310S / 1.4845 / TP310S / 06Cr25Ni20 Stainless Steel Seamless Pipe / Welded Pipe for Boiler

1. 310S Stainless Steel Seamless Pipe

1.1 Standards (International & National)

1.2 Chemical Composition & Mechanical Properties

Chemical Composition (Weight %, Typical)

Mechanical Properties (At Room Temperature)

1.3 Specifications

• Outer Diameter (OD): 6 mm – 630 mm (common ranges for boilers: 10 mm – 219 mm)
• Wall Thickness (WT): 0.8 mm – 50 mm (boiler-specific: 2 mm – 20 mm, to balance pressure resistance and heat transfer)
• Length:
  • Random length: 3 m – 12 m
  • Fixed length: Customized (e.g., 6 m, 9 m, 12 m) per customer/boiler design
• Surface Finish:
  • Pickled (default): Removes oxide scale, improves corrosion resistance;
  • Polished (optional): Ra ≤ 0.8 μm (for hygiene-sensitive boiler auxiliary systems).

1.4 Production Process

1. Raw Material Preparation: Use 310S stainless steel billets (continuous casting billets, Φ150 mm – Φ300 mm) with strict chemical composition testing.
2. Heating: Heat billets to 1100°C – 1250°C in a walking-beam furnace (ensures uniform austenite structure).
3. Piercing: Push heated billets through a piercing mill to form a hollow "tube blank" (mandrel piercing for uniform wall thickness).
4. Hot Rolling/Expanding: Reduce the tube blank’s OD and WT via hot rolling (for small OD) or hot expanding (for large OD), shaping it to target dimensions.
5. Heat Treatment: Solution annealing at 1050°C – 1150°C (eliminates internal stress, restores austenite structure, and enhances corrosion resistance), followed by rapid water quenching.
6. Cold Finishing (Optional): For precision requirements (e.g., small-diameter boiler tubes), use cold drawing to refine OD/WT tolerance, then bright annealing.
7. Inspection:
   • Non-destructive testing (NDT): Ultrasonic testing (UT) for internal defects, eddy current testing (ECT) for surface defects;
   • Dimensional inspection: Verify OD, WT, and straightness (≤1 mm/m);
   • Pressure testing: Hydrostatic test (2.5 MPa – 5 MPa) to ensure leak tightness.

1.5 Boiler-Specific Applications

• Superheater tubes (transport high-temperature steam, up to 540°C – 600°C);
• Reheater tubes (reheat steam for improved thermal efficiency);
• Main steam pipes (carry high-pressure steam from boiler to turbine, pressure up to 10 MPa – 30 MPa);
• Water wall tubes (circulate boiler feedwater, resist thermal cycling).

2. 310S Stainless Steel Welded Pipe

2.1 Standards

2.2 Chemical Composition & Mechanical Properties

• Chemical Composition: Same as 310S seamless pipe (see Section 1.2).
• Mechanical Properties:
  • Tensile Strength (σb): ≥515 MPa;
  • Yield Strength (σ0.2): ≥205 MPa;
  • Elongation (δ5): ≥30% (slightly lower than seamless due to weld seam, but still meets boiler standards);
  • Weld Seam Strength: Weld metal tensile strength ≥ 90% of base metal strength (ASTM A358 requirement).

2.3 Specifications

• Outer Diameter (OD): 10 mm – 2000 mm (boiler applications: 25 mm – 630 mm);
• Wall Thickness (WT): 0.5 mm – 30 mm (boiler-specific: 1.5 mm – 15 mm);
• Length:
  • Random length: 3 m – 12 m;
  • Fixed length: Customized (up to 18 m for large-diameter pipes);
• Welding Type:
  • TIG (Tungsten Inert Gas) welding: For small OD (≤50 mm), high weld quality (no spatter, smooth seam);
  • MIG (Metal Inert Gas) welding: For medium/large OD (>50 mm), high production efficiency;
• Surface Finish: Pickled (default) or polished (optional), same as seamless pipes.

2.4 Production Process

1. Raw Material Preparation: Use 310S stainless steel strips (thickness 0.5 mm – 30 mm) with chemical composition and flatness testing.
2. Forming: Bend the stainless steel strip into a circular/oval shape via a roll-forming machine (ensures consistent OD and roundness).
3. Welding:
   • TIG/MIG welding under inert gas (argon) to prevent oxidation of the weld seam;
   • For high-pressure boiler pipes: Use double-sided welding (root pass + fill pass) to eliminate internal weld defects.
4. Heat Treatment: Solution annealing (1050°C – 1150°C) + quenching to soften the weld seam, eliminate residual stress, and restore corrosion resistance.
5. Sizing & Straightening: Calibrate OD/WT via a sizing mill; straighten pipes to meet straightness requirements (≤1.5 mm/m).
6. Inspection:
   • Weld Seam Testing: Radiographic testing (RT) or ultrasonic testing (UT) to detect internal weld defects;
   • Leak Testing: Hydrostatic test (1.5 – 3 MPa) or pneumatic test;
   • Surface Inspection: Visual inspection (no cracks, pits) or eddy current testing (ECT).

2.5 Boiler-Specific Applications

• Boiler flue gas ducts (resist corrosive flue gases at 300°C – 800°C);
• Feedwater pipes (transport low-pressure boiler feedwater, ≤2 MPa);
• Condensate return pipes (carry condensed steam, low temperature/pressure);
• Auxiliary heat exchanger tubes (e.g., deaerator heat exchangers, ≤400°C).

3. Packaging (Common for Both Seamless & Welded Pipes)

1. Inner Packaging:
   • Each pipe is wrapped in PE film (polyethylene) to prevent moisture and dust;
   • Small-diameter pipes (≤50 mm) are bundled with steel straps (5 – 10 pieces per bundle);
   • Large-diameter pipes (>50 mm) are individually wrapped or capped (both ends) with plastic caps to prevent debris entry.
2. Outer Packaging:
   • Wooden crates: For small batches, precision pipes, or sea transport (prevents impact damage);
   • Steel racks: For large batches, long-length pipes (≥6 m) – ensures stability during loading/unloading;
   • Anti-rust treatment: Optional for long-term storage (apply anti-rust oil + VCI film to resist atmospheric corrosion).
3. Marking:
   • Each bundle/crate is labeled with: Material grade (310S/1.4845/TP310S/06Cr25Ni20), pipe type (seamless/welded), OD/WT/length, standard number, heat number, and manufacturer’s logo.