Stainless Steel Coil Tube for Fan Coil Units (FCU)
Product Overview
The Stainless Steel Coil Tube (Product No. 1471) 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 HVAC (Heating, Ventilation, and Air Conditioning) systems. This coil tube serves as the primary heat exchange medium in fan coil assemblies, facilitating efficient thermal transfer between refrigerant or heating/cooling water and ambient air. The product is engineered to meet the rigorous demands of commercial and residential climate control applications, offering superior corrosion resistance, thermal conductivity, and long-term operational reliability.
Unlike conventional copper coil tubes, the stainless steel variant provides enhanced chemical stability, extended service life, and reduced maintenance requirements, making it an increasingly preferred choice in modern HVAC engineering where durability and environmental compliance are paramount.
Material & Properties
The coil tube is fabricated from high-grade stainless steel, typically conforming to one of the following alloy specifications:
- SAE 304 (UNS S30400): Austenitic stainless steel offering excellent general corrosion resistance, formability, and weldability. Contains 18% Chromium (Cr) and 8% Nickel (Ni) — the industry-standard "18/8" stainless composition.
- SAE 316 (UNS S31600): Enhanced austenitic grade with 2–3% Molybdenum (Mo) addition, providing superior resistance to pitting and crevice corrosion in aggressive chemical environments.
- SAE 321 (UNS S32100): Stabilized austenitic grade with Titanium (Ti) addition, suitable for elevated-temperature applications up to 870°C (1600°F).
Mechanical Properties (Typical — SAE 304 Annealed Condition)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (74.7 ksi) | ASTM A270 / ASTM E8 |
| Yield Strength (0.2% offset) | ≥ 205 MPa (29.7 ksi) | ASTM A270 / ASTM E8 |
| Elongation (at break) | ≥ 40% | ASTM A270 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A270 |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | ASTM E153 |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C | ASTM E228 |
| Maximum Operating Temperature | 870°C (1600°F) | — |
| Density | 8.00 g/cm³ | — |
Corrosion Resistance Characteristics
- Excellent resistance to atmospheric corrosion and most organic acids
- High resistance to chlorinated water and mild alkaline solutions
- Resistance to stress corrosion cracking (SCC) under controlled conditions
- PASSION-TEST (Pitting Resistance Index) ≥ 19 for SAE 316 grade
Specifications
| Parameter | Specification / Range | Notes |
|---|---|---|
| Product Number | 1471 | Wenzhou Jixing Catalog Reference |
| Product Name | Stainless Steel Coil Tube (盘管) | Designed for Fan Coil Unit (FCU) integration |
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.70 mm (1/2") | Multiple sizes available per project requirement |
| Wall Thickness | 0.40 mm – 1.20 mm | Customizable based on pressure rating |
| Coil Inner Diameter (ID) | 300 mm – 1500 mm | Adaptable to FCU cabinet dimensions |
| Coil Length (Uncoiled) | 5 m – 50 m (standard); up to 200 m (custom) | Continuous seamless coil |
| Material Grade | SAE 304 / SAE 316 / SAE 321 | Selectable per application environment |
| Surface Finish | Bright Annealed (BA) / Pickled & Passivated / No. 4 Brushed | BA finish preferred for heat transfer optimization |
| Maximum Working Pressure | 1.6 MPa – 4.0 MPa (depending on OD/WT) | Hydrostatically tested at 1.5× working pressure |
| Temperature Range | -196°C to +870°C (cryogenic to high-temperature) | SAE 304: -196°C to 870°C |
| Coil Pitch (spacing between turns) | 5 mm – 15 mm | Optimized for air-side heat transfer efficiency |
| Fin Configuration | Plain tube or Integral Finned (Louvered/Plate) | Fins available for enhanced air-side heat exchange |
| Tolerance (OD) | ± 0.05 mm (precision coils) | Per ASTM A269 / ASTM A270 |
| Tolerance (Wall Thickness) | ± 10% of nominal | Standard tolerance class |
Manufacturing Process
The production of stainless steel coil tubes for fan coil unit applications follows a rigorously controlled multi-stage manufacturing sequence:
- Raw Material Selection: Cold-rolled stainless steel strip is procured from certified mills (e.g., Outokumpu, POSCO, Taigang), verified via mill test certificates (MTC) for chemical composition and mechanical properties.
- Strip Preparation: Incoming strip undergoes surface inspection, dimensional verification, and pre-cleaning to remove mill scale, oils, and contaminants.
- Pipe Forming (Seamless or Welded): Strip is fed through a roll-forming die set to produce tubular blanks. For welded tube, high-frequency induction welding (HF-W) or automatic orbital TIG welding is employed to achieve a full-penetration, leak-tight weld seam.
- Heat Treatment: The formed tube undergoes bright annealing (BA) in a protective atmosphere furnace (hydrogen or vacuum) at 1050–1100°C to relieve cold-work stresses, restore full austenitic microstructure, and achieve maximum ductility.
- Pickling & Passivation: Post-annealing, the tube is treated with a dilute nitric acid/hydrofluoric acid (HNO₃/HF) solution to remove oxide scale, followed by passivation treatment to establish a protective chromium oxide (Cr₂O₃) passive film on the surface.
