Stainless Steel Coil Tube for Fan Coil Unit Heat Exchange Systems
Product Overview
The stainless steel coil tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered heat exchange component designed specifically for Fan Coil Unit (FCU) systems in commercial HVAC (Heating, Ventilation, and Air Conditioning) applications. This product is supplied in continuous coil form, enabling efficient downstream processing into serpentine, helical, or multi-row configurations that maximize thermal transfer surface area within compact installation envelopes.
Based on rigorous thermal balance analysis of fan coil unit heat exchange characteristics, the coil tube geometry and material selection are optimized to achieve superior heat transfer coefficients while maintaining structural integrity under cyclic thermal loading conditions. The coil form factor provides inherent flexibility in installation routing and facilitates compact packaging of heat exchangers within air handling units.
Material & Properties
The stainless steel coil tube is fabricated from high-purity austenitic stainless steel grades, selected for their exceptional corrosion resistance, thermal conductivity, and mechanical durability in demanding HVAC environments.
Material Grades Available:
- 304 (UNS S30400) — General-purpose grade with excellent corrosion resistance and formability
- 316 (UNS S31600) — Enhanced molybdenum content for superior resistance to chlorides and aggressive fluids
- 316L (UNS S31603) — Low-carbon variant for improved weldability and intergranular corrosion resistance
- 321 (UNS S32100) — Titanium-stabilized grade for elevated temperature service
Key Material Properties:
- Thermal conductivity: 14.9–16.3 W/(m·K) at 20°C
- Maximum service temperature: up to 870°C (304), 870°C (316)
- Minimum service temperature: cryogenic compatible down to −196°C
- Corrosion resistance: excellent against water, steam, and non-oxidizing acids
- Mechanical strength: yield strength ≥ 205 MPa (annealed condition)
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm (¼"), 9.53 mm (⅜"), 12.70 mm (½") | ASTM A213 / EN 10216-5 |
| Wall Thickness | 0.50 mm – 1.50 mm (customizable) | ASTM A269 |
| Coil Inner Diameter (ID) | 300 mm – 600 mm (as per order) | ISO 4413 |
| Coil Length per Spool | 10 m – 500 m (continuous) | — |
| Surface Finish | 2B, BA (Bright Annealed), or Pickled & Passivated | ASTM A480 | Surface Roughness (Ra) | ≤ 0.4 μm (BA finish); ≤ 0.8 μm (2B finish) | ISO 1302 |
| Temperature Range | −40°C to +250°C (continuous operation) | — |
| Pressure Rating | Up to 1.6 MPa (design pressure, depending on wall thickness) | EN 10216-5 |
| Tolerance on OD | ±0.05 mm (precision drawn) | ASTM A213 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A269 |
| Heat Treatment | Solution annealed (1050°C – 1150°C) followed by water quench | ASTM A213 |
| Coating / Passivation | Chromic acid passivation or citric acid passivation available | ASTM A380 |
Manufacturing Process
The production of stainless steel coil tubes follows a multi-stage precision manufacturing sequence:
- Strip Preparation: Cold-rolled stainless steel strip is supplied from certified mills, verified for chemical composition (via spectroscopic analysis) and mechanical properties.
- Forming / Seam Welding: The flat strip is formed into a circular cross-section and seam-welded using continuous TIG (Tungsten Inert Gas) or laser welding under argon shielding atmosphere to prevent oxidation.
- Precision Drawing: The seamless or welded tube is cold-drawn through precision-die sets to achieve exact dimensional tolerances on OD and wall thickness.
- Solution Annealing: Tubes are heat-treated at 1050–1150°C in a controlled atmosphere furnace, followed by rapid water quenching to achieve a fully austenitic, stress-free microstructure.
- Pickling & Passivation: Surface oxides are removed via controlled acid pickling; a protective chromium oxide passive layer is formed to enhance corrosion resistance.
- Coiling: The finished tube is coiled onto precision-machined coil drums with controlled winding tension to prevent deformation or kinking.
- Quality Inspection: Each coil undergoes dimensional verification, hydrostatic pressure testing, visual surface inspection, and (where applicable) eddy current flaw detection.
Applications
- Commercial HVAC Systems: Primary component in fan coil units (FCU) for air conditioning, heating, and dehumidification in office buildings, hospitals, hotels, and shopping malls.
- Chilled Water Heat Exchangers: Serpentine coil configurations for chilled water and hot water circuits in central air handling systems.
- Industrial Process Cooling: Precision temperature control in pharmaceutical, food processing, and chemical manufacturing facilities.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration units requiring high corrosion resistance.
- Marine HVAC: Saltwater-resistant coil assemblies in shipboard air conditioning systems (316L grade recommended).
- Clean Room HVAC: Low-outgassing, high-purity stainless steel coils for semiconductor fabrication and biotech clean rooms.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality management systems and product certifications:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- CE Marking — Conformity with European directives for pressure equipment (PED 2014/68/EU)
- ASTM Compliance — Products manufactured and tested per ASTM A213, A269, A270, and A480
- EN Standards — Compliance with EN 10216-5 (seamless tubes) and EN 10217-7 (welded tubes)
- Mill Test Certificates (MTC) — EN 10204 3.1 certificates provided with each shipment
- Hydrostatic Testing — 100% pressure testing per EN 10204 / ASTM A530
- Third-Party Inspection — Available upon request (SGS, Bureau Veritas, TUV)
Unique Selling Points
Thermally Optimized Design: Coil tube dimensions and material properties are specifically calibrated based on validated thermal balance models of fan coil unit heat exchange performance, ensuring optimal coefficient of performance (COP) in installed systems.
- Continuous Coil Supply: Delivered in seamless continuous coil form, eliminating butt joints and reducing leak points in downstream heat exchanger fabrication.
- Precision Dimensional Control: ±0.05 mm OD tolerance ensures reliable fit with heat exchanger headers and expansion joints.
- Superior Corrosion Resistance: Austenitic stainless steel matrix provides decades of service life without degradation in aqueous HVAC environments.
- Low Surface Roughness: Bright annealed finish (Ra ≤ 0.4 μm) minimizes fouling accumulation, maintaining long-term heat transfer efficiency.
- Customization Capability: Flexible production parameters (OD, wall thickness, coil diameter, material grade) to meet project-specific thermal and mechanical requirements.
- Full Traceability: Each coil is batch-traceable with complete material certification documentation.
Technical Notes
Based on thermal balance analysis of fan coil unit heat exchange characteristics, the effective heat transfer area of a coil tube configuration is governed by the equation:
Q = U × A × ΔTlm
Where Q is the heat transfer rate (W), U is the overall heat transfer coefficient (W/m²·K), A is the effective heat exchange surface area (m²), and ΔTlm is the Logarithmic Mean Temperature Difference (K). The coil tube's continuous helical geometry maximizes A within a constrained volume, while the stainless steel material's thermal conductivity and surface finish properties directly influence U, collectively determining system efficiency.
Wenzhou Jixing Metal Materials Co., Ltd is committed to supplying coil tubes that meet the most demanding specifications for modern HVAC thermal management systems, backed by over three decades of metallurgical expertise and continuous process improvement.