Stainless Steel Coil Tube (Coiltube) — Anti-Freeze Design Specification

Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product Catalog No. 1545). This product is specifically designed for applications where freeze protection (Anti-Freeze) is a critical operational requirement. Unlike conventional straight-length stainless steel tubes, coil tubes are wound into continuous spiral configurations, offering superior flexibility, compact storage, and enhanced thermal retention characteristics. The product is engineered to mitigate the risk of ice formation (Freezing) within the tube lumen during low-temperature environments, making it suitable for outdoor piping systems, cold-climate infrastructure, and industrial process lines exposed to sub-zero conditions.

The coil tube geometry inherently provides a thermal mass advantage over straight tubes of equivalent wall thickness, as the coiled configuration reduces the effective heat transfer surface area exposed to ambient cold air. Combined with appropriate material selection and wall thickness optimization, this design significantly delays or prevents internal fluid freezing.

Material & Properties

Base Materials

Mechanical Properties (Typical — Annealed Condition)

Property 304 / 304L 316 / 316L 2205 Duplex
Tensile Strength (MPa) ≥ 515 ≥ 515 ≥ 550
Yield Strength (MPa, 0.2% offset) ≥ 205 ≥ 170 ≥ 450
Elongation (% at break) ≥ 40 ≥ 40 ≥ 25
Density (g/cm³) 8.00 8.03 7.80
Thermal Conductivity (W/m·K, at 100°C) 16.3 14.6 12.0
Linear Expansion Coefficient (×10⁻⁶/K, 20–100°C) 17.3 16.0 13.0
Minimum Service Temperature (°C) −196 −196 −100

Anti-Freeze Performance Characteristics

Specifications

Parameter Specification / Range
Product Name Stainless Steel Coil Tube (Coiltube)
Product Catalog No. 1545
Outer Diameter (OD) 6.0 mm – 168.3 mm (¼" – 6")
Wall Thickness 0.5 mm – 6.0 mm (custom available)
Coil Winding Diameter 500 mm – 3000 mm
Coil Length per Reel 100 m – 1000 m (configurable)
Tolerance on OD ±0.05 mm – ±0.20 mm (per ASTM A269)
Tolerance on Wall Thickness ±10% (per ASTM A269)
Surface Finish Pickled & Passivated (P&P), Brushed, or Polished (Ra ≤ 0.4 μm)
End Condition Plain Cut, Beveled, or Threaded
Applicable Standards ASTM A269 / A270, ASME SA-213, EN 10217-7, GB/T 12771
Recommended Minimum Wall Thickness for Anti-Freeze Service ≥ 1.5 mm (for OD ≤ 50 mm); ≥ 2.0 mm (for OD > 50 mm)
Packaging Coiled on wooden reels with moisture-proof wrapping; export-grade palletization available

Manufacturing Process

  1. Raw Material Procurement: Cold-rolled stainless steel strip is sourced from certified mills meeting ASTM A480 / EN 10088-2 chemical composition requirements. Incoming material undergoes spectral analysis (PMI) verification for grade confirmation.
  2. Coil Forming: The strip is fed into a precision coil forming machine (also referred to as a tube coiling machine) equipped with a cold-drawing die and mandrel system. The strip is incrementally wound around a rotating mandrel, forming a continuous spiral tube without weld seams along the length of the coil.
  3. Welding (for welded coil tube configurations): Where a longitudinal seam is required, the tube edges are joined using Tungsten Inert Gas (TIG) welding (GTAW) or Orbital Welding under a continuous argon (Ar) shielding atmosphere to ensure a clean, oxide-free weld bead.
  4. Heat Treatment: The formed coil tube undergoes solution annealing at 1050°C – 1150°C followed by rapid quenching in water or air to achieve a fully austenitic microstructure with maximum corrosion resistance and ductility.
  5. Pickling & Passivation: The annealed tube is immersed in a mixed acid solution (HNO₃ + H₂SO₄) to remove mill scale and oxide layers, followed by a nitric acid passivation step to restore the protective chromium oxide passive film.
  6. Coil Winding & Packaging: The finished tube is wound onto the designated coil diameter using a controlled tension winding system to prevent deformation. Each coil is wrapped in moisture-resistant material and secured on a hardwood reel for transportation and storage.
  7. Final Inspection: Every coil batch undergoes dimensional verification (OD, wall thickness, coil diameter), hydrostatic pressure testing (per ASTM A269, minimum test pressure calculated as P = 2St/D), and visual surface inspection for defects.

Applications

Quality Certifications & Compliance

Anti-Freeze Engineering Guidelines (Technical Advisory)

Based on extensive field experience and material science principles, the following engineering recommendations are provided to prevent coil tube freezing in low-temperature service:

  1. Wall Thickness Optimization: Selecting a minimum wall thickness of 1.5 mm (for small-bore tubes) increases the thermal mass and reduces the rate of heat loss to ambient, delaying the onset of freezing.
  2. Material Selection: Grade 316L is preferred over 304L in coastal or de-icing-salt-exposed environments, as the molybdenum (Mo) addition provides superior resistance to chloride pitting that could be exacerbated by freeze-thaw cycling.
  3. Coil Diameter Consideration: Larger coil winding diameters (≥ 1500 mm) reduce bending-induced stress concentrations that could create micro-cracks over time, potentially serving as initiation sites for corrosion and subsequent freeze-induced rupture.
  4. Insulation & Heat Tracing: External thermal insulation (e.g., closed-cell elastomeric foam, thickness ≥ 25 mm) combined with electric heat trace systems is the most reliable freeze-prevention strategy for continuous outdoor service.
  5. Drainage & Slope Design: Coil tube installations should incorporate drainage ports at low points to allow complete fluid evacuation during shutdown periods, eliminating residual water that could freeze and expand.
  6. Avoidance of Sharp Bends: Minimum bend radius should be ≥ 3× the outer diameter (OD) to prevent wall thinning at bend apexes, which creates weak points susceptible to freeze-induced hydraulic failure.

Unique Selling Points