Stainless Steel Coil Tube — Constant Water Volume Fan Coil Unit Application Grade
Product Overview
The Stainless Steel Coil Tube (Product No. 1369) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for constant water volume fan coil unit systems. This coil tube serves as the primary heat exchange element within HVAC (Heating, Ventilation, and Air Conditioning) systems, facilitating efficient thermal transfer between the circulating water medium and the ambient air stream. The product is supplied in continuous coil form, enabling seamless integration into automated manufacturing lines for fan coil unit assembly.
Unlike conventional straight-pipe configurations, the coil tube geometry provides a significantly higher surface-area-to-volume ratio, which maximizes convective and conductive heat exchange efficiency within compact installation envelopes. This design is particularly advantageous for commercial and residential fan coil units where space constraints are critical.
Material and Properties
The coil tube is fabricated from high-grade austenitic stainless steel, primarily utilizing the following material specifications:
- Material Grade: SUS304 (UNS S30400) / SUS316L (UNS S31603) — selected based on corrosion resistance requirements of the specific application environment
- Chemical Composition (SUS304): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%
- Corrosion Resistance: Excellent resistance to pitting, crevice, and intergranular corrosion in aqueous environments with dissolved oxygen and chloride ions
- Thermal Conductivity: 14–16 W/(m·K) at 20°C, providing reliable heat transfer performance
- Operating Temperature Range: −196°C to +870°C, accommodating both heating and cooling operational cycles
- Surface Finish: 2B (Cold Rolled and Annealed) or BA (Bright Annealed) finish, with surface roughness Ra ≤ 0.8 μm to minimize flow resistance
Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ9.52 mm / Φ12.70 mm / Φ15.88 mm (1/4", 1/2", 5/8") | ASTM A213 |
| Wall Thickness | 0.50 mm / 0.80 mm / 1.00 mm (selectable) | ASME B36.19M |
| Bend Radius | 15–50 mm (variable, application-dependent) | ASTM A213 |
| Coil Length | 10–500 m per coil (customizable) | — |
| Coil Inner Diameter | Φ300 mm – Φ600 mm | — |
| Flatness Deviation | ≤ 0.5% of width | GB/T 14977 |
| Pressure Rating | Up to 1.6 MPa (232 psi) at 80°C | EN 10217 |
| Water Flow Capacity | 0.5 – 3.0 L/min per tube circuit | ASHRAE 90.1 |
| Heat Transfer Efficiency | U-value ≥ 450 W/(m²·K) with fins | ISO 12100-2-1 |
| Surface Treatment | Pickled and passivated; optional electropolished | ASTM A967 |
| Coating (Optional) | Anti-corrosion polymer coating for aggressive environments | — |
| Packaging | Wooden pallet with protective wrapping; moisture-proof inner lining | ISO 4180 |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing protocol ensuring dimensional accuracy and metallurgical integrity:
- Raw Material Procurement: Cold-rolled stainless steel strip (SUS304/316L) is sourced from certified mills with full mill test certificates (MTC) and chemical analysis reports.
- Slitting and Leveling: The strip is precision-slitted to the required width and passed through a leveling mill to eliminate residual curvature and ensure flatness within tolerance.
- Coil Forming: The leveled strip is fed through a progressive-die coil former that imparts the desired helical geometry. The forming process is controlled to maintain uniform wall thickness and prevent work-hardening-induced microcracks.
- Welding: Where longitudinal seams are required, the tube is welded using TIG (Tungsten Inert Gas) welding or high-frequency induction welding with argon shielding to produce a fully fused, leak-tight seam.
- Heat Treatment: The formed coil tube undergoes solution annealing at 1050–1100°C followed by controlled cooling to restore full austenitic microstructure and eliminate residual stresses.
- Pickling and Passivation: The surface is treated with nitric-hydrofluoric acid pickling solution to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide film (Cr₂O₃) for enhanced corrosion protection.
- Hydrostatic Testing: Each coil tube batch is subjected to hydrostatic pressure testing at 1.5 times the maximum operating pressure to verify weld integrity and dimensional conformance.
