Stainless Steel Ice Storage Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Ice Storage Coil Tube (also referred to as Ice Storage Coiltube or Thermal Energy Storage Coil) is a precision-engineered heat exchange component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for thermal energy storage systems that utilize ice as a phase-change material (PCM) for latent heat storage and release. The coil tube serves as the primary heat transfer interface between the refrigerant (typically brine or ethylene glycol solution) and the ice storage medium within a tank or container.
Based on extensive simulation and experimental research into the ice formation (freezing) and ice melting (thawing) processes within coil-based thermal storage systems, this product is optimized for maximum heat transfer efficiency during both charging (ice accumulation) and discharging (ice melting) cycles. The coil tube design ensures uniform ice layer growth on the outer surface of the tube, minimizing thermal resistance and maximizing the effective storage capacity of the system.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, thermal conductivity, and mechanical integrity under repeated thermal cycling conditions.
2.1 Base Material Grades
- SAE 304 / ASTM 304 (UNS S30400) — Standard austenitic stainless steel with excellent general corrosion resistance
- SAE 316L / ASTM 316L (UNS S31603) — Enhanced resistance to chloride-induced pitting and crevice corrosion
- SAE 321 / ASTM 321 (UNS S32100) — Stabilized grade with titanium addition for improved high-temperature stability
2.2 Key Material Properties
| Property | SAE 304 | SAE 316L | SAE 321 |
|---|---|---|---|
| Carbon (C), max % | 0.08 | 0.03 | 0.08 |
| Chromium (Cr), % | 18.0–20.0 | 16.0–18.0 | 17.0–19.0 |
| Nickel (Ni), % | 8.0–10.5 | 10.0–14.0 | 9.0–12.0 |
| Molybdenum (Mo), % | — | 2.0–3.0 | — |
| Titanium (Ti), % | — | — | 5 × (C − 0.02), min |
| Thermal Conductivity at 20°C, W/(m·K) | 16.3 | 16.3 | 16.3 |
| Specific Heat Capacity, J/(kg·K) | 500 | 500 | 500 |
| Tensile Strength, MPa (min) | 515 | 485 | 515 |
| Yield Strength (0.2% offset), MPa (min) | 205 | 170 | 205 |
| Elongation, % (min) | 40 | 40 | 40 |
| Operating Temperature Range, °C | −196 to +870 | −196 to +870 | −196 to +900 |
| Corrosion Resistance (Pitting) | Good | Excellent | Good |
2.3 Surface Treatment Options
- Passivated Surface — Standard chemical passivation to enhance passive oxide layer
- Pickled & Passivated — Acid pickling followed by passivation for maximum corrosion resistance
- Mirror Polished (Ra ≤ 0.4 μm) — For applications requiring minimal fluid friction and easy cleaning
- Electropolished (Ra ≤ 0.2 μm) — For hygienic and high-purity applications
3. Specifications
3.1 Geometric Dimensions
| Parameter | Specification Range | Unit |
|---|---|---|
| Outer Diameter (OD) | 6.0 – 50.8 | mm |
| Wall Thickness (WT) | 0.5 – 3.0 | mm |
| Coil Pitch (Center-to-Center Spacing) | 15.0 – 50.0 | mm |
| Tube Length per Coil | 1.0 – 50.0 | m |
| Coil Diameter (Overall) | 100 – 1,200 | mm |
| Number of Coils per Assembly | 1 – 200 | pcs |
| End Connection Type | Flanged / Threaded / Welded / Soldered | — |
| Tolerance on OD | ±0.10 | mm |
| Tolerance on Wall Thickness | ±0.05 | mm |
| Roundness | ≤ 0.05 × OD | — |
| Straightness (per meter) | ≤ 1.0 | mm/m |
3.2 Performance Parameters
| Parameter | Typical Value | Notes |
|---|---|---|
| Heat Transfer Coefficient (Ice Formation) | 300 – 800 | W/(m²·K) |
| Heat Transfer Coefficient (Ice Melting) | 500 – 1,200 | W/(m²·K) |
| Maximum Operating Pressure | 1.6 – 6.4 | MPa |
| Design Pressure | 2.5 – 10.0 | MPa |
| Ice Formation Rate | 20 – 80 | kWh/(m²·h) |
| Thermal Cycling Fatigue Life | > 50,000 | Cycles |
| Recommended Brine Concentration | 20 – 30% | CaCl₂ or NaCl by mass |
| Operating Temperature Range (Brine) | −25 to −5 | °C |
| Maximum Flow Velocity | 1.5 – 3.0 | m/s |
3.3 Standard Dimensions (Common Configurations)
| Model Series | OD × WT (mm) | Coil Pitch (mm) | Tube Length (m) | Material | Application |
|---|---|---|---|---|---|
| IC-06 | 6.0 × 0.8 | 15 | 5.0 | 304 | Small-scale commercial |
| IC-08 | 8.0 × 1.0 | 18 | 6.0 | 304 | Medium-scale commercial |
