Stainless Steel Coil Tube (Spiral Heat Exchanger Tube) — Technical Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Category: Heat Exchanger Coil Tubing / Organic Heat Carrier Furnace Spiral Coil
Reference Standard: GB/T 14976, ASTM A269, EN 10217, ASME B31.3
1. Product Overview
Wenzhou Jixing Metal Materials Co., Ltd supplies high-performance stainless steel coil tubes (also designated as spiral coil tubing or helical heat exchanger tubes) engineered for demanding thermal-fluid applications, particularly within organic heat carrier (OHC) furnaces and industrial process heating systems. These coil tubes are precision-formed helical structures that maximize surface-area-to-volume ratios, thereby enhancing convective and radiative heat transfer efficiency in high-temperature environments.
The product design and performance parameters are informed by rigorous Computational Fluid Dynamics (CFD) simulations of spiral coil tube heat transfer characteristics in organic heat carrier furnace systems. CFD-based analysis enables optimization of helix geometry, pitch, and diameter to achieve uniform temperature distribution, minimize thermal stress concentration, and maximize heat exchange efficiency — all critical factors in preventing thermal degradation of organic heat transfer fluids.
The coil tubes are available in a wide range of stainless steel grades, configurations, and dimensional specifications, supporting both standard and custom-engineered applications across multiple industrial sectors.
2. Material & Properties
2.1 Available Stainless Steel Grades
- AISI 304 / 304L (UNS S30400 / S30403): General-purpose austenitic stainless steel with excellent corrosion resistance, weldability, and formability. Suitable for moderate-temperature heat transfer applications up to approximately 870°C.
- AISI 316 / 316L (UNS S31600 / S31603): Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion. Recommended for applications involving chlorinated organic heat transfer fluids.
- AISI 310S (UNS S31008): High-temperature austenitic grade with exceptional oxidation resistance, suitable for continuous service up to 1150°C. Ideal for high-temperature organic heat carrier furnace applications.
- AISI 321 (UNS S32100): Stabilized austenitic grade with titanium addition to prevent intergranular corrosion during welding. Suitable for elevated-temperature service environments.
- AISI 347 (UNS S34700): Niobium-stabilized austenitic grade providing excellent resistance to sensitization and intergranular corrosion at high temperatures.
- SAF 2205 (UNS S32205): Duplex austenitic-ferritic stainless steel offering high mechanical strength, excellent chloride stress corrosion cracking resistance, and improved thermal conductivity compared to austenitic grades.
2.2 Key Mechanical Properties (Typical, Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 310S | SAF 2205 |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 515 | ≥ 550 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 450 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 35 | ≥ 25 |
| Thermal Conductivity at 100°C (W/m·K) | 16.3 | 14.6 | 21.5 | 21.5 |
| Thermal Conductivity at 500°C (W/m·K) | 21.5 | 18.8 | 31.6 | 30.0 |
| Maximum Service Temperature (°C) | 870 | 870 | 1150 | 315 (in corrosive media) |
| Density (g/cm³) | 8.00 | 8.03 | 8.00 | 7.85 |
2.3 Surface Finish Options
- 2B Finish (Cold-rolled, Annealed, Bright): Standard mill finish with moderate surface roughness (Ra ≤ 0.5 μm). Suitable for most industrial heat exchanger applications.
- BA Finish (Bright Annealed): Polished surface with low roughness (Ra ≤ 0.2 μm), enhanced corrosion resistance, and improved aesthetic appearance.
- No. 4 Brushed Finish: Uniform unidirectional grain pattern with Ra of 0.4–0.8 μm. Commonly used in food-grade and pharmaceutical process applications.
- Electro-polished Finish: Ultra-smooth surface (Ra ≤ 0.1 μm) with enhanced passive film integrity. Recommended for hygienic and high-purity applications.
- Pickled and Passivated: Chemical cleaning to remove mill scale and form a uniform chromium oxide passive layer, critical for long-term corrosion resistance in aggressive environments.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Range / Options | Tolerance |
|---|---|---|
| Tube Outer Diameter (OD) | 6 mm – 108 mm (¼" – 4") | ±0.5% (per ASTM A269) |
| Tube Wall Thickness | 0.5 mm – 8.0 mm | ±10% (per ASTM A269) |
| Helix Coil Diameter | 100 mm – 2,500 mm | ±0.5% |
| Helix Pitch (Turn-to-Turn Spacing) | 10 mm – 150 mm | ±1.0% |
| Number of Turns | 1 – 500+ | As per design requirement |
| Coil Length (Developed) | 1 m – 500 m | ±1.0% |
| End Preparation | Plain, Beveled, Threaded, Flanged, or Weld Neck | Per ASME B1.20.1 / B16.5 |
| Surface Roughness (Ra) | 0.1 μm – 1.6 μm (as specified) | Per agreed specification |
| Operating Pressure | Up to 40 bar (design-dependent) | Per ASME B31.3 |
| Operating Temperature Range | −196°C to +1,150°C (grade-dependent) | Per material grade limits |
3.2 Design Parameters Optimized via CFD Analysis
The coil tube geometry is optimized using CFD-based thermal-fluid simulations that model the following critical parameters for organic heat carrier furnace applications:
- Nusselt Number (Nu): Convective heat transfer coefficient optimization for turbulent flow regimes within helical geometries, typically achieving Nu values 30–80% higher than equivalent straight-tube configurations due to secondary Dean vortex flow enhancement.
