Stainless Steel Coil Tube for HVAC Fan Coil Units
Product Catalog No.: 1075 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubing product specifically designed for integration into dry-type fan coil units (FCUs) operating within independent fresh air conditioning systems. This coil tube serves as the core heat exchange element, facilitating efficient thermal transfer between circulating refrigerant (or hot water) and the surrounding airstream. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product is engineered to meet the rigorous demands of commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) applications, ensuring superior corrosion resistance, thermal conductivity, and long-term operational reliability in diverse environmental conditions.
Unlike conventional copper coil tubes, the stainless steel variant offers enhanced durability against chloride-induced pitting corrosion, making it particularly suitable for coastal regions, marine environments, and applications involving chemically aggressive air streams. The coil tube is wound into compact serpentine configurations optimized for maximum surface area-to-volume ratios, thereby maximizing heat exchange efficiency within constrained installation spaces.
Material & Properties
Base Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, typically conforming to the following grades:
- AISI 304 (UNS S30400): General-purpose grade with excellent corrosion resistance and formability. Contains 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316 (UNS S31600): Enhanced molybdenum (Mo) grade offering superior resistance to chlorides and acidic environments. Contains 16.5% Cr, 10.5% Ni, and 2.5% Mo.
- AISI 316L (UNS S31603): Low-carbon variant of 316 suitable for welded assemblies requiring resistance to intergranular corrosion.
Key Mechanical & Physical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Ultimate) | ≥ 515 MPa (74,700 psi) | ASTM A213 / EN 10217 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29,700 psi) | ASTM A213 |
| Elongation (at Break) | ≥ 40% (min. 300 mm gauge length) | ASTM A213 |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | ASTM E153 |
| Thermal Conductivity (at 100°C) | 21.6 W/(m·K) | ASTM E153 |
| Linear Thermal Expansion (20–100°C) | 17.3 × 10⁻⁶ /°C | ASTM E228 |
| Density | 8.0 g/cm³ | — |
| Operating Temperature Range | −196°C to +450°C (−320°F to +842°F) | — |
| Corrosion Resistance (Pitting) | PRE N ≥ 24 (304) / ≥ 26 (316) | ASTM G48 |
| Surface Roughness (Internal) | ≤ 0.8 μm Ra (after pickling & passivation) | ASTM B600 |
Chemical Resistance
The austenitic stainless steel composition provides outstanding resistance to a wide spectrum of corrosive media, including:
- Dilute sulfuric acid (H₂SO₄) up to 10% concentration at ambient temperature
- Phosphoric acid (H₃PO₄) up to 80% concentration
- Atmospheric corrosion in coastal and industrial environments (salt spray test: ≥ 1000 hours per ASTM B117)
- Hydrochloric acid-resistant grades available upon specification (316L with Mo ≥ 3%)
Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 7.94 mm / 9.53 mm / 12.7 mm / 15.88 mm (⅜" / ⅜" / ⅝" / ⅝") | ±0.1 mm |
| Wall Thickness | 0.5 mm / 0.8 mm / 1.0 mm / 1.2 mm | ±10% |
| Coil Diameter (Bundle OD) | 200 mm – 800 mm (customizable) | ±2 mm |
| Coil Length (Tube Length) | 1.5 m – 12.0 m (per coil assembly) | ±5 mm |
| Number of Rows | 1 – 6 rows (configurable) | — |
| Tube Pitch (Transverse) | 15.0 mm – 25.0 mm | ±0.5 mm |
| Tube Pitch (Longitudinal) | 15.0 mm – 25.0 mm | ±0.5 mm |
| Fin Material (if finned) | Aluminum (1100-H14) / Stainless Steel (304) | — |
| Fin Thickness | 0.10 mm – 0.15 mm | ±0.01 mm |
| Fin Density (FPI) | 8 – 14 fins per inch | ±1 FPI |
| Working Pressure | 1.6 MPa (232 psi) standard / 2.5 MPa (363 psi) high-pressure | — |
| Hydrostatic Test Pressure | 2.4 MPa (348 psi) / 3.75 MPa (544 psi) | — |
| End Connections | Flared / Brazed / Welded (TIG) / Threaded (BSP/NPT) | — |
| Surface Finish | Pickled & passivated (internal & external) | — |
| Coating (optional) | None (bare SS) / Epoxy powder / PTFE | — |
| Weight (approximate) | Varies by configuration; typically 2.5 kg – 45 kg per coil | — |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip (AISI 304/316) is sourced from certified mills. Each batch undergoes spectrographic analysis (OES) to verify chemical composition and mechanical testing to confirm tensile and yield properties conform to ASTM A240/EN 10088-2 specifications.
- Slitting & Edge Preparation: The stainless steel coil is slit to precise widths using high-speed slitting lines. Edge burrs are removed to ensure uniform tube formation and prevent stress concentrations during bending.
