Stainless Steel Coil Tube for Fan Coil Unit (FCU) Heat Exchangers
Product Overview
The Stainless Steel Coil Tube (Catalogue No. 1698) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchange coil designed specifically for Fan Coil Units (FCU) and air conditioning systems. This product represents a critical component in modern HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, serving as the primary thermal transfer medium in commercial, industrial, and residential climate control applications. The coil tube is formed into serpentine or spiral configurations to maximize the heat exchange surface area while maintaining compact dimensional footprints within equipment housings.
These coil tubes are engineered to withstand the rigorous demands of continuous thermal cycling, fluid pressure differentials, and corrosive environments encountered in hydronic and refrigeration systems. The product line adheres to international standards governing heat exchanger tubing, ensuring reliable long-term performance in critical building systems.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior combination of corrosion resistance, thermal conductivity, and mechanical integrity. The primary material grades utilized include:
- AISI 304 (UNS S30408) — General-purpose austenitic stainless steel offering excellent corrosion resistance in most environments, suitable for potable water and standard HVAC applications.
- AISI 316 (UNS S31608) — Molybdenum-enhanced austenitic stainless steel providing superior resistance to chloride-induced pitting and crevice corrosion, ideal for coastal and industrial environments.
- AISI 316L (UNS S31603) — Low-carbon variant of 316 grade, optimized for welding applications where sensitization must be avoided.
Key mechanical and physical properties of the coil tube material are summarized below:
| Property | Specification |
|---|---|
| Tensile Strength (Ultimate) | ≥ 520 MPa (304) / ≥ 515 MPa (316) |
| Yield Strength (0.2% Proof) | ≥ 205 MPa (304) / ≥ 170 MPa (316) |
| Elongation (A50mm) | ≥ 40% |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) (304) / 14.6 W/(m·K) (316) |
| Operating Temperature Range | −196°C to +870°C (304) / −196°C to +870°C (316) |
| Chromium (Cr) Content | 18.0%–20.0% |
| Nickel (Ni) Content | 8.0%–10.5% |
| Molybdenum (Mo) Content | — (304) / 2.0%–3.0% (316) |
| Carbon (C) Max | 0.08% (304) / 0.03% (316L) |
| Surface Finish | 2B / BA (Bright Annealed) / Electropolished (Ra ≤ 0.4 μm) |
Specifications
The coil tube product is available in a comprehensive range of dimensions and configurations to accommodate diverse FCU designs and thermal load requirements:
| Parameter | Specification Range |
|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4") to 15.88 mm (5/8") |
| Wall Thickness | 0.40 mm to 1.50 mm |
| Coil Length (Continuous) | Up to 1,200 meters per coil |
| Coil Winding Pitch | 10 mm to 50 mm (configurable) |
| Tube Layout Pattern | Serpentine / Spiral / Double-pass / Multi-row |
| Fin Material (if applicable) | Aluminum (Al 1100) / Stainless Steel (304) |
| Fin Density | 8 FPI to 16 FPI (Fins Per Inch) |
| Maximum Working Pressure | 1.6 MPa (standard) / 2.5 MPa (reinforced) |
| Hydrostatic Test Pressure | 3.2 MPa (standard) / 5.0 MPa (reinforced) |
| Connection Type | Flared / Soldered / Brazed / Threaded / Flanged |
| Standard Length per Unit | Customized per OEM requirements (typical: 2–8 m) |
| Coating (optional) | Anti-corrosion passivation / Hydrophilic coating / PTFE coating |
Manufacturing Process
The production of Wenzhou Jixing's stainless steel coil tube follows a rigorously controlled multi-stage manufacturing process:
- Raw Material Selection & Incoming Inspection: Stainless steel strip or round bar is procured from certified mills (e.g., Outokumpu, POSCO, Taigang) and subjected to spectroscopic analysis (PMI – Portable Metal Identification) and mechanical property verification prior to processing.
- Coil Winding & Forming: Continuous tube stock is precisely wound onto mandrels using CNC-controlled coil winding machines. The winding process maintains uniform tension and pitch accuracy within ±0.1 mm tolerance, ensuring consistent heat transfer characteristics across the entire coil assembly.
