Stainless Steel Coil Tube for Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Model No. 362) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled stainless steel tubing product specifically designed for use in Fan Coil Unit (FCU) assemblies within Heating, Ventilation, and Air Conditioning (HVAC) systems. This product represents the convergence of metallurgical excellence and thermal-fluid engineering principles, addressing the critical requirements of modern hydronic air distribution systems where corrosion resistance, thermal conductivity, and mechanical durability are paramount.
In the context of fan coil unit manufacturing and selection, the coil tube serves as the primary heat exchange element—transferring thermal energy between the circulating refrigerant or hot water and the ambient air stream. The design philosophy underlying this product integrates multiple considerations including heat transfer efficiency, pressure drop minimization, freeze resistance, and long-term structural integrity under cyclic thermal loading conditions.
Material & Properties
Base Material Composition
The coil tube is fabricated from austenitic stainless steel conforming to internationally recognized standards. The primary grade utilized is SAE 304 (UNS S30400), with select applications employing SAE 316L (UNS S31603) for enhanced resistance to chloride-induced pitting and crevice corrosion.
| Property | SAE 304 (UNS S30400) | SAE 316L (UNS S31603) |
|---|---|---|
| Carbon (C) max | 0.08% | 0.03% |
| Chromium (Cr) | 18.0–20.0% | 16.0–18.0% |
| Nickel (Ni) | 8.0–10.5% | 10.0–14.0% |
| Molybdenum (Mo) | — | 2.0–3.0% |
| Tensile Strength (UTS) | ≥ 515 MPa | ≥ 485 MPa |
| Yield Strength (0.2% offset) | ≥ 205 MPa | ≥ 170 MPa |
| Elongation at Break | ≥ 40% | ≥ 40% |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) |
| Operating Temperature Range | −196°C to +870°C | −196°C to +870°C |
Key Material Advantages
- Corrosion Resistance: The passive chromium oxide film (Cr₂O₃) provides self-healing protection against atmospheric corrosion, condensation water, and mildly acidic cooling tower water.
- Cryogenic Toughness: Austenitic microstructure retains ductility at sub-zero temperatures, eliminating the risk of brittle fracture during freeze events in hydronic systems.
- Sanitary Surface: Electropolished inner surface with Ra ≤ 0.4 μm minimizes biofilm formation and maintains fluid flow efficiency over extended service life.
- Non-magnetic: Fully austenitic composition ensures non-magnetic behavior, compatible with MRI-adjacent installations and electromagnetic shielding requirements.
Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube (盘管 Coiltube), Item No. 362 |
| Tube Outer Diameter (OD) | 9.52 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8") |
| Tube Wall Thickness | 0.50 mm, 0.65 mm, 0.80 mm |
| Coil Pitch (Row Spacing) | 12.0 mm, 15.0 mm, 18.0 mm, 22.0 mm |
| Number of Rows | 2, 4, 6, 8 rows (configurable) |
| Coil Length | Custom, typically 300 mm to 1,200 mm |
| Fin Material | Aluminum (1100 or 3003 alloy), integral or slip-fit |
| Fin Density | 10 FPI to 16 FPI (Fins Per Inch) |
| Max. Working Pressure | 1.6 MPa (16 bar) at 25°C |
| Hydrostatic Test Pressure | 2.4 MPa (24 bar), 100% tested |
| Refrigerant Compatibility | R-22, R-407C, R-410A, R-134a, R-32, CO₂ (R-744) |
| Heat Transfer Capacity | Up to 12.5 kW (cooling), 14.0 kW (heating) |
| Pressure Drop (Air Side) | ≤ 80 Pa at rated airflow |
| Pressure Drop (Water/Refrigerant Side) | ≤ 50 kPa at design flow rate |
| Freeze Resistance | Withstands −35°C without structural failure |
| Service Life Expectancy | ≥ 25 years under normal operating conditions |
Manufacturing Process
Process Flow
- Raw Material Inspection: Incoming stainless steel seamless or welded tube undergoes spectrographic verification (PMI), hydrostatic testing, and dimensional gauging in accordance with ASTM A269 / ASTM A213 standards.
- Tube Straightening & Cutting: Precision straightening eliminates residual curvature from coil storage; laser or cold-shear cutting produces exact-length blanks with burr-free ends.
- U-Bend Forming: Cold U-bending is performed using CNC-controlled mandrel die sets, ensuring uniform bend radii (minimum bend radius = 3× OD) and absence of wall thinning beyond 10% of nominal thickness.
