Stainless Steel Coil Tube for HVAC Fan Coil Systems
Product No.: 1444 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (盘管 Coiltube) is a precision-engineered continuous tube product wound into a compact coil configuration, specifically designed for integration into column-type fan coil units (FCUs) within vertical air conditioning systems. This product leverages the superior corrosion resistance, thermal conductivity, and mechanical integrity of austenitic stainless steel to deliver long-cycle, high-efficiency heat exchange performance in demanding HVAC environments.
Unlike conventional copper or carbon steel tubing, the stainless steel coil tube eliminates concerns related to galvanic corrosion, dezincification, and biofouling, making it an ideal choice for applications involving humid air, chemical-laden atmospheres, and continuous thermal cycling. The coil geometry maximizes heat transfer surface area per unit volume while maintaining low hydraulic resistance, thereby optimizing the coefficient of performance (COP) of the overall air handling system.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is manufactured from Type 304 (UNS S30400) or Type 316 (UNS S31600) austenitic stainless steel, conforming to ASTM A213/A213M standards for seamless wrought austenitic stainless steel tubes. The microstructural stability of the face-centered cubic (FCC) crystal lattice ensures excellent ductility, weldability, and resistance to stress corrosion cracking (SCC) across a broad temperature range.
| Element | Type 304 (UNS S30400) | Type 316 (UNS S31600) |
|---|---|---|
| Carbon (C) | ≤ 0.08% | ≤ 0.08% |
| Manganese (Mn) | ≤ 2.00% | ≤ 2.00% |
| Chromium (Cr) | 18.00 – 20.00% | 16.00 – 18.00% |
| Nickel (Ni) | 8.00 – 10.50% | 10.00 – 14.00% |
| Molybdenum (Mo) | — | 2.00 – 3.00% |
| Silicon (Si) | ≤ 1.00% | ≤ 1.00% |
| Phosphorus (P) | ≤ 0.045% | ≤ 0.045% |
| Sulfur (S) | ≤ 0.030% | ≤ 0.030% |
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (Type 304); ≥ 530 MPa (Type 316)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40% (minimum)
- Hardness (HB): ≤ 217 (annealed condition)
- Operating Temperature Range: −196 °C to +870 °C (Type 304); −196 °C to +870 °C (Type 316)
2.3 Thermal Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20 °C; 21.5 W/(m·K) at 100 °C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100 °C)
- Specific Heat Capacity: 0.50 J/(g·K) at 20 °C
2.4 Corrosion Resistance
The passive chromium oxide film (Cr₂O₃) formed on the surface provides self-healing protection against atmospheric, aqueous, and mild chemical corrosion. Type 316 variant offers enhanced resistance to chlorides and pitting corrosion due to the presence of molybdenum, making it suitable for coastal or marine HVAC installations.
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.0 mm / 8.0 mm / 10.0 mm / 12.0 mm / 16.0 mm (custom available) |
| Wall Thickness | 0.5 mm – 2.0 mm (tolerance ±0.1 mm) |
| Coil Diameter | 100 mm – 500 mm (adjustable per system design) |
| Coil Length | 3.0 m – 30.0 m per coil (continuous) |
| Surface Finish | Mirror polished (Ra ≤ 0.2 μm) / Satin brushed (Ra ≤ 0.8 μm) / Standard annealed |
| Tolerance on OD | ±0.05 mm (precision grade) |
| Bend Radius (minimum) | 1.5× OD (cold forming) |
| Pressure Rating | ≤ 2.5 MPa (operating); ≤ 4.0 MPa (burst) |
| Weight | Approx. 0.15 – 0.80 kg/m (depending on OD and wall thickness) |
| Standard References | ASTM A213, EN 10216-5, GB/T 12771 |
4. Manufacturing Process
4.1 Seamless Tube Production
- Austere Billet Preparation: Virgin stainless steel ingots are melted in a vacuum arc remelting (VAR) or electro-slag remelting (ESR) furnace to achieve ultra-low impurity levels (S, P < 0.02%) and uniform microstructure.
- Hot Rolling / Piercing: The refined billet is heated to 1200–1250 °C and pierced on a Mannesmann-type tube mill to produce seamless hollow billets. This ensures homogeneity and absence of weld seams that could act as stress concentrators.
- Cold Drawing: The hot-rolled tube is cold-drawn through calibrated tungsten carbide dies to achieve precise dimensional tolerances (±0.05 mm on OD) and improved surface finish. Multiple passes with intermediate annealing at 1050–1100 °C are employed to manage work hardening.
4.2 Coil Winding
- Continuous Winding: The precision-drawn tube is wound onto a mandrel using a CNC-controlled coiling machine, maintaining consistent coil diameter and pitch throughout the length.
