Stainless Steel Coil Tube for Column-Mounted Fan Coil Units (FCU)
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Code: 1706
Product Category: HVAC Components — Coil Tubes
Product Overview
The stainless steel coil tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered heat exchange component specifically designed for column-mounted fan coil units (Column-mounted Fan Coil Units, CFU). These coil tubes serve as the core thermal transfer elements within the evaporator and condenser sections of HVAC (Heating, Ventilation, and Air Conditioning) systems. The product is engineered to meet the rigorous demands of commercial and industrial air conditioning applications, offering superior thermal efficiency, corrosion resistance, and long-term operational reliability in diverse environmental conditions.
As a critical component in the column-mounted fan coil unit architecture, the coil tube facilitates the exchange of thermal energy between the refrigerant circulating within the tube and the ambient air passing across the tube's exterior surface. The coil tube's geometry, material composition, and surface finish are all optimized to maximize the heat transfer coefficient while minimizing pressure drop across the refrigerant circuit.
Material & Properties
Primary Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, predominantly conforming to AISI 304 and AISI 316L grades, selected for their exceptional balance of mechanical strength, corrosion resistance, and thermal conductivity. The material specifications are as follows:
- Base Material: AISI 304 (UNS S30408) / AISI 316L (UNS S31603) austenitic stainless steel
- Carbon (C): ≤ 0.08% (304) / ≤ 0.03% (316L)
- Chromium (Cr): 18.0–20.0%
- Nickel (Ni): 8.0–10.5%
- Molybdenum (Mo): 2.0–2.5% (316L only)
- Manganese (Mn): ≤ 2.0%
- Sulfur (S): ≤ 0.03%
Key Physical and Mechanical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Density: 8.0 g/cm³
- Tensile Strength: ≥ 520 MPa (304) / ≥ 515 MPa (316L)
- Yield Strength: ≥ 205 MPa
- Elongation: ≥ 40%
- Operating Temperature Range: −196°C to +870°C
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and mild chemical corrosion; 316L grade provides additional resistance to chloride-induced pitting
- Surface Finish: BA (Bright Annealed) or No. 4 brushed finish, with optional hydrophilic/hydrophobic coating for enhanced heat transfer performance
Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | 9.52 mm / 12.7 mm / 15.88 mm (3/8" / 1/2" / 5/8") | ±0.1 mm |
| Wall Thickness | 0.5 mm / 0.8 mm / 1.0 mm | ±0.05 mm |
| Tube Length | Custom, typically 1.5 m – 6.0 m per pass | ±5 mm |
| Coil Pitch (Tube-to-Tube Spacing) | 12 mm – 25 mm (configurable) | ±0.5 mm |
| Bend Radius | 1.5× OD to 3× OD (minimum) | Per ASME B31.5 |
| Number of Rows | 1 – 6 rows (standard configurations) | As per unit design |
| Maximum Design Pressure | 2.5 MPa (refrigerant side) | Per ISO 5149 |
| Hydrostatic Test Pressure | 3.75 MPa (1.5× design pressure) | Per EN 1273 |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-407C, NH₃ (ammonia) | Per AHRI 340/440 |
| Fin Material (if applicable) | Aluminum (Al-Mg-Si alloy) or Copper-alloy fins | Per JIS H4000 |
| Fin Thickness | 0.10 mm – 0.15 mm | ±0.02 mm |
| Fin Density | 10 – 16 FPI (Fins Per Inch) | ±1 FPI |
| Coating Options | None / Hydrophilic / Anti-corrosion (TiO₂ nano-coating) | Per manufacturer spec |
| Applicable Standards | GB/T 14976, ASTM A213, EN 10216-5, ASME B31.5 | — |
Manufacturing Process
1. Raw Material Procurement and Inspection
Stainless steel seamless tubes or cold-drawn tubes are procured from certified mills (e.g., POSCO, Outokumpu, TISCO) and subjected to incoming quality control (IQC) inspections. Each batch undergoes spectrographic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition, along with mechanical property testing (tensile testing, hardness testing) and dimensional verification.
2. Cutting and End Preparation
Tubes are cut to specified lengths using precision plasma or laser cutting systems, with deburring and end-finishing operations to ensure clean, burr-free openings suitable for brazing or mechanical connection to headers (manifolds).
3. Bending and Forming
The coil tube assembly is formed using CNC (Computer Numerical Control) tube bending machines. The bending process employs a combination of mandrel-assisted bending and rotary draw bending to achieve precise bend geometries without inducing wall thinning, ovality, or wrinkling. The minimum bend radius is maintained at 1.5× the outer diameter to prevent material deformation and ensure long-term fatigue resistance.
4. Heat Treatment (Stress Relief)
Post-forming annealing is conducted at 1050°C – 1150°C in a protective atmosphere (argon or vacuum) to relieve residual stresses introduced during the bending process, restore full solution-annealed mechanical properties, and ensure dimensional stability.
