Stainless Steel Coil Tube (Double Helical Coil) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered coiled tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for applications in thermal energy storage systems, heat exchangers, and phase change heat management equipment. The coil tube geometry provides an exceptionally high surface-area-to-volume ratio, enabling efficient heat transfer and compact system design. The product is available in single-helix and double-helical coil configurations, with the double helical variant offering superior thermal performance for advanced phase change thermal energy storage (PCTES) applications.
The coil tube is fabricated from austenitic stainless steel grades, ensuring excellent corrosion resistance, mechanical integrity across a wide temperature range, and long-term operational reliability in demanding industrial environments. The product is engineered to meet the rigorous demands of energy storage, HVAC, and process engineering sectors.
2. Material & Properties
2.1 Available Material Grades
- SAE 304 (UNS S30408): The standard austenitic stainless steel offering excellent corrosion resistance, formability, and weldability. Suitable for general-purpose thermal applications.
- SAE 316 (UNS S31608): Enhanced corrosion resistance with the addition of molybdenum (Mo), ideal for chloride-rich environments and aggressive chemical service.
- SAE 316L (UNS S31603): Low-carbon variant of 316 with improved weldability and resistance to intergranular corrosion.
- SAE 321 (UNS S32108): Titanium-stabilized grade for high-temperature applications up to 870°C (1600°F).
- SAE 347 (UNS S34708): Niobium-stabilized grade for sustained high-temperature service with excellent resistance to intergranular corrosion.
2.2 Key Material Properties (SAE 304 Reference Values)
- Maximum Service Temperature: 870°C (1600°F) in continuous air
- Minimum Service Temperature: -196°C (-321°F) with retained ductility
- Tensile Strength (Annealed): ≥ 515 MPa (74.7 ksi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29.7 ksi)
- Elongation: ≥ 40%
- Thermal Conductivity (100°C): 16.3 W/(m·K)
- Specific Heat (100°C): 0.502 J/(g·K)
- Linear Thermal Expansion (20–100°C): 17.3 × 10⁻⁶ /°C
- Density: 8.00 g/cm³
- Magnetic Permeability: Non-magnetic (μᵣ ≤ 1.05 after cold work ≤ 10%)
2.3 Chemical Composition (SAE 304, wt%)
| Element | C | Si | Mn | P | S | Cr | Ni | N |
|---|---|---|---|---|---|---|---|---|
| Maximum | 0.08 | 1.00 | 2.00 | 0.045 | 0.030 | — | — | 0.10 |
| Minimum | — | — | — | — | — | 18.0 | 8.0 | — |
3. Product Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Product Type | Single-Helix Coil Tube / Double-Helical Coil Tube | — |
| Outer Diameter (OD) | 3.0 – 50.8 (1/8" – 2") | mm |
| Wall Thickness | 0.3 – 3.0 | mm |
| Coil Pitch | 5.0 – 100.0 (customizable) | mm |
| Coil Diameter | 100 – 2000 (customizable) | mm |
| Coil Length / Turns | Up to 5000 (customizable per order) | mm / turns |
| Surface Finish | Mirror (Ra ≤ 0.25 μm), Satin, Bright Annealed, No.4 Finish | — |
| Tolerance (OD) | ±0.05 – ±0.20 | mm |
| Tolerance (Wall Thickness) | ±0.03 – ±0.10 | mm |
| Operating Temperature Range | -196 to +870 | °C |
| Maximum Working Pressure | Up to 16 (depends on OD and wall thickness) | MPa |
| Double-Helix Configuration | Inner coil OD 3–20 mm; Outer coil OD 50–200 mm; Gap 5–30 mm | mm |
| Available Grades | SAE 304, 304L, 316, 316L, 321, 347 | — |
| End Finishing | Plain, Flanged, Threaded, Welded Fittings, Beveled | — |
| Customization | Full custom dimensions, geometry, and configuration available | — |
4. Manufacturing Process
The production of high-precision stainless steel coil tubes follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, surface integrity, and mechanical performance:
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Raw Material Selection and Inspection:
Virgin stainless steel wire or strip of certified grades is procured from accredited mills. Incoming material undergoes spectroscopic composition analysis (OES), mechanical property verification, and surface defect inspection prior to acceptance.
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Wire/Strip Drawing and Annealing:
Stainless steel wire or strip is cold-drawn to the required intermediate diameter. Periodic solution annealing (1050–1150°C) is performed to restore ductility and eliminate work hardening, ensuring uniform microstructure and mechanical properties.
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Seamless Tube Forming or Welded Tube Fabrication:
Depending on specifications, tubes are produced via cold-rolled seamless forming (for OD ≤ 50.8 mm) or high-frequency induction welding (HF-W) followed by internal/external grinding to achieve seamless-equivalent internal surface quality.
