Stainless Steel Coil Tube (Coiltube) for Refrigeration Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered tubular product designed specifically for refrigeration and heat exchange applications. Unlike conventional straight piping, the coiltube is formed into a continuous helical or serpentine configuration, offering superior surface-area-to-volume ratios, enhanced heat transfer efficiency, and compact installation geometry. This product is particularly valued in the repair and fabrication of direct-cooling dual-temperature dual-control refrigerators, where the coil tube method provides a reliable, long-lasting alternative to traditional brazed pipe repairs.
The coil tube method, as documented in technical literature, represents a significant advancement in refrigeration system maintenance. By utilizing pre-formed stainless steel coiltubes, technicians can replace compromised evaporator or condenser sections with minimal system disruption, ensuring restored thermal performance and extended service life of the appliance.
Material & Properties
The stainless steel coil tube is fabricated from high-grade austenitic stainless steel, typically conforming to AISI 304 (UNS S30400) or AISI 316 (UNS S31600) grades, selected for their exceptional resistance to corrosion, cryogenic toughness, and long-term structural integrity under cyclic thermal loading.
- Chemical Composition (AISI 304): Carbon ≤ 0.08%, Chromium 18.0–20.0%, Nickel 8.0–10.5%, Manganese ≤ 2.0%, Silicon ≤ 1.0%, Phosphorus ≤ 0.045%, Sulfur ≤ 0.030%
- Chemical Composition (AISI 316): Carbon ≤ 0.08%, Chromium 16.0–18.0%, Nickel 10.0–14.0%, Molybdenum 2.0–3.0%, Manganese ≤ 2.0%
- Corrosion Resistance: Excellent resistance to oxidation at temperatures ranging from −196 °C (−321 °F) to +500 °C (+932 °F); superior chloride pitting resistance (AISI 316)
- Mechanical Properties: Tensile strength ≥ 515 MPa (75 ksi); Yield strength ≥ 205 MPa (30 ksi); Elongation ≥ 40%
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 20 °C — suitable for efficient heat exchange in refrigeration circuits
- Cryogenic Performance: Maintains ductility and fracture toughness at liquid nitrogen temperatures (−196 °C), making it ideal for evaporator coil applications
- Hygienic Surface: Passivated surface with Ra ≤ 0.4 μm finish, preventing microbial growth and facilitating cleaning in food-grade applications
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Outer Diameter (OD) | 3.0 / 4.0 / 6.0 / 8.0 / 9.52 / 12.7 | mm |
| Wall Thickness | 0.5 / 0.6 / 0.8 / 1.0 / 1.2 | mm |
| Coil Diameter (Helix) | 25 – 150 (customizable) | mm |
| Coil Pitch | 8 – 25 | mm |
| Tube Length per Coil | 1.0 – 50.0 (standard); up to 200 (special order) | m |
| Material Grade | AISI 304 / AISI 316 / AISI 321 | — | Surface Finish | Bright annealed / Pickled & passivated / Polished | — |
| Operating Pressure (Maximum) | 2.5 – 4.0 (depending on wall thickness) | MPa |
| Operating Temperature Range | −196 to +500 | °C |
| Standard Reference | ASTM A269 / ASTM A213 / GB/T 14976 | — |
| End Preparation | Plain / Beveled / Threaded (BSP/NPT) | — |
| Coil Form | Spiral (helical) / Serpentine (flat) / U-bend | — |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tube blanks are sourced from certified mills, with incoming material subjected to spectroscopic analysis (OES) to verify chemical composition within specification tolerances.
- Forming & Coiling: The tube is cold-formed into the desired helical or serpentine geometry using precision CNC-controlled coiling machines. Controlled bending radii (minimum bend radius ≥ 3× OD) prevent wall thinning, ovality distortion, and work-hardening-induced cracking.
- Heat Treatment (Annealing): Post-forming bright annealing is performed in a controlled atmosphere furnace (atmosphere: endothermic gas or vacuum) at 1050–1100 °C with controlled cooling. This relieves cold-work stresses, restores full austenitic microstructure, and eliminates residual magnetic permeability.
- Pickling & Passivation: The annealed coil is immersed in a hydrofluoric-nitric acid pickling bath to remove oxide scale, followed by passivation in a citric acid or nitric acid solution to establish a stable chromium oxide protective layer (Cr₂O₃).
