Stainless Steel Ice Storage Coil Tube (Coil Tube) — Technical Specification
1. Product Overview
The Stainless Steel Ice Storage Coil Tube (Coil Tube) is a specialized thermal energy storage component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is engineered for use in ice-based thermal energy storage (Ice Thermal Energy Storage, ITES) systems, where it serves as the primary heat exchange medium for the accumulation, storage, and release of latent heat through the phase change of water to ice. The coil tube design maximizes the surface area-to-volume ratio, enabling efficient ice nucleation and growth on the external tube surface while maintaining structural integrity under repeated freeze-thaw cycles.
This product represents an advanced application of stainless steel metallurgy in the field of renewable energy and peak-shaving HVAC (Heating, Ventilation, and Air Conditioning) systems. The coil tube geometry is specifically optimized for external ice formation (外管蓄冰), ensuring uniform ice layer distribution and predictable thermal performance throughout the storage cycle.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from austenitic stainless steel conforming to international standards. The primary alloy grades employed are:
- 304 (UNS S30400 / AISI 304): General-purpose grade with excellent corrosion resistance and formability; contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- 316 (UNS S31600 / AISI 316): Enhanced corrosion resistance grade with 2–3% Molybdenum (Mo) addition; suitable for aggressive environments.
- 316L (UNS S31603 / AISI 316L): Low-carbon variant of 316 with carbon content ≤ 0.03%, ideal for welding applications and cryogenic service.
2.2 Key Physical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (Grade 304) — ensures rapid heat transfer to the surrounding water/ice medium.
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, aqueous environments, and chloride-induced pitting (particularly for 316/316L grades).
- Cryogenic Performance: Maintains ductility and mechanical strength at temperatures as low as −196°C (Liquid Nitrogen Temperature).
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C) — accommodates thermal cycling without fatigue failure.
- Surface Finish: Bright annealed (BA) or electropolished finish to promote uniform ice nucleation and facilitate ice layer detachment.
2.3 Mechanical Properties
- Tensile Strength: ≥ 515 MPa (annealed condition, Grade 304)
- Yield Strength: ≥ 205 MPa (0.2% offset)
- Elongation: ≥ 40% (as-rolled, 50mm gauge length)
- Hardness: ≤ 201 HB (annealed condition)
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Ice Storage Coil Tube (Stainless Steel) | — |
| Material Grade | 304 / 304L / 316 / 316L (Austenitic Stainless Steel) | ASTM A213 / ASTM A269 / GB/T 12771 |
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (customizable) | ASTM A213 |
| Wall Thickness | 0.5 mm – 2.0 mm | ASTM A213 |
| Coil Diameter | 50 mm – 200 mm (spiral coil) | Custom / Project-Specific |
| Pitch (Turn-to-Turn Spacing) | 8 mm – 30 mm (optimized for ice layer growth) | Engineering Design |
| Effective Length | 1.0 m – 10.0 m (per coil assembly) | Custom |
| Surface Treatment | Bright Annealed (BA) / Passivated / Electropolished | ASTM A967 |
| Operating Temperature Range | −25°C to +40°C (ice storage cycle) | Engineering Specification |
| Design Pressure | ≤ 1.6 MPa (working); ≤ 2.4 MPa (test) | ASME BPV Code / EN 10216 |
| End Connection | Flanged / Threaded / Butt-Weld (BW) / Socket-Weld (SW) | ASME B16.5 / ASME B16.11 |
| Ice Layer Thickness (Designed) | 3 mm – 12 mm (external ice accretion) | Experimental Validation |
| Cycle Life | ≥ 10,000 freeze-thaw cycles | Accelerated Testing |
| Weight (Typical) | 0.8 kg – 8.5 kg (per coil unit, depending on configuration) | — |
4. Manufacturing Process
4.1 Process Flow
- Material Selection & Incoming Inspection: Stainless steel seamless or welded tube blanks are procured conforming to ASTM A213 (seamless) or ASTM A269 (welded) specifications. Chemical composition is verified via Optical Emission Spectroscopy (OES) and mechanical properties are confirmed through tensile testing.
- Coil Forming (Cold Bending): The straight tube is precisely formed into a spiral coil geometry using CNC-controlled mandrel bending equipment. The bending process is executed under controlled strain rates to prevent wall thinning, ovality distortion, or surface cracking. Minimum bending radius is maintained at ≥ 3× OD to ensure structural integrity.
- Stress Relief Annealing: Following forming, the coil tube undergoes a controlled heat treatment cycle (typically 1050°C ± 20°C for 30 minutes, followed by controlled cooling) to relieve residual bending stresses and restore full annealed mechanical properties.
- Surface Preparation: The coil is cleaned via pickling and passivation (acid dip treatment using nitric/hydrofluoric acid solution) to remove scale, oxidation, and organic contaminants. This step is critical for promoting uniform ice nucleation on the tube surface.
- End Preparation & Welding: Tube ends are prepared for connection (beveling, threading, or flange welding). Where welding is required, Gas Tungsten Arc Welding (GTAW / TIG) is employed using matching filler wire (e.g., ER308L for Grade 304L) under inert gas shielding (Argon or Argon/Helium mixture).
