Stainless Steel Coil Tube for Fan Coil Units
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Category: Coil Tube (盘管) — HVAC & Thermal Exchange Applications
Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular component specifically designed for integration into horizontal fan coil units (Horizontal Fan Coil Unit, HFCU) and similar HVAC (Heating, Ventilation, and Air Conditioning) systems. This product is manufactured by Wenzhou Jixing Metal Materials Co., Ltd., a leading supplier in the Chinese stainless steel pipe and tube industry. The coil tube serves as the core heat exchange element within fan coil units, facilitating efficient thermal transfer between the refrigerant or hot water medium and the ambient air stream.
In the context of comfort performance evaluation for horizontal fan coil units, the coil tube's geometric configuration, material composition, and manufacturing quality directly influence thermal efficiency, pressure drop characteristics, noise generation, and overall occupant comfort. Wenzhou Jixing's coil tubes are engineered to meet the demanding requirements of modern building climate control systems while maintaining long-term structural integrity and corrosion resistance.
Material & Properties
Base Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, primarily utilizing the following grades depending on application requirements:
- AISI 304 (UNS S30408): Chromium-Nickel stainless steel with minimum 18% Cr and 8% Ni content, offering excellent general corrosion resistance and formability.
- AISI 316 (UNS S31603): Chromium-Nickel-Molybdenum stainless steel with minimum 16% Cr, 10% Ni, and 2% Mo, providing superior resistance to pitting and crevice corrosion in aggressive environments.
- AISI 321 (UNS S32100): Titanium-stabilized austenitic stainless steel suitable for elevated-temperature applications up to 870°C in continuous service.
Mechanical Properties
| Property | Specification (AISI 304) | Specification (AISI 316) |
|---|---|---|
| Tensile Strength (Minimum) | 515 MPa (74,700 psi) | 515 MPa (74,700 psi) |
| Yield Strength (0.2% Offset) | 205 MPa (29,700 psi) | 170 MPa (24,700 psi) |
| Elongation at Break (Minimum) | 40% | 40% |
| Density | 8.0 g/cm³ | 8.0 g/cm³ |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | 16.3 W/(m·K) |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C | 17.3 × 10⁻⁶ /°C |
Surface Finish
- Standard finish: 2B (Cold rolled, annealed, and bright pickled)
- Available finish: BA (Bright Annealed) for enhanced surface reflectivity
- Surface roughness (Ra): ≤ 0.8 μm for 2B finish; ≤ 0.4 μm for BA finish
Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8") |
| Tube Wall Thickness | 0.50 mm – 1.20 mm (customizable) |
| Coil Diameter | 50 mm – 300 mm (standard); up to 500 mm upon request |
| Coil Length per Unit | 2 m – 12 m (configurable based on heat exchange requirement) |
| Fin Pitch (if finned configuration) | 8 – 14 fins per inch (FPI) |
| Operating Pressure | Up to 1.6 MPa (16 bar) working pressure |
| Hydrostatic Test Pressure | 2.4 MPa (24 bar) — 1.5× working pressure |
| Operating Temperature Range | −40°C to +200°C |
| Maximum Design Temperature | 800°C (AISI 304); 870°C (AISI 321) |
| Connection Type | Flare, Groove, Threaded (NPT/BSP), or Solder/Brazed joints |
| Tolerance on OD | ±0.05 mm (±0.002") |
| Tolerance on Wall Thickness | ±10% of nominal |
| Standard Compliance | ASTM A269, ASTM A213, GB/T 12771, GB/T 21830 |
Manufacturing Process
The production of the stainless steel coil tube at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: High-purity stainless steel strip (coil) is sourced from certified mills and undergoes incoming inspection for chemical composition (via Spark OES — Optical Emission Spectrometry) and mechanical properties.
- Slitting and Leveling: The master coil is slit to the required strip width and cold-rolled to achieve the target wall thickness with controlled tolerance.
- Forming (Coiling): The flat strip is precisely formed into the desired tube diameter using a multi-station rotary draw-bend (RDB) process, ensuring uniform wall thickness distribution and geometric consistency along the coil length.
- Welding: A longitudinal weld is formed using High-Frequency Induction (HFI) welding or Laser welding technology, achieving weld strength exceeding 95% of the base material. Weld bead width is controlled to ≤ 1.0 mm for optimal flow characteristics.
- Heat Treatment: Solution annealing is performed at 1050°C – 1100°C in a protective atmosphere (nitrogen or argon) to relieve welding-induced residual stresses, restore full austenitic microstructure, and maximize corrosion resistance. The cooling rate is controlled to prevent carbide precipitation at grain boundaries.
