Stainless Steel Coil Tube for Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Product No. 867) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product specifically designed for integration into Fan Coil Units (FCU) and hydronic air distribution systems. This product represents a critical component in modern HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, where thermal transfer efficiency, corrosion resistance, and long-term structural integrity are paramount.
Unlike conventional copper or steel coil tubes, this stainless steel variant offers superior resistance to condensation-induced corrosion, chemical attack from cleaning agents, and degradation in high-humidity environments. The coil geometry enables compact heat exchange surface area within constrained installation footprints, making it ideal for commercial and residential fan coil unit assemblies.
Material & Properties
The coil tube is fabricated from high-grade stainless steel, typically conforming to the following alloy designations:
- AISI 304 (UNS S30408) — The standard grade offering excellent general corrosion resistance, formability, and weldability. Chromium content of approximately 18% and Nickel content of approximately 8% provide a stable passive oxide layer.
- AISI 316 (UNS S31608) — Enhanced grade incorporating 2–3% Molybdenum (Mo) for superior resistance to pitting and crevice corrosion, particularly in chloride-rich or coastal environments.
- AISI 316L (UNS S31603) — Low-carbon variant of 316L (Carbon ≤ 0.03%) designed for improved weldability and reduced sensitization risk during welding operations.
Key Material Properties:
- Density: 8.0 g/cm³ (Stainless Steel 304/316)
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C
- Specific Heat Capacity: 500 J/(kg·K)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (at 20–100°C)
- Yield Strength: ≥ 205 MPa (AISI 304, Annealed)
- Tensile Strength: 515–720 MPa
- Operating Temperature Range: −196°C to +870°C (AISI 304); −196°C to +870°C (AISI 316)
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.70 mm (1/2") | ASME B36.19M |
| Wall Thickness | 0.50 mm – 1.50 mm (selectable) | ASTM A269 / A213 |
| Coil Bend Radius | 15 mm – 50 mm (minimum centerline radius) | ISO 11999 |
| Coil Length (per unit) | 5.0 m – 30.0 m (customizable) | Manufacturer Specification |
| Surface Finish | 2B (Cold Rolled & Annealed), No. 4 Brushed, or Electropolished (Ra ≤ 0.4 μm) | ASTM A480 |
| Pressure Rating | ≤ 1.6 MPa (16 bar) at 25°C | ASME B31.9 |
| Hydrostatic Test Pressure | 3.2 MPa (32 bar) sustained for 10 minutes | ISO 11999 |
| Tolerance on OD | ±0.05 mm | ASTM A269 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A213 |
| End Condition | Plain end, Beveled (45°), or Threaded (G1/4, G1/2) | ISO 7-1 / BS 2779 |
| Maximum Operating Fluid Temperature | 95°C (hot water), 7°C (chilled water) | ASHRAE 15 |
| Fin Configuration (if finned) | Integral copper or aluminum fins, pitch 3.0–4.5 mm | Manufacturer Specification |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorously controlled multi-stage manufacturing workflow:
- Raw Material Inspection & Certification: Incoming stainless steel strip or seamless pipe blanks are verified against mill test certificates (MTC) conforming to ASTM/EN standards. Chemical composition is confirmed via Optical Emission Spectroscopy (OES) and corrosion resistance is validated through Salt Spray Testing (ASTM B117).
- Blank Preparation: The raw stock is cut to required lengths, cleaned of surface contaminants, and subjected to pickling and passivation treatment (nitric acid/hydrofluoric acid blend) to ensure a chemically active surface free of free iron.
- Precision Coiling (U-Bend Forming): Using CNC-controlled rotary draw bending machines, the tube is formed into uniform U-shaped bends with consistent centerline radii. The coiling process employs controlled heating (where applicable) to prevent work hardening and minimize residual stresses. Bend quality is verified through optical alignment and dimensional gauging.
- Welding (if applicable): For multi-pass coil assemblies, joints are welded using Orbital TIG (Tungsten Inert Gas) welding under argon shielding. Post-weld heat treatment (annealing at 1050°C with water quench) restores full annealed mechanical properties and eliminates sensitization.
- Finning (for finned variants): Integral fins are mechanically expanded or welded onto the tube surface using high-frequency resistance welding to achieve metallurgical bond strength exceeding 50 MPa at the fin-to-tube interface.
