Stainless Steel Coil Tube for Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Product No. 1294) is a precision-engineered coiled stainless steel tubing manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Specifically designed for integration into Fan Coil Units (FCUs), this coil tube serves as the core heat exchange element in HVAC (Heating, Ventilation, and Air Conditioning) systems. The product is engineered to meet the rigorous demands of dehumidification applications under variable operating conditions, ensuring consistent thermal performance across fluctuating load scenarios.
Unlike conventional copper coil assemblies, the stainless steel coil tube offers superior corrosion resistance, extended service life, and enhanced structural integrity, making it an ideal solution for demanding commercial and industrial HVAC environments where reliability and longevity are paramount.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, with the following key material characteristics:
- Base Alloy: SUS304 / AISI 304 (18/8 Chromium-Nickel Stainless Steel), with optional grades including SUS316 / AISI 316 for enhanced chloride resistance
- Chromium (Cr) Content: 18.0–20.0%, providing robust passive oxide layer formation
- Nickel (Ni) Content: 8.0–10.5%, ensuring excellent ductility and formability
- Carbon (C) Content: ≤0.08%, minimizing intergranular corrosion susceptibility
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 20°C — optimized for efficient heat transfer in dehumidification cycles
- Operating Temperature Range: −60°C to +450°C, accommodating extreme thermal cycling
- Corrosion Resistance: Superior resistance to condensation-induced corrosion, microbial attack, and chemical degradation common in humid HVAC environments
- Mechanical Strength: Tensile strength ≥520 MPa; yield strength ≥205 MPa
- Surface Finish: Bright annealed (BA) or pickled and passivated (PP) finish, with surface roughness Ra ≤0.4 μm to facilitate air-side heat transfer
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.7 mm (standard sizes); custom diameters available | ASME B36.19M |
| Wall Thickness | 0.5 mm – 1.5 mm (selectable based on application pressure requirements) | ASTM A269 / ASTM A213 |
| Coil Winding Diameter | 150 mm – 400 mm (configurable per FCU design) | Custom |
| Tube Length per Coil | 3 m – 25 m (continuous coil) | Custom |
| Number of Rows | 1 to 6 rows (configurable) | ASHRAE Handbook — HVAC Systems and Equipment |
| Fin Pitch | 10 FPI – 14 FPI (Fins Per Inch) | Custom |
| Maximum Working Pressure | ≤1.6 MPa (gauge) | EN 12164 |
| Hydrostatic Test Pressure | 2.4 MPa (minimum, 150% of working pressure) | ISO 4427 |
| Heat Transfer Coefficient (Air Side) | 25 – 40 W/(m²·K) | ASHRAE Fundamentals |
| Heat Transfer Coefficient (Water Side) | 3,000 – 5,500 W/(m²·K) | ASHRAE Fundamentals |
| Applicable Refrigerant / Medium | Chilled water, glycol-water mixture, ammonia-water solution | — |
| Connection Type | Flared, brazed, welded, or compression fittings | ASME B31.9 |
| Coating / Passivation Treatment | Passivation with 3–5% nitric acid solution; optional PTFE (Polytetrafluoroethylene) coating | ASTM A967 |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Hot-rolled stainless steel strip is sourced from certified mills and subjected to incoming quality inspection, including chemical composition analysis (via Optical Emission Spectrometry, OES) and mechanical property verification.
- Cold Forming & Pipe Making: The strip is precision-formed into seamless tubing using a cold-drawn or cold-rolled process, ensuring tight dimensional tolerances (±0.1 mm for OD) and uniform wall thickness.
- Heat Treatment (Solution Annealing): Tubes are annealed at 1050°C – 1100°C in a protective atmosphere to relieve residual stresses, refine grain structure, and achieve the desired austenitic microstructure.
- Precision Coiling: The formed tubes are wound into the specified coil configuration using CNC-controlled coiling machines, maintaining consistent winding tension and pitch to prevent distortion or kinking.
- Fin Attachment (if applicable): Aluminum or stainless steel fins are mechanically or diffusion-bonded to the coil tube surface to maximize the air-side heat transfer area.
- Passivation & Surface Treatment: The finished coil tube undergoes acid pickling and passivation to remove surface contaminants and establish a stable chromium oxide passive layer, ensuring long-term corrosion resistance.
