Low-Carbon Higher-Molybdenum Austenitic Stainless for Welded Aggressive Service
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UNS NUMBER
S31703
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ALLOY FAMILY
Austenitic (Mo-bearing)
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STRUCTURE
100% Austenite
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UTS (MIN)
≥515 MPa
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MAX TEMP
~870°C
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DENSITY
7.99 g/cm³
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Stainless Steel 317L (UNS S31703) is the low-carbon version of 317, with 3–4% molybdenum (PREN ~30) and carbon capped at 0.030%. It brings better pitting/crevice and acid resistance than 316L to welded FGD, pulp-bleaching, and aggressive chemical systems without sensitization risk.
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Cr
18–20%
Oxidation resistance
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Ni
11–15%
Austenite stabilizer
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Mo
3–4%
Higher pitting / crevice than 316L
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C
≤0.030%
Low carbon, weld-friendly
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UTS
≥515 MPa
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YS 0.2%
≥205 MPa
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Elong.
≥40%
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Service
-196~870°C
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What is Stainless Steel 317L?
317L pairs the higher molybdenum of 317 (3–4%) with a carbon limit of 0.030%, so welded fabrications resist intergranular attack without post-weld heat treatment. PREN of about 30 puts it clearly above 316L (~26) for pitting and crevice corrosion, and its chemistry handles a broader range of acids and oxidizing chlorides.
This is the grade most flue-gas-desulfurization (FGD) and pulp-bleaching plants specify for the wetted side. Where chloride levels are extreme — warm seawater, high-concentration brine — the super-austenitics 904L, AL6XN, and 254SMO (PREN 36–45) are the next step up. For moderate duty, 316L remains the cheaper default.
Chemical Composition (Weight %)
| Element |
Min (%) |
Max (%) |
Role in Alloy |
| Chromium (Cr) |
18.0 |
20.0 |
Oxidation resistance |
| Nickel (Ni) |
11.0 |
15.0 |
Austenite stabilizer |
| Molybdenum (Mo) |
3.0 |
4.0 |
Higher pitting / crevice than 316L |
| Carbon (C) |
— |
0.030 |
Low carbon prevents sensitization |
| Manganese (Mn) |
— |
2.00 |
Deoxidizer |
| Silicon (Si) |
— |
1.00 |
Deoxidizer |
| Phosphorus (P) |
— |
0.045 |
Impurity |
| Sulfur (S) |
— |
0.030 |
Impurity |
| Nitrogen (N) |
— |
0.10 |
Minor |
| Iron (Fe) |
Balance |
— |
Matrix former |
★ Molybdenum 3–4% (vs 2–3% in 316L) raises PREN to ~30. Carbon ≤ 0.030% prevents sensitization in welded fabrications.
Mechanical Properties
Values are for the solution-annealed condition per ASTM A240, A182 (F317L), and A312 (TP317L).
| Condition / Form |
UTS (MPa) |
YS 0.2% (MPa) |
Elong. % (min) |
Hardness (max) |
| Minimum (ASTM A240 / A182 F317L) |
≥515 |
≥205 |
40 |
217 HBW (95 HRB) |
| Typical mill-annealed |
515–690 |
205–350 |
45–55 |
155–200 HBW |
Modulus of Elasticity 193 GPa. Cold work raises strength. Not hardenable by heat treatment. 317L has slightly better creep strength than 316L.
Physical Properties
| Property |
Value |
Note |
| Density |
7.99 g/cm³ |
~316L |
| Melting Range |
1371–1421°C |
Solidus ~1371°C |
| Thermal Conductivity (20°C) |
16.2 W/m·K |
Comparable to austenitics |
| Thermal Expansion (20–100°C) |
16.0 ×10⁻⁶ /K |
Higher than carbon steel |
| Specific Heat |
0.12 kcal/kg·°C |
~500 J/kg·K |
| Electrical Resistivity |
79 µΩ·cm |
At room temp |
| Magnetic Property |
Non-magnetic* |
*Slight after cold work |
| PREN (Pitting Resistance) |
~30 |
PREN = %Cr + 3.3×%Mo + 16×%N |
Corrosion Resistance
Welded Fabrications
317L is the standard for welded FGD and pulp equipment because the low carbon prevents intergranular attack after welding. No post-weld annealing is needed.
