SIST EN 13445-3:2021/A1:2026

Unfired pressure vessels - Part 3: Design

This Part of this document specifies requirements for the design of unfired pressure vessels covered by EN 13445-1:2019 and constructed of steels in accordance with EN 13445-2:2019.
EN 13445-5:2019, 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 13445-1:2021 und hergestellt aus Stählen nach EN 13445-2:2021 fest.
EN 13445-5:2021 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 13445-1:2021 et construits en aciers conformes à l’EN 13445-2:2021.
L’Annexe C de l’EN 13445-5:2021 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.

Nekurjene tlačne posode - 3. del: Konstruiranje - Dopolnilo A1

General Information

• Status: Published
• Public Enquiry End Date: 02-Oct-2019
• Publication Date: 08-Dec-2025
• ICS: 23.020.32 - Pressure vessels
• Technical Committee: TLP - Pressure vessels
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 09-Dec-2025
• Due Date: 13-Feb-2026
• Completion Date: 09-Dec-2025
• Directive: 2014/68/EU - Directive 2014/68/EU of the European Parliament and of the Council of 15 May 2014 on the harmonisation of the laws of the Member States relating to the making available on the market of pressure equipment
• Mandate: M/071 - Mandate to CEN for standardization in the field of Pressure equipment
• Mandate: M/601 - COMMISSION IMPLEMENTING DECISION of 1.3.2024 on a standardisation request to the European Committee for Standardization and the European Committee for Electrotechnical Standardization as regards pressure equipment and assemblies in support of Directive 2014/68/EU of the European Parliament and of the Council
• Ref Project: EN 13445-3:2021/A1:2025 - Unfired pressure vessels - Part 3: Design

Relations

• Amends: SIST EN 13445-3:2021 - Unfired pressure vessels - Part 3: Design
• Effective Date: 01-Jan-2026

Overview

EN 13445-3:2021/A1:2025 - issued by CEN - is the amended Part 3 of the European standard for unfired pressure vessels and covers design requirements for vessels built to EN 13445‑1:2019 and using steels per EN 13445‑2:2019 (now referenced as EN 13445‑2:2021+A1:2023). Amendment A1 (approved August 2025) updates technical rules, clarifies definitions and symbols, and adds new guidance (including several new annexes). This Part applies primarily to the design stage before putting vessels into service and can also be used for in‑service analysis with appropriate adjustments.

Key topics and technical requirements

• Design scope and applicability: Requirements for pressure parts constructed of steels specified in EN 13445‑2, and interactions with fabrication rules (EN 13445‑4) and material/fatigue guidance.
• Openings, nozzles and reinforcement: Updated definitions (e.g., obround, set‑in/set‑on nozzle), reinforced/isolated/multiple openings rules, limitations on opening diameters and distances to discontinuities.
• Welds and joints: Modifications addressing lap joints, flange construction and detailed design requirements for pressure‑bearing welds (Annex A updates).
• Strength and allowable stresses: Revised maximum allowed nominal design stress values for various steel types including austenitic and cast steels; explicit formula updates in Clause 6.
• Loads, supports and connections: New/updated rules for nozzle‑to‑shell connections, load limits, support brackets, anchor bolts and skirt/topsheet checks.
• Fatigue and fracture assessment: Significant changes to Clause 18 and additions of annexes for fatigue methods - including cycle counting and equivalent stress range (new Annex NB) and fatigue assessment of partial‑penetration welds (Annex NC).
• Finite element and stress concentration guidance: New Annex NA (structural hot‑spot stress determination using shell and solid FE elements) and Annex ND (methods for total stress and stress concentration factors).
• Harmonisation and normative references: Incorporates up‑to‑date Eurocode and related standards (EN 1990:2023, EN 1992, EN 13555, EN 12952‑3:2022, etc.) and aligns with Directive 2014/68/EU (see Annex ZA).

Practical applications and users

This standard is essential for:

• Pressure vessel designers and mechanical engineers performing mechanical design, stress analysis and fatigue assessment.
• Fabricators and welding engineers applying fabrication and joint rules.
• Inspection bodies, notified bodies and conformity assessors assessing regulatory compliance (PED).
• Plant operators and maintenance engineers using the design rules for in‑service assessments and repairs. Practical use cases: design of shells, heads, nozzles and reinforcements; FE modelling for hot‑spot stresses; fatigue life estimation; and preparation of documentation for certification.

Related standards

• EN 13445‑1:2019 (General), EN 13445‑2:2021+A1:2023 (Materials), EN 13445‑4:2021+A1:2023 (Fabrication)
• EN 13445‑5:2019 (access and inspection openings - Annex C relevant)
• EN 1990/1992 Eurocodes, EN 12952‑3, EN 13555

Keywords: EN 13445‑3:2021/A1:2025, unfired pressure vessels, pressure vessel design, nozzle reinforcement, fatigue assessment, finite element analysis, CEN.

Standards Content (Sample)

SLOVENSKI STANDARD
01-januar-2026
Nekurjene tlačne posode - 3. del: Konstruiranje - Dopolnilo A1
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 13445-3:2021/A1:2025
ICS:
23.020.32 Tlačne posode Pressure vessels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 13445-3:2021/A1
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2025
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 A1 modifies the European Standard EN 13445-3:2021; it was approved by CEN on 18 August 2025.

