Stainless Steel Coil Tube for Fan Coil Unit (FCU) Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered heat exchanger component designed primarily for integration into Fan Coil Units (FCU) within commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) systems. This product represents a critical thermal transfer element that interfaces directly with the air stream modulated by multi-wing centrifugal fans, delivering efficient sensible and latent heat exchange in compact configurations.
Distinct from conventional serpentine tubes or bare-fin coils, this coil tube product is engineered with optimized hydraulic geometry and material selection to maximize heat transfer coefficient while minimizing pressure drop across the coil circuit. The design philosophy draws upon advanced aerodynamic and thermodynamic optimization principles, particularly those validated in studies concerning multi-wing centrifugal fan volute optimization for FCU applications, ensuring that the coil tube performance is harmonized with the surrounding airflow dynamics rather than treated in isolation.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, selected for its exceptional corrosion resistance, mechanical integrity, and long-term thermal stability under cyclic operating conditions.
- Primary Material Grade: AISI 304 / AISI 316L Stainless Steel (ASTM A269/A269M compliant)
- Corrosion Resistance: Superior resistance to chloride-induced pitting (316L grade) and general atmospheric corrosion (304 grade), with a Minimum Corrosion Potential (CP) exceeding 500 mV vs. SCE in simulated HVAC condensate environments
- Mechanical Properties: Tensile Strength ≥ 520 MPa (304), ≥ 550 MPa (316L); Yield Strength ≥ 205 MPa; Elongation at Break ≥ 40%
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (304 grade), 14.6 W/(m·K) at 20°C (316L grade)
- Operating Temperature Range: -40°C to +250°C continuous; transient exposure up to 315°C
- Surface Finish: Electropolished interior (Ra ≤ 0.4 μm) to minimize fouling factor and reduce flow resistance; mill finish or bead blasted exterior (Ra ≤ 1.6 μm)
- Wall Thickness Tolerance: ±0.05 mm for precision control of thermal resistance and pressure drop
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.70 mm (1/4" / 3/8" / 1/2") | ASTM A269 |
| Tube Wall Thickness | 0.50 mm – 1.00 mm (customizable) | ISO 11980 |
| Coil Pitch / Row Spacing | 15 mm – 50 mm (configurable per thermal load) | ASHRAE 15 |
| Coil Length per Circuit | 0.5 m – 3.0 m (standard); up to 6.0 m (special order) | — | Fin Type | Aluminum L-Fin / W-Fin / Louvered Fin (optional coating: HAP, TiO₂) | — |
| Fin Density | 8 – 14 fins per inch (FPI) | — |
| Maximum Working Pressure | 1.6 MPa (16 bar) standard; 2.5 MPa (25 bar) reinforced | EN 12729 |
| Hydrostatic Test Pressure | 2.4 MPa (24 bar) for 30 seconds, zero leakage | ISO 11980 |
| Heat Transfer Efficiency (ε) | ≥ 0.78 (water-to-air, nominal conditions) | ASHRAE Standard 15 |
| Pressure Drop (ΔP) | ≤ 15 kPa across coil at nominal flow rate | — |
| Connection Type | Flared, Brazed, Threaded (G1/2" – G1"), or Flanged | ASME B1.20.1 |
| Maximum Flow Velocity | ≤ 3.0 m/s (interior tube velocity) | — |
| Coating Options | None (bare) / Epoxy / PTFE / Black Oxide | — |
| Compliance Standards | ASME B31.3, EN 12729, ISO 11980, ASHRAE 15 | — |
Manufacturing Process
The production of the Stainless Steel Coil Tube at Wenzhou Jixing Metal Materials Co., Ltd follows a tightly controlled, multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical soundness, and thermal performance consistency across every unit produced.
- Material Selection & Incoming Inspection: Hot-rolled stainless steel strip is procured from certified mills and subjected to spectrographic analysis (PMI), chemical composition verification, and mechanical property testing prior to acceptance.
- Coil Winding & Forming: Precision CNC-controlled coil winding machines form the tube into the required serpentine geometry with tight pitch control (±0.5 mm tolerance). The winding process maintains uniform curvature radii to prevent localized stress concentration and wall thinning.
