Stainless Steel Coil Tube for Organic Heat Transfer Fluid Systems
Product No. 768 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Overview
The stainless steel coil tube (Coiltube) is a precision-engineered product designed for integration into organic heat transfer fluid (OHTF) furnace systems. Unlike conventional straight-tube configurations, the coil tube geometry provides superior surface-area-to-volume ratios, enabling enhanced convective and radiative heat exchange within closed-loop thermal systems. This product has been extensively studied through numerical simulation of internal flow heat transfer characteristics, revealing optimized thermal performance under a wide range of operating conditions.
The coiled configuration inherently promotes turbulent flow development at lower Reynolds numbers compared to straight tubes, reducing the overall heat transfer surface requirement while maintaining efficient thermal energy transfer from the heating medium to the process fluid. This makes the product particularly suitable for industrial processes requiring precise temperature control and uniform heat distribution.
Material Composition and Properties
Base Alloy Grades
- Austenitic Stainless Steels: Grade 304 (UNS S30408), Grade 316L (UNS S31603), Grade 321 (UNS S32100), and Grade 310S (UNS S31008) are the primary alloy grades utilized for coil tube applications in thermal systems.
- Key Elemental Composition (Grade 304): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%.
- Key Elemental Composition (Grade 316L): Carbon (C) ≤ 0.03%, Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%.
Mechanical and Thermal Properties
| Property | Grade 304 | Grade 316L | Grade 321 | Grade 310S |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 | ≥ 520 | ≥ 520 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 |
| Thermal Conductivity (W/m·K, 100°C) | 16.3 | 14.6 | 16.3 | 24.5 |
| Thermal Expansion (×10⁻⁶/K, 20–100°C) | 17.3 | 16.0 | 17.3 | 18.0 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 1150 |
| Corrosion Resistance (pH) | 1–14 (neutral to alkaline) | 1–14 (chloride resistant) | 1–14 (high-temp oxidation) | 1–14 (extreme oxidation) |
Technical Specifications
| Parameter | Specification | Tolerance | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | Φ6.0 – Φ50.8 mm (¼" – 2") | ±0.10 mm | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.50 – 3.00 mm | ±0.05 mm | ASTM A269 / GB/T 14976 |
| Coil Bending Radius (Centerline) | 100 – 500 mm | ±2 mm | ASME B31.3 |
| Coil Length (per spool) | 50 – 500 m | ±1 m | Manufacturer specification |
| Surface Finish | Ba < 0.4 μm (electropolished) / Ra < 1.6 μm (pickled) | — | ASTM A967 / GB/T 8890 |
| End Condition | Plain end / Beveled end (37° ±2°) | — | ASME B31.3 |
| Heat Treatment Condition | Solution annealed (1050–1150°C, water quenched) | — | ASTM A213 |
| Maximum Operating Pressure | Up to 4.0 MPa (design dependent) | — | ASME B31.3 |
| Operating Temperature Range | −196°C to +1150°C (grade dependent) | — | Material datasheet |
| Helix Angle Deviation | ≤ 1.0° | — | GB/T 12465 |
Manufacturing Process
Process Flow
- Raw Material Selection: Cold-rolled stainless steel strip of certified chemical composition is procured from qualified mills, with each batch undergoing spectroscopic verification (OES) and mechanical testing.
- Slitting and Leveling: The master coil is slit to precise width specifications and leveled to achieve flatness within ±0.2 mm/m, ensuring uniform tube wall thickness after forming.
- Tubular Forming: The flat strip is fed through a series of precision roll-forming dies that progressively bend the strip into a seamless tubular cross-section. The weld seam is formed by high-frequency induction welding (HFW) or continuous gas tungsten arc welding (GTAW), with real-time seam inspection.
- Inline Solution Annealing: The formed tube passes through a continuous protective-atmosphere annealing furnace (1050–1150°C) to relieve forming stresses, restore full austenitic structure, and homogenize microstructure. Quenching is achieved via controlled water spray or forced air.
- Pickling and Passivation: The tube is immersed in a mixed acid bath (HNO₃/HF) to dissolve scale and oxide layers, followed by passivation treatment to establish a stable chromium oxide film (Cr₂O₃) for corrosion resistance.
- Coil Bending: The straight tube is cold-bent into the specified helical coil geometry using a precision coil bending machine with hydraulic support. The bending process is controlled to maintain dimensional accuracy and prevent wall thinning below 85% of nominal thickness.
