Stainless Steel Coil Tube for Molten Salt Heat Exchanger Applications
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: JX-CT-415
Category: Coil Tube / Tubular Heat Exchanger Components
1. Product Overview
The stainless steel coil tube (Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for molten salt heat exchanger systems, particularly in single-vessel dual-coil configurations. These coil tubes serve as the critical heat transfer elements within thermal energy storage (TES) systems, enabling efficient heat absorption and release cycles in concentrated solar power (CSP) plants and industrial process heating applications.
The product represents a specialized form of continuous stainless steel tubing formed into helical or spiral configurations, optimized for maximum surface-area-to-volume ratio within confined vessel geometries. The dual-coil arrangement within a single vessel allows for simultaneous heating and cooling circuits, significantly improving thermal efficiency and system compactness.
2. Material Composition & Properties
2.1 Base Material
- Primary Alloy Grade: AISI 310S / 309 / 347H (High-temperature austenitic stainless steel)
- Alternative Grades: TP316L, TP321H, Inconel 625 (for specialized molten salt environments)
- Standard Specifications: ASTM A213, ASTM A269, GB/T 12771, GB/T 14976
2.2 Mechanical Properties (at Elevated Temperature)
| Property | AISI 310S | AISI 347H | Inconel 625 |
|---|---|---|---|
| Tensile Strength (MPa) @ 600°C | ≥ 260 | ≥ 310 | ≥ 520 |
| Yield Strength (MPa) @ 600°C | ≥ 110 | ≥ 140 | ≥ 240 |
| Maximum Service Temperature (°C) | 1150 | 1095 | 1095 |
| Thermal Conductivity (W/m·K) @ 600°C | 23.5 | 21.8 | 19.5 |
| Linear Expansion Coefficient (×10⁻⁶/K) | 17.0 | 16.5 | 13.0 |
| Corrosion Resistance (Molten Salt, 565°C) | Good | Good | Excellent |
2.3 Chemical Composition (AISI 310S)
| Element | C (%) | Cr (%) | Ni (%) | Mn (%) | Si (%) | P (%) | S (%) |
|---|---|---|---|---|---|---|---|
| Specification | ≤ 0.08 | 24.0–26.0 | 19.0–22.0 | ≤ 2.0 | ≤ 1.0 | ≤ 0.035 | ≤ 0.030 |
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ12 – Φ50 mm (customizable up to Φ89 mm) | ASTM A213 / GB/T 14976 |
| Wall Thickness (WT) | 0.8 – 4.0 mm | ASTM A213 |
| Coil Bend Diameter | 150 – 1200 mm | Customer-specific |
| Coil Length | Up to 500 m per continuous coil | — |
| Surface Finish | Pickled & Passivated (Ra ≤ 1.6 μm) | ASTM A967 |
| Tolerance on OD | ±0.05 mm (precision grade) | ISO 285 |
| Tolerance on WT | ±10% of nominal | ASTM A213 |
| End Condition | Plain end, beveled, or threaded | — |
| Heat Treatment | Solution annealed at 1050–1150°C, water quenched | ASTM A213 |
| Operating Pressure | Up to 4.0 MPa (design dependent) | ASME BPV Section I |
| Design Temperature Range | −50°C to +580°C (molten salt cycle) | — |
| Delivery Form | Coiled on steel drum or wooden crate | ISO 4180 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tube stock, sourced from certified mills (e.g., Outokumpu, Sandvik, Taigang) with full mill test certificates (MTC).
- Coil Forming (Cold Bending): Continuous tube is cold-formed into helical coils using high-precision CNC coil winding machines with controlled bending radius to prevent wall thinning and ovality.
- Stress Relief Annealing: Post-forming annealing at 1050–1100°C in a controlled atmosphere furnace to relieve residual bending stresses and restore full austenitic microstructure.
- Pickling & Passivation: Immersion in nitric/hydrofluoric acid solution followed by passivation treatment per ASTM A967 to restore chromium oxide protective layer.
