EN 13445-1:2026

• Abstract:

  This document defines the terms, definitions, quantities, symbols and units that are used throughout the EN 13445 series and gives general information on the design and manufacturing of vessels under this standard.; It also contains instructions on how to use the standard (Annex A) as well as an index which covers the whole standard (Annex B). This information is aimed to aid users of the EN 13445 series.; This document applies to unfired pressure vessels with a maximum allowable pressure greater than 0,5 bar gauge but may be used for vessels operating at lower pressures, including vacuum.; This document is not applicable to pressure vessels of the following types:; - vessels of riveted construction;; - vessels of lamellar cast iron or any other materials not included in Parts 2, 6, or 8 of the standard;; - multilayered, autofrettaged or pre-stressed vessels.; This document can be applied to the following pressure vessels, provided that account is taken of additional and/or alternative requirements resulting from the hazard analysis and from rules or instructions specific for:; - transportable vessels;; - items specifically designed for nuclear use;; - pressure vessels with a risk of overheating.; NOTE EN 14222 covers electrically fired boilers made from stainless steel and can be used as an example of additional requirements for such vessels.; Other European standards apply to industrial piping (EN 13480 series) and to water tube and shell boilers (EN 12952 series and EN 12953 series).

• Status: Published
• Publication Date: 30-Jun-2026
• ICS: 23.020.30 - Pressure vessels, gas cylinders
• Technical Committee: CEN/TC 54 - Unfired pressure vessels
• Drafting Committee: CEN/TC 54/WG 51 - A - Overall co-ordination, scope of standard and vessel classification
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 01-Jul-2026
• Due Date: 05-Sep-2028
• Completion Date: 01-Jul-2026
• Directive: Harmonized Standard2014/68/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/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: SIST EN 13445-1:2026 - Unfired pressure vessels - Part 1: General

• Replaces: EN 13445-1:2021 - Unfired pressure vessels - Part 1: General
• Effective Date: 29-Apr-2026
• Refers: EN 764-1:2015+A1:2016 - Pressure equipment - Part 1: Vocabulary
• Effective Date: 29-Jul-2026
• Refers: EN 13445-3:2026 - Unfired pressure vessels - Part 3: Design
• Effective Date: 29-Jul-2026
• Refers: EN 764-2:2012 - Pressure equipment - Part 2: Quantities, symbols and units
• Effective Date: 29-Jul-2026
• Refers: EN 13445-8:2026 - Unfired pressure vessels - Part 8: Additional requirements for pressure vessels of aluminium and aluminium alloys
• Effective Date: 29-Jul-2026
• Refers: EN 13445-5:2026 - Unfired pressure vessels - Part 5: Inspection and testing
• Effective Date: 29-Jul-2026
• Refers: EN 13445-10:2026 - Unfired pressure vessels - Part 10: Additional requirements for pressure vessels of nickel and nickel alloys
• Effective Date: 29-Jul-2026
• Refers: EN 13445-11:2026 - Unfired pressure vessels - Part 11: Additional requirements for pressure vessels of titanium and titanium alloys
• Effective Date: 29-Jul-2026
• Refers: EN 13445-6:2026 - Unfired pressure vessels - Part 6: Requirements for the design and fabrication of pressure vessels and pressure parts constructed from spheroidal graphite cast iron
• Effective Date: 29-Jul-2026
• Refers: EN 13445-4:2026 - Unfired pressure vessels - Part 4: Fabrication
• Effective Date: 29-Jul-2026
• Refers: EN 13445-2:2026 - Unfired pressure vessels - Part 2: Materials
• Effective Date: 15-Jul-2026
• Referred By: EN 1473:2016 - Installation and equipment for liquefied natural gas - Design of onshore installations
• Effective Date: 08-Jul-2026
• Referred By: EN 13060:2014+A1:2018 - Small steam sterilizers
• Effective Date: 08-Jul-2026
• Referred By: EN 1866:2005 - Mobile fire extinguishers
• Effective Date: 08-Jul-2026
• Referred By: EN 285:2006+A2:2009 - Sterilization - Steam sterilizers - Large sterilizers
• Effective Date: 08-Jul-2026

Overview

EN 13445-1:2026 is a European Standard published by CEN that provides the foundational general provisions for unfired pressure vessels. It defines crucial terms, quantities, symbols, and units used throughout the EN 13445 series and offers essential guidance on the design, manufacturing, and safe operation of pressure vessels falling within its scope. This standard is harmonized under the European Pressure Equipment Directive (PED 2014/68/EU), enabling pressure vessels designed to its requirements to be presumed compliant with essential safety requirements under EU law.

EN 13445-1:2026 is relevant for manufacturers, designers, and engineers dealing with the construction and regulation of unfired pressure vessels operating at maximum allowable pressures greater than 0.5 bar gauge. The standard is also a key reference for safety assessment, risk management, and material selection in pressure equipment projects across Europe.

Key Topics

1. Terms and Definitions

• Provides comprehensive definitions for terms used in the EN 13445 standard series, ensuring consistency and clarity across all technical documentation.

