Article
ASTM A403 is the material specification for wrought austenitic stainless steel piping fittings: elbows, tees, reducers, caps, crosses and stub ends. If you buy stainless buttweld fittings, almost every line on your order will refer to it.
What A403 covers
A403 sets the chemical composition, heat treatment, mechanical properties, testing and marking. It does not set dimensions; those come from ASME B16.9, B16.11 (for some forged items) or MSS SP-43.
WP and CR
- WP fittings are made to ASME B16.9 or B16.28 dimensions and have pressure ratings matching the corresponding pipe.
- CR fittings are made to MSS SP-43 and are intended for light-wall, low-pressure service.
Common grades
| Grade | Use |
|---|---|
| WP304 / WP304L | General corrosion resistance, water, food, mild chemicals |
| WP304H | Higher carbon for elevated temperature strength |
| WP316 / WP316L | Chloride-bearing service, chemical and marine |
| WP316H / WP316Ti | High temperature; titanium-stabilised option |
| WP317L | Higher molybdenum for stronger chemicals |
| WP321 / WP347 | Stabilised grades for 425–815 °C service |
| WP309 / WP310S | Heat and oxidation resistance |
| WP904L | Sulphuric acid and severe chloride service |
Dual-certified fittings
Fittings are often marked WP304/304L or WP316/316L. This means the material meets the low carbon limit of the L grade and the strength of the straight grade, so one fitting satisfies both specifications.
Heat treatment and testing
A403 fittings must be solution annealed and quenched, which restores corrosion resistance after forming. Tensile testing is required per heat, and welded classes need radiography or ultrasonic testing as described by the class letter (W, WX, WU). Supplementary requirements such as intergranular corrosion testing to ASTM A262 can be added by the buyer.
Reading the marking
XYZ · 4" SCH40S · WP316L-S · Heat 12345 · B16.9
This tells you the maker, size and schedule, grade and class (seamless), heat number for traceability to the test certificate, and the dimensional standard.
Frequently asked questions
Does ASTM A403 specify dimensions?
No. A403 is a material standard. Dimensions come from ASME B16.9 for WP fittings or MSS SP-43 for CR fittings.
What does WP316/316L mean?
The fitting is dual certified and meets the requirements of both 316 and 316L.
Are A403 fittings heat treated?
Yes. They must be solution annealed and quenched after forming.
Key takeaways
- A403 = material spec for austenitic stainless fittings.
- WP for B16.9 fittings, CR for light-wall MSS SP-43 fittings.
- Check grade, class and heat number on every fitting.
Need these products?
Sawariya Metal Industries supplies stainless steel pipes, flanges and buttweld pipe fittings from Mumbai to buyers in India and overseas. Send your size, grade, standard and quantity through our enquiry form and we will reply with a clear quotation and the test documents you need. You can also browse our stainless steel pipes, flanges and buttweld fittings.