# SIST EN 13445-3:2014/A5:2018

(Amendment)## Unfired pressure vessels - Part 3: Design

## Unfired pressure vessels - Part 3: Design

This Part of this European Standard specifies requirements for the design of unfired pressure vessels covered by EN 13445-1:2009 and constructed of steels in accordance with EN 13445-2:2009. EN 13445-5:2009, Annex C specifies requirements for the design of access and inspection openings, closing mechanisms and special locking elements. NOTE This Part applies to design of vessels before putting into service. It may be used for in service calculation or analysis subject to appropriate adjustment.

## Unbefeuerte Druckbehälter - Teil 3: Konstruktion

Dieser Teil 3 der Europäischen Norm legt die Anforderungen an die Konstruktion von unbefeuerten Druckbehältern

nach EN 13445-1:2014 und hergestellt aus Stählen nach EN 13445-2:2014 fest.

EN 13445-5:2014 gibt im Anhang C Bedingungen für die Konstruktion von Zugangs- und Besichtigungsöffnungen,

von Verschlüssen und besonderen Verschlusselementen.

ANMERKUNG Dieser Teil gilt für Konstruktion und Berechnung von Behältern vor der Inbetriebnahme. Er kann auch, mit

entsprechenden Anpassungen, für Berechnungen oder analytische Nachweise im Betrieb verwendet werden.

## Récipients sous pression non soumis à la flamme - Partie 3 : Conception

Cette partie de la présente norme européenne spécifie les exigences relatives à la conception des récipients sous

pression non soumis à la flamme couverts par l’EN 13445-1:2014 et construits en aciers conformes à

l’EN 13445-2:2014.

L’Annexe C de l’EN 13445-5:2014 spécifie les exigences relatives à la conception des ouvertures d’accès et

d’inspection, des mécanismes de fermeture et des éléments de verrouillage spéciaux.

NOTE Cette partie s'applique à la conception des récipients avant mise en service. Elle peut être utilisée pour les calculs

ou l'analyse en service sous réserve d'apporter les ajustements appropriés.

## Neogrevane (nekurjene) tlačne posode - 3. del: Konstruiranje - Dopolnilo A5

### General Information

### Relations

### Standards Content (Sample)

SLOVENSKI STANDARD

SIST EN 13445-3:2014/A5:2018

01-december-2018

1HRJUHYDQHQHNXUMHQHWODþQHSRVRGHGHO.RQVWUXLUDQMH'RSROQLOR$

Unfired pressure vessels - Part 3: Design

Unbefeuerte Druckbehälter - Teil 3: Konstruktion

Récipients sous pression non soumis à la flamme - Partie 3 : Conception

Ta slovenski standard je istoveten z: EN 13445-3:2014/A5:2018

ICS:

23.020.32 7ODþQHSRVRGH Pressure vessels

SIST EN 13445-3:2014/A5:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 13445-3:2014/A5:2018

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5

EUROPEAN STANDARD

NORME EUROPÉENNE

November 2018

EUROPÄISCHE NORM

ICS 23.020.30

English Version

Unfired pressure vessels - Part 3: Design

Récipients sous pression non soumis à la flamme - Unbefeuerte Druckbehälter - Teil 3: Konstruktion

Partie 3 : Conception

This amendment A5 modifies the European Standard EN 13445-3:2014; it was approved by CEN on 4 June 2018.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for inclusion of

this amendment into the relevant national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This amendment exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the

same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,

Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION

COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 13445-3:2014/A5:2018 E

worldwide for CEN national Members.

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

Contents Page

European foreword . 3

1 Modification to 5.4.2, Vessels of all testing groups, pressure loading predominantly

of non-cyclic nature . 4

2 Modifications to Clause 6, Maximum allowed values of the nominal design stress for

pressure parts . 4

3 Modifications to 17.1, Purpose . 5

4 Modifications to 17.2, Specific definitions . 5

5 Modification to 17.3, Specific symbols and abbreviations . 7

6 Modifications to 17.4, Conditions of applicability . 9

7 Modification to 17.5, General . 10

8 Modifications to 17.6, Determination of allowable number of pressure cycles . 16

9 Modifications to 17.9, Testing . 23

10 Addition of a new Annex U (informative), Guidance on negligibility of additional

thermal cycles in fatigue and ratcheting assessment . 23

2

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

European foreword

This document (EN 13445-3:2014/A5:2018) has been prepared by Technical Committee CEN/TC 54

“Unfired pressure vessels”, the secretariat of which is held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by May 2019, and conflicting national standards shall be

withdrawn at the latest by May 2019.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document has been prepared under a mandate given to CEN by the European Commission and the

European Free Trade Association, and supports essential requirements of EU Directive(s).