2. Quantities, Symbols, and Units

• Specifies standardized symbols and units for mechanical and physical quantities such as pressure, temperature, thickness, and stress, supporting accuracy in design and compliance.

3. Scope and Exclusions

• Applies to unfired pressure vessels with pressures above 0.5 bar gauge
• May be used for lower-pressure and vacuum vessels
• Excludes:
  • Riveted vessels
  • Vessels made from lamellar cast iron or materials not covered in Parts 2, 6, or 8
  • Multilayered, autofrettaged, or pre-stressed vessels

4. Instructions for Use

• Annex A provides step-by-step instructions on how to navigate and apply the EN 13445 series for pressure vessel projects, aiding users in implementation and compliance.

5. Risk Assessment

• Details on hazard identification, risk assessment, and appropriate mitigation measures in vessel design, manufacture, and installation.

6. General Information

• Overview of the interaction between the different parts of the EN 13445 standard, emphasizing the need for holistic application of all relevant parts for full compliance.

Applications

EN 13445-1:2026 is essential in a variety of industrial contexts where pressure vessel safety, durability, and regulatory compliance are critical. Typical applications include:

• Industrial manufacturing: Ensures the safe and efficient design of storage tanks, reactors, and process equipment used in chemical, petrochemical, oil & gas, and food processing industries.
• Power generation: Used in specifying pressure vessels in conventional and renewable power plants.
• Pharmaceutical and biotechnology: Supports compliance for vessels in sterile and high-purity applications.
• Research and development: Facilitates standardization in test vessels and laboratory pressure systems.
• Cross-border trade: Promotes harmonization and acceptance of pressure equipment throughout the European Economic Area under PED 2014/68/EU.

Special provisions apply when pressure vessels are:

• Intended for transport
• Designed for nuclear service
• Subject to overheating risks

Related Standards

• EN 13445-2:2026 – Materials
• EN 13445-3:2026 – Design
• EN 13445-4:2026 – Fabrication
• EN 13445-5:2026 – Inspection and Testing
• EN 13445-6:2026 – Spheroidal Graphite Cast Iron Vessels
• EN 13445-8:2026 – Aluminium & Aluminium Alloys
• EN 13445-10:2026 – Nickel & Nickel Alloys
• EN 13445-11:2026 – Titanium & Titanium Alloys
• EN 13480 Series – Industrial piping systems
• EN 12952 and EN 12953 Series – Water tube and shell boilers
• EN 764-1 & EN 764-2 – Fundamental vocabulary and quantities

EN 13445-1:2026 is the critical entry point for the EN 13445 series, providing a universal foundation for the safe, reliable, and compliant use of unfired pressure vessels in Europe and worldwide.