- Post-Bend Stress Relief: Optional heat treatment at 650–750°C to relieve residual bending stresses without sensitization, ensuring dimensional stability during service.
- Hydrostatic Testing: Each coil length is pressure-tested at 1.5× the maximum design pressure to verify weld integrity and absence of defects.
- Non-Destructive Testing (NDT): Electromagnetic acoustic testing (EMAT) or eddy current inspection is performed to detect internal and external surface defects.
- Packaging and Dispatch: Coils are wound onto protective cores, wrapped with moisture-proof film, and labeled with full traceability documentation.
Heat Transfer Performance Characteristics
Based on numerical simulation studies of internal flow heat transfer within coil tubes used in organic heat transfer fluid furnaces, the following performance characteristics have been established:
- Enhanced Turbulence: The curvature-induced centrifugal force generates secondary Dean vortices within the tube cross-section, promoting radial mixing and reducing thermal boundary layer thickness. This results in Nusselt number (Nu) values 15–30% higher than equivalent straight-tube configurations at identical Reynolds numbers.
- Pressure Drop Consideration: The additional pressure drop due to curvature is quantified by the Dean number (De = Re·√(d/D), where d is tube diameter and D is coil centerline diameter). For typical operating conditions (Re = 5,000–50,000; De = 50–500), the friction factor increase is 8–25% above straight-tube values.
- Thermal Efficiency: The compact coil geometry achieves heat transfer surface densities of 200–800 m²/m³, enabling high-temperature organic heat transfer fluid systems to operate efficiently within constrained furnace volumes.
- Temperature Uniformity: The continuous helical path ensures uniform exposure to the heat source, minimizing local hot spots and thermal stress concentrations that could compromise tube integrity over extended service life.
Applications
Primary Applications
- Organic Heat Transfer Fluid (OHTF) Furnaces: Primary heating element in closed-loop thermal oil systems for indirect heating processes, operating with synthetic organic heat transfer fluids (e.g., Therminol VP-1, Dowtherm A) at temperatures up to 400°C.
- Petrochemical Processing: Reboilers, evaporators, and process heaters in refinery and chemical plant operations requiring corrosion-resistant heat exchange surfaces.
- Food and Pharmaceutical Processing: Sterilization equipment, pasteurizers, and thermal processing reactors where sanitary-grade surfaces (Ra < 0.4 μm) and high-temperature resistance are mandatory.
- Textile Industry: Dyeing and finishing equipment requiring uniform heat distribution and resistance to acidic/alkaline dyeing solutions.
- Plastics and Rubber Processing: Extruder barrel heating, calender heating, and injection molding temperature control systems.
- Power Generation: Auxiliary heating systems, feedwater preheaters, and low-temperature waste heat recovery in combined heat and power (CHP) installations.
Unique Selling Points
- Superior Heat Transfer Efficiency: Dean vortex enhancement provides 15–30% higher heat transfer coefficients compared to straight tubes, reducing furnace size and capital expenditure.
- Compact Design: High surface-area density enables space-constrained installations without sacrificing thermal performance.
- Extended Service Life: Austenitic stainless steel microstructure combined with controlled cold-forming process yields fatigue resistance exceeding 10⁷ thermal cycles.
- Dimensional Precision: CNC-controlled coil bending ensures ±1 mm dimensional accuracy, facilitating plug-and-play installation in standard furnace configurations.
- Full Traceability: Each coil is accompanied by a mill test certificate (MTC), heat number traceability, and complete NDT documentation per EN 10204 Type 3.1.
Quality Certifications and Standards Compliance
| Certification / Standard | Scope | Applicability |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Manufacturing process |
| ISO 14001:2015 | Environmental Management System | Production operations |
| ASTM A213 / A269 | Seamless and welded austenitic stainless steel tubes | Material specification |
| EN 10216-5 | Ferritic and austenitic stainless steel tubes for pressure purposes | European conformity |
| ASME B31.3 | Process piping design and construction | System design reference |
| GB/T 12771 / GB/T 14976 | Chinese national standards for stainless steel tubes | Domestic compliance |
| EN 10204 Type 3.1 | Inspection documents – specific inspection report | Documentation and traceability |
| PED 2014/68/EU | Pressure Equipment Directive | Pressure-containing applications |
| CE Marking | European conformity assessment | EU market access |
| 3-A Sanitary Standards | Hygienic design for food/pharma | Sanitary applications (electropolished) |
Installation and Maintenance Guidelines
Thermal Expansion Accommodation: Due to the elevated coefficient of thermal