shell-connecting welds

6.1

with shaped sealer ring

The evaluation applies to both

the inner vessel wall and the

connecting weld

full-penetration welded from one

side

K 2 3,0

6.2

with separate sealer ring

The evaluation applies to both

the inner vessel wall and the weld connecting the sealer ring

and vessel wall.

(The connecting weld between

sealer ring and external jacket isevaluated as per serial no. 1.3

with K 2)

full-penetration welded from bothsides

or

full-penetration welded from one side with backing weld

K 1 3,0

7. Welded attachments, general

Prerequisite: external findings of attachment welds, to EN 25817, quality level B, excluding weld reinforcement and weld sag and

unequal leg fillet welds

7.1 full-penetration welded from both

sides

K 1 2,0

7.2 fillet-welded from both sides K 2

7.3 full-penetration welded from both

sides K 17)

7.4

Welded attachments without

application of alternating addi-

tional forces and moments

fillet-welded from both sides K 27)

7) The evaluation refes to the rib centre. For the rib end the evaluation is made for a lower class in each case.


AD

200

0 C

od

e -

Issu

e 20

11-0

1


Table 3. Examples of structural forms and welded joints with the corresponding classes (K 0, K 1, K 2 and K 3) andcorresponding stress factors η (cracks drawn in as examples)

SerialNo. Illustration Description Requirements Class η

7.5

Reinforcing plate, backing plate connected with fillet weld. Noapplication of alternating addi-tional forces and moments

s2 ≤ 1,5 ⋅ s1

r ≥ 2 ⋅ s2

K 2 2,0

7.6 full-penetration welded from bothsides

K 1

7.7

welded attachments with applica-tion of additional forces andmoments

Welded from both sides, but not fully penetrating

K 2

3,0

8. Welded attachments without application of alternating additional forces or moments. Examples

Prerequisite: external findings of attachment welds to EN 25817, quality level B, excluding weld reinforcement and weld sag andunequal leg fillet weld

8.1

vessel-to-skirt supportconnection


8.2 vessel wall with support ring K 2

8.3

welded from both side, but not fully penetrating

K 2

8.4

vessel all with stiffening ring

welded with interruption incircumferential direction

K 3

8.5

vessel wall with supporting lug(with or without backing plate)

welded from one side K 2

8.6

vessel wall with support foot(with or without backing plate)


2,0


AD

200

0 C

od

e -

Issu

e 20

11-0

1


Table 3. Examples of structural forms and welded joints with the corresponding classes (K 0, K 1, K 2 and K 3) andcorresponding stress factors η (cracks drawn in as examples)

SerialNo.

Illustration Description Requirements Class η

8.7 vessel wall with trunnion (with or without backing plate)


8.8 vessel wall with lifting lug(with or without backing plate)


8.9 vessel wall with bracket welded from one side K 2


AD

200

0 C

od

e -

Issu

e 20

11-0

1


Annex 1 to AD 2000-Merkblatt S 1


AD

200

0 C

od

e -

Issu

e 20

11-0

1


1z15==

e·p

SK – z1 z acc. to Figs. 3.1 to 3.7 in

AD 2000-Merkblatt B 2

according to 8.1.2

psDSK ·+

cos== K–

20 · s

according to Annex to AD 2000-Merkblatt B 2

2zvg e·

10p== σσ z2 z acc. to Table A 1

+⋅

⋅==∧

11

sco

2

K

2

sD

emax

z

ϕσση

For parameter calculations for this, see Fig. A 4.

Excluding the shallow conical shells (ϕ = 60–70°), which

are hardly used in practice, for pressure vessels under

cyclic pressure loading, a stress factor of η = 2,7 was

fixed accordingly in Table 3, No. 1.10/1.11.

Explanatory note on 4.1.3, Formula (3)

In order to take into account the cyclic-strength-reducing

influence of the component size, the correction factor Fd

was taken for welded joints in the endurance range given

in 7.2.6 of AD 2000-Merkblatt S 2. Dependence on thenumber of load cycles according to AD 2000-Merkblatt

S 2, formula (17), was dispensed with.

The Fd factor is also used by way of simplification for

unwelded components.

Explanatory notes on 4.2 and Figure 6

To plot a load cycle curve for unwelded components (sur-

face condition: rolling skin), calculations were conducted according to AD 2000-Merkblatt S 2 for different materials taking account of the influence of plasticity and maximum

mean stress (σ = Rp 0,2).

According to Fig. A 1 of this Annex, it is possible to indi-cate by approximation a “mean value” curve with constant

gradient exponent m = 3,5 on a double-logarithmic scale. This load cycle curve class K 0 is almost identical with the

load cycle curves for unwelded component areas accord-ing to the British Standard BS 5500 : 94 [4] or, as the casemay be, BS 7608 : 1993 [5] (curves of class C).

