What is the difference between SS 317 and SS 317L flanges?

SS 317 (UNS S31700) has a maximum carbon content of 0.080%, while SS 317L (UNS S31703) limits carbon to 0.030%. The low carbon in 317L prevents chromium carbide precipitation at grain boundaries during welding (sensitisation), making 317L the preferred choice for flanges that will be welded in the field. Mechanical properties are virtually identical: UTS 515 MPa min, Yield 205 MPa min. For flanges used as-forged without welding, either grade is acceptable.

What is the PREN of SS 317L and how does it compare to 316L?

Pitting Resistance Equivalent Number (PREN) = %Cr + 3.3×%Mo + 16×%N. For SS 317L (typical mid-composition): PREN ≈ 19 + 3.3×3.5 + 16×0.08 ≈ 32. For SS 316L (typical): PREN ≈ 17 + 3.3×2.25 + 16×0.05 ≈ 25. This ~7-point advantage means SS 317L can resist chloride pitting in significantly more aggressive environments than SS 316L.

What ASTM standard covers SS 317L flanges?

SS 317L flanges are manufactured to ASTM A182 Grade F317L for forgings. The dimensional standard is ASME B16.5 (Class 150–2500, ½″–24″ NB) or ASME B16.47 (large diameter, 26″–60″ NB). The chemical composition and mechanical properties are governed by ASTM A182. Material certification is supplied per EN 10204 3.1.

What is the equivalent grade of SS 317L in European (DIN/EN) standards?

SS 317L (UNS S31703) is equivalent to EN/DIN 1.4438 (X2CrNiMo18-15-4). SS 317 (UNS S31700) is equivalent to EN/DIN 1.4449 (X5CrNiMo17-13-4). The Japanese equivalent is SUS317L (JIS G4303). All three designations refer to the same alloy family with 3–4% Mo, 18–20% Cr, and 11–15% Ni.

What is the minimum wall temperature for SS 317L flanges?

SS 317L is an austenitic stainless steel and retains excellent toughness at cryogenic temperatures without impact testing — suitable for service down to −196°C (−320°F). Per ASME B16.5, SS 317L flanges (Material Group 2.2) may be used at temperatures from −196°C to +538°C. For temperatures above 425°C in oxidising conditions, use stabilised grades (321, 347) to avoid sensitisation in the standard 317 grade.

Where are SS 317 / 317L flanges used instead of SS 316L?

SS 317/317L flanges are specified over SS 316L when the environment is more aggressive: (1) sulphuric acid plants — especially dilute H₂SO₄ (10–70%) at elevated temperature; (2) phosphoric acid processing; (3) flue gas desulphurisation (FGD) wet scrubbers where SO₂ + chlorides are present; (4) Kraft pulp bleach plants (chlorine dioxide environments); (5) seawater services with higher chloride concentration where 316L does not meet minimum PREN requirements; (6) chemical processing with combined chloride + acidic conditions.

What filler wire is used for welding SS 317L flanges?

SS 317L flanges are welded using ER317L filler wire (AWS A5.9 / ISO 14343). This low-carbon filler matches the base material chemistry and prevents weld metal sensitisation. Post-weld heat treatment (PWHT) is not required for 317L. Inter-pass temperature should be kept below 175°C (350°F) to prevent sensitisation and preserve corrosion resistance. For flanges that will be seal-welded or nozzle-welded, ER317L is the mandatory filler for any acidic or chloride service.

What is the maximum allowable stress for SS 317L flanges at 100°C?

Per ASME Section II Part D, the allowable stress (S) for UNS S31703 (SS 317L) at 100°C (212°F) is approximately 115 MPa (16.7 ksi). At ambient temperature (38°C), S = 115 MPa. At 200°C (392°F), S = 109 MPa. At 300°C (572°F), S = 98 MPa. These values are used for pressure vessel and heat exchanger nozzle flange design. For piping, ASME B16.5 pressure class ratings govern flange selection rather than individual allowable stress calculations.

Is SS 317L better than SS 316L for sulphuric acid service?

Yes. The higher molybdenum content in SS 317L (3–4% Mo vs 2–3% in 316L) significantly improves resistance to reducing acids, including sulphuric acid. SS 317L performs well in dilute to moderate concentrations of H₂SO₄ (up to approximately 50–60% at ambient temperature). At higher concentrations (>70%) or elevated temperatures, even 317L may be insufficient and alloys like Hastelloy C276 or Alloy 20 are needed. For mild H₂SO₄ service (below 30% at <60°C), either 316L or 317L is adequate; for more demanding acid concentrations, 317L is clearly preferred.