SLOVENSKI STANDARD
01-september-2026
Nadomešča:
SIST EN 13445-1:2021
Nekurjene tlačne posode - 1. del: Splošno
Unfired pressure vessels - Part 1: General
Unbefeuerte Druckbehälter - Teil 1: Allgemeines
Récipients sous pression non soumis à la flamme - Partie 1: Généralités
Ta slovenski standard je istoveten z: EN 13445-1:2026
ICS:
23.020.32 Tlačne posode Pressure vessels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 13445-1
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2026
EUROPÄISCHE NORM
ICS 23.020.30 Supersedes EN 13445-1:2021
English Version
Unfired pressure vessels - Part 1: General
Récipients sous pression non soumis à la flamme - Unbefeuerte Druckbehälter - Teil 1: Allgemeines
Partie 1: Généralités
This European Standard was approved by CEN on 24 June 2026.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a 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 European Standard 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
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 13445-1:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Introduction . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Interdependency of the parts of the series . 9
5 Quantities, symbols and units . 9
6 Risk assessment and handling . 12
(informative) Using the standard . 14
(informative) Index . 30
(informative) List of Essential Safety Requirements . 51
(informative) History of EN 13445-1 . 60
Annex ZA (informative) Relationship between this European Standard and the essential
requirements of Directive 2014/68/EU aimed to be covered . 61
Bibliography . 62
European foreword
This document (EN 13445-1:2026) 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 December 2026, and conflicting national standards shall
be withdrawn at the latest by December 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 supersedes EN 13445-1:2021.
Annex Y provides details of significant technical changes between this European Standard and the
previous edition.
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.
A list of all parts in the EN 13445 series can be found on the CEN website.
Although these Parts may be obtained separately, it should be recognized that the Parts are
interdependent. As such, the manufacture of unfired pressure vessels requires the application of all the
relevant Parts in order for the requirements of the Standard to be satisfactorily fulfilled.
Corrections to the standard interpretations where several options seem possible are conducted through
the Migration Help Desk (MHD). Information related to the Help Desk can be found at
https://unm.fr/en/maintenance-agencies/maintenance-agency-en-13445/. A form for submitting
questions can be downloaded from the link to the MHD website. After subject experts have agreed an
answer, the answer will be communicated to the questioner. Corrected pages will be given specific issue
number and issued by CEN according to CEN Rules. Interpretation sheets will be posted on the website
of the MHD.
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, 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, Türkiye and
the United Kingdom.
Introduction
EN 13445 specifies the requirements for design, construction, inspection and testing of unfired pressure
vessels. It defines terms, definitions and symbols applicable to unfired pressure vessels.
NOTE In EN 13445 the term pressure vessel includes the welded attachments up to and including the nozzle
flanges, screwed or welded connections, or the edge to be welded at the first circumferential weld at connecting
piping or other elements. The term unfired excludes vessels that are subject to direct generated heat or flame
impingement from a fired process. This does not exclude vessels subject to electrical heating or heated process
streams.
In Parts 2 to 5 only pressure vessels manufactured from steels and steel castings as detailed in Part 2 of
this standard are covered. Parts 6, 8, 10, and 11 specifically deal with vessels of spheroidal graphite cast
iron, aluminium, nickel, and titanium, respectively, where special considerations apply.
Part 1
EN 13445-1 contains general information on the scope of the standard as well as terms, definitions,
quantities, symbols and units which are applied throughout the standard.
Part 2
EN 13445-2 deals with the general philosophy on materials, material grouping and low temperature
behaviour. It is limited to steel with sufficient ductility and, for components operating in the creep range,
sufficient creep ductility.
Part 2 also provides the general requirements for establishing technical delivery conditions and the
requirements for marking of material.
Part 3
EN 13445-3 gives the rules to be used for design and calculation under internal and/or external pressure
(as applicable), local loads and actions other than pressure. The rules provided are both design by
formula (DBF), design by analysis (DBA) and design by experiment (DBE).
The part also sets the requirements for when fatigue analysis is performed and the rules to be followed
when this is the case.
NOTE Collaborative work is in hand to harmonize flange design across European Standards.
Part 4