For welded joints, the load cycle curves of classes K 1,K 2 and K 3 from AD 2000-Merkblatt S 2 were taken.

To check the influence of plasticity in the range of lownumbers of load cycles, calculations were conducted

(conservatively) according to AD 2000-Merkblatt S 2 forthe low-strength material H II. Fig. A 4 shows that the

reduction through the ke factors (ke > 1) is relatively small

from 1000 load cycles on and only takes effect in classes

K 1 and K 2. In view of the scoope (N ≥ 1000), a global

stress increase in elastic-plastic range through ke factors

was therefore dispensed with for reasons of simplification.

For reasons of practicability (easier readability for fasterdetermination of allowable load cycles), the semi-

logarithmic presentation was chosen for the cyclic load chart as in the previous AD-Merkblatt S 1 (Edition 3.90),

Fig. 2 (N100 curves).

Explanatory note on 4.3 and Figure 7

In compliance with the former representation of the N100

and fL curves, similar curves for pressure vessels of cer-

tain design and operational boundary conditions were taken over.

Formula (8) is obtained from Formula (6) with B = 7940

from Table 1 for class K 1 and η = 3,0.

Explanatory note on 4.4

To simplify the procedure with damage accumulation in

the case of an operational load regime, no fictitious loadcycle curves according to the Haibach modification as inAD 2000-Merkblatt S 2 are contained in the endurance

range (N > 2 · 106).

As compared with the base values of allowable stress

amplitudes 2σa according to AD 2000-Merkblatt S 2, Ta-

ble 4 in the range N = 2 · 106 to 108 and in accordance

with the procedure according to AD 2000-Merkblatt S 2,

9.2, stress amplitudes with N ≥ 2 · 106 at a level of 50 %

of the endurance values 2σaD according to Table 2 of this

AD 2000-Merkblatt are regarded as negligible.

Literature

[1] AD 2000-Merkblatt S 2: Analysis for cyclic loading,

October 2004 editionHeymanns Verlag, Cologne

[2] AD 2000-Merkblätter, Series B.Heymanns Verlag, Cologne

[3] Richtlinienkatalog Festigkeitsberechnungen (RKF),Behälter und Apparate Part 5.

Edition 1986. Linde-KCA-Dresden GmbH

[4] British Standard BS 5500/1994: Specification forunfired fusion welded pressure vessels

[5] British Standard BS 7608/1993: Code of practice for fatigue design and assessment of steel structures

[6] Duan-Shou Xie and Yong-Gou Lu: Prediction of

Stress Concentration Factors for Cylindrical PressureVessels with Nozzles.

Int. J. Pressure Vessel & Piping 21 (1985)

[7] Gorsitzke, B.: Vorhersage der Ermüdungsfestigkeit

druckführender Komponenten im Energie- und Che-mieanlagenbau, Part 1 and Part 2

Z. TÜ 30 (1989) No. 2 and No. 3

[8] Gorsitzke, B: Neuere Berechnungsvorschriften zur

Ermüdungsfestigkeit von Druckbehältern.

Z. TÜ 36 (1995) No. 6 and Nos. 7/8

[9] Gorsitzke, B.: Erläuterungen zum neuen AD-Merkblatt

S 1 „Vereinfachte Berechnung auf Wechselbean-spruchung und ergänzende Hinweise“.

Z. TÜ 37 (1996) No. 6 and Nos. 7/8.

=̂

ϕ

=̂

1,5 · ez1 · ez2


AD

200

0 C

od

e -

Issu

e 20

11-0

1



AD

200

0 C

od

e -

Issu

e 20

11-0

1

Fig. A 2. Allowable number of load cycles as a function of stress range according to AD 2000-S 2 for welded joints at ambitaking into account the influence of plasticity (k factors)


AD

200

0 C

od

e -

Issu

e 20

11-0

1



AD

200

0 C

od

e -

Issu

e 20

11-0

1


Annex 3 to AD 2000-Merkblatt S 1

Simplified analysis for cyclic loading for

spheroidal graphite cast iron

1 Scope and general

1.1 The following rules on simplified analysis for cyclic

loading apply to pressure-bearing unwelded parts ofpressure vessels made of spheroidal graphite cast iron

according to DIN EN 1563, limited to the grades EN-GJS-400-15/15U, EN-GJS-400-18/U-LT and EN-GJS-350-

22/22U-L, manufactured and tested according to AD2000-Merkblatt W 3/2.

1.2 The external and internal conditions of the castings shall meet stricter requirements that reflect the require-ments of quality leves A and B as specified in DIN 1690

Part 10 (see 4.2).

