Standards · ASME and ASTM · ASTM A403/A403M

ASTM A403/A403M: Wrought austenitic stainless steel piping fittings

The material standard of the stainless buttwelding fittings to B16.9 (and forged fittings to B16.11): austenitic grades with the prefix WP, made seamless or welded from pipe, plate or forgings, with mandatory solution annealing.

Issued by: ASTM
Edition (publisher, as of 2 October 2026): 2026a
Material specification: Wrought austenitic stainless steel piping fittings
European counterpart: EN 10253-4 (1.4301, 1.4307, 1.4401, 1.4404, 1.4541, 1.4550)
Belongs with: ASME B16.9 · ASTM A182/A182M · ASME B36.19M · ASTM A234/A234M
At Zickwolff: we carry – from stock or to order, lead time on request

Scope: sizes, classes, grades

Grades WP304, WP304L, WP304H, WP316, WP316L, WP316H, WP321, WP321H, WP347, WP347H, WP310S and others. Classes by manufacture and test: WP-S seamless, WP-W welded with radiography of the fitting weld, WP-WX welded with full radiography, WP-WU with ultrasonic test, CR grades for low-pressure fittings to MSS SP-43. Strength WP316 515/205 MPa, WP316L 485/170 MPa.

Product form

Wrought fittings, seamless or welded, solution annealed.

Grades and their European counterparts

ASTM A403/A403M - Grades and their European counterparts
Grade	Type	Tensile / yield min. (MPa)	European counterpart	Limits of the comparison	At Zickwolff
WP304	austenitic stainless	515 / 205	X5CrNi18-10 1.4301 · EN 10253-4	same alloy type, carbon and molybdenum bands differ – dual certification possible	on request
WP304L	austenitic stainless	485 / 170	X2CrNi18-9 / X2CrNi19-11 1.4307 / 1.4306 · EN 10253-4	same alloy type, carbon and molybdenum bands differ – dual certification possible	deliverable
WP316	austenitic stainless	515 / 205	X5CrNiMo17-12-2 / X3CrNiMo17-13-3 1.4401 / 1.4436 · EN 10253-4	same alloy type, carbon and molybdenum bands differ – dual certification possible	on request
WP316L	austenitic stainless	485 / 170	X2CrNiMo17-12-2 1.4404 · EN 10253-4	same alloy type, carbon and molybdenum bands differ – dual certification possible	deliverable
WP321	austenitic stainless	not stated in our sources	X6CrNiTi18-10 1.4541 · EN 10253-4	same alloy type, carbon and molybdenum bands differ – dual certification possible	on request
WP347	austenitic stainless	not stated in our sources	X6CrNiNb18-10 1.4550 · EN 10253-4	same alloy type, carbon and molybdenum bands differ – dual certification possible	on request

WP304 corresponds to 1.4301, WP304L to 1.4307/1.4306, WP316 to 1.4401/1.4436, WP316L to 1.4404 (also 1.4435), WP321 to 1.4541, WP347 to 1.4550 – fittings to EN 10253-4 – 1.4571 (316Ti) has no common A403 grade.

Use in Europe: the Pressure Equipment Directive

Under the Pressure Equipment Directive an ASTM material has no presumption of conformity: it needs a European material approval or a particular material appraisal (PMA) by the equipment manufacturer, in categories III and IV assessed by the notified body. Comparisons with EN grades are orientation, never a one-to-one equivalence – chemistry bands, test scope and certificate differ. Wall thicknesses follow B36.19M schedules, EN 10253-4 uses EN ISO 1127 walls – the A403 class (S, W, WX) replaces the EN distinction of seamless and welded with test class – read the class on the certificate. Dual certification 304/304L and 316/316L is the norm.

Marking on the part

Via B16.9: manufacturer, WP316L (with class, e.g. WP316L-S), schedule or wall, NPS, heat number – low-pressure fittings to MSS SP-43 with CR.

The standard family: dimensions, material, pipe

ASME B16.9 · ASTM A182/A182M · ASME B36.19M · ASTM A234/A234M

At Zickwolff

Stainless buttwelding fittings A403 to B16.9 (usually WP304L and WP316L) are part of our range, other grades and classes we procure – with certificate 3.1 and dual certification to the EN material number.

Dimensions Dimension tables for this standard are available on request – we work from manufacturer catalogues, not from copied standard tables.

Frequently asked questions about ASTM A403/A403M

Can I use this ASTM material in a pressure line under the PED?

Yes, but without presumption of conformity: the equipment manufacturer needs a European material approval or a particular material appraisal (PMA), in categories III and IV assessed by the notified body. For equipment under Article 4(3) (sound engineering practice) this does not apply. We supply the material with certificate 3.1 – the appraisal is the manufacturer's.

Must a plant with ASME parts be inspected more often?

No – the inspection interval comes from the operating law of the country, not from the code of the part. In Germany the Betriebssicherheitsverordnung (Annex 2 Section 4) sets maximum intervals, the operator fixes the interval in the risk assessment and the inspector may shorten it (TRBS 1201 Part 2) where design or manufacture give reason to. Operators often inspect more frequently anyway. This is general information, not legal advice – the legal text is binding.

What does WP316L-S or WP316L-W mean?

S = seamless, W = welded fitting with radiography of the fitting weld, WX = welded with full radiography, WU = ultrasonic test – the class belongs on the order and the certificate.

Is there an A403 grade for 1.4571?

Not a common one – 316Ti is a European habit – in the ASME world WP316L takes its place. For an EN line in 1.4571 we supply EN 10253-4 fittings.

Parts to ASME and ASTM – from one source

Tell us standard, size (NPS and schedule or Class), material grade, certificate and quantity – we check what is in stock, what we procure and which European part would do the same job.

Send an inquiry

Your inquiry to Zickwolff

Send us what you have – designation, standard, quantity, date. We will clarify the rest with you.

One item or a question

Send inquiry

Not in stock? We procure it – single items too.

Designation, standard and quantity are enough.

Several items

Send bill of materials

200 items? One parts list is enough – we deliver complete.

Attach it as a file.

Helpful if already known: project and country, date needed, certificates, packaging and language of the packing lists. If anything is missing, we will ask.

It is urgent

Request express

When do you need it? Express delivery, to the site if required.

Tell us by when you need the material – we will tell you what is possible.

← Back to ASME and ASTM standards

Basis: the publicly accessible scopes and abstracts of ASME and ASTM (editions as of 2 October 2026), manufacturer catalogues, a trade reference catalogue DIN/EN/ASME and specialist sources for marking and impact test values – the legal statements follow Directive 2014/68/EU and the German Betriebssicherheitsverordnung. No standard text was reproduced – the current original edition is binding. Comparisons with EN grades are orientation, not equivalence. Information without guarantee, no legal advice, no prices.