EN 13445-4 specifies requirements for the manufacture of unfired pressure vessels and their connections
to non-pressure parts. It specifies requirements for material traceability, manufacturing tolerances,
welding requirements, requirements for permanent joints other than welding, production tests, forming
requirements, heat treatment, repairs and finishing operations.
Part 5
EN 13445-5 covers all those inspection and testing activities associated with the verification of the
pressure vessel for compliance with the standard, including design review by the manufacturer and
supporting technical documentation, NDT and other inspection activities including document control,
material traceability, joint preparation and welding.
The level of testing is driven by the selection of the vessel testing group. Basically, the testing group
determines the level of NDT and the joint coefficient used in the design.
In terms of NDT, the overall philosophy has been the general adoption of EN ISO 5817:2014 quality level
'C' for predominantly non-cyclic loaded vessels and level 'B' for vessels subject to cyclic loadings.
Part 6
EN 13445-6 contains special rules for material, design, fabrication, inspection, and testing of pressure
vessels made from spheroidal graphite cast iron. In general the rules in the relevant parts of parts 2–5
apply with additions and exceptions outlined in this part.
Part 7
CEN Technical Report CR 13445-7:2002 has been withdrawn.
Part 8
EN 13445-8 contains special rules for material, design, fabrication, inspection, and testing of pressure
vessels made from aluminium and aluminium alloys. In general the rules in the relevant parts of parts 2–
5 apply with additions and exceptions outlined in this part.
Part 9
CEN/TR 13445-9 details the conformance of the whole EN 13445 series to ISO 16528-1 "Boilers and
pressure vessels — Part 1: Performance requirements". This is a CEN Technical Report. The first edition
and second editions are limited to vessels of steel construction, but will be amended later to include
spheroidal graphite cast iron, aluminium, nickel and titanium.
Part 10
EN 13445-10 contains special rules for material, design, fabrication, inspection, and testing of pressure
vessels made from nickel and nickel alloys. In general, the rules in the relevant parts of parts 2–5 apply
with additions and exceptions outlined in this part.
Part 11
EN 13445-11 contains special rules for material, design, fabrication, inspection, and testing of pressure
vessels made from titanium and titanium alloys. In general, the rules in the relevant parts of parts 2–5
apply with additions and exceptions outlined in this part.
1 Scope
This document defines the terms, definitions, quantities, symbols and units that are used throughout the
EN 13445 series and gives general information on the design and manufacturing of vessels under this
standard.
It also contains instructions on how to use the standard (Annex A) as well as an index which covers the
whole standard (Annex B). This information is aimed to aid users of the EN 13445 series.
This document applies to unfired pressure vessels with a maximum allowable pressure greater than
0,5 bar gauge but may be used for vessels operating at lower pressures, including vacuum.
This document is not applicable to pressure vessels of the following types:
— vessels of riveted construction;
— vessels of lamellar cast iron or any other materials not included in Parts 2, 6, or 8 of the standard;
— multilayered, autofrettaged or pre-stressed vessels.
This document can be applied to the following pressure vessels, provided that account is taken of
additional and/or alternative requirements resulting from the hazard analysis and from rules or
instructions specific for:
— transportable vessels;
— items specifically designed for nuclear use;
— pressure vessels with a risk of overheating.
NOTE EN 14222 covers electrically fired boilers made from stainless steel and can be used as an example of
additional requirements for such vessels.
Other European Standards apply to industrial piping (EN 13480 series) and to water tube and shell
boilers (EN 12952 series and EN 12953 series).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 764-1:2015+A1:2016, Pressure equipment — Part 1: Vocabulary
EN 764-2:2012, Pressure equipment — Part 2: Quantities, symbols and units
EN 13445-2:2026, Unfired pressure vessels — Part 2: Materials
EN 13445-3:2026, Unfired pressure vessels — Part 3: Design
EN 13445-4:2026, Unfired pressure vessels — Part 4: Fabrication
EN 13445-5:2026, Unfired pressure vessels — Part 5: Inspection and testing
EN 13445-6:2026, Unfired pressure vessels — Part 6: Requirements for the design and fabrication of
pressure vessels and pressure parts constructed from spheroidal graphite cast iron
EN 13445-8:2026, Unfired pressure vessels — Part 8: Additional requirements for pressure vessels of
aluminium and aluminium alloys
EN 13445-10:2026, Unfired pressure vessels — Part 10 Additional requirements for pressure vessels of
nickel and nickel alloys
EN 13445-11:2026, Unfired pressure vessels — Part 11 Additional requirements for pressure vessels of
titanium and titanium alloys
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 764-1:2015+A1:2016,