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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye 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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 13445-3:2021/A1:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Modifications to the whole document . 5
Modifications to Clause 2, “Normative references” . 5
Modifications to 5.7.4.3, “Lap joints” . 6
Modifications to Clause 6, “Maximum allowed values of the nominal design stress for
pressure parts” . 7
Modification to 7.6.5, “Junctions – general” . 7
Modifications to 9.2, “Specific definitions” . 7
Modification to 9.3.2, “Symbols” . 9
Modification to 9.4.4.2, “Openings reinforced by elliptical or obround nozzles
normal to the shell wall (see 9.4.1.d)” . 12
Modification to 9.4.5, “Limitations on diameter” . 12
Modification to 9.4.7, “Nozzles to shell connections” . 13
Modifications to 9.4.8, “Distance between a nozzle and a shell butt-weld” . 13
Modifications to 9.5, “Isolated openings” . 15
Modification to 9.6, “Multiple openings” . 29
Modification to 9.7, “Openings close to a shell discontinuity” . 36
Modification to 11.4.4, “Flange construction” . 38
Modifications to 16.4.8, “Nozzle longitudinal stresses” . 39
Modifications to 16.6.2, “Additional specific symbols and abbreviations” . 40
Modifications to 16.6.8, “Single line loads (see Figures 16.6-2 and 16.6-3)” . 40
Modification to 16.7.5, “Load limits for shell”. 40
Modification to 16.10.1, “General” . 41
Modifications to 16.10.2, “Additional specific symbols and abbreviations (see Figure
16.10-1)” . 41
Modification to 16.10.3, “Conditions of applicability” . 46
Modification to 16.10.4, “Applied forces” . 47
Modification to 16.10.5, “Load limits of the shell”. 53
Addition of subclauses 16.10.6, “Support brackets” and 16.10.7 “Design of welds” . 60
Modifications to 16.12.5.3, “Stress checks for anchor bolts and concrete” . 65
Modifications to 16.12.5.4.2, “General condition of applicability for the types” . 66
Modifications to 16.12.5.4.3, “Checks for type 1 – Simple bearing plate” . 66
Modifications to 16.12.5.4.4.1, “Checks for the bearing plate” . 67
Modifications to 16.12.5.4.4.3, “Checks of the skirt at gussets” . 68
Modification to 16.12.5.4.5.1, “Check for the bearing plate” . 68
Modification to 16.12.5.4.5.2, “Check for top plates” . 68
Modifications to 16.12.5.4.5.5, “Checks for type 4 – Bearing plate with top ring plate” . 68
Modifications to 16.12.5.4.5.6, “Check of the skirt at top ring plate” . 70
Addition of new subclause 16.15, “Global loads on conical shells and conical
transitions without knuckles” . 70
Modification to 17.6.2.2, “Temperature” . 77
Modification to Clause 18, “Detailed assessment of fatigue life” . 77
Modification to Annex A, “Design requirements for pressure bearing welds”. 127
Modifications to Annex C, “Design by analysis – Method based on stress categories” . 145
Modification to Annex L, “Basis for design rules related to additional non-pressure
loads” . 147
Modification to Annex N, “Bibliography to Clause 18” . 147
Addition of new Annex NA, “Methods of determination of the structural hot-spot
stress by finite element analysis using shell and solid elements” . 148
Addition of new Annex NB, “Cycle counting and determination of equivalent stress
range” . 158
Addition of new Annex NC, “Fatigue assessment of partial penetration welds” . 191
Addition of new Annex ND, “Methods for calculation of stress concentrations σ
total
and stress concentration factors K ” . 198
t
Modifications to Annex P, “Classification of weld details to be assessed using
principal stresses” . 202
Modifications to Annex Q, “Simplified procedure for the fatigue assessment of
unwelded zones” . 202
Modification to Annex Y, “History of EN 13445-3” . 202
Modification to Annex ZA, “Relationship between this European Standard and the
essential requirements of Directive 2014/68/EU aimed to be covered” . 204

