Stainless Steel Coil Tube for Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Product Code: 1398) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product specifically designed for integration into Fan Coil Units (FCUs) operating under Variable Air Volume (VAV) systems. This coil tube serves as the primary heat exchange medium within HVAC (Heating, Ventilation, and Air Conditioning) terminal units, facilitating efficient thermal transfer between the working fluid (water or refrigerant) and the ambient air stream.
Unlike conventional copper or carbon steel coil tubes, the stainless steel variant offers superior corrosion resistance, extended service life, and enhanced structural integrity under variable pressure and temperature cycling conditions inherent to VAV operations. The coiled geometry maximizes the heat transfer surface area within a compact footprint, making it an ideal solution for modern energy-efficient building systems.
Material & Properties
The coil tube is fabricated from austenitic stainless steel, predominantly utilizing the following grades:
- Grade 304 (UNS S30400): General-purpose austenitic stainless steel with excellent corrosion resistance, weldability, and formability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- Grade 316 (UNS S31600): Enhanced corrosion resistance grade with 2–3% Molybdenum (Mo) addition, suitable for applications involving aggressive media or high-humidity environments.
Key Mechanical and Physical Properties:
- Tensile Strength: 515–720 MPa (Grade 304); 515–750 MPa (Grade 316)
- Yield Strength: 205–310 MPa (minimum)
- Elongation at Break: ≥40%
- Thermal Conductivity: 14–16 W/(m·K)
- Coefficient of Thermal Expansion: 16–18 × 10⁻⁶ /°C
- Operating Temperature Range: −196°C to +870°C
- Surface Finish: No. 4 Brushed or Mirror Polished (Ra ≤ 0.4 μm)
Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.7 mm / 15.88 mm | ±0.1 mm |
| Wall Thickness | 0.5 mm / 0.8 mm / 1.0 mm / 1.2 mm | ±0.05 mm |
| Coil Diameter (Bundle OD) | 150 mm – 600 mm (customizable) | ±2 mm |
| Tube Length per Circuit | 1.5 m – 6.0 m | ±5 mm |
| Number of Circuits | 1 – 12 | — |
| Fin Material | Aluminum (Al) or Stainless Steel (SS) | — |
| Fin Pitch | 10 – 14 FPI (Fins Per Inch) | ±0.5 FPI |
| Working Pressure | 1.0 – 2.5 MPa (design pressure) | — |
| Hydrostatic Test Pressure | 1.5× Design Pressure | — |
| Surface Roughness (Internal) | Ra ≤ 1.6 μm | — |
| Standard Reference | ASTM A213 / GB/T 12771 / EN 10216-5 | — |
Manufacturing Process
The production of stainless steel coil tubes involves a rigorous multi-stage manufacturing sequence:
- Material Selection and Incoming Inspection: Raw stainless steel coils are sourced from certified mills with full mill test certificates (MTC) conforming to ASTM A270 or equivalent standards. Each batch undergoes spectroscopic analysis for chemical composition verification.
- Forming and Sizing: The flat strip or raw tubing is cold-formed through precision roll-forming or seamless tube drawing processes to achieve the target OD and wall thickness with dimensional accuracy.
- Coiling and Spacing: The formed tube is wound into the designated coil geometry using computer-controlled coiling machinery. Uniform tube spacing is maintained to ensure consistent airflow distribution and optimal heat transfer performance.
- Fin Application (if applicable): Aluminum or stainless steel fins are mechanically bonded or mechanically inserted to augment the external heat transfer surface area.
- Welding and Brazing: Circuit connections and header integrations are performed using TIG (Tungsten Inert Gas) welding or high-silver-content brazing to maintain metallurgical integrity and prevent intergranular corrosion.
- Passivation and Cleaning: The completed coil tube undergoes acid pickling and passivation treatment to remove any mill scale or welding contamination, restoring the protective chromium oxide layer.
- Pressure Testing: Each unit is subjected to hydrostatic pressure testing at 1.5 times the design pressure, with a minimum hold time of 30 minutes, to verify leak-tightness and structural soundness.
Applications
The stainless steel coil tube is primarily engineered for the following applications:
- Variable Air Volume (VAV) Fan Coil Units: The coil tube operates efficiently across varying airflow rates, maintaining stable thermal performance as damper positions adjust to meet zone-specific cooling or heating demands.
- Commercial HVAC Systems: Suitable for office buildings, hospitals, hotels, and retail spaces where air quality and corrosion resistance are critical.
- Industrial Process Cooling: Utilized in chemical processing, pharmaceutical manufacturing, and food processing facilities requiring hygienic-grade heat exchange components.
- Marine and Coastal Environments: Grade 316 stainless steel coil tubes withstand saltwater-laden atmospheres without significant degradation.
- Low-Temperature Refrigeration: Austenitic stainless steel retains ductility at cryogenic temperatures, enabling reliable operation in refrigeration coils.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system with the following certifications:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- CE Marking — Conformity with European Health, Safety, and Environmental Protection Standards
- EN 10204 3.1 — Material Test Certificate per European standard
- ASTM A213 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing
- GB/T 12771 — Chinese National Standard for Welded Stainless Steel Tubes
Unique Selling Points: The integration of austenitic stainless steel into VAV fan coil unit coil tubes addresses the critical challenge of maintaining thermal efficiency while resisting corrosion-induced degradation. The product's superior fatigue resistance under cyclic thermal loading, combined with its hygienic surface characteristics and extended service life (exceeding 25 years in typical applications), delivers a total cost of ownership advantage over conventional carbon steel alternatives. The precision manufacturing tolerances ensure optimal hydraulic performance and minimal pressure drop across the coil circuit, contributing directly to energy efficiency in variable airflow operating modes.