ASTM A312 TP347H Stainless Steel Pipe
ASTM A312 TP347H Stainless Steel Pipe - High-Carbon Niobium-Stabilized Austenitic Grade
Explore ASTM A312 TP347H, a high-carbon niobium-stabilized austenitic stainless steel designed for elevated-temperature service. Details include chemical composition, mechanical and physical properties, international equivalents, and application guidelines.
Hot working, cold working, welding (all common processes), heat treatment (solution annealing), machining
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ASTM A312 TP347H Stainless Steel Pipe Introduction
ASTM A312 TP347H is an austenitic chromium-nickel stainless steel with additions of niobium and tantalum for stabilization against intergranular corrosion. The "H" designation indicates a higher carbon content (0.04–0.10%), which enhances creep strength at temperatures above 540°C (1000°F). This grade is widely used in the form of seamless and welded pipe for high-temperature applications such as boiler tubes, superheater and reheater sections, and heat exchangers in power plants and petrochemical refineries. The material is typically supplied in solution-annealed condition and offers good oxidation resistance, excellent weldability, and stability in carburizing environments. Its stabilized microstructure prevents sensitization during welding or high-temperature exposure, making it a reliable choice for long-term service under demanding thermal conditions.
ASTM A312 TP347H Stainless Steel Pipe Chemical Composition
The chemical composition of ASTM A312 TP347H shall conform to the following requirements as per ASTM A312. Iron is the balance. The niobium + tantalum content is specified to ensure stabilization; it must be at least ten times the carbon content, with a maximum of 1.00%.
- Higher carbon ensures improved high-temperature strength compared to standard 347.
- The presence of niobium prevents chromium carbide precipitation at grain boundaries.
| Element | Specified Value | Remarks |
|---|---|---|
| Carbon (C) | 0.04 – 0.10 | Increased for high-temperature strength |
| Manganese (Mn) | 2.00 max | |
| Phosphorus (P) | 0.045 max | |
| Sulfur (S) | 0.030 max | |
| Silicon (Si) | 0.75 max | |
| Chromium (Cr) | 17.0 – 19.0 | Provides corrosion and oxidation resistance |
| Nickel (Ni) | 9.0 – 13.0 | Stabilizes austenitic structure |
| Niobium (Nb) + Tantalum (Ta) | 10 × C min, 1.00 max | Stabilizing elements to prevent sensitization |
| Iron (Fe) | Balance |
ASTM A312 TP347H Stainless Steel Pipe Thermal and Electrical Physical Properties
The following physical properties are representative for ASTM A312 TP347H (UNS S34709) in the solution-annealed condition at room temperature unless otherwise noted. These values aid in design calculations for high-temperature service.
- Thermal expansion and conductivity are critical for thermal stress analysis.
- Properties are similar to those of lower-carbon 347.
| Property | Typical Value | Unit | Test Condition / Reference |
|---|---|---|---|
| Density (ρ) | 8.0 | g/cm³ (kg/m³ × 10⁻³) | 20°C |
| Modulus of Elasticity (E) | 193 (28.0 × 10⁶) | GPa (psi) | Room temperature |
| Shear Modulus (G) | 77 | GPa | Calculated |
| Poisson's Ratio (ν) | 0.28 | — | Room temperature |
| Thermal Expansion Coefficient (α) | 16.5 | µm/m·°C | 20–100°C |
| Thermal Expansion Coefficient (α) | 18.0 | µm/m·°C | 20–500°C |
| Thermal Conductivity (λ) | 16.3 | W/m·K | 100°C |
| Thermal Conductivity (λ) | 21.5 | W/m·K | 500°C |
| Specific Heat Capacity | 500 | J/kg·K | 20°C |
| Electrical Resistivity (ρₑ) | 72 | µΩ·cm | 20°C |
ASTM A312 TP347H Stainless Steel Pipe Mechanical Properties
Mechanical properties are determined on longitudinal test specimens from the pipe in solution-annealed condition. ASTM A312 specifies minimum tensile and yield strengths and elongation depending on wall thickness. The values below apply to nominal wall thickness 5/16 in. (7.94 mm) and above; for thinner walls, elongation requirements are reduced per the standard formula. No impact test or hardness limits are mandated.
