ASTM A403 covers wrought austenitic stainless steel fittings for butt welding — the grades written WP304, WP304L, WP316 and WP316L, made to ASME B16.9 dimensions. It is a different specification from A312 pipe and from A182 forged fittings, and the prefix on the grade is how you tell them apart.
Grades and minimum properties
| Grade | UNS | Min. yield (MPa) | Min. tensile (MPa) | Where it is used |
|---|---|---|---|---|
| WP304 | S30400 | 205 | 515 | General corrosion service, butt weld fittings |
| WP304L | S30403 | 170 | 485 | Welded construction where intergranular corrosion is a risk |
| WP316 | S31600 | 205 | 515 | Chloride, marine and chemical service |
| WP316L | S31603 | 170 | 485 | Welded 316 lines, low carbon |
Minimum values to ASTM A403. Fittings are normally supplied pickled and passivated; say so on the enquiry if the specification requires it.
A403 is not A312 and not A182
| Specification | Covers | Grade prefix |
|---|---|---|
| ASTM A312 | Seamless and welded stainless steel pipe | TP304, TP316 |
| ASTM A403 | Wrought stainless steel butt weld fittings | WP304, WP316 |
| ASTM A182 | Forged stainless steel socket weld, threaded and branch fittings | F304, F316 |
A butt weld elbow in WP316 is ordered to A403 and dimensioned to ASME B16.9; the pipe it joins is ordered to A312 in TP316. Both are 316, but they are not the same specification, and the mill certificate follows the fitting standard.
What to state on an A403 enquiry
Fitting, size, schedule, grade (WP304, WP304L, WP316 or WP316L), quantity, whether the finish is pickled and passivated, and whether EN 10204 3.1 or 3.2 is required.
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Related pages
Stainless butt weld fittings · Butt weld elbow · ASTM A182 forged grades
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