SS 317 / 317L Stainless Steel Flanges Manufacturer in India

SS 317L flanges manufacturer supplier India — UNS S31703

ASTM A182 F317L flange manufacturer — 1.4438 stainless steel

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What is SS 317 / 317L Stainless Steel?

Stainless Steel 317 (UNS S31700, EN 1.4449) and Stainless Steel 317L (UNS S31703, EN 1.4438) are austenitic stainless steels in the 300-series family — the direct upgrade from SS 316L when a more corrosion-resistant grade is required. The defining characteristic of both grades is their elevated molybdenum content of 3–4%, compared to 2–3% Mo in SS 316L. This additional 1% Mo produces a measurable improvement in resistance to chloride pitting, crevice corrosion, and reducing acids.

The key difference between 317 and 317L is carbon content. 317L limits carbon to ≤ 0.030% — the "L" (low carbon) designation — making it immune to sensitisation during welding. This is why 317L is the universally preferred grade for flanges and piping that will be field-welded. Standard 317 (C ≤ 0.080%) is occasionally used where welding is not required.

Tesco Steel & Engineering manufactures SS 317 / 317L flanges per ASTM A182 F317 / F317L and ASME B16.5, in all flange types from Weld Neck to Blind, in Class 150 to Class 2500. All flanges are supplied with EN 10204 3.1 Mill Test Certificates. Third-party inspection (EN 10204 3.2) is available on request.

The 317L Advantage: SS 317L has a Pitting Resistance Equivalent Number (PREN) of approximately 31–34 vs approximately 24–27 for SS 316L. This ~7-point gap is why SS 317L is the correct choice for sulphuric acid plants, FGD wet scrubbers, bleach plants, and any chloride-containing acidic process where SS 316L has proven inadequate.

Chemical Composition — SS 317 vs 317L vs 316L

Element	SS 317 (S31700 / 1.4449)	SS 317L (S31703 / 1.4438)	SS 316L (S31603) — for comparison	Role in Alloy
Carbon (C)	≤ 0.080%	≤ 0.030%	≤ 0.030%	Low C prevents sensitisation during welding
Chromium (Cr)	18.0 – 20.0%	18.0 – 20.0%	16.0 – 18.0%	Passive film formation, oxidation resistance
Nickel (Ni)	11.0 – 15.0%	11.0 – 15.0%	10.0 – 14.0%	Austenite stabiliser, SCC resistance
Molybdenum (Mo)	3.0 – 4.0%	3.0 – 4.0%	2.0 – 3.0%	Key differentiator — pitting & crevice corrosion resistance
Manganese (Mn)	≤ 2.00%	≤ 2.00%	≤ 2.00%	Austenite stabiliser
Silicon (Si)	≤ 1.00%	≤ 1.00%	≤ 1.00%	Deoxidiser
Phosphorus (P)	≤ 0.045%	≤ 0.045%	≤ 0.045%	Residual element — kept low for toughness
Sulphur (S)	≤ 0.030%	≤ 0.030%	≤ 0.030%	Residual element — low S improves corrosion resistance
Nitrogen (N)	≤ 0.10%	≤ 0.10%	≤ 0.10%	Strengthens austenite, increases PREN

Mechanical Properties — ASTM A182 F317 / F317L

Property	SS 317 (F317)	SS 317L (F317L)	Unit
Tensile Strength (UTS)	515 min	515 min	MPa (74.7 ksi)
Yield Strength (0.2% offset)	205 min	205 min	MPa (29.8 ksi)
Elongation in 2 inch	30 min	30 min	%
Reduction in Area	50 min	50 min	%
Hardness (max)	217 HB / 96 HRB	217 HB / 96 HRB	Brinell / Rockwell B
Density	8.0	8.0	g/cm³
Modulus of Elasticity	193	193	GPa
ASME B16.5 Material Group	2.2	2.2	—

SS 317L vs 316L vs 317LMN — Grade Comparison

SS 316L — When It Is Sufficient

Mild aqueous chloride environments (<200 ppm Cl⁻ at ambient temp)
Dilute acids at low temperature
Food, pharma, general chemical service
PREN ~25 — adequate for moderate service
Lower cost than 317L (~15–25% cheaper)

SS 317L — When 316L Is Not Enough

Dilute–moderate H₂SO₄ (10–60%) service
Phosphoric acid processing
FGD wet scrubbers (SO₂ + chlorides)
Kraft pulp bleach plants
PREN ~32 — clearly better for aggressive environments

