Stainless Steel Coil Tube for Thermal Energy Storage (TES) Applications
Product Series: Coiltube — Ice Storage & Evaporative Heat Exchange Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: No. 1155
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular product designed primarily for evaporative ice storage systems and thermal energy storage (Thermal Energy Storage, TES) applications. This coil tube is manufactured from high-grade austenitic stainless steel and is formed into continuous helical or spiral configurations to maximize the heat transfer surface area within a compact volumetric footprint. The product is specifically optimized for ice storage processes, where phase-change materials (Phase Change Materials, PCM) — typically water — undergo freezing and melting cycles to store and release thermal energy.
Based on rigorous simulation studies of evaporative ice coil tube ice storage processes, the geometric configuration and material selection of this product have been refined to achieve superior thermal performance, including high heat transfer coefficients, uniform ice layer formation, and minimal pressure drop during fluid circulation. The coil tube serves as the critical heat exchange interface between the refrigerant or brine circuit and the thermal storage medium.
2. Material & Properties
2.1 Base Material
- Grade: Austenitic Stainless Steel (UNS S30408 / 304 / 06Cr19Ni10; UNS S31603 / 316 / 06Cr17Ni12Mo2 available upon request)
- Standard Reference: ASTM A213 / A269; GB/T 12771; EN 10216-5
- Carbon Equivalent (CE): ≤ 0.04% (low-carbon variant for enhanced weldability and corrosion resistance)
- Chromium (Cr) Content: 18–20% (provides passive oxide film for corrosion protection)
- Nickel (Ni) Content: 8–12% (stabilizes austenitic microstructure)
- Molybdenum (Mo) Content: 2–3% (in 316 grade; enhances pitting and crevice corrosion resistance)
2.2 Mechanical Properties
- Tensile Strength: ≥ 515 MPa (75,000 psi)
- Yield Strength: ≥ 205 MPa (30,000 psi)
- Elongation: ≥ 40% (at break, indicates excellent ductility for coil forming)
- Hardness: ≤ 210 HB (annealed condition)
- Impact Toughness (Charpy V-Notch): ≥ 47 J at −40 °C (suitable for cryogenic/low-temperature ice storage service)
2.3 Thermal Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20 °C
- Specific Heat Capacity: 500 J/(kg·K)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C
- Operating Temperature Range: −196 °C to +870 °C (continuous); ice storage applications typically operate between −10 °C and +15 °C
2.4 Corrosion & Surface Properties
- Surface Finish: 2B, BA (Bright Annealed), or polished (Ra ≤ 0.4 μm)
- Pitting Resistance: PREN ≥ 19 (304 grade); PREN ≥ 24 (316 grade)
- Chloride Pitting Threshold: > 2,000 ppm Cl⁻ (316 grade in non-aerated conditions)
- Ice Adhesion Coefficient: Optimized low-surface-energy treatment available to reduce ice adhesion and facilitate de-icing cycles
3. Specifications
| Parameter | Specification | Unit | Standard / Reference |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 – 108.0 | mm | ASTM A213 |
| Wall Thickness (WT) | 0.5 – 5.0 | mm | ASTM A213 |
| Coil Pitch (Center-to-Center Spacing) | 15 – 250 | mm | Custom design per application |
| Coil Diameter (Mean) | 50 – 2,000 | mm | Custom design per application |
| Tube Length per Coil | 1 – 500 | m | Continuous coil or cut-to-length |
| Number of Turns per Coil | 1 – 5,000 | turns | Custom design per application |
| OD Tolerance | ±0.10 | mm | ASTM A213 / EN 10216-5 |
| WT Tolerance | ±10% | — | ASTM A213 |
| Coil Pitch Tolerance | ±1.0 | mm | Manufacturer specification |
| End Treatment | Plain, beveled, flared, or welded fittings | — | Per customer drawing |
| Hydrostatic Test Pressure | 1.5 × Working Pressure | — | ASTM A213 |
| Maximum Working Pressure | Up to 4.0 | MPa | Dependent on OD, WT, and grade |
| Refrigerant / Brine Compatibility | R-134a, R-404A, R-410A, CaCl₂ brine, LiBr solution | — | ASME/ANSI standards |
| Coating (Optional) | Anti-icing nano-coating, PTFE lining | — | Proprietary technology |
4. Manufacturing Process
The production of this coil tube follows a multi-stage manufacturing sequence, each step rigorously controlled to ensure dimensional accuracy, metallurgical integrity, and thermal performance:
- Raw Material Procurement & Inspection: Stainless steel seamless tubes are sourced from certified mills and subjected to chemical composition analysis (via Optical Emission Spectroscopy, OES), mechanical testing, and non-destructive examination (Non-Destructive Testing, NDT) including ultrasonic flaw detection and eddy current testing.
