Stainless Steel Coil Tube (Coiltube) — Optimized Thermal Performance Series
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Catalog No.: 1389
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product formed by winding seamless or welded stainless steel tubing into a continuous helical or spiral coil geometry. This product series is specifically designed for high-efficiency thermal exchange applications, including but not limited to coil heaters, heat exchangers, refrigeration systems, and process heating/cooling circuits. The fundamental design philosophy behind this product line draws upon advanced thermodynamic optimization principles — specifically the mathematical and engineering frameworks described in the seminal study "Optimization of Thermal Performance of Coil Heaters" — to achieve maximum heat transfer efficiency within a compact volumetric envelope.
Coil tubes differ from straight pipe sections in their inherent thermal characteristics. The curvature of the coil introduces secondary flow patterns (Dean vortices) that significantly enhance convective heat transfer coefficients compared to straight-tube configurations. Wenzhou Jixing Metal Materials Co., Ltd. leverages this phenomenon through precise control of coil geometry parameters — including coil diameter, pitch, tube cross-section, and wall thickness — to deliver optimized thermal performance across a wide range of operating conditions.
2. Material & Properties
2.1 Available Grades
- AISI 304 / ASTM 304 (UNS S30400): General-purpose austenitic stainless steel offering excellent corrosion resistance, formability, and weldability. Suitable for non-chloride-containing environments and food-grade applications.
- AISI 316 / ASTM 316 (UNS S31600): Molybdenum-enhanced austenitic grade providing superior resistance to pitting and crevice corrosion in chloride-rich environments. Preferred for marine, chemical processing, and pharmaceutical applications.
- AISI 316L / ASTM 316L (UNS S31603): Low-carbon variant of 316 for enhanced weldability and resistance to intergranular corrosion in sensitized conditions.
- AISI 321 / ASTM 321 (UNS S32100): Titanium-stabilized austenitic grade offering excellent resistance to intergranular corrosion at elevated temperatures (up to 870 °C), suitable for high-temperature heat exchanger applications.
- AISI 310S / ASTM 310S (UNS S31008): High-temperature austenitic grade with outstanding oxidation resistance, suitable for coil heaters operating in extreme thermal environments.
- Duplex 2205 (UNS S32205): Duplex austenitic-ferritic stainless steel providing high mechanical strength (approximately double the yield strength of 304/316) and excellent resistance to chloride stress corrosion cracking (SCC).
2.2 Key Physical and Mechanical Properties
| Property | 304 (UNS S30400) | 316 (UNS S31600) | 316L (UNS S31603) | 321 (UNS S32100) | 310S (UNS S31008) | 2205 (UNS S32205) |
|---|---|---|---|---|---|---|
| Yield Strength (MPa, min.) | 205 | 170 | 170 | 205 | 205 | 450 |
| Tensile Strength (MPa, min.) | 515 | 485 | 485 | 515 | 515 | 620 |
| Thermal Conductivity (W/m·K, at 20 °C) | 16.3 | 14.6 | 14.6 | 16.3 | 21.5 | 13.6 |
| Thermal Expansion Coefficient (μm/m·K, 100–300 °C) | 17.3 | 16.0 | 16.0 | 17.3 | 18.0 | 14.3 |
| Maximum Service Temperature (°C) | 870 | 870 | 870 | 900 | 1150 | 350 |
| Maximum Operating Pressure (bar, reference at 20 °C) | 350 | 350 | 350 | 350 | 350 | 500 |
| Corrosion Resistance | Good | Excellent | Excellent | Good | Good | Outstanding |
2.3 Surface Finish Options
- Pickled and Passivated (P&P): Standard finish with chromium oxide passive film, suitable for general industrial applications.
- Bright Annealed: Clean, reflective surface achieved through annealing in a controlled atmosphere furnace, ideal for hygienic and cosmetic applications.
- Electropolished (EP): Electrochemical finishing achieving Ra ≤ 0.5 μm surface roughness, meeting FDA and pharmaceutical-grade requirements.
- Brushed Finish: Aesthetic finish with directional grain pattern, suitable for architectural and decorative applications.
