Stainless Steel Coil Tube (Coiltube) — Heat Exchanger Tube for HVAC Applications
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered, continuously formed tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for integration into Fan Coil Unit (FCU) systems and heat exchanger assemblies used in commercial, industrial, and public infrastructure HVAC (Heating, Ventilation, and Air Conditioning) applications. The Coiltube serves as the primary heat transfer medium within air-handling systems, enabling efficient thermal exchange between circulating refrigerant/coolant and ambient air.
As a critical component in the HVAC supply chain, the Coiltube is engineered to meet the rigorous demands of continuous operation in high-traffic environments such as subway public areas, where fan coil units combined with fresh air supply systems and column-surface attached air supply schemes are employed to maintain thermal comfort and indoor air quality (IAQ).
Material & Properties
The Coiltube is fabricated from austenitic stainless steel grades, primarily AISI 304 (UNS S30408) and AISI 316 (UNS S31603), selected for their superior corrosion resistance, mechanical integrity, and thermal conductivity characteristics.
Key Material Properties:
- Corrosion Resistance: Excellent resistance to oxidation, chlorides, and condensation-induced corrosion — critical for high-humidity environments such as underground transit systems.
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, ensuring efficient heat transfer across the tube wall.
- Mechanical Strength: Minimum yield strength of 205 MPa (AISI 304) and 240 MPa (AISI 316), providing structural durability under cyclic thermal loading.
- Temperature Range: Operational range from −196°C to +870°C, accommodating extreme thermal cycling.
- Surface Finish: Passivated inner and outer surfaces with Ra ≤ 0.8 μm to minimize fouling and ensure laminar coolant flow.
- Hygienic Grade: Available in food-grade and medical-grade finishes compliant with FDA and EHEDG standards.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Material Grade | AISI 304 / AISI 316 / AISI 316L | ASTM A213 / ASTM A269 |
| Outer Diameter (OD) | 6.35 mm – 25.4 mm (¼" – 1") | ASME B36.19M |
| Wall Thickness | 0.5 mm – 2.0 mm | ISO 4207 |
| Coil Length | Up to 200 m per coil | Manufacturer Specification |
| Coil Inner Diameter | 150 mm – 500 mm | Customizable |
| Manufacturing Tolerance | ±0.1 mm (OD); ±0.05 mm (wall thickness) | ISO 4287 |
| Surface Treatment | Pickling & Passivation / Electropolishing | ASTM A967 |
| End Condition | Cut square / Beveled / Flanged | Per Customer Drawing |
| Pressure Rating | Up to 1.6 MPa (232 psi) working pressure | ASME B31.9 |
| Joining Method | Welded (TIG/Orbital) / Brazed / Mechanical | ASME B31.3 |
Manufacturing Process
The production of the Stainless Steel Coiltube follows a rigorously controlled multi-stage process to ensure dimensional accuracy, metallurgical quality, and surface integrity:
- Coil Slitting: Cold-rolled stainless steel strip (per ASTM A480) is slit to precise width using servo-controlled slitting lines.
- Forming (Tube Milling): The flat strip is passed through a series of progressively sized roll-forming stations, transforming the strip into a seamless tubular profile without welding.
- Welding (if applicable): For welded variants, a high-frequency resistance welding (HFW) or TIG welding process ensures full-penetration weld seams with minimum heat-affected zone (HAZ).
- Heat Treatment: Solution annealing at 1040–1120°C followed by rapid water quenching to restore full austenitic microstructure and eliminate residual stresses.
- Pickling & Passivation: Immersion in nitric/hydrofluoric acid baths removes oxide scale and forms a protective chromium oxide layer (Cr₂O₃) on the surface.
- Coiling & Packaging: Finished tubes are coiled on precision mandrels and wrapped in protective film to prevent mechanical damage and moisture ingress during transit.
Applications
The Coiltube finds extensive application across multiple sectors where reliable heat exchange and corrosion resistance are paramount:
- Subway & Underground Transit HVAC: Integrated into fan coil units (FCUs) operating in combination with fresh air supply systems and column-surface attached air supply (CSAAS) schemes in subway public areas. The stainless steel construction ensures resistance to condensate corrosion in high-humidity underground environments.
- Commercial Building HVAC: Chilled water coils, condenser tubes, and evaporator assemblies in air handling units (AHUs).
- Food & Pharmaceutical Processing: Hygienic-grade heat exchangers requiring CIP (Clean-In-Place) compatibility.
- Marine & Offshore Systems: Seawater-cooled heat exchangers leveraging AISI 316L's superior chloride resistance.
- Industrial Process Cooling: Chemical processing, power generation, and semiconductor manufacturing thermal management systems.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring product conformity to international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- EN 10204 3.1 — Third-Party Material Test Certification
- ASME Stamp Certification — Pressure Vessel & Piping Components
- CE Marking — European Conformity for Pressure Equipment Directive (PED 2014/68/EU)
- Material Traceability: Full heat-number traceability from mill certificate through final product dispatch
- Non-Destructive Testing (NDT): Eddy current and ultrasonic inspection of weld seams and tube walls per ASTM E709 and ASTM E317
Unique Selling Points
1. Seamless Corrosion-Free Performance in Harsh Environments: The austenitic stainless steel matrix provides indefinite service life in high-moisture, chloride-rich subway and coastal environments without degradation of heat transfer efficiency.
2. Precision Dimensional Control: Cold-forming technology ensures ±0.1 mm tolerance on outer diameter, guaranteeing optimal fit within fin-and-tube heat exchanger assemblies and minimizing pressure drop.
3. Continuous Coil Format: Delivered as a continuous coil up to 200 m in length, reducing the number of weld joints in field installation and enhancing system integrity and leak resistance.
4. Customizable Specifications: Full customization of OD, wall thickness, coil diameter, and surface finish to meet project-specific engineering drawings and OEM requirements.
5. Proven HVAC Integration: Validated through application in fan coil unit systems deployed in large-scale public transit infrastructure, demonstrating reliable thermal performance under continuous duty cycles.