Stainless Steel Coil Tube (Coiltube) for Refrigeration Two-Phase Flow Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component specifically designed for use in refrigeration systems, heat exchangers, and fluid distribution networks where two-phase flow (liquid-vapor mixture) occurs. This product is engineered to withstand the thermodynamic boundaries associated with refrigerant flow through coiled geometries and throttling devices, ensuring reliable performance under extreme pressure differentials, temperature gradients, and flow velocity conditions.
The coil tube is supplied in a coiled configuration that facilitates compact installation within heat exchanger assemblies, evaporator banks, condenser units, and refrigeration circuit piping. Its geometry is optimized to manage the critical flow velocity at which refrigerant transitions between single-phase and two-phase states, preventing flow instability, vibration, and performance degradation.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, thermal conductivity, and mechanical integrity under cyclic loading conditions inherent to refrigeration service.
Material Grades Available
- AISI 304 (UNS S30408) — General-purpose refrigeration service; excellent corrosion resistance; non-magnetic in the annealed condition
- AISI 316 (UNS S31608) — Enhanced resistance to chlorides and aggressive refrigerants; suitable for marine and chemical environments
- AISI 316L (UNS S31603) — Low-carbon variant for weldability and resistance to intergranular corrosion
- AISI 321 (UNS S32100) — Titanium-stabilized grade for elevated-temperature service in heat recovery systems
- AISI 904L (UNS N08904) — High-alloy grade for extreme corrosion environments and specialty refrigerant applications
Key Material Properties
- Corrosion Resistance: Superior resistance to oxidation, pitting, and crevice corrosion from refrigerants including ammonia (NH₃), hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), and natural refrigerants
- Thermal Conductivity: 14–16 W/(m·K) at 20°C (AISI 304), providing efficient heat transfer in two-phase flow environments
- Temperature Range: −196°C to +450°C (AISI 304/316), accommodating cryogenic and high-temperature refrigeration cycles
- Mechanical Strength: Minimum tensile strength ≥ 515 MPa; yield strength ≥ 205 MPa (AISI 304, annealed condition)
- Non-magnetic: Suitable for environments requiring electromagnetic compatibility
- Hygienic Surface: Passivated inner surface with roughness Ra ≤ 0.4 μm for clean fluid transport
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Type | Stainless Steel Coil Tube (Coiltube) | — |
| Outer Diameter (OD) | 3 mm – 51 mm (custom ranges available) | ASTM A213 / ASTM A269 |
| Wall Thickness | 0.3 mm – 3.0 mm | ASTM A213 / ASTM A269 |
| Coil Diameter | 150 mm – 2000 mm (configurable) | Manufacturer specification |
| Coil Length | Up to 500 m per coil (standard); custom lengths available | — |
| Surface Finish | Pickled & Passivated (P&P); Ra ≤ 0.4 μm (inner) | ASTM A479 / EN 10217-7 |
| Surface Roughness (Inner) | Ra ≤ 0.4 μm (standard); Ra ≤ 0.2 μm (hygienic grade) | EN 10305-3 |
| Surface Roughness (Outer) | Ra ≤ 1.6 μm | EN 10305-3 |
| Heat Treatment | Annealed and Pickled (A&P); Solution Annealed | ASTM A213 |
| Pressure Rating | Up to 60 bar (design dependent on OD, wall thickness, and temperature) | ASME B31.5 / EN 13480 |
| Two-Phase Flow Performance | Optimized for critical flow velocity management in refrigerant circuits | Thermodynamic boundary analysis |
| Dimensional Tolerance | OD: ±0.05 mm; Wall Thickness: ±10% (minimum ±0.02 mm) | ASTM A213 / EN 10217 |
| Maximum Operating Temperature | −196°C to +450°C (grade-dependent) | ASTM A213 |
| Minimum Bend Radius | 1.5 × OD (cold bending); 1.0 × OD (hot bending) | — |
| Welding Compatibility | TIG (GTAW), orbital welding, laser welding | ASME B31.5 / EN 13480 |
| Standards Compliance | ASTM A213, ASTM A269, EN 10217-7, EN 10305-3, JIS G3459 | — |
| Packaging | Coiled on wooden reel or steel drum; moisture-proof wrapping | ISO 11607 (for hygienic applications) |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality suitable for two-phase refrigerant flow applications.
- Raw Material Selection & Inspection: Stainless steel wire rod or seamless tube blank is sourced from certified mills (e.g., Outokumpu, Voestalpine, Tsingshan). Incoming material undergoes spectroscopic analysis (PMI — Positive Material Identification) to verify chemical composition compliance with the specified grade.
- Tube Forming: Precision drawing or cold-rolled seamless tube production is employed to achieve tight dimensional tolerances. For smaller ODs (≤ 10 mm), cold-drawing from pre-pierced rod is utilized; for larger diameters, cold-rolled or hot-forged seamless processes are applied.
- Heat Treatment (Solution Annealing): The formed tube is solution annealed at temperatures between 1050°C and 1150°C, followed by rapid water quenching. This eliminates residual stresses from cold working, restores full austenitic microstructure, and ensures maximum corrosion resistance and ductility.
- Pickling & Passivation: The annealed tube is subjected to acid pickling (mixed acid bath: HNO₃/HF or H₂SO₄/HNO₃) to remove scale, oxide layers, and surface contaminants. Subsequent passivation with dilute nitric acid (10–20% HNO₃) forms a stable chromium oxide (Cr₂O₃) protective layer on the surface, enhancing corrosion resistance.
