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When should SS 317L be used instead of SS 316L?
Short answer
Use SS 317L when SS 316L starts to pit or crevice-corrode, typically in flue-gas desulphurisation, pulp bleaching and more aggressive acid or chloride streams. SS 317L raises molybdenum to 3–4% and lifts PREN from about 24 to about 29, a modest step up before duplex or 6Mo grades.
SS 316L vs SS 317L at a glance
| Property | SS 316L | SS 317L |
|---|---|---|
| UNS | S31603 | S31703 |
| EN | 1.4404 | 1.4438 |
| Family | Austenitic stainless steel | Austenitic stainless steel |
| C (%) | 0.030 max | 0.030 max |
| Cr (%) | 16.0 – 18.0 | 18.0 – 20.0 |
| Ni (%) | 10.0 – 14.0 | 11.0 – 15.0 |
| Mo (%) | 2.00 – 3.00 | 3.0 – 4.0 |
| N (%) | 0.10 max | 0.10 max |
| Tensile strength | 485 MPa (70 ksi) | 515 MPa (75 ksi) |
| Yield strength | 170 MPa (25 ksi) | 205 MPa (30 ksi) |
| PREN | 23 – 25 | 28 – 30 |
| Density | 8 g/cm³ | 8 g/cm³ |
| Magnetic | Essentially non-magnetic when annealed; cold work can make it slightly magnetic. | Essentially non-magnetic when annealed; cold work can make it slightly magnetic. |
| Typical use | Chemical and fertiliser process piping | FGD scrubbers and absorber towers |
Which should you choose?
There's no universal "winner": the right choice depends on service conditions, codes and cost. Share your conditions with us for a recommendation.
Knowing when SS 317L is not enough
If the chloride level and temperature put SS 316L far outside its limits, SS 317L will only buy a little time. In those cases, jump to 2205, SS 904L or 6Mo, as explained in our PREN guide.
Availability
SS 317L is less widely stocked than SS 316L, especially in fittings and flanges, so lead times and minimum quantities should be checked early on projects.
Products in both grades
Related guides, comparisons and articles
Frequently asked questions
Is SS 317L weldable?
Yes, with SS 317L or higher-alloyed filler to keep the weld molybdenum at least equal to the base metal.
What is the UNS number of SS 317L?
UNS S31703.
What is the main difference between SS 316L and SS 317L?
SS 317L raises molybdenum to 3–4% and chromium and nickel slightly, lifting PREN from about 24 to about 29. It's the usual next step when SS 316L shows pitting.
When should I choose SS 316L?
Standard chloride and chemical service.
When should I choose SS 317L?
FGD, pulp bleach and more aggressive acid or chloride streams.
Can SS 316L replace SS 317L?
Only when the design, code and specification allow it. Strength, corrosion resistance and temperature limits differ, so substitution must be approved by the design authority.
Which has better pitting resistance, SS 316L or SS 317L?
Typical PREN: SS 316L 23 – 25, SS 317L 28 – 30. A higher PREN generally means better chloride pitting resistance.