Stainless Steel U-Shaped Coil Tube for Ice Storage Tanks
Product Overview
The U-Shaped Coil Tube (Model Series: CoilTube 403) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered stainless steel tubing product specifically designed for integration into ice storage tanks (Ice Storage Tanks, IST) and thermal energy storage systems. This product line represents the culmination of advanced computational fluid dynamics (CFD) simulation and structural optimization studies, ensuring superior thermal transfer efficiency, mechanical integrity, and long-term operational reliability in demanding cryogenic and sub-zero environments.
The U-shaped coil tube configuration enables a compact, high-surface-area heat exchange geometry within confined ice storage vessel footprints, maximizing the contact interface between the refrigerant or brine medium and the phase-change material (PCM) ice matrix. The design philosophy emphasizes thermal efficiency, structural rigidity under cyclic thermal loading, and corrosion resistance in chloride-containing brine solutions.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected to meet the stringent demands of low-temperature thermal cycling, brine immersion, and sustained mechanical stress. The primary material grades offered include:
- SUS304 / AISI 304 — Chromium-Nickel austenitic stainless steel (18% Cr, 8% Ni), offering excellent general corrosion resistance, weldability, and ductility. Suitable for standard brine-based ice storage applications.
- SUS316L / AISI 316L — Low-carbon, molybdenum-enhanced austenitic stainless steel (16–18% Cr, 10–14% Ni, 2–3% Mo). Provides superior resistance to pitting and crevice corrosion in chloride-rich environments. Recommended for de-icing salt solutions and high-chloride brine media.
- SUS321 / AISI 321 — Titanium-stabilized austenitic stainless steel (16–18% Cr, 9–12% Ni, 0.4–0.9% Ti). Offers enhanced resistance to intergranular corrosion and thermal cycling fatigue.
Mechanical Properties (Typical, Annealed Condition)
| Property | Unit | SUS304 | SUS316L | SUS321 |
|---|---|---|---|---|
| Tensile Strength (Rm) | MPa | ≥ 520 | ≥ 485 | ≥ 520 |
| Yield Strength (Rp0.2) | MPa | ≥ 205 | ≥ 170 | ≥ 205 |
| Elongation (A50) | % | ≥ 40 | ≥ 40 | ≥ 40 |
| Thermal Conductivity (at 20°C) | W/(m·K) | 16.3 | 14.6 | 16.3 |
| Operating Temperature Range | °C | -196 to +870 | -196 to +870 | -196 to +900 |
| Corrosion Resistance (Pitting, ASTM G48) | — | Good | Excellent | Good |
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | Φ12.7 mm – Φ38.1 mm (½" – 1½") | ASTM A269 / GB/T 12771 |
| Tube Wall Thickness | 0.8 mm – 3.0 mm | ASTM A269 / EN 10217 |
| Coil Pitch (Center-to-Center Spacing) | 25 mm – 100 mm (customizable) | — |
| U-Bend Inner Radius | ≥ 1.5 × OD (minimum) | ASME B31.9 |
| Overall Coil Length | Up to 120 meters (continuous) | — |
| Surface Finish | Pickled & Passivated (Ra ≤ 1.6 μm); Electropolished optional (Ra ≤ 0.4 μm) | ASTM A967 / ASTM A240 |
| End Preparation | Plain ends, beveled ends, or socket-weld fittings (ASME B16.3) | ASME B16.3 |
| Pressure Rating | Up to 1.6 MPa (16 bar) working pressure | ASME B31.9 / EN 12545 |
| Tolerance (OD) | ±0.1 mm (precision drawn) | EN 10217-7 |
| Tolerance (Wall Thickness) | ±10% of nominal | EN 10217-7 |
| Coil Diameter (Packaging) | Φ600 mm – Φ1200 mm | — |
| Weight per Meter (Φ19.05 × 1.5 mm) | ≈ 0.69 kg/m | — |
Manufacturing Process
The production of the U-Shaped Coil Tube follows a rigorously controlled, multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Verification: Incoming stainless steel bars or coils are subjected to spectral analysis (OES) and chemical composition verification against ASTM/EN specifications. Heat traceability documentation is maintained throughout the production lifecycle.
- Piercing & Hot Rolling: Billet stock is pierced and hot-rolled to produce seamless tube blanks with the required nominal OD and wall thickness. The hot rolling process is controlled to achieve a uniform grain structure and minimize segregation.
- Cold Drawing & Sizing: The seamless tube blanks undergo multiple passes of cold drawing through precision tungsten carbide dies to achieve the final dimensional tolerances. This process induces beneficial work hardening, improving mechanical strength by 15–25% while maintaining ductility.
- Solution Annealing: Tubes are annealed at 1050°C – 1100°C in a protective atmosphere (nitrogen or vacuum) to relieve residual stresses, restore full austenitic microstructure, and achieve the required corrosion resistance and ductility.
- Pickling & Passivation: Annealed tubes are acid-pickled (HNO₃/HF blend) to remove oxide scale, followed by passivation treatment to establish a chromium oxide passive film (Cr₂O₃) that provides long-term corrosion protection.
- U-Bend Forming: The annealed tube is formed into the U-shaped coil configuration using CNC-controlled bending machines with tooling designed to prevent wall thinning, ovality, or micro-cracking at bend locations. Bend radii are calculated based on the tube's minimum bend ratio (typically ≥ 1.5 × OD for austenitic stainless steel).
- Coil Winding: The U-bent tube is wound into the final coil geometry with precise pitch control using automated winding equipment. Pitch accuracy is maintained within ±0.5 mm.
