Stainless Steel Coil Tube for Thermal Energy Storage Systems
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed specifically for thermal energy storage (TES) applications, particularly ice storage and heat exchange systems. This product represents a critical heat transfer element within ice storage tanks, where it facilitates efficient thermal exchange between the refrigerant medium and the stored ice mass. The coil tube is engineered to operate under both freezing and thawing cycles, providing reliable performance in external ice-melting configurations and internal refrigeration processes.
Based on extensive research into thermal conductive coil tube ice storage tank external melting ice experimental studies, this product integrates advanced metallurgical design principles with practical thermal management requirements. The coil geometry maximizes surface area within a compact volume, enabling superior heat transfer coefficients while maintaining structural integrity under cyclic thermal stress.
2. Material & Properties
2.1 Base Material Composition
The coil tube is fabricated from austenitic stainless steel, typically conforming to the following grades:
- AISI 304 (UNS S30408) — General-purpose corrosion resistance with balanced mechanical properties
- AISI 316 (UNS S31608) — Enhanced pitting and crevice corrosion resistance due to molybdenum addition
- AISI 321 (UNS S32108) — Stabilized grade suitable for elevated temperature cycling applications
2.2 Key Physical Properties
- Density (ρ): 7,900 – 8,000 kg/m³
- Thermal Conductivity (k): 14 – 16 W/(m·K) at 25°C
- Specific Heat Capacity (c): 500 J/(kg·K)
- Thermal Expansion Coefficient (α): 17.3 × 10⁻⁶ /°C (20–100°C)
- Operating Temperature Range: −60°C to +350°C
2.3 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (AISI 304); ≥ 570 MPa (AISI 316)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (HB): 120 – 170
2.4 Corrosion Resistance
The austenitic stainless steel matrix provides exceptional resistance to:
- Aqueous environments including brine solutions (CaCl₂, NaCl) used in ice storage systems
- Chloride-induced stress corrosion cracking (SCC) — particularly AISI 316 grade
- Intergranular corrosion under cyclic thermal loading conditions
- Galvanic corrosion when coupled with carbon steel tank structures (with appropriate isolation)
3. Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Tube Outer Diameter (OD) | 12 / 16 / 22 / 28 / 32 / 38 | mm |
| Wall Thickness (t) | 1.0 – 3.0 | mm |
| Coil Diameter (CD) | 200 – 1,200 | mm |
| Coil Length per Assembly | 500 – 5,000 | mm |
| Number of Coils per Unit | 1 – 16 | — |
| Pitch (Center-to-Center Spacing) | 1.5 × OD – 3.0 × OD | mm |
| Maximum Working Pressure | 1.6 – 4.0 | MPa |
| Hydrostatic Test Pressure | 1.5 × Working Pressure | MPa |
| Surface Finish (Ra) | ≤ 0.8 | μm |
| End Connection Type | Threaded / Flanged / Butt-welded | — |
| Minimum Bending Radius | 5 × OD (cold bend); 3 × OD (hot bend) | — |
| Standard Compliance | ASTM A213 / ASTM A269 / EN 10216-5 | — |
| Traceability | Heat number marked; full mill certificate provided | — |
4. Manufacturing Process
4.1 Raw Material Selection
Virgin stainless steel strip or seamless pipe stock is sourced from certified mills with full chemical composition analysis and mechanical property verification. Each heat lot is traceable through a unique identification number (Heat Number) for complete quality traceability.
4.2 Tube Forming
- Coil Winding: Straight stainless steel pipe is precisely wound around a mandrel of the required coil diameter using a CNC-controlled bending machine. The bending radius is maintained within ±0.5 mm tolerance.
- Heat Treatment (if applicable): For AISI 321 grade, solution annealing at 1,050°C followed by rapid water quenching ensures full austenitic microstructure stability.
- Stress Relief: Annealing at 1,040°C with furnace cooling eliminates residual bending stresses and restores ductility.
4.3 End Preparation & Connection
- Cutting: Tube ends are cut square (±0.2 mm) using precision shearing or plasma cutting.
