Stainless Steel Coil Tube — Fan Coil Unit (FCU) Grade
Product Overview
The Stainless Steel Coil Tube (Product No. 1659) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous spiral tubing designed primarily for heat exchange applications in Fan Coil Units (FCU) and related HVAC (Heating, Ventilation, and Air Conditioning) systems. Unlike conventional straight seamless or welded tubes, coil tubes are formed in a continuous helical configuration, which maximizes the surface-area-to-volume ratio and enhances thermal transfer efficiency within compact coil assemblies.
These coil tubes serve as the core heat exchange elements in fan coil air conditioners, where they facilitate efficient heat dissipation between circulating refrigerant or water and ambient air. Their helical geometry promotes turbulent fluid flow, reducing boundary layer thickness and significantly improving the overall heat transfer coefficient compared to straight-tube configurations.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, mechanical strength, and thermal conductivity. The following materials are commonly employed:
- SUS304 / AISI 304 (UNS S30408) — The primary grade for general HVAC applications, offering excellent corrosion resistance and weldability with a maximum service temperature of 870°C.
- SUS316 / AISI 316 (UNS S31608) — Enhanced molybdenum content provides superior resistance to chlorides and acidic environments, suitable for coastal or industrial installations.
- SUS316L / AISI 316L (UNS S31603) — Low-carbon variant offering improved resistance to intergranular corrosion after welding.
Key material properties include:
- Density: 8.0 g/cm³
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Specific Heat: 0.50 J/(g·K)
- Yield Strength: ≥ 205 MPa
- Tensile Strength: 515–720 MPa
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and chemical environments per ASTM G48 and ASTM A270 standards
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) |
| Product No. | 1659 |
| Material Grade | SUS304 / SUS316 / SUS316L |
| Outer Diameter (OD) | 6.35 mm (1/4") / 9.53 mm (3/8") / 12.70 mm (1/2") / 15.88 mm (5/8") |
| Wall Thickness | 0.30 mm – 1.20 mm (customizable) |
| Coil Diameter | 25 mm – 150 mm (configurable per application) |
| Tube Length per Coil | Up to 60 m continuous coil (spooled) |
| Surface Finish | No. 4 Brushed / Mirror Polish / Pickled & Passivated |
| Manufacturing Method | Continuous Cold-Forming Spiral Coil / Seamless |
| Applicable Standards | ASTM A269 / ASTM A270 / GB/T 12771 / EN 10217-7 |
| Maximum Operating Pressure | ≤ 1.6 MPa (standard) / ≤ 2.5 MPa (reinforced) |
| Operating Temperature Range | −196°C to +400°C |
| End Treatment | Flat-cut / Beveled / Threaded (per customer requirement) |
Manufacturing Process
The production of high-quality stainless steel coil tubes involves a multi-stage precision manufacturing sequence:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to incoming quality checks including chemical composition analysis (OES spectroscopy), mechanical testing, and surface defect inspection.
- Strip Annealing & Cleaning: The coil strip undergoes controlled annealing to relieve residual stresses and ensure uniform ductility. Surface oils and oxides are removed via alkaline degreasing and acid pickling.
- Spiral Forming & Welding: The strip is fed through precision forming rollers that progressively bend it into the desired helical cross-section. Simultaneous longitudinal welding (TIG or laser welding) creates a continuous seamless-like tube. The welding parameters are precisely controlled to minimize heat-affected zone (HAZ) distortion.
- Heat Treatment & Stress Relief: Post-welding solution annealing at 1050–1150°C followed by rapid water quenching ensures a fully austenitic microstructure, restoring corrosion resistance and mechanical properties.
- Passivation Treatment: The tube surface is treated with nitric or citric acid passivation solutions to form a protective chromium oxide layer, enhancing long-term corrosion resistance.
- Dimensional & Quality Verification: Each coil is inspected for dimensional accuracy (OD, wall thickness, coil diameter), surface quality, weld integrity (dye penetrant testing per ASTM E709), and hydrostatic pressure testing (per ASTM A269).
- Packaging & Shipment: Finished coils are wrapped in protective film, placed on wooden reels, and packaged for export or domestic delivery.
Applications
The primary application of this stainless steel coil tube is in the Fan Coil Unit (FCU) heat exchanger assembly, where it functions as the refrigerant or water circuit within the coil bundle. Additional applications include:
- HVAC Systems: Fan coil units, air handling units (AHU), and chilled water cooling coils.
- Refrigeration & Air Conditioning: Evaporators and condensers requiring corrosion-resistant tubing in residential and commercial systems.
- Food Processing Equipment: Heat exchangers in dairy, beverage, and pharmaceutical processing where hygienic-grade tubing is mandatory.
- Chemical & Petrochemical Industries: Process piping and heat exchange coils exposed to corrosive media.
- Marine & Coastal Environments: HVAC installations on vessels and offshore platforms where chloride-induced corrosion is a concern.
- Cleanroom & Pharmaceutical Facilities: Precision temperature control systems requiring non-contaminating, easy-to-sanitize tubing.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems to ensure consistent product performance:
- ISO 9001:2015 — Quality Management System certification ensuring systematic quality control throughout the manufacturing chain.
- ISO 14001:2015 — Environmental Management System certification demonstrating sustainable manufacturing practices.
- CE Marking — Conformity with European health, safety, and environmental protection standards for export to EEA markets.
- ASTM A269 / A270 — Compliance with American standards for welded austenitic stainless steel tubing for general, chemical, and heat-exchange service.
- GB/T 12771 — Compliance with Chinese national standard for stainless steel seamless and welded tubes for general application.
- EN 10217-7 — European standard for non-ferrous seamless and welded tubes for pressure purposes.
- Mill Test Reports (MTR) — Each batch is accompanied by full chemical and mechanical property documentation.
- NDT Testing — Non-destructive testing including dye penetrant inspection (DPI) and eddy current testing (ECT) for weld integrity verification.
Unique Selling Points
- Superior Heat Transfer Efficiency: The continuous helical coil geometry inherently promotes turbulent flow, achieving heat transfer coefficients 20–30% higher than equivalent straight-tube designs, directly translating to smaller, lighter, and more cost-effective fan coil units.
- Exceptional Corrosion Durability: Austenitic stainless steel construction provides a service life exceeding 25 years in aggressive environments, drastically reducing maintenance and replacement costs compared to copper or carbon steel alternatives.
- Continuous Coil Supply: Available in coils up to 60 meters, minimizing waste from cutting and reducing fabrication labor for downstream coil assembly operations.
- Customization Capability: OD, wall thickness, coil diameter, and surface finish are fully customizable to meet specific OEM (Original Equipment Manufacturer) design requirements.
- Hygienic & Food-Grade Compliance: Mirror-polished or electropolished finishes meet FDA and EHEDG (European Hygienic Engineering and Design Group) standards for food and pharmaceutical applications.
- Weld-Free Assembly Option: The continuous coil form allows for brazing-free coil assembly, eliminating potential leak points and improving long-term reliability in refrigerant circuits.
Technical Note: The Fan Coil Unit (FCU) represents one of the most widely deployed terminal conditioning devices in modern commercial HVAC systems. The coil tube is the single most critical component determining the thermal performance, longevity, and energy efficiency of the entire unit. Wenzhou Jixing Metal Materials Co., Ltd. delivers coil tubes engineered to optimize every parameter of this critical interface, ensuring peak performance across the full lifecycle of the installed system.