For relationship with EU Directive, see informative Annex ZA, which is an integral part of

EN 13445-3:2014.

According to the CEN-CENELEC Internal Regulations, the national standards organisations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.

3

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

1 Modification to 5.4.2, Vessels of all testing groups, pressure loading

predominantly of non-cyclic nature

Replace the whole subclause with the following one:

“

5.4.2 Vessels of all testing groups, pressure loading predominantly of non-cyclic nature

The DBF requirements specified in Clauses 7 to 16, Annexes G and J, and in Clause 19 (for testing sub-

groups 1c and 3c only) and the DBA requirements of Annex B and Annex C provide satisfactory designs

for pressure loading of non-cyclic nature, i.e. when the number of full pressure cycles or equivalent full

pressure cycles is less than or equal to 500.

n ≤ 500 (5.4-1)

eq

The equivalent number of full pressure cycles n is given by:

eq

3

∆P

i

nn⋅ (5.4-2)

∑

eq i

P

max

In the above equation, P is the maximum permissible pressure P calculated for the whole vessel

max max

(see 3.16) in the normal operating load case (see 5.3.2.1).

For simplification, P may be replaced by the calculation pressure P.

max

NOTE The value of 500 equivalent full pressure cycles is only a rough indication. It can be assumed that for

components with irregularities of profile, strongly varying local stress distributions, subjected to additional non-

pressure loads, fatigue damage can occur before 500 cycles.

Cyclic thermal loads can be neglected if:

— for start-up and shutdown cycles, the number shall not exceed 2 000 and the rate of temperature

change at the surface shall be less than 60 °C per hour for ferritic steel sections. The designer can

specify a higher rate of surface temperature change based on favourable/good industry experience

and practice;

— if the requirements of Annex U are satisfied for operating conditions.

If these conditions on pressure and thermal loads are met, then no fatigue analysis is necessary and the

standard requirements of non-destructive testing given in EN 13445-5 shall be applied.

If these conditions cannot be met, then a fatigue assessment is necessary according to either Clause 17

or Clause 18.”.

2 Modifications to Clause 6, Maximum allowed values of the nominal design

stress for pressure parts

In 6.1.3 delete the following:

“For testing group 4 vessels, the maximum value of the nominal design stress for the normal operating

load cases shall be multiplied by 0,9.”.

a

In Table 6-1, delete the following Footnote :

a

" For testing group 4 the nominal design stress shall be multiplied by 0,9.”;

and re-name the following footnotes accordingly.

4

=

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

3 Modifications to 17.1, Purpose

Replace the whole subclause with the following one:

“

17.1.1 This clause specifies:

— an alternative to the 500 cycles rule stated in 5.4.2 for vessels predominantly subjected to pressure

fluctuations,

— a substitute to the 500 cycles rule stated in 5.4.2 for vessels subjected additionally to thermal

gradient fluctuations, and

— rules for the simplified assessment of fatigue damage due to both pressure and thermal gradients

fluctuations.

NOTE The rules in this clause are based on simplified and conservative assumptions. More precise, less

conservative results will usually be obtained by application of Clause 18.”.

In 17.1.2, replace the first sentence with the following one:

“

17.1.2 Other cyclic loads, e.g. due to variation of external loads, are normally to be assessed according

to Clause 18. However, it is permitted to take non-pressure cyclic loads into account in this clause by:”.

In 17.1.2, replace the NOTE with the following one:

“

NOTE This clause gives information for estimating the stress ranges due to pressure and thermal loads only.

When other loads are taken into account, the determination of the corresponding stress ranges is under the

responsibility of the Manufacturer.”.

