Stainless Steel Coil Tube for HVAC Fan Coil Units
Product Overview
The stainless steel coil tube (Coil Tube) is a precision-engineered heat exchanger component designed for integration into HVAC (Heating, Ventilation, and Air Conditioning) fan coil units. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product represents a specialized application of stainless steel tubing in thermal management systems where corrosion resistance, thermal efficiency, and long-term durability are critical performance parameters.
Unlike conventional copper or aluminum coil tubes, the stainless steel variant offers superior resistance to chemical degradation, microbiological corrosion (MIC), and environmental stress, making it particularly suitable for applications involving aggressive refrigerants, humid environments, or hygienic requirements. The coil tube geometry maximizes the heat transfer surface area within a compact footprint, enabling efficient thermal exchange between the working fluid and ambient air.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, with the following material specifications:
- Base Alloy: Austenitic stainless steel conforming to AISI 304 (UNS S30400) or AISI 316L (UNS S31603) grades, depending on the application's corrosion resistance requirements.
- Chemical Composition (AISI 304): Carbon (C) ≤ 0.08%, Manganese (Mn) ≤ 2.0%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Silicon (Si) ≤ 1.0%.
- Chemical Composition (AISI 316L): Carbon (C) ≤ 0.03%, Manganese (Mn) ≤ 2.0%, Chromium (Cr) 16.5–18.5%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%.
- Mechanical Properties: Tensile strength ≥ 515 MPa (for 304); ≥ 515 MPa (for 316L); Yield strength ≥ 205 MPa; Elongation ≥ 40%.
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 20°C, providing adequate thermal transfer performance while maintaining structural integrity at operating temperatures ranging from −40°C to +250°C.
- Surface Finish: Mill finish or electropolished surface with a surface roughness (Ra) of ≤ 0.4 μm, minimizing fluid friction losses and preventing biofilm accumulation.
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and mild acid/alkaline environments. AISI 316L grade provides enhanced pitting and crevice corrosion resistance due to molybdenum addition.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) |
| Material Grade | AISI 304 / AISI 316L (Customizable) |
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8") |
| Wall Thickness | 0.50 mm – 1.50 mm (Configurable) |
| Coil Diameter | 50 mm – 500 mm (Customizable per design requirement) |
| Tube Length | Standard: 1000 mm – 6000 mm; Custom lengths available |
| Operating Temperature Range | −40°C to +250°C |
| Maximum Operating Pressure | ≤ 1.6 MPa (16 bar) |
| Heat Transfer Coefficient | ≥ 800 W/(m²·K) (air-side, depending on fin configuration) |
| Surface Treatment | Pickled & passivated; optional electropolishing or passivation treatment |
| Applicable Standards | ASTM A269, ASTM A213, EN 10216-5, GB/T 14976 |
| Refrigerant Compatibility | R-410A, R-32, R-22, R-134a, R-407C, R-404A, and ammonia-based systems |
| Fin Configuration | Aluminum fins (laminated) or integral stainless steel fins |
| Order Number | 969 |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tubing is procured from certified mills, subjected to spectroscopic analysis (OES) and mechanical testing to verify compliance with specified alloy grades.
- Seam Welding / Seamless Forming: For welded coil tubes, high-frequency induction welding (HFW) is employed with precise heat input control to achieve full-penetration welds with minimal distortion. For seamless variants, cold-drawn tubing is formed to the required coil geometry.
- Coil Forming: The straight tube is passed through precision forming rollers that gradually bend the tube into the desired helical coil shape. Controlled bending rates prevent material thinning, ovality, or work hardening at the bend radius.
- Heat Treatment (if required): Solution annealing at 1050–1150°C followed by rapid water quenching restores full austenitic microstructure, eliminates residual stresses from forming, and maximizes corrosion resistance.
- Pickling & Passivation: The formed coil tube is immersed in an acid bath (nitric acid/hydrofluoric acid mixture) to remove surface oxides, scale, and contamination. Subsequent passivation with a dilute nitric acid solution establishes a stable chromium oxide passive layer.
- Fin Application (if applicable): Aluminum fins are mechanically laminated onto the coil tube surface using specialized equipment, or integral fins are formed during the tube manufacturing stage.
