ASTM A312 TP347H SCH 80 stainless steel pipe is a niobium-stabilized austenitic stainless steel pipe specifically engineered for high-temperature and high-pressure service in power plant systems. Produced in accordance with the specification issued by ASTM International, TP347H offers improved creep strength, enhanced resistance to intergranular corrosion, and superior structural stability under long-term elevated temperature exposure.
Schedule 80 (SCH 80) provides a thicker wall compared to Schedule 40, making it ideal for critical pressure-retaining components in thermal power plants.
Standard & Material Overview
Standard: ASTM A312 / A312M
Grade: TP347H (UNS S34709)
Schedule: SCH 80
Dimension Standard: ASME B36.19M
Stabilizing Element: Niobium (Columbium, Nb)
Manufacturing Type: Seamless (SMLS) / Welded (WLD)
Inspection Certificate: EN 10204 3.1 / 3.2 available
The "H" designation indicates higher carbon content compared to TP347, improving high-temperature strength and creep resistance.
Chemical Composition of TP347H
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.04 – 0.10 |
| Chromium (Cr) | 17.0 – 19.0 |
| Nickel (Ni) | 9.0 – 13.0 |
| Niobium (Nb) | ≥ 10 × C (typically 0.70–1.00) |
| Manganese (Mn) | ≤ 2.00 |
| Silicon (Si) | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
Niobium binds with carbon to prevent chromium carbide precipitation, enhancing long-term high-temperature stability.
Mechanical Properties
| Property | Minimum Value |
|---|---|
| Tensile Strength | 515 MPa |
| Yield Strength | 205 MPa |
| Elongation | 35% |
| Hardness | ≤ 201–217 HB |
TP347H provides superior creep rupture strength compared to TP304 or TP316 at elevated temperatures.
What Is Schedule 80?
Schedule 80 indicates a thicker wall stainless steel pipe classification under ASME B36.19M.
Example dimensions:
| NPS | OD (mm) | Wall Thickness SCH 80 (mm) | Wall Thickness (inch) |
|---|---|---|---|
| 2" | 60.33 | 5.54 | 0.218" |
| 4" | 114.30 | 8.56 | 0.337" |
| 6" | 168.28 | 10.97 | 0.432" |
Benefits of SCH 80:
Higher allowable working pressure
Improved mechanical strength
Increased safety margin in steam systems
Why TP347H for Power Plant Applications?
✔ Excellent Creep Strength
The higher carbon content improves long-term high-temperature performance in steam service.
✔ Stabilized Against Sensitization
Niobium prevents intergranular corrosion during welding and prolonged heat exposure.
✔ High-Temperature Oxidation Resistance
Suitable for steam pipelines and superheater systems.
✔ Proven Performance in Boiler Systems
Widely specified for pressure parts in thermal power generation facilities.
Typical Applications in Power Plants
⚡ Superheater & Reheater Systems
High-pressure steam lines
Main steam pipelines
🔥 Boiler Components
Pressure piping
Heat recovery systems
🏭 Thermal & Fossil Fuel Plants
High-temperature process piping
Steam distribution systems
🌍 Nuclear Power (Non-primary systems)
Auxiliary steam systems
TP347H vs TP347 vs TP321
| Property | TP321 | TP347 | TP347H |
|---|---|---|---|
| Stabilizing Element | Titanium | Niobium | Niobium |
| Carbon Level | Standard | Low | Higher |
| Creep Strength | Good | Better | Superior |
| Power Plant Use | Moderate | Common | Preferred |
For high-pressure, high-temperature steam systems, TP347H is often the preferred choice.
Manufacturing & Quality Control
Typical inspections include:
Chemical composition analysis
Tensile testing
Hydrostatic testing
Ultrasonic testing (UT)
Radiographic testing (RT)
PMI testing
EN 10204 3.1 certification
Third-party inspection (SGS / BV / TUV available)
All pipes are traceable by heat number for EPC project compliance.
Key Advantages for Power Plant Projects
✔ Excellent high-temperature creep resistance
✔ Superior intergranular corrosion resistance
✔ High-pressure capability (SCH 80)
✔ Stable long-term thermal performance
✔ Suitable for steam and boiler systems
✔ Proven reliability in thermal power generation
FAQ
1️⃣ What is ASTM A312 TP347H SCH 80 stainless steel pipe?
ASTM A312 TP347H SCH 80 pipe is a niobium-stabilized austenitic stainless steel pipe manufactured under the specification issued by ASTM International. It is designed for high-temperature and high-pressure service, particularly in steam and boiler systems within power plants. Schedule 80 indicates a thicker wall for increased pressure resistance.
2️⃣ Why is TP347H commonly used in power plant steam systems?
TP347H offers:
Enhanced creep strength at elevated temperatures
Niobium stabilization to prevent intergranular corrosion
Improved long-term thermal stability
Reliable performance in high-pressure steam lines
These characteristics make it suitable for superheater and reheater piping.
3️⃣ What does the "H" mean in TP347H?
The "H" designation indicates a higher carbon content (0.04–0.10%), which improves high-temperature strength and creep resistance compared to standard TP347.
This makes TP347H more suitable for prolonged exposure to high-temperature steam service.
4️⃣ What is the difference between TP347H and TP321?
Both are stabilized grades:
TP321 is stabilized with titanium
TP347H is stabilized with niobium
TP347H generally offers better creep strength in high-temperature steam service
For critical boiler and superheater systems, TP347H is often preferred.
5️⃣ What does Schedule 80 mean for stainless steel pipe?
Schedule 80 (SCH 80) refers to a thicker wall thickness under ASME B36.19M.
Benefits include:
Higher allowable working pressure
Increased structural strength
Greater safety margin in high-pressure steam systems
6️⃣ Is TP347H suitable for continuous high-temperature service?
Yes. TP347H performs well in:
Continuous service at elevated temperatures
High-pressure steam environments
Long-term creep conditions
It is widely specified for thermal power generation systems.
7️⃣ Is seamless or welded TP347H pipe better for power plant projects?
Seamless pipes are typically preferred for:
High-pressure steam lines
Critical pressure-retaining components
Safety-sensitive systems
Welded pipes may be used in less critical auxiliary systems.
8️⃣ What inspection documents are provided for EPC projects?
Manufacturers generally supply:
EN 10204 3.1 MTC
Chemical composition report
Mechanical test report
Hydrostatic test report
Ultrasonic testing (UT)
Radiographic testing (RT)
PMI (Positive Material Identification)
Third-party inspection (SGS / BV / TUV upon request)
Full heat number traceability is standard for power plant compliance.
9️⃣ How does TP347H compare to TP304 or TP316 in power plants?
Compared to TP304 or TP316:
TP347H has better creep strength
More suitable for high-temperature steam systems
Designed specifically for long-term elevated temperature service
304 and 316 are generally used for lower temperature process systems.
🔟 How do I select a reliable TP347H SCH 80 supplier for power plant projects?
Key considerations include:
Compliance with ASTM A312
Accurate SCH 80 dimensional tolerances
Experience supplying power plant or EPC projects
Complete inspection documentation
Stable raw material sourcing
On-time delivery capability
For critical steam systems, technical support and strict quality control are essential.