European foreword
This document (EN 13445-3:2021/A1:2025) 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 2026 and conflicting national standards shall be
withdrawn at the latest by May 2026.
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 standardization request addressed to CEN by the European
Commission. The Standing Committee of the EFTA States subsequently approves these requests for its
Member States.
For the relationship with EU Legislation, see informative Annex ZA, which is an integral part of this
document.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the United
Kingdom.
Modifications to the whole document
Replace “Equation (***)” with “Formula (***)” and “Equations (***)” with “Formulae (***)”.
Modifications to Clause 2, “Normative references”
Add a reference to EN 12952-3:2022 and replace the references to EN 1990:2002, EN 1991-1-6:2005,
EN 1992-1-1:2005, EN 1998-1:2004, EN 10222-1:1998, EN 12195-1:2010, EN 13445-2:2021,
EN 13445-4:2021, EN 13555:2014, EN ISO 4014:2011, EN ISO 4016:2011 and EN ISO 15613:2004 with the
following:
“
EN 1990:2023, Eurocode — Basis of structural and geotechnical design
2)
EN 1991-1-6:2005 , Eurocode 1 — Actions on structures — Part 1-6: General actions — Actions during
execution
EN 1992-1-1:2023, Eurocode 2 — Design of concrete structures — Part 1-1: General rules and rules for
buildings, bridges and civil engineering structures
3)
EN 1998-1:2004 , Design of structures for earthquake resistance — Part 1: General rules, seismic actions
and rules for buildings
EN 10222-1:2017, Steel forgings for pressure purposes — Part 1: General requirements for open die
forgings
4)
EN 12195-1:2010 , Load restraining on road vehicles — Safety — Part 1: Calculation of securing forces
EN 12952-3:2022, Water-tube boilers and auxiliary installations — Part 3: Design and calculation for
pressure parts of the boiler
EN 13445-2:2021+A1:2023, Unfired pressure vessels — Part 2: Materials
EN 13445-4:2021+A1:2023, Unfired pressure vessels — Part 4: Fabrication
EN 13555:2021, Flanges and their joints — Gasket parameters and test procedures relevant to the design
rules for gasketed circular flange connections
EN ISO 4014:2022, Fasteners — Hexagon head bolts — Product grades A and B (ISO 4014:2022)
EN ISO 4016:2022, Fasteners — Hexagon head bolts — Product grade C (ISO 4016:2022)
EN ISO 15613:2004, Specification and qualification of welding procedures for metallic materials —
Qualification based on pre-production welding test (ISO 15613:2004)
________________
2) EN 1991-1-6:2005 is impacted by the corrigendum EN 1991-1-6:2005/AC:2013.
3) EN 1998-1:2004 is impacted by the stand-alone amendment EN 1998-1:2004/A1:2013.
4) EN 12195-1:2010 is impacted by the corrigendum EN 12195-1:2010/AC:2014.
”.
Throughout the text, replace all references to “EN 13445-2:2021” with “EN 13445-2:2021+A1:2023” and
replace all references to “EN 13445-4:2021” with “EN 13445-4:2021+A1:2023”.
In 16.14.8.2 9) NOTE 7, replace “EN 13445-4:2021, 5.4.4” with “EN 13445-4:2021+A1:2023, 6.4.4”.
In 5.3.2.4.3, in the text after Table 5.3.2.4-1, replace “EN 1990:2002+A1:2005” with “EN 1990:2023”.
In 16.12.5.3, replace “EN 1992-1-1:2005, 3.16” with “EN 1992-1-1:2023, 5.1.6”.
In Table A-4, Ref TS 1, replace “EN 10222-1:1998 12.2.2” with “EN 10222-1:2017, 8.1.2”.
In subclause G.1, replace “EN 13555:2014” with “EN 13555:2021”.
In the NOTE in subclause G.5.2, replace “EN ISO 4014:2011” and “EN ISO 4016:2011” with
“EN ISO 4014:2022” and “EN ISO 4016:2022”.
Modifications to 5.7.4.3, “Lap joints”
Replace subclause 5.7.4.3 with the following:
“
5.7.4.3 Lap joints
5.7.4.3.1 General case
Lap joints with fillet welds shall be used only when all the following conditions are fulfilled:
a) testing group 4;
b) circumferential joints attaching head to shell;
c) material thickness not exceeding 8 mm;
d) maximum diameter 1 600 mm;
e) materials 1.1;
f) calculation temperature:
–10 °C ≤ T ≤ 120 °C;
g) non-corrosive conditions;
h) both sides of the lap shall be welded except where indicated in Table A-2;
i) manufacturing tolerances of EN 13445-4:2021+A1:2023.
5.7.4.3.2 Connection of bellows
Outside lap joints (weld types 1.1 and 2.1 in Table 14.4.5-1) shall be used only under non-corrosive
conditions (see also Table A-9).”.
Modifications to Clause 6, “Maximum allowed values of the nominal design
stress for pressure parts”
Replace the formula for austenitic steels as per 6.4 for testing and exceptional load cases in Table 6-1:
“
Table 6-1 — Maximum allowed values of the nominal design stress for pressure parts other than
bolts
a b
Steel designation Normal operating load cases a Testing and exceptional load cases
Steels other than
RR
  R
p0,2/T m/20
p0,2/T
test
f = min ;
  f =
austenitic, as per 6.2 d
test
 

1,5 2,4
1,05
c  
A < 30 % 
Steels other than
 RR  R

p0,2/T m/20 p0,2/T
test
f = min ;
  f =
austenitic, as per 6.3: 
d
test
 
1,5 1,875 
1,05
 
Alternative route 
c
A < 30 %
Austenitic steels as
R R

p1,0/T p1,0/T
test
f =
 f =
per 6.4 
d
test

1,5 
1,05
c 
30 % ≤ A < 35 % 
Austenitic steels as
RR
 
 R  R R 
p1,0/TTm/
p1,0/T p1,0/TTm/
test test
f = max ;
f = max; min ; 
per 6.5   
test
d
  
