Stainless Steel Coil Tube — Low-Flow Heat Exchanger Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: JX-611
Category: Heat Exchanger Components / Coil Tubing
1. Product Overview
The JX-611 Stainless Steel Coil Tube is a precision-engineered helically wound tube designed for integration into shell-and-tube heat exchangers, air-cooled heat exchangers, and compact thermal management systems operating under low-flow-rate conditions. This product line has been extensively studied and validated for its performance characteristics regarding external convective heat transfer (External Convective Heat Transfer) under conditions of low Reynolds number flow and induced mechanical vibration.
Coil tubes offer significant advantages over straight tubes in heat exchange applications due to their compact geometry, enhanced surface-to-volume ratio, and the secondary flow patterns generated within the helical curvature. The centripetal acceleration induced by the helical winding creates a Dean number-dependent secondary circulation, which intensifies turbulence and improves the overall heat transfer coefficient even at low flow velocities where conventional straight tubes would exhibit laminar or transitional flow regimes.
Research conducted on this product series — specifically the study titled "Research on the Effect of Coil Tube Vibration on External Convective Heat Transfer at Low Flow Velocity" — has demonstrated that controlled mechanical vibration of coil tubes can further augment external convective heat transfer coefficients by disrupting thermal boundary layers and promoting fluid mixing in the annular region surrounding the helical bundle.
2. Material & Properties
2.1 Base Material Options
- Austenitic Stainless Steels: SUS304 (UNS S30400), SUS316 (UNS S31600), SUS316L (UNS S31603)
- Duplex Stainless Steels: SUS31803 (UNS S31803), SUS2205 (UNS S31803)
- Super Duplex: UNS S32750 (for high-pressure and high-temperature applications)
- Heat-Resistant Grades: SUS310S (UNS S31008), Inconel 625 (UNS N06625) — available upon special order
2.2 Mechanical Properties (Typical — Cold-Wound Condition)
| Property | SUS304 (UNS S30400) | SUS316L (UNS S31603) | SUS321 (UNS S32100) |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 | ≥ 485 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ≥ 170 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HV) | ≤ 210 | ≤ 210 | ≤ 210 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 14.6 | 16.3 |
| Thermal Expansion Coefficient (×10⁻⁶/K) | 17.3 | 16.0 | 17.3 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | −196 to +1150 |
| Maximum Design Pressure (MPa) | 15 (standard) | 15 (standard) | 20 (special) |
2.3 Corrosion Resistance
- SUS304 grade provides excellent resistance to atmospheric corrosion, dilute acids, and organic compounds
- SUS316L grade offers superior resistance to pitting and crevice corrosion in chloride-containing environments (Pitting Resistance Equivalent Number, PREN ≥ 24)
- SUS321 grade is stabilized against intergranular corrosion through titanium stabilization (Ti ≥ 4.75×C)
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 6.0 mm – 38.1 mm (¼" – 1½") |
| Tube Wall Thickness | 0.5 mm – 3.0 mm (precision tolerance ±0.05 mm) |
| Helical Coil Diameter (Center-to-Center) | 50 mm – 500 mm |
| Coil Pitch (Helix Spacing) | 10 mm – 50 mm (customizable) |
| Number of Turns | 3 – 200 turns |
| Coil Length (Unwound) | Up to 120 m continuous |
| Surface Finish | 2B, BA (Bright Annealed), or Electropolished (Ra ≤ 0.4 μm) |
| End Treatment | Plain, Beveled, Flared, Threaded, or Weld-Prepared |
| Winding Tolerance | Diameter: ±0.5 mm; Pitch: ±0.3 mm |
| Applicable Standards | ASTM A213, ASTM A269, EN 10216-5, JIS G3459, GB/T 14976 |
| Heat Treatment | Solution Annealed + Water Quenched; Optional Stress-Relief Annealing |
| Non-Destructive Testing (NDT) | 100% Eddy Current Inspection; Radiographic Testing (RT) upon request |
4. Manufacturing Process
4.1 Process Flow
- Material Preparation: Selection of certified seamless or welded stainless steel tube stock conforming to the specified grade and dimensions. Incoming material undergoes chemical composition verification (OES) and mechanical property testing.
- Surface Cleaning & Degreasing: Solvent cleaning and acid pickling to remove scale, oxide, and surface contaminants prior to forming.
- Helical Winding: Precision CNC-controlled coil winding using a mandrel-forming technique. The tube is wound around a calibrated mandrel at a controlled feed rate to ensure uniform helix geometry, consistent wall thickness, and minimal residual stress.
- Welding of Coil Joints: Where continuous length requirements exceed single-length tube stock, orbital TIG welding (Tungsten Inert Gas) is employed with internal gas shielding (Argon, 99.99% purity) to maintain metallurgical integrity at the weld joint.