3. Specifications
3.1 Geometric Parameters
| Parameter | Range / Options | Unit | Notes |
|---|---|---|---|
| Tube Outer Diameter (OD) | 3.0 – 50.8 | mm | Custom diameters available upon request |
| Tube Wall Thickness | 0.3 – 3.0 | mm | Selected based on pressure rating and thermal load |
| Coil Diameter (Center-to-Center) | 50 – 2000 | mm | Determines compactness and thermal performance |
| Coil Pitch (Center-to-Center between Turns) | 10 – 150 | mm | Affects flow distribution and heat transfer area |
| Number of Turns / Layers | 1 – 50+ | — | Determined by required heat transfer surface area |
| Total Tube Length | 1 – 100 | m | Continuous coil length |
| Tolerance on OD | ±0.05 – ±0.10 | mm | Per ASTM A213 / A269 |
| Tolerance on Wall Thickness | ±10% (min.) | — | Per ASTM A213 / A269 |
| Surface Roughness (Internal) | Ra 0.4 – 1.6 | μm | EP finish available for Ra ≤ 0.5 μm |
3.2 Thermal Performance Parameters
| Parameter | Typical Value | Unit | Reference Condition |
|---|---|---|---|
| Overall Heat Transfer Coefficient (U-value) | 800 – 2500 | W/m²·K | Shell-and-coil configuration, water-to-water |
| Enhancement Factor (vs. Straight Tube) | 1.5 – 3.0 | — | Dean number-dependent; Re = 1000–50000 |
| Maximum Heat Flux | 200 – 800 | kW/m² | Dependent on fluid, flow rate, and geometry |
| Pressure Drop per Coil Length | 0.5 – 5.0 | bar/m | Fluid-dependent; optimized for minimal ΔP |
| Service Temperature Range | −196 to 1150 | °C | Grade-dependent (310S for high-temperature) |
3.3 Applicable Standards
- ASTM A213: Standard Specification for Seamless and Wrought Austenitic Stainless Steel Tubing for High-Temperature Service
- ASTM A269: Standard Specification for Seamless and Wrought Austenitic Chromium-Chromium-Nickel Stainless Steel Tubing for Chemical and Other Severely Corrosive Services
- ASTM A270: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Application
- EN 10216-5: Heat-resistant, Cr-Ni and Cr-Ni-Mo Stainless Steel Tubes and Fittings — Part 5: Technical Delivery Conditions for Non-Heat-Exchanger Tubes
- ASME B31.3: Process Piping Code (for pressure-containing applications)
- ISO 1143: Stainless Steel Tubes — General Tolerances on Dimensions
- GB/T 12771: Chinese National Standard for Stainless Steel Seamless Tubes for General Purposes
4. Manufacturing Process
The production of optimized stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage process designed to ensure dimensional accuracy, metallurgical integrity, and thermal performance:
- Raw Material Procurement and Inspection: Stainless steel wire rod or seamless tubing is sourced from certified mill suppliers. Incoming material undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition, and ultrasonic testing (UT) to detect internal defects.
- Tube Forming (if starting from wire rod): Cold-drawn or hot-forged seamless tubes are produced via rotary piercing or capstan drawing processes. Alternatively, precision-welded tubes are manufactured using Automatic Tube Welding (ATW) with laser or TIG (Tungsten Inert Gas) welding technology, followed by hot isostatic pressing (HIP) for weld joint integrity.
- Coil Winding: Tubes are wound onto precision-engineered mandrels using CNC-controlled coil winding machinery. The winding process maintains strict control over coil diameter, pitch, and turn-to-turn alignment to minimize stress concentrations and ensure uniform thermal performance. The winding speed and tension are optimized to prevent tube deformation or kinking.
- Heat Treatment: Annealing (solution heat treatment) is performed at 1050–1150 °C followed by rapid water quenching to restore full austenitic microstructure, relieve residual stresses introduced during winding, and maximize corrosion resistance. For stabilized grades (321, 347), a stabilization anneal is performed at 850–880 °C.
- Pickling and Passivation: Surface oxide scale is removed using a controlled acid bath (nitric/hydrofluoric acid blend or citric acid for environmentally sensitive applications), followed by passivation to establish a uniform chromium oxide protective film.
- Precision Machining of End Connections: Coil ends are prepared with flanges, threaded fittings, socket-weld connections, or U-bend terminations as specified. TIG welding is employed for all weld joints with helium back-purging to ensure internal weld quality.
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Quality Inspection: Each coil assembly undergoes comprehensive non-destructive testing (NDT):
- Visual Inspection (VT): Surface and weld appearance verification
- Pressure Testing: Hydrostatic or pneumatic testing at 1.5× working pressure for a minimum dwell time of 30 minutes
- Penetrant Testing (PT): Surface defect detection on welds and critical areas
- Eddy Current Testing (ECT): Internal and external defect detection for seamless tubes
- Dimensional Verification: CMM (Coordinate Measuring Machine) or laser scanning for coil geometry accuracy
- Packaging and Dispatch: Coils are protected with moisture-absorbent packaging, anti-corrosion coatings, and custom wooden crates or steel containers for safe transportation.
5. Applications
The optimized thermal performance