Property	SS 316L (S31603)	SS 317L (S31703)	SS 317LMN (S31726)
Mo content	2.0–3.0%	3.0–4.0%	4.0–5.0%
Cr content	16.0–18.0%	18.0–20.0%	17.0–20.0%
N content	≤ 0.10%	≤ 0.10%	0.10–0.20%
Typical PREN	~25	~32	~36
UTS (MPa)	515 min	515 min	515 min
Yield (MPa)	205 min	205 min	240 min (N-strengthened)
H₂SO₄ resistance	Adequate for dilute, mild conditions	Good for dilute–moderate concentrations	Excellent — near 904L performance
Relative cost	Baseline	~20% above 316L	~35% above 316L
ASTM Forging Grade	A182 F316L	A182 F317L	A182 F317LMN

SS 317 / 317L Flange Types & Specifications

Flange Type	Standard	Size Range	Pressure Class	Typical Application
Weld Neck	ASME B16.5	½″ – 24″ NB	150 – 2500	High-pressure process piping, acid plant headers
Slip-On	ASME B16.5	½″ – 24″ NB	150 – 600	Low-pressure headers, FGD ductwork connections
Blind	ASME B16.5	½″ – 24″ NB	150 – 2500	Line isolation, tank/vessel manholes
Socket Weld	ASME B16.5	½″ – 4″ NB	150 – 2500	Instrument connections, small-bore corrosive service
Threaded	ASME B16.5	½″ – 4″ NB	150 – 2500	Gauge connections, instrument taps
Lapped Joint	ASME B16.5	½″ – 24″ NB	150 – 2500	Systems requiring frequent dismantling, stub end connections
Long Weld Neck	ASME B16.5 / B16.47	½″ – 24″ NB	150 – 2500	Pressure vessel nozzles, reactor flanges
Spectacle Blind	ASME B16.48	½″ – 24″ NB	150 – 1500	Line isolation / bypass in acid process systems
Orifice Flanges	ASME B16.36	1″ – 16″ NB	300 – 2500	Flow measurement in corrosive acid lines
Plate / Flat Flanges	DIN 2573 / EN 1092-1	DN 15 – DN 600	PN 6 – PN 100	European piping, pump connections

Corrosion Resistance of SS 317L Flanges

Corrosive Environment	SS 316L Performance	SS 317L Performance	Notes
Sulphuric Acid H₂SO₄ (dilute, <30% at <60°C)	Acceptable	Good	317L preferred; higher Mo reduces corrosion rate
Sulphuric Acid H₂SO₄ (30–60% at <60°C)	Marginal/Insufficient	Acceptable	317L significantly outperforms 316L; check corrosion data
Phosphoric Acid H₃PO₄ (up to 85%)	Acceptable (impure)	Good	317L preferred for wet-process phosphoric acid
Nitric Acid HNO₃ (dilute)	Good	Good	Both adequate; 304L also acceptable for nitric acid only
Hydrochloric Acid HCl (any conc.)	Not recommended	Not recommended	Use Hastelloy C276 or Titanium Gr.2 for HCl service
Chloride pitting (seawater, brines)	Moderate (PREN ~25)	Better (PREN ~32)	317L suitable for higher chloride concentrations than 316L
Crevice corrosion (chloride environments)	Moderate risk at >40°C	Lower risk — higher Mo	T&G face type reduces crevice risk at gasket face
Stress Corrosion Cracking (chloride SCC)	Susceptible (>60°C)	Susceptible (>60°C)	Both are austenitic — use duplex or nickel alloy for SCC service
Caustic (NaOH, KOH) — dilute	Good	Good	Both suitable for dilute caustic; avoid concentrated hot caustic
FGD wet scrubbers (SO₂ + Cl⁻ + H₂O)	Insufficient	Good	317L is standard specification for FGD scrubber flanges
Pulp bleach plant (ClO₂, Cl₂)	Insufficient	Good	317L standard in Kraft bleach sequence flanges

Welding SS 317L Flanges

Parameter	SS 317 (Standard Carbon)	SS 317L (Low Carbon)
Filler wire (AWS A5.9)	ER317 or ER317L	ER317L (mandatory for corrosive service)
Electrode (AWS A5.4)	E317-16 / E317-15	E317L-16 / E317L-15
Preheat required	None	None
Post-Weld Heat Treatment (PWHT)	May be required for thick sections	Not required — low C prevents sensitisation
Max inter-pass temperature	175°C (350°F)	175°C (350°F)
Sensitisation risk	Present for C ≤ 0.080% at 425–870°C	Negligible — low C prevents Cr₂₃C₆ precipitation
Weld process	GTAW, GMAW, SMAW, SAW	GTAW, GMAW, SMAW, SAW
Shielding gas	Argon or Ar/He mix	Argon or Ar/He mix

