Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit Application Series

Product Overview

The Stainless Steel Coil Tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1074) is a precision-engineered continuous coil form of stainless steel tubing specifically designed for hydronic heating and cooling applications, including fan coil units (FCUs), air handling units (AHUs), and radiant floor systems. This product is supplied in coil form to facilitate seamless automated forming, bending, and brazing operations in downstream manufacturing environments, thereby eliminating the need for cut-length welding and minimizing thermal stress points within the coil assembly.

Stainless steel coil tubes offer superior resistance to condensation-induced corrosion — a well-documented failure mode in fan coil unit heat exchangers where sub-atmospheric dew-point conditions generate persistent moisture on cold-surface tubing. Unlike conventional carbon steel or copper alternatives, stainless steel coil tubing maintains structural integrity and hygienic surface quality under prolonged condensate exposure, making it an ideal material for HVAC (Heating, Ventilation, and Air Conditioning) coil assemblies operating in high-humidity environments.

Material & Properties

The coil tube is manufactured from austenitic stainless steel grades selected for optimal combinations of corrosion resistance, thermal conductivity, formability, and weldability:

Property Grade 304 Grade 316 / 316L
Density (ρ) 7.93 g/cm³ 7.98 g/cm³
Thermal Conductivity (k) at 20°C 16.3 W/(m·K) 14.6 W/(m·K)
Linear Expansion Coefficient (α) at 20°C 17.3 × 10⁻⁶ /K 16.0 × 10⁻⁶ /K
Yield Strength (Rp0.2) — Annealed ≥ 205 MPa ≥ 170 MPa
Tensile Strength (Rm) — Annealed 515 – 730 MPa 485 – 730 MPa
Maximum Operating Temperature 870°C (oxidizing) 870°C (oxidizing)
Corrosion Resistance (ASTM G48, 5% NaCl, 60°C) Moderate Excellent
Surface Roughness (Ra) — Typical 0.10 – 0.40 μm 0.10 – 0.40 μm

Specifications

Parameter Specification
Outer Diameter (OD) 6.0 mm – 25.4 mm (1/4" – 1")
Wall Thickness (WT) 0.30 mm – 1.50 mm
Coil Inner Diameter (ID) 200 mm – 600 mm (customizable)
Coil Length per Roll 50 m – 500 m (configurable)
Coil Weight per Roll 200 kg – 1,000 kg (typical)
Dimensional Tolerance — OD ± 0.05 mm (per ASTM A213 / GB/T 12771)
Dimensional Tolerance — WT ± 10% of nominal
Surface Finish 2B (Cold Rolled Annealed Bright), BA (Bright Annealed), or No. 4 Brushed
Hydrostatic Test Pressure ≥ 2.0 MPa (minimum 30-second hold, zero leakage)
Coil Forming Speed Up to 200 m/min (continuous production)
Packaging VCI (Vapor Corrosion Inhibitor) paper wrap, wooden pallet, shrink-wrapped

Manufacturing Process

The production of stainless steel coil tubing at Wenzhou Jixing Metal Materials Co., Ltd. follows a tightly controlled multi-stage process:

  1. Strip Preparation: Cold-rolled stainless steel strip is sourced from certified mills (e.g., POSCO, Outokumpu, TISCO), inspected for surface quality, and verified against material test certificates (MTC, Mill Test Certificate).
  2. Slitting: The master coil is slit to precise strip widths using a high-speed slitting line to ensure uniform edge quality and minimal coil set.
  3. Forming & Welding (ERW / TIG): The strip is formed into a circular cross-section and longitudinally welded using either Electric Resistance Welding (ERW) for higher production rates or Tungsten Inert Gas (TIG) welding for superior weld integrity. The weld seam is ground and inspected for continuity.
  4. Heat Treatment / Annealing: Solution annealing at 1050°C – 1150°C in a protective atmosphere (endothermic gas or vacuum) eliminates cold-work hardening and restores full austenitic microstructure.
  5. Pickle & Passivate: Post-annealing acid pickling (HNO₃/HF blend) removes scale, followed by nitric acid passivation to establish a protective chromium oxide film (Cr₂O₃).
  6. Coiling: The finished tube is wound into coils on precision coilers with controlled tension to prevent ovality, kinking, or coil springback.
  7. Quality Inspection: Each coil undergoes 100% hydrostatic testing, dimensional verification (OD, WT, roundness), visual surface inspection, and random chemical/spectral analysis (PMI — Positive Material Identification).

Applications

The stainless steel coil tube is engineered for demanding thermal-fluid applications where corrosion resistance and long service life are paramount:

Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management and compliance with international standards:

Unique Selling Points

Condensation-Resistant Engineering: Based on extensive field analysis of fan coil unit condensation failure modes, this coil tube product is specifically optimized to resist the corrosive effects of persistent condensate exposure. The combination of austenitic stainless steel chemistry, optimized surface finish, and controlled wall thickness ensures minimal electrochemical attack even under continuous sub-dew-point operating conditions.