Stainless Steel Coil Tube — Fan Coil Unit (FCU) System Application Grade
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular product designed primarily for integration into Fan Coil Unit (FCU) systems that exhibit combined thermal and hydraulic characteristics. These coil tubes serve as the core heat exchange and fluid distribution elements within HVAC (Heating, Ventilation, and Air Conditioning) systems, where reliable thermal transfer efficiency and long-term hydraulic integrity are paramount.
Unlike conventional straight pipe segments, coil tubes are manufactured in continuous helical or spiral configurations, offering superior compactness, enhanced surface-area-to-volume ratios, and optimized turbulent flow characteristics that facilitate efficient heat dissipation within confined system geometries. The product is engineered to withstand cyclic thermal loading, sustained hydraulic pressure differentials, and the corrosive environments commonly encountered in commercial and industrial HVAC installations.
2. Material & Properties
Coiltube products are fabricated from high-grade austenitic stainless steel, with the following material options available based on application requirements:
- 304 Stainless Steel (UNS S30400): General-purpose grade with excellent corrosion resistance and formability; suitable for most HVAC thermal-hydraulic applications.
- 316L Stainless Steel (UNS S31603): Enhanced resistance to chlorides and pitting corrosion; preferred for coastal or chemically aggressive environments.
- 321 Stainless Steel (UNS S32100): Stabilized against intergranular corrosion at elevated operating temperatures.
Key material properties include:
- Thermal Conductivity: 14–16 W/(m·K) — ensuring efficient heat transfer between the working fluid and ambient medium.
- Coefficient of Thermal Expansion: ~17 × 10⁻⁶ /°C — compatible with differential expansion tolerances in FCU assemblies.
- Operating Temperature Range: −40 °C to +450 °C.
- Maximum Design Pressure: Up to 2.5 MPa (depending on wall thickness and coil diameter).
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and mild chemical corrosion per ASTM G48 testing protocols.
3. Specifications
| Parameter | Specification / Range | Unit | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | 6.0 – 50.8 | mm | ASTM A269 / A213 |
| Wall Thickness | 0.5 – 3.0 | mm | ASTM A269 |
| Coil Pitch (Helical Spacing) | 5.0 – 25.0 | mm | Custom / OEM Specification |
| Coil Diameter (Mean) | 50 – 500 | mm | Customer-Specific |
| Tube Length (Uncoiled) | 1.0 – 60.0 | m | — |
| Surface Finish | Bright Annealed / Pickled (Ra ≤ 0.8 μm) | — | ASTM A473 |
| End Form | Plain / Beveled / Flanged / Threaded | — | ASME B36.19M |
| Pressure Test | 1.5 × Design Pressure, 30-second hold | MPa | ASTM A269 Clause 10 |
| Material Grade Options | 304 / 304L / 316 / 316L / 321 | — | ASTM A213 / A269 |
| Coil Mass (Typical) | 5 – 80 | kg | — |
4. Manufacturing Process
The production of precision stainless steel coil tubes follows a multi-stage process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Material Selection & Inspection: Raw stainless steel strip or seamless tube stock is sourced from certified mills, undergoing spectroscopic composition analysis (OES) and mechanical property verification prior to processing.
- Forming & Coil Winding: Using CNC-controlled coil winding machinery, the tube is precisely helically formed around calibrated mandrels. The winding process maintains controlled curvature radii to prevent material thinning, micro-cracking, or work-hardening at the coil bends.
- Welding (for welded coil configurations): Where longitudinal welds are required, TIG (Tungsten Inert Gas) welding is employed with argon back-purging to achieve full-penetration, corrosion-resistant weld seams conforming to AWS D17.9 standards.
- Heat Treatment & Annealing: Post-forming solution annealing at 1050–1150 °C followed by controlled cooling restores the austenitic microstructure, eliminates residual stresses, and ensures uniform corrosion resistance.
- Pickling & Passivation: The coil surface is treated with a controlled acid bath (nitric/hydrofluoric acid blend) to remove scale and oxide layers, followed by passivation to establish a stable chromium oxide film.
- Dimensional Inspection & NDT: Each coil undergoes dimensional measurement (OD, wall thickness, coil pitch, mean diameter) and non-destructive testing (eddy current or ultrasonic) to detect internal or surface defects.
- Pressure & Leak Testing: Hydrostatic pressure testing at 1.5× design pressure with a 30-second hold time verifies structural integrity and weld quality.
- Packaging & Dispatch: Coils are protected with anti-corrosion wrapping, moisture-absorbent desiccants, and secured on wooden pallets or steel frames for shipment.
5. Applications
The stainless steel coil tube is designed for integration into complex thermal-hydraulic systems, with primary applications including:
- Fan Coil Unit (FCU) Systems: Serves as the primary heat exchange coil within FCU assemblies where mixed thermal and hydraulic characteristics demand high-efficiency heat transfer under variable flow conditions.
- Commercial HVAC Systems: Used in air handling units, chillers, and condensers in office buildings, hotels, hospitals, and retail facilities.
- Industrial Process Cooling: Applied in chemical processing, pharmaceutical manufacturing, and food processing where corrosion resistance and hygiene standards are critical.
- Marine & Coastal Applications: 316L-grade coil tubes are utilized in marine HVAC systems exposed to saline atmospheres and high-humidity environments.
- Refrigeration & Cryogenic Systems: Employed as evaporator and condenser coils in refrigeration circuits operating at low temperatures.
- Geothermal & District Heating Systems: Serves as the heat transfer element in ground-source heat exchangers and district energy distribution networks.
Technical Note: In fan coil unit systems exhibiting combined thermal and hydraulic characteristics, the coil tube geometry directly influences the system's thermal-hydraulic coupling behavior. The helical coil configuration promotes secondary flow patterns (Dean vortices) that enhance convective heat transfer coefficients by 20–40% compared to straight-tube configurations, thereby improving overall system COP (Coefficient of Performance).
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality assurance protocols aligned with international standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System certification.
- ISO 45001:2018 — Occupational Health and Safety Management System.
- CE Marking (EU) — Conformity with European directives for pressure equipment and machinery safety.
- EN 10204 3.1 — Material test certificates providing third-party verification of chemical composition and mechanical properties.
- ASME BPV Code — Compliance for pressure vessel and heat exchanger component applications.
- ASTM A269 / A213 — Standards governing stainless steel welded and seamless tube specifications.
- GB/T 12771 — Chinese national standard for stainless steel welded tubes (where applicable).
7. Unique Selling Points
- Thermal-Hydraulic Optimization: Coil geometry engineered specifically for FCU systems with mixed thermal and hydraulic characteristics, delivering superior heat transfer performance under variable flow regimes.
- Precision Manufacturing Tolerances: CNC-controlled winding ensures dimensional consistency within ±0.1 mm for coil pitch and ±0.5% for OD, enabling seamless integration into tight-tolerance HVAC assemblies.
- Full Material Traceability: Each coil tube is traceable from raw material mill certificate through final dispatch, supporting regulatory compliance in critical infrastructure applications.
- Custom Configuration Capability: Flexible manufacturing allows customization of coil diameter, pitch, OD, wall thickness, end forms, and material grade to match specific OEM system designs.
- Extended Service Life: Superior corrosion resistance of austenitic stainless steel ensures operational lifespans exceeding 25 years under typical HVAC service conditions, significantly reducing lifecycle maintenance costs.