EN 764-2:2012 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
NOTE To aid the user, some of the most important terms and definitions from EN 764-1 have been repeated
here.
3.1
assembly
several pieces of pressure equipment assembled by a manufacturer to constitute an integrated and
functional whole
3.2
fluid
gas, liquid and vapour in their pure phase as well as mixtures thereof
Note 1 to entry: A fluid may contain a suspension of solids.
3.3
hazard
potential source of harm
3.4
hazard category
category of the pressure vessel taking into account the potential hazards
3.5
joint coefficient
reduction coefficient, which is applied to the nominal design stress
Note 1 to entry: E.g. used for a welded joint and related to the testing group.
3.6
main pressure bearing parts
parts which constitute the envelope under pressure, essential for the integrity of the equipment
3.7
manufacturer
individual or organization responsible for the design, fabrication, testing, installation where relevant, and
compliance with the requirements of the relevant product standard, whether executed by him or a
subcontractor
Note 1 to entry: The manufacturer may subcontract one or more of the above mentioned tasks under its
responsibility.
3.8
material manufacturer
individual or organization that produces material in the basic product form used in the manufacture of
pressure components
3.9
maximum allowable pressure
PS
maximum pressure for which the pressure vessel is designed as specified by the manufacturer
3.10
maximum allowable temperature
TS
max
maximum temperature for which the pressure vessel is designed as specified by the manufacturer
3.11
minimum allowable temperature
TS
min
minimum temperature for which the pressure vessel is designed as specified by the manufacturer
3.12
pipelines
piping or system of piping designed for the conveyance of any fluid or substance to or from an installation
(onshore or offshore) starting from and including the first isolation device located within the installation
and including all the annexed equipment designed specifically for pipelines
3.13
piping
tubing, fittings, expansion joints, hoses or other pressure-bearing components, intended for the transport
of fluid, connected together and integrated into a pressure system
3.14
pressure vessel
housing and its direct attachments up to the coupling point connecting it to other equipment, designed
and built to contain fluids under pressure
Note 1 to entry: A vessel may be composed of more than one chamber.
3.15
required thickness
thickness excluding corrosion or any other allowances specified in the EN 13445 series
Note 1 to entry: The minimum thickness that the component can have in service to fulfil the standard.
3.16
risk
combination of the probability of occurrence of harm and the severity of that harm
3.17
significant hazard
hazard which has been identified as associated with the pressure vessel and which requires specific
action by the designer to eliminate or to reduce the risk according to the risk assessment
3.18
testing factor
reduction factor taking into account the amount of NDT testing in castings, applied on the nominal design
stress to take account of possible manufacturing deficiencies
3.19
testing group
grouping which determines the appropriate level of non-destructive testing (NDT) on a welded joint
Note 1 to entry: The testing group of a vessel is not linked to the hazard category.
3.20
weldment
weld metal, heat affected zone and adjacent base material(s)
4 Interdependency of the parts of the series
Parts 2 to 6 and parts 8, 10 and 11 of EN 13445, together with Part 1, form a consistent set of
specifications which shall be followed for compliance to the standard.
NOTE Part 9 of this series is published as a CEN Technical Report. It is not a European Standard.
5 Quantities, symbols and units
Quantities, symbols and units to be used for pressure equipment shall be in accordance with Tables 5-1
and 5-2 and EN 764-2:2012.
NOTE 1 Other symbols used in specific parts of this document are tabulated in the relevant part.
NOTE 2 The choice of the appropriate multiple (decimal multiple or sub-multiple) of a unit is governed by
convenience, the multiple chosen for a particular application being one which leads to numerical values within a
practical range. Therefore, when indicating quantities, it is recommended that decimal multiple or sub-multiple
quantities are chosen such that the resulting values are easy to handle, e.g. between 0,1 and 1 000. The non-SI units,
bar for pressure and L for volume are used on the nameplate.
Table 5-1 — Quantities for space and time
Quantity Symbol Unit
Time t s, min, h
Frequency f Hz
a
any Latin letter
Dimension mm
Length l mm
Thickness e mm
Corrosion allowance c mm
Diameter d, D mm
Radius r, R mm
Area A, S mm
b c
Volume, capacity V mm
Weight W N, kN
d
Density ρ kg/mm
Second moment of area Ι mm
Section modulus Z mm
Acceleration γ m/s
a
any Greek letter
Plane angle rad, °
a
Symbols may use any lower-case letter, except for those defined elsewhere in this table.
b
volume may also be given in m or L.
c
litre "L" is a non-SI unit which may be used with SI units and their multiples.
d
Density may also be given in kg/m .

