Stainless Steel Coil Tube for Fan Coil Unit (FCU) Heating Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered heat exchange component manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for integration into Fan Coil Units (FCU) within commercial and residential heating, ventilation, and air conditioning (HVAC) systems. This product represents a critical element in hydronic heating applications where thermal efficiency, corrosion resistance, and long-term durability are paramount.
Unlike conventional copper coil assemblies, the stainless steel coil tube offers superior resistance to chemical degradation, thermal cycling fatigue, and mechanical vibration—making it an ideal material choice for demanding HVAC environments where water quality variability and continuous operational cycles are common.
Material & Properties
Base Material Composition
- Grade: Austenitic Stainless Steel (AISI 304 / AISI 316L)
- Chemical Composition (AISI 304): Chromium (Cr) ≥ 18.0%, Nickel (Ni) ≥ 8.0%, Manganese (Mn) ≤ 2.0%, Carbon (C) ≤ 0.08%, Silicon (Si) ≤ 1.0%
- Chemical Composition (AISI 316L): Chromium (Cr) ≥ 16.5%, Nickel (Ni) ≥ 10.0%, Molybdenum (Mo) 2.0–3.0%, Carbon (C) ≤ 0.03%
- Surface Treatment: Passivated (Pickling & Passivation) or Electropolished finish
Mechanical & Physical Properties
- Tensile Strength: ≥ 520 MPa (AISI 304); ≥ 515 MPa (AISI 316L)
- Yield Strength: ≥ 205 MPa
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C
- Operating Temperature Range: -200°C to +870°C
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and intergranular corrosion; AISI 316L additionally resistant to chlorides and acidic environments
Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 8 mm / 10 mm / 12 mm (customizable) |
| Tube Wall Thickness | 0.5 mm – 1.0 mm |
| Coil Pitch (Spacing) | 15 mm – 25 mm (adjustable per design) |
| Number of Rows | 1 – 4 rows (configurable) |
| Fins per Inch (FPI) | 10 – 12 FPI (aluminum fin attachment) |
| Fin Material | Aluminum (Al-Mg1) or Copper-plated Aluminum |
| Maximum Working Pressure | 1.6 MPa (16 bar) |
| Hydrostatic Test Pressure | 2.4 MPa (24 bar) |
| Maximum Flow Velocity | 2.5 m/s (water side) |
| Overall Heat Transfer Coefficient (U-value) | ≥ 50 W/(m²·K) (air/water) |
| Standard Length | 600 mm – 2400 mm |
| Connection Type | Flanged / Threaded / Brazed / Welded |
| Applicable Media | Water, Glycol-water mixture, Brine |
| Service Life | ≥ 25 years (under normal operating conditions) |
Manufacturing Process
- Material Selection & Inspection: Raw stainless steel seamless or welded tubing is sourced from certified mills. Incoming material undergoes spectrographic analysis (OES) to verify chemical composition and mechanical property testing per ASTM A269 / EN 10217-7.
- Cutting & Deburring: Tubes are precision-cut to specified lengths using automated laser or cold-saw cutting machines, followed by mechanical deburring to ensure clean end faces suitable for brazing or welding.
- Coil Forming (Bending): Tubes are formed into serpentine or U-bend coil configurations using CNC-controlled hydraulic bending machines. Bending radii are controlled to prevent wall thinning, wrinkling, or ovality exceeding 5% of nominal OD.
- Fin Insertion (Finning): Aluminum fins are inserted into the coil assembly using a fin insertion machine, achieving uniform fin spacing and proper engagement with tube surfaces. Brazing bond strength is verified per ASTM B827.
- Brazing: The tube-fin assembly undergoes vacuum brazing (atmosphere: N₂ or vacuum < 10⁻³ mbar) at temperatures between 620°C and 680°C, using phosphorus-copper or silver-bearing brazing filler metals (AWS BCuP-6).
- Pressure Testing: Each coil assembly is hydrostatically tested at 1.5× maximum working pressure (2.4 MPa) for a minimum of 30 minutes to detect leaks or structural defects.
- Surface Treatment: Post-brazing pickling and passivation is performed to remove oxidation scales and restore the passive chromium oxide layer, ensuring optimal corrosion resistance.
- Final Inspection & Packaging: Dimensional verification, visual inspection, and pressure test documentation are completed. Products are packaged in protective foam-lined cartons with desiccant to prevent moisture damage during transit.
