Standards · Standards worlds

EN and ASME compared: eight axes on which the standards worlds differ

Neither world is better. Both build safe piping – but they think differently in eight places: how a standard becomes law, how a material is described, how thick a wall must be, what a flange is called and who certifies in the end. The table sets the axes side by side, the paragraphs explain them.

Worlds: EN 13445 / EN 13480 under the Pressure Equipment Directive · ASME BPVC VIII / B31 as a code
Axes: legal nature · materials · calculation · flanges · pipes · production testing · marking · recognition
Figures: orders of magnitude from secondary sources – no standard tables
Inspection intervals: come from the operating country, not from the code (see FAQ)

The eight axes

EN versus ASME: eight axes with note (as of 09/2026, secondary sources)
Axis	EN world	ASME world	Note
Legal nature	Harmonised standards (EN 13445, EN 13480) under the Pressure Equipment Directive 2014/68/EU: presumption of conformity, CE marking, notified body by category – the standard itself is voluntary.	A code with stamp: the ASME Boiler and Pressure Vessel Code and B31 become law through state or provincial legislation (USA, Canada) – the Authorized Inspector and the code stamp (U, S, PP) certify compliance.	Neither world is "stricter" – one works through directive plus standard, the other through code plus inspector.
Materials	Material number plus product standard (EN 10216-2, EN 10222-2) plus inspection certificate to EN 10204 – harmonised material standards carry the presumption of conformity.	SA materials of Section II with allowable stresses listed in the code itself (Section II Part D) – the mill test report follows the ASTM specification.	An ASTM material in a PED pressure part needs a European approval for materials or a particular material appraisal – see the ASTM profiles.
Design calculation	EN 13445: safety factor about 1.5 on the yield strength at room temperature – vessels often come out lighter.	ASME VIII Division 1: safety factor about 3.5 on the tensile strength – more wall, more material.	The difference is material cost, not inspection cost – the figures are orders of magnitude from secondary sources (standards not purchased).
Flanges	PN designation (PN 6 to 400) to EN 1092-1 with pressure-temperature tables per material group – dimensions in millimetres.	Class designation (150 to 2500) to ASME B16.5/B16.47 with rating tables per material group – bolt holes and bolts in inches.	Class and PN are not convertible, bolt patterns differ – see the pairings and the rule of thumb "Class 150 is not 150 psi".
Pipe	Outside diameter × wall thickness in millimetres (EN 10220, EN ISO 1127) with delivery standards EN 10216/10217.	NPS and schedule (B36.10M, B36.19M) with material specifications A106, A333, A312.	Most outside diameters coincide, four do not – the wall series are different systems – see the rule of thumb "Schedule is not a wall thickness".
Fabrication inspection	Testing group and radiography percentage per weld class (EN 13445-5, EN 13480-5) – the extent of NDT follows the testing group chosen in the design.	Joint efficiency E in the wall thickness formula: full radiography E = 1.0, spot E = 0.85, none E = 0.7 (Section VIII Div. 1) – B31.3 ties the extent to the fluid service category.	Both worlds trade wall thickness against inspection – with different knobs.
Marking and certification	CE marking on the assembly, inspection certificate 3.1 or 3.2 to EN 10204 for the material, manufacturer marks to the product standard.	Code stamp and data report for the equipment, mill test report for the material, part marking to B16.5/B16.9 and MSS SP-25.	A 3.1 certificate and a mill test report certify similar things on different forms – read what is certified, not the title.
Recognition and procurement of standards	EN standards are bought one by one and need the directive behind them – recognition follows the EEA and bilateral agreements.	The ASME code is an expensive package that is recognised worldwide with one document – the strength of the second world in export projects.	Our procurement advice for ASME/ASTM parts is on the profile pages: standard, size, grade, certificate, quantity.

“To ASME” means three things

Whoever orders “to ASME” means one of three things – and should say which. First the dimensions: a flange to ASME B16.5, a fitting to B16.9, a pipe to B36.10M, possibly with a European material and a 3.1 certificate – the most common case in stock. Second dimensions plus material: additionally an ASTM material such as A105 or A234 WPB with mill test report. Third the design of the whole line to ASME B31.3 or B31.1 – then calculation, scope of testing and documentation of the code apply too. The ASME and ASTM profiles show what we supply to each standard.

The axis calculation explains why a vessel to EN 13445 is often lighter than the same to ASME VIII Division 1: the EN calculates with about 1.5 on the yield strength at room temperature, the code with about 3.5 on the tensile strength. That is a difference in material cost – not in safety and not in inspection cost. The figures are orders of magnitude from secondary sources; we have not purchased the standards for this and reproduce no standard tables.

What the comparison means for stock and purchasing

Flanges and pipes. PN is not Class and NPS is not DN – the dimensions differ even if the nominal size sounds the same. What fits together is shown on Mixing standards worlds; the mapping is done by the standards translator. Materials. A material of one world is not a material of the other, even if the analysis is similar; under the Pressure Equipment Directive ASTM materials need an appraisal – see Materials between the worlds.

Certification. The EN world certifies compliance with the order by the inspection certificate 3.1 to EN 10204; the ASME world certifies compliance with the ASTM standard by the mill test report. Both contain analysis and mechanical values, but not the same test programme. Recognition. The ASME stamp is recognised worldwide with one document; the EN needs the directive behind it and applies where the directive applies. Which regions demand which world is shown on Standards worlds by region.

Not legal advice. This page explains how standards become binding. It is not legal advice – have your contract checked.

Frequently asked questions

Is ASME stricter than EN?

Neither. ASME VIII Div. 1 calculates with a higher factor on tensile strength, EN 13445 with a lower one on yield strength and demands more elsewhere (material testing, testing groups). Both routes lead to safe components; the difference is material cost and documentation.

Must a plant with ASME parts be inspected more often?

In Germany the Betriebssicherheitsverordnung (Annex 2 Section 4) sets maximum intervals – the operator fixes the interval in the risk assessment, the inspector may shorten it (TRBS 1201 Part 2). In the USA in-service inspection follows API 510 (vessels) and API 570 (piping) and the jurisdiction – again operating law, not the construction code. This page explains how standards become binding. It is not legal advice – have your contract checked. Rule of thumb: The inspection interval comes from the operating country, not from the code.

Can I use an EN material in an ASME line?

To B31.3 only by the routes the code provides for “unlisted materials” – with evidence of the properties. Conversely an ASTM material under the Pressure Equipment Directive needs a European Approval for Materials or a particular material appraisal.

What is an Authorized Inspector?

An inspector provided by an inspection agency and commissioned by the National Board who supervises manufacture to the ASME code and releases the stamp – the counterpart of the notified body under the Pressure Equipment Directive, but per manufacture, not per manufacturer.

I have a specification to ASME and stock to EN – what now?

The specification decides. Often the first reading of “to ASME” suffices (dimensions to B16.5/B16.9 with EN material and 3.1 certificate); we check this with you against the ASME dimension table and the profiles.

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Tell us standard, edition and destination country – we tell you what fits from stock and what needs a counterpart.

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As of 2 October 2026. Statements taken from forewords and scopes of standards, legal texts (Pressure Equipment Directive, German Betriebssicherheitsverordnung), standards bodies, inspection bodies and technical articles; regional list approved 30 September 2026. No standard text reproduced. Not legal advice.