| Property | Required Value | Unit | Test Condition |
|---|---|---|---|
| Tensile Strength (Rm) | 75 min (515) | ksi (MPa) | Room temperature, longitudinal |
| Yield Strength (ReH 0.2% offset) | 30 min (205) | ksi (MPa) | Room temperature, longitudinal |
| Elongation (A) in 2 in. (50 mm) | 35 min | % | Wall thickness ≥ 5/16 in. (7.94 mm) |
| Elongation (A) for thinner wall | Reduced 1.5% per 1/32 in. decrease | % | Example: 0.25 in. wall → 32% min; 0.1875 in. → 29.5% min |
ASTM A312 TP347H Stainless Steel Pipe Fully Equivalent Material Standards and Substitute Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ASME SA312 | TP347H (UNS S34709) | Identical to ASTM A312 TP347H; dual certified |
| Europe | EN 10216-5 | X6CrNiNb18-10 (1.4912) | High-carbon niobium-stabilized 18Cr-10Ni steel for pressure purposes |
| Japan | JIS G3459 | SUS 347H TP | Corresponding JIS grade for high-temperature piping |
| China | GB/T 14976 | 1Cr19Ni11Nb | High-carbon grade with Nb stabilization, used for fluid transport |
ASTM A312 TP347H Stainless Steel Pipe Application Introduction
ASTM A312 TP347H is engineered for long-term exposure at temperatures up to approximately 815°C (1500°F) under oxidizing and mildly carburizing conditions. Its niobium stabilization and optimized carbon content provide superior resistance to sensitization and creep rupture. Key benefits include:
- Excellent resistance to intergranular corrosion after welding without post-weld heat treatment.
- High creep-rupture strength compared to non-stabilized or low-carbon grades.
- Good oxidation resistance up to 870°C.
Product Applications: Seamless stainless steel pipe and tube for high-temperature service, Welded pipe for non-critical high-temperature lines, Boiler and superheater tubes, Heat exchanger tubes, Furnace tubes and piping systems
Processed into products: Boiler superheater and reheater sections, Ethylene cracking furnace tubes, Reformer tubes, High-temperature process piping spools and bends, Flanges and fittings (when produced from matching grade), Expansion joints and bellows in hot service
Application industries: Oil and gas refining (furnace tubes, transfer lines), Chemical and petrochemical plants (reactors, heat exchangers), Power generation (boiler superheater and reheater tubes), Waste incineration and thermal processing, Aerospace (high-temperature ducting)
ASTM A312 TP347H Stainless Steel Pipe Similar or Proximate Substitute Materials
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ASTM A312 | TP347 (UNS S34700) | Lower carbon version (max 0.08% C); slightly lower high-temperature strength but better weldability in thick sections |
| USA | ASTM A312 | TP321H (UNS S32109) | Titanium-stabilized austenitic steel; similar high-temperature service; often interchangeable but not identical |
| USA | ASTM A312 | TP304H (UNS S30409) | High-carbon 18-8 without stabilizing elements; lower elevated-temperature strength and risk of sensitization |
| USA | ASTM A312 | TP316H (UNS S31609) | Molybdenum-bearing high-carbon grade; better pitting resistance and similar creep strength |
Notes:
Welding: TP347H is readily weldable by all common fusion and resistance methods. Filler metals such as ER347 or ER347Si are recommended. Post-weld heat treatment is not required for corrosion resistance but may be applied for stress relief. Heat Treatment: Solution annealing is performed at 1040–1150°C (1900–2100°F) followed by rapid cooling. The material can be cold worked to enhance strength but must be re-annealed if maximum ductility is needed. Testing: In addition to the standard mechanical tests, supplementary tests like intergranular corrosion (ASTM A262 Practice E or C) and ultrasonic examination may be specified by the purchaser.
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