Stainless Steel Coil Tube (Coiltube) for Air Conditioning & Refrigeration Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered seamless coil tube product designed specifically for air conditioning (A/C) and refrigeration systems. Drawing upon advanced development methodologies originally pioneered for seamless internal-threaded copper coil tubes, this stainless steel variant offers superior corrosion resistance, enhanced mechanical durability, and extended service life in demanding thermal exchange environments. The product is supplied in continuous coil form, enabling efficient downstream processing, heat exchanger fabrication, and integration into evaporator and condenser assemblies.
Material & Properties
The Coil Tube is fabricated from high-grade austenitic stainless steel, predominantly conforming to ASTM A213 (Specification for Seamless Austenitic Stainless Steel Tubing for Heat-Transfer and Similar Applications) and GB/T 12771 standards. The material composition ensures excellent resistance to pitting corrosion, chloride-induced stress corrosion cracking, and thermal fatigue cycling.
- Base Alloy Grades: 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), 316L (UNS S31603), 321 (UNS S32100)
- Chemical Composition (Typical – Grade 304): Carbon ≤ 0.08%, Chromium 18.0–20.0%, Nickel 8.0–10.5%, Manganese ≤ 2.0%, Silicon ≤ 1.0%, Sulfur ≤ 0.030%
- Mechanical Properties: Tensile Strength ≥ 515 MPa, Yield Strength ≥ 205 MPa, Elongation ≥ 40%, Hardness ≤ 92 HRB
- Thermal Conductivity: 16.3 W/(m·K) at 100°C (Grade 304)
- Maximum Service Temperature: 870°C (oxidation resistance); sustained thermal cycling capability at up to 400°C
- Corrosion Resistance: Equivalent to or exceeding copper tube performance in non-chlorinated environments; significantly superior in chloride-rich or humid atmospheric conditions
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 4.0 mm – 25.4 mm (custom ranges available) | GB/T 12771, ASTM A213 |
| Wall Thickness | 0.30 mm – 1.50 mm | — |
| Coil Inner Diameter (CID) | 300 mm – 1200 mm | — |
| Coil Length | Continuous coil, 50 m – 500 m per coil | — | Manufacturing Process | Seamless Piercing → Cold Drawing → Coiling (Continuous) | ISO 11307, EN 10217 |
| Surface Finish | Mirror Polish (Ra ≤ 0.1 μm), Electropolished, or Industrial Matte | GB/T 14976 |
| Internal Configuration | Plain bore, Internal Helical Groove, or Internal Thread (per customer specification) | — |
| Pressure Rating | Up to 2.5 MPa (dependent on OD/WT combination) | ASME B31.9 |
| Temperature Range | −196°C to +400°C (continuous service) | — |
| Heat Treatment | Solution Annealed (1050–1100°C, water quench) | ASTM A213 |
| Packaging | Wooden crate or export-grade pallet with moisture barrier | — |
Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous, multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality suitable for thermal exchange applications:
- Rod Preparation: High-purity stainless steel round bars are supplied from certified mills and undergo strict incoming inspection for chemical composition (via Optical Emission Spectroscopy, OES) and physical properties.
- Hot Piercing: Solid round bars are heated to 1100–1200°C and pierced on a Mannesmann-type or continuous piercing mill to produce seamless hollow billets, eliminating the presence of weld seams that could compromise pressure integrity.
- Hot Rolling / Reheating: Pierced billets are hot-rolled to approximate target dimensions while maintaining full austenitic microstructure.
- Solution Annealing: Tubes are solution-annealed at 1050–1100°C followed by rapid water quenching to dissolve carbides, homogenize the microstructure, and achieve maximum ductility and corrosion resistance.
- Cold Drawing: Annealed tubes are cold-drawn through precision tungsten carbide (WC) dies to achieve final OD, wall thickness, and dimensional tolerances (±0.05 mm). This process induces beneficial work hardening while maintaining elongation above 35%.
