ASTM A213 TP347 Stainless Steel Seamless Pipes

TP347 (UNS S34700) is a niobium (Nb)-stabilized austenitic chromium-nickel stainless steel. Its core characteristic is the addition of niobium (Nb content ≥10×C%, and ≤1.0%), which preferentially forms stable niobium carbides (NbC), thereby effectively suppressing the precipitation of chromium carbides at grain boundaries. This design provides TP347 with excellent resistance to sensitization and intergranular corrosion during welding or long-term exposure to the sensitization temperature range (450-900°C), while also exhibiting superior microstructural stability at high temperatures compared to titanium-stabilized grades.

Material Characteristics and Core Advantages

Excellent High-Temperature Creep Strength:

The addition of niobium not only provides a stabilizing effect but also forms fine niobium carbonitride precipitates, significantly enhancing the material's creep-rupture strength and creep resistance within the 600-750°C temperature range. Its high-temperature mechanical properties are superior to those of TP321.

Outstanding Oxidation and Carburization Resistance:

Performs well in high-temperature oxidizing and carburizing atmospheres, with a continuous service temperature up to approximately 870°C.

Balance of Weldability and Corrosion Resistance:

The low carbon content (≤0.08%) combined with niobium stabilization maintains good resistance to intergranular corrosion after welding, making it suitable for components where post-weld heat treatment is undesirable.

Strong High-Temperature Microstructural Stability:

Exhibits low tendency for carbide agglomeration during long-term high-temperature service, resulting in slow performance degradation.

Primary Application Areas

Power Station Boilers: High-temperature superheater and reheater tube sections in subcritical and supercritical units.

Petrochemical Industry: Convection and radiant section tubes in cracking and reformer furnaces.

High-Temperature Heat Exchange Equipment: High-temperature, high-pressure heat exchangers in chemical and metallurgical industries.

Special Environment Piping: High-temperature corrosion-resistant piping in nitric acid plants and auxiliary nuclear power plant systems.

Standards and Quality Assurance

Chemical Composition Control: Strict control of the niobium-to-carbon ratio (Nb/C ≥10) to ensure the stabilization effect.

Heat Treatment Requirements: Mandatory solution heat treatment (1040-1150°C), with stabilization treatment applied as necessary.

Performance Verification: Provision of high-temperature creep-rupture strength data is required, complying with allowable stress values specified in ASME BPV Code Section II, Part D.

Non-Destructive Examination: 100% eddy current or ultrasonic testing to ensure freedom from defects.

Dimensional Accuracy: Adherence to strict boiler tube tolerance standards (ASTM A1016).

Selection Guidance and Key Considerations

Comparison and Selection vs. TP321:

TP347 should be prioritized for service conditions above 625°C; for lower temperatures where resistance to sensitization is the primary concern, the more cost-effective TP321 may be considered.

Understanding High-Temperature Strength Boundaries:

For extreme high-temperature sections >650°C in ultra-supercritical units, the higher-carbon variant with special heat treatment, TP347H, should be selected.

Key Welding Process Points:

The use of low-carbon welding consumables is recommended, with interpass temperature controlled to ≤150°C to maintain corrosion resistance in the weld zone.

Suitability for Corrosive Environments:

Has limited resistance to pitting corrosion in chloride-ion containing environments. Selection of molybdenum-bearing grades like TP317L should be considered based on specific media characteristics.

Chemical Composition

Mechanical Properties

Physical Properties

Grade Specification Comparison