Stainless Steel Coil Tube — Product Technical Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Catalog No.: 1669
Classification: Literature Learning / Technical Reference
1. Product Overview
The Stainless Steel Coil Tube (盘管) is a precision-engineered tubular product formed by cold-bending or hot-bending stainless steel seamless tubes into a continuous helical or serpentine coil configuration. This product form is widely utilized in thermal management systems, heat exchangers, refrigeration loops, and industrial process equipment where compact volumetric heat transfer performance is paramount.
Unlike straight tube sections, coil tubes offer significantly greater surface-area-to-volume ratios, enabling enhanced convective heat exchange within constrained installation spaces. The curvature of the coil introduces secondary flow effects — including Dean vortices (二次流) — which naturally intensify turbulence and improve thermal performance without the need for additional internal surface treatments or flow promoters.
Wenzhou Jixing Metal Materials Co., Ltd. supplies coil tubes in a range of diameters, wall thicknesses, and coil geometries, manufactured from high-grade austenitic and duplex stainless steels to meet demanding corrosion resistance and mechanical integrity requirements across diverse operating environments.
2. Material & Properties
2.1 Applicable Grades
- Austenitic Stainless Steels: SUS304 (ASTM 304), SUS304L, SUS316 (ASTM 316), SUS316L, SUS321 (ASTM 321), SUS310S
- Duplex Stainless Steels: SUS31803 (2205), SUS32750 (2507)
- Super Austenitic: SUS904L, SUS630
2.2 Key Material Properties
- Corrosion Resistance: Superior resistance to pitting, crevice, and general corrosion in acidic, alkaline, and chloride-containing environments, attributed to the high chromium (Cr ≥ 18%) and molybdenum (Mo ≥ 2%) content in grades such as 316L.
- Mechanical Strength: Tensile strength typically ranges from 520–720 MPa depending on grade and cold-work degree; yield strength ≥ 205 MPa (SUS304, annealed).
- Thermal Conductivity: 14–16 W/(m·K) for austenitic grades; adequate for heat transfer applications while maintaining structural integrity at elevated temperatures.
- Thermal Stability: Retains mechanical properties up to 870 °C (SUS304) and 1090 °C (SUS310S), making coil tubes suitable for high-temperature process loops.
- Hygienic Surface Finish: Available with electropolished (Ra ≤ 0.4 μm) or passivated surfaces for pharmaceutical, food-grade, and semiconductor applications.
- Cryogenic Performance: Maintains ductility and toughness at temperatures as low as −196 °C (liquid nitrogen service), making coil tubes ideal for cryogenic heat exchangers and ice-storage systems.
2.3 Heat Transfer Enhancement Characteristics
Research referenced in the product literature — including experimental studies on coil tube ice-storage and enhanced heat transfer (《塑料盘管蓄冰及其强化传热的实验研究》) — demonstrates that helical coil geometries produce Dean numbers (De) between 10 and 100 for typical operating Reynolds numbers (Re = 2,000–50,000). These Dean vortices increase the local Nusselt number (Nu) by 20–60% compared to equivalent straight-tube heat transfer, providing a measurable and repeatable thermal performance advantage.
Note: The Dean number is defined as De = Re · √(d/2D), where d is the tube inner diameter and D is the coil mean diameter. Higher De values correlate with stronger secondary flow and greater heat transfer enhancement.
3. Specifications
| Parameter | Specification Range | Standard / Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6 mm – 114 mm (¼" – 4½") | ASTM A213 / A269; GB/T 12771 |
| Tube Wall Thickness | 0.5 mm – 6.0 mm | ASTM A213; EN 10216-5 |
| Coil Mean Diameter (CMD) | 100 mm – 2,000 mm | Customer specification |
| Coil Pitch / Spacing | 10 mm – 100 mm | Customer specification |
| Coil Length (per piece) | 3 m – 60 m | — |
| Minimum Bending Radius | ≥ 3D (where D = tube OD) | ASTM A213, Clause 12 |
| Surface Finish | Mill finish (Ra ≤ 1.6 μm), brushed, electropolished (Ra ≤ 0.4 μm), passivated | ASTM A967; ISO 15871 |
| End Condition | Plain, beveled, thread-rolled, or tube-end formed | Customer drawing |
| Operating Temperature Range | −196 °C to +870 °C (SUS304); up to +1090 °C (SUS310S) | Grade-dependent |
| Maximum Operating Pressure | Up to 30 MPa (design-dependent) | ASME B31.3; PED 2014/68/EU |
| Tolerance on OD | ±0.05 mm to ±0.20 mm (per diameter class) | ASTM A213, Table M2 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A213 |
4. Manufacturing Process
4.1 Raw Material Procurement
Stainless steel seamless tubes are sourced from certified mills conforming to ASTM A213 (for boiler, heat exchanger, and heat-transfer applications) or ASTM A269 (for general applications). Each heat lot is accompanied by a mill test certificate (MTC) documenting chemical composition (per ASTM A240) and mechanical properties.
4.2 Coil Forming
- Coil Tube Cold Bending: Straight tubes are fed through a precision bending machine equipped with a mandrel die set. Cold bending is performed at ambient temperature, preserving the full mechanical properties of the material. The bending radius is controlled to a minimum of 3D to prevent wall thinning below 85% of original thickness and to avoid ovality exceeding 8%.
- Hot Bending (for large diameters or tight radii): For tubes with OD > 50 mm or when bending radii below 3D are required, the tube is locally heated to 800–950 °C (within the austenitizing range for austenitic grades) and bent using a hydraulic press or rotary-draw bending machine. Post-bending solution annealing is performed to restore full corrosion resistance.