- Annealing & Stress Relief: Tubes are solution-annealed at 1,050–1,100 °C followed by controlled cooling to achieve a fully austenitic microstructure with optimal ductility for subsequent forming operations.
- Coil Forming (Cold Bending): Precision CNC-controlled mandrel bending machines form the straight tubes into helical or spiral coil configurations. The bending radius is calculated to avoid wall thinning, ovality, or material deformation beyond acceptable limits. Multi-axis control ensures consistent pitch and alignment.
- Post-Form Annealing (Optional): For applications requiring full recovery of mechanical properties after cold forming, the formed coils may undergo stress-relief annealing at 870–925 °C.
- End Preparation & Fitting: Tube ends are prepared according to customer specifications — options include plain cut ends, beveled ends, threaded fittings, flanged connections, or brazed/soldered cap assemblies.
- Surface Treatment: Depending on the application, the coil may undergo passivation (nitric acid or citric acid treatment), electropolishing, or application of anti-icing surface coatings to minimize ice adhesion during thermal cycling.
- Hydrostatic Pressure Testing: Each coil assembly is pressure-tested at 1.5 times the maximum working pressure to verify leak-tightness and structural integrity. Test duration is maintained for a minimum of 3 minutes with no observable pressure drop.
- Final Inspection & Packaging: Finished products undergo dimensional verification (laser measurement or CMM), visual inspection, and NDT. Coils are packaged in protective wrapping with wooden crates or steel bands to prevent mechanical damage during transit.
5. Applications
5.1 Primary Applications
- Ice Storage Systems (Thermal Energy Storage): The coil tube serves as the heat exchange element within evaporative ice storage tanks, where refrigerated brine circulates through the coils to freeze water into ice layers. During peak demand periods, the stored ice melts to provide cooling capacity. This application is the primary design basis for the product, validated through computational simulation of ice nucleation, growth, and melt-off dynamics.
- Peak-Shaving & Load Shifting: In commercial and industrial HVAC systems, ice storage enables off-peak ice production and on-peak cooling delivery, reducing electricity costs and grid load.
- Backup Refrigeration: Ice storage systems provide emergency cooling capacity during power outages or chiller failures, critical for pharmaceutical storage, food processing, and data center cooling.
5.2 Secondary Applications
- Evaporative condensers and heat exchangers in industrial refrigeration
- Heat recovery systems in chemical and petrochemical processing
- Superconducting magnet cooling circuits (cryogenic applications)
- Food and beverage pasteurization and thermal processing equipment
- Pharmaceutical and biotechnology process heat exchange
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope | Relevance |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Ensures consistent quality across all production stages |
| ISO 14001:2015 | Environmental Management System | Minimizes environmental impact of manufacturing |
| ISO 45001:2018 | Occupational Health & Safety | Worker safety in production facilities |
| ASTM A213 / A269 | Material & Mechanical Properties | Defines acceptable grades, dimensions, and test methods |
| EN 10216-5 | European Tube Standards | Compliance with EU market requirements |
| GB/T 12771 | Chinese National Standard | Compliance with PRC market requirements |
| ASME B31.5 | Piping Code for Refrigeration | Pressure design and installation compliance |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive | Market access for pressurized applications in EU |
| Mill Test Certificates (MTC) | EN 10204 Type 3.1 | Traceability of material origin and test results |
7. Unique Selling Points
- Simulation-Validated Design: The coil geometry and material selection have been validated through computational fluid dynamics (Computational Fluid Dynamics, CFD) and phase-change heat transfer simulations of the ice storage process, ensuring optimal ice layer uniformity, thermal efficiency, and cycle durability. This distinguishes the product from generic coil tubes not designed for phase-change thermal storage.
- Superior Low-Temperature Performance: The austenitic stainless steel microstructure retains excellent toughness and dimensional stability at sub-zero temperatures (down to −196 °C), preventing brittle fracture during repeated freeze-thaw cycling — a critical advantage over carbon steel alternatives.
- Anti-Icing Surface Technology (Optional): Proprietary nano-scale surface coatings reduce ice adhesion forces by up to 60%, facilitating rapid de-icing and reducing energy consumption during the melt cycle. This extends system efficiency and reduces operational downtime.
- Customizable Geometric Parameters: Coil pitch, diameter, tube OD, and wall thickness can be tailored to specific system requirements, enabling integration into compact or large-scale ice storage tanks with optimized heat transfer performance.
- Corrosion Resistance in Brine Environments: The 316-grade option provides exceptional resistance to chloride-induced pitting and crevice corrosion in calcium chloride (CaCl₂) and lithium bromide (LiBr) brine solutions commonly used in ice storage systems, extending service life beyond 25 years.
- Full Traceability & Certification: