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TP317L seamless stainless steel pipe and tube (UNS S31703, EN 1.4438, DIN X2CrNiMo19-14-4) is a low-carbon austenitic alloy designed for superior resistance to pitting, crevice corrosion, and intergranular attack in chloride-rich environments. Composed of 18-20% chromium, 12-15% nickel, 3-4% molybdenum, and ≤0.03% carbon, it builds on the base of 316L by increasing molybdenum content and reducing carbon, eliminating carbide precipitation risks in welded components. Manufactured via seamless extrusion and cold-drawing to meet ASTM A312 and ASME SA312, it offers uniform wall thickness and a smooth bore for optimal flow characteristics.
The extra molybdenum (4% vs. 2% in 316L) elevates its Critical Pitting Temperature (CPT) to 60°C, making it suitable for more aggressive chloride solutions than standard 300-series steels.
Enhanced Chloride Resistance: Resists pitting in 10,000 ppm Cl⁻ at 60°C and crevice corrosion under gaskets in 5,000 ppm Cl⁻ + 1,000 ppm Fe³⁺, outperforming 316L in stagnant saline environments.
Intergranular Corrosion Immunity: Ultra-low carbon (≤0.03%) prevents chromium carbide formation at grain boundaries, even after sensitization at 650°C for 2 hours.
High-Temperature Performance: Maintains ductility up to 800°C and resists oxidation in intermittent service up to 900°C, suitable for steam sterilization and furnace applications.
Excellent Weldability: Can be welded using all standard methods with 317L filler metal; no post-weld heat treatment is required, though rapid cooling minimizes sigma phase formation.
Marine Desalination: Used in seawater pre-treatment systems, RO membrane housings, and brine discharge pipelines, enduring 35,000 ppm Cl⁻ at 40°C.
Chemical Processing: Ideal for fatty acid distillation columns, soap manufacturing reactors, and pipelines handling sodium hypochlorite (bleach).
Food & Beverage (High-Salt): Employed in cheese brining vats, pickle processing lines, and equipment cleaned with chlorinated alkaline solutions.
Power Generation: Suitable for condenser tubes in coastal power plants and wastewater treatment heat exchangers exposed to chloride-laden cooling water.
Q: How does TP317L differ from TP316L?
A:317L has higher molybdenum (4% vs. 2%) and nitrogen (0.1% vs. trace), increasing PREN (Pitting Resistance Equivalent Number) from 32 to 40, making it 25% more resistant to chloride pitting.
Q: Can TP317L be used in hydrofluoric acid?
A:No, molybdenum reacts with HF; use nickel-copper alloys like Monel 400 or Hastelloy B3 for HF service.
Q: What is the recommended heat treatment for TP317L?
A:Solution annealing at 1050-1150°C followed by water quenching to dissolve any intermetallic phases and optimize corrosion resistance.
Q: Is TP317L magnetic?
A:No, it remains non-magnetic in its as-welded and annealed states, though heavy cold working may induce slight magnetism (≤5% permeability).
317L (UNS S31703) is a low carbon corrosion resistant austenitic chromium-nickel-molybdenum stainless steel. The high levels of these elements assure the steel has superior chloride pitting and general corrosion resistance to the conventional 304/304L and 316/316L grades. The steel provides improved resistance relative to 316L in strongly corrosive environments containing sulfurous media, chlorides, and other halides.
The low carbon content of 317L enables it to be welded without intergranular corrosion resulting from chromium carbide precipitation enabling it to be used in the as-welded condition.
The grade 317L is non-magnetic in the annealed condition. It cannot be hardened by heat treatment; however the material will harden due to cold working. 317L can be easily welded and processed by standard shop fabrication practices.