- Quality Inspection & Testing: Each coil tube undergoes hydrostatic pressure testing, dimensional verification (using laser measurement systems), visual inspection, and, where required, non-destructive testing (NDT) including ultrasonic testing (UT) and dye penetrant inspection (DPI).
Applications
The Stainless Steel Coil Tube is specifically engineered for the following application domains:
- Fan Coil Units (FCUs) — Dehumidification Applications: The coil tube serves as the primary heat exchanger in FCUs operating under variable load conditions. During dehumidification cycles, the coil tube's low thermal mass and high surface-to-volume ratio enable rapid coil surface temperature reduction below the dew point, effectively condensing moisture from the airstream. This is critical in environments requiring precise humidity control, such as data centers, laboratories, clean rooms, and pharmaceutical manufacturing facilities.
- Commercial HVAC Systems: Suitable for use in office buildings, hotels, hospitals, and educational institutions where reliable and corrosion-free heat exchange is essential for occupant comfort and indoor air quality (IAQ).
- Industrial Process Cooling: Employed in precision air conditioning systems for semiconductor fabrication, electronics assembly, and chemical processing plants where aggressive chemical exposure is a concern.
- Residential HVAC Applications: Used in premium residential split-system and packaged units where long-term durability and low maintenance are valued.
- Marine & Coastal Environments: The inherent chloride resistance of SUS316-grade coil tubes makes them suitable for HVAC installations in coastal regions, offshore platforms, and marine vessels.
Performance Under Variable Operating Conditions
A distinguishing characteristic of this coil tube product is its optimized performance in variable operating condition scenarios, particularly during dehumidification applications in Fan Coil Units. Key performance attributes include:
- Thermal Inertia Management: The stainless steel material provides an optimal balance between thermal conductivity and heat capacity, enabling rapid response to changes in chilled water flow rate and temperature while maintaining stable coil surface temperatures.
- Condensate Control: The smooth inner and outer surface finish (Ra ≤0.4 μm) minimizes condensate film thickness on the tube interior, reducing fouling resistance and maintaining consistent heat transfer performance over extended operating cycles.
- Variable Speed Compatibility: The coil tube design is compatible with Variable Frequency Drive (VFD)-controlled pumps and Variable Air Volume (VAV) systems, ensuring efficient operation across a wide range of part-load conditions.
- Anti-Fouling Properties: The passivated stainless steel surface exhibits reduced adhesion of biological and particulate contaminants, extending the service interval between cleaning cycles.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and holds the following certifications and standards compliance:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System certification
- CE Marking — Compliance with European Union directives for construction products
- EN 12164 — Conformity with European standard for metallic tubes and pipes for heat exchangers
- ASTM A269 / ASTM A213 — Compliance with American material specifications for austenitic stainless steel tubing
- GB/T 12771 — Compliance with Chinese national standard for stainless steel seamless tubes for general application
- ASME B36.19M — Compliance with American Society of Mechanical Engineers dimensional standards for stainless steel tubes
- RoHS (Restriction of Hazardous Substances) Compliance — Free from lead, mercury, cadmium, and other restricted substances
- REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) Compliance — Full compliance with EU chemical safety regulations
Each production batch is accompanied by a Material Test Certificate (MTC) conforming to EN 10204 Type 3.1, certifying chemical composition, mechanical properties, and traceability of the raw material.
Unique Selling Points
- Superior Corrosion Resistance: Unlike copper coil alternatives, the stainless steel coil tube eliminates the risk of galvanic corrosion when paired with aluminum fins, extending system service life by 2–3 times in aggressive condensation environments.
- Optimized for Dehumidification Performance: Engineered specifically for variable operating condition dehumidification applications in Fan Coil Units, ensuring consistent latent heat removal across fluctuating loads.
- Low Maintenance & Long Service Life: The passivated stainless steel surface resists scaling, fouling, and biofilm formation, reducing maintenance frequency and total cost of ownership (TCO).
- Customizable Configurations: Available in a wide range of diameters, wall thicknesses, coil winding configurations, and fin densities to meet specific OEM design requirements.
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, supporting circular economy principles and reducing the environmental footprint of HVAC systems over their lifecycle.
- Comprehensive Quality Assurance: Every coil tube undergoes rigorous multi-stage inspection and testing, backed by full traceability documentation and international quality certifications.