Stainless Steel Coil Tube — Catalytic Cracking Unit Regenerator Heat Extraction Tube (Coiltube)
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a specialized heat-extraction tube designed for high-temperature service environments within FCCU (Fluid Catalytic Cracking Unit) Regenerators. These coil tubes are integral components of heat recovery systems, where they absorb thermal energy from the regenerator catalyst bed and transfer it to process water or steam, thereby optimizing energy efficiency and reducing overall fuel consumption in petroleum refining operations.
This product represents a critical engineering solution for severe thermal cycling conditions, high-temperature oxidation resistance, and long-term mechanical integrity in continuous-duty industrial applications. The coiltube design is specifically engineered to withstand the extreme operating temperatures (up to 750°C / 1382°F) and erosive catalyst particle environments inherent in regenerator service.
2. Material & Properties
The coil tubes are fabricated from high-performance austenitic and heat-resistant stainless steels, selected based on the specific thermal and mechanical demands of the regenerator heat extraction application. The following material grades are typically specified:
- SAE 310 / UNS S31008 — Chromium-Nickel austenitic stainless steel with exceptional high-temperature oxidation resistance and thermal stability up to 1150°C.
- SAE 309 / UNS S30908 — Commonly used as welding filler material for dissimilar metal joints between 310-grade tube and carbon steel headers.
- SAE 347H / UNS S34709 — Stabilized austenitic grade (Nb-stabilized) for improved resistance to intergranular corrosion and sensitization at elevated temperatures.
- SAE 321H / UNS S32109 — Titanium-stabilized variant offering excellent resistance to thermal fatigue and scale formation.
Key Mechanical & Physical Properties (Typical for Grade 310H)
| Property | Specification |
|---|---|
| Tensile Strength (RT) | ≥ 515 MPa (74.7 ksi) |
| Tensile Strength (800°C) | ≥ 150 MPa (21.8 ksi) |
| Yield Strength (RT, 0.2% offset) | ≥ 205 MPa (29.7 ksi) |
| Elongation (RT) | ≥ 40% |
| Thermal Conductivity (RT) | ~26 W/(m·K) |
| Linear Thermal Expansion (20–800°C) | 18.5 × 10⁻⁶ /°C |
| Maximum Continuous Service Temperature | 1150°C (2094°F) |
| Oxidation Resistance (Air) | Continuous exposure up to 1099°C without significant scale growth |
| Corrosion Resistance (Sulfidation) | Resistant to cyclic sulfidation up to 800°C |
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coiltube (Heat Extraction Coil Tube) |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
| Item Number | 1219 |
| Applicable Standard — Tube | ASTM A213 TP310H, ASTM A269, GB/T 14976 |
| Applicable Standard — Welding | ASME Section IX, AWS D10.9, ISO 13919 |
| Outer Diameter (OD) | 25 mm – 89 mm (1" – 3½") |
| Wall Thickness | 2.0 mm – 6.0 mm |
| Coil Diameter (Mean) | 1.5 m – 6.0 m (configurable per design) |
| Tube Length per Coil | 15 m – 120 m (continuous coil) |
| Surface Finish | Mill finish or polished (Ra ≤ 0.8 μm upon request) |
| Heat Treatment | Solution annealed at 1040–1120°C, followed by water quench |
| Maximum Operating Temperature | 750°C (1382°F) in regenerator service |
| Maximum Operating Pressure | ≤ 3.0 MPa (435 psi) |
| Service Medium | Water / Low-pressure steam / Process fluid |
| Design Life | ≥ 15 years in continuous FCCU regenerator service |
| Applicable Codes | ASME BPVC Section I, TEMA, API 530 |
4. Manufacturing Process
The production of high-quality coiltubes for regenerator heat extraction service involves a rigorous multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and long-term reliability:
- Raw Material Selection & Inspection: Hot-rolled stainless steel strip or tube blanks conforming to ASTM A213 TP310H chemical composition requirements. Incoming material undergoes full spectrographic analysis (OES — Optical Emission Spectroscopy) and mechanical property verification.
- Pipe Forming & Seam Welding: Continuous straight-seam tube forming using precision roll-forming equipment. The longitudinal seam is welded by GMAW (Gas Metal Arc Welding) or GTAW (Gas Tungsten Arc Welding) processes using matching filler wire (e.g., ER309L or ER310L per AWS A5.9/A5.11).
- Solution Annealing: The formed tube undergoes full solution annealing at 1040–1120°C in a protective atmosphere (nitrogen or vacuum) furnace, followed by rapid water quenching. This process dissolves carbides, restores full austenitic structure, and maximizes corrosion resistance.
- Pickling & Passivation: Post-welding acid pickling (nitric/hydrofluoric acid blend) to remove oxide scale, followed by passivation treatment to establish a protective chromium oxide film.