- Dimensional Inspection: Final products are inspected for outer diameter, wall thickness, bend radius, and surface finish using calibrated gauges, ultrasonic thickness testers, and surface profilometers.
- Coiling and Packaging: The inspected coil tube is wound onto a steel core, wrapped with protective film, and secured on a wooden pallet for shipping.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. is primarily engineered for use in the following application domains:
- Constant Water Volume Fan Coil Units: The coil tube serves as the core heat exchange component in constant water volume (CV) fan coil units, where a fixed flow rate of water is circulated through the coil to maintain consistent thermal output. This design is widely deployed in commercial buildings, hotels, hospitals, and office complexes.
- Variable Air Volume (VAV) Systems: The coil tube integrates with VAV terminal units to provide precise temperature control in zoned HVAC systems.
- Casette and Concealed Ceiling Units: The compact coil geometry is ideal for installation within suspended ceiling plenums in commercial and residential spaces.
- Industrial Process Cooling: The corrosion-resistant properties of SUS316L grade make the coil tube suitable for heat exchange in chemical processing, food and beverage manufacturing, and pharmaceutical production facilities.
- Marine HVAC Systems: The superior chloride resistance of austenitic stainless steel renders the coil tube appropriate for marine and offshore HVAC installations where salt spray corrosion is a concern.
Quality Certifications and Compliance
The coil tube product is manufactured under a comprehensive quality management system and conforms to the following international and national standards:
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System certification
- ASTM A213 / ASTM A269 — Specification for seamless and welded austenitic stainless steel tubular products for boiler, heat exchanger, and similar service
- EN 10217-7 — Technical delivery conditions for austenitic stainless steel tubes for heat exchangers
- GB/T 14977 — Chinese national standard for cold-rolled stainless steel seamless tubes
- GB/T 17897 — Chinese national standard for stainless steel welded tubes for heat exchangers
- ASME B36.19M — Dimensions and tolerances for welded and seamless wrought stainless steel pipe and tube
- ASTM A967 — Standard practice for chemical cleaning and passivation of stainless steel parts
- SGS Testing Report — Third-party verification of chemical composition, mechanical properties, and dimensional accuracy
- Mill Test Certificate (MTC) — EN 10204 3.1 — Full material traceability documentation
Unique Selling Points
1. Constant Water Volume Optimization: The coil tube geometry is specifically engineered for constant water volume fan coil unit operation, ensuring uniform flow distribution and consistent thermal performance across the entire heat exchange surface, minimizing hot spots and thermal stratification.
2. Superior Corrosion Durability: With SUS304 and SUS316L material options, the coil tube provides exceptional resistance to corrosion in humid, chemically aggressive, and chloride-laden environments, extending service life beyond 20 years under normal operating conditions.
3. High Heat Transfer Efficiency: The optimized coil pitch and tube diameter combination maximizes turbulent flow within the tube, achieving U-values exceeding 450 W/(m²·K) when paired with aluminum fins — significantly outperforming conventional straight-tube designs.
4. Precision Manufacturing: Automated coil forming and TIG welding processes ensure consistent dimensional accuracy (±0.1 mm tolerance on OD), uniform wall thickness, and leak-free weld seams verified by 100% hydrostatic testing.
5. Flexible Customization: Wenzhou Jixing Metal Materials Co., Ltd. offers fully customizable coil tube configurations — including variable outer diameters, wall thicknesses, coil lengths, and bend radii — to meet project-specific design requirements.
6. Full Traceability: Each batch is accompanied by a complete EN 10204 3.1 Mill Test Certificate, SGS third-party inspection report, and chemical analysis documentation, ensuring complete material traceability and regulatory compliance.
Conclusion
The Stainless Steel Coil Tube (Product No. 1369) from Wenzhou Jixing Metal Materials Co., Ltd. represents a high-performance, precision-engineered solution for constant water volume fan coil unit heat exchange applications. Combining the corrosion resistance of austenitic stainless steel with optimized coil geometry and rigorous quality control, this product delivers reliable thermal performance, extended service life, and full compliance with international standards — making it an ideal choice for commercial HVAC, industrial process cooling, and marine applications worldwide.