Stainless Steel Coil Tube (Coiltube) — Direct Evaporation Ice Storage Application
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Code: 1393
Classification: Technical Literature & Research Reference
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product designed specifically for direct evaporation ice storage systems and other thermal energy management applications. Unlike conventional straight-pipe heat exchangers, coil tubes are wound into continuous spiral or helical configurations that maximize the heat transfer surface area within a compact envelope. This geometry enables highly efficient phase-change heat exchange processes, making the product particularly suitable for ice storage refrigeration systems where the refrigerant evaporates directly inside the tube, causing the surrounding water to freeze into ice for thermal energy storage.
The product draws upon extensive research into the freezing process of direct evaporation ice storage coil systems, incorporating findings related to ice formation dynamics, heat transfer coefficient optimization, and long-term thermal cycling performance. Wenzhou Jixing Metal Materials Co., Ltd leverages these technical insights to deliver coil tubes that maintain structural integrity and thermal efficiency under repeated freeze-thaw cycles.
2. Material & Properties
2.1 Base Material
- Primary Grade: Austenitic Stainless Steel (奥氏体不锈钢) — typically AISI 304 (UNS S30400) or AISI 316 (UNS S31600)
- Alternative Grades: AISI 316L (UNS S31603) for enhanced corrosion resistance in aggressive environments
- Material Form: Cold-rolled seamless or welded stainless steel tubing
2.2 Key Mechanical Properties
- Tensile Strength: ≥ 520 MPa (AISI 304); ≥ 515 MPa (AISI 316)
- Yield Strength: ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness: ≤ 230 HB (annealed condition)
- Impact Toughness at Low Temperature: Retains ductility down to −196°C (cryogenic capability)
2.3 Thermal Properties
- Thermal Conductivity: 14–16 W/(m·K) at 20°C
- Specific Heat Capacity: ~500 J/(kg·K)
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C
- Operating Temperature Range: −196°C to +450°C
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, aqueous environments, and refrigerant media (R-134a, R-404A, R-507, ammonia, CO₂)
- Chloride pitting resistance (AISI 316): PREN ≥ 24
- No risk of galvanic corrosion when paired with compatible materials
- Immune to intergranular corrosion after proper stabilization or low-carbon processing
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6 mm – 51 mm (customizable) | ASTM A269 / GB/T 12771 |
| Wall Thickness | 0.5 mm – 3.0 mm | ASTM A269 / EN 10216 |
| Coil Winding Diameter | 100 mm – 800 mm (configurable) | Manufacturer specification |
| Coil Length (Straightened Equivalent) | Up to 60 m per coil | — |
| Winding Pitch | 3 mm – 15 mm (adjustable per application) | — |
| Surface Finish | 2B, No. 4, Mirror (Ra ≤ 0.4 μm), or Electropolished | ASTM A240 |
| Pressure Rating | Up to 2.5 MPa (design pressure) | ASME B31.5 |
| Refrigerant Compatibility | HFC, HFO, HCFC, NH₃, CO₂, Hydrocarbons | ASHRAE 34 |
| Dimensional Tolerance | ±0.1 mm (OD); ±10% (wall thickness) | ASTM A269 |
| Welding Quality | Full-penetration butt welds; 100% visual inspection; optional RT/PT | ASME BPV Section VIII |
| Coating / Passivation | Acid passivation (nitric acid or citric acid) | ASTM A967 |
4. Manufacturing Process
4.1 Raw Material Preparation
High-purity austenitic stainless steel billets or coils are procured from certified mills. Incoming materials undergo spectroscopic analysis (OES) and mechanical testing to verify chemical composition and mechanical properties prior to processing.
4.2 Cold Drawing / Seamless Forming
Tubing is produced via cold drawing or seamless piercing processes to achieve precise dimensional tolerances and superior grain structure. The cold work process enhances mechanical strength while maintaining ductility necessary for coil winding operations.
4.3 Annealing & Stress Relief
Intermediate annealing at 1050–1150°C followed by controlled cooling relieves residual stresses accumulated during forming. This step ensures dimensional stability during subsequent winding and prevents springback.
