Stainless Steel Coil Tube for External-Melting Ice Thermal Storage Systems
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Catalogue No.: 1423
Classification: Literature-Based Technical Reference
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component designed specifically for external-melting ice thermal storage (Ice Bank) systems. This product serves as the core heat exchange element in dynamic thermal energy storage (TES) applications, where ice is formed on the exterior surface of the coil tube during the charging phase and subsequently melted during the discharging phase. The coil tube transfers thermal energy between the refrigerant flowing through its interior and the water-ice medium surrounding its exterior, enabling efficient cold storage and on-demand cooling delivery.
Based on extensive research into the dynamic characteristics of external-melting ice coil thermal storage systems, this product has been optimized for superior thermal conductivity, mechanical durability under repeated freeze-thaw cycles, and resistance to corrosion in aqueous environments. The coil geometry provides a high surface-area-to-volume ratio, maximizing heat transfer efficiency while minimizing pumping power requirements.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, selected for its exceptional combination of thermal conductivity, corrosion resistance, and mechanical integrity under cryogenic and sub-zero operating conditions.
Material Composition (Typical)
- Grade: SUS304 / SUS316L (ASTM A213 TP304 / TP316L)
- Carbon (C): ≤ 0.08% (304) / ≤ 0.03% (316L)
- Chromium (Cr): 18.0–20.0%
- Nickel (Ni): 8.0–10.5%
- Molybdenum (Mo): 2.0–2.5% (316L only)
- Chloride (Cl): ≤ 0.03%
- Manganese (Mn): ≤ 2.0%
- Phosphorus (P): ≤ 0.045%
- Sulfur (S): ≤ 0.030%
Mechanical & Physical Properties
- Thermal Conductivity (k): 14.9–16.3 W/(m·K) at 20°C
- Operating Temperature Range: −196°C to +315°C
- Tensile Strength (Rm): ≥ 520 MPa (annealed condition)
- Yield Strength (Rp0.2): ≥ 205 MPa
- Elongation (A50mm): ≥ 40%
- Density (ρ): 7.93 g/cm³
- Linear Thermal Expansion (α): 16–18 × 10⁻⁶ /K (20–100°C)
- Freeze-Thaw Cycle Endurance: ≥ 50,000 cycles without degradation
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC) in chloride-containing environments
Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | Φ9.52 mm / Φ12.70 mm / Φ15.88 mm / Φ19.05 mm | ±0.10 mm |
| Wall Thickness | 0.81 mm / 1.02 mm / 1.22 mm / 1.65 mm | ±0.05 mm |
| Tube Length (per coil) | 15 m – 120 m (customizable) | ±0.5% |
| Coil Diameter (CD) | Φ300 mm – Φ1200 mm | ±5 mm |
| Bend Radius | ≥ 3D (D = outer diameter) | Per ASME B31.3 |
| Surface Finish | Bright annealed / Pickled and passivated | Surface roughness Ra ≤ 0.4 μm |
| Pressure Rating | Up to 2.5 MPa (working pressure) | Hydrostatic test at 3.75 MPa |
| Refrigerant Compatibility | Ammonia (NH₃), Water-Glycol, CO₂, HFCs | — |
| Ice Formation Rate | 0.5 – 2.0 kg ice / (m²·h) | Depends on geometry and flow |
| Melting Time (discharge) | 2 – 8 hours (system-dependent) | — |
| Design Life | ≥ 25 years | Under normal operating conditions |
Manufacturing Process
The production of stainless steel coil tubes for ice thermal storage applications follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Coil Slitting and Cutting: Cold-rolled stainless steel coil is slit to precise widths and cut to required lengths using CNC-controlled slitting lines, minimizing material waste and ensuring edge quality.
- Tubular Forming: The flat strip is cold-formed into a circular tube using a roll-forming machine with precision tooling. The forming process maintains a uniform wall thickness and minimizes work hardening effects.
- Welding (if applicable): For welded tube construction, longitudinal seams are formed using Automatic Welding (AW) or TIG (Tungsten Inert Gas) welding with argon backing gas to prevent oxidation. Weld quality is verified through radiographic testing (RT) or dye penetrant inspection (PT).
