Stainless Steel Coil Tube for Fan Coil Unit Water Circuit Systems
Product Overview
The stainless steel coil tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered serpentine tubing product designed specifically for fan coil unit (FCU) water circuit systems in HVAC (Heating, Ventilation, and Air Conditioning) applications. This product represents an advanced evolution in heat exchanger tubing technology, incorporating improved hydraulic design principles to enhance thermal efficiency, reduce pressure drop, and extend service life in demanding commercial and industrial environments.
Unlike conventional copper or brass coil tubes, the stainless steel coil tube offers superior corrosion resistance, mechanical durability, and long-term reliability, making it an ideal solution for applications where water quality variability, chemical exposure, or stringent hygienic requirements are concerns.
Material & Properties
Base Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, primarily utilizing the following grades:
- AISI 304 (UNS S30400) — Chromium-Nickel austenitic stainless steel with excellent general corrosion resistance and formability
- AISI 316 (UNS S31600) — Chromium-Nickel-Molybdenum austenitic stainless steel offering enhanced resistance to pitting and crevice corrosion
- AISI 316L (UNS S31603) — Low-carbon variant of 316 for superior weldability and resistance to intergranular corrosion
Key Material Properties
- Corrosion Resistance: Exceptional resistance to atmospheric corrosion, chlorides, and acidic environments; pitting resistance equivalent number (PREN) ≥ 24 for 316 grade
- Thermal Conductivity: 14–16 W/(m·K) at 20°C, providing adequate heat transfer performance for water-based heat exchanger applications
- Mechanical Strength: Yield strength ≥ 205 MPa (304) to ≥ 170 MPa (316L); tensile strength ≥ 515 MPa
- Temperature Range: Operational range from −196°C to +870°C (continuous); suitable for hot water heating circuits up to 120°C and chilled water circuits down to −10°C
- Hygienic Surface Finish: Ra ≤ 0.4 μm achievable for pharmaceutical and food-grade applications
- Non-magnetic: Fully austenitic microstructure ensures non-magnetic properties
Technical Specifications
| Parameter | Specification |
|---|---|
| Product Type | Serpentine Coil Tube (盘管 Coiltube) |
| Material Grade | AISI 304 / 304L / 316 / 316L |
| Outer Diameter (OD) | 6.0 mm – 12.7 mm (1/4" – 1/2") |
| Wall Thickness | 0.5 mm – 1.0 mm |
| Tube Length (Per Coil) | 3 m – 15 m (configurable) |
| Coil Bend Diameter | 30 mm – 100 mm |
| Bend Radius | ≥ 2D (D = outer diameter) |
| Surface Treatment | Passivated / Electropolished / Mirror Polished |
| Maximum Working Pressure | 1.6 MPa – 4.0 MPa (depending on specification) |
| Design Temperature | −10°C to +120°C (standard); −40°C to +150°C (special order) |
| Hydraulic Design | Optimized serpentine layout for uniform flow distribution and minimal ΔP |
| Connection Type | Flared / Compression / Soldered / Welded (per customer specification) |
| Delivery Form | Coiled on reel / Bundled in protective packaging |
| Compliance Standards | ASTM A213 / EN 10217 / GB/T 14976 / ISO 4323 |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, material integrity, and performance reliability:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to spectroscopic analysis (OES), mechanical testing, and surface quality inspection prior to acceptance.
- Slitting & Coiling: The strip is precision-slitted to the required width and tolerance (±0.05 mm) and wound onto mandrels to achieve the target coil diameter.
- Forming & Bending: Using CNC-controlled roll-forming and bending equipment, the tube is shaped into the serpentine coil configuration with controlled bend radii to prevent wall thinning, ovality, or wrinkling. Minimum bend radius of 2D is maintained to preserve structural integrity.
- Welding (if applicable): End-to-end welds are performed via TIG (Tungsten Inert Gas) welding under argon shielding to achieve hermetic, full-penetration joints with minimal heat-affected zone (HAZ).
- Heat Treatment: Solution annealing at 1050°C–1150°C followed by rapid water quenching to restore full austenitic microstructure and eliminate residual stresses introduced during cold forming.
- Surface Finishing: Passivation treatment using citric acid or nitric acid solutions to remove free iron and enhance passive film formation. Electropolishing is available for hygienic-grade applications.
- Hydrostatic Pressure Testing: Each coil is subjected to hydrostatic testing at 1.5× the maximum working pressure for a minimum hold time of 60 seconds to verify leak-tightness and structural integrity.
- Final Inspection & Packaging: Dimensional verification, visual inspection, and material certification documentation are completed. Products are packaged with protective end caps and moisture-barrier wrapping.
Applications
The stainless steel coil tube is engineered for a wide range of water circuit applications, particularly in fan coil unit systems:
- Commercial HVAC Systems: Primary heat exchanger tubing in fan coil units for office buildings, hotels, hospitals, and shopping centers
- Industrial Process Cooling/Heating: Precision temperature control in chemical processing, pharmaceutical manufacturing, and food processing plants
- Domestic Heating Systems: Underfloor radiant heating circuits and radiator coil assemblies
- Chilled Water Distribution: Low-temperature water circuits in data centers, cleanrooms, and laboratory environments
- Marine & Offshore Applications: Corrosion-resistant tubing for shipboard HVAC systems and offshore platform cooling circuits
- Food & Beverage Industry: Hygienic-grade heat exchanger coils for pasteurization, brewing, and dairy processing
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring product conformity with international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- CE Marking — Conformity with European Union health, safety, and environmental protection standards
- EN 10204 3.1 — Material Test Certificates issued by authorized inspection personnel
- ASTM A213 — Compliance with standard specification for seamless austenitic stainless steel tubes
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes for general purposes
- SGS / BV / TUV — Third-party inspection and verification available upon request
Unique Selling Points
1. Superior Corrosion Performance: Unlike copper-based coil tubes susceptible to dezincification and stress corrosion cracking in aggressive water chemistries, stainless steel coil tubes maintain structural integrity over extended service lives exceeding 20 years under normal operating conditions.
2. Optimized Hydraulic Design: Incorporating lessons from advanced fan coil unit water circuit design methodologies, the serpentine geometry is engineered to achieve uniform flow distribution, minimize pressure drop (ΔP), and maximize heat transfer coefficient (U-value).
3. Material Versatility: Multiple grade options (304, 304L, 316, 316L) allow customers to select the optimal balance of cost, corrosion resistance, and mechanical properties for their specific application environment.
4. Full Traceability: Every coil tube batch is traceable to mill certificates, heat numbers, and processing records, ensuring complete supply chain transparency and compliance with regulatory requirements.
5. Custom Engineering Capability: Flexible manufacturing infrastructure supports custom coil geometries, dimensions, surface finishes, and connection configurations to meet project-specific design requirements.