Stainless Steel Coil Tube — Fan Coil Unit (FCU) Series
1. Product Overview
The Stainless Steel Coil Tube (product reference No. 1385) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for integration into Fan Coil Units (FCUs) and fresh air distribution systems within commercial and residential HVAC (Heating, Ventilation, and Air Conditioning) installations. This coil tube is formed into serpentine or spiral configurations to maximize heat transfer surface area within compact envelopes, serving as the primary heat exchange medium in chilled water or hot water circulation loops.
The product is specifically engineered for applications in Guangzhou-region climate conditions (tropical monsoon climate, high humidity, ambient temperatures ranging from 13°C to 38°C), where corrosion resistance, thermal efficiency, and long-term durability are critical performance parameters.
2. Material & Properties
2.1 Base Material
- Primary Alloy: AISI 304 (UNS S30408) / AISI 316L (UNS S31603) austenitic stainless steel
- Chemical Composition (AISI 304): C ≤ 0.08%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Cr 18.0–20.0%, Ni 8.0–10.5%, Fe (balance)
- Chemical Composition (AISI 316L): C ≤ 0.03%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%, Fe (balance)
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (AISI 304), ≥ 515 MPa (AISI 316L)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation: ≥ 40% (A50 mm)
- Hardness: ≤ 92 HRB
- Density: 7.93 g/cm³
2.3 Thermal & Corrosion Properties
- Thermal Conductivity (20°C): 16.3 W/(m·K) (AISI 304)
- Operating Temperature Range: −196°C to +870°C
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, mild acids, and chlorinated environments (AISI 316L grade)
- Pitting Resistance (PREN): ≥ 19 (AISI 304), ≥ 24 (AISI 316L)
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 9.52 mm / 12.70 mm / 15.88 mm / 19.05 mm (3/8", 1/2", 5/8", 3/4") |
| Wall Thickness | 0.50 mm – 1.50 mm (customizable) |
| Tube Length (per coil) | 2.0 m – 12.0 m (adjustable per application) |
| Coil Diameter (bend radius) | Min. 25 mm (R ≥ 2.5 × OD) |
| Row Configuration | 1-row, 2-row, 3-row, 4-row serpentine |
| Pitch (Longitudinal) | 19.05 mm (3/4") standard; custom available |
| Pitch (Transverse) | 19.05 mm (3/4") standard; custom available |
| Surface Finish | Bright annealed (BA), Ra ≤ 0.4 μm |
| Heat Exchange Capacity | Up to 50 kW per coil assembly |
| Design Pressure | 1.6 MPa (standard); 2.5 MPa (high-pressure variant) |
| Applicable Fluids | Chilled water (7/12°C), hot water (45/60°C), glycol-water mixtures |
| Service Life | ≥ 25 years under normal operating conditions |
4. Manufacturing Process
- Raw Material Procurement: Hot-rolled stainless steel strip is sourced from certified mills (e.g., Outokumpu, POSCO, Tsingshan) with full mill test certificates (MTC) per EN 10204 3.1.
- Slitting & Leveling: Strip is slit to required width and cold-rolled to achieve target wall thickness with dimensional tolerance of ±0.05 mm.
- Tube Forming: Precision roll-forming machines convert flat strip into seamless round tubes with consistent OD and wall thickness, using hydraulic bending at controlled temperatures to avoid work hardening.
- Coil Bending: Tubes are bent into serpentine or spiral coil configurations using CNC-controlled mandrel bending systems, ensuring uniform bend radius (R ≥ 2.5 × OD) without ovality exceeding 10%.
- Welding: U-bends and return bends are formed and welded using TIG (Tungsten Inert Gas) welding with argon shielding gas to maintain interior purity and prevent oxidation.
- Purging & Cleaning: Interior surfaces are argon-purged during welding and subsequently cleaned using eco-friendly citric acid solutions to remove mill scale and flux residues.
- Pressure Testing: Each coil assembly undergoes hydrostatic pressure testing at 1.5× design pressure (≥ 2.4 MPa) for a minimum of 30 minutes with zero leakage tolerance.
- Surface Treatment: Optional passivation treatment (nitric acid or citric acid-based) to enhance chromium oxide layer stability and corrosion resistance.
- Final Inspection: Dimensional verification, visual inspection, and sampling for chemical composition analysis and mechanical property testing.
5. Applications
5.1 Primary Applications
- Commercial HVAC Systems: Fan Coil Units (FCUs) for office buildings, hotels, shopping malls, and hospitals in the Guangzhou and Pearl River Delta region.
- Residential Air Conditioning: Concealed ceiling-mounted units in high-rise residential complexes requiring corrosion-resistant heat exchangers.
- Industrial Process Cooling: Heat recovery and temperature regulation in pharmaceutical, food processing, and semiconductor manufacturing facilities.
- Fresh Air Handling Units (AHUs): Integrated coil tubes for pre-conditioning incoming outdoor air before distribution.
- Marine & Coastal Environments: HVAC installations in coastal areas where high salinity demands superior corrosion resistance (AISI 316L grade).
5.2 Regional Suitability — Guangzhou Climate
Guangzhou's subtropical climate (average annual temperature 22°C, relative humidity 75–80%, annual rainfall 1,600–2,000 mm) imposes stringent demands on coil tube durability. The stainless steel construction eliminates concerns of iron oxide corrosion, internal scaling, and fluid contamination that plague carbon steel alternatives, ensuring consistent thermal performance over decades of service.
6. Quality Certifications & Standards Compliance
| Standard / Certification | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| GB/T 4237-2015 | Chinese national standard for cold-rolled stainless steel strip and plate |
| ASTM A213/A269 | American standard for seamless austenitic stainless steel tubing |
| EN 10217-7 | European standard for seamless austenitic stainless steel tubes |
| JIS G3459 | Japanese Industrial Standard for stainless steel tubes for general use |
| GB 50736-2012 | Chinese standard for design of HVAC systems in civil buildings |
| SGS Testing Report | Third-party material verification and mechanical property validation |
7. Unique Selling Points
- Superior Corrosion Resistance: Full stainless steel construction eliminates internal rust formation, maintaining clean heat transfer surfaces and fluid purity throughout the service life — a critical advantage in humid Guangzhou climate conditions.
- High Thermal Efficiency: Precision-drawn smooth inner surfaces (Ra ≤ 0.4 μm) minimize fluid flow resistance and maximize convective heat transfer coefficients (h ≥ 3,500 W/(m²·K)).
- Customizable Configurations: Flexible tube diameters, wall thicknesses, row counts, and pitch dimensions allow optimization for specific thermal loads and spatial constraints.
- Extended Service Life: Designed for ≥ 25-year operational lifespan without replacement, significantly reducing lifecycle costs compared to copper or carbon steel alternatives.
- Environmental Compliance: 100% recyclable material; no lead, cadmium, or other hazardous substances; compliant with RoHS and REACH directives.
- Low Maintenance: Non-scaling interior surfaces eliminate periodic descaling procedures, reducing operational downtime and chemical consumption.
Note: This product specification is formulated in accordance with the principles of fan coil unit plus fresh air system (FCU + Fresh Air System) selection and calculation methodologies, as referenced in the technical literature on HVAC system design for the Guangzhou region. All dimensional and performance data should be verified against project-specific thermal load calculations prior to procurement.