5. Surface Treatment and Coating
The tube surface is cleaned through pickling and passivation (using citric acid or nitric acid solutions) to remove scale and contaminants. Optional surface coatings — including hydrophilic coatings to promote condensate drainage or TiO₂ nano-coatings for self-cleaning and anti-bacterial properties — are applied via chemical vapor deposition (CVD) or electrostatic spray methods.
6. Fin Stamping and Insertion (for Finned Coil Assemblies)
Aluminum fins are stamped from coil stock using high-speed die-stamping machines and inserted into the tube array at precise pitch intervals. The fins are mechanically bonded to the tubes through expansion, crimping, or brazing processes to ensure tight thermal contact.
7. Brazing and Assembly
Tube-to-header connections are brazed using silver-based filler alloys (Ag-Cu type, e.g., BCu915Ag or BAg-8) in a vacuum brazing furnace or controlled-atmosphere (nitrogen) furnace. The brazing temperature is maintained between 620°C and 720°C, ensuring full penetration and leak-free joints.
8. Pressure Testing and Quality Assurance
Each completed coil assembly undergoes:
- Hydrostatic Pressure Test: 3.75 MPa for 30 minutes, with zero leakage tolerance
- Helium Leak Detection: For critical applications, helium sniffing or mass spectrometry leak detection at sensitivity ≤ 1×10⁻⁸ Pa·m³/s
- Dimensional Inspection: CMM (Coordinate Measuring Machine) verification of critical dimensions
- Visual Inspection: Full-surface visual and dye-penetrant examination of all welds and joints
9. Final Cleaning and Packaging
Assembled coils are flushed with nitrogen to remove any residual flux or contaminants, then packaged in protective wrapping with desiccant bags to prevent oxidation during storage and transit.
Applications
Primary Applications
- Column-Mounted Fan Coil Units (CFU): The primary application domain — these coil tubes serve as evaporator/condenser cores in vertical column-mounted fan coil units used for localized temperature control in commercial buildings, hotels, hospitals, and institutional facilities.
- Chilled Water Systems: Integration into constant-volume and variable-volume chilled water distribution systems for precise zone-level thermal management.
- Heat Pump Systems: Utilization in air-source and ground-source heat pump terminal units where the coil tube acts as the indoor heat exchanger.
Industry Sectors
- Commercial HVAC: Office buildings, shopping malls, retail spaces, and hospitality establishments
- Healthcare Facilities: Hospitals, clinics, and laboratories requiring stringent air quality and temperature control
- Industrial Processes: Electronics manufacturing cleanrooms, food processing plants, and pharmaceutical production facilities
- Residential High-End: Luxury residential complexes and villas with individual zone climate control
- Special Environments: Coastal/marine environments, chemical processing areas, and high-humidity regions where corrosion resistance is paramount
Quality Certifications and Compliance
International Standards Compliance
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management
- ASME B31.5 — Pressure Piping, Process Piping
- EN 1273 — Heat Exchangers — Brazed Tube-in-Tube Heat Exchangers
- EN 10216-5 — Seamless Steel Tubes for Heat Exchangers
- ASTM A213 — Seamless Austenitic Stainless Steel Tubes for Heat-Transfer
- AHRI 340/440 — Performance rating standards for unitary air-conditioning and heat pump equipment
Material Certifications
- EN 10204 Type 3.1 — Material test certificates with full chemical and mechanical analysis
- Mill Test Reports (MTR) — Traceable documentation from certified steel mills
- NACE MR0175 / ISO 15156 — Compliance for sour service environments (where applicable)
Product-Specific Certifications
- CRAA (China Refrigeration and Air-Conditioning Industry Association) — Member certification
- CE Marking — European Conformity for HVAC components
- UL/CSA — Underwriters Laboratories / Canadian Standards Association listing (for North American market)
- SASO — Saudi Standards, Metrology and Quality Organization (for Middle East market)
Unique Selling Points
1. Premium Material Selection: Wenzhou Jixing Metal Materials Co., Ltd employs only certified grade stainless steel from internationally recognized mills, ensuring superior corrosion resistance and thermal performance far exceeding standard carbon steel alternatives.
2. Precision CNC Manufacturing: Full CNC-controlled bending, cutting, and assembly processes guarantee dimensional accuracy within ±0.1 mm tolerances, ensuring optimal fit and function within column-mounted fan coil unit architectures.
3. Extended Service Life: The austenitic stainless steel construction provides a design service life exceeding 25 years, significantly outperforming copper or aluminum alternatives in corrosive environments, reducing total cost of ownership (TCO).
4. Customizable Configurations: Flexible design parameters (tube diameter, wall thickness, row count, fin density, coil pitch) allow tailored solutions for specific thermal loads and unit dimensions, accommodating both standard and non-standard fan coil unit designs.
5. Advanced Surface Coatings: Optional hydrophilic and self-cleaning TiO₂ nano-coatings enhance condensate drainage efficiency by up to 40% and provide anti-bacterial properties, improving indoor air quality (IAQ) and reducing maintenance frequency.
6. Rigorous Quality Assurance: Multi-stage inspection protocols including spectrographic analysis, hydrostatic testing, helium leak detection, and CMM dimensional verification ensure 100