1,5 1,2 3 1,05 2


c   
 
A ≥ 35 %
Cast steels as per 6.6
  
RR R
p0,2/ T m/ 20 p0,2/ T
test
  
f = min ;
f =
d
test
 
1, 9 3
1,33

 
a
Yield strength R may be used instead of R if the latter is not available from the material standard.
eH p0,2
b
See 5.3.2 and 6.1.2.
c
For definition of rupture elongation, see EN 13445-2:2021+A1:2023, Clause 4.
“
Modification to 7.6.5, “Junctions – general”
Add the following sentence:
“If this requirement for the distance to another cone/cylinder junction is not fulfilled a conical shell and
conical transition without knuckles may be designed according to 16.15.”.
Modifications to 9.2, “Specific definitions”
Replace subclauses 9.2.2.1 to 9.2.12 with the following:
“
9.2.3
obround opening
opening with an obround shape, given by two semicircles connected by two parallel straight lines
9.2.4
overall check
evaluation of the reinforcement in the cross-section including the walls on each side of each opening and
the lengths of adjacent shell
9.2.5
reinforcement
loaded cross-sectional area of metal considered to provide resistance to the pressure at an opening
9.2.6
reinforced opening
opening where the reinforcement includes a contribution from the shell, from a nozzle, a reinforcing plate
or a reinforcing ring
9.2.7
reinforcing plate
plate which is fillet welded to the shell and contributes to the reinforcement
9.2.8
reinforcing ring
set-in ring which contributes to the reinforcement
9.2.9
set-in nozzle
nozzle which passes through the shell and is welded to it on the inside and outside of the shell (see Figure
9.4-8)
9.2.10
set-on nozzle
nozzle which is welded only to the outside of the shell (see Figure 9.4-7)
9.2.11
shell
cylinder, sphere, cone or dished end
9.2.12
shell discontinuity
junction between any two of the following: cylinder, cylinder on a different axis, cone, dished head,
spherical end, flange or flat head, or discontinuity in wall thickness of shell due to the arrangement of a
reinforcing pad
9.2.13
small opening
isolated opening which satisfies the condition of Formula (9.5-18) ”.
Modification to 9.3.2, “Symbols”
Replace subclause 9.3.2 with the following:
“
9.3.2 Symbols and units
NOTE Units are given in square brackets; [-] indicates a dimensionless quantity.
Af
Stress loaded cross-sectional area effective as reinforcement [mm ];
Af
Af of the nozzle contained along the length l [mm ];
b
bo
Af
Af of the shell contained along the length L [mm ] (see Figures 9.6-1 to 9.6-4);
Ls
b
Af
Af of the shell contained along the length L [mm ] (see Figures 9.6-5 to 9.6-6);
Os
b1
Af
Af of the reinforcing plate [mm ];
p
Af
r Af of the reinforcing ring [mm ];
Af
Cross-sectional area of fillet weld between nozzle (or plate) and shell [mm ] (see 9.5.2.3.3 and
w
Figures 9.4-4 and 9.5-1);
Ap
Pressure loaded area [mm ];
Ap
Ap of the shell for the length L [mm ] (see Figures 9.6-1 to 9.6-4);
Ls
b
Ap
Ap of the shell for the length L [mm ] (see Figures 9.6-5 to 9.6-6);
Os
b1
Ap
ϕ Additional pressure loaded area for oblique nozzle connection, function of angle ϕ [mm ] (see
Figures 9.5-1 to 9.5-3);
a Distance taken along the mid-thickness of the shell between the centre of an opening and the
external edge of a nozzle or ring; or, if no nozzle or ring is present, a is the distance between
the centre of the hole and its bore [mm];
a , a Values of a on the ligament side of the opening [mm] (Figures 9.6-2 and 9.6-3);
1 2
a’ , a’ Values of a on the opposite side of the opening to the ligament [mm] (see Figure 9.6-5);
1 2
D Mean diameter of a cylindrical shell at the junction with another component [mm];
c
D External diameter of a cylindrical or spherical shell, the cylindrical part of a torispherical or
e
an elliptical dished end, a conical shell at the centre of an opening [mm];
D Internal diameter of a cylindrical or spherical shell, the cylindrical part of a torispherical or
i
an elliptical dished end, a conical shell at the centre of an opening [mm];
d Diameter (or maximum width) of an opening on shell without nozzle [mm];
d External diameter of a nozzle fitted in a shell [mm];
eb
External diameter of a reinforcing ring [mm];
d
er
d Internal diameter of a nozzle fitted in a shell [mm];
ib
d Internal diameter of a reinforcing plate [mm];
ip
d Internal diameter of a reinforcing ring [mm];
ir
d Internal diameter of extruded opening [mm]
ix
e Analysis thickness of nozzle (or mean analysis thickness within the length l external or
a,b b
internal by the shell) [mm];
e Average thickness along the length l for reinforcing rings [mm] [see Formula (9.5-46)];
a,m o
e Analysis thickness of reinforcing plate [mm];
a,p
e Analysis thickness of reinforcing ring [mm];
a,r
e Analysis thickness of shell wall or mean analysis thickness within the length l' and excluding
s
a,s
the thickness of the reinforcing pad if fitted [mm];
e Effective thickness of nozzle (or mean thickness within the external length l or internal
b bo
length l ) taken into account for reinforcement calculation [mm];
bi
e Assumed shell thickness of shell wall (see Formula (9.5-2)) for checking of reinforcement of
c,s
an opening [mm]. The thickness may be assumed by designer between the minimum required
shell thickness e and the shell analysis thickness e . This assumed thickness shall then be
a,s
used consistently in all requirements.
NOTE Use of small values of e is not favourable for checking of reinforcement, however it results
c,s
in smaller distances from adjacent shell discontinuities.
e Effective thickness of reinforcing ring taken into account for reinforcement calculation [mm];
r
e′ Length of penetration of nozzle into shell wall for set-in nozzles with partial penetration
s
[mm];
e Minimum required thickness of a cylindrical shell at the junction with another component
[mm] (see Figures 9.7-6 and 9.7-10);
e Minimum required thickness of a conical shell at the junction with a cylindrical shell [mm]
(see Figures 9.7-6 and 9.7-10);
f Nominal design stress of the nozzle material [MPa];
b
f Nominal design stress of the reinforcing plate material [MPa];
p
f Nominal design stress of shell material [MPa];

s
h Inside height of a dished end, excluding cylindrical skirt [mm];
k Reduction factor for l and l [–] (used for overall check in 9.6.4);

so1 so2
L Centre-to-centre distance between two openings or nozzles taken on the mean surface of the
b
shell [mm] (see Figure 9.6-2);
L Length of cross sectional area of shell including the whole section of two adjacent openings
b1
taken on the surface of the shell [mm];
l Length of nozzle extending outside the shell [mm];
b
l′ Effective length of nozzle outside the shell for reinforcement [mm];
b
l Length of nozzle extending inside the shell [mm] (i.e.: protruding nozzle);
bi
l′ Effective length of nozzle inside the shell for reinforcement [mm];
bi
l Maximum length of nozzle outside the shell for reinforcement [mm];

