Last verified 19 August 2026.
The comparison
| Property | 317L | 317LMN | Evidence |
|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 220 MPa | 290 MPa | E3 E3 |
| Tensile strength Rm, minimum | 520 MPa | 580 MPa | E3 E3 |
| Elongation A, minimum | 40 % | 35 % | E3 E3 |
| PREN | 28 — | 33 — | E3 E3 |
| Density | 8.0 g/cm³ | 8.0 g/cm³ | E3 E3 |
| Modulus of elasticity | 200 GPa | 200 GPa | E3 E3 |
| Thermal conductivity | 14 W/(m·K) | 14 W/(m·K) | E3 E3 |
Proof strength Rp0.2, minimum (EN) — different product forms — Quarto plate against cold rolled coil and sheet. The grades differ and so does what was tested, so the gap between these two numbers is not all material
Tensile strength Rm, minimum — different product forms — Quarto plate against cold rolled coil and sheet. The grades differ and so does what was tested, so the gap between these two numbers is not all material
Elongation A, minimum — different product forms — Quarto plate against cold rolled coil and sheet. The grades differ and so does what was tested, so the gap between these two numbers is not all material
Where each side’s numbers come from
See 317L and 317LMN — each page lists every source, every demotion and every gap. Nothing on this page is derived from anything not on those two, and our coverage limits are stated separately.
Where a PREN appears above, read it as a ranking number rather than a qualification: what PREN can and cannot tell you.
When to choose which
317L. Flue gas desulphurisation, pulp and paper bleaching, and process streams where 316L is pitting but the environment does not justify a six-molybdenum alloy. It is also specified where an existing 316L design is being uprated without redrawing it, because the mechanical minima on plate are identical and nothing structural has to change.
317LMN. Flue gas desulphurisation absorbers, pulp bleaching and chemical process equipment where 316L and 317L are pitting but a six-molybdenum alloy cannot be justified. The nitrogen strengthening is a genuine bonus rather than a side effect: at the same wall thickness the vessel takes more pressure, so the uprating is not purely a corrosion decision.
Against 317L: Availability and the size of the step. Four points of pitting ranking is a modest gain for a grade that many stockists do not hold in every form, and where the service is genuinely aggressive it is not enough. In practice the decision is usually between staying at 316L and jumping to a super-austenitic or a duplex, with 317L squeezed in between.
Against 317LMN: Stock and the size of the gap it fills. Few distributors hold it in every form, and the band between 317L and 254 SMO is narrow enough that many projects step straight over it. High molybdenum also makes it prone to sigma phase, so welding needs controlled heat input and procedure qualification, which erodes the saving against a super-austenitic.
What this comparison does not cover
- Only plate minima are established here; sheet and hot rolled are not.
- Critical pitting temperature, which is what separates this grade from 316L in service.
- Elevated temperature strength, fatigue and fracture toughness.
- Composition limits, not established.
- Crevice corrosion, which the pitting ranking number does not predict.
- Critical pitting temperature is not established here, and the pitting ranking number is a poor substitute in this band.
- Only cold rolled minima are carried; plate figures differ and are named in the notes rather than tabulated.
- Welding heat input limits and sigma phase risk.
Generated from data/materials/317l.yaml and 317lmn.yaml.