Spiral Coil Tube (Coil Tube) — Stainless Steel Heat Transfer Coiling System
Product Overview
The Spiral Coil Tube (Coil Tube) is a precision-engineered stainless steel tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for thermal exchange applications, including spiral coil water tank systems, heat recovery units, and industrial heating/cooling circuits. The coil tube is formed from high-grade austenitic stainless steel wire or seamless tube, wound into a helical or spiral geometry that maximizes the surface-area-to-volume ratio, thereby enhancing convective and conductive heat transfer efficiency.
Based on extensive research into heat transfer characteristics of spiral coil tube water tanks under varying operating modes, this product has been optimized for superior thermal performance across both laminar and turbulent flow regimes. The helical geometry inherently induces secondary flow patterns (Dean vortices), which disrupt the thermal boundary layer and promote uniform heat distribution, resulting in significantly improved heat transfer coefficients compared to straight-tube configurations.
Material & Properties
Material Grades
- SUS304 / AISI 304 (1.4301): General-purpose austenitic stainless steel with excellent corrosion resistance, formability, and weldability. Suitable for most aqueous and atmospheric environments.
- SUS316 / AISI 316 (1.4401): Enhanced molybdenum-bearing austenitic grade offering superior resistance to pitting and crevice corrosion, particularly in chloride-containing or marine environments.
- SUS321 / AISI 321 (1.4541): Titanium-stabilized grade for elevated-temperature service, resisting sensitization and intergranular corrosion up to 870 °C.
- SUS316L / AISI 316L (1.4435): Low-carbon variant of 316 for improved weldability and resistance to sensitization in welded assemblies.
Mechanical Properties (Typical for SUS304)
- Tensile Strength (抗拉强度): ≥ 520 MPa
- Yield Strength (屈服强度): ≥ 205 MPa
- Elongation (延伸率): ≥ 40%
- Density (密度): 7.93 g/cm³
- Thermal Conductivity (热导率): 16.3 W/(m·K) at 100 °C
- Specific Heat Capacity (比热容): 500 J/(kg·K)
- Thermal Expansion Coefficient (热膨胀系数): 17.3 × 10⁻⁶ /K (20–100 °C)
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Product Type | Spiral Coil Tube (Helical Wound) | — |
| Material Grade | SUS304 / 316 / 321 / 316L | — |
| Tube Outer Diameter (OD) | 6 – 50 | mm |
| Tube Wall Thickness | 0.5 – 3.0 | mm |
| Coil Pitch (螺旋间距) | 15 – 150 | mm |
| Coil Outer Diameter | 100 – 2000 | mm |
| Coil Length (展开长度) | 1 – 50 | m |
| Surface Finish | Ba & No. 4 / Mirror / Matte | — |
| Surface Roughness (Ra) | ≤ 0.4 (Polished) / ≤ 0.8 (Brushed) | μm |
| Maximum Operating Temperature | −40 to +800 | °C |
| Maximum Operating Pressure | Up to 4.0 | MPa |
| Winding Mode | Single Helix / Multi-Layer Spiral / Double Helix | — |
| End Connection | Flanged / Threaded / Welded / Socket | — |
| Passivation Treatment | Available (Citric Acid / Nitric Acid) | — |
| Packing | Export-grade wooden crate / Plastic wrap | — |
Manufacturing Process
- Raw Material Inspection: Incoming stainless steel wire or seamless tube is verified against material certificates (Mill Test Reports / MTRs), confirming chemical composition, mechanical properties, and traceability to the heat number.
- Cold Drawing / Annealing: The base material undergoes cold drawing to achieve precise dimensional tolerances (±0.05 mm). Intermediate annealing cycles at 1050–1100 °C followed by water quenching restore full austenitic microstructure and ductility.
- Coil Forming (螺旋成型): A CNC-controlled spiral winding machine (CNC 螺旋绕制机) wraps the tube into the specified helical geometry. The forming process is cold-worked without heat input to preserve the metallurgical integrity of the austenitic matrix.
- Pitch and Diameter Calibration: Real-time servo feedback ensures uniform coil pitch and consistent helix angle throughout the winding length, critical for predictable hydraulic resistance and heat transfer performance.
- End Processing: Tube ends are cut, deburred, and prepared for the selected connection type (welding prep, threading, or flange welding). All welds are performed using GTAW (Gas Tungsten Arc Welding) or ORBT (Orbital Ring Tack) with inert gas shielding (Ar/He) to prevent oxidation.