- Pickling and Passivation: The tube is immersed in a mixed acid solution (HNO₃ + H₂SO₄) to remove oxide scale, followed by passivation in a dilute nitric acid bath to establish a protective chromium oxide film on the surface.
- Coil Winding: The formed tube is wound into the specified coil configuration using CNC-controlled coiling equipment, maintaining consistent pitch and alignment.
- Quality Inspection: Each coil undergoes dimensional verification (laser micrometry), hydrostatic pressure testing, visual inspection of weld quality, and surface finish measurement.
Applications
Primary Applications
- Horizontal Fan Coil Units (HFCU): The coil tube serves as the primary heat exchanger element in concealed and exposed horizontal fan coil units used for residential and commercial HVAC systems. The coiled configuration maximizes heat transfer surface area within a compact envelope.
- Vertical Fan Coil Units (VFCU): Similar thermal exchange function in gravity convection units and vertical air handling systems.
- Chilled Water Cooling Systems: Integration into central chilled water distribution systems for large commercial buildings.
- Hot Water Heating Systems: Utilization in hydronic heating applications where stainless steel's corrosion resistance provides long-term service reliability.
Secondary Applications
- Industrial process cooling and heating heat exchangers
- Refrigeration evaporator and condenser coils
- Air source heat pump units
- Commercial kitchen ventilation and cooling systems
- Marine HVAC systems (AISI 316 grade for saltwater resistance)
- Pharmaceutical and food-grade thermal processing equipment
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and product certifications to ensure compliance with international and national standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and continuous improvement |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System certification |
| CE Marking | European Conformity marking for products intended for the European Economic Area market |
| EN 10216-5 | European standard for seamless and welded stainless steel tubes for pressure purposes |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes for general engineering |
| GB/T 21830 | Chinese national standard for welded stainless steel tubes for food industry |
| ASME B31.3 | Process piping code compliance for pressure system applications |
| NSF/ANSI 61 | National Sanitation Foundation certification for potable water system components (where applicable) |
Unique Selling Points
The coil tube products from Wenzhou Jixing Metal Materials Co., Ltd. distinguish themselves through several key advantages:
- Superior Corrosion Resistance: The austenitic stainless steel composition provides exceptional resistance to oxidation, pitting, and crevice corrosion, ensuring a service life exceeding 25 years in typical HVAC applications without degradation of heat transfer performance.
- Precision Manufacturing: CNC-controlled forming and coiling processes deliver dimensional tolerances of ±0.05 mm on outer diameter, ensuring optimal fit within fan coil unit housings and minimizing turbulence-induced noise.
- Enhanced Comfort Performance: The uniform coil geometry and smooth internal surface finish contribute to balanced airflow distribution, reduced pressure drop across the coil, and lower fan power consumption — directly improving the comfort performance metrics (thermal comfort index, air velocity uniformity, and acoustic performance) of horizontal fan coil units.
- Customization Capability: Wenzhou Jixing offers flexible configuration options including custom coil diameters, tube lengths, fin configurations, and special alloy grades to meet specific OEM requirements.
- Full Traceability: Each production batch is accompanied by a Mill Test Certificate (MTC) and heat number traceability documentation in accordance with ISO 10204 Type 3.1 requirements.
- Cost-Effective Alternative: Compared to copper coil tubes, stainless steel coil tubes offer a 30–40% cost reduction while providing superior mechanical strength and corrosion resistance, making them an increasingly preferred material for next-generation HVAC heat exchangers.
Technical Notes
In the evaluation of comfort performance for horizontal fan coil units, the coil tube characteristics have a direct and quantifiable impact on the following performance parameters:
- Temperature Uniformity: The coil tube's thermal conductivity and geometric arrangement determine the temperature distribution across the discharge air stream, affecting the Mean Radiant Temperature (MRT) and operative temperature perceived by occupants.
- Air Velocity Distribution: Pressure drop characteristics of the coil tube assembly influence air velocity profiles, which must remain below 0.2 m/s for occupied zones to prevent draft discomfort.
- Acoustic Performance: The smooth internal surface and uniform weld quality minimize turbulence noise generation, contributing to sound pressure levels below 35 dBA at standard operating conditions.
- Humidity Control: The coil tube surface temperature relative to the dew point determines the dehumidification capacity of the unit, which is critical for maintaining Relative Humidity (RH) within the 40–60% comfort range.
Wenzhou Jixing Metal Materials Co., Ltd. remains committed to advancing stainless steel coil tube technology through continuous R&D investment, ensuring that their products contribute to the next generation of energy-efficient, comfort-optimized HVAC systems worldwide.