- Hydrostatic & Pneumatic Testing: Each coil unit undergoes 100% pressure testing at 3.2 MPa (hydrostatic) or equivalent pneumatic pressure. Leak detection employs helium sniffing or soap-bubble methods to ensure zero leakage.
- Final Surface Treatment: Electropolishing (where specified) removes surface roughness to Ra ≤ 0.4 μm, enhancing both fluid dynamics performance and corrosion resistance. A final passivation cycle ensures full chromium oxide film reformation.
- Quality Assurance & Packaging: Finished coils are inspected per ISO 9001 protocols, labeled with traceable heat numbers, and packaged in protective wrapping with moisture-absorbing desiccants for shipment.
Applications
The stainless steel coil tube is engineered for deployment in the following application domains:
- Fan Coil Units (FCU): Serves as the primary heat exchange element in unitary and concealed-mounted fan coil systems used in commercial buildings, hotels, hospitals, and residential HVAC installations. The coil tube transfers thermal energy between the circulating hydronic fluid (chilled or hot water) and the airstream.
- Air Handling Units (AHU): Integrated into larger air handling systems for zone-level temperature control in multi-story commercial and institutional buildings.
- Condensing Coils in Refrigeration: Utilized in refrigeration and air conditioning condenser units where resistance to refrigerant degradation and environmental corrosion is critical.
- Industrial Process Cooling: Employed in heat exchangers for chemical processing, pharmaceutical manufacturing, and food processing applications where sanitary-grade materials are mandated.
- Marine HVAC Systems: The AISI 316/316L grade variants provide exceptional resistance to saltwater corrosion in marine and coastal HVAC installations.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains the following quality certifications and regulatory compliances for this product line:
- ISO 9001:2015 — Quality Management System certification ensuring consistent production quality and continuous improvement processes.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- CE Marking — Conformity with European directives including the Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing components.
- ASME Stamp — Compliance with ASME B31.9 (Piping and Piping Components for HVAC Systems) for pressure system applications.
- Material Certifications: Full traceability via EN 10204 3.1 Mill Test Certificates (MTC) and 3.2 Inspection Certificates upon request, confirming chemical composition, mechanical properties, and heat treatment history.
- NACE No. 0286 — Compliance with standard practices for cleaning, passivation, and descaling of stainless steel surfaces.
Unique Selling Points
1. Superior Corrosion Resistance: The stainless steel construction provides 3–5× longer service life compared to carbon steel alternatives in humid, condensing environments typical of fan coil unit operation, eliminating the need for periodic replacement due to internal corrosion.
2. Sanitary-Grade Surface Finish: Electropolished surfaces (Ra ≤ 0.4 μm) prevent biofilm accumulation and facilitate cleaning, making this product suitable for pharmaceutical, food-grade, and healthcare HVAC applications.
3. Precision Coiling Geometry: CNC-controlled bending ensures uniform coil pitch and consistent bend radius, optimizing airflow distribution across the heat exchange surface and maximizing heat transfer efficiency (U-value).
4. Full Traceability: Each coil tube carries a unique heat number and production batch identifier, enabling complete supply chain traceability from raw material to finished product — a critical requirement for regulated industries.
5. Customizable Configuration: Available in multiple OD, wall thickness, coil length, and surface finish options, allowing OEMs to tailor the product to specific fan coil unit design parameters and thermal load requirements.
Performance Test Laboratory Context
The development and validation of this coil tube product were informed by performance testing conducted within a dedicated Fan Coil Unit Performance Test Laboratory. This facility enables comprehensive evaluation of coil tube assemblies under controlled conditions, including:
- Measurement of total and sensible heat transfer capacity per AHRI (Air-Conditioning, Heating, and Refrigeration Institute) Standard 210/240
- Pressure drop analysis across the coil at design and off-design flow rates
- Condensate drainage performance evaluation
- Acoustic performance characterization (sound power level and sound pressure level)
- Long-duration corrosion testing via accelerated Salt Spray Testing (ASTM B117, minimum 1000 hours without red rust)
These laboratory validations ensure that the stainless steel coil tube meets or exceeds the thermal performance, durability, and safety requirements specified in international HVAC standards, providing OEM partners and end-users with a reliable, high-performance heat exchange component.