Stainless Steel Coil Tube for Thermal Energy Storage Panels
Product Overview
The Stainless Steel Coil Tube (also referred to as Coiled Tube or Continuous Coil Pipe) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for integration into Coiled Tube Thermal Energy Storage Panels (盘管式蓄冷板), where it serves as the primary heat transfer medium within phase-change energy storage systems. The coil tube is formed into a continuous serpentine or spiral configuration that maximizes heat exchange surface area within a compact panel footprint, enabling efficient latent heat storage and release cycles during both charging (solidification) and discharging (melting) phases of the thermal energy storage process.
Numerical studies on the melting process of coiled tube thermal storage panels have demonstrated that the geometric configuration, material properties, and dimensional tolerances of the coil tube directly influence the melting rate, temperature uniformity, and overall thermal efficiency of the storage system. Wenzhou Jixing Metal Materials Co., Ltd. supplies coil tubes engineered to optimize these performance parameters through rigorous material selection, precision cold-forming techniques, and comprehensive quality assurance protocols.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, with the following material grades available:
- ASTM A269 / ASTM A270 Type 304 (UNS S30400) — General-purpose grade with excellent corrosion resistance and formability; Chromium (Cr) 18–20%, Nickel (Ni) 8–10.5%.
- ASTM A269 / ASTM A270 Type 316L (UNS S31603) — Enhanced corrosion resistance with Molybdenum (Mo) 2–3% addition; ideal for aggressive chemical environments and long-term thermal cycling.
- ASTM A269 Type 321 (UNS S32100) — Titanium-stabilized grade (Ti ≥ 5×C) offering superior resistance to intergranular corrosion at elevated temperatures.
Key mechanical and thermal properties of the coil tube include:
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, ensuring efficient heat transfer between the working fluid and the phase-change material (PCM) within the storage panel.
- Specific Heat Capacity: 500 J/(kg·K) at 20°C.
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C), compatible with controlled dimensional stability during repeated thermal cycling.
- Yield Strength: ≥ 205 MPa (Type 304, annealed condition); ≥ 275 MPa (Type 316L, cold-worked condition).
- Tensile Strength: 515–720 MPa depending on grade and cold-work level.
- Operating Temperature Range: −196°C to +870°C (Type 304); −196°C to +870°C (Type 316L).
Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.0 mm (custom sizes available) | ±0.1 mm |
| Wall Thickness | 0.5 mm – 2.0 mm | ±10% of nominal |
| Coil Pitch (Center-to-Center Spacing) | 15 mm – 60 mm (application-dependent) | ±0.5 mm |
| Coil Diameter (Loop Diameter) | 20 mm – 150 mm | ±1.0 mm |
| Tube Length per Coil Assembly | 3 m – 50 m (configurable) | ±50 mm |
| Surface Finish | Mirror Polish (Ra ≤ 0.4 μm) / Brushed (Ra ≤ 1.6 μm) / Pickled & Passivated | ASTM A967 |
| End Condition | Plain Cut / Beveled / Threaded (per request) | ASME B1.20.1 (for threaded) |
| Pressure Rating | Up to 1.6 MPa (PN16) at 200°C | ASME B31.3 / EN 13480 |
| Material Grade | 304 / 304L / 316L / 321 (per customer specification) | ASTM A269 / A270 |
| Maximum Operating Temperature | 870°C (continuous); 1100°C (intermittent) | Grade-dependent |
| Packaging | Wooden crate / Export-grade corrugated box with desiccant | ISO 4180 |
Manufacturing Process
The production of precision stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a multi-stage manufacturing workflow optimized for dimensional accuracy, metallurgical integrity, and thermal performance:
- Raw Material Selection & Inspection — Cold-rolled stainless steel strip or seamless pipe blanks are sourced from certified mills. Incoming material undergoes spectral analysis (PMI), chemical composition verification (ASTM E1), and mechanical property testing (ASTM A370).
- Pipe Forming — Cold-rolled strip is formed into seamless tube via rotary forming or plate roll welding, followed by TIG (Tungsten Inert Gas) welding with argon shielding (ASTM A269 Type 1 or Type 2). Alternatively, precision seamless tubes are drawn from hot-forged billets per ASTM A213/A269.
