Stainless Steel Coil Tube — Parallel Ice-Storage Application Grade
Product Code: 1509 | Category: Coil Tube (Coiltube) | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
This technical specification describes the stainless steel coil tube product engineered for use in parallel ice-coil thermal energy storage systems. The design and performance characteristics have been validated through research into the ice-melting behavior of parallel ice-coil thermal storage devices, ensuring reliable thermal exchange under repeated freeze-thaw cycles.
1. Product Overview
The Stainless Steel Coil Tube is a precision-manufactured tubular component formed into a continuous helical or serpentine coil configuration. It serves as the primary heat-exchange medium within ice-coil thermal energy storage (TES) systems, where it facilitates the transfer of thermal energy between a cold carrier fluid (typically ethylene glycol or propylene glycol solution) and the surrounding ice matrix.
In a parallel ice-coil thermal storage configuration, multiple coil tubes are arranged in parallel within an insulated storage tank. The system leverages the latent heat of fusion of water (approximately 334 kJ/kg) to store and release thermal energy, providing peak-shaving capabilities for district cooling, commercial HVAC, and industrial refrigeration applications.
Research into the ice-melting characteristics of parallel ice-coil devices has demonstrated that the geometry, wall thickness, and material conductivity of the coil tube directly influence the melting rate uniformity, heat-transfer efficiency, and long-term structural integrity of the storage system. The product described herein is specifically optimized to address these performance-critical parameters.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from austenitic stainless steel, selected for its superior corrosion resistance, low thermal conductivity (reducing parasitic heat gain), and mechanical durability under cyclic thermal loading. The primary grade options are:
- 304 (UNS S30408 / 1.4301): General-purpose grade with excellent corrosion resistance and formability. Suitable for glycol-based cold carriers with pH > 4.0.
- 316L (UNS S31603 / 1.4404): Enhanced grade with molybdenum (Mo) addition for superior resistance to chlorides and aggressive environments. Recommended for applications involving salt-containing fluids or coastal installations.
- 321 (UNS S32103 / 1.4541): Titanium-stabilized grade offering improved resistance to intergranular corrosion at elevated temperatures.
2.2 Key Mechanical and Thermal Properties
| Property | 304 Grade | 316L Grade |
|---|---|---|
| Density (g/cm³) | 8.00 | 8.03 |
| Thermal Conductivity at 20 °C (W/m·K) | 16.3 | 14.6 |
| Thermal Expansion Coefficient at 20 °C (×10⁻⁶/°C) | 17.3 | 16.0 |
| Tensile Strength (MPa, minimum) | 520 | 485 |
| Yield Strength (MPa, minimum) | 205 | 170 |
| Elongation (%) | ≥ 40 | ≥ 40 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 |
| Corrosion Resistance | Good (general environments) | Excellent (chloride-containing environments) |
| Weldability | Excellent | Excellent |
| Magnetic Properties | Non-magnetic (annealed) | Non-magnetic (annealed) |
2.3 Chemical Composition (Typical)
| Element | 304 (wt%) | 316L (wt%) |
|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.03 |
| Chromium (Cr) | 18.00 – 20.00 | 16.50 – 18.50 |
| Nickel (Ni) | 8.00 – 10.50 | 10.00 – 14.00 |
| Molybdenum (Mo) | — | 2.00 – 3.00 |
| Iron (Fe) | Balance | Balance |
| Manganese (Mn) | ≤ 2.00 | ≤ 2.00 |
| Sulfur (S) | ≤ 0.03 | ≤ 0.03 |
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 19 mm, 22 mm, 25 mm, 32 mm, 38 mm, 48 mm | ±0.1 mm |
| Wall Thickness | 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 2.0 mm | ±0.05 mm |
| Coil Pitch (Center-to-Center Spacing) | 15 mm – 100 mm (customizable) | ±0.5 mm |
| Coil Diameter | 50 mm – 500 mm (standard); up to 1000 mm (custom) | ±1.0 mm |
| Tube Length per Coil | 1 m – 50 m (standard); up to 200 m (special order) | ±0.5% |
| Coil Height (Axial) | 100 mm – 2000 mm (customizable) | ±2.0 mm |
| End Finish | Plain cut, beveled, threaded (NPT/BSP), or flanged | — |
3.2 Surface Finish
| Finish Type | Surface Roughness (Ra) | Application | ≤ 0.8 μm | General thermal storage |
|---|---|---|
| ≤ 0.4 μm | High-efficiency heat exchange | |
| ≤ 0.2 μm | Hygienic / food-grade applications |
3.3 Performance Characteristics
- Heat Transfer Coefficient: Enhanced by the coil geometry, providing a surface-area-to-volume ratio optimized for rapid ice formation and uniform melting in parallel-coil configurations.
