Stainless Steel Coil Tube for Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Product No. 394) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product designed specifically for high-performance fan coil units (FCUs) and large temperature differential chilled water systems (Large ΔT Chilled Water Systems). These coil tubes serve as the core heat exchange elements in commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) systems, where thermal efficiency, corrosion resistance, and long-term operational reliability are critical performance parameters.
Unlike conventional copper or carbon steel coil tubes, the stainless steel coil tube offers superior resistance to scaling, pitting, and crevice corrosion—particularly in high-temperature differential environments where the supply water temperature can range from 7°C to 12°C while return water temperatures may reach 17°C to 22°C. This significant temperature gradient (ΔT) creates challenging thermal and chemical conditions that demand robust material integrity and dimensional stability.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades, primarily SAE 304 (UNS S30400) and SAE 316L (UNS S31603), selected for their excellent mechanical properties, weldability, and corrosion resistance in aqueous environments.
- SAE 304 Stainless Steel: Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni), providing excellent general corrosion resistance suitable for standard chilled water applications with pH levels between 6.5 and 9.0.
- SAE 316L Stainless Steel: Enhanced with 2.0%–3.0% Molybdenum (Mo) and reduced carbon content (<0.03% C), offering superior resistance to chloride-induced pitting and crevice corrosion, making it ideal for coastal or chemically aggressive environments.
- Surface Finish: Available in No. 4 brushed finish (Ra ≤ 0.8 μm) or electropolished finish (Ra ≤ 0.4 μm) to minimize flow resistance and inhibit biofilm accumulation.
- Wall Thickness Tolerance: ±10% of nominal wall thickness, ensuring uniform heat transfer coefficients across the coil assembly.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管 / Coil Tube) |
| Product Number | 394 |
| Material Grade | SAE 304 / SAE 316L (Austenitic Stainless Steel) |
| Outer Diameter (OD) | 9.52 mm, 12.7 mm, 15.88 mm, 19.05 mm (customizable) |
| Wall Thickness | 0.8 mm – 1.5 mm (±10% tolerance) |
| Coil Diameter | 150 mm – 500 mm (adjustable per application) |
| Coil Length | Up to 5,000 mm per continuous coil |
| Number of Rows | 2, 3, 4, or 6-row configurations |
| Tube Pitch (Lateral) | 15 mm – 25 mm |
| Row Pitch (Longitudinal) | 20 mm – 35 mm |
| Operating Temperature Range | -40°C to +200°C |
| Maximum Operating Pressure | 1.6 MPa (232 psi) |
| Thermal Conductivity | 16.3 W/(m·K) at 25°C |
| Surface Treatment | Passivation, Electropolishing, or PTFE (Polytetrafluoroethylene) Coating |
| Compliance Standards | ASTM A213, ASME B36.19M, EN 10217-7 |
| Welding Process | TIG (Tungsten Inert Gas) Welding / Orbital Welding |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and optimal thermal performance:
- Raw Material Selection: Cold-rolled stainless steel strip (CRSS) is sourced from certified mills, with each batch verified through Positive Material Identification (PMI) testing via X-ray fluorescence (XRF) spectrometry to confirm alloy composition compliance.
- Coil Forming: Precision CNC-controlled coil winding machines form the strip into the specified coil geometry with controlled spring-back compensation algorithms, ensuring tight dimensional tolerances (±0.5 mm on coil diameter).
- U-Bend Forming: Hydraulic U-bend machines create the return bends connecting adjacent coil rows, with a minimum bend radius of 1.5× OD to prevent wall thinning and stress concentration.
- Welding: Header connections and tube-to-header joints are fabricated using Tungsten Inert Gas (TIG) welding with argon shielding gas (purity ≥ 99.99%), followed by internal purge to prevent oxidation of the weld root.
- Surface Finishing: The completed coil assembly undergoes passivation treatment using a nitric acid or citric acid solution to remove free iron contamination and establish a protective chromium oxide (Cr₂O₃) passive film.
