Stainless Steel Spiral Coil Tube — Supercritical Fluid Heat Transfer Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Code: 687
1. Product Overview
The Stainless Steel Spiral Coil Tube (hereinafter referred to as "Spiral Coil Tube" or "Coil Tube") is a specialized stainless steel tubing product engineered for high-performance thermal-hydraulic applications, particularly in supercritical fluid (Supercritical Fluid, SCF) heat transfer systems. Unlike conventional straight tubes, the continuous helical geometry of the coil tube introduces secondary flow (Secondary Flow, Dean Vortices) within the annular cross-section, significantly enhancing turbulent heat transfer (Turbulent Heat Transfer) characteristics even at moderate Reynolds numbers.
This product line is specifically designed and validated based on advanced numerical simulation methodologies, including Computational Fluid Dynamics (CFD) analysis of supercritical fluid turbulent heat transfer within spiral coil configurations. The geometric parameters, material selection, and manufacturing tolerances have been optimized to maximize heat transfer efficiency while maintaining structural integrity under extreme thermal and pressure conditions.
2. Material & Properties
2.1 Base Material Grades
- Austenitic Stainless Steel (奥氏体不锈钢): AISI 304 (UNS S30400), AISI 316 (UNS S31600), AISI 316L (UNS S31603)
- High-Temperature Alloys (高温合金): Inconel 625 (UNS N06625), Inconel 718 (UNS N07718) — available upon special order
- Super-Austenitic Grades (超奥氏体等级): Alloy 20 (UNS N08200), Alloy 625 (UNS N06625) — for extreme corrosion environments
2.2 Key Mechanical & Thermal Properties
| Property | 304 Grade | 316L Grade | Unit |
|---|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 | ≥ 485 | MPa |
| Yield Strength (屈服强度, 0.2% offset) | ≥ 205 | ≥ 170 | MPa |
| Elongation (延伸率) | ≥ 40 | ≥ 45 | % |
| Thermal Conductivity (导热系数, 20°C) | 16.3 | 14.6 | W/(m·K) |
| Thermal Conductivity (导热系数, 500°C) | 21.5 | 19.0 | W/(m·K) |
| Specific Heat Capacity (比热容, 20°C) | 500 | 500 | J/(kg·K) |
| Linear Thermal Expansion (线膨胀系数, 20–500°C) | 17.3 | 17.0 | ×10⁻⁶/K |
| Density (密度, 20°C) | 8.00 | 8.03 | g/cm³ |
| Maximum Service Temperature (最高使用温度) | 870 | 870 | °C |
| Corrosion Potential (Cr, %) | 18–20 | 17–19 | % |
| Nickel Content (Ni, %) | 8–10 | 10–14 | % |
2.3 Surface Finish Options
- Pickled & Annealed (酸洗退火, PA): Matte finish, Ra ≤ 0.8 μm
- Mechanically Polished (机械抛光): Ra ≤ 0.4 μm
- Electrolytic Polished (电解抛光, EP): Ra ≤ 0.1 μm — recommended for supercritical fluid applications to minimize surface-induced flow separation
- Passivated (钝化处理): Enhanced corrosion resistance layer, ASTM A967 compliant
3. Technical Specifications
3.1 Geometric Dimensions
| Parameter | Specification Range | Standard/Tolerance |
|---|---|---|
| Outer Diameter (外径, OD) | Φ3.0 mm – Φ50.8 mm | ASTM A269 / ASME B36.19M |
| Wall Thickness (壁厚) | 0.3 mm – 3.0 mm | ±10% of nominal |
| Coil Winding Diameter (盘绕直径) | Φ50 mm – Φ2000 mm | Custom per application |
| Coil Length (盘管长度) | 1 m – 200 m (continuous) | Custom per application |
| Helix Pitch (螺旋节距) | 20 mm – 500 mm | ±0.5 mm tolerance |
| Curvature Ratio (曲率比, D/d) | 10 – 200 | Optimized per thermal-hydraulic requirement |
| Coil Turns (盘圈数) | 1 – 5000 turns | ±1 turn tolerance |
3.2 Thermal-Hydraulic Performance Parameters
| Parameter | Typical Value / Range | Notes |
|---|---|---|
| Enhanced Nusselt Number (增强努塞尔数, Nu/Nu_straight) | 1.5 – 4.0× | Dependent on Dean number (De) and Reynolds number (Re) |
| Applicable Reynolds Number Range (雷诺数范围) | Re = 500 – 500,000 | Turbulent flow regime enhanced by Dean vortices |
| Operating Pressure (工作压力) | Up to 35 MPa | Hydrostatic tested at 1.5× working pressure |
| Operating Temperature Range (工作温度范围) | −196°C to +870°C | Cryogenic to supercritical conditions |
| Pressure Drop Factor (压降系数, f_coil/f_straight) | 1.5 – 3.0× | Trade-off with enhanced heat transfer |
3.3 Applicable Standards & Codes
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing
- ASTM A312 — Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Chromium-Chromium-Nickel Stainless Steel Tubing
- ASME B36.19M — Stainless Steel Pipe
- EN 10216-5 — Heat-Exchanger and Refrigeration Equipment Tubes
- GB/T 12771 — Stainless Steel Seamless Tubes for Fluid Transport
- GB/T 14976 — Seamless Stainless Steel Tubes for Fluid Transport
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Inspection (原材料检验): Incoming stainless steel seamless tube undergoes spectroscopic analysis (Spectroscopic Analysis, OES) to verify chemical composition compliance with ASTM/GB standards. Heat treatment certificates are reviewed.