- Serpentine Forming: Flat serpentine coils are produced by pressing straight tubes into a serpentine pattern using a series of precision dies, commonly used in automotive and HVAC heat exchangers.
4.3 Post-Forming Treatment
- Solution Annealing: For cold-worked coils, solution annealing at 1050–1150 °C followed by rapid water quenching restores full austenitic microstructure and maximum corrosion resistance.
- Pickling and Passivation: The coil surface is treated with a mixed acid pickling solution (HNO₃ + HF) followed by nitric acid passivation per ASTM A967 to remove oxide scale and form a protective chromium oxide film.
- Electropolishing (optional): For hygienic applications, the coil is electropolished to achieve a surface roughness of Ra ≤ 0.4 μm and a minimum chromium content of 19% in the surface layer.
4.4 Quality Inspection
- Dimensional Inspection: OD, wall thickness, coil pitch, and bend radius are verified using calipers, ultrasonic thickness gauges, and coordinate measuring machines (CMM).
- Non-Destructive Testing (NDT): Eddy current testing (per ASTM E3096) or magnetic particle inspection (for ferritic grades) is performed to detect surface and near-surface defects. Hydrostatic testing (per ASTM A213, Clause 16) verifies pressure integrity at 1.5× the maximum design pressure.
- Visual Inspection: 100% visual examination for surface defects, dents, and deformation per ASTM A213, Clause 14.
5. Applications
5.1 Thermal Energy Storage (TES) Systems
Coil tubes are extensively used in ice-storage thermal energy storage systems, where stainless steel coils are immersed in water tanks and used to freeze water into ice slurry or ice blocks during off-peak hours. The enhanced heat transfer characteristics of the coil geometry — as documented in experimental research on coil tube ice storage — enable rapid charge/discharge cycles, making the system highly efficient for peak-load shifting in commercial HVAC applications.
5.2 Heat Exchangers
- Shell-and-Tube Heat Exchangers: Coil tubes serve as the tube bundle in compact heat exchangers for process heating, cooling, and condensation.
- Air-Cooling Heat Exchangers: Serpentine coil tubes are used in air-cooled condensers for refrigeration and chemical processing.
- Plate-and-Coil Heat Exchangers: Hybrid designs combining flat plate channels with coil inserts for enhanced turbulence.
5.3 Industrial Process Equipment
- Reactor Cooling Jackets: Coil tubes embedded in reactor walls for precise temperature control in exothermic chemical reactions.
- Distillation Columns: Internal coil tubes for reboilers and condensers in petroleum refining and chemical distillation.
- Precipitation and Crystallization Vessels: Coil tubes maintain precise thermal conditions for controlled crystallization processes.
5.4 Food, Pharmaceutical, and Beverage Industry
- Pasteurizers and Sterilizers: Electropolished coil tubes for sanitary heating and cooling of milk, juice, and pharmaceutical solutions.
- CIP (Clean-In-Place) Systems: Coil tubes designed for chemical cleaning without disassembly.
- Brewing and Fermentation: Coil coils in fermentation tanks for temperature regulation during brewing and biological fermentation.
5.5 Refrigeration and Cryogenics
- Evaporators and Condensers: Coil tubes in refrigeration systems for ammonia, hydrofluorocarbon (HFC), and natural refrigerant (CO₂, NH₃) circuits.
- Cryogenic Heat Exchangers: Stainless steel coil tubes for liquid nitrogen (LN₂), liquid oxygen (LOX), and liquid natural gas (LNG) service, leveraging the excellent low-temperature toughness of austenitic grades.
5.6 Power Generation
- Boiler Tube Coils: In supercritical and ultra-supercritical boilers, coil tubes are used for compact heat transfer surfaces.
- Turbine Cooling Coils: Internal coil tubes in gas turbine blades for film cooling and internal convection cooling.
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — covers manufacturing, inspection, and traceability of coil tube production. |
| ISO 14001:2015 | Environmental Management System — governs environmental controls during production. |
| ISO 45001:2018 | Occupational Health and Safety Management System. |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for coil tubes used in pressure vessels and piping systems. |
| ASME / NB Stamp | American Society of Mechanical Engineers certification for pressure-containing applications. |
| EN 10204 Type 3.1 | Inspection Certificate issued by authorized personnel of the manufacturer, confirming conformity to specified standards. |
| ASTM A213 / A269 | Material specification for seamless austenitic stainless steel tubing. |
| GB/T 12771 (China National Standard) | Stainless steel seamless tubes for general applications — Chinese domestic standard compliance. |
| GB/T 21890 (China National Standard) | Welded stainless steel tubes for general applications (if applicable to welded coil tube variants). |
| EAF (European Aluminium Federation) / PED | European conformity for pressure equipment components. |
7. Unique Selling Points
- Superior Heat Transfer Performance: The helical coil geometry generates Dean vortices that enhance convective heat transfer by 20–60% over equivalent straight tubes, reducing overall heat exchanger footprint and capital cost.
- Wide Material Selection: Available in over 10 stainless steel grades covering general purpose (304/304L), high-corrosion (316/316L), high-temperature (310S/904L), and duplex (2205/2507) applications, ensuring optimal material selection for any service environment.
- Full Traceability: Every coil tube batch is traceable to its raw material heat number, with complete chemical and mechanical test data provided in EN 10204 Type 3.1 Inspection Certificates.
- Custom Coil Geometry: Flexible manufacturing capability to produce custom coil diameters, pitches, and lengths per customer drawings, with tight dimensional tolerances (±0.05 mm on OD for small diameters).
- Hygienic Grade Option: Electropolished and passivated surfaces (Ra