Stainless Steel Coil Tube for Fan Coil Unit (FCU) Systems
Product Overview
The stainless steel coil tube (盘管/Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product specifically designed for integration into fresh air and fan coil unit (Fan Coil Unit, FCU) systems. As a critical heat exchanger component, the coil tube facilitates efficient thermal transfer between the circulating refrigerant or hot water medium and the ambient air, enabling optimal heating, cooling, and dehumidification performance in commercial and residential HVAC (Heating, Ventilation, and Air Conditioning) applications.
This product represents a convergence of metallurgical precision and thermal engineering, leveraging the inherent corrosion resistance and mechanical integrity of stainless steel to deliver long-service-life heat exchange solutions in demanding environmental conditions.
Material & Properties
Base Material
- Primary Alloy: Austenitic stainless steel conforming to ASTM A213/A213M or EN 10217-7 specifications
- Typical Grades: SUS 304 (UNS S30408), SUS 316 (UNS S31603), SUS 316L (UNS S31603L)
- Alternative Grades: SUS 321 (UNS S32100), Duplex 2205 (UNS S32205) for high-chloride environments
Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (for SUS 304, annealed condition)
- Yield Strength: ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness: ≤ 230 HB (annealed condition)
Thermal & Physical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS 304)
- Specific Heat Capacity: 500 J/(kg·K)
- Linear Thermal Expansion: 17.3 × 10⁻⁶ /°C (20–100°C)
- Density: 7.93 g/cm³
- Maximum Operating Temperature: 870°C (SUS 304), 925°C (SUS 316)
- Corrosion Resistance: Excellent resistance to atmospheric, acidic, and chloride-containing environments; pitting resistance equivalent number (PREN) ≥ 18 for SUS 316
Key Metallurgical Characteristics
- Non-magnetic (paramagnetic) in the annealed condition
- Excellent weldability with low sensitization tendency
- Resistance to intergranular corrosion (IGC) in stabilized or low-carbon grades
- Outstanding cryogenic performance down to −196°C
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8") | ASTM A213 / EN 10217-7 |
| Wall Thickness (WT) | 0.50 mm – 1.50 mm (tolerance ±10%) | ISO 443 |
| Coil Diameter (CD) | 150 mm – 600 mm (customizable) | Manufacturer specification |
| Coil Pitch / Spacing | 15 mm – 30 mm (adjustable per heat transfer requirement) | ASHRAE 90.1 |
| Tube Length (per coil) | 2.0 m – 12.0 m (continuous coil) | — |
| Surface Finish | Bright annealed (BA), No. 1 pickled, or polished (Ra ≤ 0.8 μm) | ASTM A480 / ASTM A666 |
| Heat Treatment | Solution annealed at 1050°C – 1150°C, followed by rapid quenching | ASTM A213 |
| Working Pressure (Design) | ≤ 1.6 MPa (standard), ≤ 2.5 MPa (reinforced) | EN 12952 / TSG D0001 |
| Operating Temperature Range | −40°C to +250°C (standard medium) | — |
| Welding Method | TIG (GTAW) with inert gas shielding (Ar 99.9%) | EN ISO 6947 / ASME IX |
| Hydrostatic Test Pressure | 1.5 × working pressure (minimum 2.4 MPa) | EN 12952 |
| Dimensional Tolerance | OD: ±0.05 mm; WT: ±10%; Straightness: ≤ 1 mm/m | ISO 443 / EN 10217-7 |
Manufacturing Process
1. Raw Material Selection & Incoming Inspection
Hot-rolled stainless steel strip or seamless tube blanks are sourced from certified mills and subjected to spectroscopic analysis (OES), mechanical testing, and surface inspection to verify grade composition and mechanical properties prior to processing.
2. Cold Drawing & Sizing
The raw tube stock undergoes multi-pass cold drawing through precision tungsten carbide (WC) dies to achieve the target outer diameter and wall thickness. This process enhances mechanical strength by work hardening while maintaining the austenitic microstructure.
3. Intermediate Annealing (if required)
For multi-stage drawing operations, intermediate solution annealing at 1050°C–1150°C relieves accumulated cold work stresses, restores ductility, and ensures dimensional accuracy in subsequent drawing passes.
4. Precision Coiling / Bending
The drawn tube is fed through a CNC-controlled coiling machine with servo-driven roll stations to form the specified coil geometry. The coiling process maintains constant bending radius to prevent ovalization, cracking, or wall thinning at bend locations. The coil pitch is controlled to within ±0.5 mm.
5. Welding & Assembly
Tube-to-plate joints (fins or header connections) are fabricated using TIG (Tungsten Inert Gas, GTAW) welding with high-purity argon shielding. Back-purging with argon ensures oxide-free weld penetration. Weld joints are inspected via visual examination (VT) and, where applicable, dye penetrant testing (PT) per ASTM E709.
