Stainless Steel Coil Tube — Fan Coil Unit (FCU) Application Grade
1. Product Overview
The Stainless Steel Coil Tube (Product No. 245) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered seamless or welded tubing product, cold-formed into helical or serpentine coil configurations. This product is specifically designed for integration into Fan Coil Units (FCU), air handling units (AHU), and heat exchanger assemblies within commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) systems. The coil tube serves as the primary heat transfer medium, facilitating efficient thermal exchange between the refrigerant/heat transfer fluid and the ambient air stream.
Unlike conventional carbon steel coil tubes, the stainless steel variant offers superior resistance to corrosion, extended service life, and enhanced performance under high-humidity and dehumidification conditions — critical parameters in modern HVAC system design and selection calculations.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for optimal combinations of thermal conductivity, mechanical strength, and corrosion resistance.
- Primary Grades: SUS304 (UNS S30400), SUS316L (UNS S31603), and SUS321 (UNS S32100)
- Chemical Composition (SUS304): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%
- Thermal Conductivity: 14.9–16.8 W/(m·K) at 20°C
- Operating Temperature Range: −196°C to +870°C
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and chemical corrosion; suitable for high-humidity dehumidification environments where condensate formation is prevalent
- Mechanical Properties: Yield strength ≥ 205 MPa; Tensile strength ≥ 515 MPa; Elongation ≥ 40%
- Surface Finish: 2B (No. 4) finish or BA (Bright Annealed) finish, with surface roughness Ra ≤ 0.8 μm
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm (⅛"), 9.52 mm (⅜"), 12.70 mm (½"), 15.88 mm (⅝") | ASTM A213 / GB/T 12771 |
| Tube Wall Thickness | 0.50 mm – 1.50 mm (customizable) | ASTM A269 / EN 10216-5 |
| Coil Pitch (Center-to-Center) | 12 mm – 50 mm (adjustable per design) | Manufacturer specification |
| Coil Diameter (Overall) | 100 mm – 600 mm | Per project requirement |
| Coil Length | Up to 30 m per continuous coil | — |
| Number of Rows (in FCU Application) | 2 rows, 3 rows, 4 rows, 6 rows | ASHRAE Standard 15 |
| Fin Spacing (if finned) | 1.8 mm – 3.2 mm (22 FPI – 38 FPI) | — |
| Fin Material | Aluminum (1100-H14) or Stainless Steel | — |
| Maximum Working Pressure | 2.5 MPa (365 psi) | — |
| Hydrostatic Test Pressure | 3.75 MPa (540 psi) | ASTM A269 |
| Refrigerant Compatibility | R-22, R-407C, R-410A, R-134a, R-32, R-404A | ASHRAE 34 |
| Heat Transfer Coefficient (Air Side) | 25 – 60 W/(m²·K) | ASHRAE Handbook — HVAC Components |
4. Manufacturing Process
The production of high-quality stainless steel coil tubes involves a multi-stage, precisely controlled manufacturing sequence:
- Material Selection & Incoming Inspection: Stainless steel strip or seamless pipe stock is sourced from certified mills and subjected to spectroscopic analysis (OES) to verify chemical composition and traceability.
- Tube Forming: Raw stock is formed into round cross-section tubes via cold-rolling or seamless piercing processes, followed by precision diameter control using diamond dies.
- Welding (if applicable): For welded tubing, high-frequency induction welding (HFW) or orbital TIG (Tungsten Inert Gas) welding is employed, with weld seam integrity verified by 100% eddy current testing.
- Heat Treatment / Annealing: Tubes undergo solution annealing at 1050°C – 1150°C in a protective atmosphere (argon or hydrogen) to relieve residual stresses and restore full austenitic microstructure.
- Precision Coiling: The straight tube is cold-bent into helical or serpentine coil configurations using CNC-controlled coiling machines, ensuring uniform bend radius (R ≥ 3D) to prevent ovalization and wall thinning.
- Fin Attachment (if finned): Aluminum or stainless steel fins are mechanically or brazed onto the coiled tube using a high-precision finning machine, ensuring consistent fin-to-tube contact resistance.
- Surface Treatment: Pickling and passivation are performed to remove mill scale and oxide layers, forming a protective chromium oxide film. Optional electropolishing may be applied for pharmaceutical-grade applications.
- Pressure Testing & Final Inspection: Each coil assembly undergoes 100% hydrostatic pressure testing at 1.5× working pressure, followed by visual inspection, dimensional verification, and leak detection (helium sniff test for critical applications).
5. Applications
The stainless steel coil tube is widely deployed in the following application domains:
- Commercial HVAC Systems: Fan coil units in office buildings, hotels, hospitals, and shopping malls, where the coil tube facilitates precise temperature and humidity control. The coupling of cold air ratio and dehumidification coefficient in selection calculations ensures optimal coil tube sizing for latent and sensible heat loads.
- Industrial Process Cooling: Chilled water coils for food processing, pharmaceutical clean rooms, and electronics manufacturing where corrosion-free operation is mandatory.
- Chiller & Condenser Units: Integral heat exchange coils in centrifugal, screw, and rotary chiller systems.
- Air Source Heat Pumps: Evaporator and condenser coil assemblies in residential and commercial heat pump systems.
- Marine & Offshore HVAC: High-salinity environment air conditioning systems where stainless steel's chloride resistance provides critical durability advantage over carbon steel.
- Specialty Applications: Laboratory ventilation systems, nuclear facility HVAC, and aerospace environmental control systems requiring traceable, certified materials.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets international standards:
- ISO 9001:2015 — Quality Management System certification for design, manufacturing, and service processes.
- ISO 14001:2015 — Environmental Management System, ensuring sustainable and eco-friendly production practices.
- ISO 45001:2018 — Occupational Health and Safety Management System.
- EN 10204 Type 3.1 — Third-party material inspection certificates for all delivered products.
- ASTM A213 / A269 / A270 — Compliance with American Society for Testing and Materials standards for seamless and welded austenitic stainless steel tubing.
- GB/T 12771 / GB/T 13296 — Compliance with Chinese National Standards for stainless steel seamless and welded tubing.
- EN 10216-5 — European standard for welded stainless steel tubes for technical applications.
- JIS G3446 / JIS G3459 — Japanese Industrial Standards for stainless steel tubes.
- NSF/ANSI 61 — Drinking water system components certification (for potable water applications).
- UL / CE Marking — Component-level safety certification for integration into certified HVAC equipment.
7. Unique Selling Points
Superior Corrosion Performance in Dehumidification Environments: The austenitic stainless steel construction eliminates the risk of internal and external corrosion caused by condensate water — a common failure mode in carbon steel coil tubes operating under high-humidity, low-temperature conditions. This directly correlates to improved indoor air quality (IAQ) and elimination of microbial growth on coil surfaces.
Extended Service Life: With proper installation and maintenance, the stainless steel coil tube offers a design life of 20–25 years, significantly exceeding the 8–12 year typical life of carbon steel alternatives.
Precision Engineering for HVAC Selection Optimization: The product is engineered to support rigorous selection calculations based on the coupling of cold air ratio (CAR) and dehumidification coefficient (DC), enabling engineers to achieve optimal thermal-hydraulic performance with minimal energy consumption.
Full Traceability: Each coil tube batch is accompanied by a complete material traceability dossier, including mill test certificates, heat numbers, and chemical/mechanical property reports.
Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers flexible customization of tube diameter, wall thickness, coil pitch, fin density, and overall dimensions to meet project-specific thermal load requirements.