- Coil Winding: The straightened tube is precisely wound into coil form using computerized CNC coil winding equipment, ensuring uniform pitch, concentricity, and minimal mechanical distortion. The coil is secured with stainless steel strapping.
- Optional Finning: For enhanced heat transfer, integral louvered fins or plate fins may be mechanically expanded onto the tube OD using a specialized fin-expansion machine, achieving a mechanical bond without welding.
- Quality Inspection: Each coil undergoes dimensional verification (OD, wall thickness, coil diameter, pitch), surface inspection (visual and magnetic particle testing), and hydrostatic pressure testing at 1.5× the rated working pressure.
- Packaging: Coils are wrapped in protective polyethylene film, placed on wooden pallets with corner protectors, and labeled with product identification, batch number, and traceability documentation.
Applications
The stainless steel coil tube (Product No. 1471) is specifically engineered for the following application domains:
- Fan Coil Units (FCU): Primary application — serving as the heat exchange coil in air handling units for commercial buildings, hotels, hospitals, and residential HVAC systems. The coil tube carries chilled water or hot water while air is circulated across the coil by fans.
- Chilled Water Systems: Integration into central chilled water distribution systems where corrosion resistance is critical due to the presence of inhibitors, glycol solutions, or treated water.
- Condensing Units: Use as condenser coils in vapor-compression refrigeration and heat pump systems where the tube is exposed to humid, potentially corrosive outdoor air.
- Industrial Process Cooling: Application in food processing, pharmaceutical, and chemical industries where sanitary-grade (SAE 316) tubing is required for product-contact or proximity applications.
- Marine HVAC: Deployment in shipboard and offshore HVAC systems where resistance to saltwater (chloride) corrosion is essential.
- Chiller Outlets and Heat Exchangers: Use in shell-and-tube heat exchangers and plate-fin heat exchangers within district cooling and heating networks.
Rational Selection Guidelines for Fan Coil Units
The selection of coil tube specifications for fan coil units should be guided by the following engineering considerations:
- Heat Load Calculation: The coil tube capacity (based on OD, wall thickness, length, and fin configuration) must be sized to meet the calculated sensible and latent heat loads of the conditioned space, with a design margin of 10–15%.
- Water Side Pressure Drop: Tube diameter and coil layout must be optimized to minimize pumping energy while maintaining adequate water flow velocity (0.5–1.5 m/s) to prevent sedimentation and ensure efficient heat transfer.
- Air Side Performance: Coil pitch, fin density, and tube layout (staggered vs. in-line) directly influence air-side pressure drop and heat transfer coefficient. Louvered fins with 25–30% louver angle provide optimal performance for FCU applications.
- Material Compatibility: Stainless steel coil tubes must be evaluated for compatibility with the specific water treatment program and refrigerant type used in the system to avoid galvanic corrosion or stress corrosion cracking.
- Fouling Factor: The coil design should account for long-term fouling by incorporating adequate surface area margin (typically 5–10%) to maintain rated performance over the design life.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management and certification programs to ensure product conformity and international market acceptance:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing and quality assurance processes.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- ASME BPV Code — Compliance with American Society of Mechanical Engineers Boiler and Pressure Vessel Code for pressure-containing components where applicable.
- ASTM A269 / ASTM A270 — Conformity with American Society for Testing and Materials standards for seamless and welded austenitic stainless steel tubing.
- EN 10217-7 / EN 10216-5 — Compliance with European standards for stainless steel seamless and welded tubes for pressure applications.
- JIS G3459 / JIS G3460 — Conformity with Japanese Industrial Standards for seamless and welded austenitic stainless steel tubing.
- CE Marking — Conformity with European Union directives for product safety and market access.
- Mill Test Certificate (MTC / EN 10204 3.1) — Each batch is accompanied by a third-party verified material test certificate documenting chemical composition, mechanical properties, and heat treatment condition.
Unique Selling Points
- Superior Corrosion Resistance: Stainless steel construction eliminates the corrosion and scaling issues common with copper coil tubes, extending service life by 3–5× in aggressive water environments and reducing long-term total cost of ownership (TCO).
- Cryogenic to High-Temperature Capability: Operational range from -196°C to +870°C makes this coil tube suitable for both deep-cooling applications and high-temperature heat recovery systems without material degradation.
- Sanitary-Grade Option: SAE 316L variant available with electropolished internal surface finish (Ra ≤ 0.4 μm), meeting FDA and EHEDG requirements for food and pharmaceutical applications.
- Customizable Coil Geometry: CNC-controlled winding allows precise customization of coil diameter, pitch, and length to match specific FCU cabinet dimensions and thermal performance requirements.
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, supporting green building certifications (LEED, BREEAM, Green Star) and reducing lifecycle carbon footprint compared to copper alternatives.
- Integrated Finning Technology: Proprietary mechanical fin-expansion process achieves high bond strength without thermal distortion, ensuring reliable long-term heat transfer performance.
- Full Traceability: Every coil is traceable to its mill heat number, production batch, and inspection records, providing complete quality documentation for engineering and regulatory compliance.
Technical Data Summary
| Item | Value |
|---|---|
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
| Product Code | 1471 |
| Product Category | Coil Tube (盘管) — HVAC / FCU Application |
| Primary Material | Austenitic Stainless Steel (SAE 304 / 316 / 321) |