Views: 1 Author: Site Editor Publish Time: 2026-06-12 Origin: Site
In petrochemical, marine, and LNG plants, stainless steel butt-welded fittings affect safety and service life. ASTM A403/A403M is the global standard for wrought austenitic stainless steel butt-welded fittings. It strictly defines material composition, manufacturing, mechanical properties, and testing. This ensures ASTM A403 fittings run reliably under high pressure and corrosion.
ASTM A403/A403M covers wrought austenitic stainless steel fittings for pressure piping. Products include:
Welded connection,Changes pipe direction. Long radius (R=1.5D), short radius (R=1.0D). Materials: 304, 316L. Good corrosion resistance.
Splits or combines flow. Materials: 304, 316L. Welded ends. Strong sealing and pressure resistance.
Connects different pipe sizes. Concentric for vertical pipes. Eccentric avoids gas or liquid pockets.
Closes pipe ends. Standard elliptical shape.
Size range: NPS 1/2" to 48" (DN15 to DN1200). Larger sizes available.
Wall thickness: SCH10 to SCH160, XXS.
Used with lap joint flange. Long and short types.
Prefix | Standard | Use |
WP | ASME B16.9/B16.11 | Standard pressure fittings, most common |
CR | MSS SP-43 | Lightweight, low pressure |
Grade | UNS | Property | Application |
WP304 | S30400 | General corrosion resistance | Chemical, food |
WP304L | S30403 | Low carbon, good weldability | Post-weld no heat treatment |
WP309 | S30900 | High temperature resistance | Furnace parts |
WP310 | S31000 | Higher temperature | Heat treatment |
WP316 | S31600 | Contains molybdenum, resists pitting | Marine, chemical |
WP316L | S31603 | Low carbon + molybdenum | Welding, harsh corrosion |
WP321 | S32100 | Contains titanium | High temp, welding sensitive |
WP347 | S34700 | Contains niobium | High temp, welding sensitive |
Grade | UNS | Property | PRE value |
WPS31254 | S31254 | 6% molybdenum, super austenitic | ~43 |
WPS31266 | S31266 | 6% Mo + nitrogen | ~44 |
Grade | C | Mn | P | S | Si | Ni | Cr | Mo |
WP304 | ≤0.08 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 8.0-11.0 | 18.0-20.0 | --- |
WP304L | ≤0.035 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 8.0-13.0 | 18.0-20.0 | --- |
WP316 | ≤0.08 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 10.0-14.0 | 16.0-18.0 | 2.00-3.00 |
WP316L | ≤0.035 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 10.0-16.0 | 16.0-18.0 | 2.00-3.00 |
WP321 | ≤0.08 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 9.0-12.0 | 17.0-19.0 | --- |
WP347 | ≤0.08 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 9.0-13.0 | 17.0-19.0 | --- |
Grade | Tensile min (ksi [MPa]) | Yield min (ksi [MPa]) | Elongation min (%) |
WP304 / WP316 | 75 [515] | 30 [205] | 28 |
WP304L / WP316L | 70 [485] | 25 [170] | 28 |
WP321 / WP347 | 75 [515] | 30 [205] | 28 |
WPS31254 | 94 [650] | 44 [300] | 35 |
ASTM A403 divides WP grades into four classes based on process and testing:
Class | Method | NDT | Application |
S | Seamless | None | High pressure, corrosion, critical lines |
W | Welded | RT or UT (spot check) | General industrial |
WX | Welded | 100% RT | Higher safety lines |
WU | Welded | 100% UT | Where RT is not suitable |
CR grade (lightweight) has no class division.
All fittings must be solution heat treated unless agreed otherwise.
Grade | Minimum Temperature |
WP304 / WP304L / WP316 / WP316L | 1900°F [1040°C] |
WP321 / WP347 | 1950°F [1065°C] |
WP309 / WP310 | 1940°F [1060°C] |
WPS31254 | 2100°F [1150°C] |
Accuracy: ±25°F [±15°C].
Cooling: water quench or rapid cool.
After repair welding: re-heat treat.
Test | Requirement | Standard |
Chemical analysis | Per heat | ASTM A751 |
Tensile test | 1 sample per heat lot | ASTM A403 |
Visual | 100% | Visual + tools |
Dimensional | Per ASME B16.9/B16.11 | ASME |
Class | Method | Acceptance |
WX | 100% RT | ASME VIII-1 UW-51 |
WU | 100% UT | ASME VIII-1 Appendix 12 |
ASTM – A351, A743, A744, A751, A960, E112, E165, G48
ASME – B16.9 (core), B16.11, BPVC Section VIII, Section IX
MSS – SP-43, SP-79, SP-83, SP-95, SP-97
AWS – A5.4, A5.9, A5.22, A5.39 (welding materials)
ASNT – SNT-TC-1A (NDT personnel)
Aspect | ASTM A403 (Wrought) | ASTM A182 (Forged) |
Products | BW elbows, tees, reducers | Flanges, SW/threaded fittings |
Material source | Pipe, plate, forgings, bar | Forgings, bar |
Typical grades | WP304/L, WP316/L | F304/L, F316/L |
Process | Forming + welding | Forging + machining (no welding) |
Prefix | WP | F |
Rule: Use A403 for BW fittings, A182 for flanges in same system. Do not mix.
ASTM A403 = material standard (chemistry, properties, heat treat, testing)
ASME B16.9 = dimension standard (type, size, tolerance)
A403 references B16.9 for dimensions. CR grade uses MSS SP-43.
Grade: Choose 304/316 based on corrosion. Use L grade for heavy welding or no post-weld heat treatment.
Class: S for high pressure/corrosion. W for general. WX for critical safety.
Heat treat: Required by default. Re-do after repair welding.
Documents: Supplier must provide full MTR.