- Coiling: The processed tube is wound into a coil on a precision-controlled coiling head. The coil diameter and pitch are calibrated to ensure uniform curvature without introducing plastic deformation or residual bending stresses that could compromise two-phase flow stability.
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Quality Control & Testing:
- Dimensional Inspection: OD and wall thickness measured at multiple points using ultrasonic thickness gauges and optical comparators
- Chemical Analysis: Confirmed via optical emission spectrometry (OES) or XRF (X-ray Fluorescence)
- Pressure Testing: Hydrostatic pressure test at 1.5× working pressure for a minimum hold time of 30 seconds
- Surface Inspection: Visual and eddy current testing for surface defects, cracks, and inclusions
- Heat Treatment Verification: Hardness testing (Vickers HV) to confirm annealed condition
- Flow Performance Verification: Two-phase flow characterization testing to validate critical flow velocity parameters under representative refrigerant conditions
- Packaging & Dispatch: Coils are wrapped in moisture-proof film, secured on wooden reels or steel drums, and labeled with material certificates, heat numbers, and traceability documentation.
Applications
The stainless steel coil tube is engineered for demanding applications where two-phase refrigerant flow, thermal cycling, and corrosion resistance are critical performance factors:
- Refrigeration Systems: Evaporator coils, condenser coils, and interconnecting piping in commercial and industrial refrigeration plants using R-134a, R-410A, R-32, R-404A, R-507, ammonia (NH₃), CO₂ (R-744), and hydrocarbon refrigerants
- Throttling Devices: Piping sections upstream and downstream of expansion valves and capillary tubes where refrigerant undergoes rapid pressure reduction and phase transition
- Heat Exchangers: Coil-side tubing in shell-and-coil heat exchangers, plate-fin condensers, and air-cooled evaporators
- Cryogenic Applications: Liquefied natural gas (LNG) transfer lines, supercritical CO₂ refrigeration systems, and low-temperature process cooling circuits
- Food & Beverage Industry: Hygienic-grade refrigeration piping for dairy, beverage, and pharmaceutical processing where food-grade compliance is mandatory
- Heat Pump Systems: Vapor-compression heat pump circuits requiring durable coil tubing for seasonal thermal cycling
- Automotive & Marine HVAC: Compact coil assemblies for vehicle air conditioning and marine refrigeration systems
- Process Cooling: Industrial process cooling loops, chiller systems, and thermal management in electronics manufacturing
Two-Phase Flow Performance Characteristics
A distinguishing feature of this coil tube product is its optimization for two-phase refrigerant flow management. The coil geometry, surface finish, and dimensional precision are designed to control the critical flow velocity — the threshold at which the refrigerant transitions between single-phase and two-phase flow regimes within the tube. Key performance aspects include:
- Flow Stability: Smooth inner surface finish (Ra ≤ 0.4 μm) minimizes flow disturbances and promotes predictable two-phase flow patterns (stratified, wavy, slug, annular)
- Pressure Drop Control: Precise dimensional tolerances enable accurate prediction of frictional and acceleration pressure drops in two-phase flow, critical for system design and throttling device sizing
- Thermal Boundary Management: The tube wall thickness and material thermal conductivity are selected to manage heat transfer rates at the thermodynamic boundary between liquid and vapor phases
- Churn Flow Prevention: Coil diameter and pitch are optimized to prevent transition to churn flow, which can cause flow instability and reduced heat transfer efficiency
- Dropout Avoidance: Geometry is designed to prevent liquid film breakup and droplet formation at the thermodynamic boundary, ensuring efficient vapor transport downstream of throttling devices
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification systems to ensure compliance with international standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System certification
- EN 10204 Type 3.1 — Third-party inspection certificate for material conformity
- CE Marking — European Conformity for pressure equipment and piping components
- PED 2014/68/EU — Pressure Equipment Directive compliance (where applicable)
- NSF/ANSI 61 — Drinking water system components certification (for food-grade applications)
- 3-A Sanitary Standards — Dairy and food processing equipment certification (for hygienic-grade products)
- ASME B31.5 — Compliance with pressure piping and piping components code
- Mill Test Certificates (MTC) — Full chemical and mechanical test data provided for every heat/lot
Unique Selling Points
- Two-Phase Flow Optimization: Coil geometry specifically engineered for refrigerant two-phase critical flow velocity management, ensuring stable and efficient operation across the thermodynamic boundary
- Precision Dimensional Control: Tight tolerances on OD and wall thickness enable accurate system design calculations for pressure drop, heat transfer, and flow regime prediction
- Hygienic Surface Quality: Ultra-low roughness inner surface (Ra ≤ 0.2 μm available) meets food-grade and pharmaceutical standards
- Wide Material Selection: Multiple stainless steel grades available to match specific refrigerant chemistries and operating environments
- Full Traceability: Heat-number traceability from raw material mill through final product, with complete chemical and mechanical test documentation
- Custom Engineering: Custom coil diameters, pitches, lengths, and tube dimensions available to meet specific system design requirements
- Cryogenic to High-Temperature Capability: Operational range from −196°C to +450°C accommodates the full spectrum of refrigeration and heat pump applications
- Comprehensive Certification: Multi-standard compliance including ISO, CE, PED, NSF, and 3-A certifications for global market access
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