Table 5-2 — Mechanical quantities
a
b
Quantity Symbol Unit
Force F N
Moment M .
N mm
c
Pressure p, P bar , MPa
Temperature T °C
Linear expansion coefficient α µm/m°C
Normal stress σ MPa
Shear stress MPa
τ
Nominal design stress f MPa
Tensile strength R MPa
m
Yield strength R MPa
e
1 % proof strength R MPa
p1.0
Proof strength at temperature T R MPa
p/T
Upper yield strength ReH MPa
0,2 % proof strength R MPa
p0,2
0,2 % proof strength at temperature T R MPa
p0,2/T
Ultimate tensile strength at temperature T R MPa
m/T
Modulus of elasticity E MPa
Shear modulus G MPa
Poisson's ratio -
υ
Strain ε %
Elongation after rupture/fracture A %
Impact energy KV J
Hardness HB, HV -
Joint coefficient z -
Safety factor S -
a
Quantities without a temperature index normally refer to room temperature.
b
Some of these symbols, such as R, f, are not part of ISO 31.
c
"bar" is a non-SI unit which may be used with SI units and their multiples. The unit bar shall be used on nameplates,
certificates, drawings, pressure gauges and instrumentation and is always used as a gauge pressure. This is in line with
the requirements of the Pressure Equipment Directive 2014/68/EU.
NOTE The use of symbols for temperature may be different from the PED.
6 Risk assessment and handling
6.1 Hazards
Pressure vessels according to this document shall be designed, constructed, installed and equipped under
consideration of all significant hazards and risks that can arise when the vessel is erected, tested and
operated in accordance with the manufacturer’s instructions or else are reasonably foreseeable.
Such hazards shall be analysed by the manufacturer prior to designing the vessel. Apart from normal
hazards connected to the operation of the vessel (see EN 13445-3:2026, 5.3), the following hazards shall
be considered (as applicable):
— corrosion and chemical attack;
— wear;
— external fire;
— reasonably foreseeable misuse of the vessel.
6.2 Hazard removal and risk reduction
6.2.1 General
As far as practically feasible, the vessel shall be designed as to remove or reduce the respective risk. If
removal of a certain hazard is not feasible, the vessel shall be designed and equipped to protect against
the respective risk or (as a final measure) information be given on the hazard and what measures are to
be taken to reduce the risks from the hazard. Such information shall be given through warning signs and
in the operating instructions.
NOTE The procedure to follow is outlined in Figure 6.2–1.
6.2.2 Design considerations
If it is envisaged that safety accessories will have to be fitted to the vessel, the vessel shall be equipped
with the necessary connections for such accessories.
NOTE The selection, application and installation of safety related accessories intended to protect pressure
vessels during operation are covered in EN 764-7:2002.
Figure 6.2-1 — Hazard consideration
(informative)
Using the standard
A.1 Purpose
This annex is designed to facilitate the introduction to the use of the standard.
This annex only gives a general overview of the requirements of the standard. Reference shall always be
made to the standard text itself, and not all requirements are necessarily mentioned in this annex.
A.2 General
The standard is harmonized under the Pressure Equipment Directive (2014/68/EU). This means that if
an unfired pressure vessel meets the requirements of the standard, this pressure vessel can be presumed
to conform to those essential safety requirements in Annex I of the Directive which are listed in the
Annexes ZA of the individual parts of the standard.
NOTE 1 A compilation of all Annexes ZA can be found as Annex X of this Part 1.
In this connection, it should be understood that the standard is indivisible. The design and manufacture
of unfired pressure vessels requires the application of all relevant Parts of the standard for the
requirements of the standard to be fulfilled.
NOTE 2 Part 9 is not a mandatory part of the standard in this sense.
This standard applies to unfired pressure vessels with the limitations and exclusions stated in Clause 1
of this Part 1.
A.3 Prerequisites
Prior to designing and manufacturing a pressure vessel under the standard, the manufacturer shall
establish a number of prerequisites:
— The conditions under which the vessel will be operating.
— Load cases to be considered are enumerated in EN 13445-3:2026, 5.3.1 to 5.3.2 and also in clause 6
of this Part 1.
— The category of the vessel (I to IV) as defined in the Directive.
NOTE 1 The category determines the type of inspection document required for the materials of the main
pressure-bearing parts, as stated in Annex I, section 4.3 of the Directive (Inspection Documents are defined in
EN 10204:2004). The category can also influence performance of welding, NDT qualification and particular material
appraisals (see A.4.2).
— The assessment module (as defined in the directive) to be used.
The choice of module can affect the participation of a notified body and/or a recognized third party
organization or user inspectorate in the inspection and testing of the vessel (It should be noted that
the use of user inspectorates is not necessarily permitted in all member states).
— The testing group of the vessel according to EN 13445-5:2026, 6.6.1.2. The available testing groups
depend upon the material group, thickness, and welding method. Testing Group 4 is further limited
with regards to pressure, temperature, content, number of cycles, and dimensions.
Although the same testing group normally applies to the whole vessel, it is (with the exception of
Group 4) permissible to have different testing groups apply to different parts (e.g., welds).
NOTE 2 The testing group affects not only the testing requirements but also design and manufacturing aspects,
e.g. joint coefficient, permitted weld details and required weld production tests.
A.4 Materials
A.4.1 General
Specific requirements for steels are given in Part 2.
Specific rules for spheroidal graphite cast iron, aluminium, nickel/nickel alloys, and titanium/titanium
alloys are given in EN 13445-6:2026 (see A.8 in this annex), EN 13445-8:2026 (see A.9 in this annex),
EN 13445-10:2026 (see A.10 in this annex), and EN 13445-11:2026 (see A.11 in this annex) respectively.
In some instances, references are made from these parts to EN 13445-2:2026.
A.4.2 Permitted materials
Only materials which are qualified for pressure equipment may be used. Qualification of materials can be
made in three different ways
— Materials from European harmonized standards, see EN 13445-2:2026, 4.3.1.
Certain materials supplied in accordance with European material Standards are accepted as qualified
for use in pressure-bearing parts. These materials are enumerated in EN 13445-2:2026, Table E.2-1.
— Materials with a European Approval for Materials (EAM), see EN 13445-2:2026, 4.3.2.
Materials with an EAM, which states that they can be used for products under the PED, are qualified
for use in relevant products according to this standard.
EAMs are published in the Official Journal, and the European Commission maintains a list of EAMs on
its web site.
— Materials with a Particular Material Appraisal (PMA), see EN 13445-2:2026, 4.3.3.
Materials, which have been subject to a PMA are qualified. This appraisal is carried out by the
manufacturer (and in certain cases checked by a Notified Body).
NOTE The European Commission and Member States have in November 2006 agreed on ”Guiding Principles
for the contents of Particular Materials Appraisals". This document is published on:
https://ec.europa.eu/docsroom/documents/10642?locale=en
Whichever method of qualification is used, the qualification does not necessarily cover the suitability of
the material with regards to the environment and content of the vessel, i.e. corrosion, erosion, etc. The
manufacturer will always have to evaluate the material's resistance to such action.
Whichever way the material has been qualified, all other rules in Part 2 will have to be fulfilled.
A.4.3 Prevention of brittle fracture
Rules for prevention against brittle fracture are given in EN 13445-2:2026, Annex B.
Three different routes are allowed:
— Code of practice (EN 13445-2:2026, B.2.2).
— More flexible approach based on fracture mechanics and operating experience (EN 13445-2:2026,
B.2.3).
— Application of fracture mechanics analysis (EN 13445-2:2026, B.2.4).
The first two methods are limited to certain materials and thicknesses.
The third method requires detailed work in fracture mechanics, and the standard only contains guidance

