304H Buttweld Pipe Fittings
ASTM A403 WP304H / EN 1.4948 (X6CrNi18-11) — the controlled higher-carbon version of 304 with coarser grain size for greater creep strength at elevated temperature. Power-boiler superheater piping and high-temperature process lines. EN 10253-4 Type B and ASME B16.9. EN 10204 3.1 standard; 3.2 TPI on request.
½″–48″
Size Range
C 0.04–0.10
Creep Carbon
18Cr-8Ni
304 base, no Mo
EN 10204
3.1 Std / 3.2 On Req.
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304H Grade Equivalents
| ASTM | EN W.Nr. | EN Name | UNS | ASME P-No. |
|---|---|---|---|---|
| A403 WP304H (fittings) | 1.4948 | X6CrNi18-11 | S30409 | 8, Gr 1 |
| A182 F304H (flanges) | 1.4948 | X6CrNi18-11 | S30409 | 8 |
| A312 TP304H (pipe) | 1.4948 | X6CrNi18-11 | S30409 | 8 |
| A240 304H (plate) | 1.4948 | X6CrNi18-11 | S30409 | 8 |
Chemical Composition — 304H / 1.4948
| Standard | C | Cr | Ni | Mo | Mn | Si |
|---|---|---|---|---|---|---|
| ASTM A403 WP304H | 0.04–0.10 | 18.0–20.0 | 8.0–11.0 | — | ≤2.0 | ≤1.0 |
| EN 1.4948 (X6CrNi18-11) | 0.04–0.10 | 18.0–20.0 | 8.0–11.0 | — | ≤2.0 | ≤1.0 |
The controlled carbon (0.04–0.10%) and coarser grain size distinguish 304H from 304L — they raise creep-rupture strength for long-term elevated-temperature service. 304H contains no molybdenum and is not intended for chloride service.
Mechanical Properties — 304H / 1.4948
| Standard | Min. UTS (MPa) | Min. YS (MPa) | Elongation (%) | Grain Size | HT Condition |
|---|---|---|---|---|---|
| ASTM A403 WP304H | 515 | 205 | ≥35% | ASTM No. 7 or coarser | Solution annealed |
| EN 1.4948 (EN 10253-4) | 500–700 | ≥200 | ≥35% | Controlled | Solution annealed |
High-Temperature Service & Welding
✓ No PWHT Required — supplied solution annealed.
304H (ASTM A403 WP304H / EN 1.4948) is austenitic and does not require post-weld heat treatment. It is welded with a matching ER308H / ER308 filler; keep inter-pass temperature ≤150°C. ASME P-No. 8, Group 1.
Why 304H over 304L for High Temperature
- Creep strength: the controlled carbon and coarser grain give higher creep-rupture strength for service above ~525°C.
- Code use: 304H carries ASME B31.1 / B31.3 allowable stresses at elevated temperature where 304L is de-rated.
- Typical service: power-boiler superheater piping and high-temperature process and refinery lines (non-chloride).
304H Fitting Types Available
90° Elbow (LR & SR)
Long Radius & Short Radius
ASME B16.9
45° Elbow
Long Radius
ASME B16.9
Equal Tee
Straight tee, equal branch
ASME B16.9
Reducing Tee
Reduced branch outlet
ASME B16.9
Concentric Reducer
Inline bore reduction
ASME B16.9
Eccentric Reducer
Flat bottom / top configurations
ASME B16.9
End Cap
Pipe end closure
ASME B16.9
Stub End (Lap Joint)
For use with lap joint flanges
ASME B16.9
Cross / Lateral
Four-way and angled branch
ASME B16.9
304H, 316H, 321H or 347H: When 304H Is the Right Call
Best fit: dry, hot service
304H is the economical first choice for steam and superheater piping, heater outlets and hot-gas lines where no water or acid condenses in service or at shutdown.
Watch-out: sensitisation
The 0.04–0.10% carbon that gives 304H its creep strength also makes it prone to sensitisation when held at roughly 425–815°C. If the line can see wet, sulphur-bearing conditions at shutdown (the polythionic acid risk in refinery units), stabilised 321H or 347H is usually specified instead.
When to step up to 316H
Choose 316H when you need more creep strength at the same temperature, or better resistance to chloride pitting in condensate. It costs more because of its molybdenum.
Ordering tips
- Ask for dual-certified 304/304H if your piping spec allows it
- Check that the certificate shows carbon within 0.04–0.10%
- State any grain-size requirement from your piping spec
Ready to order 304H high-temperature fittings?
Specify size, schedule, fitting type, standard (ASME B16.9 or EN 10253-4 Type B), and required MTR (EN 10204 3.1 or 3.2). We respond within 1 business day.
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