- Tube Forming (Spiral Welding): The slit strip is formed into round tubes using a spiral welding process with TIG (Tungsten Inert Gas) or resistance welding. The weld seam is ground smooth to achieve internal surface roughness ≤ 0.8 μm Ra, minimizing flow resistance and fouling potential.
- Heat Treatment (Annealing): Welded tubes undergo solution annealing at 1050–1150°C followed by controlled cooling (air or water quench) to relieve residual stresses, restore full austenitic microstructure, and achieve the required mechanical properties.
- Pickling & Passivation: Tubes are immersed in a hydrofluoric-nitric acid pickling bath to remove mill scale and oxidation. Subsequent passivation with citric or nitric acid solution forms a protective chromium oxide (Cr₂O₃) layer, enhancing passive corrosion resistance.
- Coil Bending & Forming: Annealed tubes are bent into precise serpentine coil configurations using CNC-controlled bending machines. Bend radii are maintained at ≥ 3× tube OD to prevent wall thinning and cracking. Fixture jigs ensure consistent pitch and alignment across all rows.
- Fin Insertion (if finned coil): Aluminum or stainless steel fins are mechanically inserted into the formed tube coils using hydraulic fin-insertion presses. Fin-to-tube bonding is achieved through mechanical interlock or brazing.
- End Cap & Header Assembly: U-bends or end caps are welded (TIG) to connect tube rows into a continuous circuit. Headers (inlet/outlet manifolds) are assembled and welded to the coil bundle.
- Pressure Testing & Leak Detection: Each coil assembly undergoes hydrostatic pressure testing at 1.5× working pressure for a minimum of 30 minutes. Helium leak detection (≤ 1×10⁻⁹ Pa·m³/s) is performed on critical applications.
- Final Inspection & Packaging: Completed coils are inspected for dimensional accuracy, surface quality, and weld integrity. Protective caps are installed on open ends, and coils are packaged in moisture-barrier wrapping with desiccant for shipment.
Applications
The Stainless Steel Coil Tube is engineered for deployment in a broad spectrum of HVAC and thermal management applications, with particular emphasis on the following:
Primary Applications
- Dry-Type Fan Coil Units: Serves as the primary evaporator or condenser coil in dry FCUs operating within independent fresh air conditioning systems. The dry coil design prevents moisture accumulation, making it ideal for environments requiring strict humidity control (e.g., data centers, pharmaceutical cleanrooms, electronics manufacturing).
- Independent Fresh Air Systems: Integrated into standalone fresh air handling units (FAHU) that deliver conditioned outdoor air separately from recirculated air, ensuring superior indoor air quality (IAQ) and compliance with ventilation standards (ASHRAE 62.1, EN 16798).
- Commercial HVAC: Ceiling-mounted, wall-mounted, and ducted fan coil units in office buildings, hospitals, hotels, shopping malls, and educational facilities.
- Industrial Process Cooling: Chilled water coil applications in food processing, chemical plants, and electronics manufacturing where corrosion resistance is paramount.
Sector-Specific Applications
- Marine & Offshore: HVAC systems on cruise ships, naval vessels, and offshore platforms where chloride-laden atmospheres demand superior corrosion resistance.
- Pharmaceutical & Biotech: GMP (Good Manufacturing Practice) compliant cleanroom conditioning with contamination-free stainless steel surfaces.
- Food & Beverage: Cooling coils in food storage, refrigeration, and processing environments requiring hygienic, easy-to-clean surfaces.
- Coastal & Tropical Regions: Building HVAC in salt-spray environments where copper alternatives fail prematurely.
- Data Centers: Precision air conditioning for server rooms requiring dry-coil operation to prevent condensation on sensitive electronic equipment.
Unique Selling Points
The Wenzhou Jixing Stainless Steel Coil Tube distinguishes itself through the following competitive advantages:
- Superior Corrosion Longevity: Austenitic stainless steel construction provides 3–5× the service life of copper coil tubes in corrosive environments, reducing lifecycle replacement costs and maintenance frequency.
- Dry-Operation Compatibility: Optimized coil geometry and surface passivation minimize condensation formation, enabling reliable dry-coil operation in humidity-sensitive environments.
- Hygienic Surface Quality: Pickled and passivated internal surfaces (≤ 0.8 μm Ra) inhibit bacterial growth and biofilm formation, meeting FDA and EHEDG (European Hygienic Engineering Design Group) standards for food-grade and pharmaceutical applications.
- Design Flexibility: Customizable coil dimensions, row configurations, tube pitches, and connection types accommodate diverse OEM requirements and retrofit scenarios.
- Energy Efficiency: High thermal conductivity of stainless steel combined with optimized fin geometry delivers competitive COP (Coefficient of Performance) values, reducing operational energy consumption.
- Full Traceability: Each coil is serialized with material certification documentation, enabling complete supply chain traceability from raw steel mill to final installation.