Stainless Steel Spiral Coil Tube — Technical Specification
Product Overview
The Stainless Steel Spiral Coil Tube (catalog reference: No. 895) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for thermal exchange applications, leveraging the inherent advantages of helically wound stainless steel tubing to achieve superior convective heat transfer coefficients compared to conventional straight-tube heat exchangers. The spiral coil geometry induces secondary flow patterns—namely Dean vortices—that enhance turbulent mixing within the tube bore, thereby significantly increasing the Nusselt number and overall heat transfer effectiveness.
This product line draws upon advanced research findings regarding the flow and heat transfer performance of novel spiral coil heat exchangers, incorporating optimized coil pitch, curvature radius, and wall thickness parameters to maximize thermal efficiency while maintaining acceptable pressure drop characteristics. The product is suitable for use in air-source heat pump systems, solar thermal collectors, industrial process heating, and cryogenic applications.
Material & Properties
Material Grades
- AISI 304 / 1.4301 (CF8M): Austenitic stainless steel offering excellent corrosion resistance, formability, and weldability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316 / 1.4401 (CF3M): Enhanced austenitic grade with 2–3% Molybdenum (Mo) addition, providing superior resistance to pitting and crevice corrosion in chloride-containing environments.
- AISI 321 / 1.4541 (CF8C): Titanium-stabilized austenitic grade suitable for elevated-temperature applications up to 870°C (1598°F), with resistance to intergranular corrosion.
Mechanical Properties (AISI 304, Annealed Condition)
- Tensile Strength (UTS): ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Density: 8.0 g/cm³ (0.289 lb/in³)
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
Corrosion Resistance
The passive chromium oxide film (Cr₂O₃) formed on the surface provides self-healing protection against atmospheric and aqueous corrosion. The product exhibits a Pitting Resistance Equivalent Number (PREN) of ≥ 19 for Grade 304 and ≥ 24 for Grade 316, ensuring long-term service life in aggressive environments.
Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 19 mm (customizable) |
| Tube Wall Thickness | 0.5 mm – 2.0 mm |
| Coil Inner Diameter (Helix Diameter) | 40 mm – 200 mm |
| Coil Pitch (Helix Spacing) | 10 mm – 40 mm |
| Coil Length (Developed) | 1 m – 50 m (customized per order) |
| Surface Finish | Bright Annealed (BA), Pickled & Passivated (PP), or Polished (Ra ≤ 0.4 μm) |
| Curvature Ratio (D/d) | ≥ 4.0 (optimized for heat transfer enhancement) |
| Dimensional Tolerance | ±0.1 mm (OD), ±0.05 mm (wall thickness) |
| Operating Temperature Range | −196°C to +600°C (Grade 304); up to +870°C (Grade 321) |
| Maximum Operating Pressure | 1.5 MPa (typical); up to 4.0 MPa for thick-wall configurations |
| Standard Reference | ASTM A269, ASTM A270, EN 10217-7, GB/T 12771 |
Manufacturing Process
- Raw Material Inspection: Cold-rolled stainless steel strip or seamless tubing is received with mill certification (MTC) and subjected to spectrographic analysis (OES), confirming chemical composition compliance with the specified grade.
- Cut-off and Forming: Continuous stainless steel tubing is cut to required length and fed into a rotary-die forming machine. The tubing is progressively bent around a mandrel to achieve the desired helical pitch and coil diameter with controlled plastic deformation.
- Heat Treatment (if required): For coils exhibiting work-hardening during forming, a solution annealing treatment at 1050–1100°C followed by rapid air or water quenching restores full austenitic microstructure and ductility.
- Pickling and Passivation: The formed coil is immersed in a mixed acid solution (HNO₃/HF) to remove scale and contaminants, followed by a nitric acid passivation step to regenerate the protective chromium oxide layer.
- End Finishing: Tube ends are deburred, beveled, and prepared for welding or flaring connections. Optional end fittings (threaded, flanged, or socket-weld) may be applied.
- Quality Inspection: Each coil undergoes dimensional verification (caliper and micrometer measurement), visual inspection for surface defects, and optional hydrostatic pressure testing (1.5× working pressure) to ensure leak-tight integrity.
Applications
- Air-Source Heat Pumps (ASHP): Spiral coil tubes serve as evaporator/condenser elements, exploiting the enhanced heat transfer from turbulent secondary flow to improve Coefficient of Performance (COP).
- Solar Thermal Collectors: Used as absorber tubes in evacuated tube and flat-plate collectors, where high surface-area-to-volume ratio maximizes solar energy absorption.
- Industrial Process Heat Exchangers: Applied in shell-and-coil exchangers for chemical processing, food and beverage pasteurization, and pharmaceutical sterilization.
- Cryogenic Systems: Grade 304/321 coils are employed in LNG (Liquefied Natural Gas) vaporizers and liquid nitrogen storage systems where low-temperature ductility is critical.
- Refrigeration and HVAC: Compact spiral coils used in evaporators, condensers, and intermediate coolers for space-constrained installations.
- Waste Heat Recovery: Spiral coil configurations deployed in flue gas heat recovery units to capture low-grade thermal energy efficiently.
Quality Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent manufacturing quality and process control.
- ISO 14001:2015 — Environmental Management System certification for sustainable production practices.
- EN 10204 3.1 — Material Test Certificate (MTC) with third-party inspection verification for each batch.
- CE Marking — Compliance with European Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing applications.
- ASTM/ASME Compliance — Products manufactured and tested in accordance with ASTM A269/A270 and ASME B31.3 process piping standards.
- GB/T 12771 — Compliance with Chinese national standard for stainless steel seamless tubes and pipes.
Unique Selling Points
- Enhanced Heat Transfer Performance: The helical geometry generates Dean vortices that increase the local Reynolds number and disrupt the thermal boundary layer, achieving 30–50% higher heat transfer coefficients compared to equivalent straight tubes at the same flow rate.
- Compact Design: High surface-area-to-volume ratio enables significant thermal duty in minimal installation footprint, ideal for space-constrained applications.
- Corrosion Resistant Longevity: Austenitic stainless steel construction ensures service life exceeding 20–30 years in aggressive environments without degradation of thermal performance.
- Low Fouling Tendency: Enhanced turbulence promotes self-cleaning action, reducing maintenance intervals and operational downtime.
- Customizable Geometry: Coil diameter, pitch, and tube dimensions are tailored to specific thermal-hydraulic requirements, enabling optimized system integration.
- Low-Temperature Capability: No ductile-to-brittle transition in austenitic microstructure ensures reliable performance down to cryogenic temperatures (−196°C).
Note: This product specification is based on research findings from the study "Investigation on Flow and Heat Transfer Performance of Novel Spiral Coil Heat Exchangers", which demonstrates that optimized spiral coil configurations with curvature ratios (D/d) between 4.0 and 8.0 and dimensionless pitch parameters yield the best compromise between heat transfer enhancement and acceptable pressure drop penalty. Wenzhou Jixing Metal Materials Co., Ltd. incorporates these validated design parameters into their production specifications to deliver thermally superior coil tube products.