Stainless Steel Coil Tube for Fan Coil Units (FCU) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Product No. 449) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed primarily for integration into Fan Coil Units (FCUs) and related HVAC (Heating, Ventilation, and Air Conditioning) systems. Unlike conventional carbon steel or copper coil tubes, this product leverages the superior corrosion resistance, mechanical integrity, and long-term thermal stability of austenitic stainless steel to deliver extended service life in demanding indoor air-handling environments.
Coil tubes serve as the critical heat exchange medium within FCUs, transferring thermal energy between a circulating fluid (water or refrigerant) and ambient air. The coiled geometry maximizes the surface area-to-volume ratio, enabling efficient convective and conductive heat transfer within compact installation footprints. Wenzhou Jixing's stainless steel coil tube is engineered to meet the rigorous demands of commercial, industrial, and residential HVAC applications where reliability and hygiene are paramount.
2. Material Composition & Properties
2.1 Grade Selection
The primary material grade employed is Austenitic Stainless Steel, specifically conforming to the following international standards:
- ASTM A213 TP304 / TP316L — Seamless stainless steel tubing for heat exchangers
- EN 10216-5 — Heat exchanger and radiator tubes
- GB/T 14976 — Chinese national standard for cold-rolled or cold-drawn seamless stainless steel tubes
2.2 Chemical Composition (Typical — Grade 304/316L)
| Element | Grade 304 (%) | Grade 316L (%) |
|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.03 |
| Chromium (Cr) | 18.0 – 20.0 | 16.5 – 18.5 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 | ≤ 0.030 |
| Iron (Fe) | Balance | Balance |
2.3 Key Mechanical & Physical Properties
| Property | Grade 304 | Grade 316L |
|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 |
| Elongation (% at break) | ≥ 40 | ≥ 40 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 14.6 |
| Operating Temperature Range (°C) | -196 to +870 | -196 to +870 |
| Density (kg/m³) | 8.00 | 8.03 |
2.4 Surface Finish Options
- Pickled & Passivated (PP) — Standard finish; removes scale and forms a protective chromium oxide layer
- Bright Annealed (BA) — Smooth, reflective surface; reduced roughness for enhanced heat transfer
- Electropolished (EP) — Ultra-smooth surface (Ra ≤ 0.4 μm); ideal for hygienic and pharmaceutical applications
3. Dimensional Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 – 25.4 mm (¼" – 1") | ASTM B730 / ASHRAE 15 |
| Wall Thickness (WT) | 0.5 – 1.5 mm | — |
| Coil Diameter (CD) | 50 – 300 mm | — |
| Coil Length (CL) | 1 – 50 m (customizable) | — |
| Coil Pitch (P) | 8 – 30 mm | ASHRAE 15 |
| OD Tolerance | ±0.05 mm | ASTM A213 |
| WT Tolerance | ±10% | ASTM A213 |
| Surface Roughness (Ra) | 0.8 – 3.2 μm (standard); ≤ 0.4 μm (EP) | ISO 1302 |
| End Forming | Plain, Flanged, Soldered, Brazed, or Custom | — |
4. Manufacturing Process
The production of Wenzhou Jixing's stainless steel coil tube follows a rigorously controlled multi-stage manufacturing workflow:
- Raw Material Procurement & Inspection — Ingot or strip material sourced from certified mills; verified via spectroscopic analysis (OES) and mechanical testing prior to processing.
- Tube Forming — Seamless tubes produced via Autoclave Annealing (AOD) or VAC (Vacuum Arc Remelting) casting, followed by hot rolling and cold drawing to achieve precise OD and WT tolerances. Alternatively, welded tubing may be produced via TIG (Tungsten Inert Gas) welding with argon shielding.
- Heat Treatment — Solution annealing at 1040–1150°C followed by rapid water quench to ensure full austenitic microstructure and maximum corrosion resistance.
- Coil Forming (Cold Bending) — Precision CNC-controlled coiling machines form the tube into the specified spiral geometry. Bending radius is carefully calibrated to avoid wall thinning, ovalization, or work hardening at the bend apex. Minimum bend radius typically ≥ 4× OD.
