Stainless Steel Coil Tube (Coiltube) — HVAC Fan Coil Unit Series
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered, continuous-length tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for integration into Series-Parallel Dry Fan Coil (FCU) systems with Independent Fresh Air Conditioning configurations. As a critical heat exchange component, the coil tube serves as the primary medium for thermal energy transfer within HVAC (Heating, Ventilation, and Air Conditioning) systems, delivering superior performance in both heating and cooling cycles.
Unlike conventional copper or aluminum coil tubes, the stainless steel variant offers exceptional corrosion resistance, mechanical durability, and long-term thermal stability, making it an ideal choice for demanding industrial and commercial HVAC applications where reliability and service life are paramount.
2. Material & Properties
2.1 Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, with the primary grades including:
- SUS 304 (UNS S30408) — Standard austenitic stainless steel with excellent general corrosion resistance and formability
- SUS 316 (UNS S31608) — Enhanced molybdenum-bearing grade for superior resistance to chloride-induced pitting and crevice corrosion
- SUS 321 (UNS S32108) — Titanium-stabilized grade providing improved resistance to intergranular corrosion at elevated temperatures
2.2 Key Material Properties
- Chemical Composition: Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Molybdenum (Mo) ≤ 2.0% (for 316 grade)
- Thermal Conductivity: 14–16 W/(m·K) at 20°C — optimized for efficient heat exchange in dry fan coil configurations
- Operating Temperature Range: -196°C to +870°C, ensuring reliability across extreme environmental conditions
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, acidic environments, and non-oxidizing acids
- Mechanical Strength: Tensile strength ≥ 520 MPa; Yield strength ≥ 205 MPa; Elongation ≥ 40%
- Hygienic Properties: Non-toxic, non-contaminating, and fully compliant with food-grade and pharmaceutical-grade standards
3. Technical Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Catalog No. | 650 | Wenzhou Jixing Internal Classification |
| Material Grade | SUS 304 / SUS 316 / SUS 321 | ASTM A213 / ASTM A269 |
| Outer Diameter (OD) | 6.35 mm – 25.4 mm (¼" – 1") | ±0.1 mm tolerance |
| Wall Thickness | 0.5 mm – 2.0 mm | ±0.05 mm tolerance |
| Coil Diameter | 50 mm – 200 mm | Customizable per project requirements |
| Coil Length (per spool) | 5 m – 50 m (continuous) | ±1 m tolerance |
| Surface Finish | 2B / BA (Bright Annealed) / Polished | Ra ≤ 0.4 μm (for BA finish) |
| Tube Form | Coiled (spooled) — continuous helical configuration | Per coil winding specification |
| End Condition | Plain / Beveled / Flanged | Customizable |
| Pressure Rating | Up to 1.6 MPa (232 psi) at 20°C | ASME B31.5 compliant |
| Heat Exchange Efficiency | Optimized for dry fan coil systems with independent fresh air | U-value ≥ 40 W/(m²·K) typical |
| Packaging | Wooden pallet / Steel drum / Protective film wrapping | Export-standard moisture protection |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Selection & Incoming Inspection: Stainless steel strip (coil) sourced from certified mills undergoes rigorous chemical composition analysis (spectrometry), mechanical property testing, and surface quality verification.
- Precision Cold Forming (Tube Rolling): The stainless steel strip is fed through a series of progressively reducing roller stations in a rotary tube mill, forming a seamless circular cross-section with tight dimensional tolerances.
- Welding (if applicable): For welded coil tubes, a high-frequency induction or laser welding process is employed to create a hermetic longitudinal seam with minimal heat-affected zone (HAZ).
- Heat Treatment (Annealing): The formed tube undergoes solution annealing at 1050°C – 1150°C in a controlled atmosphere furnace to relieve residual stresses, restore full austenitic microstructure, and achieve optimal corrosion resistance.
- Pickling & Passivation: Post-annealing oxide scale is removed via acid pickling (nitric/hydrofluoric acid blend), followed by passivation treatment to form a protective chromium oxide layer.
- Coil Winding: The processed tube is wound into a helical coil configuration on precision-controlled winding machines, ensuring uniform pitch, consistent diameter, and minimal mechanical distortion.
- Surface Finishing: Optional BA (Bright Annealed) or mechanical polishing treatments are applied to achieve the required surface roughness for optimal heat transfer performance in fan coil applications.
- Final Quality Inspection: Each coil undergoes dimensional verification (OD, wall thickness, coil diameter), pressure testing, leak detection, and visual/NDT (Non-Destructive Testing) examination.