- Surface Finishing: Electropolishing, mechanical polishing, or passivation treatment is applied as specified. Electropolishing achieves Ra ≤ 0.2 μm and enhances the passive chromium oxide layer (Cr₂O₃).
- Quality Inspection: Final inspection includes dimensional verification (OD, wall thickness, pitch), helix angle measurement, hydrostatic pressure testing (1.5× working pressure), visual surface inspection, and optional eddy current testing for wall thickness uniformity.
- Packaging: Coils are individually wrapped in moisture-proof plastic film, separated by protective foam, and secured in export-grade wooden crates with desiccant packets to prevent atmospheric corrosion during transit.
Applications
- Spiral Coil Water Tanks (螺旋盘管水箱): Primary application — immersed coil heat exchangers for domestic hot water systems, solar thermal water heaters, and industrial process water heating. Research demonstrates that spiral coil configurations achieve 20–35% higher heat transfer efficiency than straight-tube alternatives under turbulent flow conditions.
- Industrial Heat Exchangers: Shell-and-coil heat exchangers for chemical processing, pharmaceutical manufacturing, and food-grade pasteurization systems requiring sanitary-grade stainless steel construction.
- Refrigeration and HVAC: Condenser and evaporator coil tubes for commercial refrigeration units and heat pump systems operating with refrigerants such as R134a, R410A, and ammonia.
- Geothermal Heat Recovery: Immersed spiral coil systems for ground-source heat pump (GSHP) applications, where the high surface-area ratio maximizes thermal exchange with circulating geothermal fluid.
- Oil and Gas Industry: Heat tracing coils and process coil heat exchangers for pipeline temperature maintenance in offshore platforms and subsea applications.
- Power Generation: Feedwater preheating coils and condenser tubes in thermal power plants, leveraging the corrosion resistance of austenitic grades in high-temperature, high-pressure water circuits.
- Food and Beverage Processing: CIP-cleanable (Clean-in-Place) sanitary coil assemblies for milk pasteurization, beer brewing, and beverage heating systems, meeting FDA and 3-A Sanitary Standards.
Quality Certifications & Standards Compliance
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- EN 10204 / EN 10204-3.1 — Material Test Certificate (Mill Test Report) compliance
- ASTM A269 / A270 — Standard Specifications for Stainless Steel Welded/Seamless Austenitic Chromium and Chromium-Nickel Steel Tubing
- ASME BPV Code — Boiler and Pressure Vessel Code (Section VIII, Division 1) compliance for pressure-containing applications
- DIN EN 10217-7 — Non-alloy and alloy steel tubes for pressure purposes — Technical delivery conditions
- JIS G 3448 — Japanese Industrial Standard for Stainless Steel Seamless Tubes
- GB/T 12771 — Chinese National Standard for Stainless Steel Welded Tubes for General Purposes
- CE Marking — European Conformity for Pressure Equipment Directive (PED 2014/68/EU)
- NSF/ANSI 61 — Drinking Water System Components (where applicable for potable water applications)
Unique Selling Points
- Superior Heat Transfer Performance: The helical geometry induces Dean secondary flow, enhancing the Nusselt number (Nu) by 20–35% compared to straight-tube baselines. This translates to reduced coil length and lower pressure drop for equivalent thermal duty.
- Customizable Geometry: CNC-controlled winding allows precise customization of coil pitch, helix angle, and layer configuration to match specific thermal-hydraulic design requirements.
- Full Material Traceability: Every coil tube is traceable to its heat number with complete chemical and mechanical test documentation, ensuring compliance with international standards.
- Corrosion Resistant Design: Available in multiple austenitic grades (304, 316, 321, 316L) with optional electropolished and passivated surfaces to resist aggressive media and extend service life.
- Pressure Vessel Code Compliance: Designed and manufactured to ASME BPV Code standards, enabling use in certified pressure-containing systems without additional design review.
- Scalable Production: Manufacturing capacity accommodates both small-batch custom orders and large-scale industrial supply, with consistent quality maintained across production volumes.
Technical Note: Research on spiral coil tube water tank heat transfer characteristics under different operating modes (natural convection, forced convection, and mixed convection) demonstrates that the heat transfer coefficient (h) increases proportionally with the Reynolds number (Re) in turbulent flow regimes (Re > 2300). The spiral coil configuration achieves optimal thermal performance at a helix angle of 45°–60°, balancing convective enhancement against hydraulic friction losses. These findings have been incorporated into the design optimization parameters of Wenzhou Jixing Metal Materials' coil tube product line.