- Spring-Back Control: Post-winding spring-back is compensated algorithmically to ensure the final coil geometry meets design specifications without residual stress exceeding 50 MPa.
- End Sealing: Coil ends are crimped or welded to prevent unraveling during transport and installation.
4.3 Surface Treatment & Finishing
- Pickling & Passivation: The coil tube is subjected to hydrofluoric/nitric acid pickling followed by nitric acid passivation to remove scale and enrich the passive oxide layer to ≥ 5 μm thickness.
- Precision Polishing: For mirror finish variants, multi-stage mechanical polishing using cerium oxide and diamond slurry achieves Ra ≤ 0.2 μm surface roughness.
- Hydrostatic Testing: Each coil undergoes 100% hydrostatic pressure testing at 3.0 MPa for a minimum of 30 seconds to verify integrity and absence of leaks.
4.4 Quality Inspection
- Dimensional Verification: Laser scanning and coordinate measuring machine (CMM) inspection for OD, wall thickness, and coil geometry.
- Non-Destructive Testing (NDT): Eddy current (EC) testing for subsurface defects; ultrasonic (UT) testing for wall thickness verification.
- Chemical Analysis: Optical emission spectrometry (OES) and direct current arc spectrometry for full chemical composition verification.
- Microstructural Examination: Metallographic analysis confirming fully austenitic structure (≥ 95% austenite by XRD) with no delta ferrite or martensite.
5. Applications
5.1 Primary Application: Vertical Air Conditioning Systems
The stainless steel coil tube serves as the core heat exchange element in column-type fan coil units deployed in vertical (tower-style) air conditioning systems. These systems are prevalent in:
- Commercial High-Rises: Office towers, hotel buildings, and mixed-use developments requiring zoned thermal management.
- Hospital & Healthcare Facilities: Where hygienic, corrosion-resistant heat exchange is critical to prevent microbial growth and maintain indoor air quality (IAQ).
- Pharmaceutical & Cleanroom Environments: GMP-compliant facilities requiring non-contaminating, easy-to-sanitize heat exchange surfaces.
- Marine & Coastal Installations: Buildings exposed to salt-laden atmospheres where chloride-induced corrosion of copper or carbon steel is a significant concern.
- Food & Beverage Processing: Facilities requiring sanitary-grade tubing that can withstand aggressive cleaning chemicals (CIP systems).
5.2 Secondary Applications
- Chilled water distribution loops in district cooling systems
- Condenser and evaporator coils in industrial refrigeration
- Heat recovery units (HRUs) for energy-efficient building ventilation
- Process heating/cooling coils in chemical and petrochemical plants
6. Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 14001:2015 | Environmental Management System compliance |
| ASTM A213 / A213M | Material specification for seamless austenitic stainless steel tubes |
| EN 10216-5 | European standard for welded austenitic stainless steel tubes (where applicable) |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes for fluid transport |
| ASME B31.9 | Pressure piping code compliance for refrigeration and condenser tubing |
| NSF/ANSI 61 | Drinking water system components certification (where applicable) |
| CE Marking | European Conformity for mechanical safety and product compliance |
| MTC Type 3.1 | Mill Test Certificate (EN 10204) with full chemical and mechanical data |
7. Unique Selling Points
- Superior Corrosion Resistance: Elimination of galvanic corrosion and dezincification risks inherent to copper-based coil tubes, extending service life to 25+ years in aggressive environments.
- Hygienic Surface Integrity: Mirror-polished finish (Ra ≤ 0.2 μm) prevents biofilm adhesion, facilitating easy sanitization and compliance with pharmaceutical and food-grade standards.
- Thermal Cycling Durability: Full austenitic microstructure provides exceptional fatigue resistance under repeated thermal expansion/contraction cycles, preventing microcrack initiation and propagation.
- Non-Magnetic Properties: Ideal for MRI rooms and magnetic-sensitive environments where ferromagnetic materials are prohibited.
- Recyclability: 100% recyclable with no loss of material properties, supporting sustainable building practices and LEED/Green Star certification credits.
- Dimensional Precision: CNC-controlled coiling ensures consistent heat transfer performance across every unit, reducing system imbalance and energy waste.
Technical Note: The application of stainless steel coil tubes in column-type fan coil units represents a paradigm shift from traditional copper-fin-tube heat exchangers. The integration of austenitic stainless steel's passive corrosion resistance with optimized coil geometry yields a heat exchange component that outperforms conventional alternatives in total cost of ownership (TCO), particularly in corrosive or hygienically sensitive environments. Field data from vertical HVAC installations demonstrates a 30–40% reduction in maintenance frequency and a 15–20% improvement in long-term thermal efficiency compared to copper coil equivalents.