- Seam Welding: TIG (Tungsten Inert Gas) welding is performed at the tube seam with argon back-purging to ensure full penetration and a smooth, defect-free weld bead. Weld quality is verified via dye penetrant testing (PT) or radiographic testing (RT) per ASME Section V.
- Heat Treatment (Annealing): Post-welding solution annealing at 1050°C – 1150°C followed by rapid water quenching eliminates residual welding stresses, restores full austenitic microstructure, and maximizes corrosion resistance.
- Fin Attachment (if applicable): Aluminum fins are mechanically crimped or brazed onto the tube surface using specialized finning equipment. Fin-to-tube contact resistance is minimized through controlled crimp force and surface preparation.
- Electropolishing: The interior bore undergoes electrochemical polishing to achieve a surface roughness (Ra) of ≤ 0.4 μm, removing micro-oxides, residual contaminants, and work-hardened layers. This step is critical for reducing fouling factor and ensuring long-term hydraulic efficiency.
- Pressure Testing: Each coil assembly undergoes 100% hydrostatic pressure testing at 1.5× the maximum working pressure for a minimum dwell time of 30 seconds. Electronic data logging records pressure decay for traceability.
- Final Inspection & Packaging: Dimensional verification (OD, wall thickness, pitch, length), visual inspection, and certification documentation are completed. Coils are wrapped in protective film and packed in moisture-barrier containers for shipment.
Applications
The Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd is engineered for demanding thermal management applications where reliability, corrosion resistance, and long service life are paramount. Key application domains include:
- Fan Coil Units (FCU): Integration as the primary heat exchanger element in FCU systems, where the coil tube interfaces with optimized multi-wing centrifugal fan volutes to achieve superior air-side heat transfer with minimal energy consumption. The aerodynamic optimization of the fan volute — as studied in the referenced literature — ensures that the airflow distribution across the coil face is uniform, preventing localized hot spots and maximizing the effective heat transfer area.
- Commercial HVAC Systems: Chilled water cooling coils and hot water heating coils in office buildings, hotels, hospitals, and retail facilities.
- Industrial Process Cooling: Heat exchangers in chemical processing, pharmaceutical manufacturing, and food and beverage production where hygienic standards and chemical resistance are required.
- Marine & Offshore HVAC: Corrosion-resistant coil assemblies for shipboard air conditioning and ventilation systems exposed to salt-laden atmospheres.
- Refrigeration & Cold Storage: Evaporator and condenser coils in low-temperature applications requiring reliable operation at sub-zero conditions.
- Data Center Cooling: Precision air handling coils for high-density server room thermal management.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality management systems and holds the following certifications and compliance credentials:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing and quality assurance processes
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices
- ISO 45001:2018 — Occupational Health and Safety Management System certification
- EN 10204 3.1 — Certificate of conformity for material testing and product certification
- CE Marking — Compliance with European Union directives for pressure equipment and HVAC components
- ASME / PE Stamp — Pressure Equipment compliance for applications exceeding 0.5 bar
- Third-Party Testing: Products tested and verified by SGS, Bureau Veritas, and TUV Rheinland for material composition, mechanical properties, and thermal performance
Unique Selling Points
1. Aerodynamic-Thermal Co-Design: Unlike conventional coil tubes designed in isolation, this product is engineered with awareness of the surrounding airflow dynamics — particularly the optimized multi-wing centrifugal fan volute — ensuring that the coil tube's fin geometry, pitch, and row arrangement are harmonized with the fan's pressure-volume characteristics for maximum system-level COP (Coefficient of Performance).
2. Electropolished Interior Surface: The Ra ≤ 0.4 μm interior finish significantly reduces the fouling factor compared to standard mill-finish tubes, extending maintenance intervals and preserving heat transfer efficiency over the product lifecycle.
3. Dual-Grade Material Options: Customers can select between AISI 304 (cost-optimized for general HVAC) and AISI 316L (premium corrosion resistance for aggressive environments), providing flexibility across diverse application requirements.
4. Precision Dimensional Control: CNC-driven manufacturing with ±0.05 mm wall thickness tolerance and ±0.5 mm pitch tolerance ensures consistent thermal performance and reliable integration with standard FCU housings and fan assemblies.
5. Full Traceability & Certification: Every production lot is accompanied by EN 10204 3.1 material certificates, hydrostatic test records, and dimensional inspection reports, providing complete supply chain traceability for critical infrastructure applications.