EN 13445
The European Standard for Unfired Pressure Vessels
EN 13445 is the harmonized European standard that provides comprehensive rules for the design, fabrication, and inspection of unfired pressure vessels operating above 0.5 bar. Recognized across the European Economic Area, it is the primary path to demonstrating compliance with the Pressure Equipment Directive (PED) 2014/68/EU.
Calculate with NextGenWhat is EN 13445?
EN 13445 is a series of European standards published by CEN (European Committee for Standardization) that defines the requirements for unfired pressure vessels made of steels, nickel alloys, and other metallic materials.
First published in 2002 as a replacement for various national standards across Europe, EN 13445 unified pressure vessel design practices under a single, harmonized framework. It applies to vessels that are not directly exposed to flames or combustion gases, covering a wide range of industrial equipment including heat exchangers, reactors, columns, storage tanks, and air receivers.
The standard is structured into eleven parts. Parts 1 to 5 form the core, covering general requirements, materials, design, fabrication, and inspection. Parts 6, 8, 10 and 11 extend the standard to additional materials (cast iron, aluminium, nickel, titanium), while Parts 7 and 9 are CEN Technical Reports on PED conformity assessment and ISO 16528 compliance.
Key Facts
- Published by: CEN (TC 54)
- First edition: 2002
- Scope: Unfired pressure vessels > 0.5 bar
- Harmonized with: PED 2014/68/EU
- Materials: Steels, nickel alloys, aluminium, titanium, cast iron
- Replaces: National codes (BS 5500, CODAP, AD Merkblatt, VSR, etc.)
The Eleven Parts of EN 13445
Part 1 General
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 Materials
Deals with the general philosophy on materials, material grouping and low temperature behaviour. Limited to steel with sufficient ductility and, for components in the creep range, sufficient creep ductility. Also provides general requirements for technical delivery conditions and material marking.
Part 3 Design
Gives the rules for design and calculation under internal and/or external pressure, local loads and actions other than pressure. Provides Design by Formulae (DBF), Design by Analysis (DBA) and Design by Experiment (DBE). Also sets requirements for fatigue analysis. This is the core calculation section used by pressure vessel engineers daily.
Part 4 Fabrication
Specifies requirements for the manufacture of unfired pressure vessels and their connections to non-pressure parts, including material traceability, manufacturing tolerances, welding requirements, permanent joints other than welding, production tests, forming, heat treatment, repairs and finishing operations.
Part 5 Inspection and Testing
Covers inspection and testing activities for compliance verification, including design review, NDT, document control, material traceability, joint preparation and welding. The testing group determines the NDT level and the joint coefficient used in design. NDT follows EN ISO 5817 quality level 'C' for non-cyclic and 'B' for cyclic loadings.
Part 6 Spheroidal Graphite Cast Iron
Special rules for material, design, fabrication, inspection and testing of pressure vessels made from spheroidal graphite cast iron. The rules in Parts 2–5 apply with additions and exceptions outlined in this part.
Part 7 PED Conformity Assessment CEN/TR
CEN Technical Report providing guidance on how to use the conformity assessment procedures in the Pressure Equipment Directive.
Part 8 Aluminium and Aluminium Alloys
Special rules for material, design, fabrication, inspection and testing of pressure vessels made from aluminium and aluminium alloys. The rules in Parts 2–5 apply with additions and exceptions outlined in this part.
Part 9 ISO 16528 Conformance CEN/TR
CEN Technical Report detailing the conformance of the EN 13445 series to ISO 16528-1 “Boilers and pressure vessels — Part 1: Performance requirements”.
Part 10 Nickel and Nickel Alloys
Special rules for material, design, fabrication, inspection and testing of pressure vessels made from nickel and nickel alloys. The rules in Parts 2–5 apply with additions and exceptions outlined in this part.
Part 11 Titanium and Titanium Alloys New — 2024
The latest addition to the EN 13445 series (September 2024). Special rules for material, design, fabrication, inspection and testing of pressure vessels made from titanium and titanium alloys.
