Stainless Steel Coil Tube — Spiral-Wound Heat Exchange Coil
Product Overview
The Stainless Steel Coil Tube (also known as Spiral-Wound Coil or Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is formed by cold-winding a continuous stainless steel strip into a compact spiral geometry, resulting in a high surface-area-to-volume ratio that is exceptionally suited for heat exchange, fluid conveyance, and thermal management applications. The coil tube design eliminates the need for traditional welding joints along the tube length, thereby minimizing potential leak paths and enhancing structural integrity under cyclic thermal loading.
Informed by experimental research on heat exchange performance of coil tubes under water film conditions, this product line is optimized for scenarios where convective heat transfer occurs between a flowing fluid and the external or internal surface of the coil. The spiral geometry inherently promotes secondary flow (Dean vortices) within the tube, significantly enhancing turbulent heat transfer coefficients compared to straight-tube configurations.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, thermal conductivity, and mechanical durability across a wide temperature range.
- Primary Grades: AISI 304 (UNS S30400), AISI 316 (UNS S31600), AISI 321 (UNS S32100), and AISI 316L (UNS S31603) for low-carbon applications
- Corrosion Resistance: Excellent resistance to oxidation, pitting, and intergranular corrosion due to the high chromium (Cr ≥ 18%) and molybdenum (Mo ≥ 2% for 316 series) content
- Thermal Conductivity: 14–16 W/(m·K) at 20°C, providing efficient thermal energy transfer
- Mechanical Strength: Tensile strength of 515–720 MPa; yield strength ≥ 205 MPa (annealed condition)
- Operating Temperature Range: −196°C to +870°C (grade-dependent)
- Surface Finish: BA (Bright Annealed), 2B, No. 4 Brushed, or custom matte finish (Ra ≤ 0.8 μm available upon request)
Specifications
| Parameter | Specification Range | Unit |
|---|---|---|
| Outer Diameter (OD) | 6 – 159 | mm |
| Wall Thickness | 0.3 – 6.0 | mm |
| Coil Pitch (Helix Spacing) | 2 – 50 | mm |
| Coil Diameter (Centerline) | 20 – 2000 | mm |
| Tube Length per Coil | 1 – 50 | m |
| Pressure Rating | Up to 4.0 | MPa |
| Tolerance on OD | ±0.05 | mm |
| Tolerance on Pitch | ±0.1 | mm |
| End Preparation | Plain, Beveled, Threaded, or Flanged | — |
| Standard Compliance | ASTM A213, GB/T 12771, EN 10217, JIS G3459 | — |
Manufacturing Process
- Raw Material Inspection: Incoming stainless steel strip undergoes spectroscopic analysis (OES) to verify chemical composition and mechanical property certification (mill test report).
- Edge Preparation & Leveling: The strip edges are deburred, and the strip is passed through a leveling mill to ensure flatness within ±0.1 mm/m.
- Spiral Winding (Cold Forming): The leveled strip is fed into a precision winding machine where it is helically wound around a mandrel at controlled tension. The winding speed, pitch, and tension are computer-controlled (CNC) to maintain dimensional accuracy throughout the coil length.
- Seam Welding: A high-frequency (HF) or TIG (Tungsten Inert Gas) welding process is applied along the strip overlap seam to create a hermetic, full-penetration weld. Weld quality is verified via dye penetrant testing (PT) or eddy current inspection.
- Heat Treatment (Annealing): The wound coil is annealed at 1050–1150°C followed by controlled cooling to relieve residual stresses, restore full austenitic microstructure, and achieve maximum corrosion resistance.
- Pickling & Passivation: The annealed coil is treated with a nitric acid–hydrofluoric acid (HNO₃–HF) pickling bath to remove oxide scale, followed by passivation to form a protective chromium oxide film.
- Dimensional Inspection & Testing: Final products undergo hydrostatic pressure testing (typically 1.5× working pressure for 30 seconds), dimensional verification via laser gauging, and visual surface inspection.
Applications
- Heat Exchangers & Heat Recovery Systems: Spiral coil tubes are ideal for air-cooled heat exchangers, condensers, evaporators, and thermal oil systems where enhanced convective heat transfer is required.
- Chemical Processing: Used in reactors, digesters, and heat exchangers handling corrosive media (acids, alkalis, chlorides) where stainless steel's passivity is critical.
- Pharmaceutical & Food Industry: Sanitary-grade coil tubes (Ra ≤ 0.4 μm) for CIP (Clean-In-Place) and SIP (Sterilization-In-Place) compatible heat transfer loops.
- Refrigeration & HVAC: Compact coil assemblies for chillers, cooling towers, and air handling units leveraging the high surface-area-to-volume ratio.
- Power Generation: Feedwater preheaters, economizers, and condenser tubes in power plants where thermal cycling resistance is essential.
- Automotive & Aerospace: Compact thermal management coils for engine cooling, battery thermal regulation, and hydraulic system heat rejection.
Unique Selling Points
- Leak-Free Continuous Geometry: The spiral-wound design minimizes weld seams, reducing failure points by up to 90% compared to traditional U-tube or hairpin configurations.
- Enhanced Heat Transfer: The helical curvature induces Dean secondary flows, increasing the Nusselt number (Nu) by 30–60% over straight-tube equivalents at equivalent Reynolds numbers.
- Compact Footprint: Achieves 40–70% higher heat transfer area per unit volume than shell-and-tube designs, enabling space-constrained installations.
- Thermal Fatigue Resistance: The continuous spiral geometry distributes thermal stresses uniformly, extending service life under cyclic operating conditions.
- Customizability: Pitch, coil diameter, tube OD, wall thickness, and end connections are fully customizable to meet specific engineering requirements.
Quality Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management
- ASME Section VIII — Pressure Vessel and Piping Components (where applicable)
- CE Marking — Compliance with European Pressure Equipment Directive (PED 2014/68/EU)
- Mill Test Reports (MTR): Provided per heat lot with full chemical analysis and mechanical property data
- Third-Party Inspection: Available upon request (SGS, TÜV, Bureau Veritas, Lloyd's Register)
Note: All products manufactured by Wenzhou Jixing Metal Materials Co., Ltd. comply with the applicable national and international standards listed above. Custom specifications, non-standard geometries, and special material grades are available upon submission of engineering drawings or technical data sheets.