Stainless Steel Coil Tube for Fan Coil Unit Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for integration into fan coil unit (FCU) systems combined with fresh air distribution networks. This product category falls under the broader classification of pre-formed coil tubes used in HVAC (Heating, Ventilation, and Air Conditioning) applications, where reliable thermal exchange performance, corrosion resistance, and structural integrity are paramount.
These coil tubes serve as the primary heat exchange elements within fan coil units, facilitating the transfer of thermal energy between the circulating refrigerant or hot water and the ambient air stream. Their helical coil geometry maximizes the surface area-to-volume ratio, thereby enhancing heat dissipation efficiency within compact spatial constraints typical of modern building HVAC installations.
Material & Properties
Base Material Composition
- Grade Options: SUS304 (UNS S30400), SUS316 (UNS S31600), and SUS321 (UNS S32100) austenitic stainless steel grades
- Chromium (Cr) Content: 18.0%–20.0% by mass, providing superior passive film formation and oxidation resistance
- Nickel (Ni) Content: 8.0%–10.5% by mass, ensuring stable austenitic microstructure at operating temperatures
- Molybdenum (Mo) Content: 2.0%–3.0% by mass (SUS316 grade), enhancing pitting and crevice corrosion resistance
- Carbon (C) Content: ≤0.08% by mass, minimizing carbide precipitation and intergranular corrosion susceptibility
Key Performance Properties
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, providing efficient heat transfer performance
- Operating Temperature Range: −196°C to +870°C, accommodating extreme thermal cycling conditions
- Corrosion Resistance: Excellent resistance to atmospheric, chemical, and microbial corrosion in humid HVAC environments
- Mechanical Strength: Tensile strength ≥515 MPa (annealed condition); Yield strength ≥205 MPa
- Elongation: ≥40% at fracture, ensuring ductility during forming and installation
- Hygienic Surface: Passivated surface finish with Ra ≤0.4 μm, inhibiting bacterial colonization and biofilm formation
Specifications
| Parameter | Specification | Tolerance | Test Standard |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.52 mm / 12.70 mm / 15.88 mm | ±0.10 mm | ASTM A554 |
| Wall Thickness | 0.50 mm / 0.71 mm / 1.00 mm | ±0.05 mm | ASTM A554 |
| Coil Pitch (Helical Spacing) | 10 mm – 25 mm (configurable) | ±0.5 mm | Enterprise Standard |
| Coil Height (Active Length) | 300 mm – 1,200 mm | ±2 mm | Enterprise Standard |
| Number of Passes | 2-pass / 4-pass / 6-pass / 8-pass | — | Design Specification |
| Tube Material | SUS304 / SUS316 / SUS321 | — | ASTM A270 / GB/T 12771 |
| Surface Finish | Pickled & Passivated (2B / BA finish) | Ra ≤ 0.4 μm | ASTM A403 |
| Maximum Working Pressure | 1.6 MPa (hot water) / 2.5 MPa (refrigerant) | — | EN 12981 |
| Hydrostatic Test Pressure | 3.2 MPa (100% tested) | — | GB/T 24511 |
| End Preparation | Plain ends / Flared ends / Threaded connections | — | ASME B31.9 |
| Heat Exchange Capacity | Up to 8.5 kW (per unit, 6-pass configuration) | — | ASHRAE Standard 34 |
| Refrigerant Compatibility | R22 / R410A / R134a / R32 / CO₂ (R744) | — | ASHRAE Standard 15 |
Manufacturing Process
Process Flow
- Raw Material Procurement: Sourcing certified cold-rolled stainless steel strip (CRSS) conforming to ASTM A554 or GB/T 3280 specifications. Each batch undergoes spectroscopic verification via XRF (X-Ray Fluorescence) analysis to confirm elemental composition.
- Coil Winding & Forming: Precision CNC-controlled spiral winding machines form the stainless steel strip into helical coil geometry with controlled pitch accuracy. The forming process employs progressive die sets to maintain dimensional consistency along the full coil length.
- Tube Welding (where applicable): For seamless coil tube configurations, high-frequency induction welding (HF-IW) or orbital TIG (Tungsten Inert Gas) welding is employed. Weld seams are subsequently ground flush to eliminate stress concentrations and ensure uniform wall thickness.
- Heat Treatment: Solution annealing at 1050°C–1150°C followed by controlled air or water quenching to achieve the required austenitic microstructure and mechanical properties. Stress-relief annealing at 600°C–800°C may follow to reduce residual forming stresses.
- Pickling & Passivation: Immersion in a mixed acid bath (HNO₃ + HF) to remove oxide scale and surface contaminants, followed by nitric acid passivation (20% HNO₃, 60°C, 30 minutes) to establish a protective chromium oxide passive film (Cr₂O₃).
- Quality Inspection: 100% hydrostatic pressure testing at 3.2 MPa for 60 seconds, dimensional verification via laser micrometry, visual inspection under magnification (5×), and eddy current (EC) flaw detection per ASTM E309.