- Tube Expansion & Fin Attachment (if applicable): For finned coil configurations, the tubes undergo mechanical or hydraulic expansion to achieve a tight interference fit with aluminum or stainless steel fins. This ensures optimal thermal contact and eliminates air gaps that would reduce heat transfer efficiency.
- Welding & Brazing: U-bends and header connections are formed using TIG (Tungsten Inert Gas) welding or vacuum brazing in a nitrogen-protected atmosphere. This prevents oxidation and maintains the metallurgical integrity of the austenitic stainless steel.
- Hydrostatic Pressure Testing: Each coil assembly undergoes 100% hydrostatic pressure testing at 1.5 times the maximum working pressure, with a minimum dwell time of 30 seconds, to verify structural integrity and leak-tightness.
- Surface Treatment & Passivation: The completed coil is cleaned and passivated using nitric acid or citric acid solutions to remove scale, welding discoloration, and contaminants, restoring the full corrosion resistance of the passive chromium oxide layer.
- Final Quality Inspection: Comprehensive dimensional checks, visual inspection, and non-destructive testing (NDT) including dye penetrant testing (PT) or ultrasonic testing (UT) are performed prior to packaging and dispatch.
Applications
The stainless steel coil tube for fan coil units finds extensive application across multiple industries:
- Commercial HVAC Systems: Primary heat exchanger coils in ceiling-mounted, wall-mounted, and concealed fan coil units for office buildings, hotels, hospitals, and shopping centers.
- Residential Climate Control: Compact coil assemblies in cassette units and ducted FCUs for high-end residential applications requiring corrosion-resistant components.
- Industrial Process Cooling: Heat rejection coils in process air handlers, clean rooms, and precision temperature control environments in semiconductor manufacturing, pharmaceutical production, and food processing facilities.
- Marine & Offshore Systems: 316/316L grade coils for HVAC systems on vessels and offshore platforms where chloride-laden atmospheric conditions demand maximum corrosion resistance.
- Food & Beverage Industry: Sanitary-grade coil assemblies for food processing plants, breweries, and dairy facilities requiring cleanability and compliance with food safety regulations.
- Data Center Cooling: High-efficiency coils in air handling units serving precision cooling for server rooms and telecommunications infrastructure.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following international standards:
- ISO 9001:2015 — Quality Management Systems certification, demonstrating systematic control over all manufacturing and quality assurance processes.
- ISO 14001:2015 — Environmental Management Systems certification, reflecting commitment to sustainable manufacturing practices.
- EN 10216-5 — European standard for welded stainless steel tubes for pressure purposes.
- ASTM A269 / A270 — American standards for seamless and welded austenitic stainless steel tubing.
- ASME B31.9 — Pressure Piping, Refrigeration Piping and Heat-Transfer Components compliance.
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes for fluid transport.
- NSF/ANSI 61 — Drinking water system components certification (where potable water applications are specified).
- CE Marking — Conformity with European Union directives for machinery and pressure equipment.
Unique Selling Points
- Superior Corrosion Resistance: The austenitic stainless steel construction provides exceptional longevity in aggressive environments, eliminating the need for frequent replacement associated with carbon steel alternatives.
- Customizable Configurations: Flexible manufacturing capabilities allow OEM-specific coil geometries, dimensions, and connection types tailored to precise thermal performance requirements.
- High Thermal Efficiency: Precision winding tolerances and optional fin treatments ensure maximum heat transfer coefficient, reducing energy consumption in HVAC systems by up to 15% compared to standard configurations.
- Full Traceability: Each coil batch carries complete material traceability documentation, including mill certificates, chemical composition reports, and mechanical test results.
- Extended Service Life: Engineered for a minimum 15-year operational lifespan under normal service conditions, providing total cost of ownership (TCO) advantages over lower-grade alternatives.
Note: All specifications are subject to engineering review and may be customized to meet specific project requirements. Wenzhou Jixing Metal Materials Co., Ltd. provides technical consultation and sample testing services upon request.