| IC-10 | 10.0 × 1.2 | 20 | 8.0 | 316L | Industrial process |
| IC-12 | 12.7 × 1.5 | 25 | 10.0 | 316L | Large-scale HVAC |
| IC-16 | 16.0 × 1.8 | 30 | 12.0 | 304 | Utility-scale storage |
| IC-20 | 20.0 × 2.0 | 35 | 15.0 | 321 | High-temperature cycling |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection — Procurement of certified cold-rolled stainless steel strip or seamless tube blanks meeting ASTM/ASME standards
- Coil Winding — Precision CNC-controlled winding of tube onto mandrels to achieve exact pitch, diameter, and length specifications
- Welding (if applicable) — TIG (Tungsten Inert Gas) welding or orbital welding of end connections and header assemblies; welds are performed under argon shielding to prevent oxidation
- Heat Treatment — Solution annealing at 1010–1120°C followed by rapid water quenching to restore full austenitic microstructure and mechanical properties
- Pickling & Passivation — Removal of oxide scale and weld discoloration via nitric/hydrofluoric acid bath; subsequent passivation with dilute nitric acid to restore chromium oxide protective layer
- Pressure Testing — Hydrostatic or pneumatic pressure testing at 1.5× design pressure to verify integrity
- Non-Destructive Testing (NDT) — Visual inspection, dimensional verification, and optional dye penetrant testing (DPT) or ultrasonic testing (UT) of welds
- Final Inspection & Packaging — Quality assurance audit, labeling, protective wrapping, and palletization for shipment
4.2 Quality Control Points
- Incoming material certification (Mill Test Certificate — MTC, EN 10204 3.1)
- In-process dimensional checks at winding station
- Post-weld radiographic testing (RT) for critical joints (per ASME Section VIII, Div. 1)
- Final dimensional audit against customer drawing (tolerance verification)
- Corrosion testing — Salt spray test (ASTM B117) minimum 500 hours for 316L grade
5. Applications
5.1 Primary Applications
- Ice Storage Air Conditioning (ISAC) Systems — Off-peak energy storage for commercial and industrial HVAC; ice is formed during low-demand/low-cost electricity periods and melted during peak cooling demand to reduce peak electrical load
- Peak Shaving & Demand Management — Reduction of peak cooling load by 30–60%, enabling smaller chiller equipment and significant energy cost savings
- Thermal Energy Storage (TES) Systems — Integration with solar cooling, district cooling, and combined heat and power (CHP) systems
- Process Cooling — Industrial processes requiring stable, high-capacity cold supply (food processing, pharmaceutical manufacturing, chemical processing)
- Backup Refrigeration — Emergency cooling capacity for critical facilities (data centers, hospitals, cold storage) during power outages
- Cryogenic Applications — Low-temperature heat exchangers and cryogenic fluid handling systems
5.2 Ice Storage System Integration
The coil tubes are typically installed within an insulated tank (polyethylene or stainless steel) filled with water. During the charging cycle, sub-zero brine (ethylene glycol or calcium chloride solution) flows through the coil tubes, causing ice to form on the outer surface. During the discharging cycle, ambient-temperature or warm water flows through the coils, melting the ice and providing chilled water to the cooling load. Simulation and experimental research have demonstrated that the coil tube geometry, pitch, and material properties directly influence:
- Uniformity of ice layer distribution
- Rate of heat transfer during both freezing and melting
- Long-term thermal cycling stability
- System efficiency and round-trip energy efficiency (RT-EE)
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Description | Applicability |
|---|---|---|
| ASTM A213 / A269 | Standard Specification for Seamless Austenitic Stainless Steel Tubing | Material compliance |
| ASME BPV Section VIII, Div. 1 | Rules for Construction of Pressure Vessels | Pressure vessel components |
| EN 10216-5 | Seamless and Welded Stainless Steel Tubes for Technical Purposes | European market compliance |
| ISO 4306 | Stainless Steel Tubes for General Purposes | General dimensional & material |