Stainless Steel Spiral Coil Tube (Coiltube) — Model No. 374
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Category: Literature Study Reference — Thermal Energy Systems
1. Product Overview
The Stainless Steel Spiral Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular component characterized by its continuous helical winding geometry. This product is specifically designed for high-efficiency thermal exchange applications, particularly within concentrated solar thermal systems, where it functions as an internal heat absorption medium inside dish-type solar collectors. The spiral configuration maximizes the surface-area-to-volume ratio, thereby enhancing convective and radiative heat transfer performance within compact spatial constraints.
Based on the academic research documented in "Numerical Study on Photothermal Characteristics of Dish Solar Collector with Built-in Spiral Coil Tube", this product represents a critical component in advanced photothermal energy harvesting systems. The coil tube serves as the primary working fluid conduit, absorbing concentrated solar radiation and transferring thermal energy to the working fluid (typically water, thermal oil, or supercritical CO₂) through a combination of direct solar absorption and convective heat exchange.
2. Material & Properties
The Coiltube is manufactured from high-grade austenitic stainless steel, selected for its exceptional combination of thermal conductivity, corrosion resistance, and mechanical integrity under cyclic thermal loading conditions.
- Primary Material Grade: SUS304 / AISI 304 (1.4301) — General-purpose austenitic stainless steel with superior corrosion resistance and formability
- High-Temperature Grade Option: SUS310S / AISI 310S (1.4845) — Enhanced creep resistance for prolonged operation at temperatures exceeding 800°C
- High-Conductivity Option: SUS321 / AISI 321 (1.4541) — Titanium-stabilized variant for applications requiring resistance to intergranular corrosion at elevated temperatures
Key Material Properties
| Property | SUS304 | SUS310S | SUS321 |
|---|---|---|---|
| Density (kg/m³) | 7,900 | 8,000 | 7,900 |
| Thermal Conductivity at 20°C (W/m·K) | 16.3 | 21.5 | 16.3 |
| Thermal Conductivity at 500°C (W/m·K) | 21.5 | 31.0 | 21.5 |
| Specific Heat Capacity at 20°C (kJ/kg·K) | 0.50 | 0.50 | 0.50 |
| Maximum Service Temperature (°C) | 870 | 1,150 | 900 |
| Tensile Strength (MPa, annealed) | ≥520 | ≥520 | ≥520 |
| Yield Strength (MPa, annealed) | ≥205 | ≥205 | ≥205 |
| Corrosion Resistance (acid dew point) | Good | Excellent | Excellent |
| Coefficient of Thermal Expansion (10⁻⁶/K, 20–800°C) | 18.0 | 18.6 | 18.0 |
3. Technical Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Tube Outer Diameter (OD) | 8 – 50 (customizable) | mm |
| Tube Wall Thickness | 0.5 – 3.0 | mm |
| Coil Pitch (center-to-center) | 10 – 80 | mm |
| Coil Diameter (mean) | 50 – 600 | mm |
| Helix Angle (from axis) | 5° – 45° | ° |
| Total Coil Length (unwound) | 1.0 – 50.0 | m |
| Number of Turns | 5 – 500 | — |
| Surface Finish (inner) | Electropolished / Ra ≤ 0.4 μm | — |
| Surface Finish (outer) | Mirror polished / Ra ≤ 0.2 μm (selective coating available) | — |
| Pressure Rating (working) | Up to 25.0 (at 200°C) | MPa |
| Hydrostatic Test Pressure | 1.5 × Working Pressure | MPa |
| Operating Temperature Range | −196 to +870 (SUS304) / +1,150 (SUS310S) | °C |
| Connection Method | Butt-weld, Socket-weld, Flanged, or Threaded (NPT/BSP) | — |
| Coating Options | None / Selective absorber coating (Al₂O₃, TiO₂, CuCrN, etc.) | — |
| Standard Compliance | ASTM A269, ASTM A270, EN 10217, JIS G3459 | — |
4. Manufacturing Process
The production of the Stainless Steel Spiral Coil Tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and optimal thermal performance:
- Raw Material Selection & Verification: Cold-rolled stainless steel strip or seamless tube stock is procured from certified mills. Each batch undergoes spectroscopic analysis (OES) and mechanical testing to verify compliance with the specified grade requirements.
- Tube Forming / Pipe Drawing: Seamless tubes are drawn to the required outer diameter and wall thickness through multi-pass cold or hot drawing operations. Dimensional tolerance is maintained within ±0.05 mm.
- Solution Annealing: Tubes are solution-annealed at 1,050–1,100°C followed by rapid water quenching to achieve a fully austenitic microstructure, eliminating residual stresses and ensuring maximum corrosion resistance.
