Stainless Steel Coil Tube (Coiltube) — Heat Exchanger Grade

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for use in heat exchanger assemblies, particularly within coking waste gas heat exchange systems. The coil tube is produced in a continuous helical or spiral configuration, enabling compact installation within confined spaces while maximizing the effective heat transfer surface area. This product category is extensively applied in industrial waste heat recovery, flue gas cooling, and thermal management systems where space efficiency and thermal performance are critical design parameters.

The coil tube geometry provides superior convective heat transfer characteristics compared to straight-tube arrangements, owing to the induced secondary flow patterns (Dean vortices) generated within the curved tube cross-section. This results in enhanced turbulent mixing and an increase in the overall heat transfer coefficient (U-value) by approximately 20–40% relative to equivalent straight-tube configurations.

2. Material & Properties

The coil tubes are manufactured from high-grade austenitic stainless steel grades, selected for their outstanding combination of corrosion resistance, thermal stability, and mechanical integrity under elevated-temperature operating conditions.

2.1 Primary Alloy Grades

2.2 Key Material Properties (Typical — TP316L Annealed Condition)

Property Specification
Chemical Composition — Cr 16.5–18.5%
Chemical Composition — Ni 10.0–14.5%
Chemical Composition — Mo 2.0–2.5%
Chemical Composition — C (Max) 0.030%
Tensile Strength (Rm) ≥ 485 MPa (70 ksi)
Yield Strength (Rp0.2) ≥ 205 MPa (30 ksi)
Elongation (A50) ≥ 40%
Thermal Conductivity (20°C) 16.3 W/(m·K)
Thermal Conductivity (500°C) 25.7 W/(m·K)
Coefficient of Thermal Expansion (20–100°C) 17.5 × 10−6 /K
Maximum Service Temperature 870°C (1600°F)
Corrosion Resistance Equivalent to 316L in ASTM G48 A-Criteria (pitting); excellent in sulfuric acid (≤ 10%, < 60°C)

3. Specifications

Parameter Specification
Product Standard ASTM A269 / A213; EN 10216-5; GB/T 12771
Outer Diameter (OD) 6.0 mm – 50.8 mm (¼" – 2")
Wall Thickness 0.5 mm – 3.0 mm (0.020" – 0.118")
Coil Bend Radius ≥ 2.0 × OD (minimum); typical 3.0–5.0 × OD
Coil Length per Spool 50 m – 500 m (configurable)
Surface Finish Pickled & Passivated (Ra ≤ 0.8 μm); optional electropolished (Ra ≤ 0.4 μm)
End Condition Plain ends; U-bend ends; threaded ends; socket-weld prepared
Tolerance — OD ± 0.10 mm (for OD ≤ 25 mm); ± 0.15 mm (for OD > 25 mm)
Tolerance — Wall Thickness ± 10% of nominal
Pressure Rating Up to 25 bar (g) continuous; 37.5 bar (g) hydrostatic test
Operating Temperature Range −196°C to +870°C (−320°F to +1600°F)
Heat Treatment Solution Annealed at 1050–1150°C followed by water quench
Non-Destructive Testing 100% eddy current (ECT); optional penetrant testing (PT)

4. Manufacturing Process

The production of stainless steel coil tubes follows a rigorously controlled multi-stage process to ensure dimensional accuracy, metallurgical homogeneity, and mechanical reliability:

  1. Raw Material Selection & Ingot Casting: High-purity austenitic stainless steel ingots are produced via vacuum arc remelting (VAR) or vacuum induction melting (VIM) to minimize inclusions and ensure uniform chemical composition within ASTM/EN specifications.
  2. Hot Rolling & Annealing: Ingot billets are hot-rolled into seamless tube blanks at temperatures between 1100–1200°C, followed by controlled air cooling and a full solution annealing cycle at 1050–1150°C with rapid water quenching to achieve a fully austenitic, stress-free microstructure.
  3. Pilot Mill & Cross-Rolling (Cold Forming): The hot-rolled tube blanks are cold-worked through pilot mills and cross-rolling stands to achieve the final outer diameter and wall thickness with tight tolerances. This cold working stage induces beneficial strain hardening, improving yield strength while maintaining ductility within specified limits.
  4. Intermediate Annealing (if required): For multi-pass cold reduction sequences, intermediate annealing cycles are performed to restore ductility and prevent cracking during subsequent forming operations.
  5. Coil Winding / Helical Forming: The straight tube is wound onto a precision-machined mandrel using a CNC-controlled coil winding machine. The winding process employs constant-tension control systems and real-time geometric monitoring to maintain consistent bend radius (typically 3.0–5.0 × OD), pitch accuracy, and helical uniformity throughout the coil length.
  6. Pickling & Passivation: The formed coil tube undergoes chemical pickling (mixed acid bath: HNO3 + H2SO4) to remove oxide scale, discoloration, and surface contaminants. A subsequent passivation treatment (dilute nitric acid or citric acid) establishes a stable chromium oxide passive film, ensuring optimal corrosion resistance.
  7. Quality Inspection & Testing: Every coil tube spool undergoes comprehensive quality verification including 100% automated eddy current testing for surface and near-surface defect detection, dimensional measurement (OD, wall thickness, bend radius, pitch), hydrostatic pressure testing at 1.5× design pressure, and visual inspection of surface finish.
  8. Packaging & Dispatch: Qualified coil tubes are coiled on protective wooden reels with VCI (Volatile Corrosion Inhibitor) paper wrapping and shrink-wrapped for moisture protection during storage and transportation.

5. Applications

The stainless steel coil tube finds extensive application across multiple industrial sectors, with particular emphasis on thermal management and heat exchange systems:

5.1 Coking Waste Gas Heat Exchange Systems

In coke oven battery operations, coil tubes are the primary heat transfer elements in waste gas recuperators and heat exchangers. The waste gas discharged from coke ovens at temperatures ranging from 700°C to 850°C carries substantial thermal energy that is recovered through coil-type heat exchangers. The helical coil configuration enables:

5.2 Additional Industrial Applications

6. Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification systems to ensure full regulatory compliance and customer confidence:

6.1 Quality Management System

6.2 Product Standards & Certifications

6.3 Third-Party Inspection & Testing

7. Unique Selling Points