Stainless Steel Coil Tube — Fan Coil Unit (FCU) Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered product designed primarily for use in Fan Coil Unit (FCU) air conditioning systems. This coil tube is formed into a continuous serpentine configuration, offering superior heat exchange efficiency, corrosion resistance, and long-term structural integrity in demanding HVAC (Heating, Ventilation, and Air Conditioning) environments. The product is engineered to meet the most stringent energy-saving requirements for modern commercial and residential climate control installations.
As a core component in fan coil unit systems, the coil tube directly impacts the thermal performance, system longevity, and overall energy efficiency (EER — Energy Efficiency Ratio) of the installed HVAC unit. Wenzhou Jixing Metal Materials Co., Ltd has developed this product line with a focus on optimizing the balance between hydraulic flow characteristics and heat transfer surface area, ensuring maximum thermal exchange with minimal pressure drop.
Material & Properties
Base Material
- Grade Options: SUS304 (UNS S30400), SUS316L (UNS S31603), and SUS321 (UNS S32100)
- Composition (SUS304 typical): Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤2.0%, Carbon (C) ≤0.08%, Silicon (Si) ≤1.0%, Phosphorus (P) ≤0.045%, Sulfur (S) ≤0.030%
- Surface Treatment: Bright annealed finish or passivated surface for enhanced passive film stability
Mechanical Properties
- Tensile Strength: ≥520 MPa (SUS304), ≥550 MPa (SUS316L)
- Yield Strength: ≥205 MPa
- Elongation at Break: ≥40%
- Hardness: ≤92 HRB (annealed condition)
Corrosion & Thermal Properties
- Pitting Resistance (PREN): SUS304: ≥19; SUS316L: ≥24
- Operating Temperature Range: −196°C to +870°C (SUS304); −270°C to +870°C (SUS316L)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS304)
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and chemical environments; superior performance in chloride-containing media (SUS316L)
Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 6.35 mm, 8.00 mm, 9.53 mm, 10.00 mm, 12.70 mm |
| Wall Thickness | 0.50 mm, 0.60 mm, 0.80 mm, 1.00 mm |
| Tube Length (per coil) | Customizable; standard range 3.0 m – 15.0 m |
| Coil Winding Pitch | 12 mm – 25 mm (configurable per heat exchanger design) |
| Coil Diameter | 100 mm – 500 mm (custom winding) |
| Number of Rows | 1-row, 2-row, 3-row, 4-row configurations |
| Flow Velocity (nominal) | 1.5 m/s – 3.0 m/s (optimal heat transfer range) |
| Pressure Drop (nominal) | ≤ 50 kPa at rated flow |
| Surface Finish | Bright annealed (Ra ≤ 0.8 μm) or passivated |
| End Forming | Flared, U-bend, crimped, or flat-plate welded terminations |
| Standard Length Options | 2.0 m, 3.0 m, 4.0 m, 6.0 m, 10.0 m, 12.0 m, 15.0 m |
| Applicable Standards | ASTM A269, ASTM A778, GB/T 12771, EN 10216-5 |
Manufacturing Process
- Raw Material Inspection: Incoming stainless steel strip/coil is verified for chemical composition (spectroscopic analysis), mechanical properties, and surface quality per ASTM A269 specifications.
- Slitting & Leveling: The master coil is precision-slitted to the required width and leveled to eliminate coil set, ensuring dimensional accuracy for tube forming.
- Tube Forming (Cold Roll Forming): The strip is cold-formed through a multi-station roll mill into the specified circular cross-section. This process induces beneficial work hardening while maintaining precise wall thickness uniformity (±0.05 mm tolerance).
- Seam Welding: A high-frequency resistance welding (HFRW) or orbital TIG welding process creates a continuous longitudinal seam. Weld integrity is verified through 100% ultrasonic testing or dye penetrant inspection.
- Coil Winding: The formed tube is wound into the serpentine coil configuration using computer-controlled CNC winding machinery. Winding pitch, coil diameter, and number of turns are precisely controlled to meet heat exchanger design specifications.
- U-Bend Forming: End bends (U-bends) are formed using hydraulic bending equipment to ensure consistent bend radii and prevent wall thinning or kinking at the bend locations.
- Heat Treatment (Annealing): Solution annealing at 1050°C – 1150°C followed by rapid water quenching to restore full ductility, eliminate residual stresses, and stabilize the austenitic microstructure.
- Surface Treatment: Pickling and passivation treatment removes scale and contaminants, establishing a stable chromium oxide passive film for maximum corrosion resistance.
