Stainless Steel Coil Tube for HVAC Air-Conditioning Unit Coil Sections
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Catalog No.: 1277
1. Product Overview
The Stainless Steel Coil Tube (盘管/Coiltube) is a precision-engineered tubular component specifically designed for the coil section of air-conditioning units and HVAC (Heating, Ventilation, and Air Conditioning) systems. This product is manufactured as a continuous helical coil, providing an optimal surface-area-to-volume ratio that maximizes heat exchange efficiency within confined equipment envelopes.
Unlike conventional straight-tube heat exchangers, the coil tube configuration offers superior thermal performance due to the inherent turbulence generated within the coiled geometry. This turbulence disrupts the laminar boundary layer, enhancing convective heat transfer coefficients between the working fluid (typically refrigerant, chilled water, or glycol solution) and the ambient air or secondary medium. The product is engineered to meet the rigorous thermal, mechanical, and corrosion-resistance demands of modern air-conditioning unit design.
Wenzhou Jixing Metal Materials Co., Ltd. applies advanced metallurgical processing and tight dimensional control to deliver coil tubes that integrate seamlessly into air-conditioning unit coil assemblies, ensuring long service life and minimal pressure drop under design flow conditions.
2. Material & Properties
2.1 Base Alloy Grades
- AISI 304 / UNS S30408: The primary grade for general-purpose coil applications. Contains 18–20% Chromium (Cr) and 8–10.5% Nickel (Ni), providing excellent general corrosion resistance, good formability, and weldability. Suitable for most indoor air-conditioning and HVAC environments.
- AISI 316L / UNS S31603: Enhanced grade for applications involving chlorinated environments, coastal installations, or chemical-laden air streams. The addition of 2–3% Molybdenum (Mo) significantly improves pitting and crevice corrosion resistance.
- AISI 321 / UNS S32100: Stabilized with Titanium (Ti), recommended for elevated-temperature applications where sensitization (chromium carbide precipitation at grain boundaries) must be avoided.
- AISI 316Ti / UNS S31635: Combines Molybdenum and Titanium stabilization for high-temperature and high-corrosion-resistance scenarios.
2.2 Mechanical Properties (Typical for Annealed Condition)
| Property | 304 / 304L | 316L | 321 |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 485 MPa | ≥ 515 MPa |
| 0.2% Proof Stress (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ≥ 205 MPa |
| Elongation after Fracture (A50mm) | ≥ 40% | ≥ 40% | ≥ 40% |
| Hardness (HV) | ≤ 210 | ≤ 210 | ≤ 210 |
| Density (ρ) | 8.00 g/cm³ | 8.03 g/cm³ | 8.00 g/cm³ |
| Thermal Conductivity (λ, 20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | 16.3 W/(m·K) |
| Coefficient of Thermal Expansion (α, 20–100°C) | 17.3 × 10⁻⁶ /K | 16.0 × 10⁻⁶ /K | 17.3 × 10⁻⁶ /K |
2.3 Corrosion Resistance
All specified grades exhibit outstanding resistance to atmospheric corrosion, non-oxidizing acids, and organic compounds. The 316L grade additionally provides superior resistance to chloride-induced pitting and intergranular corrosion, making it the preferred selection for outdoor condenser coils, marine HVAC applications, and installations in industrial environments with elevated chloride concentrations.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.0 mm | ASME B36.19M / GB/T 12771 |
| Wall Thickness (t) | 0.5 mm – 2.0 mm | ASME B36.19M / EN 10216-5 |
| OD Tolerance | ± 0.10 mm | — |
| Wall Thickness Tolerance | ± 10% of nominal | — |
| Coil Mean Diameter (CMD) | 50 mm – 300 mm | Custom per project requirement |
| Coil Pitch (P) | 15 mm – 60 mm | Custom per coil section design |
| Number of Turns | 10 – 500 (continuous) | Custom |
| Tube Length per Coil (L) | 3 m – 150 m | Custom |
| Surface Finish | No. 4 Brushed / 2B / Mirror (Ra ≤ 0.4 μm) | ASTM A480 |
| End Condition | Plain / Beveled / Flanged / Threaded | Per customer drawing |
| Operating Temperature Range | −196°C to +870°C (304); −196°C to +870°C (316L) | — |
| Maximum Operating Pressure | Up to 2.5 MPa (design dependent) | ASME BPVC Section VIII |
| Heat Treatment Condition | Solution Annealed (SA) at 1010–1150°C, water or air quenched | ASTM A270 / ASTM A554 |
| Applicable Standards | ASTM A554, ASTM A270, ASME B36.19M, EN 10216-5, GB/T 12771, JIS G3446 | — |
4. Manufacturing Process
4.1 Raw Material Preparation
Manufacturing commences with the procurement of certified cold-rolled stainless steel coil strip from approved mill sources. Each incoming batch undergoes rigorous incoming inspection including visual examination, dimensional verification, and spectroscopic chemical analysis (Optical Emission Spectroscopy, OES) to confirm compliance with the specified alloy composition. Certificates of Analysis (CoA) and Mill Test Reports (MTR) are reviewed and archived.