- Precision Sizing & Calibration — The formed tube passes through a series of calibrating rolls to achieve the required outer diameter and wall thickness within specified tolerances. Online optical measurement systems monitor dimensional compliance in real time.
- Coil Forming (Coiling) — The straight tube is mechanically coiled into the required spiral or serpentine geometry using CNC-controlled coiling machines. Coil pitch, loop diameter, and total turn count are precisely programmed to match thermal storage panel design specifications.
- Heat Treatment & Annealing — Post-coiling solution annealing (1050–1150°C, followed by controlled cooling) relieves residual stresses induced during cold forming, restoring full austenitic microstructure and mechanical properties.
- Pickling & Passivation — The annealed coil tube is treated with citric or nitric acid pickling solution to remove oxide scale, followed by passivation to establish a protective chromium oxide film (minimum 10% Cr₂O₃ content per ASTM A967).
- Non-Destructive Testing (NDT) — Each coil assembly undergoes 100% hydrostatic pressure testing (typically 1.5× working pressure), eddy current inspection of weld seams (ASTM E309), and visual surface examination.
- Final Inspection & Documentation — Comprehensive dimensional verification, material traceability documentation (Mill Test Reports, MTR), and certificate of compliance are prepared for each batch.
Applications
The stainless steel coil tube produced by Wenzhou Jixing Metal Materials Co., Ltd. finds extensive application in the following sectors:
- Thermal Energy Storage Systems — Primary application in coiled tube latent heat storage panels using paraffin wax, salt hydrates, or other phase-change materials (PCM) for building HVAC load shifting, industrial waste heat recovery, and solar thermal energy storage.
- Cold Storage & Refrigeration — Coil tubes integrated into evaporator panels and refrigeration coils for commercial cold rooms, walk-in freezers, and food processing facilities.
- Solar Thermal Collectors — Heat transfer tubes in evacuated tube solar collectors and concentrated solar power (CSP) systems where high-temperature resistance and corrosion durability are critical.
- Process Heat Exchangers — Spiral and coil configurations in plate-fin and shell-and-coil heat exchangers for chemical processing, pharmaceutical manufacturing, and food & beverage industries.
- Automotive & Aerospace Thermal Management — Lightweight coil tube assemblies in battery thermal management systems (BTMS) for electric vehicles and heat rejection systems in aerospace applications.
- Building Energy Systems — Integration into underfloor radiant heating/cooling panels and thermal buffer storage units for smart building energy management.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications and complies with the following international standards:
- ISO 9001:2015 — Quality Management Systems certification ensuring consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management Systems certification for sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
- CE Marking — Conformity with European Union directives for product safety and market access.
- ASME BPV Code — Compliance for pressure vessel and piping components where applicable.
- ASTM A269 / A270 / A213 — Full compliance with American Society for Testing and Materials standards for stainless steel tubing.
- EN 10216-5 / EN 10217-7 — European standard compliance for stainless steel tubes for heat exchangers and pressure purposes.
- JIS G3459 — Japanese Industrial Standard compliance for austenitic stainless steel tubes.
Note: All products are accompanied by a full Mill Test Report (MTR) including chemical composition analysis, mechanical property data, hydrostatic test results, and heat treatment documentation, ensuring complete traceability from raw material to finished coil assembly.
Unique Selling Points
- Precision Coil Geometry — CNC-controlled coiling ensures exact pitch and loop diameter control (±0.5 mm), directly enhancing thermal performance predictability in energy storage panel designs validated through numerical simulation.
- Full Material Traceability — End-to-end traceability from mill certificate to final product, enabling compliance with critical industry regulations in pharmaceutical, food, and aerospace sectors.
- Custom Engineering Capability — Flexible customization of tube diameter, wall thickness, coil configuration, surface finish, and end treatments to match specific thermal storage panel designs and system integration requirements.
- Superior Corrosion Resistance — Type 316L and 321 grades offer extended service life in aggressive environments, reducing maintenance frequency and total cost of ownership (TCO) over the system lifecycle.
- Thermal Cycling Durability — Solution-annealed microstructure and controlled cold-work levels ensure reliable performance through thousands of thermal cycling events without stress corrosion cracking (SCC) or fatigue failure.