1.3 If the number of load cycles with pressure fluctua-

tions between the unpressurized condition and the maxi-mum allowable pressure p (start-ups and shutdowns) and

the range (p–p) of any number of pressure fluctuations

relative to p1) do not exceed the following values, this

annex need not be used.

a) N100 ≤ 100000 and (p–p) ≤ 50 % of p1) for EN-GJS-400-

15/15U

b) N100 ≤ 6000 and (p–p) ≤ 35 % of p1) for EN-GJS-400-

18/18U-LT and EN-GJS-350-22/22U-LT

Here, geometries with a shape-dependent stress factor ηnot exceeding 3,5 are assumed.

The limit values of the number of load cycles N100 may be

increased to 2,4 times if the test conditions correspondingto quality level A are met.

1.4 Unless otherwise specified in this annex, all the otherrules in the main body of this AD 2000-Merkblatt are

applicable.

2 Determination of allowable number of

load cycles

2.1 The fictitious pseudoelastic stress range for de-termining the allowable number of load cycles shall be

calculated according to formula (2). In this, the stress

factor η shall be estimated from Table 3. Here, values

greater than η = 2,5 need not be taken into accoount. For

structures that cannot be classified according to this ta-

ble, the η values shall be proven unless η = 2,5 has been

included in the calculation.

The wall thickness correction factor Fd shall be calculated

as appropriate according to formula (3) and instad of theexponent 0,25 the value 0,1 shall be used and for wall

thicknesses se > 150 mm the correction factor shall be

limited to Fd = 0,84. Formula (4) applies for the tempera-

ture correction factor fT*.

2.2 The allowable number of load cycles for component

areas with cast skin surfaces in the range 10³ ≤ N ≤ 2 · 106

shall be calculated as a function of the stress range ac-cording to formula (2), if necessary from formula (6) with

m = 8,333.

1) The calculation pressure pr may also be used instead of p.

The calculation constant B values shall be taken from

Table A 1. Here, the notch effects from surface roughnessand the maximum possible influence of working pressure

mean stresses have already been taken into account.

The knee-point number of load cycles ND from which the

fatigue behaviour is no longer dependent on the number

of load cycles is fixed at N = 2 · 106. For quality level A,

the allowable number of load cycles may also be takenfrom Figure A 6.

The design curves shown in Figure A 6 are based ondamage curves corresponding to a failure probabilitiy ofapproximately 2,3 % (see [1]).

Table A 1. Calculation constants B and strength

characteristic values 2 σaD

Constant B103 ≤ N ≤ 2 · 106

2σaD [N/mm2]

N ≥ 2 · 106

Quality level A B A B

Material grade

EN-GJS-

400-15/15U EN-GJS-

400-18/18U-LT

787 708 138 124

EN-GJS-

350-22/22U-LT

732 659 128 116

2.3 For the spezial case of pressure-bearing parts with

geometries with a shape-dependent stress factor η= 2,5,

temperatures T* ≤ 100 °C, wall thicknesses se ≤ 25 mm

and pressure fluctuations between 0 and pr, the allowable

number of load cycles in the range 1000 ≤ Nzul ≤ 2 · 106

may be determined according to

Nzul = N100 · fL (A1)

with

N100 = [B / (2.5 · K20/S)]8.333 (A2)

fL = [pr / (p–p)]8.333 (A3)

The values N100 and fL may also be taken from Figure A 7

and Figure A 8.

The acceptable pressure fluctuation range relative to pr for

these vessels for a number of load cycles N ≥ 2 · 106 shall

be calculated according to

(p–p) / pr = 2σaD / 2,5 · K20/S) (A4)

with 2σaD from Table A 1.

2.4 The calculation procedure to take into account anoperational load regime shall be carried out as appropriate

according to 4.4 of the main body of this AD 2000-Merkblatt. The damage portions of load regimes whose

stress range 2σaD is less than 70 % of the 2σaD values may

be disregarded here.

3 Design

3.1 When designing castings, it shall be noted that de-

signs may be produced that are covered with a stress

factor η = 2,5. If it is not possible to estimate the η value

(see stress factors η in Table 3), detailed proof of the

stress factor η or a calculation according to annex 5 of AD

2000-Merkblatt S 2 shall be provided.

σ*a2

∧ ∨

∧ ∨

∧ ∨

∧ ∨

∧ ∨


AD

200

0 C

od

e -

Issu

e 20

11-0

1



AD

200

0 C

od

e -

Issu

e 20

11-0

1

[email protected]

Beuth Verlag GmbH

Publisher: Source of supply:

D-10772 BerlinTel. +49 30 / 26 01-22 60Fax +49 30 / 26 01-12 60

Verband der TÜV e.V.

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


AD

200

0 C

od

e -

Issu

e 20

11-0

1

ad 2000-mb - s1 -02-2005

Documents