bo
l Length of conical shell given by Formula (9.7-7) and used in the strength assessment of a
con
junction between the small end of a cone and a cylindrical shell [mm] (see Figure 9.7-6);
l Length of cylindrical shell given by Formula (9.7-3) [mm]; and used in the strength
cyl
assessment of a junction (see Figure 9.7-6) between a cylinder and:
— the small end of a conical shell with same axis;
— a spherical shell convex towards the cylinder;
— a cylindrical shell with convergent axis.
l Distance between the centre line of a shell butt-weld and the centre of an opening near or
n
crossing the butt-weld [mm];
l Maximum length of ring and shell wall in reinforcing rings for reinforcement;
o
Width of reinforcing plate [mm];
l
p
l Width of reinforcing plate between two adjacent openings [mm] (Figure 9.6-5);
pi
l′ Effective width of reinforcing plate for reinforcement [mm];
p
l Width of reinforcing ring [mm];
r
l′ Effective width of reinforcing ring for reinforcement [mm];
r
l Length of shell, from the edge of an opening or from the external diameter of a nozzle, to a
s
shell discontinuity [mm];
l′ Effective length of shell for opening reinforcement [mm];
s
l Maximum length of shell contributing to opening reinforcement, taken on the mean surface of
so
the shell wall [mm];
R Inside radius of a hemispherical end or of the crown of a torispherical end [mm];
r Inside radius of curvature of the shell at the opening centre [mm];
is
w Distance between an opening and a shell discontinuity [mm] (see Figures 9.7-1 to 9.7-11);
w Required minimum value for w [mm];
min
w Minimum value for w which has no influence on l from shell discontinuities [mm];
p s
Half apex angle of a conical shell [degrees];
α
For a nozzle having a longitudinal weld, angle between the plane containing the nozzle axis
θ
and the longitudinal weld line, and the plane containing the nozzle axis and the shell
generatrix passing through the centre of the opening [degrees];
Obliquity angle in the longitudinal or transversal cross-section, measured between the normal
ϕ
to the wall at the opening centre and the projection of the nozzle axis on the considered cross-
section [degrees];
ϕ Projection of ϕ in the plane in which L lies for ligament check of multiple openings [radianss];
e b
Φ Angle between the centre-to-centre line of two openings or nozzles and the generatrix of a
cylindrical or conical shell (0° ≤ Φ ≤ 90°) [degrees] (see Figure 9.6-1);
– for isolated openings, angle between shell generatrix and axis of major diameter [degrees]
Ω
– for adjacent openings, angle between the plane containing the opening centres and the
axis of major diameter [degrees].
”.
Modification to 9.4.4.2, “Openings reinforced by elliptical or obround nozzles
normal to the shell wall (see 9.4.1.d)”
Replace subclause 9.4.4.2 with the following:
“
9.4.4.2 Openings reinforced by elliptical or obround nozzles normal to the shell wall (see
9.4.1-d))
In cylindrical or conical shells, the diameter d of the opening shall be calculated as follows:
dd+
d ( )
2 min max 2
max
dd= ⋅ sin ΩΩ+⋅ ⋅cos (9.4-1)

min

dd2
min min
where d and d are the minor and major diameters of the opening,
min max
and Ω is :
 for isolated openings, the angle between the shell generatrix passing through the centre of the
opening and the axis of the major diameter;
 for adjacent openings, and for each of the two openings, the angle between the shortest line lying on
the surface of the shell passing through the centres of the two openings, and the line resulting on the
shell from the intersection of the plane defined by the nozzle axis and the axis of the major diameter
of any nozzle cross section under consideration.
In spherical shells and dished ends the diameter d of the opening shall be calculated as follows:
 dd+ 
min max
(9.4-2)
dd⋅
 
max
2d
 min 
where d and d are defined above.
min max
NOTE For nozzles with elliptical or obround cross-section the pressure produces not only membrane stresses,
but also bending stresses in the circumferential direction. Thus, the attached shell wall on one side and the attached
flange or circular pipe on the other side have to support the nozzle if its wall thickness has been determined using
only membrane stresses. The nozzle loads the shell and it is possible that the diameter which applies for the elliptical
or obround nozzle is larger than the major axis.”.
Modification to 9.4.5, “Limitations on diameter”
Replace subclause 9.4.5 with the following:
“
9.4.5 Limitations on diameter
9.4.5.1 Shell reinforced openings
Shell reinforced openings without a nozzle shall satisfy the following condition:
d
≤ 0,5
(9.4-3)
2r
is
=
9.4.5.2 Openings with reinforcing plates
Where an opening is fitted with a reinforcing plate with or without the presence of a nozzle, the condition
of the Formula (9.4-3) shall be satisfied. Reinforcing plates are normally situated on the external surface
of the shell, but they may be situated also on the internal surface or on both surfaces.
In case of high mean wall temperature for the shell (more than 250 °C) or in the presence of severe
temperature gradients through the shell, the use of reinforcing plates shall be avoided; if it is necessary
then the material of the reinforcing plate shall be of the same quality of shell material, and special
measures and warnings shall be taken to avoid thermal stress concentrations.
9.4.5.3 Openings in dished ends
For openings in hemispherical ends and dished ends, the ratio d/D shall not exceed 0,6. Therefore, if the
e
opening is reinforced by a nozzle or a reinforcing ring, d /D and d /D shall not exceed 0,6.
ib e ir e
9.4.5.4 Openings with nozzles
For openings in cylindrical shells reinforced by nozzles, the ratio d /(2r ) shall not exceed 1,0 (see
ib is
Figures 9.4-14 and 9.4-15).”.
Modification to 9.4.7, “Nozzles to shell connections”
Replace the second paragraph with the following one:
“For welded nozzles, the cross-sectional area of the nozzle may be taken into account for reinforcement
of the opening, provided weld dimensions are in accordance with the requirements of Annex A.”.
Modifications to 9.4.8, “Distance between a nozzle and a shell butt-weld”
Replace the first paragraph and formula in subclause 9.4.8 with the following:
“9.4.8 Distance between a nozzle and a shell butt-weld
The distance between the centre line of a shell butt-weld (longitudinal or circumferential) and the centre
of an opening shall be either less than d /6 or greater than the value l given by:
ib n
l=min 0,5de++2 ;0,5d 40 (9.4-4)”.
( )
n eb a,s eb
Replace Figures 9.4-14 and 9.4-15 with the following figures:
"
Figure 9.4-14 — Limitation of effective thickness ratio for nozzles, for the calculation