- Quality Inspection: Each coil tube undergoes dimensional verification (OD, wall thickness, coil diameter, pitch), leak testing (pressure test at 1.5× operating pressure), visual inspection, and surface roughness measurement.
- Packaging & Dispatch: Approved products are packaged in moisture-proof wrapping with protective end caps to prevent mechanical damage during transit.
Applications
The stainless steel coil tube is engineered for a diverse range of thermal management and fluid handling applications:
- HVAC Fan Coil Units: Primary application domain—serves as the heat exchange element in fan coil units for commercial buildings, hospitals, and industrial facilities. The stainless steel construction eliminates concerns about galvanic corrosion when paired with aluminum fins and enhances longevity in humid or chemically aggressive indoor environments.
- Chiller & Condenser Systems: Utilized in shell-and-tube heat exchangers where water-side corrosion or refrigerant compatibility demands corrosion-resistant materials.
- Food & Beverage Processing: Employed in pasteurization, sterilization, and temperature control systems where sanitary standards (FDA, 3-A) require non-toxic, easily cleanable materials.
- Pharmaceutical & Biotechnology: Applied in cleanroom HVAC systems and process cooling/heating loops where hygienic design and resistance to cleaning agents (CIP/SIP) are mandatory.
- Marine & Coastal Environments: AISI 316L coil tubes provide critical protection against chloride-induced pitting corrosion in marine HVAC systems and offshore platform climate control.
- Industrial Process Cooling: Used in chemical processing plants, semiconductor fabrication cleanrooms, and data center liquid cooling systems where fluid compatibility and long-term reliability are paramount.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that all coil tube products meet international standards:
- ISO 9001:2015 — Quality Management System certification, demonstrating adherence to internationally recognized quality management practices.
- ISO 14001:2015 — Environmental Management System certification, reflecting commitment to sustainable manufacturing practices and environmental stewardship.
- CE Marking — Conformity with European health, safety, and environmental protection standards for HVAC components.
- ASTM / ASME Compliance — Materials and fabrication conform to ASTM A269 (Austenitic Stainless Steel Tubing), ASTM A213 (Seamless and Welded Austenitic Stainless Steel Tubing), and ASME B31.5 (Refrigeration Piping and Heat Transfer Components).
- NB (National Supervision) Certification — For pressure vessel and heat exchanger components subject to Chinese regulatory oversight.
- Third-Party Material Testing: All incoming raw materials and finished products are verified through independent laboratory testing, including Chemical Composition Analysis (OES), Mechanical Property Testing (tensile, hardness), and Non-Destructive Testing (NDT) including dye penetrant inspection (DPI) and eddy current testing.
Unique Selling Points
- Superior Corrosion Resistance: Unlike copper or carbon steel coil tubes, stainless steel construction provides exceptional resistance to galvanic corrosion, acid attack, and chloride pitting—significantly extending service life in aggressive environments.
- Hygienic Design: Smooth internal surfaces (Ra ≤ 0.4 μm) prevent biofilm formation and facilitate complete fluid drainage, making the product ideal for sanitary and pharmaceutical applications.
- Thermal Stability: Maintains mechanical integrity and dimensional stability across a wide operating temperature range (−40°C to +250°C), suitable for both heating and cooling applications.
- Customizability: Flexible manufacturing capability allows tailoring of coil diameter, pitch, tube length, wall thickness, and fin configuration to specific system design requirements.
- Refrigerant Compatibility: Compatible with next-generation low-GWP refrigerants (R-32, R-1234yf) without risk of material degradation or refrigerant absorption.
- Long-Term Cost Efficiency: Although the initial material cost is higher than copper, the extended service life (15–25+ years), reduced maintenance frequency, and elimination of corrosion-related failures result in superior total cost of ownership (TCO).
Technical Note: The application of stainless steel coil tubes in fan coil units addresses a critical gap in HVAC design—balancing thermal efficiency with long-term durability in corrosive environments. The study referenced in the product documentation (Application Analysis of Air Volume Testing of Fan Coil Units) highlights the importance of precise airflow characterization in optimizing coil tube performance. Proper air volume testing ensures that the coil tube operates within its designed thermal load range, preventing underperformance, excessive energy consumption, or premature degradation due to thermal cycling stress.