4.2 Key Process Advantages
- Continuous Production: The coil tube format enables uninterrupted manufacturing and installation, eliminating the need for field welding of individual tube sections
- Dimensional Consistency: Automated roller-forming and CNC-controlled winding ensure uniformity across the entire coil length
- Minimal Waste: The coiled format reduces offcuts and material waste by up to 95% compared to straight-length tube fabrication
5. Applications
5.1 Primary Application — HVAC Fan Coil Systems
The coil tube is purpose-engineered for Series-Parallel Dry Fan Coil Units with Independent Fresh Air Conditioning Systems. In this configuration:
- The stainless steel coil tube serves as the heat exchanger core, facilitating efficient thermal transfer between the circulating fluid (water/glycol) and the air stream
- The dry-type design prevents condensate formation, eliminating the risk of microbial growth and improving indoor air quality (IAQ)
- The independent fresh air supply ensures continuous ventilation without recirculation of stale indoor air
- The coil tube's corrosion resistance is critical for long-term operation in environments with variable humidity and chemical exposure
5.2 Secondary Applications
- Commercial Building HVAC: Office buildings, hotels, hospitals, and retail complexes requiring reliable temperature control
- Industrial Process Cooling: Precision temperature control in manufacturing facilities, data centers, and laboratories
- Food & Pharmaceutical Processing: Hygienic fluid transfer in cleanroom environments where contamination control is mandatory
- Marine & Offshore Systems: HVAC applications in environments with high salinity and chloride exposure
- Chilled Beam & Radiant Cooling Systems: Secondary distribution piping in advanced building climate control systems
6. Quality Certifications & Compliance
6.1 Manufacturing Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices
- ISO 45001:2018 — Occupational Health and Safety Management System certification
6.2 Product & Material Standards
- ASTM A213 / A213M — Standard Specification for Seamless Austenitic Stainless Steel Tubing for High-temperature Service
- ASTM A269 / A269M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Other Severely Corrosive Services
- JIS G3459 — Japanese Industrial Standard for Cold-Drawn Seamless Stainless Steel Tubing
- GB/T 12771 — Chinese National Standard for Welded Stainless Steel Tubing for Fluid Transport
- ASME B31.5 — Code for Pressure Piping, Process and Industrial
6.3 Testing & Verification
- Hydrostatic Pressure Testing: Each coil is pressure-tested at 1.5× the maximum design pressure to verify structural integrity and leak-tightness
- Chemical Composition Verification: Spectroscopic analysis confirms compliance with specified grade requirements (Cr, Ni, Mo, C content)
- Mechanical Property Testing: Tensile, hardness, and impact tests conducted per ASTM E8/E8M and ASTM E10 standards
- Corrosion Testing: Salt spray testing (ASTM B117) and intergranular corrosion testing (ASTM A240) validate long-term durability
- Dimensional Inspection: Ultrasonic wall thickness measurement and optical dimensional verification at multiple points along the coil length
7. Unique Selling Points
1. Superior Corrosion Resistance: Stainless steel coil tubes offer 5–10× the service life of copper alternatives in corrosive environments, drastically reducing maintenance frequency and total cost of ownership (TCO).
2. Optimized for Dry Fan Coil Systems: Specifically engineered for series-parallel dry fan coil configurations with independent fresh air, delivering high heat transfer efficiency without condensate-related issues.
3. Continuous Coil Format: Eliminates field joints and connection points, reducing leak risk and simplifying installation in large-scale HVAC projects.
4. Full Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers flexible customization of dimensions, material grades, surface finishes, and coil configurations to meet project-specific requirements.
5. End-to-End Quality Assurance: From raw material sourcing through final inspection, a comprehensive quality management system ensures every coil tube meets international standards.
8. Conclusion
The Wenzhou Jixing Stainless Steel Coil Tube (Catalog No. 650) represents a premium-grade heat exchange solution purpose-built for modern HVAC fan coil systems. By leveraging the inherent advantages of austenitic stainless steel — exceptional corrosion resistance, high mechanical strength, and long-term thermal stability — this product delivers reliable, efficient, and durable performance across a wide spectrum of commercial, industrial, and specialized applications. Its compatibility with series-parallel dry fan coil and independent fresh air conditioning systems positions it as a forward-looking choice for building engineers and HVAC designers committed to energy efficiency, indoor air quality, and lifecycle cost optimization.