Applications of SS 317 / 317L Flanges by Industry

Industry	Application	Why 317L Over 316L
Sulphuric Acid Plants	Absorber tower flanges, weak acid condensers, dilution system piping	Higher Mo resists dilute-to-moderate H₂SO₄ corrosion rates
Phosphoric Acid Processing	Wet-process phosphoric acid plant pipe flanges, evaporator nozzles	317L handles impure phosphoric acid where 316L corrodes
FGD / Flue Gas Desulphurisation	Wet scrubber inlet/outlet flanges, absorber nozzles, slurry piping	SO₂ + Cl⁻ environment demands PREN >30
Pulp & Paper / Kraft	Bleach plant flanges, ClO₂ generator connections, white liquor headers	Chlorine dioxide and oxidising bleach chemicals attack 316L
Chemical Processing	Mixed acid reactors, chloride + acid combined service, pharmaceutical intermediates	Broader corrosion resistance across mixed environments
Petrochemical	Sour crude fractionation, amine scrubbing units, acetic acid plants	Mild reducing acid + some chloride presence requires PREN >30
Marine & Offshore	Seawater pipe flanges, offshore process headers, desalination pre-treatment	Higher PREN reduces pitting risk in warm seawater (>35°C)
Food & Beverage	Acidic food processing lines, CIP systems with acidic cleaning agents	Better resistance to organic acid + cleaning chemical combinations
Power Generation	Condenser water boxes, cooling water flanges with seawater	Higher Mo prevents pitting in chloride-bearing cooling water

Standards & Specifications for SS 317 / 317L Flanges

Category	Standard	Scope
Flange Dimensions	ASME B16.5	Pipe flanges Class 150–2500, ½″–24″ NB
Flange Dimensions	ASME B16.47 Series A & B	Large diameter flanges, NPS 26–60
Flange Dimensions	EN 1092-1	European metric flanges, PN 2.5–400
Flange Dimensions	MSS SP-44	Steel pipeline flanges
Material — Forgings	ASTM A182 F317 / F317L	Stainless steel forgings for piping — standard flange material specification
Material — Bar	ASTM A276 / A479	SS 317/317L bar for machined or small-bore flanges
Material — Plate	ASTM A240 Type 317 / 317L	Plate for slip-on and plate flanges
Material — European	EN 10222-5	Steel forgings for pressure vessels — 1.4449 (317) / 1.4438 (317L)
Material — Japanese	JIS G4303	SUS317 / SUS317L stainless steel bar
Inspection	EN 10204 3.1 / 3.2	Material test certificate — works (3.1) or TPI witness (3.2)
Piping Code	ASME B31.3	Process piping — 317L in Material Group 2.2
Weld Filler	AWS A5.9 ER317L	Bare wire for GTAW/GMAW welding of 317L flanges
Weld Electrode	AWS A5.4 E317L-16	Covered electrode for SMAW welding of 317L flanges

SS 317 / 317L Grade Cross-Reference

Standard	SS 317 Designation	SS 317L Designation
UNS (USA)	S31700	S31703
ASTM A182 (USA)	F317	F317L
EN / DIN (Europe)	1.4449 / X5CrNiMo17-13-4	1.4438 / X2CrNiMo18-15-4
JIS (Japan)	SUS317	SUS317L
BS (UK)	317S16	317S12
Common trade name	SS 317	SS 317L

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Quick Specifications

Grade	SS 317 / SS 317L
UNS	S31700 / S31703
EN / DIN	1.4449 / 1.4438
ASTM Forging	A182 F317 / F317L
Mo Content	3.0 – 4.0%
Typical PREN	~32 (vs ~25 for 316L)
UTS	515 MPa min
Yield	205 MPa min
Temp Range	−196°C to +538°C
B16.5 Group	Material Group 2.2
Filler Wire	ER317L
PWHT	Not required (317L)
Cert	EN 10204 3.1 / 3.2

Choose 317L Over 316L When:

Dilute–moderate H₂SO₄ (>10%) service
Phosphoric acid plants
FGD wet scrubber systems
Kraft pulp bleach plant piping
Chloride concentration exceeds 316L limits
Combined chloride + acid environments
PREN requirement > 28

SS Grades — Compare

317L Flange Types

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Testing & Inspection

Chemical composition (OES / XRF)
Tensile and hardness testing
Dimensional inspection per B16.5
Intergranular corrosion test (ASTM A262 Practice E)
Pitting corrosion test (ASTM G48)
Dye penetrant (PT) inspection
Hydrostatic test on request
PMI (XRF) — Mo content verification
EN 10204 3.1 / 3.2 MTCs