- Deburring & Cleaning: Internal and external burrs are removed; surfaces are cleaned to remove cutting residues and oxides.
- Threading/Flanging: Threaded connections are machined per ISO 7-1 or NPT standards; flanged ends are welded per ASME B16.5.
- Butt Welding: Where required, tube ends are prepared (beveled per AWS D10.9) and TIG welded with matching filler metal (ER308L or ER316L).
4.4 Assembly & Integration
Multiple coil units are assembled into headers (manifold connections) using brazed or welded joints. The complete coil assembly is designed for integration into ice storage tank manifolds, with inlet and outlet ports configured for either forced or natural circulation flow patterns.
4.5 Quality Control
- Visual Inspection: 100% inspection for surface defects, distortion, and dimensional accuracy.
- Dimensional Verification: Coil diameter, pitch, and length verified using calibrated gauges and CMM (Coordinate Measuring Machine) where applicable.
- Pressure Testing: Each assembly undergoes hydrostatic pressure testing at 1.5× working pressure for a minimum dwell time of 30 minutes with zero leakage acceptance.
- NDT (Non-Destructive Testing): Welded joints inspected by Dye Penetrant Testing (PT) per ASTM E709 or Magnetic Particle Inspection (MT) per ASTM E709.
- Chemical & Mechanical Verification: Spectroscopic analysis (OES) confirms composition; tensile test coupons from production lots verify mechanical properties.
5. Applications
5.1 Ice Storage Thermal Energy Systems
The primary application is within ice storage tanks for peak-shaving and load-shifting in HVAC (Heating, Ventilation, and Air Conditioning) systems. The coil tube serves as the heat exchange surface where refrigerant (typically ethylene glycol or calcium chloride brine at −5°C to −10°C) flows through the coil to freeze the surrounding water mass into ice.
5.2 External Ice Melting Configuration
In the external melting ice configuration, the coil tube facilitates controlled thawing of the stored ice mass. Warm water or ambient air flows through or around the coil to gradually melt ice from the exterior surface inward, releasing stored thermal energy for cooling applications. This configuration offers superior temperature uniformity and reduced thermal shock compared to internal melting methods.
5.3 Additional Applications
- Industrial process cooling with thermal energy storage
- Building district cooling systems
- Commercial refrigeration systems
- Cryogenic heat exchangers
- Food processing thermal management
- Pharmaceutical cold storage systems
6. Quality Certifications
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification |
| ISO 14001:2015 | Environmental Management System certification |
| EN 10204 3.1 | Material test certificate — independent inspection body |
| ASTM A213 | Standard Specification for Seamless Austenitic Stainless Steel Tubing |
| EN 10216-5 | Non-alloy and alloy steel tubes for pressure purposes |
| PED 2014/68/EU | Pressure Equipment Directive compliance (Category I-IV) |
| ASME BPE | Biosystems and Pharmaceutical Equipment (where applicable) |
| Mill Test Certificate (MTC) | Full chemical and mechanical analysis per heat number |
7. Unique Selling Points
- Optimized Coil Geometry: Based on experimental research into thermal conductive coil tube ice storage configurations, the pitch and diameter ratios are optimized for maximum heat transfer area per unit volume, achieving Nusselt number improvements of 15–25% over conventional designs.
- Thermal Cycle Durability: The austenitic stainless steel matrix withstands over 100,000 freeze-thaw cycles without degradation of mechanical properties or corrosion resistance.
- Full Traceability: Every coil tube assembly is traceable to its original mill heat number, providing complete material lineage documentation.
- Custom Engineering: Coil dimensions, materials, and connection types are customizable to meet specific system requirements, from small commercial installations to large-scale district cooling projects.
- Research-Validated Design: Product specifications are informed by experimental studies on thermal conductive plastic coil tube ice storage tank external melting configurations, ensuring proven thermal performance.
Note: This product is manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product Reference No. 1117). Technical data presented herein is based on standard specifications and experimental research findings. Specific performance characteristics may vary depending on operating conditions, fluid properties, and system configuration. Consult the manufacturer for project-specific engineering support.