Spiral Coil Tube (Coiltube) — Stainless Steel Heat Exchange Coil
1. Product Overview
The Spiral Coil Tube (Coiltube) is a precision-engineered stainless steel tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed specifically for thermal energy storage and heat exchange applications, particularly in phase change thermal storage systems (Phase Change Material — PCM storage devices). The spiral coil geometry maximizes the heat transfer surface area within a compact volume, enabling efficient thermal energy absorption and dynamic heat release in subcooled operating conditions.
Based on extensive research into the dynamic heat release characteristics of spiral coil subcooled phase change thermal storage devices, this coil tube product is engineered to deliver superior thermal performance, mechanical integrity, and long-term reliability under cyclic thermal loading conditions. The continuous spiral winding configuration eliminates joints and welds along the heat transfer path, reducing thermal resistance and minimizing the risk of leakage in high-temperature applications.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade austenitic stainless steel, with the following material options available:
- 304 Stainless Steel (UNS S30408): General-purpose grade offering excellent corrosion resistance and formability. Suitable for moderate-temperature thermal storage applications.
- 316L Stainless Steel (UNS S31603): Low-carbon variant with added molybdenum (2–3%), providing enhanced resistance to pitting and crevice corrosion in aggressive chemical environments.
- 321 Stainless Steel (UNS S32100): Titanium-stabilized grade with superior resistance to intergranular corrosion, ideal for high-temperature cycling applications exceeding 400°C.
2.2 Key Material Properties
- Thermal Conductivity: 14–16 W/(m·K) at 20°C, ensuring efficient heat conduction through the tube wall.
- Specific Heat Capacity: ~500 J/(kg·K), contributing to thermal inertia in the system.
- Coefficient of Thermal Expansion: 16–18 × 10⁻⁶ /K, enabling dimensional stability under thermal cycling.
- Maximum Service Temperature: Up to 870°C (304/321 grades).
- Corrosion Resistance: Excellent resistance to oxidation, acids, alkalis, and chloride-containing media (particularly 316L grade).
- Mechanical Strength: Minimum tensile strength of 515 MPa (304 annealed); minimum yield strength of 205 MPa.
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Product Type | Spiral Coil Tube (Continuous Helical Winding) |
| Material Grade | 304 / 316L / 321 Stainless Steel |
| Outer Diameter (OD) | 6 mm – 50 mm (customizable) |
| Wall Thickness | 0.5 mm – 3.0 mm |
| Coil Diameter (Helix Mean Diameter) | 50 mm – 600 mm |
| Coil Pitch (Turn Spacing) | 10 mm – 50 mm |
| Coil Length / Number of Turns | Up to 100 m continuous length (customizable) |
| Surface Finish | Pickled & Passivated (Ra ≤ 0.8 μm); Mirror polish available on request |
| Operating Pressure | Up to 2.5 MPa (design dependent) |
| Operating Temperature Range | −196°C to +870°C |
| Winding Method | Continuous cold spiral winding (seamless, no longitudinal welds) |
| Standards Compliance | ASTM A213 / ASME SA-213 / EN 10216-5 / GB/T 14976 |
| Available Configurations | Single coil, multi-coil bundle, concentric coil assembly |
4. Manufacturing Process
4.1 Raw Material Preparation
High-purity stainless steel seamless tubes conforming to ASTM A213 or ASME SA-213 specifications are selected as the base material. Incoming material undergoes spectroscopic verification (OES analysis) to confirm chemical composition, followed by dimensional inspection and surface quality assessment.
4.2 Cold Spiral Winding (Forming)
The tube blank is fed through a precision CNC spiral winding machine equipped with programmable forming dies. The continuous cold-winding process produces a uniform helical coil geometry with the following critical process parameters:
- Controlled winding tension to prevent ovalization (eccentricity ≤ 1.5% of OD)
- Precise pitch control with ±0.5 mm tolerance
- Constant bending radius to avoid material thinning at the inner curve (minimum wall thickness reduction ≤ 15%)
- Stress-relief annealing (optional) at 1050°C followed by controlled cooling to eliminate residual bending stresses
4.3 Heat Treatment
Following winding, coils may undergo solution annealing at 1010–1120°C with rapid water quenching to restore full austenitic microstructure, ensuring maximum corrosion resistance and ductility. Stress-relief treatment at 425–550°C is available for applications requiring dimensional stability without full recrystallization.