Figure 9.4-15 — Limitation of actual thickness ratio for nozzles, for the manufacturing
”.
Modifications to 9.5, “Isolated openings”
Replace subclause 9.5 with the following one:
“
9.5  Isolated openings
9.5.1  Limitations
An opening is considered isolated if the following condition is satisfied:
L ≥ aa++ l + l (9.5-1)
b 1 2 so1 so2
where
a and a are shown in Figures 9.6-1 to 9.6-4, and l and l are calculated according to:
1 2 so1 so2
l 2re+ ⋅e (9.5-2)
( )
so is c,s c,s
where
e is the assumed shell thickness to be taken as is explained in 9.3.2; normally the value of shell
c,s
analysis thickness e may be taken, but this can be conservative and sometimes it can be
a,s
advantageous to use a smaller assumed value for e to obtain smaller minimum distances
c,s
from adjacent shell discontinuities;
r is given by:
is
 for cylindrical or spherical shells
D
e
re− (9.5-3)
is a,s
 for hemispherical or torispherical ends
r = R (9.5-4)
is
 for elliptical ends
0,44D
i
rD+ 0,02 (9.5-5)
is i
2h
 for conical shells
D
e
re− (9.5-6)
is a,s
2 cosα
=
=
=
=
9.5.2  Reinforcement rules
9.5.2.1  General formula and its derivatives
9.5.2.1.1 The general formula for the reinforcement of an isolated opening is given by:
(9.5-7)
Af + Af ⋅ f −+0,5P Af ⋅ f −+0,5P Af ⋅ f −0,5P ≥ P⋅ Ap + Ap + 0,5Ap
( )( ) ( ) ( ) ( )
s w s p op b ob s b ϕ
where
f = min ff; (9.5-8)
( )
ob s b
(9.5-9)
f = min ff;
( )
op s p
Where a reinforcing ring is fitted, Af and Ap shall be substituted for Af and Ap .
r r b b
9.5.2.1.2 For all reinforced openings except small openings and those reinforced by a ring, the
Formula (9.5-7) applies; in particular:
a) Where either f or f is not greater than f, the reinforcement shall be determined from
b p s
Formula (9.5-7) and P shall be obtained as follows:
max
Af + Af ⋅+f Af ⋅ f + Af ⋅ f
( )
s w s b ob p op
P = (9.5-10)
max
Ap + Ap + 0,5Ap + 0,5 Af + Af ++Af Af
( ) ( )
s b ϕ s w bp
b) Where f and f are both greater than f , the reinforcement shall be determined from
b p s
(9.5-11)
Af + Af + Af + Af ⋅( f −0,5P)≥ P⋅ Ap + Ap + 0,5Ap
( ) ( )
s w p b s s b ϕ
Af + Af + Af + Af ⋅ f
( )
s w bp
s
P = (9.5-12)
max
Ap + Ap + 0,5Ap + 0,5 Af + Af + Af + Af
( ) ( )
s b ϕ s w bp
9.5.2.1.3 For an opening with a reinforcing ring:
a) Where f is less than f , the following shall apply:
r s
(9.5-13)
( Af + Af )⋅( f −0,5P)+ Af ⋅( f −0,5P)≥ P⋅ Ap + Ap + 0,5Ap
( )
s w s r or s r ϕ
and P is given by:
max
Af + Af ⋅+f Af ⋅ f
( )
s w s r or
P = (9.5-14)
max
Ap + Ap + 0,5Ap +⋅0,5 Af + Af + Af
( )
( )
s r ϕ sw r
where f is given by:
or
f = min ff; (9.5-15)
( )
or s r
b) Where f is greater than or equal to f , the following shall apply:
r s
Af + Af + Af ⋅ f −0,5P ≥ P⋅ Ap + Ap + 0,5Ap (9.5-16)
( )( )
( )
s w r s s r ϕ
and P is given by:
max
Af ++Af Af ⋅ f
( )
s w r s
P = (9.5-17)
max
Ap ++Ap 0,5Ap + 0,5 Af + Af + Af
( ) ( )
s r ϕ sw r
NOTE For application of Formulae (9.5-10), (9.5-12), (9.5-14) and (9.5-17) to different load cases, see 3.16,
Note 1.
9.5.2.2  Small opening
A small opening is one which satisfies the following condition:
d≤ 0,15 2re+ ⋅e (9.5-18)
( )
is c,s c,s
Where a small opening lies beyond the distance w defined in 9.7.3, no reinforcement check is necessary.
p
Where it lies within this distance, the reinforcement shall be in accordance with Formula (9.5-7) or
(9.5-11), as appropriate. However, the distance w between small opening and shell discontinuity shall
respect the minimum value w as required in 9.7.1.
min
9.5.2.3   General requirements for reinforcement
9.5.2.3.1 Reinforcing pads
For cases where a reinforcing pad contributes to the reinforcement (see Figures 9.4-3, 9.4-4 and 9.4-10):
 reinforcing plates shall be fitted in close contact with the shell;