- Hydrostatic Testing: Each coil assembly undergoes 100% hydrostatic pressure testing at 1.5× the maximum operating pressure for a minimum hold time of 30 seconds, ensuring zero leakage.
- Dimensional Inspection: Coiling diameter, pitch, tube OD, and wall thickness are verified using laser measurement systems and ultrasonic thickness gauges. Ovality is maintained within ±0.5% of nominal OD.
- Final Cleaning & Packaging: Internal bore flushing removes any residual particulates. Coils are packaged in moisture-proof wrapping with desiccant packs and labeled with batch traceability identifiers.
Applications
The stainless steel coil tube finds extensive application across multiple industrial and domestic sectors:
- Refrigeration & Air Conditioning: Evaporator coils, condenser coils, and capillary tube assemblies in domestic refrigerators (including direct-cooling dual-temperature dual-control models), commercial refrigeration units, and heat pump systems. The coil tube method enables efficient repair of failed evaporator circuits without requiring full compressor replacement.
- Automotive Industry: Radiator tubes, intercooler piping, and HVAC condenser coils for passenger vehicles and commercial fleets.
- Food & Beverage Processing: Heat exchangers, pasteurization coils, and hygienic fluid transfer lines where food-grade surface finish and corrosion resistance are mandatory (compliant with FDA 21 CFR and EC 1935/2004).
- Chemical & Petrochemical Industry: Reactor coil tubes, heat recovery systems, and process piping in corrosive environments (AISI 316 grade preferred for chloride-containing media).
- Pharmaceutical Manufacturing: Sterilizable heat exchangers and fluid handling coils meeting GMP (Good Manufacturing Practice) requirements.
- Domestic Appliances: Washing machine heating elements, dishwasher circulation coils, and water heater heat transfer assemblies.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management infrastructure ensuring full traceability and regulatory compliance:
- ISO 9001:2015 — Quality Management System certification, ensuring consistent production quality and continuous improvement processes
- ISO 14001:2015 — Environmental Management System certification, demonstrating responsible environmental practices in manufacturing
- ISO 45001:2018 — Occupational Health and Safety Management System certification
- EN 10204 3.1 Certificates — Material test certificates issued for each production batch, confirming compliance with ASTM/EN/GB standards
- CE Marking — Conformity with European directives for products intended for the European Economic Area (EEA)
- RoHS Compliance — Restriction of Hazardous Substances directive compliance for electronics and appliance integration
- Mill Test Reports (MTR): Available for each heat number, documenting chemical analysis, mechanical test results, and heat treatment records
Unique Selling Points
1. Superior Heat Transfer Efficiency: The helical coil geometry inherently promotes turbulent fluid flow at lower Reynolds numbers compared to straight tubes, enhancing convective heat transfer coefficients by 20–40%.
2. Compact Installation Footprint: Coiltube configurations achieve equivalent thermal capacity in 30–50% less installed volume than equivalent straight-tube heat exchangers, critical for space-constrained appliance designs.
3. Cryogenic Reliability: Austenitic stainless steel retains full ductility and impact toughness at ultra-low refrigerant temperatures, eliminating the risk of brittle fracture that affects carbon steel alternatives.
4. Extended Service Life: Resistance to intergranular corrosion, stress corrosion cracking (SCC), and pitting ensures operational longevity exceeding 15–20 years under normal refrigeration duty cycles.
5. Repair-Friendly Design: The coil tube method facilitates field-serviceable replacement of damaged evaporator sections in direct-cooling refrigerators, reducing downtime and total cost of ownership for end-users.
6. Full Traceability: Every coil tube is serialized with heat number, batch code, and manufacturing date, enabling complete supply chain traceability from raw material to end-product installation.
Conclusion
Wenzhou Jixing Metal Materials Co., Ltd.'s Stainless Steel Coil Tube represents a premium solution for demanding thermal management applications. Combining metallurgical excellence, precision manufacturing, and rigorous quality assurance, this product delivers reliable performance across the full spectrum of refrigeration, industrial heat exchange, and hygienic processing environments. The coil tube method, as validated through extensive field application in direct-cooling dual-temperature dual-control refrigerator repair, demonstrates the practical versatility and economic advantages of coiled stainless steel tubing over conventional straight-pipe alternatives.