4 Modifications to 17.2, Specific definitions

Replace Definition 17.2.7 by the following:

“

17.2.7

equivalent number of full pressure cycles

number n of full pressure cycles that cause the same damage as all the applied cycles of various

eq

sources and ranges

Note 1 to entry: For pressure loading only, n is given by Formula (17.5–1).

eq

Note 2 to entry: For pressure + thermal loading, is given by Formula (17.5–4).”.

n

eq

5

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

Replace Definition 17.2.9 by the following:

“

17.2.9

range

value from maximum to minimum (stress or load) in the cycle (twice the amplitude)”.

Replace Definition 17.2.10 by the following:

“

17.2.10

pseudo-elastic stress

stress calculated assuming purely linear elastic material behaviour”.

Replace Definition 17.2.13 by the following:

“

17.2.13

pressure stress factor

factor for determination of the maximum structural stress that may occur under pressure loading in a

vessel detail, due to the geometrical configuration of component(s)”.

Add the following new definitions after Definition 17.2.13:

“

17.2.14

thermal stress factor

factor for determination of the maximum structural stress that may occur under some thermal gradient

type in a vessel detail, due to the geometrical configuration of component(s)

17.2.15

adjacent point

point to be considered for determination of the metal temperature difference on which thermal stresses

are estimated.

Note 1 to entry: They are defined as any two points:

— on the inside and outside surfaces, for a gradient through the thickness;

— along the surface within a distance for a gradient along the longitudinal and/or circumferential

1,75 D ⋅ e

directions of a shell;

— along the surface within a distance 3,5R, for a gradient along the longitudinal and/or circumferential

directions of a flat end, where R is the radius of the point at the highest temperature in the flat end.

6

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

17.2.16

metal temperature difference between adjacent points

temperature difference between adjacent points, determined by reference to the metal temperature at

these points (not the fluid temperature at these points)

17.2.17

theoretical stress concentration factor

ratio of notch stress, calculated on purely elastic basis, to structural stress at same point".

Change accordingly the numbering for Definitions 17.2.14 to 17.2.17.

Replace Definitions 17.2.16 (to be renumbered as 17.2.20) with the following one:

“

17.2.20

critical area

area where the total cumulative fatigue damage (usage factor) exceeds the value D = 0,5”.

max

5 Modification to 17.3, Specific symbols and abbreviations

Replace the whole table with the following one:

"

Symbol Description Unit

C fatigue class C (see Table 17–4) MPa

lowest fatigue class C (see 17.5.4.1) MPa

C

min

allowable number of full pressure cycles

N

eq

D total fatigue damage index, see Formula (17.7–1)

maximum allowable value of total fatigue damage index in non-critical areas

D

max

correction factor to account for influence of wall thickness on fatigue resistance

C

e

CT correction factor to account for influence of temperature on fatigue resistance

E Young's modulus of the material MPa

effective stress concentration factor

K

f

theoretical stress concentration factor

K

t

k number of pressure ranges which together form the loading specification

N allowable number of cycles obtained from the relevant fatigue design curve (suffix i

th

refers to number for i stress range, ik= 1,. )

n number of applied stress cycles

(suffix i refers to number for i th stress range, iq= 1,. )

7

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

Symbol Description Unit

equivalent number of full pressure cycles

n

eq

number of applied pressure cycles

n

P

(suffix i refers to number for i th pressure range, iq= 1,. )

i

number of applied cycles of temperature difference

n

T

(suffix j refers to number for j th range of temperature difference, kq= 1,. )

k

number of applied cycles of combined pressure + temperature difference

n

PT

(suffix k refers to number for k th range of pressure + temperature difference,

kq= 1,. )

k

R radius of the point at the highest temperature in the flat end mm

r transition radius at junction of walls mm

metal temperature difference between adjacent points (see 17.2.15) °C

T

diff

minimum operating temperature during a cycle °C

T

min

maximum operating temperature during a cycle °C

T

max

T* assumed mean cycle temperature °C

u ovality (of circular cross section of a vessel)

α thermal expansion coefficient of the material (°C)-1

δ parameter for measure of misalignment, peaking or flat mm

∆P

pressure range calculated from the algebraic difference of the maximum and MPa

minimum pressures which apply in the cycle under consideration. Vacuum and

other external pressures stress shall be considered negative

NOTE In that case, some cycles may have a range ΔP greater than the maximum

calculation pressure Pmax of the vessel or part thereof.