EN 13445-3 Design Clauses
Part 3 is the heart of EN 13445, providing detailed design-by-formula rules for pressure vessel components. The following table lists all major design clauses and annexes, showing which calculations are supported by NextGen software.
| Clause | Description | NextGen |
|---|---|---|
| Clause 5 | Basic design criteria — loading conditions, design pressure, temperature, safety factors | |
| Clause 6 | Maximum allowed stress values — nominal design stress for all material groups | |
| Clause 7 | Shells under internal pressure — cylindrical, spherical, and conical sections | |
| Clause 8 | Shells under external pressure — buckling analysis, stiffener ring design | |
| Clause 9 | Openings in shells — nozzle reinforcement, ligament efficiency, multiple openings | |
| Clause 10 | Flat ends — circular and non-circular flat heads, stayed and unstayed | |
| Clause 11 | Flanges — integral, loose, and reverse flanges with gasket interaction | |
| Clause 12 | Bolted domed ends — pressure-loaded and bolted closure heads | |
| Clause 13 | Heat exchanger tubesheets — fixed, floating head, and U-tube configurations | |
| Clause 14 | Expansion bellows — fatigue life, spring rate, and stability analysis | |
| Clause 15 | Rectangular section vessels — design rules for non-circular cross-sections | |
| Clause 16 | Additional non-pressure loads — wind, seismic, dead loads, and piping forces | |
| Clause 17 | Simplified fatigue assessment — screening criteria and conservative fatigue evaluation | |
| Clause 18 | Detailed fatigue assessment — S-N curves, cycle counting, cumulative damage | |
| Clause 19 | Creep design — high-temperature time-dependent design rules | |
| Clause 20 | Reinforced flat walls design rules | |
| Clause 21 | Circular flat ends with radial reinforcement ribs | |
| Clause 22 | Static analysis of tall vertical vessels on skirts |
Annexes
| Annex | Description | NextGen |
|---|---|---|
| Annex E | Departure from true circle — out-of-roundness assessment method | |
| Annex F | Allowable external pressure for vessels with out-of-circularity deviations | |
| Annex G | Alternative flange design rules — simplified method for standard flanges | |
| Annex J | Alternative heat exchanger tubesheet design — additional calculation methods | |
| Annex S | Creep stress extrapolation — time-dependent strength prediction |
Additional Verifications
Beyond the core EN 13445-3 clauses, NextGen also supports calculations per related standards frequently used alongside EN 13445:
- EN 1591-1 — Flanges and their joints (gasket-based calculation)
- EN 1092-1 — Steel flanges (PN designated)
- EN 1759-1 — Steel flanges (Class designated)
- WRC Bulletins — Local loads on nozzles (WRC 107/537)
- EN 13480 — Metallic industrial piping
- EJMA — Standards of the Expansion Joint Manufacturers Association
- TEMA — Standards of the Tubular Exchanger Manufacturers Association
- ASME PCC-1 — Guidelines for Pressure Boundary Bolted Flange Joint Assembly
- PD 5500 — Specification for unfired pressure vessels (British Standard)
- Nozzle PRO — FEA-based nozzle analysis
PED Compliance and EN 13445
The Pressure Equipment Directive (PED) 2014/68/EU is mandatory legislation across all EU and EEA member states. EN 13445, as a harmonized standard under the PED, provides a presumption of conformity with the directive's essential safety requirements.
When a pressure vessel is designed and manufactured in accordance with EN 13445, the manufacturer benefits from a presumption of conformity with the PED. This means the vessel is assumed to meet the directive's Essential Safety Requirements (ESRs) without additional proof, significantly simplifying the conformity assessment process.
How EN 13445 Supports PED Conformity
- Annex I (ESR 1 – General): Parts 1, 3, and 5 establish design methodology, safety factors, and inspection requirements aligned with PED Annex I general provisions.
- Annex I (ESR 4 – Materials): Part 2 ensures that only materials meeting EN-specified mechanical properties and testing requirements are used.
- Annex I (ESR 3 – Manufacturing): Part 4 addresses welding, forming, and heat treatment requirements corresponding to PED manufacturing ESRs.
- Annex I (ESR 5 – Commissioning): Part 5 defines hydrostatic test pressures and acceptance criteria consistent with PED commissioning requirements.