6. Solution Annealing & Pickling
The assembled coil tube undergoes a final solution heat treatment (1050°C–1150°C, water or air quench) to dissolve carbide precipitates formed during welding, followed by acid pickling (HNO₃/HF mixture) and passivation to restore the full corrosion resistance of the alloy surface.
7. Non-Destructive Testing (NDT)
- Hydrostatic Pressure Test: All coils tested at 1.5× design pressure for a minimum hold time of 30 seconds
- Dimensional Inspection: Coordinate measuring machine (CMM) verification of coil diameter, pitch, and tube geometry
- Visual & Dye Penetrant Inspection: 100% weld joint examination
- Optional: Eddy current testing (ECT) for wall thickness verification
8. Final Surface Treatment & Packaging
Coils are cleaned, passivated, and optionally coated with anti-corrosion conformal coatings. Each unit is individually wrapped in protective film and packed in moisture-barrier cartons for shipment.
Applications
Primary Applications
- Fan Coil Units (FCU): Heat exchange coils in commercial and residential HVAC systems for air conditioning, heating, and dehumidification
- Fresh Air Handling Systems: Integration with fresh air supply units for thermal pre-conditioning of ventilation air
- Chilled Water & Hot Water Systems: Secondary heat exchange in central plant distribution networks
Industry Sectors
- Commercial buildings (offices, hotels, shopping malls, hospitals)
- Industrial process cooling/heating (pharmaceutical, food & beverage, electronics manufacturing)
- Marine and offshore HVAC (leveraging SUS 316/316L for chloride resistance)
- Data center thermal management
- Cleanroom and laboratory environmental control
System Integration Context
In a typical fresh air plus fan coil unit system, the stainless steel coil tube operates as the core thermal interface. The coil tube is finned (typically with aluminum fins) and housed within an air duct casing. Coolant (chilled water at 6–12°C or hot water at 40–60°C) circulates through the coil tube while air passes over the finned surface, achieving sensible and latent heat transfer. The design calculations—encompassing air-side heat transfer coefficients, water-side flow velocities, and overall thermal resistance—must comply with ASHRAE Handbook–HVAC Systems and Equipment guidelines.
Quality Certifications & Standards Compliance
Product Certifications
- ISO 9001:2015 – Quality Management System
- ISO 14001:2015 – Environmental Management System
- CE Marking – Conformity with EU directives (Pressure Equipment Directive 2014/68/EU, where applicable)
- EN 12952 – Water-heating boilers and water heaters, parts and components
- EN 10217-7 – Non-ferrous metallic tubes for heat exchangers and heat transfer equipment
Material Certifications
- EN 10204 3.1 – Material test certificates with full chemical and mechanical data
- Mill Test Reports (MTR) – Traceable to heat number with full spectrographic analysis
- ASTM A213/A213M – Specification for austenitic stainless steel seamless tubing
Performance Verification
- Heat transfer coefficient verified per ASHRAE Standard 15 (Methods of Evaluating Thermal Performance of Heat Exchangers)
- Pressure drop calculations validated against vendor performance curves
- Corrosion resistance confirmed via salt spray testing (ASTM B117, ≥ 1000 hours for SUS 316)
Unique Selling Points
Superior Corrosion Durability: Unlike carbon steel or copper alternatives, the austenitic stainless steel coil tube provides exceptional resistance to corrosion from condensate, humid air, and chemical contaminants—eliminating premature failure and reducing lifecycle maintenance costs by up to 60%.
- Extended Service Life: Designed for 20–25 year operational lifespan in standard HVAC duty cycles, significantly exceeding copper coil alternatives in aggressive environments
- Hygienic & Food-Safe: Surface finish and material grade meet FDA and NSF standards, suitable for pharmaceutical and food-grade HVAC applications
- Customizable Geometry: CNC-precision coiling enables bespoke coil dimensions, pitch, and configurations tailored to specific thermal load calculations
- Non-Magnetic: Austenitic composition ensures non-magnetic properties, critical for MRI facilities and precision electronics cleanrooms
- Full Traceability: Every coil tube batch is traceable from raw material mill heat number through final NDT results, ensuring complete supply chain accountability
- Energy Efficiency Contribution: The smooth bore surface and precision geometry minimize flow resistance, reducing pump energy consumption and improving system COP (Coefficient of Performance)
Technical Notes & Design Considerations
Important: In systems where the coil tube operates with deionized or low-conductivity water, ensure adequate water treatment to prevent concentration cell corrosion. Maintain water velocity between 0.5 m/s and 2.0 m/s to avoid both laminar fouling and erosive corrosion. For applications involving ammonia refrigerants or chloride-containing process fluids, SUS 316L is recommended over SUS 304 to ensure adequate pitting and crevice corrosion resistance.
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Reference: Coiltube Series (Catalog No. 1500)