∆T range of metal temperature difference between adjacent points (adjacent points are °C

defined at 17.2.15)

2

∆σ

pseudo-elastic stress range N/mm

2

fictitious stress range for insertion into the fatigue design curves N/mm

∆σ *

2

reference stress range of fatigue design curves N/mm

∆σ

R

2

endurance limit at constant stress range N/mm

∆σ

D

2

cut-off limit N/mm

∆σ

Cut

κ thermal stress factor for a vessel detail, given in Table 17–2

η

pressure stress factor for a vessel detail, given in Table 17–1

maximum pressure stress factor found throughout the vessel

η

max

NOTE The pressure P used in Clause 17 is defined in 3.16, NOTE 3.

max

”.

8

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

6 Modifications to 17.4, Conditions of applicability

Replace the Subclause 17.4.1 with the following one:

“

17.4.1 This clause applies to pressure-bearing components and junctions of pressure vessels designed

in accordance with Clauses 7 to 16 without Clause 15, Clauses 20 and 21 and Annex G (i.e. those clauses

and annexes where design by formula applies), with the exception of:

— bellows;

— heat exchanger tubesheets.

NOTE 1 Fatigue assessment of heat exchanger tubesheets can be performed using Annex J of this Standard.

Application of this clause to jacketed vessels is permitted if subjected to pressure cycles only. For

jacketed vessels subjected to both pressure and thermal cycles, application is limited to the non-

jacketed parts.

NOTE 2 It is not necessary to check flanges and their bolts if the adjacent shells are designed according to this

Clause.

It is assumed that the vessels have been designed, manufactured and tested in accordance with all other

requirements of this standard.”.

Replace Entry 17.4.4 with the following one:

“

17.4.4 This clause applies only to components operating below the creep range. Thus, the fatigue

design curves are applicable up to 375 °C for ferritic steels and 425 °C for austenitic steels.”.

Replace Entry 17.4.5 with the following one:

“

17.4.5 As regards weld defects:

For application of this clause, the following conditions (as required by EN 13445-5:2014, Annex G) shall

be met in addition to the general acceptance criteria for weld imperfections given in EN 13445-5:2014:

— no undercut,

— no root concavity,

— no lack of penetration for full penetration welds, except as permitted by Table 17-4,

— 100 % inspection, visually and by NDT, with acceptance criteria as specified in EN 13445-5:2014,

Annex G, of all critical areas.”.

Replace Entry 17.4.8 with the following one:

“

17.4.8 Vessels which fulfil the requirements of 17.5.3 or 17.5.4 or 17.5.5 are of non-cyclic nature and

the standard requirements of non-destructive testing given in EN 13445-5 shall be applied.”.

9

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

Add the following new numbered entries:

“

17.4.9 For application of 17.6, instructions for appropriate maintenance shall be included in the

operating instructions.

NOTE Recommendations on appropriate maintenance are given in Annex M.

17.4.10 Guidance for metal temperature estimates:

For cases where significant thermal loading occurs, attention is drawn to the importance of

approximating as closely as possible the temperature distributions that appear in the vessel walls

during service, in order to reduce as much as possible the conservatism of the thermal stress estimate

and resulting fatigue assessment.

In this respect, the quite common approach which consists in taking the fluid temperature variations as

representative of the temperature variations of the vessel wall surface is not recommended because it

generally leads to strong over-estimates of the real thermal gradients. As far as possible these gradients

should be determined from thermal calculations (even simple ones based on analytic models) in which

the thermal exchange which takes place at the fluid-metal interface is taken into account.

To enable such calculations, enough information on the thermodynamic conditions attached to the

process should be obtained from the Purchaser (e.g.: fluid heating or cooling rate, thermal exchange

coefficient at fluid-metal interface, etc.).”.

7 Modification to 17.5, General

Replace the whole subclause with the following one (Figures 17.5-1, 17.5-2 and 17.5-3 are thereby

deleted):

“

17.5 General

17.5.1 Pressure and temperature ranges to be considered for the fatigue assessment:

The various ranges ()∆P to be considered for the fatigue assessment shall be obtained by applying a

i

cycle counting method described in Annex NB and considering fluctuations of the pressure P instead of

fluctuations of stress.

The various ()∆T to be considered for the fatigue assessment shall be obtained by applying the same

diff i

cycle counting methods but considering fluctuations of the metal temperature difference T instead of

diff

fluctuations of stress.