4.2 Coil Winding and Forming
- Strip Feeding and Leveling: The cold-rolled strip is fed through a precision leveling roll set to eliminate residual mill curvature and ensure uniform flatness prior to forming.
- Helical Coil Winding: A CNC-controlled coil winding machine forms the strip into a continuous helical coil geometry. The machine parameters—spindle rotation rate, feed rate, and mandrel diameter—are programmed according to the target Coil Mean Diameter (CMD) and Coil Pitch (P) specifications. This process maintains consistent dimensional accuracy throughout the entire coil length.
- Longitudinal Seaming: The longitudinal joint is formed using one of the following methods:
- Welded Coil: Continuous longitudinal TIG (Tungsten Inert Gas) welding or laser welding is applied to join the strip edges. The weld bead is subsequently ground flush to achieve a smooth internal bore surface.
- Seamless Coil: In select high-pressure applications, seamless tube is cut and formed into the coil geometry, eliminating the longitudinal weld entirely.
- End Forming: Coil ends are trimmed to precise length and formed to the required end condition (beveled, flanged, or threaded) for integration into the air-conditioning unit header or manifold assembly.
4.3 Heat Treatment (Solution Annealing)
The formed coil tube is subjected to solution annealing to relieve residual stresses introduced during the cold-forming process and to restore full austenitic microstructure. The coil is heated to 1010–1150°C in a controlled-atmosphere furnace (protective atmosphere or vacuum), held for sufficient soaking time to achieve uniform austenitization, and then rapidly cooled (water quench or controlled air quench) to preserve the single-phase austenitic structure. This process ensures maximum ductility, corrosion resistance, and freedom from sensitization.
4.4 Surface Finishing
Post-annealing, the coil tube surface is cleaned and finished to the specified grade. Options include:
- 2B Finish: Cold-rolled, annealed, and slightly pickled. Standard matte appearance.
- No. 4 Brushed Finish: Medium-grit abrasive brushing for a directional satin appearance.
- Mirror Polish: Multi-stage polishing to achieve a surface roughness of Ra ≤ 0.4 μm, recommended for applications where fouling resistance is critical.
4.5 Quality Inspection and Testing
- Dimensional Inspection: 100% measurement of OD, wall thickness, CMD, pitch, and total coil length using precision micrometers, bore gauges, and coordinate measuring machines (CMM).
- Visual and Dye Penetrant Inspection (DPI): All weld seams and coil surfaces are inspected for cracks, porosity, and surface defects in accordance with ASTM E709.
- Hydrostatic Pressure Test: Each coil is subjected to a hydrostatic test at 1.5× the maximum design pressure, held for a minimum of 30 seconds with no leakage or visible deformation, per ASTM A554.
- Corrosion Testing: Random samples undergo salt spray testing (ASTM B117) and intergranular corrosion testing (ASTM A262 Practice E) to verify material integrity and corrosion resistance.
- Chemical and Mechanical Verification: Periodic lot sampling for OES chemical analysis and tensile testing per ASTM A388.
5. Applications
The Stainless Steel Coil Tube is specifically engineered for integration into the coil sections of air-conditioning units and related HVAC systems. Key application areas include:
- Commercial Air-Conditioning Units: Evaporator and condenser coil assemblies in rooftop units (RTUs), packaged terminal air conditioners (PTACs), and split-system indoor/outdoor units. The coil tube serves as the refrigerant flow channel within the heat exchange core.
- Chilled Water Coil Sections: Used in air handling units (AHUs) and fan coil units (FCUs) where chilled water circulates through the coil tube to provide sensible and latent cooling.
- Heat Pump Systems: Dual-function coils for reversible heating and cooling cycles in residential and commercial heat pump installations.
- Industrial Process Cooling: Air-cooled condensers and evaporators in industrial process refrigeration systems where corrosion resistance is paramount.
- Marine and Coastal HVAC: Outdoor condenser coils in marine air-conditioning units, coastal data centers, and offshore platform HVAC systems where chloride-induced corrosion is a primary design concern. The 316L grade is specifically recommended for these environments.
- Food-Grade and Pharmaceutical HVAC: Cleanroom air-conditioning systems in food processing plants, pharmaceutical manufacturing facilities, and laboratories where hygienic surface conditions and resistance to chemical cleaning agents are required.
- Data Center Cooling: Precision air-conditioning coil sections for high-density server room cooling applications requiring reliability and long service life.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management infrastructure to ensure that all coil tube products meet international standards and regulatory requirements:
- ISO 9001:2015: Quality Management System certification covering all aspects of design, manufacturing, inspection, and delivery.
- ISO 14001:2015: Environmental Management System certification demonstrating commitment to sustainable manufacturing practices and environmental stewardship.
- ISO 45001:2018: Occupational Health and Safety Management System certification.
- ASME Section VIII: Manufacturing processes and inspection protocols are aligned with ASME Boiler and Pressure Vessel Code requirements for pressure-containing components.
- EN 10204 3.1 Certificate: Material Test Certificates issued in accordance with EN 10204 Type 3.1, providing independent verification of chemical composition and mechanical properties by a qualified third-party inspector.