Stainless Steel Coil Tube — Fan Coil Unit Application (Low-Temperature & Large ΔT Performance)
1. Product Overview
The Stainless Steel Coil Tube (also referred to as Stainless Steel Coil Tubing or Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 918). This coil tube is specifically designed for use in Fan Coil Units (FCUs) and hydronic heat exchange systems operating under low-temperature and large temperature differential (Large ΔT) conditions. The product is supplied in continuous coil form, facilitating downstream forming, bending, and integration into heat exchanger assemblies with minimal waste and high manufacturing efficiency.
The coil tube serves as the primary heat transfer element in fan coil unit applications, where it carries chilled or hot water through a serpentine or spiral configuration to exchange thermal energy with ambient air. Its design and material selection ensure reliable thermal performance, mechanical integrity, and corrosion resistance across extreme operating envelopes.
2. Material & Properties
2.1 Material Grades
- Austenitic Stainless Steel — Primary grades include SUS304 (UNS S30408), SUS316 (UNS S31603), and SUS316L (UNS S31603L).
- Super-Austenitic Grades — Available upon request for applications requiring enhanced resistance to pitting and crevice corrosion (e.g., SUS317L).
2.2 Key Material Properties
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and chemical corrosion due to high chromium (Cr ≥ 18%) and nickel (Ni ≥ 8%) content; Mo addition in 316/316L grades provides superior pitting resistance.
- Cryogenic Performance: Maintains ductility and tensile strength at temperatures as low as −196°C (−321°F), making it suitable for low-temperature hydronic loops.
- Thermal Conductivity: Approximately 14–16 W/(m·K) at 20°C, providing adequate heat transfer while offering inherent resistance to thermal shock.
- Mechanical Strength: Yield strength ≥ 205 MPa (304), ≥ 170 MPa (316L); ultimate tensile strength ≥ 515 MPa (304).
- Hygienic Surface: Electro-polished or passivated interior surface with roughness Ra ≤ 0.4 μm, preventing biofilm accumulation.
3. Technical Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ12.7 mm (standard); custom sizes available |
| Wall Thickness (WT) | 0.3 mm – 1.5 mm |
| Tolerance on OD | ±0.05 mm (precision grade) |
| Tolerance on Wall Thickness | ±10% of nominal |
| Coil Length | Up to 500 m per coil (continuous) |
| Coil Inner Diameter | Φ150 mm – Φ300 mm |
| Surface Finish | Bright Annealed (BA), Pickled & Passivated, Electro-polished |
| Surface Roughness (Interior) | Ra ≤ 0.4 μm (electro-polished); Ra ≤ 0.8 μm (BA) |
| Operating Temperature Range | −196°C to +450°C |
| Maximum Operating Pressure | Up to 1.6 MPa (design dependent) |
| Bend Radius (Minimum) | ≥ 2× OD without wall thinning |
| Standards Compliance | ASTM A213/A213M, ASTM A269/A269M, GB/T 12771, JIS G3459 |
| Packaging | Wooden pallet with moisture-proof wrapping; coil protected with steel bands |
4. Manufacturing Process
- Hot Rolling: Stainless steel strip is hot-rolled to approximate dimensions, followed by descaling and acid pickling.
- Cold Reduction: The strip undergoes cold rolling to achieve precise wall thickness and dimensional tolerances, inducing beneficial work hardening.
- Forming / Pipe Welding: The flat strip is formed into a tubular cross-section and welded using High-Frequency Induction (HFW) or Orbital TIG welding under inert gas shielding (argon) to ensure a hermetic, contamination-free weld seam.
- Pipe Finishing: Internal and external sizing, followed by annealing in a controlled atmosphere (vacuum or nitrogen) to relieve residual stresses and restore full austenitic microstructure.
- Surface Treatment: Electro-polishing or mechanical polishing to achieve the required surface roughness and corrosion resistance.
- Coiling: The finished tube is wound onto a coil in a continuous length, with controlled tension to prevent deformation.
- Quality Inspection: 100% visual inspection, dimensional verification via laser gauging, and sampling for hydrostatic pressure testing (per ASTM A213) and chemical composition analysis (OES/SEM).
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCUs): The coil tube forms the heat exchange core in FCUs used in commercial HVAC systems, particularly under low-temperature and large temperature differential operating conditions where thermal efficiency and material reliability are critical.
- Chilled Water Distribution Systems: Used in secondary loop piping for chilled water distribution in large-scale commercial and industrial facilities.
- Heat Exchanger Cores: Integrated into plate-fin or shell-and-tube heat exchangers for air conditioning, refrigeration, and process cooling.
5.2 Secondary Applications
- Food and beverage processing equipment (hygienic fluid transfer)
- Pharmaceutical manufacturing (CIP/SIP-compatible piping)
- Cryogenic systems (LNG, liquid nitrogen transfer)
- Marine and offshore platforms (seawater-resistant heat exchange)
- Automotive radiators and thermal management components
6. Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- CE Marking — European Conformity for pressure equipment (PED 2014/68/EU)
- EN 10204 3.1 — Inspection Certificates (third-party verified)
- ASTM A213 / A213M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for High-Temperature Service
- ASTM A269 / A269M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Allied Uses
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubes for Fluid Transport
- RoHS & REACH Compliance — Restriction of Hazardous Substances
7. Unique Selling Points (USPs)
7.1 Superior Low-Temperature Performance: The coil tube retains full mechanical integrity and impact resistance at cryogenic temperatures, validated through research on fan coil unit performance under large temperature differentials (ΔT up to 25°C). This eliminates the risk of brittle fracture that affects carbon steel alternatives in chilled water systems.
7.2 Corrosion-Free Longevity: The austenitic stainless steel matrix provides decades of service life in aggressive aqueous environments, eliminating the need for chemical treatment, cathodic protection, or frequent replacement — significantly reducing Total Cost of Ownership (TCO).
7.3 Precision Dimensional Control: Tight tolerances on OD and wall thickness (±0.05 mm) ensure uniform heat transfer coefficients across the entire coil assembly, optimizing FCU thermal performance and energy efficiency.
7.4 Hygienic Surface Quality: Electro-polished interiors with Ra ≤ 0.4 μm prevent microbial colonization, making the product suitable for food-grade and pharmaceutical applications without additional treatment.
7.5 Continuous Coil Supply: Delivered in continuous coils up to 500 m, minimizing splices and joints, reducing leak points, and enabling high-speed automated forming and integration into heat exchanger manufacturing lines.
8. Conclusion
The Stainless Steel Coil Tube (Product No. 918) from Wenzhou Jixing Metal Materials Co., Ltd. represents a high-performance, corrosion-resistant tubular solution purpose-built for fan coil unit and hydronic heat exchange applications. Its proven performance under low-temperature, large-temperature-differential conditions — supported by rigorous testing research — establishes it as the material of choice for engineers demanding reliability, efficiency, and longevity in demanding thermal management systems.