317L Buttweld Pipe Fittings
ASTM A403 WP317L / EN 1.4438 (X2CrNiMo18-15-4) — 18Cr-13Ni-3.5Mo low-carbon austenitic stainless steel with 3-4% molybdenum for high-chloride and acid service where 316L is marginal. FGD scrubbers, pulp bleach plants, phosphoric and sulphuric acid piping. EN 10253-2 Type B and ASME B16.9. EN 10204 3.1 standard; 3.2 TPI on request.
½″–48″
Size Range
PRE ~30
Pitting Index
3–4% Mo
vs 2–3% in 316L
EN 10204
3.1 Std / 3.2 On Req.
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317L Grade Equivalents
| ASTM | EN W.Nr. | EN Name | UNS | ASME P-No. |
|---|---|---|---|---|
| A403 WP317L (fittings) | 1.4438 | X2CrNiMo18-15-4 | S31703 | 8, Gr 1 |
| A182 F317L (flanges) | 1.4438 | X2CrNiMo18-15-4 | S31703 | 8 |
| A312 TP317L (pipe) | 1.4438 | X2CrNiMo18-15-4 | S31703 | 8 |
| A240 317L (plate) | 1.4438 | X2CrNiMo18-15-4 | S31703 | 8 |
Chemical Composition — 317L / 1.4438
| Standard | C | Cr | Ni | Mo | Mn | Si | N |
|---|---|---|---|---|---|---|---|
| ASTM A403 WP317L | ≤0.035 | 18.0–20.0 | 11.0–15.0 | 3.0–4.0 | ≤2.0 | ≤1.0 | — |
| EN 1.4438 (X2CrNiMo18-15-4) | ≤0.030 | 17.5–19.5 | 13.0–16.0 | 3.0–4.0 | ≤2.0 | ≤1.0 | ≤0.11 |
The 3.0–4.0% molybdenum content (versus 2.0–3.0% in 316L) is the defining feature of 317L — it raises the pitting resistance equivalent to roughly PRE 29–30 and improves resistance to reducing acids and chloride-induced pitting.
Mechanical Properties — 317L / 1.4438
| Standard | Min. UTS (MPa) | Min. YS (MPa) | Elongation (%) | Max. Hardness | HT Condition |
|---|---|---|---|---|---|
| ASTM A403 WP317L | 515 | 205 | ≥35% | 217 HBW | Solution annealed |
| EN 1.4438 (EN 10253-2) | 500–700 | ≥200 | ≥35% | 215 HBW | Solution annealed |
Heat Treatment & Corrosion Considerations
✓ No PWHT Required — 317L supplied and used in the solution annealed condition.
Like all austenitic stainless steels, 317L (ASTM A403 WP317L / EN 1.4438) does not require post-weld heat treatment. It does not undergo martensitic transformation during welding and is not susceptible to hydrogen cracking. The fitting is delivered solution annealed and no further heat treatment is needed for code-compliant welded joints.
Why 317L over 316L — Molybdenum Advantage
- Higher Mo (3–4%): superior resistance to pitting and crevice corrosion in chloride and reducing-acid media compared with 316L.
- Typical service: FGD scrubbers and flue-gas ducts, pulp and paper bleach plants, phosphoric and dilute sulphuric acid piping.
- Filler metal: ER317L (GTAW / TIG) or E317L-16 (SMAW). Match filler to preserve weld-metal molybdenum.
- ASME P-No.: 8, Group 1. Weld procedure qualification per ASME IX or ISO 15614-1.
⚠ Chloride SCC Warning
Although 317L resists pitting better than 316L, it is still an austenitic grade and remains susceptible to chloride stress corrosion cracking (SCC) above approximately 60°C. For seawater, high-chloride brines, or hot chloride service with SCC risk, specify duplex 2205 (EN 1.4462) or super duplex 2507 (EN 1.4410). Contact our technical team to confirm material selection for your service conditions.
317L 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
316L vs 317L — Key Differences
| Property | 316L (WP316L / 1.4404) | 317L (WP317L / 1.4438) |
|---|---|---|
| Molybdenum | 2.0–3.0% | 3.0–4.0% |
| PRE (approx.) | ~24 | ~29–30 |
| Chloride pitting resistance | Good | Better |
| Typical service | General process piping | FGD, pulp bleach, acids |
| PWHT | Not required | Not required |
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