Stainless Steel U-Shaped Coil Tube for Ice Storage Tank Systems
Product Overview
The Stainless Steel U-Shaped Coil Tube (Coiltube) is a precision-engineered tubing product designed specifically for thermal energy storage applications, particularly in ice storage tank (蓄冰槽) systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube product represents the culmination of advanced simulation-driven design and structural optimization techniques. The product is engineered to maximize heat transfer efficiency while maintaining mechanical integrity under cyclic thermal loading conditions inherent to phase-change thermal storage systems.
The U-shaped coil tube configuration provides an optimal balance between surface area density, flow resistance, and structural stability within confined ice storage tank geometries. This design philosophy has been validated through finite element analysis (FEA) and computational fluid dynamics (CFD) simulations, ensuring reliable performance across the full operational envelope.
Material and Properties
The coil tube is fabricated from austenitic stainless steel grades selected for their exceptional combination of corrosion resistance, thermal conductivity, and mechanical durability in aqueous environments.
- Primary Material Grade: SUS304 / ASTM A269 TP304 — the industry standard for general-purpose thermal applications, offering excellent resistance to pitting and crevice corrosion in brine solutions.
- Alternative Grade: SUS316L / ASTM A269 TP316L — recommended for high-chloride environments where enhanced resistance to localized corrosion is required.
- Key Mechanical Properties:
- Tensile Strength: ≥ 520 MPa (SUS304), ≥ 515 MPa (SUS316L)
- Yield Strength: ≥ 205 MPa
- Elongation: ≥ 40% (at fracture)
- Operating Temperature Range: −196°C to +450°C
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS304)
- Corrosion Resistance: Excellent resistance to dilute sulfuric, phosphoric, and hydrochloric acids; superior performance in deionized water and brine solutions (NaCl, CaCl₂)
- Weldability: Excellent; suitable for TIG (GTAW) and orbital welding without preheating
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 12 mm / 16 mm / 19 mm / 22 mm / 25 mm | ASTM A269 |
| Tube Wall Thickness | 0.8 mm – 2.0 mm (standard); 0.5 mm – 2.5 mm (custom) | ASTM A269 |
| Coil Pitch (U-Bend Spacing) | 20 mm – 100 mm (configurable per thermal load) | Custom Engineering |
| U-Bend Radius | 1.5× OD – 3.0× OD (optimized for minimum stress concentration) | ASME B31.3 |
| Coil Length per Section | 3,000 mm – 12,000 mm (modular) | Custom Engineering | Surface Finish | Mirror polish (Ra ≤ 0.4 μm) or Matte finish (Ra ≤ 1.6 μm) | ASTM A269 |
| Tolerance (OD) | ±0.05 mm | ISO 1128 |
| Coil Diameter Tolerance | ±0.5% | ISO 1128 |
| Pressure Rating | Up to 2.5 MPa (design pressure at 0°C) | ASME B31.3 |
| Design Life | ≥ 25 years (cyclic thermal loading, 50,000 freeze-thaw cycles) | Internal Standard |
Manufacturing Process
The production of the U-shaped coil tube follows a rigorously controlled multi-stage manufacturing process, integrating simulation-guided design optimization with precision fabrication techniques:
- Material Selection and Incoming Inspection: Certified stainless steel bar stock or seamless tube undergoes spectroscopic analysis (PMI) to verify chemical composition compliance with ASTM/EN standards.
- Simulation-Driven Design Optimization: Structural and thermal simulations (FEA/CFD) are conducted to determine optimal coil geometry, pitch, and bend radius configurations that minimize thermal stress concentrations and maximize heat exchange efficiency within the ice storage tank volume.
- Precision Coil Winding: High-precision CNC-controlled coil winding machines form the U-shaped tube geometry with controlled tension to prevent ovalization and residual stress accumulation. The winding parameters (speed, tension, radius) are calibrated based on simulation results.
- U-Bend Formation: Controlled cold-bending or warm-bending processes create the U-shaped turns at calculated intervals. Bend radius is maintained at ≥ 1.5× OD to minimize stress risers and ensure fatigue resistance.