- Pickling & Passivation — Immersion in nitric acid/hydrofluoric acid blend (or citric acid for environmentally controlled processes) to remove oxidation scale, followed by passivation to re-establish the protective Cr₂O₃ passive film.
- Quality Control & Testing — Comprehensive inspection regime including dimensional verification, hydrostatic pressure testing, eddy current testing (ECT) for wall integrity, and visual surface inspection.
- End Processing & Packaging — Tube ends are cut, deburred, and formed (flanged/brazed) as specified. Coils are protected with moisture-absorbent packaging and shipped on wooden pallets or in protective crates.
5. Applications
The stainless steel coil tube is integral to a diverse range of thermal management and fluid distribution systems:
5.1 HVAC Systems (Primary Application)
- Fan Coil Units (FCUs) — Chilled water or hot water coil tubes for commercial building air conditioning
- Cassette & Concealed Duct FCUs — Custom coil configurations for ceiling-mounted and ducted installations
- Vertical Radiators & Panel Heaters — Heating coils for residential and light commercial applications
5.2 Industrial Applications
- Process Cooling & Heating — Heat exchangers in chemical, petrochemical, and pharmaceutical plants
- Food & Beverage Processing — Pasteurization, sterilization, and refrigeration systems requiring hygienic-grade tubing
- Power Generation — Condenser tubes and steam coil assemblies
5.3 Specialized Applications
- Marine & Offshore — Corrosion-resistant heat exchange coils in seawater-cooled systems
- Cleanroom & Laboratory HVAC — High-purity air handling with electropolished coil surfaces
- Automotive & Transportation — Cabin heating/cooling coils for rail and bus HVAC systems
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management infrastructure ensuring adherence to international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — Ensures consistent product quality and continuous improvement |
| ISO 14001:2015 | Environmental Management System — Sustainable manufacturing practices |
| EN 10204 3.1 | Material Test Certificate — Third-party verified material conformity documentation |
| CE Marking | European Conformity — Compliance with EU Machinery and Pressure Equipment Directives |
| ASTM A213 | Standard Specification for Seamless Ferritic, Austenitic, and Martensitic Stainless Steel Tubing for Heat Exchangers |
| GB/T 14976 | Chinese National Standard for Cold-Rolled/Cold-Drawn Seamless Stainless Steel Tubes |
| ASHRAE 15 | Standard for the Construction of Air-Cooling and Air-Heating Coils |
7. Unique Selling Points
- Superior Corrosion Resistance — Austenitic stainless steel composition provides exceptional resistance to condensation-induced pitting, chloride attack, and acidic condensate corrosion that commonly degrades carbon steel coils, resulting in service lives exceeding 20–25 years.
- Hygienic Compliance — Electropolished surface finish eliminates micro-pores and crevices where bacterial biofilm can accumulate, meeting EHEDG (European Hygienic Engineering Design Group) and 3-A sanitary standards for food-grade and pharmaceutical applications.
- Precision Engineering — CNC-controlled coil forming ensures consistent pitch, bend radius, and dimensional accuracy, optimizing heat transfer coefficients and minimizing pressure drop across the coil assembly.
- Customization Capability — Flexible manufacturing parameters (OD, WT, coil diameter, pitch, length, end forming) enable tailored solutions for OEM integrators and specialized engineering projects.
- Full Traceability — Each coil lot is accompanied by a comprehensive material test certificate (MTC) with heat number traceability, ensuring full supply chain accountability from raw material to finished product.
8. Conclusion
Wenzhou Jixing Metal Materials Co., Ltd.'s stainless steel coil tube (Product No. 449) represents a state-of-the-art solution for HVAC and industrial heat exchange applications. By combining the intrinsic durability and corrosion resistance of austenitic stainless steel with precision manufacturing and rigorous quality assurance, this product delivers unmatched reliability, energy efficiency, and total cost of ownership advantage over conventional coil tube alternatives. The product's versatility across commercial, industrial, and hygienic applications underscores its position as a preferred component in modern thermal management systems.