PED Classification
The PED classifies pressure equipment into four categories (I through IV) based on fluid type, maximum allowable pressure (PS), and volume (V) or nominal size (DN). The higher the category, the more stringent the conformity assessment procedure.
| Category | Assessment Modules |
|---|---|
| I | Module A (internal production control) |
| II | Modules A2, D1, E1 |
| III | Modules B+D, B+F, B+E, B+C2, H |
| IV | Modules B+D, B+F, G, H1 |
EN 13445 is listed in the Official Journal of the European Union as a harmonized standard under PED 2014/68/EU.
EN 13445 vs Other Pressure Vessel Codes
Engineers often need to choose between or compare international pressure vessel codes. The table below highlights the key differences between EN 13445, ASME VIII, and AD 2000 Merkblatt.
| Aspect | EN 13445 | ASME VIII Div. 1 & 2 | AD 2000 Merkblatt |
|---|---|---|---|
| Issuing body | CEN (European) | ASME (USA) | VdTÜV (Germany) |
| Geographic scope | EU / EEA countries | Worldwide (dominant in Americas, Asia) | Germany, Central Europe |
| PED harmonization | Yes — Listed in the Official Journal of the EU | Partial — Accepted with gaps | Yes — Listed in the Official Journal of the EU |
| Design approach | Advanced semi-analytical approach: DBF + DBA, close to modern structural mechanics | Div. 1: traditional DBF / Div. 2: DBF + DBA (elastic, elastoplastic, fatigue) / Div. 3: very high pressure | Strongly prescriptive DBF with high safety coefficients |
| Safety factor (tensile) | 2.4 on Rm | 3.5 on Rm (Div. 1) / 2.4 (Div. 2) | 2.4 on Rm |
| Fatigue analysis | Comprehensive (Clauses 17 & 18) | Div. 2 only (detailed) | AD 2000 S1/S2 (simplified) |
| Creep design | Clause 19 + Annex S | Div. 1 & Div. 2 (Part 5) via ASME IID time-dependent allowables | AD 2000 S6 |
| Material system | EN standards (EN 10028, EN 10222, etc.) with PED traceability (EN 10204 certificates) | ASME SA/SB specifications — extensive database for oil & gas and chemical plants | EN + DIN materials (W.Nr.) with stricter restrictions on some steels |
| Allowable stress conservatism | Generally less conservative — optimized wall thicknesses, lighter components | Div. 1: conservative (thicker walls) / Div. 2: comparable to EN 13445 | Conservative — high safety margins, often heavier components |
| External loads | Clause 16: wind, seismic, dead loads, piping forces — with Eurocode references | Div. 2 (4.1): general provisions; local loads via WRC auxiliary codes | AD S3/S4: wind and additional loads (simplified) |
| Rectangular vessels | Clause 15 | Div. 1 (Part UNC) & Div. 2 (4.12) | AD B5, B5/1 |
| Expansion bellows | Clause 14 | Div. 1 (Part UEB) & Div. 2 (4.19) | AD B13 (single-ply only) |
| Complexity & best use cases | Complex and detailed — ideal for custom designs, advanced verifications, and weight optimization. Requires advanced calculation software. | Div. 1: easy to apply, global reference for international projects. Div. 2: more demanding but powerful for optimized designs. | Simpler to apply — preferred in German regulatory contexts and for standardized equipment. |
| License / access | Purchase from CEN members | BPVC subscription or purchase | Purchase from Beuth Verlag |
Strengths of EN 13445
Advanced semi-analytical approach close to modern structural mechanics. Less conservative allowable stresses enable optimized wall thicknesses and lighter vessels. Dedicated clauses for rectangular vessels, expansion bellows, and reinforced flat walls. Comprehensive fatigue, creep, and external load methodologies with Eurocode integration. Direct PED compliance. Ideal for custom designs and weight optimization — NextGen software makes these advanced calculations fast and accessible.
When to use ASME
The global reference standard for international projects, especially in North America, the Middle East, and Asia. Required by NBIC for vessels registered in US jurisdictions. Div. 1 is widely used and easy to apply; Div. 2 offers advanced elastic and elastoplastic analysis comparable to EN 13445 DBA; Div. 3 covers very high pressure applications.
When to use AD 2000
Strongly prescriptive approach preferred in German regulatory contexts and by manufacturers with DIN traditions. Simpler to apply for standardized equipment, with high safety margins that result in robust but heavier components. Often used as an alternative or complement to EN 13445 in Central Europe.
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