Stainless Steel Internal Heat Recovery Coil Tube (Coiltube)
1. Product Overview
The Stainless Steel Internal Heat Recovery Coil Tube (Product Catalog No. 1397) is a precision-engineered coiled tube component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed specifically for internal heat recovery systems, this coiltube serves as a critical heat exchange medium in high-efficiency thermal management applications. The coil geometry maximizes the surface-area-to-volume ratio, enabling superior thermal transfer efficiency within compact installations. This product line is engineered to withstand demanding operating conditions involving high temperatures, corrosive media, and cyclic thermal stress, making it suitable for industrial process heating, waste heat recovery, and energy-efficient thermal loop systems.
The coil tube is fabricated from high-grade austenitic and duplex stainless steels, offering exceptional corrosion resistance, mechanical strength, and long-term structural integrity under aggressive chemical environments. The continuous coil configuration eliminates the need for intermediate supports or joints over extended lengths, thereby reducing potential leak points and maintenance requirements.
2. Material & Properties
2.1 Available Grades
- Austenitic Stainless Steels: AISI 304 (1.4301), AISI 304L (1.4307), AISI 316 (1.4401), AISI 316L (1.4404), AISI 321 (1.4541), AISI 347 (1.4549)
- Duplex Stainless Steels: AISI 2205 (1.4462), AISI 2507 Super Duplex (1.4410)
- Custom Alloys: Custom compositions available upon request for specialized service conditions
2.2 Key Material Properties (Typical — AISI 316L)
| Property | Specification |
|---|---|
| Tensile Strength (Rm) | ≥ 485 MPa (ASTM A213/A269) |
| Yield Strength (Rp0.2) | ≥ 205 MPa |
| Elongation (A50) | ≥ 40% |
| Operating Temperature Range | −196 °C to +650 °C (continuous) |
| Corrosion Resistance | Excellent against acids, alkalis, chlorides, and organic solvents |
| Thermal Conductivity | 16.3 W/(m·K) at 20 °C |
| Thermal Expansion Coefficient | 17.3 × 10⁻⁶ /K (20–100 °C) |
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 mm – Φ50.8 mm (custom sizes available) | ASTM A213 / ASME SA-213 |
| Wall Thickness | 0.5 mm – 3.0 mm | ASTM A269 / ASME SA-269 |
| Coil Diameter (CD) | Φ100 mm – Φ2000 mm | Custom / Client Drawing |
| Coil Length | 1 m – 500 m (continuous) | — |
| Surface Finish | Pickled & Passivated (P&P), 2B, No. 4, Mirror (Ra ≤ 0.4 μm) | ASTM A967 |
| Forming Process | Continuous cold coil winding / Hot coil winding | Internal Procedure |
| Welding Compatibility | TIG (GTAW), Orbital TIG, Laser Welding | ASME Section IX |
| Pressure Rating | Up to 4.0 MPa (design dependent) | PVDF / PED 2014/68/EU |
| End Preparation | Beveled, Plain, Threaded (as required) | ASME B1.20.1 |
| Tolerance (OD) | ±0.05 mm to ±0.10 mm | ASTM A511 |
4. Manufacturing Process
4.1 Process Flow
- Material Selection & Incoming Inspection: Certified mill sheets or seamless tubes are procured and subjected to chemical composition analysis (OES — Optical Emission Spectrometry) and mechanical property verification.
- Surface Preparation: Tubes undergo pickling and passivation treatment to remove oxide scales and establish a protective chromium oxide layer, ensuring optimal corrosion resistance.
- Coil Winding: Continuous cold or hot coiling is performed on CNC-controlled coil winding machines. The winding parameters (diameter, pitch, tension) are precisely controlled to ensure dimensional accuracy and uniform stress distribution throughout the coil.
- Welding — Internal Heat Recovery Configuration: The coil tube segments are joined using Tungsten Inert Gas (TIG) welding, also known as Gas Tungsten Arc Welding (GTAW), or Orbital TIG welding for automated, repeatable weld quality. Weld parameters are optimized to minimize Heat Affected Zone (HAZ) distortion and maintain metallurgical integrity. Back-purging with high-purity argon (≥ 99.99%) is employed to prevent internal oxidation. Weld qualification follows ASME Section IX procedures.
- Post-Weld Treatment: Welded joints undergo solution annealing (1050–1150 °C) followed by rapid quenching to restore full austenitic microstructure and maximize corrosion resistance. Final pickling and passivation complete the surface preparation.
