304 Buttweld Pipe Fittings
ASTM A403 WP304 / EN 1.4301 (X5CrNi18-10) — 18Cr-8Ni austenitic stainless steel for general-purpose chemical, food and water treatment service. Note: for all welded piping, specify 304L (EN 1.4307, C ≤0.030%) to prevent sensitization in the HAZ. ASME B16.9 and EN 10253-2 Type B.
½″–48″
Size Range
PRE ~18
Pitting Index
515 MPa
Min UTS (ASTM)
Specify 304L
for welded
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304 Grade Equivalents
| ASTM | EN W.Nr. | EN Name | UNS | ASME P-No. |
|---|---|---|---|---|
| A403 WP304 | 1.4301 | X5CrNi18-10 | S30400 | 8, Gr 1 |
| A182 F304 (flanges) | 1.4301 | X5CrNi18-10 | S30400 | 8 |
| A312 TP304 (pipe) | 1.4301 | X5CrNi18-10 | S30400 | 8 |
| A403 WP304L (low-C) | 1.4307 | X2CrNi18-9 | S30403 | 8 |
Chemical Composition — WP304 / EN 1.4301
| Standard | C (max) | Cr | Ni | Mn (max) | Si (max) | N |
|---|---|---|---|---|---|---|
| ASTM A403 WP304 | ≤0.070 | 18.0–20.0 | 8.0–11.0 | ≤2.0 | ≤1.0 | — |
| EN 1.4301 (EN 10253-2) | ≤0.070 | 17.5–19.5 | 8.0–10.5 | ≤2.0 | ≤1.0 | ≤0.11 |
No Mo: PRE ~18, significantly lower than 316L (~24). No chloride or acid corrosion resistance benefit from Mo. For chemical or marine service, specify 316L (EN 1.4404). PRE = %Cr + 3.3×%Mo + 16×%N.
Mechanical Properties — WP304 / EN 1.4301
| Standard | Min. UTS | Min. YS | Elongation | Max Hardness |
|---|---|---|---|---|
| ASTM A403 WP304 | 515 MPa | 205 MPa | ≥35% | 202 HBW |
| EN 1.4301 (EN 10253-2) | 500–700 MPa | ≥210 MPa | ≥45% | 215 HBW |
Heat Treatment & Sensitization
No PWHT Required
Austenitic stainless steels including 304/1.4301 do not require post-weld heat treatment (PWHT) for stress relief. Solution annealing (1010–1120°C, water quench) is the mill condition and restores full corrosion resistance if required after fabrication.
Sensitization Risk — Specify 304L for Welded Construction
C ≤0.070% in standard 304 creates sensitization risk in the heat-affected zone during welding. Chromium carbides (M₂₃C₆) precipitate at grain boundaries between 425–815°C, depleting local Cr and reducing corrosion resistance — a phenomenon called sensitization. 304 is appropriate for non-welded applications (flanged and threaded joints) only. For all welded piping, specify 304L (EN 1.4307, C ≤0.030%).
Welding Guidelines
Recommended Filler
ER308L (GTAW/GMAW) or E308L (SMAW). Use the L-grade filler even when base metal is standard 304 — this avoids weld sensitization regardless of base metal carbon content. Do not use ER308 / E308 on welded assemblies.
ASME P-Number
P-No. 8, Group 1. Same grouping as 304L, 316, 316L — WPS qualified on 304 is typically applicable to 304L.
Preheat
Not required for austenitic stainless steel. Keep inter-pass temperature ≤150°C to limit sensitization exposure time and prevent distortion.
Shielding Gas
Argon (GTAW/GMAW). Back purge with argon recommended for full-penetration welds to prevent oxidation of the root.
304 vs 304L — Which Should I Specify?
| Property | 304 / EN 1.4301 | 304L / EN 1.4307 |
|---|---|---|
| C max | ≤0.070% | ≤0.030% |
| Sensitization risk | Risk in HAZ | None |
| Min. YS | 205–210 MPa | 170–175 MPa |
| Preferred for welded construction | No | Yes |
| Typical use | Non-welded flanged/threaded joints | All welded piping systems |
Available Fitting Types — ASTM A403 WP304
Elbows — 90° & 45°
Long Radius (1.5D) and Short Radius (1D). ASME B16.9 / EN 10253-2 Type B. ½″–48″.
180° Return Bends
Long Radius and Short Radius. ASME B16.9. ½″–24″.
Equal & Reducing Tees
ASME B16.9 / EN 10253-2 Type B. ½″–48″.
Concentric & Eccentric Reducers
ASME B16.9 / EN 10253-2 Type B. ½″×¼″ through 48″×36″.
Pipe Caps
ASME B16.9 / EN 10253-2 Type B. ½″–24″.
Lap Joint Stub Ends
ASME B16.9 Type A & B. ½″–24″. Used with loose flanges.
Crosses (4-Way)
ASME B16.9. ½″–12″.
Laterals (45° Y)
ASME B16.9. ½″–12″.
Flanges — All Types
Weld Neck, Slip-On, Blind, Socket Weld, RTJ. ASME B16.5 / B16.47. ASTM A182 F304.
Frequently Asked Questions
Should I specify 304 or 304L for pipe fittings?
For welded pipe systems, 304L (ASTM A403 WP304L / EN 1.4307, C ≤0.030%) is strongly preferred. Standard 304 (WP304 / EN 1.4301, C ≤0.070%) risks sensitization in the heat-affected zone during welding — chromium carbides form at grain boundaries, reducing corrosion resistance locally. 304L prevents this with its low carbon. In practice, 304L should be the default specification for virtually all welded piping; standard 304 is only appropriate for non-welded applications (flanged joints, threaded connections) or where the slightly higher strength matters.
What is the European equivalent of ASTM A403 WP304?
EN 1.4301 (X5CrNi18-10) is the European equivalent for standard 304. The low-carbon 304L corresponds to EN 1.4307 (X2CrNi18-9). Both are covered under EN 10253-2 for buttweld pipe fittings. For European PED 2014/68/EU projects, specify 1.4307 (304L) or 1.4301 (304) by EN W.Nr.
Ready to order 304 stainless fittings?
Specify size, schedule, fitting type, standard (ASME B16.9 or EN 10253-2 Type B), and whether you require 304 or 304L. EN 10204 3.1 MTR included as standard; 3.2 TPI on request.
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