Applications
Primary Application: Fan Coil Units (FCU) in Heating Systems
The stainless steel coil tube serves as the core heat exchange element within Fan Coil Units, which are terminal units used in central air-conditioning and heating systems. The FCU operates by circulating heated or chilled water through the coil tube while a fan forces air across the finned coil surface, transferring thermal energy to or from the air stream.
Specific Application Domains
- Commercial Buildings: Office complexes, retail centers, hotels, and hospitals where precise temperature control and air quality are essential.
- Residential HVAC: High-end residential buildings utilizing central hydronic heating systems with individual room temperature regulation.
- Industrial Processes: Clean rooms, pharmaceutical facilities, and food processing plants requiring corrosion-resistant heat exchange components.
- Marine & Coastal Environments: AISI 316L coil tubes are particularly suited for coastal buildings and marine applications where chloride-induced corrosion is a concern.
- Geothermal Systems: Integration with ground-source heat pump systems for energy-efficient space heating and cooling.
Operational Principle in FCU Systems
In a typical FCU heating application, hot water (typically 60–80°C) flows through the stainless steel coil tube at controlled velocities. The thermal energy is conducted through the tube walls to the attached aluminum fins, which present a large surface area for convective heat transfer to the moving air stream. The stainless steel material maintains dimensional stability and corrosion resistance under continuous thermal cycling, ensuring consistent heat transfer performance over decades of operation.
Quality Certifications & Standards Compliance
Applicable Standards
- Material Standards: ASTM A269 (Stainless Steel Tubing for Heat Exchangers); EN 10217-7 (Heat Exchanger Tubes); JIS G3459
- Welding/Brazing Standards: AWS D10.9 (Brazing of Stainless Steel); ISO 13919 (Brazing of Copper and Copper Alloys)
- Product Standards: EN 14773 (Space Heaters – General Requirements); UL 1995 (Unitary Air-Conditioning and Air-Source Heat Pump Equipment)
- Pressure Vessel Standards: ASME Section VIII (where applicable for pressurized components)
Certification Programs
- ISO 9001:2015: Quality Management System certification ensuring consistent manufacturing quality
- ISO 14001:2015: Environmental Management System certification for sustainable manufacturing practices
- CE Marking: Conformity with European Union directives for HVAC components
- SGS / BV Inspection: Third-party quality verification available upon request
- Mill Test Reports (MTR): Provided with each batch, documenting chemical composition, mechanical properties, and heat treatment records
Unique Selling Points
- Exceptional Corrosion Resistance: The austenitic stainless steel construction provides immunity to the corrosion failures commonly experienced with copper coil tubes in systems with variable water chemistry, significantly extending service life beyond conventional materials.
- Thermal Cycling Durability: Superior resistance to thermal fatigue ensures reliable performance across millions of heating/cooling cycles without degradation of heat transfer efficiency.
- Hygienic Surface Properties: Smooth, non-porous surfaces prevent biofilm formation and microbial growth—critical for pharmaceutical, food, and healthcare applications.
- Full Recyclability: Stainless steel is 100% recyclable without loss of material properties, supporting sustainable building practices and green building certification programs (LEED, BREEAM).
- Custom Engineering Capability: Wenzhou Jixing Metal Materials Co., Ltd offers tailored coil configurations—including non-standard pitches, multi-row designs, and specialized connection geometries—to meet specific FCU design requirements.
- Reduced Maintenance Costs: The extended service life and resistance to fouling result in lower total cost of ownership (TCO) compared to conventional copper coil alternatives, particularly in aggressive water environments.
Technical Notes
Design Consideration: When integrating stainless steel coil tubes into FCU systems, engineers should account for the lower thermal conductivity of stainless steel (approximately 16.3 W/(m·K)) compared to copper (approximately 398 W/(m·K)). This necessitates optimized fin geometry, increased fin density, or slightly larger coil surface area to achieve equivalent heat transfer performance. Computational Fluid Dynamics (CFD) modeling is recommended for detailed thermal design validation.
Water Treatment: Although stainless steel coil tubes offer superior corrosion resistance, proper water treatment remains essential to prevent scaling and optimize long-term performance. Water quality should meet ASHRAE Guideline 12 or equivalent standards.
Conclusion
The Stainless Steel Coil Tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd represents a technically advanced solution for heat exchange applications in Fan Coil Units within heating systems. By combining the proven reliability of austenitic stainless steel with precision manufacturing techniques, this product delivers outstanding performance, durability, and value for demanding HVAC applications worldwide. The integration of this coil tube technology into modern heating systems exemplifies the metallurgical advances that enable more efficient, sustainable, and long-lasting building services infrastructure.