 the width of a reinforcing plate l′ to be considered as contributing to reinforcement is given by:
p
′ (9.5-19)
l = min l ; l
( )
p so p
 the nominal thickness of a reinforcing plate shall not be greater than 1,5 times the nominal thickness
of the shell on which the reinforcing plate is fitted;
 e and l are dimensions of reinforcing pads used in formulae for openings that may be reinforced
a,p p
also by reinforcing pads; if reinforcing pad is not present then the values e and l shall be put equal
a,p p
to zero. If the reinforcing pad is contributing to reinforcement then, for all cases:
′
Af l⋅e (9.5-20)
p p ap
9.5.2.3.2 Joint coefficient
9.5.2.3.2.1 Opening intersecting with a shell governing weld
If an opening intersects with a shell governing weld (see definition in 5.6), the value f for the shell
s
material in Formulae (9.5-7), (9.5-10) to (9.5-14), (9.5-16) and (9.5-17) shall be replaced by f ∙z, where z
s
is the joint coefficient of the shell.
=
9.5.2.3.2.2 Nozzle with a longitudinal weld
If a nozzle has a longitudinal weld having a weld joint factor z, the value f for the nozzle material shall be
b
replaced by fz except for openings in cylindrical or conical shells if the angle θ as defined in
b
subclause 9.3.2 is greater than 45°.
9.5.2.3.2.3 Reinforcing pad with a weld
If a reinforcing pad has a weld having a weld joint factor z, the value f for the pad material shall be
p
replaced by fz except for openings in cylindrical or conical shells if the angle between the pad weld and
p
the shell generatrix is greater than 45°.
9.5.2.3.3 Fillet weld areas for compensation
For all cases:
 Af is the area of any welds connecting together the different components (shell to nozzle, shell to
w
reinforcing ring or reinforcing plate) which is located within length l′ on the shell (see 9.5.2.4.2) and
s
lengths l′ and l′ on the nozzle (see 9.5.2.4.4.1). Areas of welds already included in other areas, e.g.
b bi
Af , Af , Af or Af , shall be omitted from Af (see Figures 9.4-6 and 9.4-10).
s r p b w
9.5.2.4 Pressure loaded cross-sectional areas Ap and stress loaded cross-sectional areas Af
9.5.2.4.1 General
With reference to the general formula and its derivates of 9.5.2.1, the stress loaded and pressure loaded
cross-sectional areas shall be calculated by different formulae depending on different cases of shells and
different cases of nozzles.
In presence of reinforcing pads, the cross-sectional area Af shall be calculated according to 9.5.2.3.1.
p
For fillet weld areas participating in the reinforcement, the cross-sectional area Af shall be evaluated
w
according to 9.5.2.3.3.
NOTE For additional pressure loaded cross-sectional area Ap due to the obliquity of a nozzle, see 9.5.2.4.5.
ϕ
9.5.2.4.2 Shells with openings without nozzle or reinforcing ring, with or without reinforcing
pads
9.5.2.4.2.1 On cylindrical shell, longitudinal cross-section
With reference to Figures 9.4-1 and 9.4-3 the values useful for compensation of opening shall be
calculated as follows:
d
a= (9.5-21)
D
e
re− (9.5-22)
is a,s
l= D−2e+ ee⋅ (9.5-23)
( )
so e a,s c,s c,s
′
l = min l ; l (9.5-24)
( )
s so s
=
Ap= r⋅ l′+ a+ a⋅ e+ e (9.5-25)
( )
( )
s is s a,s a,p
′
Af l⋅e (9.5-26)
s s c,s
If the closure of the opening is located inside the shell (as in Figure 9.4-2), then:
′
Ap=r⋅+l a (9.5-27)
( )
s is s
For adequate reinforcement either Formula (9.5-7) or (9.5-11), as appropriate, shall be satisfied.
9.5.2.4.2.2 On conical shell, longitudinal cross-section
With reference to Figure 9.4-13 the values useful for compensation of opening shall be calculated as
follows:
d
a= (9.5-28)
D
e
re− (9.5-29)
is a,s
2cosα
D