- Tube Straightening & End Preparation (管材矫直与端部处理): The raw tube is cold-drawn and straightened to achieve dimensional accuracy. End faces are cut perpendicular (±0.5°) and deburred.
- Spiral Coiling (螺旋盘绕成型): The straight tube is coiled onto precision mandrels (Precision Mandrels) using CNC-controlled coiling machines. The coiling process maintains constant curvature ratio (D/d) and helix pitch throughout the entire length, critical for uniform thermal-hydraulic performance.
- Solution Annealing (固溶退火): Post-forming annealing at 1050–1150°C followed by rapid water quenching restores full austenitic structure and eliminates residual stresses introduced during cold coiling. This step is essential for restoring corrosion resistance and mechanical properties.
- Pickling & Passivation (酸洗钝化): Surface oxide scale is removed using a mixed acid solution (nitric acid + hydrofluoric acid). A protective chromium oxide passivation layer is then formed to ensure corrosion resistance.
- Precision Dimensional Inspection (精密尺寸检测): Outer diameter, wall thickness, coil diameter, pitch, and length are verified using Coordinate Measuring Machines (CMM), ultrasonic thickness gauges (Ultrasonic Thickness Gauge, UT), and laser scanning systems.
- Pressure Testing (压力测试): Each coil tube assembly undergoes hydrostatic pressure testing (Hydrostatic Pressure Test) at 1.5× the maximum design pressure for a minimum hold time of 30 seconds, per ASTM A269 requirements.
- Non-Destructive Testing (无损检测, NDT): Eddy current testing (Eddy Current Testing, ECT) and ultrasonic testing (Ultrasonic Testing, UT) are performed to detect internal and surface defects. Radiographic testing (Radiographic Testing, RT) is available for critical applications.
4.2 Process Control & Quality Assurance
The manufacturing process adheres to ISO 9001:2015 Quality Management System requirements. Critical process parameters — including coiling speed, mandrel diameter accuracy, annealing temperature uniformity (±10°C), and cooling rate — are monitored in real-time via SCADA systems. Statistical Process Control (Statistical Process Control, SPC) charts are maintained for key dimensional parameters to ensure consistency across production batches.
5. Applications
5.1 Supercritical Fluid Heat Transfer Systems (超临界流体换热系统)
The spiral coil tube geometry is particularly advantageous for supercritical fluid applications, including supercritical carbon dioxide (Supercritical Carbon Dioxide, sCO₂) power cycles, supercritical water reactors (Supercritical Water Reactor, SCWR), and supercritical methane processes. Numerical simulations (Numerical Simulation) of turbulent heat transfer in spiral coil configurations demonstrate that the Dean vortices generated by the helical curvature enhance near-wall mixing, effectively mitigating the adverse effects of property variations near the pseudocritical temperature (Pseudocritical Temperature). This results in heat transfer enhancement factors of 1.5–4.0× compared to equivalent straight tubes.
5.2 Heat Exchangers (换热器)
- Shell-and-Coil Heat Exchangers (壳盘管换热器): Compact heat exchange units where the spiral coil tube serves as the tube-side or shell-side heat transfer element
- Plate-Fin Coil Heat Exchangers (板翅盘管换热器): High-efficiency air-cooled systems for petrochemical and power generation applications
- Double-Pipe Spiral Heat Exchangers (双管螺旋换热器): Concentric spiral configurations for precise temperature control
5.3 Cryogenic Applications (低温应用)
- Liquefied Natural Gas (Liquefied Natural Gas, LNG) processing systems
- Liquid Oxygen/Nitrogen/Hydrogen storage and distribution
- Cryogenic pump manifolds and cold boxes
5.4 Other Industrial Applications (其他工业应用)
- Chemical process reactors and reboilers (化学工艺反应器与再沸器)
- Pharmaceutical and food-grade fluid transport (食品级流体输送)
- Oil and gas industry — subsea umbilicals and flow lines (海底脐带与管线)
- Nuclear power plant instrumentation and control piping (核电站仪表与控制管路)
- Solar thermal power plant heat collection loops (太阳能热发电集热环路)
6. Unique Selling Points (独特卖点)
- CFD-Validated Geometry: Coil tube dimensions are optimized based on validated numerical simulations of supercritical fluid turbulent heat transfer, ensuring peak thermal-hydraulic performance for specific operating conditions.
- Enhanced Heat Transfer Efficiency: The helical geometry generates Dean vortices (Dean Vortices) that intensify turbulent mixing, providing 50–300% heat transfer enhancement over straight tubes at equivalent Reynolds numbers.
- Compact Footprint: The coiled configuration achieves high heat transfer surface area within a minimal installation volume, ideal for space-constrained applications.
- Full Process Traceability: Every coil tube is traceable from raw material heat number through all manufacturing stages to final inspection, with complete documentation packages.
- Wide Material Range: Availability