- Hydrostatic Pressure Testing: Each coil tube assembly undergoes 100% hydrostatic pressure testing at 1.5 × working pressure (minimum 2.4 MPa) for a dwell time of 30 seconds to verify weld integrity and structural soundness.
- Final Inspection & Packaging: Dimensional inspection (OD, wall thickness, straightness, pitch), surface quality verification, and material certification documentation are completed prior to protective packaging (moisture-barrier wrapping, desiccant inclusion, and wooden crate or steel-frame containment).
Structural Optimization & Simulation
A distinguishing feature of this product line is the incorporation of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) simulation-driven design optimization. The U-shaped coil tube geometry is iteratively refined through the following simulation framework:
- Thermal-Fluid Simulation (ANSYS Fluent / COMSOL Multiphysics): The heat transfer coefficient between the tube surface and the surrounding ice/brine matrix is modeled under steady-state and transient conditions. Optimization targets include maximizing the overall heat transfer coefficient (U-value) while minimizing pressure drop across the coil circuit.
- Structural FEA (ANSYS Mechanical / Abaqus): The coil tube is subjected to simulated cyclic thermal loading (ΔT = -20°C to +60°C), internal pressure loading, and mechanical vibration to evaluate stress concentrations at U-bend locations, fatigue life, and structural safety factors (minimum safety factor ≥ 2.5).
- Topology Optimization: Coil pitch, tube diameter, and U-bend radius are parametrically optimized to achieve the best trade-off between thermal performance, pressure drop, and mechanical robustness for the target application.
"Simulation-based structural optimization reduces material usage by up to 12% while maintaining or improving thermal transfer efficiency and fatigue life — a hallmark of modern engineered heat exchange components."
Applications
The U-Shaped Coil Tube for Ice Storage Tanks finds application in a diverse range of thermal energy storage and heat exchange systems:
- Ice Storage Thermal Energy Storage (TES) Systems: Primary application — the coil tube serves as the heat exchange element within ice storage tanks, enabling off-peak refrigeration production and peak-load shifting for commercial HVAC systems. The ice matrix acts as a phase-change material (PCM), storing latent heat at approximately 0°C (334 kJ/kg).
- Commercial & Industrial Refrigeration: Ice storage tanks for cold storage facilities, food processing plants, and pharmaceutical cold chain systems.
- Cold Room Freezing Systems: Integration into blast freezing and quick-freezing chambers for the food and beverage industry.
- Marine & Offshore Applications: Refrigeration and ice-making systems for commercial fishing vessels and offshore platforms, leveraging the corrosion resistance of SUS316L in marine environments.
- Building Energy Management Systems (BEMS): Integration into smart grid-compatible thermal storage systems for energy demand response and peak shaving.
- Process Cooling in Chemical & Petrochemical Industries: Low-temperature process cooling loops requiring reliable, corrosion-resistant heat exchange tubing.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and product certification portfolio to ensure full traceability, compliance, and customer confidence:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management Systems — certified for manufacturing of stainless steel tubes and coil products |
| ISO 14001:2015 | Environmental Management Systems — sustainable manufacturing practices |
| CE Marking (EU) | Conformity with European directives for pressure equipment and construction products |
| EN 10204 3.1 | Material Test Certificate — third-party inspection body certification for chemical and mechanical properties |
| ASTM A269 | Standard specification for seamless austenitic stainless steel tube |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes |
| ASME B31.9 | Pressure piping code for cryogenic service (applicable for pressure rating verification) |
| NACE MR0175 / ISO 15156 | Materials for use in H₂S-containing environments (SUS316L grade, if applicable) |
Unique Selling Points
- Simulation-Optimized Design: Each coil tube geometry is refined through iterative CFD and FEA simulation, ensuring optimal thermal performance and structural integrity — a differentiator over conventionally designed coil tubes.
- Full Traceability: From raw material heat number to final coil assembly, complete material traceability is maintained with EN 10204 3.1 third-party test certificates.
- Custom Engineering: Tube diameter, wall thickness, coil pitch, U-bend radius, and overall coil length are customizable to meet specific application requirements and tank geometry constraints.
- Corrosion Resilience: SUS316L grade option provides exceptional resistance to chloride-induced pitting and crevice corrosion, extending service life in aggressive brine environments.
- Low-Temperature Capability: Austenitic stainless steel retains full ductility and toughness down to cryogenic temperatures (-196°C), eliminating the risk of brittle fracture under thermal cycling.
- Hygienic Surface Finish: Electropolished finish option (Ra ≤ 0.4 μm) suitable for food-grade and pharmaceutical applications where surface contamination control is critical.
Technical Notes
When integrating the U-Shaped Coil Tube into ice storage tank systems, the following engineering considerations should be observed:
- Ensure adequate insulation between the coil tube and the tank wall to minimize heat ingress from the ambient environment.
- Design the brine/refrigerant flow circuit to maintain a velocity of 0.5 – 2.0 m/s within the tube to promote turbulent flow and maximize heat transfer coefficient.
- Implement thermal expansion joints or flexible connections at the tank interface to accommodate differential thermal expansion between the coil tube and the tank shell.
- For SUS316L applications in chloride environments, monitor the chloride ion concentration in the brine medium and ensure it remains below 2000 ppm to prevent stress corrosion cracking (SCC).
- Periodic non-destructive testing (NDT) — including eddy current testing (ECT) and visual inspection — is recommended at 12-month intervals to detect any incipient corrosion or mechanical damage.