4.4 Surface Treatment
- Pickling: Immersion in mixed acid solution (HNO₃ + HF) to remove oxide scale and decarburized surface layers.
- Passivation: Nitric acid treatment to restore the chromium oxide passive film, enhancing corrosion resistance.
- Electropolishing (optional): Electrochemical polishing to achieve Ra ≤ 0.4 μm surface roughness for hygienic or high-efficiency heat transfer applications.
4.5 Quality Inspection
- Dimensional verification using CMM (Coordinate Measuring Machine) for coil diameter, pitch, and tube cross-section
- Eddy current testing for wall thickness uniformity and surface defect detection
- Hydrostatic pressure testing at 1.5× working pressure for leak-tightness verification
- Spectroscopic (OES) composition analysis per batch
- Hardness testing (Rockwell B or Vickers) for mechanical property confirmation
5. Applications
5.1 Phase Change Thermal Energy Storage (PCM TES)
This is the primary application domain. The spiral coil tube serves as the internal heat transfer enhancement element within encapsulated PCM containers. The coiled geometry significantly increases the heat transfer area-to-volume ratio, reducing the charging and discharging time of the thermal storage device. Research on dynamic heat release characteristics has demonstrated that spiral coil configurations achieve 30–50% improvement in heat transfer rate compared to straight tube arrangements under subcooled operating conditions.
5.2 Industrial Heat Exchangers
- Shell-and-coil heat exchangers for process heating and cooling
- Reboilers and condensers in chemical processing plants
- Waste heat recovery systems in power generation and industrial furnaces
5.3 Solar Thermal Systems
Spiral coil tubes are employed as absorber elements in concentrated solar thermal collectors and solar water heating systems, where their high surface-area ratio maximizes solar radiation absorption efficiency.
5.4 Cryogenic Applications
304L/316L stainless steel coil tubes are suitable for cryogenic liquid transfer and storage systems operating at temperatures as low as −196°C (liquid nitrogen temperature), owing to the excellent low-temperature toughness of austenitic stainless steels.
5.5 Food and Pharmaceutical Industry
The hygienic surface finish and corrosion resistance of passivated stainless steel coils make them ideal for pasteurization systems, sterilization equipment, and pharmaceutical process heating/cooling circuits.
6. Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System certification for consistent manufacturing quality
- ISO 14001:2015 — Environmental Management System compliance
- CE Marking — Conformity with European health, safety, and environmental protection standards
- Material Certification: Mill test certificates (MTC) per EN 10204 3.1 for each production batch
- Standards Adherence: ASTM A213, ASME SA-213, EN 10216-5, GB/T 14976, JIS G3447
- Third-Party Inspection: Available upon request (SGS, BV, TUV, or equivalent)
7. Unique Selling Points
- Seamless Continuous Spiral Geometry: Eliminates longitudinal welds, providing superior pressure integrity and reduced thermal resistance compared to bent-tube coil alternatives.
- Research-Validated Performance: Product design informed by peer-reviewed research on dynamic heat release characteristics of subcooled phase change thermal storage systems, ensuring optimized thermal performance.
- Customizable Geometry: Full parametric customization of coil diameter, pitch, tube OD, wall thickness, and total length to match specific system design requirements.
- Wide Material Selection: Multiple stainless steel grades available to address diverse environmental and temperature requirements.
- High Precision Manufacturing: CNC-controlled winding with tight tolerances on coil geometry ensures uniform heat transfer performance across the entire coil assembly.
- Full Traceability: Batch-level material certification and comprehensive inspection documentation for regulatory compliance and quality assurance.
Company: Wenzhou Jixing Metal Materials Co., Ltd.
Product Category: Stainless Steel Coil Tube (Coiltube) — Heat Exchange & Thermal Storage Components
Product Code: No. 239
Application Focus: Phase Change Thermal Energy Storage, Industrial Heat Exchange