- Hydrostatic Pressure Testing: Each coil tube is pressure-tested at 1.5× the maximum operating pressure (2.4 MPa) for a minimum dwell time of 15 minutes to verify structural integrity and weld soundness.
- Final Inspection: Visual inspection, dimensional verification using calipers and gauge blocks, and optional Eddy Current Testing (ECT) for subsurface defect detection.
Applications
The stainless steel coil tube is engineered for demanding thermal management applications where reliability and longevity are paramount:
- Fan Coil Units (FCUs) in Large Temperature Differential Chilled Water Systems: The primary application scenario involves commercial building HVAC systems operating with supply water temperatures as low as 7°C and return water temperatures reaching 22°C. The stainless steel construction resists the thermal shock and condensation-induced corrosion inherent in such high-ΔT environments.
- Commercial and Institutional HVAC Systems: Office buildings, hospitals, hotels, educational facilities, and shopping centers requiring high-efficiency air handling with minimal maintenance.
- Process Cooling in Food and Pharmaceutical Industries: Where hygienic requirements mandate corrosion-resistant, cleanable, and non-contaminating heat exchange surfaces.
- Industrial Refrigeration and Cold Storage: Low-temperature evaporator coils operating at temperatures below ambient, requiring materials resistant to frost and moisture.
- Marine and Coastal HVAC Installations: SAE 316L grade coil tubes provide exceptional resistance to salt-laden atmospheric conditions and chloride-rich condensate.
- Data Center Cooling Systems: Precision cooling for high-density server environments where system uptime and thermal consistency are critical.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality assurance framework ensuring product conformity with international standards:
- ISO 9001:2015 — Quality Management System certification covering all stages of design, manufacturing, and inspection.
- ISO 14001:2015 — Environmental Management System certification demonstrating sustainable manufacturing practices.
- ASTM A213 — Standard specification for austenitic stainless steel seamless, cold-drawn or cold-rolled tubing.
- ASME B36.19M — Dimensional requirements for welded and seamless wrought stainless steel pipe and tubing.
- EN 10217-7 — European standard for seamless stainless steel tubes for mechanical and thermal uses.
- NB Certification (National Boiler Bureau, China) — Authorization for pressure vessel and heat exchanger component manufacturing.
- CE Marking — Conformity with European Union directives for machinery and pressure equipment.
Unique Selling Points
1. Superior Corrosion Resistance in High-ΔT Environments: The austenitic stainless steel matrix provides exceptional resistance to the corrosive effects of condensate, dissolved oxygen, and chlorides that are prevalent in large temperature differential chilled water systems. This eliminates the need for aggressive chemical treatment of the water loop and significantly extends service life beyond 20 years under normal operating conditions.
2. Optimized for Large Temperature Differential Systems: Engineered specifically for applications where supply and return water temperatures exhibit a differential of 10°C or greater, addressing the unique thermal cycling and condensation challenges identified in academic research on fan coil unit performance.
3. Enhanced Heat Transfer Efficiency: The precision-formed coil geometry with optimized tube pitch and row configuration maximizes the heat transfer surface area per unit volume, achieving overall heat transfer coefficients (U-values) of 800–1,200 W/(m²·K) depending on flow configuration and fin density.
4. Reduced Maintenance and Total Cost of Ownership: The elimination of copper tube replacement cycles and the inherent resistance to scaling and fouling result in a 40–60% reduction in lifecycle maintenance costs compared to conventional copper coil assemblies.
5. Customizable Configuration: Flexible design parameters including tube diameter, wall thickness, coil geometry, and row count allow tailoring to specific thermal load requirements and installation constraints.
Wenzhou Jixing Metal Materials Co., Ltd. is committed to delivering premium-grade stainless steel coil tube solutions that meet the evolving demands of modern thermal management systems, backed by rigorous quality control, extensive testing protocols, and decades of metallurgical expertise.