- Pressure Drop (ΔP): Balancing heat transfer enhancement against acceptable hydraulic resistance, with typical ΔP values of 10–80 kPa per meter of coil length depending on flow velocity and geometry.
- Heat Transfer Coefficient (U): Overall heat transfer coefficient optimization targeting values of 250–600 W/m²·K for liquid-liquid organic heat carrier applications.
- Temperature Uniformity: Minimizing radial and axial temperature gradients to prevent localized thermal decomposition of organic heat transfer fluids (e.g., Dowtherm A, Therminol VP-1, YS series).
- Thermal Stress Distribution: Identifying and mitigating stress concentration points at coil bends and support saddles to ensure fatigue life and structural integrity.
4. Manufacturing Process
4.1 Raw Material Procurement
Stainless steel coil stock is procured from certified mill sources with full traceability documentation. Incoming material undergoes rigorous inspection including chemical composition verification via Spectroscopic Analysis (OES) and Optical Emission Spectrometry, mechanical property testing, and visual surface quality assessment in accordance with ASTM A269 and EN 10217 standards.
4.2 Cold Forming / Coil Bending
The flat stainless steel coil stock is precision-formed into helical coil geometry using advanced CNC-controlled coil bending machinery. The forming process involves:
- Uncoiling and Feeding: Continuous feeding of flat coil stock through calibrated guide rollers to ensure consistent material flow.
- Helical Forming: Simultaneous bending along two orthogonal axes using synchronized forming rollers to produce a uniform helical geometry with precise pitch and diameter control.
- Springback Compensation: Real-time adjustment of forming parameters to compensate for elastic springback, ensuring dimensional accuracy within specified tolerances.
- Cut-off and End Preparation: Precision cutting to specified lengths with end finishing (beveling, threading, or flanging) as required by the application specification.
4.3 Heat Treatment (if applicable)
For applications requiring enhanced mechanical properties or stress relief after cold forming, the coil tubes may undergo:
- Solution Annealing: Heating to 1010–1150°C followed by rapid cooling to restore full austenitic microstructure and maximum corrosion resistance.
- Stress Relief: Heating to 300–400°C for austenitic grades to relieve residual stresses introduced during cold forming without sensitization risk.
- Pickling and Passivation: Immersion in a mixed acid solution (HNO₃/HF) to remove oxide scale, followed by passivation to establish a uniform chromium oxide (Cr₂O₃) protective film.
4.4 Quality Inspection
- Dimensional Inspection: Laser scanning or CMM (Coordinate Measuring Machine) verification of helix diameter, pitch, tube OD, and wall thickness.
- Visual Inspection: 100% visual examination for surface defects, deformation, or processing damage.
- Non-Destructive Testing (NDT): Magnetic particle inspection (MT) or eddy current testing (ECT) for subsurface defect detection where applicable.
- Hydrostatic Testing: Pressure testing at 1.5× the maximum operating pressure for a minimum hold time of 30 seconds to verify leak tightness.
- Chemical Composition Verification: Spectroscopic confirmation of alloy composition against mill certificates.
5. Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd are deployed across a wide range of industrial thermal-fluid and process heating applications:
- Organic Heat Carrier (OHC) Furnaces: Primary application domain — spiral coil tubes serve as the heat exchange surface for heating organic heat transfer fluids (e.g., diphenyl oxide, triphenyl methane, YS synthetic oils) to process temperatures of 200–400°C. CFD-optimized coil geometry ensures uniform heat distribution and prevents localized overheating that could cause thermal decomposition.
- Industrial Process Heating Systems: Heating of chemical reactors, distillation columns, and process streams in petrochemical, pharmaceutical, and food processing industries.
- Shell-and-Tube Heat Exchangers: Coil tubes used as the tube bundle component in compact heat exchanger designs requiring high surface-area-to-volume ratios.
- Steam Generators and Boilers: Helical coil configurations for efficient steam generation in low-pressure industrial boiler systems.
- Refrigeration and Cryogenic Systems: Coil tubes for evaporator and condenser applications in industrial refrigeration systems operating at cryogenic temperatures.
- Food and Beverage Processing: Hygienic-grade coil tubes (electro-polished, 316L) for milk pasteurization, beer brewing, and pharmaceutical liquid heating systems.
- Power Generation: Auxiliary heating systems and feedwater preheating coils in power plant balance-of-plant systems.
- Plastics and Polymer Processing: Temperature control coils for extruders, injection molding machines, and polymer reaction vessels.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and product certification framework:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control throughout the manufacturing lifecycle. |
| ISO 14001:2015 | Environmental Management System certification demonstrating commitment to sustainable manufacturing practices. |
| ASME B31.3 |