Stainless Steel Coil Tube (Coiltube) — Dry Fan Coil Unit Application Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered heat exchange component designed primarily for integration into Dry Fan Coil Units (Dry Fan Coil Units, DFCU) and similar HVAC (Heating, Ventilation, and Air Conditioning) systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this coil tube product combines the corrosion resistance and structural integrity of austenitic stainless steel with optimized coil geometry to deliver superior thermal transfer performance in dehumidification and temperature regulation applications.
The coil tube functions as the core heat exchange element within dry fan coil systems, where air flows across the coiled stainless steel tubes to achieve sensible heat removal without introducing latent moisture into the air stream. This design principle is critical in environments requiring precise humidity control, such as cleanrooms, pharmaceutical facilities, and advanced manufacturing plants.
Material & Properties
Base Material Composition
- Primary Alloy Grade: SUS304 / 304L (ASTM A269, ASTM A213)
- Alternative Grade: SUS316 / 316L (for enhanced chloride resistance in aggressive environments)
- Chromium (Cr) Content: 18.0–20.0 wt%
- Nickel (Ni) Content: 8.0–10.5 wt%
- Molybdenum (Mo) Content (316 series): 2.0–2.5 wt%
- Carbon (C) Maximum: 0.08% (304), 0.03% (304L/316L)
Key Performance Properties
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, condensate water, and mild chemical exposure; superior to carbon steel and copper alternatives in chloride-rich environments
- Thermal Conductivity: 16.3 W/(m·K) at 20°C — balanced thermal transfer suitable for dry-type heat exchange
- Operating Temperature Range: −196°C to +870°C (continuous service)
- Hygienic Surface Finish: Ra ≤ 0.8 μm (electropolished), preventing microbial adhesion
- Non-magnetic: Austenitic structure ensures non-magnetic properties for sensitive electronic environments
Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.70 mm (1/2") | ASTM B730, ±0.05 mm |
| Wall Thickness | 0.50 mm – 1.50 mm | ASTM B730, ±10% |
| Coil Diameter (Bend Radius) | 50 mm – 300 mm (configurable) | Internal standard, ±2 mm |
| Tube Length (Straight Segment) | 1.0 m – 6.0 m (custom) | ±10 mm |
| Surface Finish | Ba & Bright Annealed (2B), Electropolished (EP) | Ra ≤ 0.8 μm (EP grade) |
| End Condition | Plain end, Flared, Threaded (BSP/NPT) | Per customer specification |
| Coating Option | None (bare), PTFE coating, Anti-condensation coating | Optional |
| Maximum Operating Pressure | 1.6 MPa (16 bar) | Hydrostatic test at 2.4 MPa |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-407C, Water/Glycol | ASME PTC 25 compliant |
| Weight (Typical, 9.52 mm OD × 0.8 mm wall) | 0.16 kg/m | Calculated per ASTM B730 |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, surface integrity, and mechanical reliability:
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip is sourced from certified mills (e.g., Outokumpu, POSCO, Taigang). Incoming material undergoes spectroscopic analysis (OES) and mechanical testing to verify chemical composition and tensile properties.
- Coil Winding & Forming: Precision CNC coil-winding machinery forms the stainless steel strip into the designated coil geometry. Tension control systems maintain uniform coil pitch and diameter throughout the winding process, ensuring consistent heat transfer surface area.
- Welding (if applicable): For seamless-to-seamless configurations, orbital TIG (Tungsten Inert Gas) welding is employed. Weld parameters are controlled to minimize heat-affected zone (HAZ) distortion and ensure full penetration with minimal residual stress.
- Heat Treatment: Solution annealing at 1050°C–1150°C followed by controlled water quenching restores full austenitic microstructure, eliminates residual stresses, and maximizes corrosion resistance.
- Surface Finishing: Mechanical polishing followed by electropolishing removes surface contaminants and achieves the required Ra value. The electropolishing process also passivates the surface, forming a chromium-rich oxide layer that enhances long-term corrosion protection.