on it. It may only be used after agreement between the concerned parties.
A.4.4 Material grouping
Materials are grouped in EN 13445-2:2026, Table A-1 with respect to major chemical elements, specified
minimum tensile test data. This grouping is used throughout the standard to decide design,
manufacturing, and inspection aspects.
A.5 Design
A.5.1 General
Most of the requirements for design are to be found in EN 13445-3.
NOTE Specific design rules for vessels manufactured from spheroidal graphite cast iron, aluminium,
nickel/nickel alloys, and titanium/titanium alloys are given in EN 13445-6:2026 (see A.8 in this annex),
EN 13445-8:2026 (see A.9 in this annex), EN 13445-10:2026 (see A.10 in this annex), and EN 13445-11:2026 (see
A.11 in this annex), respectively.
A.5.2 Design for static loads
There are four different methods for design, which may be used either separately or in combination with
each other
— Design by formula (DBF)
These rules are contained in EN 13445-3:2026, Clauses 7 to 16, 20 to 22 and Annexes F, G and J.
For simple geometries such as cylinders and spheres, formulae can be given where pressure and
geometrical dimensions give the required minimum thicknesses directly.
For more complicated geometries, a trial-and-error approach shall be used in most cases. The
designer will have to assume the analysis thickness(e ), and use the formulae to compute the stresses
a
and/or the load ratios as applicable. These stresses and/or load ratios are then compared with
allowable values. EN 13445-3:2026, Figure 5-1 shows the relations between different thickness
definitions.
In the design formulae of components having a governing weld, the weakening effect of that weld is
accounted for by means of a joint coefficient z. The maximum allowed value of this coefficient
depends upon the testing group of the weld as specified in EN 13445-3:2026, Table 5.6-1 and
EN 13445-5:2026, Table 6.6.1-1.
NOTE Governing welds are defined in EN 13445-3:2026, 5.6.
For two types of components, flange connections and heat exchanger tubesheets, multiple sets of
rules are given (in EN 13445-3:2026, Clause 11, Annex G, and in EN 13445-3:2026, Clause 13 and
Annex J, respectively). The alternative rules of EN 13445-3:2026, Annexes G and J are based on more
advanced methods than their corresponding main clause, and are expected to lead to more
appropriate and less conservative designs. Either set can be used at the designer's option within the
limitations given for each set.
— Annex G is recommended for the design of flange connections where the flanges are subject to
strong leak-tightness requirements, significant thermal cycling, and/or significant additional
loads (forces or moments). It implies that the bolt stress is controlled by the use of a defined
tightening procedure.
— Annex J is recommended for the design of heat exchanger tubesheets subject to relatively low
cyclic loading.
— Design by analysis using direct assessment of failure modes (DBA - Direct Route)
These rules are contained in EN 13445-3:2026, Annex B.
For each failure mode a specific assessment method is provided (e.g. limit analysis for assessment of
gross plastic deformation, shakedown analysis for progressive deformation).
— Design by analysis using stress categorization (DBA – Method based on stress categories)
These rules are contained in EN 13445-3:2026, Annex C.
Stresses shall be computed (in most cases using finite element methods) and divided into different
categories. The stresses in each category are then compared to allowable values for the respective
category.
— Design by experiment (DBE)
These rules are contained in EN 13445-3:2026, Annex T.
Design by experiment always includes a burst test and may be supplemented by control of
deformation and a fatigue test. It can either be used separately (with limitations given in
EN 13445-3:2026, T.4.1) or as a verification of DBF or DBA calculations.
DBF is the most common and simple way to design vessels. All DBF rules cover pressure. Some kinds of
non-pressure loads can be taken into account through use of EN 13445-3:2026, Clauses 16 and 22.
DBA is used to assess structural shapes and load configurations not covered by DBF. It may also be used
as an alternative to DBF. Between the two possible DBA routes, that in EN 13445-3:2026, Annex B is
expected to be less conservative or more realistic than that in EN 13445-3:2026, Annex C, as being based
on more advanced methods.
A.5.3 Design in the creep range
— Design by formula (DBF)
The rules contained in EN 13445-3:2026, Clause 19 allow the design of vessels or vessel parts for
loading of predominantly non-cyclic nature (less than 500 equivalent full pressure cycles or the
number of equivalent full pressures cycles, given by the alternative rule stated in
EN 13445-3:2026, 17.5.4). (The DBA rules in EN 13445-3:2026, Annex B may be used when
interaction between creep and fatigue occurs.)
Different sets of rules are used depending on whether the vessel is subjected to a single creep load
case (use EN 13445-3:2026, 19.8.1) or multiple creep load cases (use EN 13445-3:2026, 19.8.2).
In both cases, the joint factor is modified by the weld creep strength reduction factor according to
EN 13445-3:2026, 19.6.
NOTE A procedure for the determination of the weld creep strength reduction factor by tests is given in
EN 13445-2:2026, Annex C.
— Design by Analysis – Direct Route
Design by Analysis in the creep range is covered in EN 13445-3:2026, Annex B. The design checks to
be considered (in addition to those for operation below the creep range listed in
EN 13445-3:2026, B.5.1.2) are listed in EN 13445-3:2026, B.5.1.3.
A.5.4 Design for cyclic loads (fatigue)
Each vessel which is subjected to more than a certain number (given in EN 13445-3:2026,
Formula (5.4-1) or by the alternative rule of EN 13445-3:2026, 17.5.4) of equivalent full pressure cycles
shall be checked against fatigue. The standard provides two methods, and either method can be used at
the designer's option.
— A simplified fatigue analysis (EN 13445-3: 026, Clause 17)
This simplified method uses coefficients for different geometries and different weld details to
compute the maximum number of fatigue cycles allowed. It is essentially applicable to vessels
predominantly subject to pressure fluctuations, with however some provisions to account (to a
certain extent) for other load fluctuations.
It will normally give more conservative results than a detailed fatigue analysis.
— A detailed fatigue analysis (EN 13445-3:2026, Clause 18)
This method presumes a detailed stress analysis at all critical points (in practice mostly using finite
