347H Stainless Steel Seamless Pipe ASTM A312 DN10-DN400

Alloy 347H Stainless Steel Tubing / ASTM A312 Austenitic Stainless Pipes TP347H for Industrial

Products Specification

Introduction of 347H Stainless Steel
I. Material Overview
347H (UNS S34709) is a niobium-stabilized austenitic stainless steel. By adding the niobium (Nb) element, it significantly enhances the resistance to intergranular corrosion, making it a core material for high-temperature and high-pressure environments. Its composition is based on chromium (17%-19%) and nickel (9%-13%), supplemented by niobium (≥10×C%), forming a stable niobium carbide (NbC) structure. This effectively prevents chromium carbides from precipitating at grain boundaries and avoids stress corrosion cracking. This material maintains organizational stability in the range of -196℃ to 850℃ and has both high strength and oxidation resistance, suitable for severe working conditions such as power station boilers and chemical reactors.
II. Core Performance Advantages
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High-temperature mechanical properties
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Strength and plasticity balance: At room temperature, the tensile strength is≥515 MPa, the yield strength is≥205 MPa, and the elongation is≥35%. At high temperatures of 600°C, the allowable stress remains above 100 MPa, which is better than conventional austenitic steels such as 304H in terms of creep resistance. The creep rupture strength is about 15% higher than that of 321H during long-term service at 550-700°C, suitable for supercritical power station steam pipes (design temperature 482°C/pressure 20.55 MPa).
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Corrosion and oxidation resistance
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Intergranular corrosion protection: The niobium element preferentially combines with carbon to suppress chromium depletion and resist corrosion by media such as nitric acid and acetic acid after welding or long-term heating below 650°C. High-temperature oxidation protection: The chromium oxide film is stable in air at 750-800°C, and the oxidation limit is 850°C (non-pressurized components), suitable for boiler superheater tubes.
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Processing and welding performance
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Cold and hot processing adaptability: Supports processes such as forging and rolling, but cold forming requires control of work hardening (multi-pass forming + intermediate annealing is recommended). Welding process optimization: It is recommended to use niobium-stabilized welding materials (such as ER347H) and use TGF-347 argon-free welding wire to improve efficiency. Thick-walled weldments require strict temperature control to avoid reheat cracking.
III. Key Heat Treatment Process
Heat treatment is a critical link to ensure the performance of 347H:
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Solution treatment: Heat at 980-1150°C and then quickly cool to dissolve carbides and obtain a single austenite structure.
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Stabilization treatment: For welded parts, keep at 890-910°C for insulation (constant temperature time≥50 hours) to promote the complete precipitation of NbC and eliminate residual stress. Note: Pipes with wall thicknesses greater than 37mm are prone to cracking due to thermal stress and require control of heating uniformity.
IV. Typical Application Fields
Field
Application scenario
Performance requirements
Power industry
Supercritical boiler superheater tubes (Φ51×8mm), reheater tubes, main steam pipes
High-temperature strength, oxidation resistance, and resistance to intergranular corrosion
Chemical industry
Chemical reactors and other equipment
Corrosion resistance to various media
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347H stainless steel, with its excellent performance, is widely used in various fields and plays an important role in modern industrial production