- Quality Control & Testing:
- Dimensional inspection using coordinate measuring machines (CMM) and laser micrometers
- Hydrostatic pressure testing at 1.5× maximum operating pressure for minimum 30 seconds
- Visual inspection under magnification (5×) for surface defects
- Eddy current testing for internal and external flaw detection
- Spectroscopic verification of final chemical composition
- Packaging & Traceability: Each coil tube is individually identified with a unique batch code, packaged in moisture-barrier packaging, and accompanied by a mill certificate (EN 10204 Type 3.1) documenting material origin, test results, and heat number.
Applications
Primary Application: Dry Fan Coil Units
The stainless steel coil tube is the heat exchange core of dry fan coil units, which operate on the principle of sensible heat removal. Air is circulated across the coil tube by a fan, and the refrigerant (or chilled water) flowing inside the tube absorbs heat from the air without reaching the dew point. This eliminates condensate formation, making the system ideal for:
- Pharmaceutical Cleanrooms: ISO 14644-compliant environments requiring strict humidity control
- Electronics Manufacturing: Semiconductor fabrication and precision assembly areas
- Hospital Operating Rooms: Sterile environments where condensate would compromise air quality
- Archival & Museum Storage: Climate-controlled preservation of sensitive materials
- Food Processing: Hygienic cooling where stainless steel prevents cross-contamination
Secondary Applications
- Industrial process cooling and heating
- Refrigeration evaporator and condenser assemblies
- Heat exchangers in chemical processing plants
- Automotive thermal management systems
- Marine HVAC systems (316L grade for seawater resistance)
- Solar thermal collector assemblies
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and holds the following certifications applicable to this product:
| Certification | Scope | Standard |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Quality system covering design, manufacturing, and supply |
| ISO 14001:2015 | Environmental Management System | Environmental control in production processes |
| ISO 45001:2018 | Occupational Health & Safety | Workplace safety and hazard management |
| EN 10204 Type 3.1 | Material Certification | Third-party inspection and test reports for each batch |
| CE Marking | EU Compliance | Compliance with EU Machinery Directive and Pressure Equipment Directive |
| ASTM B730 | Product Standard | Standard specification for austenitic stainless steel tubing |
| ASME B31.3 | Pressure Piping | Compliance for process piping applications |
Unique Selling Points
1. Superior Corrosion Resistance: Unlike copper or carbon steel alternatives, the austenitic stainless steel coil tube provides exceptional resistance to condensate-induced corrosion, significantly extending service life in humid HVAC environments.
2. Hygienic Design: The electropolished surface finish (Ra ≤ 0.8 μm) eliminates crevices and surface roughness where bacteria can colonize, making this product suitable for FDA-regulated and pharmaceutical applications.
3. Dry-Type Optimization: The coil geometry is specifically engineered for dry fan coil operation, maximizing sensible heat transfer while minimizing the risk of condensate formation — a critical advantage over conventional coil designs.
4. Full Traceability: Every coil tube ships with complete material traceability documentation, enabling compliance with GMP (Good Manufacturing Practice) and ISO 13485 requirements in regulated industries.
5. Custom Configurability: Flexible customization of tube dimensions, coil pitch, end configurations, and surface treatments allows OEM (Original Equipment Manufacturer) partners to integrate this product seamlessly into proprietary system designs.
Technical Notes
When integrating the stainless steel coil tube into dry fan coil assemblies, the following engineering considerations should be observed:
- Ensure proper flow distribution across the coil face to prevent localized dry-out or over-cooling
- Maintain minimum air velocity of 0.5 m/s across the coil to prevent condensate accumulation
- Use compatible gaskets and fittings (stainless steel or PTFE-based) to avoid galvanic corrosion
- Perform periodic pressure testing and visual inspection per ASME PTC 25 maintenance guidelines
- For glycol-based systems, verify compatibility with the specific glycol formulation and concentration
This product represents a convergence of metallurgical excellence and thermal engineering, delivering a reliable, long-life heat exchange solution for the most demanding dry fan coil applications.