Stainless Steel Coil Tube — Fan Coil Unit (FCU) Heat Exchanger Component
Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular component designed primarily for use in Fan Coil Unit (FCU) systems, which serve as terminal units in commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) applications. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this coil tube product represents a critical heat exchange element that facilitates efficient thermal transfer between the circulating refrigerant or hot water and the ambient air stream within fan coil assemblies.
Coil tubes are formed by drawing and bending stainless steel wire or thin-wall tubing into helical configurations, creating a high surface-area-to-volume ratio that maximizes convective and radiative heat exchange. The product is classified under industrial literature reference No. 1199 and is integral to the performance optimization of domestic fan coil unit systems in the Chinese HVAC market.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, selected for its exceptional corrosion resistance, thermal conductivity, and mechanical durability under cyclic thermal loading conditions.
- Primary Alloy Grades: AISI 304 (UNS S30408), AISI 316 (UNS S31608), and AISI 321 (UNS S32100)
- Corrosion Resistance: Superior resistance to chloride-induced pitting and crevice corrosion, particularly in humid environments typical of HVAC condensate exposure
- Thermal Conductivity: 14–16 W/(m·K) at ambient temperature, ensuring efficient heat transfer across the tube wall
- Mechanical Strength: Yield strength ≥ 205 MPa (AISI 304); tensile strength ≥ 515 MPa
- Operating Temperature Range: −196°C to +870°C (AISI 304); extended to +1100°C (AISI 316 in oxidizing atmospheres)
- Surface Finish: Electropolished or passivated to achieve Ra ≤ 0.4 μm for minimized fouling and enhanced fluid dynamics
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 12.7 mm (1/8" to 1/2") | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.3 mm – 1.0 mm | ISO 13929 |
| Coil Pitch | 2.0 mm – 6.0 mm | Manufacturer tolerance ±0.1 mm |
| Coil Length | 0.5 m – 12.0 m (customizable) | Project-specific |
| Helix Diameter | 50 mm – 500 mm | Per heat exchanger design |
| Material Grade | AISI 304 / 316 / 321 | ASTM A270 / EN 10217-7 |
| Maximum Operating Pressure | 1.6 MPa – 4.0 MPa | ASME BPV Code Section VIII |
| Surface Treatment | Electropolished / Chemical Passivation | ASTM A967 |
| Hydrostatic Test Pressure | 1.5× Maximum Operating Pressure | GB/T 24511 |
| Welding Method | TIG (GTAW) / Orbital Welding | ISO 15614-1 |
| Maximum Heat Flux | Up to 80 kW/m² | ASHRAE Handbook — HVAC Systems and Equipment |
Manufacturing Process
The production of stainless steel coil tubes for fan coil unit applications follows a rigorous multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tubing conforming to ASTM A269/A270 specifications, with certified chemical composition and mechanical property test reports.
- Coil Winding & Forming: Computerized CNC (Computer Numerical Control) winding machines form the helical coil geometry with precise pitch control, utilizing servo-driven tension systems to prevent work hardening and deformation.
- Tube Expansion & Fitting: End tubes are mechanically expanded or brazed into copper or stainless steel header manifolds, creating a hermetic fluid circuit with leak-tight joints.
- Welding Operations: TIG (Tungsten Inert Gas) welding is employed for header-to-coil junctions, with argon gas shielding to prevent oxidation. Orbital welding ensures consistent bead geometry for high-cycle fatigue resistance.
- Heat Treatment: Solution annealing at 1040–1150°C followed by water quenching restores full austenitic microstructure and eliminates residual stresses from cold forming.
- Surface Finishing: Electropolishing removes the work-hardened surface layer, producing a smooth, chromium-rich passive film that enhances corrosion resistance and reduces microbial adhesion.
- Quality Inspection: 100% hydrostatic pressure testing, dimensional verification via laser scanning, and surface defect detection using eddy current or dye penetrant methods.
Applications
The stainless steel coil tube serves as the core heat exchange element in a wide range of thermal management systems:
- Fan Coil Units (FCU): Primary application — integrated into air-side terminal units for commercial buildings, hospitals, hotels, and data centers, where the coil tube transfers thermal energy between the water/refrigerant loop and the airstream.
- VRF (Variable Refrigerant Flow) Systems: Used in multi-split air conditioning systems for precise temperature modulation across multiple zones.
- Chilled Water Distribution: Coil tubes in air handlers and roof units for large-scale commercial cooling.
- Industrial Process Cooling: Heat exchangers in food processing, pharmaceutical manufacturing, and chemical production lines requiring hygienic-grade stainless steel construction.
- Marine & Offshore HVAC: Corrosion-resistant coil assemblies for shipboard and offshore platform climate control systems.
- Clean Room Environments: Low-particulate coil designs for semiconductor fabrication, biotechnology, and laboratory facilities.
Quality Certifications & Standards Compliance
All products manufactured by Wenzhou Jixing Metal Materials Co., Ltd are produced in accordance with internationally recognized quality management systems and industry standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices
- GB/T 14976 — Chinese National Standard for seamless stainless steel tubes for general use
- GB/T 24511 — Chinese National Standard for pressure vessel welding quality requirements
- ASTM A269 / A270 — American material specifications for austenitic stainless steel tubing
- EN 10217-7 — European standard for stainless steel tubes for pressure purposes
- ASME BPV Code — Boiler and Pressure Vessel Code compliance for pressure-rated applications
- CE Marking — Conformity with European Machinery and Pressure Equipment Directives
- UL / CSA Listing — Available for North American market compliance upon request
Unique Selling Points
The Wenzhou Jixing stainless steel coil tube product distinguishes itself in the competitive HVAC component market through several key advantages:
- Superior Corrosion Durability: The use of 316-grade stainless steel provides extended service life in high-humidity and condensate-rich environments, significantly reducing maintenance intervals compared to copper or aluminum coil alternatives.
- Hygienic Construction: Electropolished surfaces with Ra ≤ 0.4 μm prevent biofilm accumulation, making the product suitable for food-grade and pharmaceutical applications without additional coating requirements.
- Precision CNC Manufacturing: Automated coil winding ensures dimensional consistency (±0.05 mm tolerance on pitch), resulting in optimized airflow distribution and enhanced heat transfer efficiency within fan coil assemblies.
- Thermal Performance Optimization: The high surface-area-to-volume ratio of the helical coil geometry, combined with the thermal conductivity of austenitic stainless steel, achieves heat exchange coefficients exceeding 80 W/(m²·K) under standard operating conditions.
- Full Traceability: Each production batch is accompanied by mill test certificates (MTC), chemical analysis reports, and mechanical property documentation, enabling complete supply chain traceability for OEM integrators.
- Customization Capability: Flexible manufacturing parameters (diameter, pitch, length, material grade) allow tailored solutions for specific fan coil unit designs and thermal load requirements.
Conclusion
The stainless steel coil tube produced by Wenzhou Jixing Metal Materials Co., Ltd represents a technologically advanced, quality-certified component essential to the performance and reliability of modern fan coil unit systems. Its adherence to international material and manufacturing standards, combined with superior corrosion resistance and thermal efficiency, positions it as a preferred solution for OEM manufacturers and system integrators in the global HVAC industry. As domestic Chinese fan coil unit technology continues to advance in performance and energy efficiency, the coil tube remains a foundational element whose quality directly influences system-level thermal output, operational longevity, and total cost of ownership.