- Pressure Testing & Inspection: Each coil assembly is hydrostatically or pneumatically pressure-tested to 1.5× the design pressure. Non-Destructive Testing (NDT) methods including Visual Testing (VT), Penetrant Testing (PT), Ultrasonic Testing (UT), and Radiographic Testing (RT) are applied as per applicable standards.
- Final Assembly & Packaging: Completed coil tubes are protected with anti-corrosion packaging materials and shipped in protective enclosures to prevent mechanical damage during transit.
4.2 Welding Considerations for Internal Heat Recovery Coiltube
The welding of internal heat recovery coil tubes presents unique challenges due to the confined geometry and the requirement for leak-tight, corrosion-resistant joints. Key considerations include:
- Heat Input Control: Low heat input techniques (≤ 2.5 kJ/mm) are preferred to limit grain growth in the HAZ and prevent sensitization (chromium carbide precipitation at grain boundaries, particularly in 304/316 grades).
- Filler Metal Selection: Matching filler metals (e.g., ER316L for AISI 316L base material) are used per AWS A5.9/A5.18 specifications to ensure homogeneity of weld metal properties.
- Interpass Temperature: Maintained below 150 °C to prevent tempering effects and ensure consistent mechanical properties.
- Root Pass Quality: Complete root penetration with back-purging is critical for internal heat recovery applications where fluid-side integrity is paramount.
5. Applications
- Industrial Waste Heat Recovery: Coiltubes serve as heat exchange elements in waste heat recovery (WHR) systems, recovering thermal energy from exhaust gases, flue gases, and process streams in power generation, petrochemical, and manufacturing industries.
- Internal Heat Exchangers: Installed within process vessels or reactors to provide internal heating or cooling, enabling precise temperature control in chemical reactors, polymerization units, and distillation columns.
- Energy Recovery Ventilators (ERV): Compact coil configurations are used in ventilation and HVAC systems to pre-condition incoming air streams by recovering thermal energy from exhaust air.
- Food & Pharmaceutical Processing: Sanitary-grade coil tubes (316L, electropolished) are employed in pasteurization, sterilization, and process heating systems where hygiene and corrosion resistance are critical.
- Marine & Offshore Systems: Duplex stainless steel coiltubes are used in ballast water heat management, engine cooling loops, and oil platform thermal systems.
- Geothermal & Solar Thermal Systems: Coil tubes function as heat collection elements in geothermal heat exchangers and concentrated solar thermal power plants.
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and supply chain |
| ISO 3834 | Quality requirements for welding of metallic materials |
| EN 10204 3.1 | Inspection certificates — material test reports per European standard |
| ASME Section IX | Welding and Brazing Qualifications for pressure vessel applications |
| ASTM A213 / A269 | Standard specifications for austenitic stainless steel seamless tubes |
| EN 10217-7 | European standard for seamless stainless steel tubes for pressure purposes |
| PED 2014/68/EU | European Pressure Equipment Directive compliance (Category I–IV) |
| 3.2 Material Test Reports | Third-party inspection certificates available upon request |
7. Unique Selling Points
- Superior Thermal Efficiency: The optimized coil geometry provides up to 40% greater heat transfer surface area per unit volume compared to straight tube configurations, significantly improving thermal recovery efficiency.
- Integrated Manufacturing: Wenzhou Jixing Metal Materials Co., Ltd. offers vertically integrated production from raw material selection through coil winding, welding, and post-weld treatment, ensuring consistent quality control at every stage.
- Expertise in Internal Heat Recovery Welding: The manufacturer possesses documented technical expertise in the welding of internal heat recovery coil tubes, with qualified welding procedures and certified welders following international standards.
- Customization Capability: Flexible manufacturing parameters allow for tailored coil diameters, tube dimensions, surface finishes, and end preparations to meet specific engineering drawings and application requirements.
- Full Traceability: Each production batch is traceable from mill certificate through final inspection, supporting regulatory compliance and quality assurance in critical applications.
- Extended Service Life: The combination of high-grade stainless steel materials, controlled welding processes, and comprehensive post-weld heat treatment ensures long-term durability and minimal maintenance in demanding industrial environments.
Technical Note: For applications involving chloride-containing environments (e.g., seawater, chemical processing), the use of AISI 316L or Duplex 2205/2507 grades is strongly recommended to mitigate the risk of Pitting Corrosion (PC) and Crevice Corrosion (CC). For high-temperature service above 450 °C, stabilized grades such as AISI 321 or AISI 347 should be specified to prevent sensitization-induced Intergranular Corrosion (IGC).