- End-Fixing Welds: The coil ends are welded to inlet/outlet headers or connection fittings using precision orbital welding or manual TIG welding with full-penetration welds.
- Heat Treatment: Solution annealing at 1050–1150°C followed by rapid water quenching to restore full austenitic microstructure and maximize corrosion resistance. Optional stress-relief annealing at 420–500°C for vibration-critical applications.
- Pickling & Passivation: Immersion in mixed acid solution (HNO₃/HF) followed by nitric acid passivation to establish a protective chromium oxide film (Cr₂O₃) on the surface.
- Quality Inspection: 100% dimensional inspection (OD, wall thickness, coil diameter, pitch), eddy current testing for wall thickness uniformity and defect detection, and hydrostatic pressure testing at 1.5× design pressure.
4.2 Vibration Characterization Protocol
For coil tubes intended for applications involving mechanical vibration (e.g., pump-driven systems, reciprocating machinery, or flow-induced vibration scenarios), an additional vibration characterization protocol is available:
- Modal analysis to determine natural frequencies of the coil assembly
- Vibration amplitude measurement under simulated operating conditions
- Thermal performance testing under controlled vibration amplitudes (0.05 mm – 2.0 mm) and frequencies (10 Hz – 200 Hz)
- Boundary layer disruption analysis to quantify enhancement of external convective heat transfer coefficient (Nu number enhancement)
5. Applications
5.1 Primary Application Domains
- Shell-and-Tube Heat Exchangers: Coil tubes serve as the internal heat transfer surface within shell-and-tube configurations, providing compact design and enhanced thermal performance in low-flow-rate service.
- Air-Cooled Heat Exchangers (ACHE): Helical coil arrangements maximize heat transfer area within limited footprint, suitable for process cooling and refrigeration.
- Refrigeration & HVAC Systems: Evaporator and condenser coils for industrial refrigeration, heat pump systems, and chiller units.
- Chemical Processing: Reactor cooling coils, distillation column condensers, and heat recovery systems in petrochemical and pharmaceutical plants.
- Food & Beverage Industry: Pasteurization, sterilization, and heat recovery systems requiring sanitary-grade (electropolished) surfaces.
- Marine & Offshore: Seawater coolers, condensate recovery systems, and platform heat exchangers.
- Power Generation: Feedwater heaters, condensers, and waste heat recovery systems in combined-cycle power plants.
- Low-Flow Thermal Management: Systems where fluid velocity is inherently low (e.g., gravity-fed systems, natural circulation loops), where coil geometry provides essential enhancement of heat transfer via Dean vortex mechanisms.
5.2 Vibration-Enhanced Heat Transfer Applications
Based on research findings regarding coil tube vibration effects at low flow rates, this product is particularly suited for applications where:
- Flow velocity is below the critical threshold for turbulent transition in straight tubes (Re < 2300)
- Additional heat transfer enhancement is required without increasing pumping power
- Mechanical vibration is inherent to the operating environment (e.g., adjacent to compressors, pumps, or reciprocating equipment)
- Fouling resistance reduction is desired through vibration-induced boundary layer disruption
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering all manufacturing processes |
| ISO 14001:2015 | Environmental Management System |
| ASME Stamp | Section VIII Div. 1 (upon request) for pressure vessel components |
| TÜV Certification | Independent third-party quality audit |
| Material Traceability | Full mill certification (EN 10204 3.1) with heat number traceability |
| Hydrostatic Testing | 100% tested at 1.5× design pressure, minimum hold time 30 seconds |
| Eddy Current Testing | 100% inline inspection per ASTM E309 / ASTM E709 |
| Weld Inspection | Visual (VT) 100%; Radiographic Testing (RT) or Ultrasonic Testing (UT) per ASME Section V |
7. Unique Selling Points
Research-Validated Performance: The JX-611 Coil Tube series is backed by published research demonstrating measurable enhancement of external convective heat transfer coefficients under low-flow vibration conditions. This provides engineering confidence in performance predictions for challenging low-velocity applications.
- Enhanced Heat Transfer at Low Flow Rates: The helical geometry inherently generates Dean vortices that improve convective heat transfer by 30–80% compared to equivalent straight tubes at the same flow rate, making this product ideal for applications where high pumping power is undesirable or impractical.
- Vibration-Robust Design: Engineered to maintain structural integrity and thermal performance under mechanical vibration, with optional stress-relief annealing to minimize fatigue risk in dynamic service.
- Compact Thermal Performance: Achieves high heat transfer area density within minimal volumetric footprint, reducing equipment size and installation space requirements.
- Multi-Grade Material Availability: From standard austenitic grades to super duplex and nickel-based alloys, covering service conditions from cryogenic to high-temperature and from mild to severely corrosive environments.
- Full Traceability & Quality Assurance: Every coil tube is accompanied by complete mill certificates, dimensional reports, NDT documentation, and hydrostatic test records.
- Customization Capability