Pitting & Crevice Corrosion
The 3–4% molybdenum gives PREN ~30, clearly better than 316L in chloride and bromide. Still limited in warm/stagnant seawater; for aggressive chloride use 904L or 254SMO.
FGD & Pulp Service
317L resists the acid + chloride slurries of flue-gas desulfurization and pulp bleaching better than 316L, which is why it is widely specified on the wetted side of these plants.
Acid Resistance
Better than 316L across many oxidizing acids and chlorides. For strong reducing acids, step up to 904L or a nickel alloy.
Stainless Steel 317L vs Similar Grades — Selection Guide
| If you need... |
Choose... |
Why |
| Welded FGD / pulp, >316L need |
317L |
Mo 3–4%, PREN ~30, no PWHT |
| Warm seawater / extreme Cl⁻ |
904L / 254SMO |
PREN 36–45 |
| General chloride |
316L |
Lower cost |
| Aggressive acid, non-welded |
317 |
Slightly stronger |
Applicable Standards
| Standard |
Product Form |
| ASTM A240 |
Plate, sheet, strip |
| ASTM A182 F317L |
Forged flanges & fittings |
| ASTM A312 TP317L |
Seamless & welded pipe |
| ASTM A403 WP317L |
Butt-weld fittings |
| ASTM A276 / A479 |
Bar, rod, forging stock |
| EN 1.4438 |
European equiv. |
HT PIPE Supply — Stainless Steel 317L Product Forms
| Product Form |
Specifications |
HT PIPE Supply |
| Seamless Pipe |
ASTM A312 TP317L |
✅ Available |
| Welded Pipe |
ASTM A312 TP317L |
✅ Available |
| Forged Flanges |
ASTM A182 F317L, ASME B16.5 |
✅ In stock |
| Butt-Weld Fittings |
ASTM A403 WP317L |
✅ Available |
| Plate / Sheet |
ASTM A240 |
✅ Available |
| Bar / Rod |
ASTM A276 / A479 |
✅ Available |
HT PIPE supplies 317L in pipe, flanges, fittings, plate, and bar for FGD, pulp, and aggressive chemical service, with full MTRs and PMI on request.
Project Experience — Stainless Steel 317L
HT PIPE supplies 317L for flue-gas-desulfurization, pulp/paper, and aggressive chemical process systems.
| Project |
Product |
Specification |
| FGD Absorber Tower (Asia) |
317L Plate + Forgings |
A240, A182 |
| Pulp Bleaching Line (Europe) |
317L Pipe + Fittings |
A312, A403 |
| Aggressive Acid Process (China) |
317L Flanges + Pipe |
A182 F317L, A312 |
We advise 317L vs 316L and provide PMI verification for acid/chloride service.
| FREQUENTLY ASKED QUESTIONS |
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FAQ — Stainless Steel 317L
| What is the difference between 317L and 316L? |
| 317L has more molybdenum (3–4% vs 2–3%) and a wider nickel range, raising PREN from ~26 to ~30. That gives better pitting/crevice resistance and a broader chemical range for a moderate cost premium. |
| What is the difference between 317L and 317? |
| 317L caps carbon at 0.030% (vs up to 0.08% for 317) to avoid weld sensitization. Use 317L for welded fabrications that will not be post-weld annealed. |
| Why is 317L used in FGD? |
| FGD scrubbers expose steel to acid + chloride slurries. 317L's PREN ~30 and low-carbon weldability make it the standard wetted-side material, with 904L/254SMO for the most aggressive zones. |
| Is 317L good in seawater? |
| Better than 316L but still not enough for warm/stagnant seawater. For aggressive chloride use 904L, AL6XN, or 254SMO. |
| What filler is used for 317L? |
| ER317L / E317L keeps the weld deposit low-carbon and matching. Avoid plain 316L filler where the higher molybdenum is needed. |
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Need Stainless Steel 317L for Aggressive Service?
HT PIPE supplies 317L seamless pipe, butt-weld fittings, forged flanges, and plate with full MTR documentation. Contact our technical team for material selection and welding advice.
Request a Quote |
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