Stainless Steel Heat Exchange Coil Tube for Natural Gas Dehydration Systems

Product Overview

The Stainless Steel Heat Exchange Coil Tube (Coiltube) is a precision-engineered continuous spiral tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product Reference No. 923). Designed specifically for integration into natural gas dehydration units, this coil tube serves as a critical heat exchange element within glycol-based (TEG) and molecular sieve dehydration processes. The coiltube is supplied in continuous coil form, enabling efficient installation in shell-and-coil heat exchangers, condensate coolers, and regeneration reboilers without the need for field welding or mechanical fittings, thereby significantly reducing leak points and enhancing system integrity.

Unlike conventional straight-tube heat exchangers, the coiltube geometry provides superior heat transfer coefficients due to the enhanced turbulence generated by the helical curvature, resulting in 30–50% higher overall heat transfer effectiveness compared to equivalent straight-tube configurations. This product represents a specialized solution addressing the severe corrosion challenges encountered in natural gas processing environments where hydrogen sulfide (H₂S), carbon dioxide (CO₂), chlorides, and water coexist.

Material & Properties

The coil tube is fabricated from austenitic stainless steel grades selected for maximum resistance to sour gas corrosion, pitting, and stress corrosion cracking (SCC) in high-temperature, high-pressure dehydration environments.

Specifications

Parameter Specification Standard / Test Method
Outer Diameter (OD) 12.7 mm – 50.8 mm (1/2" – 2") ASTM A213 / ASME SA-213
Wall Thickness (WT) 0.8 mm – 3.2 mm (32 GA – 12 GA) ASTM A213 / ASME SA-213
Coil Diameter (CD) 100 mm – 600 mm (4" – 24") Custom per engineering drawing
Pitch / Spacing 15 mm – 50 mm (adjustable) Per ASME B31.3 Process Piping Code
Length per Coil Up to 300 m continuous (no welds) Supplier specification
Surface Finish Pickled & passivated, Ra ≤ 0.4 μm ASTM A967
End Condition Plain, beveled, or socket-welded ends ASME B16.11 / B16.25
Pressure Rating Up to 40 bar (580 psi) at 150°C ASME BPVC Section VIII
Heat Treatment Solution annealed at 1040–1120°C, water quenched ASTM A240 / ASME SA-240
Coil Tolerance (OD) ±0.05 mm (±0.002") ISO 4287

Manufacturing Process

  1. Coil Winding: Precision helical winding of seamless or welded stainless steel tubing onto calibrated mandrels using CNC-controlled winding machines. The winding process maintains uniform pitch and concentricity with ±0.5 mm tolerance throughout the coil length.
  2. Heat Treatment (Solution Annealing): The coiled tubing is annealed in a protective atmosphere (argon or vacuum) at 1040–1120°C to dissolve carbides, relieve residual stresses introduced during cold winding, and restore full austenitic microstructure. This step is essential to prevent intergranular corrosion sensitization.
  3. Pickling and Passivation: The annealed coil undergoes chemical pickling (nitric-hydrofluoric acid blend) to remove scale and oxidation, followed by passivation treatment to establish a chromium-rich passive oxide layer (Cr₂O₃) on the surface, providing long-term corrosion protection.
  4. Hydrostatic Testing: Each coil is hydrostatically tested at 1.5× the maximum design pressure (typically 60 bar minimum) for a minimum dwell time of 15 minutes to verify weld integrity and dimensional conformity.
  5. Non-Destructive Examination (NDE): Eddy current testing (ECT) per ASTM E709 is performed on the entire coil length to detect surface and near-surface defects. Radiographic testing (RT) per ASME V Article 2 is applied to all welded joints (if applicable).
  6. Final Inspection and Packaging: Dimensional verification using laser measurement systems, visual inspection, and certification documentation preparation. Coils are packaged in wooden crates with desiccant and VCI (Volatile Corrosion Inhibitor) wrapping for moisture protection during transit.

Applications

Anti-Corrosion Design Features

The coiltube design incorporates multiple layers of corrosion protection strategies, drawing from field experience in natural gas dehydration applications:

  • Material Selection: Minimum 2.5% Mo content (316L) provides threshold pitting resistance equivalent number (PREN) ≥ 24, sufficient for chloride concentrations up to 5,000 ppm at operating temperatures below 60°C
  • Elimination of Weld Joints: Continuous coil construction eliminates circumferential welds that serve as corrosion initiation sites in sour environments
  • Enhanced Turbulence: The helical geometry generates Dean vortices that increase wall shear stress, preventing deposition of iron sulfide (FeS) scales and maintaining effective heat transfer
  • Passive Film Stability: Solution annealing and passivation ensure a stable, self-healing chromium oxide film even in transient wet-dry cycling conditions
  • Low Carbon Content: 316L grade limits carbon to ≤ 0.03%, preventing chromium carbide precipitation and intergranular sensitization during thermal cycling

Quality Certifications

Unique Selling Points