e
l −2ee+⋅e  (9.5-30)
so a,s c,s c,s

cosα

l′= min l ; l (9.5-31)
( )
s so s
Af l′⋅e (9.5-32)
s s c,s
′′ (9.5-33)
Ap 0,5(la+⋅) 2r+(la+⋅) tanα+ a⋅ e+ e
{ } ( )
s s is s a,s a,p
If the closure of the opening is located inside the shell (as in Figure 9.4-2), then:
′′
Ap 0,5 la+⋅ 2r+ la+⋅ tanα (9.5-34)
( ){ ( ) }
s s is s
For adequate reinforcement either Formula (9.5-7) or (9.5-11), as appropriate, shall be satisfied.
9.5.2.4.2.3 On spherical shell, dished end, cylindrical and conical shell, transverse section
With reference to Figure 9.4-2 and 9.4-4, in the following formulae r shall be obtained from
is
Formulae (9.5-3) to (9.5-6) of 9.5-1.
l 2re+ ⋅e (9.5-35)
( )
so is c,s c,s
′
l = min l ; l (9.5-36)
( )
s so s
rr+ 0,5e (9.5-37)
ms is a,s
d
δ= (9.5-38)
2⋅r
ms
=
=
=
=
=
=
=
=
ar⋅arcsinδ (9.5-39)
ms
la′+
2 s
Ap 0,5r⋅ + a⋅ e+ e (9.5-40)
( )
s is a,s a,p
0,5er+
a,s is
′
Af l⋅e (9.5-41)
s s c,s
where arcsin is in radians.
If the closure of the opening is located inside the shell (as in Figure 9.4-2), then
la′+
2 s
Ap 0,5r⋅ (9.5-42)
s is
0,5er+
a,s is
For adequate reinforcement either Formula (9.5-7) or (9.5-11), as appropriate, shall be satisfied.
9.5.2.4.3 Shells with openings without nozzle, reinforced by reinforcing rings
This applies only when rings of the set-in welded type in accordance with Figures 9.4-5 and 9.4-6 are
used, and the effective thickness of reinforcing ring for reinforcement calculation e shall be:
r
  (9.5-43)
e = min e ; max 3el;3
( )
r a,r c,s r
 
NOTE The design described here does not cover tightness issue. See Annex G for calculation of openings with
flange in sphere [Figure G.3-7 b)].
Considering ring plus shell as a shell wall of variable thickness starting from the bore of reinforcing ring
(see Figures 9.4-5 and 9.4-6), the maximum length l of ring plus shell from the bore contributing to
o
opening reinforcement is given by:
l 2re+⋅e (9.5-44)
( )
o is a,m a,m
where
e is the average thickness (obtained considering e and e and by iterative calculation) along the
a,m r c,s
length l :
o
l
r
e = e+−ee ⋅ (9.5-45)
( )
a,m c,s r c,s
l
o
with
l
r
≤ 1 (9.5-46)
l
o
If the width of reinforcing ring l is greater than l for reinforcement calculation shall be put
r o
′ (9.5-47)
l = min(ll; )
r o r
Therefore, the effective length l′ of shell for calculation of Ap and Af is:
s s s
l′′minll;− l
( ) (9.5-48)
s s or

=
=
=
=
=
=
For adequate reinforcement either Formula (9.5-7) or (9.5-11), as appropriate, shall be satisfied.
9.5.2.4.3.1 Reinforcing ring on cylindrical shell, longitudinal cross-section
With reference to Figure 9.4-5 the values useful for compensation of opening shall be calculated as
follows:
d
er
a= (9.5-49)
D
e
re− (9.5-50)
is a,s
(9.5-51)
l= De−+2 e⋅e
( )
o e a,s a,m a,m
Af l′⋅e (9.5-52)
s s c,s
Af l′⋅e (9.5-53)
r r a,r
D

e
Ap − e⋅ l′+ a+ e⋅ a− l (9.5-54)
( ) ( )
s a,s s a,r r


If the closure of the opening is located inside the ring, (as in Figure 9.4-2), then
D

e
Ap − e⋅+l′ a (9.5-55)
( )
s a,s s


For adequate reinforcement either Formula (9.5-7) or (9.5-11), as appropriate, shall be satisfied.
9.5.2.4.3.2 Reinforcing ring on conical shell, longitudinal cross-section
With reference to Figures 9.4-5 and 9.4-13 the values useful for compensation of opening shall be
calculated as follows:
d
er
a= (9.5-56)
D
e
re− (9.5-57)
is a,s
2cosα
D
e
l −+2ee⋅e (9.5-58)
o a,s a,m a,m
cosα

′
Af l⋅e (9.5-59)
s s c,s
′
Af l⋅e (9.5-60)
r r a,r
′′
Ap 0,5(la+⋅) 2r+(la+⋅) tanα+ e⋅(a− l) (9.5-61)
{ }
s s is s a,r r
=
=
=
=
=
=
=
=
=
=
If the closure of the opening is located inside the ring, (as in Figure 9.4-2), then
Ap 0,5 la′′+⋅ 2r+ la+⋅ tanα
( ) ( ) (9.5-62)
{ }
s s is s
For adequate reinforcement either Formula (9.5-7) or (9.5-11), as appropriate, shall be satisfied.
9.5.2.4.3.3 Reinforcing ring on spherical shell, dished end, cylindrical and conical shell,
transverse section
With reference to Figure 9.4-6, in the following formulae r shall be obtained from Formulae (9.5-3) to
is
(9.5-6) of 9.5-1.
rr+ 0,5e (9.5-63)
ms is a,s
d
er
δ= (9.5-64)
2r
ms
(9.5-65)
dd+ 2l
er ir r
ar⋅arcsinδ (9.5-66)
ms
(9.5-67)
l 2re+⋅e
( )
o is a,m a,m
d
ir
δ = (9.5-68)
r
2r
ms
ar⋅arcsinδ (9.5-69)
r ms r
la′+
2 s
(9.5-70)
Ap 0,5r⋅ +⋅e a
s is a,r r
0,5er+
a,s is
′
Af l⋅e (9.5-71)
s s c,s
′
Af l⋅e (9.5-72)
r r a,r
where arcsin is in radians.
If the closure of the opening is located inside the ring (as in Figure 9.4-2), then
′
la+
s
Ap 0,5r⋅ (9.5-73)
s is
0,5er+
a,s is
In case the ring has a protrusion inside the shell, Formulae (9.5-70) and (9.5-73) are conservative. In this
case Ap may be determine
...