- Coil Winding: The annealed tube is wound into the specified coil geometry using CNC-controlled winding machinery to maintain consistent bend radius (minimum 3D — three times the tube diameter) and avoid work hardening or plastic deformation.
- Non-Destructive Testing (NDT):
- 100% RT (Radiographic Testing) of all weld seams per ASME Section V Article 2
- ET (Eddy Current Testing) for wall thickness measurement and defect detection
- PT (Penetrant Testing) of surface-critical areas
- Hydrostatic Pressure Testing: Each coil is pressure-tested at 1.5× the maximum design pressure (minimum 4.5 MPa) with no leakage or visible deformation.
- Dimensional Inspection: Verification of OD, wall thickness, coil diameter, and overall length per ASTM A213 and customer specifications.
5. Welding Material Selection — Critical Design Considerations
Based on extensive engineering experience documented in the study "Selection of Welding Materials for Catalytic Cracking Unit Regenerator Heat Extraction Coiltube," the following principles govern welding material selection:
- Dissimilar Metal Joints: Where 310H coil tubes are welded to carbon steel (e.g., SA-106 Gr. B) headers or support structures, ER309L (AWS A5.9) / E309L (AWS A5.4) filler metal is recommended. The 309L grade provides adequate dilution tolerance, preventing excessive chromium and nickel concentration in the weld metal while maintaining ductility and crack resistance.
- Like-to-Like Joints: For 310H-to-310H welds, ER310L / E310L filler is specified to maintain high-temperature strength and oxidation resistance.
- Weld Preheat: Preheat temperature of 150–200°C is recommended for thick-section joints to minimize residual stress and prevent cold cracking.
- Interpass Temperature: Limited to ≤ 250°C for multi-pass welds to avoid grain growth and sensitization.
- Post-Weld Heat Treatment (PWHT): Solution treatment at 1065°C for 1 hour per 25 mm thickness, followed by air or forced-air cooling, is required for joints exceeding 6 mm wall thickness.
6. Applications
The stainless steel coiltube product is primarily designed for the following industrial applications:
- FCCU Regenerator Heat Extraction: Primary application — heat recovery from the regenerator catalyst bed in fluid catalytic cracking units, converting thermal energy into medium-pressure steam for process use.
- Petrochemical Heat Exchangers: High-temperature process heat exchange in ethylene crackers, reformers, and coker units.
- Boiler Tubing: Waterwall tubes and superheater tubes in industrial boilers operating at elevated temperatures.
- Power Generation: Heat recovery steam generators (HRSGs) in combined-cycle power plants.
- Industrial Furnaces: Burner tubes and radiant sections in continuous annealing and heat treatment furnaces.
- Environmental Systems: Flue gas heat recovery and waste heat boilers in cement and glass manufacturing.
7. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management systems and certifications ensuring product conformity to international standards:
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management |
| ASME "S" Stamp | Pressure Vessel / Piping Components |
| EN 10204 Type 3.1 | Material Test Certificates (MTC) |
| ASTM A213 / A269 | Tube Material Conformance |
| ASME Section IX | Welding Procedure Qualification (WPQ/WPS) |
| API 5CT / API 5L | Where applicable for process piping integration |
8. Unique Selling Points
- Engineered for Extreme Environments: Materials and design specifically validated for FCCU regenerator service with continuous exposure to temperatures exceeding 700°C and abrasive catalyst particle impingement.
- Expert Welding Material Selection: Drawing from documented engineering experience (Reference No. 1219), the company provides technically justified welding procedure specifications that minimize weld defects, reduce cracking susceptibility, and maximize service life.
- Full Traceability: Each coil tube is traceable from raw material heat number through all manufacturing stages, with complete documentation including MTC, NDT reports, and hydrostatic test records.
- Customizable Coil Geometry: Flexible manufacturing capability allows customization of coil diameter, tube dimensions, and configuration to match specific regenerator design requirements.
- Proven Long-Term Reliability: Design life exceeding 15 years in continuous service, validated by field performance data from major petrochemical installations.
- Comprehensive Testing Protocol: 100% non-destructive examination coverage ensuring zero-defect delivery and maximum operational safety.
9. Technical Notes & Recommendations
Note: The selection of welding materials for coiltube fabrication in regenerator service is a critical design decision that directly impacts long-term reliability. Studies have demonstrated that improper filler metal selection — particularly the use of 308L instead of 309L for dissimilar joints involving 310H and carbon steel — can result in weld metal dilution issues, reduced creep strength, and premature failure under thermal cycling conditions. Wenzhou Jixing Metal Materials Co., Ltd adheres to rigorous welding material selection protocols as documented in their engineering knowledge base (Item No. 1219), ensuring optimal metallurgical compatibility and extended service life for all fabricated coiltube assemblies.