ASTM A358 347H EFW Stainless Steel Pipe Class 1 Niobium Stabilized High Carbon

Shaanxi Shangyou Stainless Steel Co., Ltd. supplies ASTM A358 347H EFW stainless steel pipe for global EPC contractors, refinery engineers, power plant fabricators, and petrochemical processors requiring niobium-stabilized, high-carbon austenitic piping with optimized creep resistance at elevated temperatures. Produced to ASTM A358/A358M, this specification covers electric-fusion-welded austenitic stainless steel pipe formed from plate or sheet with filler metal added during the welding process .

ASTM A358 is the standard specification for large-diameter EFW stainless steel pipe, covering sizes from NPS 8 to NPS 110 . Class 1 requires double welding with filler metal in all passes and 100% radiography, making it the standard for critical high-temperature process piping in refineries and power plants . 347H (UNS S34709) is the high-carbon, niobium-stabilized variant of 347 (C 0.04-0.10%, Nb ≥10×C%) . Niobium stabilization prevents sensitization in the heat-affected zone during welding, preserving intergranular corrosion resistance without post-weld heat treatment . 347H is specifically engineered for service at temperatures where creep and stress rupture properties are important .

ASTM A358 347H EFW pipe is specified for large-diameter, high-temperature piping systems requiring creep resistance and intergranular corrosion stability in the 425-850°C service range.

Typical applications include :

• Petroleum refining: catalytic crackers ("cat crackers"), fired heater tubes, transfer lines
• Power generation: superheater manifolds, boiler external piping, steam lines
• Chemical and petrochemical processing: furnace components, reactor vessels
• Gas and steam turbine components
• Thermal energy storage systems

Key selection considerations: Choose 347H over 321H when the service environment involves strongly oxidizing media or polythionic acid stress corrosion cracking—347H offers slightly improved corrosion resistance in these conditions . Niobium stabilization (minimum 10× carbon content) provides superior structural stability compared to titanium stabilization, particularly for long-term thermal exposure. The higher, controlled carbon range (0.04-0.10%) maximizes creep rupture strength . Select Class 1 for critical process piping requiring maximum weld seam integrity—double-welded construction with 100% RT is standard for refineries and power plants . Recommended filler metal is ER347, which must have minimum 0.04% carbon to match the H-grade properties . The required solution annealing temperature is 1040°C with water quench or rapid cool .

Shangyou Stainless Steel provides value-added processing including custom cutting, beveling, and end protection for large-diameter EFW pipes.

All pipes are packed with export-standard protection including protective end caps, steel strapping, waterproof wrapping, and steel frames or wooden pallets.

Quality documents include MTC 3.1, inspection reports, packing list, and heat number traceability. Third-party inspection (SGS, TUV, BV) can be arranged upon request.

1. What is ASTM A358?

ASTM A358 is the standard specification for electric-fusion-welded austenitic stainless steel pipe for high-temperature and general corrosive service .

2. What is the difference between 347 and 347H?

347 has max 0.08% carbon; 347H has 0.04-0.10% carbon. The H-grade is specifically intended for service where creep and stress rupture properties are important .

3. What is the UNS number for 347H?

UNS S34709 .

4. What is Class 1 under ASTM A358?

Class 1 requires double welding with filler metal in all passes and 100% radiography—the highest weld quality level in the specification .

5. What is the solution annealing temperature for 347H?

1900°F (1040°C) with water quench or rapid cool .

6. Is filler metal required for Class 1?

Yes, Class 1 requires filler metal in all passes. Recommended filler metal is ER347 with minimum 0.04% carbon content .

7. What is the maximum service temperature for 347H?

Good oxidation resistance up to approximately 850°C .

8. Why is niobium added to 347H?

Niobium stabilizes the alloy by binding carbon, preventing chromium carbide precipitation (sensitization) in the heat-affected zone during welding, even under demanding operating conditions .

9. What size range does ASTM A358 cover?

NPS 8 to NPS 110 (DN200 to DN2750) .

10. What are typical applications for A358 347H pipe?

Petroleum refining (cat crackers), power generation (superheaters), chemical processing, and high-temperature furnace equipment .

Request a Quote

Need ASTM A358 347H EFW stainless steel pipe Class 1 for high-temperature refinery, power generation, or petrochemical service? Send requirements including grade, class, NPS/wall thickness/length, end finish, quantity, and service temperature/conditions.

Shangyou Stainless Steel provides custom sizes, processing, and export solutions for global B2B customers.