- Hydrostatic Testing: Each coil undergoes pressure testing at 1.5× design pressure to verify weld integrity and structural soundness.
- Non-Destructive Testing (NDT): Visual inspection (VT), eddy current testing (ET) for wall thickness verification, and radiographic testing (RT) for weld joints.
- Packaging & Shipping: Coils are wound onto protective steel drums with moisture-absorbing desiccants, shrink-wrapped, and palletized for international shipment.
4.2 Key Manufacturing Capabilities
- Minimum bend radius: 3× tube OD (maintaining <3% wall thinning)
- Continuous coil length capability: up to 500 meters without intermediate welds
- Simultaneous dual-coil winding for matched-pair heat exchanger assemblies
- In-house hydraulic expansion and end-forming for header connections
5. Applications
5.1 Primary Applications
- Concentrated Solar Power (CSP) Plants: Thermal energy storage systems using binary nitrate salt mixtures (Solar Salt: 60% NaNO₃ / 40% KNO₃) at operating temperatures of 290–565°C.
- Molten Salt Heat Release Heat Exchangers: Single-vessel dual-coil configurations where hot and cold salt circuits operate simultaneously within a shared containment vessel.
- Industrial Process Heating: High-temperature thermal oil systems and direct-fired heater coil replacements.
- Power Generation: Feedwater heaters, economizers, and superheater elements in fossil and nuclear power plants.
5.2 Dual-Coil Heat Exchanger Configuration Advantages
The single-vessel dual-coil arrangement, as studied and optimized in thermal engineering literature, provides the following engineering benefits:
- Reduced vessel footprint by approximately 30–40% compared to dual-vessel configurations
- Improved heat recovery efficiency through direct thermal coupling between hot and cold coils
- Simplified piping and reduced insulation requirements
- Lower overall system cost through material optimization
6. Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 3834-2 | Welding Quality Requirements |
| EN 10204 3.1 | Material Test Certificate |
| ASME Section VIII Div. 1 | Pressure Vessel Code (for pressure-containing applications) |
| NACE MR0175 / ISO 15156 | Corrosion-resistant materials for oil & gas |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance |
| GB/T 12771 | Chinese National Standard for seamless stainless steel tubes |
7. Unique Selling Points
- Specialized Molten Salt Expertise: Decades of accumulated engineering knowledge in dual-coil heat exchanger optimization, ensuring coil geometries are tailored for maximum thermal performance in salt-based thermal storage systems.
- High-Temperature Integrity: Materials and manufacturing processes validated for continuous cycling between 290°C and 565°C without creep deformation or intergranular corrosion.
- Precision Coil Geometry: CNC-controlled forming ensures uniform bend radii and spacing, critical for consistent flow distribution and heat transfer coefficients across the entire coil length.
- Custom Engineering Support: Full design-to-delivery capability including thermal-hydraulic simulation, finite element analysis (FEA) for thermal stress, and custom coil layout optimization for specific vessel dimensions.
- Complete Traceability: Every coil is traceable from raw material mill heat number through all manufacturing and inspection stages, ensuring full supply chain accountability.
- Extended Service Life: Conservative design margins and premium material grades ensure a design life exceeding 25 years in continuous-duty molten salt applications.
8. Technical Support & Documentation
Wenzhou Jixing Metal Materials Co., Ltd. provides comprehensive technical documentation including:
- Mill Test Certificates (MTC) per EN 10204 3.1
- Heat Treatment Records with full thermocouple data
- NDT Reports (VT, ET, RT) with photographic documentation
- Hydrostatic Test Reports with pressure-time hold records
- Dimensional Inspection Reports with coordinate data
- Warranty certificate with minimum 2-year performance guarantee
Disclaimer: All specifications are subject to final confirmation based on specific project requirements, operating conditions, and applicable codes. Wenzhou Jixing Metal Materials Co., Ltd. reserves the right to modify specifications with prior notification to the purchaser.