GRADE PROFILE
317L — S31703 / TP317L
317L is a 316L whose molybdenum rises from 2–2.5% to 3–4%, with chromium and nickel raised accordingly. Its PREN climbs from 25 to a range of 28 to 33. It is the grade for acidic chlorinated media that 316L can no longer hold, and it has no exact EN equivalent.
- Austenitic
- PREN 28–33
- Cost index 140
When to choose it
Where 316L pits and the medium is acidic rather than saline. Flue gas desulphurisation and gas scrubbing, cooking liquors and bleaching circuits in pulp and paper, dilute sulphuric and phosphoric acids. These are media where molybdenum works against pitting in the presence of acid, ground on which heavily molybdenum-alloyed austenitics remain relevant.
On heat exchangers and chemical process piping it is a useful intermediate step between 316L and 904L, whose cost is markedly higher.
When not to choose it
In seawater and hot brines. Duplex 2205 or a super austenitic hold better there, often for less: 317L is the wrong answer to a good question, because it adds molybdenum without changing metallurgical family.
As a default substitute for 316L. The molybdenum premium is only justified when the medium demands it, and on ordinary piping it returns nothing.
In hydrochloric acid, even dilute: no stainless holds that medium.
And in stagnant chlorinated water, where crevice corrosion governs. PREN does not describe it; joint design and the absence of dead legs matter more than the grade.
Composition
| Element | % |
|---|---|
| C | ≤ 0.035 |
| Mn | ≤ 2 |
| P | ≤ 0.045 |
| S | ≤ 0.03 |
| Si | ≤ 1 |
| Cr | 18–20 |
| Ni | 11–15 |
| Mo | 3–4 |
Mechanical properties
| Standard | Form | Rm (MPa) | Rp0.2 (MPa) | A (%) | Hardness |
|---|---|---|---|---|---|
| ASTM A312/A312M, tableau 2 | tube soudé et sans soudure, état hypertrempé | ≥ 515 | ≥ 205 | ≥ 35 | — |
Designations and standards
| Reference | Designation |
|---|---|
| EN (numeric) | 1.4438 |
| EN (symbolic) | X2CrNiMo18-15-4 |
| ASTM / AISI | TP317L |
| UNS | S31703 |
| JIS | SUS317L |
| AFNOR | — |
Tube product standards :
- ASTM A312/A312M
- ASTM A213/A213M
- ASME SA312
Availability
Available in welded and seamless tube. Structured dimensional data for this grade is not yet documented in our reference set: send us your sizes and we will check with our partner stocks and mills. EN 10204 3.1 material certificates supplied with the goods.
Related grades
- 316L (1.4404) — the starting point, worth comparing before stepping up in molybdenum.
- 904L (1.4539) — the step above for acids, with very high copper and nickel.
- Duplex 2205 (1.4462) — the change of family when the problem becomes saline rather than acidic.
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Frequently asked questions
- Does 317L have a European equivalent?
- Not an exact one. 1.4438 (X2CrNiMo18-15-4) is close and serves as the usual cross-reference, but the composition ranges do not overlap perfectly. If your specification names one of the two, do not substitute the other without validation.
- 317L or 904L for sulphuric acid?
- It depends on concentration and temperature. 904L, with its copper and 24 to 26% nickel, holds conditions where 317L gives up — but it costs more than twice as much. 317L covers moderate dilutions.
- Why is its PREN given as such a wide range?
- Because the molybdenum range in ASTM A312 is wide, 3 to 4%. A heat at 3.0% and a heat at 4.0% do not give the same PREN. On a borderline application, the certificate chemistry decides, not the grade designation.