ASTM A403 Stainless Steel Pipe Fittings

Austenitic Grades (300 Series)

ASTM A403 · EN 1.4301

WP304 / WP304L / WP304H

Standard 18Cr-8Ni austenitic. 304L for low-carbon weld sensitisation control. 304H for elevated temperature creep strength above 500°C.

EN: 1.4301 (304) · 1.4307 (304L) · 1.4948 (304H)

ASTM A403 · EN 1.4404 ★ Most Ordered

WP316 / WP316L / WP316H

18Cr-8Ni-2Mo. Molybdenum addition for superior chloride corrosion resistance. 316L for welded assemblies. 316H for creep service.

EN: 1.4401 (316) · 1.4404 (316L) · 1.4910 (316H)

ASTM A403 · EN 1.4541

WP321

18Cr-8Ni-Ti. Titanium-stabilised for sensitisation-resistant high-temperature service 425–900°C. Heat exchangers, exhaust systems.

EN: 1.4541 · Max service: 900°C

ASTM A403 · EN 1.4550

WP347 / WP347H

18Cr-8Ni-Nb. Niobium-stabilised. Similar to 321 but better resistance to intergranular corrosion at higher temperatures. Nuclear and refinery service.

EN: 1.4550 (347) · 1.4961 (347H)

ASTM A403 · EN 1.4438

WP317L

18Cr-15Ni-3.5Mo. Higher Mo than 316L. Pulp and paper, aggressive chloride environments, dilute H₂SO₄.

EN: 1.4438 · PRE ≈ 29

ASTM A403 · EN 1.4547

WP6Mo (254 SMO)

20Cr-18Ni-6Mo-N. Super-austenitic. PRE >43. Seawater service, FGD systems, hot chloride solutions.

EN: 1.4547 · PRE >43

Duplex & Super-Duplex Grades

ASTM A815 · EN 1.4462 ★ Popular

WP2205 (Duplex 2205)

22Cr-5Ni-3Mo-N. Dual austenite/ferrite microstructure. 2× yield strength of 316L. PRE ≈ 35. Offshore, desalination, oil & gas sour service.

EN: 1.4462 · NACE MR0175 compliant · HRC ≤28

ASTM A815 · EN 1.4410

WP2507 (Super-Duplex)

25Cr-7Ni-4Mo-N. Super-duplex. PRE >40. Seawater cooling, FGD scrubbers, offshore umbilicals. Highest strength and corrosion resistance in the duplex family.

EN: 1.4410 · PRE >40

ASTM ↔ EN Stainless Steel Cross-Reference

ASTM Grade	Common Name	EN Designation	W.Nr.	Cr %	Ni %	Mo %	Key Feature
WP304	304	X5CrNi18-10	1.4301	17.5–19.5	8–10.5	—	General purpose
WP304L	304L	X2CrNi19-11	1.4307	17.5–19.5	8–12	—	C ≤0.030%, welded
WP304H	304H	X6CrNi18-10	1.4948	18–20	8–11	—	C 0.04–0.10%, creep
WP316	316	X5CrNiMo17-12-2	1.4401	16.5–18.5	10–13	2.0–2.5	Mo for chloride resistance
WP316L	316L	X2CrNiMo17-12-2	1.4404	16.5–18.5	10–13	2.0–2.5	Most widely ordered SS grade
WP316H	316H	X6CrNiMo17-13-2	1.4910	16.5–18.5	11–14	2.0–2.5	C 0.04–0.10%, creep
WP321	321	X6CrNiTi18-10	1.4541	17–19	9–12	—	Ti-stabilised, 425–900°C
WP347	347	X6CrNiNb18-10	1.4550	17–19	9–12	—	Nb-stabilised, nuclear
WP317L	317L	X2CrNiMo18-15-4	1.4438	18–20	11–15	3.0–4.0	High Mo, pulp/paper
WP6Mo	254 SMO	X1CrNiMoCuN20-18-7	1.4547	19.5–20.5	17.5–18.5	6.0–6.5	Super-austenitic, PRE >43
WP2205	Duplex 2205	X2CrNiMoN22-5-3	1.4462	21–23	4.5–6.5	2.5–3.5	PRE ≈ 35, high strength
WP2507	Super-Duplex	X2CrNiMoN25-7-4	1.4410	24–26	6–8	3.0–5.0	PRE >40, seawater

Grade Selection Guide

›General process piping, ambient chlorides: WP316L (1.4404)
›Elevated temperature 425–900°C, sensitisation concern: WP321 or WP347
›Creep service above 500°C: WP304H or WP316H
›Offshore / sour gas, NACE MR0175: WP2205 Duplex
›Seawater cooling, FGD scrubbers: WP2507 Super-Duplex or 6Mo
›Pharmaceutical / food grade Ra surface finish: WP316L (electropolished)
›Nuclear service: WP347 or WP347H
›Cryogenic / LNG: WP304L (to −196°C)

L vs H vs Standard — What the Suffix Means

›No suffix (WP304, WP316): C ≤0.08%. Dual-certified with L grades if C ≤0.030% is met on the heat certificate.
›L suffix (WP304L, WP316L): Low carbon ≤0.030%. Prevents sensitisation (chromium carbide precipitation) at HAZ in welded assemblies. No solution anneal required after welding for normal service.
›H suffix (WP304H, WP316H): Higher carbon 0.04–0.10%. Improved creep rupture strength at elevated temperature. Mandatory for ASME B31.3 service above 538°C.
›L and H are mutually exclusive — a WP316L fitting cannot be marked H. Dual 304/304L cert is common; 304/304H is not.