element methods).
In both analyses, the intensity of the fatigue loading is measured, at any vessel point, by a "damage factor"
from which the "critical areas" of the vessel can be found. In these areas, more NDT is required, as defined
in EN 13445-5:2026, Annex G.
A.5.5 Nominal design stresses
The nominal design stress f to be introduced into the formulae giving the minimum required thickness
or to be used to calculate the allowable stresses shall be computed as detailed in
EN 13445-3:2026, Clause 6 (except for operation in the creep range where EN 13445-3:2026, 19.5 is to
be used, which gives different values depending on whether lifetime monitoring is used or not).
NOTE 1 The concept of nominal design stress is not used within EN 13445-3:2026, Annex B. In this annex,
allowable loads are directly derived from the material characteristics.
NOTE 2 For non-austenitic steels there are two alternative sets of design stresses, the normal one in
EN 13445-3:2026, 6.2 and the Alternative Route in EN 13445-3:2026, 6.3, which permits higher stresses under
certain conditions.
A.5.6 Weld details
Butt welds are preferred for all welded joints, but joggle joints, joints with permanent backing strips, and
lap joints are permitted for certain circumferential joints, provided that the restrictions given in
EN 13445-3:2026, 5.7.4 are observed.
Allowable weld designs with material and geometry limitations are listed in EN 13445-3:2026, Annex A.
A.5.7 Access openings
The standard specifies a minimum number and size of access openings which are detailed in
EN 13445-5:2026, C.2 to C.4.
Rules for closing mechanisms and locking devices are given in EN 13445-5:2026, C.5.
A.6 Manufacturing
A.6.1 General
Most of the requirements for manufacturing are to be found in EN 13445-4:2026.
NOTE Specific rules for vessels manufactured from spheroidal graphite cast iron, aluminium, nickel/nickel
alloys, and titanium/titanium alloys are given in EN 13445-6:2026 (see A.8 in this annex), EN 13445-8:2026 (see
A.9 in this annex), EN 13445-10:2026 (see A.10 in this annex), and EN 13445-11:2026, respectively.
A.6.2 Tolerances
The standard specifies manufacturing tolerances both for vessel parts themselves and for welds:
— Permitted shape tolerances for vessels under internal pressure are specified in EN 13445-4:2026,
6.4.
Shape tolerances for vessels under external pressure shall not exceed those given for internal
pressure, but they shall also fulfil the requirements of EN 13445-3:2026, 8.5.1 (cylindrical and
conical shells) and EN 13445-3:2026, 8.7.2 (spherical shells). Larger shape deviations may be
accepted, but lead to reduced allowable external pressures. The rules for computing these reduced
pressures are given in EN 13445-3:2026, Annex F.
The rules cited above are absolute requirements of the standard. For other measurements,
recommended maximum tolerances are given in EN 13445-4:2026, Annex A.
EN 13445-3:2026, Annexes D and E give directions for measuring shape deviations in vessels under
external pressure.
— There are two sets of requirements on alignment at welds, for middle-line alignment
(EN 13445-4:2026, 6.2) and for surface alignment (EN 13445-4:2026, 6.3). Both sets shall be
observed simultaneously.
A.6.3 Forming
The standard covers both cold forming and hot forming, and EN 13445-4:2026, 10.3 specifies the
temperatures (depending upon material) at which forming shall be performed.
Formed parts may have to be heat-treated after forming. For cold-formed parts this requirement depends
both on the material group and on the amount of deformation during forming. Formulae to compute this
deformation are given in EN 13445-4:2026, 10.2.
The requirements for heat treatment after hot forming depend on the material group and on the product
form (see EN 13445-4:2026, 10.4).
If heat treatment is performed, the standard (depending on material group and heat treatment condition)
requires tests on test coupons. The samples, the type of coupons and tests are specified in
EN 13445-4:2026, 10.5 and 10.6.
A.6.4 Welding
The welding rules are to be found in EN 13445-4:2026, Clauses 7, 8, and 12 (the last one covers repairs).
The standard specifies three prerequisites for welding:
— the manufacturer shall have a welding procedure specification (WPS), see EN 13445-4:2026, 8.2;
— the welding procedure shall have been qualified (WPQR), see EN 13445-4:2026, 8.3;
— the welder or welding operator shall have been qualified, see EN 13445-4:2026, 8.4.
The requirements generally refer to other European Standards, with the addition of some extra
requirements regarding mechanical testing of welding procedure qualification tests.
A.6.5 Production tests on welds
In many cases, production tests are required on longitudinal and circumferential governing (see
EN 13445-3:2026, 5.6) welds as specified in EN 13445-4:2026, Clause 9. The amount of required
production tests is specified in EN 13445-4:2026, 9.2 (for some special welds in EN 13445-3:2026, 5.7.4)
and depends upon material group, testing group, welding method and material thickness and vary widely
from no tests at all to one test per 100 m of weld or one test per vessel. When a specified number of tests
have passed successfully, the standard allows a reduction in the frequency of the production tests.
The actual testing and the acceptance criteria are given in EN 13445-4:2026, 9.3 and 9.4.
A.6.6 PWHT (Post Weld Heat Treatment)
In some cases, the welding procedure will require that a PWHT be carried out after welding as defined in
EN 13445-4:2026, Clause 11. Holding times and holding temperatures are specified in
EN 13445-4:2026, Table 11.1-1 and depend upon material group and nominal thickness. For some
material groups, PWHT is waived for low thicknesses, but can still be desirable, e.g., when there is risk of
stress corrosion. For materials submitted to PWHT, which are not listed in this table, this treatment shall
be performed according to a procedure established in agreement with the material manufacturer, or in
conformity with other recognized codes.
If the PWHT temperature is too close to the maximum tempering temperature or the holding time
exceeds a certain number, the effect of the PWHT on the mechanical properties shall be demonstrated
either on test coupons heat treated with the vessel or test coupons subjected to a simulated PWHT.
Heat treatment is to be documented according to EN 13445-5:2026, 6.8.
A.6.7 Other types of joints
Procedures and operators for mechanical roller expansion shall have been qualified, see
EN 13445-4:2026, Annex C.
References for th
...