ASTM A403
Wrought austenitic stainless steel piping fittings
Covers wrought austenitic stainless steel piping fittings — elbows, tees, reducers, caps and stub ends — in seamless and welded construction, with grades named WP304, WP316L, WP904L and so on.
- Pipe fittings
- ASME SA-403
- 7 grades supplied to it
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is ASTM A403?
ASTM A403 is the material specification for wrought austenitic stainless steel pipe fittings — elbows, tees, reducers, caps and stub ends made from seamless or welded stainless material. Grades carry a WP prefix when the fittings follow ASME dimensions (ASME B16.9, ASME B16.11) and a CR prefix when they follow MSS SP-43 light-wall dimensions. ASME adopts it as SA-403.
ASTM A403 at a glance
| Product | Wrought buttweld fittings (and other wrought fittings) for pressure piping |
|---|---|
| Material family | Austenitic stainless steel — 304, 316, 321, 347, 310S, 904L and others |
| Grade prefix | WP (ASME dimensions) · CR (MSS SP-43 dimensions) |
| WP classes | S seamless · W welded (welds radiographed or ultrasonically examined) · WX welded, all welds radiographed · WU welded, all welds ultrasonically examined |
| Heat treatment | Solution annealed |
| ASME designation | SA-403 (Section II) |
ASTM A403 grades — WP and CR designations
The grade name tells the mill both the alloy and the dimensional standard. CR grades have no construction class.
ASTM A403 vs A182 vs A234 vs A815
Four fitting specifications that buyers mix up. The material family and the way the fitting is made decide which one applies.
| Specification | Material | Typical products |
|---|---|---|
| ASTM A403 | Austenitic stainless | Wrought buttweld fittings — elbows, tees, reducers, caps |
| ASTM A182 | Stainless, duplex and alloy steel forgings | Flanges and forged socket-weld / threaded fittings |
| ASTM A234 | Carbon and Cr-Mo alloy steel | Wrought buttweld fittings — WPB, WP11, WP22 |
| ASTM A815 | Duplex, ferritic and martensitic stainless | Wrought buttweld fittings — e.g. WPS32205, WPS32750 |
Matching components for an A403 line
A typical 316L process line; the same pattern applies to the other grades.
| Component | Specification | Grade |
|---|---|---|
| Pipe | ASTM A312 | TP316L |
| Buttweld fittings | ASTM A403 | WP316L |
| Flanges | ASTM A182 | F316L |
| Stud bolts | ASTM A193 | B8M (or B7 where the bolting is not wetted) |
| Nuts | ASTM A194 | 8M (or 2H with B7) |
How to write ASTM A403 on a purchase order
Name the product, size, material specification and grade, the dimensional standard and the certificate. An example line:
Illustrative only — sizes, tests, inspection level and any project values come from your purchase specification.
ASTM A403 edition and verification status
Which edition we have confirmed, and what is still being checked before any numerical requirement is published here.
| Current edition (publisher listing) | A403/A403M-26a — checked 7 October 2026 |
|---|---|
| Full-text verification | In progress — numerical requirements are published here only after the current text has been reviewed |
| Edition on your order | The edition named in your purchase order or design code governs — confirm it with your enquiry |
What to know before ordering to ASTM A403
The points that decide whether material to ASTM A403 is accepted at inspection.
- Class WP is made to ASME B16.9 / B16.11; Class CR is made to MSS SP-43.
- The suffix S, W or WX shows seamless, welded, or welded with full radiography.
- Dimensions come from ASME B16.9, not A403.
Grades and products we supply to ASTM A403
How ASTM A403 fits into an order
A purchase order line is only complete when it names the material standard, the dimensional standard and the inspection document. Miss one and the mill, the inspector and the buyer can each read the order differently.
Standards used with ASTM A403
Same family
ASTM A403 — questions buyers ask
What is ASTM A403?
ASTM A403 is the material specification for wrought austenitic stainless steel pipe fittings — elbows, tees, reducers, caps and stub ends made from seamless or welded stainless material. Grades carry a WP prefix when the fittings follow ASME dimensions (ASME B16.9, ASME B16.11) and a CR prefix when they follow MSS SP-43 light-wall dimensions. ASME adopts it as SA-403.
What is the difference between WP and CR grades in ASTM A403?
WP grades are made to ASME dimensional standards such as B16.9 and carry a construction class (S, W, WX or WU). CR grades are made to MSS SP-43 light-wall dimensions and have no class. The alloy can be identical — WP316L and CR316L are both 316L.
What do S, W, WX and WU mean after an A403 grade?
They describe construction and weld examination: S is seamless; W is welded, with the fitting maker’s welds (and any filler-metal welds in the starting pipe) examined by radiography or ultrasonics; WX is welded with all welds radiographed; WU is welded with all welds ultrasonically examined. Write the class after the grade, e.g. WP316L-W.
Is ASTM A403 the same as ASME SA-403?
Technically yes for a given edition. SA-403 is the ASME Section II adoption of A403; pressure-equipment designs call for the SA designation and most certificates show both.
Should socket-weld fittings be ordered to A403 or A182?
Small-bore forged socket-weld and threaded fittings to ASME B16.11 are normally ordered to ASTM A182 F-grades (e.g. F316L). A403 is the usual specification for wrought buttweld fittings.
Does A403 cover duplex fittings?
No. A403 is austenitic only. Duplex and super duplex buttweld fittings are ordered to ASTM A815 (e.g. WPS32205, WPS32750).
Which grades do you supply to ASTM A403?
SS 904L, SS 304, SS 304L, SS 310 / 310S, SS 316 / 316L, SS 321, SS 347 — see the table on this page for the exact product and designation.
What is the current edition of ASTM A403?
The publisher's listing checked on 7 October 2026 shows A403/A403M-26a as the current edition. The edition that governs an order is the one named in the purchase order or design code. Full-text review of the current edition is in progress, so numerical requirements are not published on this page yet.
Do you supply certificates to this standard?
Yes. Material is supplied with mill test certificates to EN 10204 3.1 showing the standard, grade and heat number; 3.2 with third-party inspection on request.
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026