ASME VIII-1 U-Tube Heat Exchanger Clad UNS N06600 for Chlor-Alkali Process NACE MR0175​

The ASME VIII-1 U-Tube Heat Exchanger is designed specifically for the Chlor-Alkali Process, featuring a UNS N06600 (Inconel 600) alloy lining that complies with NACE MR0175 certification for Sulfide Stress Cracking (SSC) resistance. It is suitable for extreme conditions involving high chloride ions, high-temperature alkaline, and sulfur-containing media, such as in the production of vinyl chloride and caustic soda evaporators. Its double-pass U-tube design enhances turbulence, reduces fouling, and improves heat transfer efficiency by over 40%.

Base Material and Lining Material Parameters

Advantages of UNS N06600 Alloy

• Corrosion Resistance: Corrosion rate in 80°C concentrated NaOH solution < 0.01 mm/year; withstands 50% boiling hydrochloric acid.
• Mechanical Properties: High-temperature creep resistance (strength ≥ 240 MPa at 700°C), elongation ≥ 30%.
• Process Compatibility: Supports TIG welding (filler ERNiCr-3) and hot extrusion forming; lining thickness ≥ 3 mm.

Cladding Process and Documentation Requirements

Key Cladding Steps

1. Welding Material Selection: Use ERNiCr-3 wire (AWS A5.14), matching the N06600 alloy composition to prevent carbon migration.
2. Process Specifications:
   • Preheat temperature: 90-120°C (carbon steel substrate)
   • Interpass temperature: ≤ 150°C
   • Post-weld heat treatment: 980°C solution annealing + water quench (to eliminate residual stress).

Required Quality Documentation

1. Welding Procedure Qualification (WPS/PQR): Compliant with ASME Section IX, covering all positional welding parameters.
2. Non-Destructive Testing Report:
   • Lining PT (Penetrant Testing) 100% coverage, no cracks or porosity.
   • Tube-to-tube sheet weld RT (Radiographic Testing) per ASME Sec. V standards.
3. Corrosion Testing Report:
   • Neutral salt spray test (ASTM B117) ≥ 1000 hours without delamination.
   • Accelerated corrosion test in chlor-alkali medium (40% NaOH + 5% NaCl, 90°C).
4. NACE MR0175 Certification: Verification of hydrogen sulfide stress cracking performance (H₂S partial pressure ≥ 0.3 kPa).

Technical Advantages and Design Innovations

1. High-Efficiency Heat Transfer Structure:

   • U-tube double-pass design increases turbulence by 60%, reducing biological fouling compared to single-pass designs.
   • Optimized corrugated tubes (wall thickness 0.8 mm), heat transfer coefficient 8% higher than copper tubes.

2. Adaptability to Extreme Conditions:

   • Thermal shock resistance: No leakage under a sudden temperature change of 200°C (simulating chlor-alkali process start-stop cycles).
   • Seismic design: Passes ASME Sec. III NF-level certification (nuclear power plant application standards).

3. Lifespan and Maintenance Costs:

   • Design lifespan ≥ 20 years (average lifespan of copper tube heat exchangers is 10 years).
   • Removable tube bundle design reduces maintenance time by 50%.

Industry Applications and Certification Endorsements

• Core Applications: Vinyl chloride reactor condensation, caustic soda evaporation concentration, sulfur-containing wastewater treatment.
• Typical Clients:
  • China Chlor-Alkali Chemical Group (30 units in service, failure rate < 0.5 times/year).
  • Middle East petrochemical base (seawater cooling + high-sulfur crude oil conditions).
• Full Chain Certifications:
  • ASME VIII-1 2025 (Pressure Vessel)
  • NACE MR0175/ISO 15156-3 (Sulfide Corrosion Resistance)
  • PED 2014/68/EU (EU Pressure Equipment Directive).