- Coil Assembly & Brazing: Individual U-tubes are arranged in serpentine pattern and joined at headers using phosphorus-free silver brazing alloy (e.g., Orlovac 1018 or equivalent), with filler metal composition Ag 30% / Cu 70% for compatibility with stainless steel.
- Fin Insertion / Finning: Aluminum fins are either insert-finned (roll-bonded) or slip-fitted onto the completed tube array, creating the extended surface heat exchange structure.
- Pressure Testing: 100% hydrostatic testing at 1.5× working pressure for 5 minutes with zero leakage tolerance; supplemented by helium leak detection at 10⁻⁷ mbar·L/s sensitivity for critical applications.
- Surface Treatment & Coating: Optional epoxy or polyurethane coating applied to fin surfaces for additional corrosion protection in aggressive environments (coastal, industrial).
- Final Quality Assurance: Dimensional verification, visual inspection, and performance testing (airflow, pressure drop, heat transfer capacity) per ASHRAE Standard 34 and EN 12830.
Design Philosophy Considerations
The manufacturing of coil tubes for fan coil units involves a fundamental tension between competing design objectives. On one hand, maximizing heat transfer surface area demands tight coil pitch and high fin density; on the other hand, excessive fin density increases air-side pressure drop, reducing fan efficiency and increasing energy consumption. The optimal design balances these factors through computational fluid dynamics (CFD) simulation and empirical performance validation, ensuring the coil tube achieves rated thermal capacity while maintaining system-level COP (Coefficient of Performance) targets.
Applications
- Commercial HVAC: Primary heat exchange element in ceiling-mounted, wall-mounted, and ducted fan coil units for office buildings, shopping centers, and hospitality facilities.
- Residential Climate Control: Indoor units of ductless mini-split systems and radiant floor heating distribution loops.
- Industrial Process Cooling: Chilled water distribution in semiconductor clean rooms, pharmaceutical manufacturing, and food processing facilities where sanitary requirements mandate stainless steel construction.
- Marine & Offshore: HVAC systems in vessels and offshore platforms where salt spray corrosion and vibration resistance are critical.
- Medical Facilities: Infection control HVAC systems in hospitals requiring non-toxic, non-corrosive, and easily sterilizable heat exchange components.
- Freeze-Drying Equipment: Vacuum jacketed coil tubes in pharmaceutical and biological freeze-dryers operating at sub-zero temperatures.
Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| EN 12830 | Heating and Cooling Coils — Specifications and Performance |
| ASHRAE Standard 34 | Rating of Air-Cooled Heat Exchangers |
| ASTM A213 / A269 | Material Specification for Stainless Steel Tubing |
| ASME BPV Section I | Pressure Vessel / Boiler Code Compliance |
| CE Marking (EU) | Conformity with European Machinery and Pressure Equipment Directives |
| RoHS 2011/65/EU | Restriction of Hazardous Substances |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects (where applicable) |
Unique Selling Points
- Superior Freeze-Tolerance: Unlike copper or carbon steel coils, the austenitic stainless steel construction withstands inadvertent freeze events without cracking, significantly reducing field service calls and warranty claims.
- Extended Service Life: Resistance to galvanic corrosion when paired with aluminum fins (via appropriate isolation or coating) and immunity to condensation water corrosion extends operational life to 25+ years versus 10–15 years for copper coils in comparable environments.
- Multi-Concept Design Integration: The product embodies lessons learned from competing design philosophies—balancing thermal performance, manufacturability, and lifecycle cost—resulting in an optimized solution that transcends single-parameter optimization.
- Custom Configurability: Flexible geometry (tube OD, wall thickness, coil pitch, row count) enables precise matching to specific FCU performance requirements, from low-capacity residential units to high-capacity commercial systems.
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, contributing to circular economy goals and reducing the embodied carbon footprint of HVAC installations over their lifecycle.
Conclusion
The Stainless Steel Coil Tube (Item No. 362) from Wenzhou Jixing Metal Materials Co., Ltd. represents a mature, standards-compliant product that addresses the evolving demands of the HVAC industry. By integrating metallurgical best practices with thermal engineering optimization, this coil tube delivers reliable heat exchange performance, exceptional durability, and total cost-of-ownership advantages across a broad spectrum of commercial, industrial, and residential applications. The product's development reflects a deep understanding of the competing design philosophies inherent in fan coil unit manufacturing—demonstrating that the optimal solution emerges not from prioritizing a single performance metric, but from achieving harmonious balance across all critical system parameters.