- Spiral Coiling (Helical Winding): The straight tube is wound into a precise helical geometry using CNC-controlled coil winding machinery. The coiling process employs computerized tension control to prevent cross-sectional deformation, ovality, or work-hardening. Real-time laser measurement ensures coil pitch and diameter accuracy within ±0.5 mm tolerance.
- Stress Relief Annealing: Post-coiling stress relief is performed at 450–550°C to recover ductility and eliminate residual stresses introduced during the forming operation, without sensitization of the microstructure.
- Surface Treatment:
- Electropolishing: Applied to the inner bore to achieve a mirror finish (Ra ≤ 0.4 μm), reducing flow resistance and preventing fouling in high-temperature fluid applications.
- Selective Absorber Coating: For solar thermal applications, a high-absorptance, low-emissivity coating (e.g., CuCrN, Al₂O₃, or TiO₂-based ceramic coatings) is applied via Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD) to maximize solar absorption efficiency (α ≥ 0.95) while minimizing thermal radiation losses (ε ≤ 0.10).
- End Preparation & Connection Fitting: Tube ends are cut to precise lengths, deburred, and prepared for the selected connection method (welding, threading, or flanging).
- Quality Inspection & Testing:
- Visual inspection and dimensional verification using Coordinate Measuring Machine (CMM)
- Hydrostatic pressure testing at 1.5× working pressure
- Helium leak detection for vacuum integrity verification
- Spectroscopic chemical composition analysis
- Surface coating thickness and adhesion testing (for coated variants)
- Thermal cycling endurance testing (−196°C to +870°C, 1,000 cycles)
5. Applications
The Stainless Steel Spiral Coil Tube is engineered for demanding thermal and energy systems where compact heat exchange geometry, high-temperature tolerance, and long service life are paramount:
- Concentrated Solar Thermal (CST) Systems: Primary application in dish-type and parabolic trough solar collectors, where the coil tube serves as the internal heat absorption medium. Numerical studies confirm that spiral coil configurations achieve thermal efficiencies of 65–82% in dish collector systems with focal temperatures up to 600°C.
- Industrial Heat Exchangers: Shell-and-coil heat exchangers for chemical processing, petrochemical, and pharmaceutical industries requiring compact, high-efficiency thermal exchange surfaces.
- Supercritical Power Generation: Supercritical CO₂ (sCO₂) Brayton cycle power plants, where the coil tube operates as a primary heat exchanger component at temperatures exceeding 500°C and pressures above 20 MPa.
- Refrigeration & Cryogenic Systems: Expansion coils and evaporator assemblies for industrial refrigeration plants and cryogenic liquefaction facilities.
- Automotive & Aerospace Thermal Management: Compact heat rejection coils for waste heat recovery systems, battery thermal management, and onboard cooling loops in electric vehicles and aerospace platforms.
- Nuclear Energy Systems: Intermediate heat exchanger (IHX) components for Generation IV nuclear reactor concepts (e.g., High-Temperature Gas-Cooled Reactors, HTGR) requiring corrosion-resistant, radiation-tolerant coil assemblies.
- Food & Beverage Processing: Sanitary-grade heating and cooling coils for pasteurization, sterilization, and thermal processing equipment (FDA-compliant 304/316L grades).
- Geothermal Energy Systems: Downhole heat exchanger coils for enhanced geothermal systems (EGS) and binary cycle power plants.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — Ensures consistent product quality and customer satisfaction through systematic process control |
| ISO 14001:2015 | Environmental Management System — Demonstrates commitment to sustainable manufacturing practices and environmental protection |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| CE Marking | European Conformity — Compliance with applicable EU directives for pressure equipment and machinery |
| EN 10204 3.1 | Material Test Certificate — Full traceability of material origin, composition, and mechanical properties |
| ASTM A269 / A270 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe/Tubing for Chemical and Fossil Fuel Industry |
| EN 10217-7 / EN 10217-8 | European Standard for Stainless Steel Tubes for Pressure Purposes |
| ASME BPV Code Section I | Boiler and Pressure Vessel Code compliance for pressure-containing components |
| TÜV Rheinland | Independent third-party quality and safety certification |
| RoHS / REACH | Compliance with European restrictions on hazardous substances and chemical regulations |
7. Unique Selling Points
- Superior Thermal Performance: The optimized helical geometry, validated through computational fluid dynamics (CFD) and numerical photothermal modeling, delivers up to 35% higher heat transfer coefficient compared to straight-tube configurations of equivalent surface area.
- Enhanced Fouling Resistance: The spiral flow pattern induces secondary Dean vortices that continuously disrupt boundary layer formation, significantly reducing fouling accumulation and maintaining thermal efficiency over extended service