- Hydrostatic Pressure Testing: Each coil tube is subjected to hydrostatic pressure testing at 2.0× the maximum design pressure (typically 1.5 MPa – 3.0 MPa) to verify weld integrity and structural soundness.
- Final Inspection & Packaging: Dimensional verification (OD, wall thickness, straightness, coil geometry), visual inspection, and protective packaging with desiccant and anti-corrosion wrapping.
Applications
Primary Application: Fan Coil Unit (FCU) Systems
The stainless steel coil tube serves as the heat exchange core in fan coil unit air conditioning systems. These systems are the dominant choice for zoned climate control in:
- Commercial Buildings: Office towers, hotels, hospitals, retail centers, and educational facilities
- Residential HVAC: High-end residential units, villas, and apartments with central air conditioning
- Industrial Environments: Clean rooms, laboratories, data centers, and process control areas
Energy Efficiency Advantages
In the context of the "Most Energy-Saving Solution for Fan Coil Unit Air Conditioning Systems" (风机盘管空调系统最节能方案), the stainless steel coil tube offers the following advantages over traditional copper tube alternatives:
- Reduced Fouling Resistance: The passive chromium oxide layer significantly reduces biofilm and scale adhesion, maintaining heat transfer efficiency over extended operational cycles
- Lower Maintenance Costs: Superior corrosion resistance eliminates the need for frequent chemical cleaning or descaling treatments
- Extended System Lifespan: Design life exceeding 25 years in standard HVAC service conditions, compared to 10–15 years for carbon steel alternatives
- Improved COP (Coefficient of Performance): Consistent thermal conductivity and minimal degradation of heat transfer surfaces over time
Additional Applications
- Refrigeration and cold storage systems
- Heat recovery units and energy recovery ventilators (ERV)
- Chilled water distribution coils
- Industrial process heat exchangers
- Marine and offshore HVAC systems (SUS316L grade)
Quality Certifications & Standards Compliance
Manufacturing Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Conformity with European Directive requirements
Product Standards Compliance
- ASTM A269/A269M — Standard Specification for Seamless and Wrought Stainless Steel Tubing, Assembled by Welding
- ASTM A778/A778M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Service
- GB/T 12771 — Chinese National Standard for Stainless Steel Tubes for Fluid Transportation
- EN 10216-5 — European Standard for Welded Stainless Steel Tubes for Technical Applications
- JIS G3446 — Japanese Industrial Standard for Welded Austenitic Stainless Steel Tubes
Testing & Inspection Protocols
- 100% ultrasonic weld inspection per ASTM E317
- Hydrostatic pressure testing per ASTM A269 Section 11
- Chemical composition verification via OES (Optical Emission Spectroscopy)
- Dimensional inspection per GB/T 12771 tolerances
- Intergranular corrosion testing per ASTM A262 Practice E (SUS316L grade)
- Third-party inspection available (SGS, BV, TUV)
Unique Selling Points
"Engineering Excellence for Maximum Energy Efficiency in HVAC Applications"
- Precision Engineering: CNC-controlled coil winding ensures ±0.5 mm dimensional accuracy in coil geometry, optimizing heat exchanger performance and reducing air-side pressure drop
- Superior Corrosion Performance: The passive film stability of austenitic stainless steel provides 5–10× longer service life compared to carbon steel tubes in HVAC condensate environments
- Energy-Saving Design: Optimized tube diameter and wall thickness ratios minimize pressure drop while maximizing heat transfer surface area, directly improving system COP and reducing fan energy consumption
- Customization Capability: Full customization of coil geometry, tube dimensions, end configurations, and material grades to match specific heat exchanger design requirements
- Sustainability: Stainless steel is 100% recyclable with no loss of material properties, supporting circular economy objectives and reducing lifecycle carbon footprint
- Manufacturing Expertise: Leveraging advanced cold-forming and welding technologies to produce high-integrity, leak-free coil tubes at competitive production volumes
Technical Notes
When specifying the stainless steel coil tube for fan coil unit applications, engineers should consider the following design parameters:
- Ensure adequate flow velocity (1.5–3.0 m/s) to maintain turbulent flow conditions and maximize convective heat transfer coefficients
- Select SUS316L grade for applications involving chlorinated water treatment chemicals or coastal/marine environments
- Verify compatibility between stainless steel coil tube and aluminum fins (galvanic corrosion potential is negligible in normal HVAC service conditions)
- Specify appropriate end-forming method based on connection type (flared for direct expansion systems, crimped for brazed connections, flat-plate welded for integrated manifolds)
- Account for thermal expansion differential between stainless steel (α = 17.3 × 10⁻⁶ /°C) and aluminum fins (α = 23.1 × 10⁻⁶ /°C) in heat exchanger assembly design