To distinguish whether the pressure and the thermal cycles act simultaneously or not simultaneously

the load history (variation with time) of the both loads shall be considered. When the duration time of

the cycle (time from minimum value via maximum value to minimum value) from one load type (e.g.

pressure) is overlapped with the duration time of the other load type (e.g. temperature differences)

then these cycles act simultaneously. On the contrary, if during the complete cycle time of one load type

the other load type does not change then the cycles act not simultaneously.

The ∆P ranges are normally valid for assessment of all vessel parts subjected to the same pressure

fluctuations. In case where pressure fluctuations result (at least partly) from hydrostatic pressure or

from pressure differences between adjacent vessel chambers, the pressure ranges may be different

from part to part.

10

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

The ∆T ranges are valid only for assessment of the vessel detail where the particular metal

diff

temperature difference fluctuations considered take place. If the most critical detail for fatigue under

combined pressure + thermal loading is not known at first, all candidate details should be investigated

and the corresponding sets of ∆T established.

diff

17.5.2 The calculations according to 17.6 shall be performed for the various components of the vessels.

The lowest life obtained is the fatigue life of the vessel.

17.5.3 Pressure and temperature ranges which may be neglected for the fatigue assessment:

When designs meet the requirements:

η ≤ 3,

f ≤ 160 MPa with f taken at the calculation temperature T,

CC⋅

e T

pressure fluctuations of range ∆P lower than the following percentages of P can be neglected,

max

regardless of their number:

for C = 40

3,5 % of P

max

for C = 56

4,5 % of P

max

for C = 63

P

5,5 % of

max

for C = 71

6 % of P

max

for C = 80

7 % of P

max

for C = 90 and Class UW

7,5 % of P

max

Otherwise, if the number of start-up and shut-down cycles at operating pressure is smaller than 500

and if no cycle of intermediate range between operating pressure and the neglected fluctuations occur:

for C = 40

6 % of P

max

for C = 56

8,5 % of P

max

for C = 63

9,5 % of P

max

for C = 71

11 % of P

max

for C = 80

12,5 % of P

max

for C = 90 and Class UW

14 % of P

max

480

For other values of η and f, the above percentages shall be multiplied by the ratio .

η ⋅ f

This rule for neglecting pressure ranges is applicable:

— for the vessel as a whole if the same ΔP acts on all vessel parts,

— component by component if different ΔP act on different parts (see 17.5.1, fourth paragraph).

11

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

For simplification, P may be replaced by the calculation pressure P.

max

For guidance on negligible thermal cycles ()∆T see Annex U.

diff i

17.5.4 Alternative to the 500 cycles rule stated in 5.4.2:

Provided the conditions required in 17.5.4.2 are fulfilled, the condition stated in 5.4.2, Formula (5.4-1),

for checking the number of full pressure cycles (or equivalent number of full pressure cycles) against

the uniform 500 cycles limit valid for any vessel designed according to EN 13445-3 may be disregarded

and replaced by condition (17.5-1):

3

∆P

i

nn= ⋅≤ N (17.5-1)

∑

eq P,i eq

P

max

i

where:

is the equivalent number of full pressure cycles,

n

eq

is the number of pressure cycles at pressure ranges ΔP lower than or equal to the full

n i

P,i

pressure P

is the maximum permissible pressure calculated in the normal operating load case

P

max

(see 5.3.2.1)

NOTE 1

In Formula (17.5–1), n is defined as in Formula (5.4–2).

eq

is the allowable number of full pressure cycles defined in 17.5.4.1.

N

eq

Condition (17.5-1) may be checked:

— for the vessel as a whole, with calculated using for ∆P the pressure fluctuations acting at the

n

eq i

location where their range is maximum and for P the maximum permissible pressure of the

max

vessel (see 3.16),

∆P

— component by component, with n calculated using for the pressure fluctuations acting on the

i

eq

component and for P the maximum permissible pressure of the same component.

max

NOTE 2 The check component by component is of interest only if the range of the pressure fluctuations varies

along the vessel due to additional hydrostatic pressure, or if the vessel has parts which separate different pressure

chambers.

For simplification, P may be replaced by the calculation pressure P.

max

Use of Formula (17.5-1) to calculate is valid under the condition that the contribution of non-

n

eq

pressure loads to cyclic loading can be neglected.

