SS 317 / 317L
Fasteners
Manufacturer India
SS 317/317L — One More Percent of Mo Changes the Application
SS 317 (UNS S31700) and SS 317L (UNS S31703) are the higher-molybdenum variants of the 316/316L austenitic stainless family. The only structural difference between 317L and 316L is molybdenum: 317L contains 3.0–4.0% Mo vs 316L’s 2.0–3.0% Mo. This single alloy change raises the Pitting Resistance Equivalent (PRE) from approximately 24 (316L) to approximately 28 (317L) — a meaningful step up for applications at the upper edge of 316L’s corrosion capability.
The applications where the extra 1% Mo makes a decisive difference: pulp and paper bleach plant where chloride concentrations fluctuate and 316L shows borderline pitting performance; FGD (flue gas desulphurisation) scrubbers where the combination of SO₂, Cl⁻, and moisture attacks 316L preferentially; dilute sulphuric acid and sulphite pulping liquors where the additional Mo passivates the alloy surface more effectively; and pharmaceutical and food processing applications where 316L is specified but trace chloride or sulphate contamination is suspected.
317 vs 317L selection: The “L” designation indicates low carbon — ≤0.030% C for 317L vs ≤0.080% C for standard 317. Low carbon prevents chromium carbide precipitation at the heat-affected zone during welding, eliminating sensitisation and intergranular corrosion risk. 317L is the standard specification for most fastener applications — the weld zone and HAZ corrosion risk of standard 317 is eliminated by specifying 317L. Standard 317 is used only where carbon content is not a concern — non-welded, non-thermally-cycled service.
Compared with SS 904L (PRE≈36): 317L is the correct choice when the service environment is close to the 316L failure boundary but does not require the full PRE≈36 of 904L. 904L has significantly higher Ni (23–28% vs 317L’s 11–15%) and contains copper — both add cost that may not be justified if PRE≈28 is sufficient. 317L is typically 30–50% lower cost than 904L on a per-kg basis.
Compared with Duplex 2205 (PRE≈35): for applications where PRE is the primary criterion and strength is a secondary benefit, Duplex 2205 often replaces both 317L and 904L in modern plant design — its higher strength (≥620 MPa vs 317L’s ≥515 MPa) is an additional benefit. However, duplex is not preferred in all austenitic stainless specifications, and 317L remains the correct austenitic choice when duplex is not acceptable.
PMI XRF verification is important for 317L because the Mo content (3–4%) must be confirmed above the 316L maximum (3%). XRF can distinguish 317L from 316L by Mo content — a critical QC step since 317L and 316L are visually identical and priced differently. All Akbar Fasteners 317L bar stock is PMI-verified before machining to confirm Mo ≥3.0%.
SS 317 · 317L · 316L — Composition Comparison
The single alloy difference that separates 317L from 316L is molybdenum — 3.0–4.0% vs 2.0–3.0%. The carbon limit separates 317 from 317L — ≤0.030% vs ≤0.080%. All three grades available from Akbar Fasteners from certified ASTM bar stock.
SS 316L
SS 317L
SS 317
317L PRE≈28 — Position in the SS Ladder
317L sits between 316L and 904L in the stainless PRE hierarchy. One step above 316L, one step below 904L, and comparable to Duplex 2205 in pitting resistance but with lower strength. PRE = %Cr + 3.3×%Mo + 16×%N.
317 / 317L Fastener Types & Standards
317L is the stocking grade (low-carbon, weld-safe). Standard 317 available on order. All forms from ASTM A193 certified S31703/S31700 bar stock, PMI-verified before machining. Matched heat supply available.
317L Stud Bolts
Fully threaded stud bolts in 317L for ASME B16.5 pressure flanges in pulp and paper bleach plant, FGD scrubbers, and dilute H₂SO₄ service where 316L B8M stud bolts are failing. Class 150–600, M12–M100, lengths to 3,000mm. Matched heavy hex nuts (ASTM A194 Grade 8MN) from same certified heat on request.
Hex Bolts
Full thread and partial thread hex bolts in 317L. M6–M100. Pulp and paper digester equipment cover bolts, FGD absorber ductwork connections, bleach plant equipment structural bolts, and all chemical plant applications where 316L hex bolt pitting is the documented failure mode and a simple Mo step-up resolves the problem without moving to exotic alloy.
Hex Nuts
Standard hex and heavy hex nuts in 317L. M6–M100. ASTM A194 Grade 8MN (317L) is the matching nut for ASTM A193 B8MN stud bolts — the standard 317L stud bolt assembly combination. Matched from same certified S31703 heat for single MTC. All from PMI-verified ASTM A194 bar stock confirming Mo ≥3.0%.
Washers
Plain flat and spring helical washers in 317L. M5–M100. Matched-grade washers for complete 317L stud bolt assembly in pulp and paper, FGD, and sulphite process equipment — one MTC covers stud bolt, nut, and washer from the same S31703 certified bar stock heat.
Threaded Rods
Full thread and end-thread in 317L. M6–M100, lengths to 3,000mm. Pulp and paper hanger systems, FGD ductwork structural rods, bleach plant structural tie-rods, and chemical plant equipment support rods where 316L threaded rod pitting has been observed and a direct grade substitution to 317L is the preferred remediation approach.
