Spiral Coil Tube for Stepped Phase Change Heat Storage Systems
Product Overview
The Spiral Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered stainless steel tubular component specifically designed for integration into spiral coil tube-in-shell stepped phase change heat storage (PCTES) units. These coil tubes serve as the critical heat transfer medium within latent heat thermal energy storage systems, enabling efficient absorption, storage, and release of thermal energy through phase change materials (PCMs) encapsulated within shell-and-coil configurations.
This product represents a specialized segment of the stainless steel coil tube industry, distinguished by its optimized geometry for maximizing heat transfer surface area within compact shell volumes, thereby achieving superior thermal performance in both charging and discharging cycles of thermal energy storage applications.
Material & Properties
The coil tubes are fabricated from high-grade austenitic stainless steel, selected for their exceptional combination of corrosion resistance, thermal conductivity, mechanical strength, and long-term structural integrity under cyclic thermal loading conditions.
- Base Material: Austenitic stainless steel conforming to standards such as ASTM A269, ASTM A312, EN 10217, or GB/T 12771
- Common Grades: SUS304 (UNS S30408), SUS316L (UNS S31603), SUS321 (UNS S32100), SUS310S (UNS S31008)
- Corrosion Resistance: Excellent resistance to oxidation and corrosion in high-temperature environments up to 800°C (SUS310S) or 450°C (SUS304), suitable for prolonged exposure to aqueous PCM media
- Thermal Conductivity: 14–16 W/(m·K) at 25°C (SUS304), providing reliable heat transfer capability
- Mechanical Properties: Tensile strength ≥ 520 MPa, yield strength ≥ 205 MPa, elongation ≥ 40% (SUS304 annealed condition)
- Thermal Stability: Maintains dimensional accuracy and mechanical properties through repeated thermal cycling without significant creep or deformation
- Surface Finish: Ra ≤ 0.8 μm (electropolished or passivated finish) to minimize fouling and enhance convective heat transfer coefficients
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (customizable) | ASTM A269 / GB/T 12771 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | ASTM A269 / GB/T 12771 |
| Coil Pitch | 10 mm – 80 mm (adjustable per design) | Per application requirements |
| Coil Diameter | 50 mm – 600 mm (customizable) | Per application requirements |
| Tube Length (Uncoiled) | Up to 12,000 mm per continuous coil | Manufacturer standard |
| Operating Temperature Range | -40°C to +450°C (SUS304); -40°C to +800°C (SUS310S) | Material datasheet |
| Design Pressure | Up to 6.0 MPa (gauge) | ASME BPV Code Section VIII |
| End Connection Types | Flanged, threaded (BSPP/BSPT/NPT), socket welded, or custom | ASME B1.20.1 / GB/T 7306 |
| Tolerance on OD | ±0.05 mm (precision grade) | ASTM A269 / EN 10217 |
| Tolerance on Wall Thickness | ±0.03 mm (precision grade) | ASTM A269 / EN 10217 |
| Surface Treatment | Pickling, passivation, electropolishing (optional) | ASTM A967 / GB/T 4237 |
| Heat Treatment Condition | Solution annealed (1050–1150°C), water quenched | Per material grade specification |
Manufacturing Process
The production of spiral coil tubes for phase change heat storage applications follows a rigorous multi-stage manufacturing workflow to ensure dimensional precision, metallurgical integrity, and consistent performance:
- Raw Material Selection & Inspection: High-purity stainless steel seamless tubes are procured from certified mills, with incoming inspection covering chemical composition analysis (spectrometry), mechanical property verification, and visual surface examination.
- Dimensional Calibration: Tubes undergo precision sizing and straightening to ensure uniform OD and wall thickness tolerances prior to coiling operations.
- Coil Forming (Cold Coiling): Tubes are fed through precision CNC-controlled coiling machines using hydraulic or mechanical winding heads. The coil pitch, coil diameter, and total length are programmed to exact specifications, with real-time dimensional monitoring via laser sensors.