- Intermediate Annealing: Where multiple drawing passes are required, intermediate annealing at 1050°C prevents excessive strain hardening and cracking.
- Coiling: Drawn tubes are wound onto precision-controlled coiling stands at controlled tension to produce uniform coil geometry without kinking, ovality, or residual stress concentration.
- Surface Finishing: Tubes may undergo electropolishing (removing 5–15 μm of surface layer), passivation (citric or nitric acid treatment), or mirror polishing to achieve specified surface roughness.
- Non-Destructive Testing (NDT): 100% eddy current testing (ECT) is performed to detect internal and external surface defects; hydrostatic pressure testing at 1.5× working pressure verifies pressure integrity.
- Final Inspection & Packaging: Dimensional verification, surface inspection, and packaging per customer or export specification.
Applications
- Air Conditioning Evaporators & Condensers: The primary application domain, where the coil tube serves as the refrigerant flow channel in heat exchanger assemblies for residential, commercial, and industrial HVAC systems.
- Refrigeration Systems: Used in walk-in coolers, cold storage units, and refrigerated transport where corrosion resistance to cleaning agents and humid environments is critical.
- Heat Recovery Units: High-efficiency heat exchangers in heat pump systems leveraging the thermal conductivity and durability of stainless steel.
- Automotive A/C Components: Lightweight coil tubes for vehicle air conditioning evaporators and condensers, particularly in corrosion-prone coastal or road-salt environments.
- Industrial Process Cooling: Heat exchangers in chemical processing, pharmaceutical, and food-grade applications requiring sanitary-grade materials.
- Heat Pumps & Solar Thermal Systems: Coil tubes integrated into closed-loop heat transfer circuits for residential and commercial heat pump installations.
Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System
- GB/T 12771 — Seamless Stainless Steel Tubes for Fluid Transport (Chinese National Standard)
- ASTM A213 / A269 — American Society for Testing and Materials Standards for Stainless Steel Tubing
- EN 10217-7 — European Standard for Cold Drawn Precision Tubes for Mechanical and General Engineering Purposes
- ASME B31.9 — Pressure Piping Code for Refrigeration and Air-Conditioning Piping and Heat Exchangers
- SGS / BV / TUV — Third-party material inspection and certification available upon request
- Mill Test Reports (MTR): Provided with each shipment, including chemical analysis, mechanical test data, and NDT results
Unique Selling Points
1. Seamless Construction: The absence of a longitudinal weld seam eliminates potential leakage paths and stress concentration points, ensuring superior pressure integrity and fatigue resistance over the product's service life.
2. Superior Corrosion Resistance vs. Copper: Unlike traditional copper coil tubes, the stainless steel variant resists ammonia-based refrigerants, chlorinated cleaning solutions, and coastal salt-laden atmospheres without degradation, extending system service intervals.
3. Internal Thread / Groove Option: Available with internal helical grooves or threads that increase the effective heat transfer surface area by up to 40% and promote turbulent flow, significantly improving thermal efficiency while reducing tube length requirements.
4. Precision Dimensional Control: Cold-drawing tolerance of ±0.05 mm on OD and wall thickness ensures consistent fitment with brazing fixtures, expansion tools, and heat exchanger headers.
5. Continuous Coil Supply: Delivered in continuous coil form (up to 500 m), enabling high-throughput automated cutting and forming operations, reducing scrap rates, and minimizing downstream labor costs.
6. Full Traceability: Each coil is batch-traceable from raw material mill certification through all manufacturing stages, supporting regulatory compliance and quality assurance requirements in automotive and aerospace-adjacent applications.
Technical Notes
Wenzhou Jixing Metal Materials Co., Ltd. offers full customization capabilities including non-standard OD/WT combinations, specialized surface treatments, custom coil diameters, and tailored packaging for export markets. Technical consultation is available for application-specific engineering support, including thermal performance modeling and material selection guidance for specific refrigerant systems (R134a, R410A, R32, R1234yf, and natural refrigerants such as ammonia and CO₂).