- Bright Annealing: Tubes undergo bright annealing in a continuous belt furnace under controlled reducing atmosphere (endothermic gas or vacuum) at 1050–1150°C to relieve residual stresses, restore full annealed ductility, and produce a clean, oxide-free surface.
- Coil Winding: Annealed tubes are wound into precise helical coils using a CNC coil winding machine. The winding process controls coil diameter, pitch, and overlap to within specified tolerances. Bend radii are maintained at ≥ 3D to prevent kinking or thinning.
- Pickling and Passivation: The completed coil tube assembly is subjected to pickling (acid immersion) to remove any residual scale or discoloration, followed by passivation treatment to enhance the chromium oxide passive layer and improve corrosion resistance.
- Quality Inspection: Final inspection includes dimensional measurement (OD, wall thickness, coil diameter), hydrostatic pressure testing, surface finish verification, and visual examination for defects.
Applications
The stainless steel coil tube is integral to a wide range of thermal energy storage and heat exchange systems:
- Ice Thermal Storage (Ice Bank) Systems: Primary application in commercial and industrial ice storage systems where ice is formed on the coil exterior during off-peak hours and melted during peak cooling demand, reducing peak electrical load and enabling demand-side management.
- External-Melting Ice Storage: Specifically optimized for systems where ice melts from the outside inward, providing predictable and controllable discharge rates as studied in dynamic characteristic research.
- Commercial Refrigeration: Supermarket cold chain systems, walk-in freezers, and blast chillers requiring reliable sub-zero operation.
- Process Cooling: Industrial processes requiring precise temperature control and thermal buffering, including chemical processing, pharmaceutical manufacturing, and food processing.
- Building HVAC Systems: Peak-shaving applications in large commercial buildings, data centers, and hospitals to reduce energy costs and improve grid stability.
- Cryogenic Applications: Low-temperature storage and transport systems where stainless steel's cryogenic toughness is essential.
- Marine and Offshore: Cold storage systems on vessels and offshore platforms where corrosion resistance and mechanical robustness are paramount.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and adheres to international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ASTM A213 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing
- EN 10217-7 — Heat-Resistant, Hermetic and Cryogenic Tubes and Fittings — Austenitic Stainless Steel Tubes
- JIS G3459 — Stainless Steel Tubes for Heat Exchangers
- GB/T 17705 — Chinese National Standard for Stainless Steel Tubes for Heat Exchangers
- ASME B31.3 — Process Piping Code Compliance
- Hydrostatic Testing — 100% tested at 1.5× working pressure with zero leakage
- Mill Test Reports (MTR) — Full chemical and mechanical property documentation provided with each shipment
- Third-Party Inspection — Available upon request (SGS, BV, Lloyd's Register)
Unique Selling Points
- Optimized for Dynamic Thermal Storage: Designed based on published research into external-melting ice coil dynamic characteristics, ensuring predictable ice formation and melting profiles with high coefficient of performance (COP).
- Superior Freeze-Thaw Durability: Engineered to withstand over 50,000 freeze-thaw cycles without microstructural degradation, crack initiation, or dimensional change.
- Enhanced Thermal Performance: Bright-annealed surface finish with Ra ≤ 0.4 μm promotes efficient nucleation and uniform ice layer formation on the tube exterior.
- Corrosion-Free Longevity: 316L grade option provides exceptional resistance to chloride-induced pitting and stress corrosion cracking, extending service life in humid and chemically aggressive environments.
- Customizable Geometry: Flexible coil diameter, tube length, and OD configurations to match specific system design requirements and optimize heat transfer surface area.
- Energy Efficiency Contribution: Enables peak-load shifting and demand response, reducing overall energy consumption by 20–30% in commercial cooling applications.
Technical Note: The dynamic characteristics of external-melting ice coil thermal storage systems are governed by complex interactions between convective heat transfer from the refrigerant, conductive heat transfer through the tube wall, and phase-change dynamics of the ice layer. The design of the coil tube geometry—particularly the tube diameter, wall thickness, and coil pitch—directly influences ice nucleation sites, ice growth uniformity, and discharge rate predictability. Wenzhou Jixing Metal Materials Co., Ltd. applies this research-driven design philosophy to deliver coil tubes that maximize thermal storage density and system reliability.