4.4 Precision Coil Winding
Tube blanks are fed through CNC-controlled winding machines that apply uniform tension and precise pitch control. The winding process employs computerized tension regulation to ensure consistent coil geometry, critical for uniform heat transfer performance in ice storage applications. Winding parameters are calibrated based on the specific thermal load requirements of the end application.
4.5 Surface Treatment & Passivation
Finished coils undergo pickling and passivation treatment (ASTM A967) to remove surface oxides and contaminants. This establishes a protective chromium oxide film that maximizes corrosion resistance. Optional electropolishing reduces surface roughness to Ra ≤ 0.4 μm, minimizing fouling potential in refrigeration circuits.
4.6 Quality Inspection
- Dimensional Verification: Laser micrometry and CMM inspection
- Pressure Testing: Hydrostatic or pneumatic testing at 1.5× design pressure
- NDE (Non-Destructive Examination): Eddy current (ET) for wall thickness mapping; dye penetrant (PT) for surface defects
- Chemical Analysis: Spectrographic verification of alloy composition
- Visual Inspection: 100% inspection of welds and surface finish
5. Applications
5.1 Direct Evaporation Ice Storage Systems
The primary application domain for these coil tubes is direct evaporation ice storage (DEIS) systems, where refrigerant evaporates directly within the coil tube, transferring latent heat from surrounding water to the refrigerant and forming ice on the tube outer surface. Research into the freezing process has identified key performance factors including:
- Ice layer thickness distribution and its effect on thermal resistance
- Optimal refrigerant flow velocity for uniform ice formation
- Coil geometry optimization for maximizing ice storage density
- Long-term cycling performance and ice adhesion/detachment dynamics
5.2 Additional Applications
- Plate-Fin Heat Exchangers: Coil tubes as refrigerant-side components in commercial refrigeration units
- Cryogenic Systems: Liquefied natural gas (LNG) and cryogenic storage applications leveraging low-temperature toughness
- Process Cooling: Industrial cooling coils for chemical, pharmaceutical, and food processing
- Heat Recovery Systems: Waste heat capture and thermal energy storage
- Hydronic Heating/Cooling: Radiator coils and underfloor heating systems
- Evaporator Coils: Air-conditioning and refrigeration evaporators
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ASME BPV Section VIII | Pressure Vessel & Piping Components |
| EN 10204 3.1 | Material Test Certification |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive Compliance |
| ASTM A269 | Welded Austenitic Stainless Steel Tubing |
| GB/T 12771 | Chinese National Standard — Stainless Steel Tubing |
| UL / CSA | Refrigeration Equipment Safety (where applicable) |
7. Unique Selling Points
- Research-Driven Design: Product specifications informed by published academic research on direct evaporation ice storage coil freezing dynamics, ensuring optimal thermal performance under actual operating conditions.
- Cryogenic Resilience: Maintains full mechanical integrity at temperatures as low as −196°C, enabling reliable operation in extreme cold environments without brittle fracture risk.
- Customizable Geometry: Winding diameter, pitch, and tube dimensions are fully configurable to match specific thermal load requirements, maximizing system efficiency for each application.
- Superior Corrosion Performance: Austenitic stainless steel construction eliminates the need for internal coatings or linings, reducing maintenance requirements and extending service life beyond 25 years.
- Full Traceability: Each coil tube batch is accompanied by mill test certificates (MTC) with full chemical analysis, mechanical test results, and heat number traceability per EN 10204 3.1.
- Multi-Grade Availability: Multiple stainless steel grades (304, 316, 316L) available to address varying corrosion environments and budget requirements.
Technical Note: The direct evaporation ice storage application requires careful consideration of the ice formation process on the coil tube outer surface. The thermal resistance of the growing ice layer increases over time, which can reduce the heat transfer rate. Wenzhou Jixing's coil tube geometry is optimized to minimize this effect through precise winding pitch control and tube surface finish engineering, ensuring consistent ice storage performance throughout the system's operational life.