- Welding: TIG welding (GTAW) with inert gas shielding (Ar or Ar/He mixture) joins tube sections and U-bends. Weld parameters are optimized to prevent sensitization and ensure full penetration with minimal heat-affected zone (HAZ).
- Post-Weld Heat Treatment: Solution annealing at 1050°C – 1150°C followed by rapid water quenching restores full austenitic structure and eliminates residual stresses introduced during forming and welding.
- Surface Treatment: Pickling and passivation (HNO₃/HF solution treatment) removes oxide scale and establishes a protective chromium oxide layer. Optional electropolishing achieves mirror surface finish for enhanced flow characteristics and reduced fouling.
- Final Inspection and Testing: Dimensional verification, hydrostatic pressure testing (1.5× design pressure), visual and dye penetrant inspection (DPI) of welds, and optional eddy current testing (ECT) for wall thickness uniformity.
Applications
The stainless steel U-shaped coil tube is purpose-engineered for the following critical applications:
- Ice Storage Tank Systems (蓄冰槽): Primary application — the coil tube serves as the heat exchanger element within ice thermal energy storage tanks, facilitating efficient freezing of water into ice and subsequent heat absorption during discharge cycles. The optimized U-shaped geometry maximizes contact area between the refrigerant and the ice mass while maintaining structural integrity under thermal cycling.
- Chilled Water Distribution Systems: Integration into commercial building HVAC systems for peak-load shifting and energy cost optimization.
- Process Cooling in Industrial Applications: Precision temperature control in pharmaceutical, food processing, and chemical manufacturing facilities.
- Cryogenic Applications: Low-temperature storage and transport systems requiring materials that maintain ductility at sub-zero temperatures.
- Marine and Offshore Systems: Corrosion-resistant heat exchange in seawater-cooled thermal management systems.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and certifications ensuring product reliability and regulatory compliance:
- Quality Management System: ISO 9001:2015 Certified
- Product Standards: ASTM A269/A269M (Seamless and Welded Austenitic Stainless Steel Tubing), EN 10217-7, JIS G3447
- Pressure Vessel Standards: ASME B31.3 (Process Piping), ASME BPVC Section VIII
- Material Certification: EN 10204 Type 3.1 mill test certificates provided with each shipment
- Welding Procedures: ASME Section IX qualified welding procedure specifications (WPS) and qualified welder performance records (WQR)
- Environmental Compliance: RoHS compliant; REACH compliant; no restricted substances
- Testing Protocols: Hydrostatic testing, spectroscopic composition analysis, mechanical property testing (tensile, hardness), and non-destructive testing (NDT) per ASTM E165 (DPI) and ASTM E2307 (ECT)
Unique Selling Points
The stainless steel U-shaped coil tube from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself through several key competitive advantages:
- Simulation-Optimized Design: Unlike conventional coil tubes produced with empirical design parameters, this product incorporates structural and thermal simulation results to optimize geometry for maximum performance within ice storage tank applications. This approach minimizes stress concentrations at U-bends and ensures uniform heat transfer distribution.
- Extended Service Life: The combination of solution-annealed microstructure, optimized bend geometry, and controlled manufacturing tolerances delivers fatigue resistance exceeding 50,000 freeze-thaw cycles, significantly outperforming industry benchmarks.
- Modular Configurations: Available in standardized module lengths that can be field-assembled to accommodate varying tank geometries and thermal loads, reducing installation complexity and customization lead times.
- Corrosion Resilience: Full austenitic stainless steel construction with passivated surface finish ensures long-term reliability in aggressive brine environments without degradation of thermal performance or structural integrity.
- End-to-End Engineering Support: From simulation-based design consultation through manufacturing and post-installation monitoring, the company provides comprehensive technical support tailored to the specific thermal storage application requirements.
Technical Note: The structural optimization of U-shaped coil tubes for ice storage tanks addresses the critical challenge of thermal stress accumulation at bend regions during repeated freeze-thaw cycles. Through simulation-driven design, stress concentrations at the inner fiber of U-bends are reduced by up to 35% compared to standard coil geometries, directly translating to enhanced fatigue life and reduced maintenance requirements over the system's operational lifespan.