- Assembly & Integration: Coil tubes are assembled into header manifolds (inlet/outlet distributors) using orbital TIG welding. The complete heat exchanger assembly undergoes leak testing via nitrogen pressure decay method (≤1% pressure drop over 24 hours).
- Packaging: Individual units are wrapped in protective PE film, placed in wooden crates with desiccant packs, and labeled with traceability documentation including heat number, test certificate, and compliance declarations.
Process Control Features
- In-line automated dimensional monitoring with SPC (Statistical Process Control) data logging
- Real-time weld quality monitoring via ultrasonic thickness gauging and visual inspection stations
- Full traceability system linking each production batch to raw material mill certificates and final test reports
- Clean room assembly environment (ISO 14644 Class 8) for hygienic-grade applications
Applications
Primary Application Domains
- Commercial HVAC Systems: Fan coil units for office buildings, hotels, shopping malls, and hospitals where precise temperature and humidity control is required. The coil tube serves as the core heat exchange element within the FCU evaporator or condenser section.
- Fresh Air Systems (新风系统): Integration with dedicated outdoor air systems (DOAS) to provide conditioned ventilation air while maintaining indoor air quality (IAQ) standards per ASHRAE 62.1.
- Industrial Process Cooling: Precision temperature control in pharmaceutical manufacturing, food processing, electronics assembly, and laboratory environments.
- Marine & Offshore Applications: Corrosion-resistant coil tubes for HVAC systems aboard vessels and offshore platforms exposed to salt-laden atmospheres.
- Residential High-End Systems: Multi-zone ductless mini-split systems and radiant cooling/heating coil installations in luxury residential buildings.
System Integration Context
In the Guangzhou-region fan coil unit plus fresh air system configurations, these stainless steel coil tubes are selected based on calculated thermal loads, indoor design conditions (typically 24°C dry-bulb, 60% RH for cooling; 20°C dry-bulb, 40% RH for heating), and the required number of cooling/heating seasons. The selection methodology follows the principles outlined in ASHRAE Handbook—HVAC Applications, incorporating simultaneous sensible and latent heat removal calculations.
Quality Certifications & Compliance
Certification Body Approvals
- ISO 9001:2015 — Quality Management System certification covering design, manufacturing, and delivery processes
- ISO 14001:2015 — Environmental Management System certification ensuring sustainable manufacturing practices
- ISO 45001:2018 — Occupational Health and Safety Management System certification
- CE Marking — Conformity with European directives including EN 12981 (Refrigerating systems and heat pumps — Components) and EN 14524 (Refrigerating systems — Heat exchangers)
- UL Listed — Underwriters Laboratories certification for electrical safety and performance
- CRAA (China Refrigeration and Air-Conditioning Association) — Member certification and product standard compliance
Material & Product Test Standards
- ASTM A270 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing
- ASTM A554 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Heat-Exchange Equipment
- GB/T 12771 — Stainless Steel Seamless Tubes for General Purposes (Chinese National Standard)
- GB/T 24511 — Technical Specification for Stainless Steel Tubes for Heat Exchangers
- EN 10217 — Technical Delivery Conditions for Stainless Steel Tubes for Technical Purposes
- ASME B31.9 — Refrigeration Piping and Heat Transfer Components
- ASHRAE Standard 34 — Safety and Environmental Classification of Refrigerants
- ASHRAE Standard 15 — Safety Standard for Refrigeration Systems
Performance Validation
- Third-party heat exchange capacity testing per EN 1273 and ASHRAE Standard 17
- Accelerated corrosion testing (salt spray per ASTM B117, 1,000 hours minimum for SUS316 grade)
- Cyclic pressure fatigue testing (≥10⁶ cycles at 1.5× design pressure)
- Thermal cycling validation (−40°C to +120°C, 500 cycles without degradation)
Unique Selling Points
- Superior Corrosion Durability: The austenitic stainless steel construction provides a service life exceeding 25 years in aggressive HVAC environments, significantly outperforming conventional copper or aluminum coil alternatives in humid or chemically contaminated air streams.
- Hygienic Performance: The passivated stainless steel surface resists microbial growth and biofilm formation, making these coil tubes ideal for healthcare facilities, pharmaceutical plants, and food-grade applications where contamination control is critical.
- Enhanced Thermal Efficiency: Precision helical geometry with optimized pitch and pass count delivers up to 15% greater heat transfer coefficient compared to standard fin-and-tube configurations, reducing fan power consumption and improving overall system COP (Coefficient of Performance).
- Refrigerant Versatility: Full compatibility with next-generation low-GWP (Global Warming Potential) refrigerants including R32, R1234yf, and CO₂ (R744), ensuring future-proof system design in compliance with evolving environmental regulations (Montreal Protocol Kigali Amendment).
- Design Flexibility: Modular coil tube configurations allow custom adaptation to specific thermal load requirements, spatial constraints, and system architecture, from compact residential units to large-scale commercial installations.
- Full Traceability: Each production unit carries a unique identification code linked to comprehensive material certificates, process records, and test data, enabling complete supply chain traceability and simplified maintenance documentation.