- Springback Compensation: Advanced coiling algorithms account for elastic springback (typically 3–5% for austenitic grades) to ensure the final coil geometry matches design intent after release from the mandrel.
- End Preparation & Connection Fabrication: Tube ends are machined, beveled, or fitted with flanges/threads per customer specification using automated welding or threading equipment.
- Heat Treatment (if required): Post-forming stress relief annealing may be applied at 1050–1150°C followed by rapid water quenching to restore full austenitic microstructure and eliminate residual stresses from cold forming.
- Surface Treatment: Pickling and passivation are performed to remove scale, oils, and contaminants, establishing a protective chromium oxide passive film. Electropolishing is available for ultra-clean surface requirements.
- Non-Destructive Testing (NDT): Each coil tube undergoes comprehensive inspection including hydrostatic pressure testing (at 1.5× design pressure for minimum 30 seconds), eddy current testing (ECT) for wall thickness and defect detection, and visual inspection of all welds and connections.
- Final Dimensional Verification & Packaging: Coil dimensions are verified using coordinate measurement systems (CMM). Approved products are wrapped in protective packaging, labeled with traceability documentation, and prepared for shipment.
Applications
The spiral coil tubes are purpose-engineered for a diverse range of thermal energy storage and heat exchange applications:
- Stepped Phase Change Heat Storage Units: Primary application in spiral coil tube-in-shell configurations where the coil tube serves as the heat transfer surface between the working fluid (e.g., molten salt, thermal oil, or aqueous solution) and the encapsulated PCM. The stepped architecture enables multi-temperature-level thermal storage for improved energy utilization efficiency.
- Solar Thermal Energy Storage Systems: Integration into concentrated solar power (CSP) plants and solar water heating systems for thermal energy buffering and load-shifting.
- Industrial Waste Heat Recovery: Capture and storage of low-to-medium grade waste heat from industrial processes (glass manufacturing, cement production, steel mills) for subsequent reuse.
- Building Heating & Cooling Systems: Thermal energy storage for district heating networks, commercial buildings, and HVAC systems to flatten peak load demands.
- Process Heating & Cooling: Use in food processing, chemical manufacturing, and pharmaceutical industries requiring precise temperature control and thermal buffering.
- Automotive Thermal Management: Component integration in hybrid and electric vehicle battery thermal management systems for thermal regulation.
Unique Selling Points
- Optimized Geometry for Maximum Heat Transfer: The spiral coil design provides a high surface-area-to-volume ratio, significantly enhancing convective heat transfer coefficients and reducing thermal resistance within the PCM enclosure.
- Superior Thermal Cycling Durability: Austenitic stainless steel coil tubes maintain structural integrity through thousands of thermal cycling events without fatigue cracking or dimensional drift.
- Customizable Configuration: Full customization of coil pitch, diameter, tube dimensions, and end connections to match specific system design requirements and performance targets.
- Corrosion-Resistant in Aggressive Environments: SUS316L grade offers exceptional resistance to chloride-induced pitting and crevice corrosion, ensuring long service life in aqueous PCM systems.
- Traceability & Quality Assurance: Complete material traceability from mill certificate to final product, with comprehensive NDT documentation for each unit.
Quality Certifications & Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System certification |
| ISO 14001:2015 | Environmental Management System certification |
| ISO 45001:2018 | Occupational Health & Safety Management System certification |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for pressurized components |
| ASTM A269 / A312 | Material and dimensional conformance for seamless stainless steel tubes |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes |
| EN 10217 | European standard for stainless steel seamless tubes for pressure purposes |
| ASME BPV Code Section VIII | Pressure vessel and component design compliance |
| TÜV / SGS Testing Reports | Independent third-party material and performance verification |
Note: All specifications listed are indicative and subject to final confirmation based on specific project requirements. Custom engineering solutions are available upon request. Wenzhou Jixing Metal Materials Co., Ltd. maintains a dedicated engineering team to support design consultation, prototype development, and performance validation for phase change heat storage applications.