Stainless Steel Coil Tube (Coiltube) — Parallel Ice-Making Thermal Storage System Component
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), as manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered coiled tubular product designed specifically for integration into parallel ice-making thermal storage devices (Parallel Ice-Making Thermal Energy Storage Systems). These coil tubes serve as the primary heat exchange elements within latent heat storage modules, facilitating efficient heat transfer between the refrigerant circuit and the phase-change material (typically water-to-ice conversion) during both charging (ice-making) and discharging (cooling) cycles.
Based on extensive research into the ice-making characteristics of parallel ice coil thermal storage devices (Research on Ice-Making Characteristics of Parallel Ice Coil Thermal Storage Devices), this product has been optimized for maximum thermal performance, mechanical integrity, and long-term durability under cyclic thermal stress conditions. The coiltube design enables compact volumetric heat exchange within constrained system footprints while maintaining uniform flow distribution across parallel channels.
2. Material & Properties
2.1 Base Material
The coil tubes are fabricated from high-grade stainless steel conforming to international standards, with the following material options available:
- AISI 304 (UNS S30408) — Austenitic stainless steel with excellent general corrosion resistance and cryogenic toughness; the standard grade for ice-making applications.
- AISI 316 (UNS S31608) — Molybdenum-enhanced austenitic stainless steel offering superior resistance to chlorides, brines, and de-icing salts.
- AISI 321 (UNS S32103) — Titanium-stabilized austenitic stainless steel for applications requiring elevated temperature resistance.
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (304) / ≥ 515 MPa (316)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40% (ensures formability during coiling)
- Cryogenic Toughness: Retains full ductility down to −196°C (liquid nitrogen temperature)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (304 grade)
2.3 Surface Characteristics
- Surface Finish: 2B (cold-rolled and annealed) or No. 4 brushed finish
- Surface Roughness (Ra): ≤ 0.4 μm (inner surface, optimized for reduced flow resistance)
- Pickling & Passivation: Fully pickled and passivated to ensure a stable chromium oxide passive layer
3. Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Designation | Stainless Steel Coil Tube (Coiltube) | — |
| Material Grade | AISI 304 / 316 / 321 (selectable) | ASTM A269 / A213 |
| Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") | ASTM A269 |
| Wall Thickness | 0.5 mm – 3.0 mm | ASTM A269 |
| Coil Diameter | 50 mm – 300 mm (configurable) | Project-specific |
| Coil Length | 1 m – 100 m (continuous or discrete) | Project-specific |
| Tolerance on OD | ±0.05 mm (precision grade) | ASTM A269 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A269 |
| Operating Temperature Range | −40°C to +150°C | — |
| Operating Pressure | Up to 1.6 MPa (16 bar) | EN 10217 / ASME |
| Heat Exchange Fluid | Water, brine, ethylene glycol, ammonia | — |
| End Connection Types | Welded, flanged, threaded, or expanded | ASME B16.5 / B1.20.1 |
| Maximum Ice-Making Cycle | ≥ 10,000 cycles (design life) | Internal testing |
4. Manufacturing Process
4.1 Raw Material Procurement & Inspection
Stainless steel strip or tube stock is procured from certified mill suppliers with full material traceability (Mill Test Certificates conforming to EN 10204 Type 3.1). Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition and hardness testing to confirm annealing condition.
4.2 Precision Forming & Coiling
- Tubing Straightening — Multi-roller straightening to achieve dimensional straightness ≤ 1 mm/m.
- Coil Winding — CNC-controlled coiling on precision mandrels to achieve uniform coil diameter, consistent pitch, and controlled residual stress distribution. The winding process is monitored to prevent inter-coil contact and potential fretting corrosion.
- End Forming — Precision end preparation (beading, threading, or flattening) for subsequent welding or mechanical connection.
4.3 Welding & Joining
Where continuous coils are segmented or connected to headers, TIG welding (GTAW — Gas Tungsten Arc Welding) is employed using matching filler wire (e.g., ER308L for 304 base metal). Weld parameters are optimized to minimize heat-affected zone (HAZ) sensitization, and all welds undergo visual and, where required, dye penetrant inspection (DPI) per ASTM E165.