Socket Cap Screws
Hex socket cylindrical head in 317L. M4–M30. Bleach plant heat exchanger baffle screws, FGD absorber internal fixtures, sulphite process equipment internal connections, and instrument flange screws where 316L socket cap screw pitting is a recurring maintenance problem resolved by 317L’s additional Mo content.
Matched Assembly Sets
317L stud bolts + ASTM A194 Grade 8MN heavy hex nuts + 317L washers from the same S31703 certified bar heat. Single MTC, PMI report, and COC for the complete stud bolt assembly — simplified TPI documentation for pulp and paper and FGD EPC projects specifying 317L as a direct 316L substitute where pitting has occurred.
Custom 317L
Non-standard AF dimensions, inch UNC/UNF thread, fine pitch, flanged hex (DIN 6921), coupling nuts (DIN 6334), and drawing-specific configurations in 317L. Contact sales@akbarfasteners.in with your drawing, thread pitch, and documentation requirement.
317L Grade Selection Matrix
317L is the incremental upgrade from 316L — one additional percent of Mo. The correct choice when 316L fails or is marginal and the full PRE≈36 of 904L is not yet justified by the corrosion environment.
| Environment / Criterion | SS 317L This Page | SS 316L | SS 904L | Duplex 2205 |
|---|---|---|---|---|
| CORROSION RESISTANCE | ||||
| PRE (Pitting Index) | ≈28 | ≈24 | ≈36 | ≈35 |
| Pulp & paper bleach plant (Cl⁻ fluctuating) | ✔ Standard grade | Marginal pitting risk | Better | Better |
| FGD scrubber (SO₂ + Cl⁻ + moisture) | ✔ Upgrade from 316L | Borderline failure | Better | Better |
| Dilute H₂SO₄ (5–20% ambient) | ✔ Good | Marginal | Better (with Cu) | Good |
| Moderate Cl⁻ seawater (intermittent) | Good | Pitting risk | Better | ✔ Preferred |
| Weld zone IGC resistance (317L) | ✔ 317L ≤0.030% C | ✔ 316L ≤0.030% C | ✔ ≤0.020% C | ✔ Low C duplex |
| COST & AVAILABILITY | ||||
| Relative cost vs 316L | 1.3–1.6× 316L | Baseline 1× | 3–4× 316L | 1.5–2× 316L |
| Availability (India stocking) | Good availability | ✔ Widest stock | Limited stock | Good availability |
| Best application position | 316L fails; 904L unjustified | Standard corrosion | When 317L insufficient | Strength + corrosion |
If 317L insufficient: SS 904L (PRE≈36) · Incoloy 825 · Hastelloy C276
317L Application Areas
Applications where 316L pitting is the observed failure mode and the extra Mo in 317L provides the needed corrosion margin without requiring exotic alloy.
Pulp & Paper
sulphite digester bolts
FGD Systems
absorber structural fasteners
Dilute H₂SO₄
acid mine drainage flanges
Chemical Processing
sulphite compound service
Coastal / Marine
PRE≈28 marine bolts
Power Generation
scrubber ductwork fasteners
Food Processing
cleaning-in-place flanges
Water Treatment
slightly elevated Cl⁻ flanges
317 / 317L Standards Coverage
Same ISO 9001:2015 quality system as our complete stainless steel fastener range. PMI XRF confirms Mo ≥3.0% before machining — the critical distinction from 316L.
Complete Documentation Package
S31703 Traceable
Conformance
317L Confirmed
Tensile · Hardness
TÜV · BV · Lloyds
Related Fastener Grades
316L below 317L. 904L above 317L. Duplex 2205 an alternative. Hastelloy C276 for aggressive mixed acid.
SS 316L Fasteners
The baseline stainless grade below 317L. When service conditions are within 316L’s PRE≈24 capability — food, pharma, standard chemical, marine deck — 316L is the correct and lower-cost choice. Specify 317L only when 316L pitting is documented.
View SS Range →SS 904L Fasteners
When 317L’s PRE≈28 is still insufficient — 904L’s higher Ni, Mo (4–5%), and Cu give PRE≈36 with specific H₂SO₄ resistance that 317L’s Mo alone does not provide. The next logical step when 317L fails in sulphuric acid or high-chloride service.
View 904L Page →Duplex 2205 / 2507
An alternative to 317L at similar cost — Duplex 2205 (PRE≈35) provides comparable pitting resistance to 904L with higher mechanical strength (≥620 MPa). Where additional strength is valued alongside the PRE improvement over 316L, Duplex 2205 is the preferred modern choice.
View SS Range →Hastelloy C276 Fasteners
When the corrosion environment exceeds all stainless steel grades — aggressive H₂SO₄, mixed acids, or hot concentrated FGD where Duplex and 904L also fail. Hastelloy C276’s PRE≈66 and Ni-Cr-Mo alloy chemistry provide the next level of corrosion resistance.
View C276 Page →Need SS 317 or
317L Fasteners?
Grade (317 or 317L) · product form · size · quantity · matched stud set requirement · documentation. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
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