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Cold Coiling / Helical Forming:
Precision CNC-controlled coiling machines wind the tube into single-helix or double-helical configurations. The forming process employs controlled bending with internal mandrel support to prevent ovality, wrinkling, and wall thinning. Coil pitch, diameter, and turn count are controlled to ±0.5% tolerance.
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Stress Relief Annealing:
Post-forming stress relief annealing at 400–500°C eliminates residual bending stresses, ensuring dimensional stability during subsequent heat treatment and service. This step is critical for maintaining geometric accuracy in precision thermal applications.
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Surface Treatment:
Coil tubes undergo pickling and passivation (nitric acid/hydrofluoric acid solution) to remove oxide scale and form a protective chromium oxide film. Optional electropolishing or mechanical polishing achieves mirror-finish surfaces (Ra ≤ 0.25 μm) for enhanced hygienic and corrosion performance.
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Quality Control and Testing:
Each batch undergoes comprehensive inspection including: dimensional verification (CMM or laser measurement), hydrostatic pressure testing (1.5× working pressure), surface roughness measurement, and magnetic particle or dye penetrant inspection for defect detection.
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Packaging and Delivery:
Finished coil tubes are individually wrapped in protective film, placed in moisture-absorbent packaging, and secured in wooden crates or custom shipping containers to prevent mechanical damage during transit.
5. Applications
5.1 Primary Application Domains
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Phase Change Thermal Energy Storage (PCTES):
The double helical coil configuration is particularly optimized for use in latent heat thermal energy storage systems. The nested double-helix geometry maximizes the heat exchange surface area while maintaining structural compactness, enabling efficient charging and discharging of phase change materials (PCMs) such as paraffin waxes, salt hydrates, and metal alloys. This configuration has been demonstrated to improve heat transfer coefficients by 30–60% compared to conventional single-tube designs.
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Heat Exchangers and Refrigeration Systems:
Coil tubes serve as the core heat transfer elements in shell-and-coil heat exchangers, air-cooled condensers, evaporators, and refrigeration coil assemblies. The high surface-area-to-volume ratio facilitates efficient thermal exchange in both sensible and latent heat transfer modes.
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Industrial Process Heating and Cooling:
Used in chemical processing, petrochemical, and pharmaceutical industries for precise temperature control of process fluids, reactors, and heat recovery systems.
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Geothermal and Solar Thermal Systems:
Coil tubes are employed as heat collectors in borehole geothermal heat exchangers and solar thermal collectors, leveraging the corrosion resistance of stainless steel for long-term outdoor and subterranean service.
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Food and Beverage Industry:
Sanitary-grade mirror-finish coil tubes (Ra ≤ 0.25 μm) are used in dairy processing, brewing, and beverage pasteurization systems where hygienic standards (EHEDG, 3-A) are mandated.
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Automotive and Aerospace Thermal Management:
Compact coil tube assemblies are integrated into vehicle thermal management systems, including battery cooling, cabin HVAC, and engine oil cooling circuits.
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Medical and Laboratory Equipment:
Precision coil tubes are used in autoclaves, sterilizers, laboratory heating mantles, and medical imaging equipment cooling loops.
5.2 Double Helical Coil — Unique Performance Advantages
The double helical coil configuration, as studied in the research on "Double Helical Coil Phase Change Heat Storage Optimization," offers distinct performance advantages:
- Enhanced Heat Transfer Coefficient: The dual-coil arrangement creates a confined annular flow channel that promotes turbulent flow at lower Reynolds numbers, increasing the Nusselt number (Nu) and overall heat transfer efficiency.
- Reduced Thermal Resistance: The close coupling between inner and outer coils minimizes the thermal conduction path through the phase change material, reducing thermal resistance by up to 40%.
- Compact Design: The nested geometry achieves the same heat transfer area in a footprint 50–70% smaller than equivalent parallel-tube arrays.
- Uniform Heat Distribution: The helical winding promotes uniform radial temperature distribution, mitigating the thermal stratification issues common in single-tube designs.
- Scalability: The modular double-helix design scales linearly with system requirements, from laboratory-scale prototypes to industrial mega-watt installations.
6. Quality Certifications and Standards Compliance
6.1 International Standards
- ASTM A213 / A269: Standard specification for austenitic stainless steel seamless, welded, and heavily cold-worked austenitic stainless steel tubing.
- EN 10216-5 / EN 10217-7: European standard for welded and cold-drawn austenitic stainless steel tubes.
- ASME BPV Section VIII: Compliance for pressure vessel and heat exchanger applications.
- ISO 15496: Mechanical properties of cold-drawn austenitic stainless steel wire.
- ASTM A312: Specification for seamless and welded austenitic stainless steel tubes for chemical and heat-transfer equipment.
6.2 Quality Management Certifications
- ISO 9001:20