When this condition is not met, a fatigue life assessment of the vessel is necessary and shall be

performed using the rule given in 17.5.5 (if applicable), a simplified fatigue analysis according to the

rest of Clause 17 (Subclauses 17.6 to 17.7) or a detailed fatigue analysis according to Clause 18.

NOTE 3 The rule given in 17.5.5 allows taking into account additional cycles of thermal origin only. The rest of

Clause 17 is mainly devoted to pressure and thermal cycles, but can take into account loading cycles of other

origins (see 17.1.2). Clause 18 enables consideration of all types of loading cycles.

12

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SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

17.5.4.1 Allowable number of full pressure cycles based on nominal design stress, weld types

and maximum stress factor:

The allowable number of full pressure cycles is given by:

3

C ⋅⋅C C

6 min e T

N =2⋅ 10 ⋅ (17.5-2)

eq

η ⋅ f

max

where

is the lowest fatigue class C among all welded joints of the vessel or the class of the

C

min

component if a check component by component is made, or C = 40 MPa alternatively as

min

a conservative assumption.

The value C = 40 MPa shall be used if the vessel includes welded details which cannot be

min

found (directly or by assimilation) in Table 17–4 and are likely to present a low fatigue

resistance.

For vessels which do not contain any welded zone, the C = 90 shall be used.

min

is the thickness correction for e > 25 mm , as defined in 17.6.2.1

C

e

is the temperature correction for >°100 C , as defined in 17.6.2.2.

T *

C

T

is the maximum pressure stress factor found throughout the vessel:

η

max

In looking for the maximum pressure stress factor η , shape deviations (mainly peaking)

max

at longitudinal seam welds should always be considered, because they often may be source

of high values of η.

f

is the nominal design stress at calculation temperature of the load case for which P is

max

calculated.

If, for simplification, n is calculated using the calculation pressure P instead of P , as permitted by

eq

max

5.4.2, f is the nominal design stress, at the corresponding calculation temperature.

When applying this formula:

— η shall be selected according to Table 17-1.

max

In case where the vessel comprises details for which no η value is given in Table 17-1 and no

conservative value of η can be safely estimated, Formula (17.5-2) is not applicable and condition (17.5-

1) shall not be used.

— the thickness to be considered for calculation of C shall be the largest of all components involved

e

in the welded joints of the fatigue class C .

min

— the temperature T * to be considered for calculation of C shall be calculated taking for T and

max

T

T respectively the maximum and minimum temperatures occurring during the whole cycling

min

period.

13

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EN 13445-3:2014/A5:2018 (E)

— the nominal design stress f to be considered shall be the largest of all materials involved in the

welded joints of the fatigue class C . In case of uncertainty, the largest among all vessel

min

components shall be used.

In case where the allowable number of full pressure cycles N given by Formula (17.5-2) is lower than

eq

500, the design should be modified to reach that number.

The curves showing the number of cycles N given by Formula (17.5-2) greater than or equal to 500

eq

η = 3 and where no correction is needed (i.e. when

are plotted in Figure 17.5-1 for the case where

max

C = 1 and C = 1 ).

e t

Key

1 = class 90 5 = class 56

2 = class 80 6 = class 40

3 = class 71 7 = 500 cycles

4 = class 63

Figure 17.5–1 — Allowable number of equivalent full pressure cycles (assuming η = 3 and

max

CC 1

)

eT

17.5.4.2 Conditions of application of Formula (17.5-2):

3.P

max

— No pressure cycle range ∆P shall be greater than ;

i

η

max

— No welded flat end shall be designed using the alternative rule of 10.4.4.4;

— No flat end shall have pairs of adjacent openings designed as a fictitious single opening using the

alternative calculation given at end of 10.6.2.1.

14

= =

---------------------- Page: 16 ----------------------

SIST EN 13445-3:2014/A5:2018

EN 13445-3:2014/A5:2018 (E)

17.5.5 Substitute to the 500 cycles rule stated in 5.4.2 or to the alternative rule stated in 17.5.4,

for cases where thermal cycles cannot be neglected

17.5.5.1 Global assessment

When the 500 cycles rule stated in 5.4.2 or the alternative rule stated in

**...**

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