- Non-Destructive Testing (NDT): Welded joints undergo 100% Visual Inspection (VT) and selected Penetrant Testing (PT) or Ultrasonic Testing (UT) to verify weld integrity. Hydrostatic pressure testing is performed at 1.5× design pressure for a minimum of 2 minutes.
- Final Inspection & Packaging: Dimensional verification (OD, wall thickness, coil diameter, pitch) is conducted using calibrated instruments. Each coil tube is tagged with material certification, heat number, and test data before protective packaging for shipment.
4.2 Critical Manufacturing Considerations
The spiral coil geometry requires precise control over pitch uniformity (± 0.5 mm tolerance) to ensure consistent ice layer thickness distribution around the coil circumference. Non-uniform pitch results in differential ice growth rates, leading to asymmetric thermal performance and potential mechanical stress concentrations during the freeze-thaw cycle.
5. Applications
5.1 Primary Applications
- Ice Thermal Energy Storage (ITES) Systems: The coil tube serves as the heat exchanger within ice storage tanks, enabling off-peak electricity utilization for ice production and subsequent discharge of cooling capacity during peak demand periods.
- Commercial HVAC Peak-Shaving: Large commercial facilities (shopping malls, office buildings, data centers) employ ice storage coil systems to reduce peak electrical load and associated demand charges.
- Industrial Process Cooling: Intermittent cooling requirements in manufacturing processes are met through ice storage discharge, reducing the need for oversized chiller plants.
5.2 Secondary Applications
- Cryogenic Heat Exchangers: Low-temperature process applications requiring reliable heat transfer at sub-zero temperatures.
- Marine & Offshore Cooling Systems: Corrosion-resistant coil configurations for saltwater environments.
- Research & Development: Experimental platforms for studying ice nucleation kinetics, ice layer morphology, and thermal storage efficiency (as referenced in the academic study on ice layer thickness measurement and external ice storage performance).
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
- ASTM A213: Standard Specification for Stainless Steel, Nickel-Cobalt Alloy, and Titanium Alloy Seamless, Cold-Drawn or Cold-Formed Tubes for High Temperature Service
- ASTM A269: Standard Specification for Stainless Steel and Nickel Alloy Welded, Cold-Drawn or Cold-Formed Austenitic Chromium-Nickainless Steel Tube for Chemical and Similar Severe Service
- GB/T 12771: Chinese National Standard for Stainless Steel Seamless Tubes for General Purposes
- GB/T 14976: Chinese National Standard for Stainless Steel Seamless Tubes for Fluid Transport
- EN 10216: European Standard for Seamless and Welded Steel Tubes for Mechanical and Thermal Uses
- ASME BPV Code Section VIII: Boiler and Pressure Vessel Code (for pressure-containing applications)
6.2 Quality Assurance System
- ISO 9001:2015: Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001:2015: Environmental Management System certification for sustainable manufacturing practices.
- Mill Test Certificate (MTC): Provided with each batch, including chemical composition, mechanical properties, and heat treatment records.
- Third-Party Inspection: Available upon request from recognized inspection bodies (e.g., SGS, Bureau Veritas, TUV).
6.3 Testing Protocols
- Chemical Analysis (OES + Spectrophotometry)
- Tensile Testing (ASTM A370)
- Hydrostatic Pressure Testing (1.5× PWHT)
- Dimensional Inspection (CMM / Laser Measurement)
- Surface Roughness Measurement (Ra ≤ 0.8 μm for heat transfer optimization)
- Freeze-Thaw Cycle Durability Testing (≥ 10,000 cycles at −10°C / +20°C)
7. Unique Selling Points
- Optimized Coil Geometry for Ice Storage: Pitch and coil diameter are engineered specifically for uniform external ice accretion, validated through experimental ice layer thickness measurement studies.
- Superior Cryogenic Compatibility: Austenitic stainless steel maintains full ductility at ice storage operating temperatures, eliminating brittle fracture risk.
- Extended Service Life: Designed and tested for ≥ 10,000 freeze-thaw cycles without degradation of heat transfer performance or structural integrity.
- Customizable Configurations: Flexible dimensional options (OD, wall thickness, coil diameter, pitch, effective length) to accommodate diverse system designs and thermal load requirements.
- Academic-Validated Performance: Product design informed by rigorous experimental research on ice layer thickness measurement and external ice storage performance characteristics.
8. Technical Notes
The external ice storage mechanism relies on the formation of a solid ice layer on the outer surface of the coil tube as refrigerant (typically brine or ammonia solution) flows through the tube at sub-zero temperatures (typically −5°C to −10°C). The ice layer acts as the thermal energy storage medium, with a latent heat of fusion of approximately 334 kJ/kg. Upon system discharge, warm water or heat transfer fluid melts the ice layer, releasing stored cooling capacity. The coil tube must maintain dimensional stability, surface integrity, and thermal conductivity throughout this cyclic process to ensure reliable long-term operation.
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Catalog Reference: Item No. 1037 — Coil Tube (盘管)