- Cyclic Durability: Designed to withstand ≥ 10,000 freeze-thaw cycles without measurable degradation in mechanical properties or dimensional accuracy.
- Maximum Operating Pressure: Up to 1.6 MPa (standard); up to 4.0 MPa (heavy-wall configuration).
- Flow Velocity Compatibility: Optimized for carrier fluid velocities of 0.5 – 3.0 m/s to maintain turbulent flow and maximize convective heat transfer.
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing workflow designed to ensure dimensional precision, material integrity, and consistent performance:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip is procured from certified mills and subjected to spectroscopic analysis (OES), tensile testing, and corrosion testing (ASTM A967 passivation verification) prior to acceptance.
- Coil Forming: The flat strip is fed through a precision roll-forming machine equipped with multi-station tooling. Progressive forming stations gradually bend the strip into the target circular cross-section, maintaining tight control over OD, wall thickness, and roundness. The process is monitored in real time by laser diameter sensors and roundness gauges.
- Seam Welding (if applicable): For welded-tube configurations, a TIG (Tungsten Inert Gas) or orbital welding process is employed. A protective argon (Ar) or argon-helium (Ar/He) gas mixture shields the weld zone from oxidation. Post-weld inspection includes 100% visual examination and periodic helium leak testing (leak rate < 1 × 10⁻⁹ Pa·m³/s).
- Coil Winding: The formed tube is wound into the specified coil geometry using a CNC-controlled winding machine. Pitch accuracy, coil diameter, and axial alignment are controlled to within the tolerances specified in Section 3.
- Stress Relief Annealing: Coils are subjected to a controlled annealing cycle (typically 850–950 °C for 3060 minutes, followed by controlled cooling) to relieve residual stresses introduced during forming and winding. This step is critical for preventing stress corrosion cracking (SCC) and ensuring dimensional stability during thermal cycling.
- Surface Passivation & Cleaning: All coils undergo acid pickling and passivation treatment per ASTM A967 to remove mill scale and contamination, restoring the full passive chromium oxide film. Final cleaning removes any residual particulates.
- Hydrostatic Pressure Testing: Each coil is subjected to 100% hydrostatic pressure testing at 1.5× the maximum operating pressure for a minimum dwell time of 30 seconds to verify integrity.
- Final Dimensional Inspection: Coils are inspected for OD, wall thickness, coil pitch, coil diameter, and overall length using calibrated measuring instruments. Non-conforming units are rejected.
- Packaging & Shipment: Qualified coils are wrapped in protective PE film, placed in wooden crates or steel export containers, and labeled with material certificates and traceability codes.
5. Applications
The stainless steel coil tube is specifically engineered for parallel ice-coil thermal energy storage systems, but its robust design also suits a broad range of related applications:
5.1 Primary Application — Parallel Ice-Coil Thermal Energy Storage
In a parallel ice-coil TES system, multiple stainless steel coil tubes are immersed in a water-filled insulated tank. During off-peak hours, a chilled glycol solution circulates through the coils, extracting heat from the surrounding water and forming a layer of ice around each coil tube. During peak demand periods, the flow direction is reversed: ambient or warm water is circulated through the coils, and the stored ice melts, releasing latent heat to provide cooling. Research into the ice-melting characteristics of such parallel configurations has shown that:
- The coil geometry and spacing directly affect the uniformity of the ice-melting front, with optimized pitch spacing reducing uneven melting and maintaining stable discharge temperatures.
- The stainless steel material provides a favorable balance of thermal conductivity and corrosion resistance, ensuring long-term efficiency without degradation from repeated ice formation and dissolution.
- The parallel arrangement allows modular scaling of storage capacity by adding or removing coil units, providing operational flexibility.
5.2 Additional Applications
- District Cooling Systems: Large-scale thermal storage for urban district cooling networks, enabling peak-load shifting and grid balancing.
- Commercial & Industrial HVAC: Ice-based thermal storage for commercial buildings, hotels, hospitals, and manufacturing facilities to reduce peak electricity demand.
- Industrial Refrigeration: Cold storage warehouses, food processing plants, and pharmaceutical cold-chain facilities requiring reliable, energy-efficient refrigeration.
- Heat Exchanger Coils: General-purpose heat exchange applications in chemical processing, power generation, and marine systems.
- Automotive & Aerospace: Precision coil tubes for fuel delivery systems, hydraulic lines, and thermal management systems where corrosion resistance and lightweight performance are required.
- Medical & Laboratory Equipment: Hygienic-grade coil tubes for autoclaves, sterilization systems, and analytical instruments requiring high-purity fluid handling.
6. Quality Certifications & Standards Compliance
The stainless steel coil tube product conforms to the following international and national standards, and the manufacturer maintains the following quality certifications:
6.1 Applicable Standards
| Standard | Description |
|---|---|
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and F |