4.4 Pickling, Passivation & Cleaning
Post-fabrication, the coil tubes undergo a comprehensive acid pickling and passivation treatment (nitric/hydrofluoric acid blend) to remove weld scale, restore the passive chromium oxide layer, and achieve a corrosion-resistant surface. Final ultrasonic cleaning ensures freedom from particulate contamination.
4.5 Non-Destructive Testing (NDT)
- Helium Leak Testing — All coil assemblies tested at 0.5 MPa with leak rate ≤ 1×10⁻⁷ mbar·L/s.
- Pressure Testing — Hydrostatic test at 1.5× operating pressure for minimum 30 minutes.
- Dimensional Inspection — CMM or laser scanning for coil geometry verification.
5. Applications
5.1 Ice-Making Thermal Energy Storage Systems
The primary application of this coiltube product is in parallel ice-coil thermal storage devices, where multiple coil tubes are arranged in parallel within a storage tank containing water. During the charging phase, refrigerant (or chilled water) flows through the coil tubes, extracting heat from the surrounding water and causing ice formation on the tube surfaces. During discharge, the stored latent heat is released for cooling loads. The parallel arrangement ensures:
- Uniform heat distribution across the storage volume
- Reduced pressure drop compared to single-circuit designs
- Scalable capacity through modular addition of coil units
- Improved ice-making efficiency through optimized flow velocity
5.2 Additional Applications
- Cold Chain Logistics — Refrigerated containers and cold storage facilities
- Building HVAC Systems — Peak-shaving and load management thermal storage
- Process Cooling — Industrial chillers, dairy processing, and pharmaceutical cooling
- Marine Refrigeration — Vessel cold rooms and fish freezing systems
- Supermarket Display Cooling — Open refrigeration cases with thermal storage
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system with the following certifications and standards compliance:
| Certification / Standard | Scope of Application |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management |
| EN 10204 Type 3.1 | Material Test Certificates (Mill Certificates) |
| ASTM A269 / A213 | Stainless Steel Tubing Specifications |
| ASME B31.5 | Pressure Piping (Refrigeration & Condenser) |
| PED 2014/68/EU | Pressure Equipment Directive (where applicable) |
| CE Marking | European Conformity |
| SGS / BV Third-Party Inspection | Independent verification of product quality |
7. Unique Selling Points
Research-Driven Design Optimization: This coiltube product line is informed by rigorous academic research into the thermodynamic performance of parallel ice-coil thermal storage configurations, ensuring that geometric parameters (coil pitch, tube diameter, layout) are optimized for maximum ice-making rate and thermal efficiency.
- Superior Cryogenic Performance: Austenitic stainless steel retains full mechanical properties at sub-zero temperatures, eliminating the risk of brittle fracture that affects carbon steel alternatives in ice-making environments.
- Enhanced Corrosion Resistance: The passive chromium oxide layer provides excellent resistance to ice brines, glycol solutions, and chlorinated de-icing agents, ensuring long service life without degradation.
- Parallel Configuration Efficiency: The modular coil design enables parallel flow distribution, reducing system pressure drop by up to 60% compared to series arrangements while maintaining uniform ice nucleation across all tube surfaces.
- Full Traceability: Every coil tube carries a unique identification marking with complete material traceability from raw mill certification through final inspection, supporting compliance with critical infrastructure standards.
- Customizable Geometric Parameters: Coil diameter, pitch, tube count, and connection types are tailored to specific system design requirements, enabling seamless integration into OEM thermal storage assemblies.
- Low Flow Resistance: Precision-manufactured inner surface finish (Ra ≤ 0.4 μm) minimizes hydraulic friction, reducing pumping energy consumption in the refrigeration circuit.
- Cycle Fatigue Resistance: Designed and tested for ≥ 10,000 thermal cycling operations, ensuring reliability in continuous commercial operation scenarios.
8. Conclusion
The Stainless Steel Coil Tube (Coiltube) from Wenzhou Jixing Metal Materials Co., Ltd. represents a state-of-the-art solution for ice-making thermal energy storage applications. Combining metallurgical excellence, precision manufacturing, and research-backed design optimization, this product delivers superior thermal performance, mechanical reliability, and corrosion durability in demanding cryogenic environments. Its compliance with international quality standards and full traceability documentation make it suitable for integration into critical commercial, industrial, and infrastructure cooling systems worldwide.