Stainless Steel Coil Tube — Catalytic Cracking Regenerator Heat Recovery Tube
Product Overview
The Stainless Steel Coil Tube (Coiltube, 盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for high-temperature heat recovery systems within catalytic cracking units (FCCU, Fluid Catalytic Cracking Unit) and analogous severe-service industrial environments. These coil tubes are installed inside the regenerator vessel to extract thermal energy from the circulating catalyst stream, thereby recovering waste heat, improving overall process thermal efficiency, and reducing fuel consumption in downstream systems.
Drawn from extensive field failure analysis studies — notably the documented investigation of heat recovery coil tube failures in the Luoyang Refinery FCC regenerator — the design philosophy of this product integrates critical lessons learned regarding high-temperature oxidation, thermal fatigue, cyclic stress cracking, and abrasive wear mechanisms. The resulting product is engineered to deliver superior service life, resistance to thermal degradation, and mechanical integrity under the most demanding operating conditions encountered in petroleum refining and petrochemical processing.
Material & Properties
The coil tubes are fabricated from high-grade austenitic and austenitic-ferritic stainless steel grades selected to provide optimal combinations of high-temperature strength, oxidation resistance, thermal fatigue resistance, and resistance to sulfidation and chloridation attack inherent in FCC regenerator environments.
Primary Material Grades
- 310S (UNS S31008) — Superior hot strength up to 1150 °C; excellent resistance to cyclic oxidation and scaling in reducing and oxidizing atmospheres.
- 347H (UNS S34709) — Stabilized austenitic grade with niobium addition; outstanding resistance to intergranular corrosion and thermal fatigue; recommended for sustained service above 480 °C.
- 321H (UNS S32109) — Titanium-stabilized austenitic grade; excellent resistance to sensitization and intergranular corrosion in high-temperature service.
- TP347H / TP321H (ASME SA-213) — Heat-exchanger grade seamless tubes meeting ASME Boiler and Pressure Vessel Code requirements for high-temperature applications.
- 06Cr19Ni10 (GB/T 12771) — Equivalent Chinese standard grade for general stainless steel coil tube applications.
Typical Mechanical Properties (at 20 °C)
| Property | 310S | 347H | 321H |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 515 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa |
| Elongation (A50) | ≥ 40 % | ≥ 40 % | ≥ 40 % |
| Density (ρ) | 8.03 g/cm³ | 8.00 g/cm³ | 8.00 g/cm³ |
| Thermal Conductivity (λ, 100 °C) | 21.5 W/(m·K) | 16.3 W/(m·K) | 16.3 W/(m·K) |
| Maximum Continuous Service Temperature | 1150 °C | 980 °C | 980 °C |
| Corrosion Potential (Scheffler Diagram) | — | ≥ 0.07 % Nb (stabilized) | ≥ 0.02 % Ti (stabilized) |
Key Material Advantages
- High-Temperature Oxidation Resistance: The chromium oxide (Cr₂O₃) passive film formed on the tube surface provides a continuous protective barrier against scale formation at temperatures exceeding 800 °C, directly addressing the primary failure mode identified in the Luoyang Refinery regenerator coil tube investigation.
- Thermal Fatigue Resistance: Enhanced elongation and fatigue limit properties enable the coil tubes to withstand repeated thermal cycling (ΔT up to 300 °C per cycle) without crack initiation or propagation.
- Intergranular Corrosion Resistance: Stabilization treatments (Ti or Nb additions) prevent chromium carbide precipitation at grain boundaries, eliminating the sensitization-induced intergranular attack that was a contributing factor in historical coil tube failures.
- Resistance to Hot Sulfidation: Elevated chromium and nickel content provides resistance to sulfidation attack from SO₂/SO₃ and H₂S present in the regenerator flue gas atmosphere.
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ25 mm – Φ114 mm (custom sizes available) | ASTM A213 / GB/T 12771 |
| Wall Thickness (WT) | 1.5 mm – 6.0 mm (tolerance ±10 %) | ASTM A213 / ASME B36.19M |
| Coil Bend Radius (R) | 3D – 10D (D = outer diameter) | Project-specific design |
| Tube Length per Coil | Up to 60 m per continuous coil | — |
| Coil Diameter (Bundle OD) | Up to 2,400 mm | — |
| Surface Finish | Pickled & Passivated (Ra ≤ 0.8 μm) | ASTM A967 / GB/T 4237 |
| End Treatment | Plain end, beveled end, or socket-weld end | ASME B16.25 |
| Manufacturing Method | Seamless (hot-rolled, cold-drawn) or ERW welded with full penetration weld | ASTM A213 / GB/T 14976 |
| Heat Treatment | Solution annealed at 1050 °C – 1150 °C, water or air cooled | ASTM A213 / ASME SA-213 |
| Maximum Operating Temperature | Up to 1,050 °C (grade-dependent) | — |
| Maximum Operating Pressure | Up to 2.5 MPa (design-dependent) | ASME BPV Code Section VIII |
| Dimensional Tolerance (OD) | ±0.05D (minimum ±0.05 mm) | ASTM A213 |
| Dimensional Tolerance (WT) | ±10 % of nominal | ASTM A213 |
| Roundness | ≤ 2 % of OD | ASTM A213 |
| Coil Straightness | ≤ 0.3 % of coil length per meter | — |
Manufacturing Process
The manufacturing of high-performance coil tubes follows a rigorously controlled multi-stage process designed to ensure metallurgical integrity, dimensional accuracy, and resistance to the failure mechanisms documented in FCC regenerator field studies.
Process Flow
- Raw Material Selection & Inspection: Certified stainless steel seamless tubes or steel strip are procured from qualified mills with full mill test reports (MTR). Incoming material undergoes chemical composition analysis (spectrometry), mechanical testing, and visual inspection per ASTM A213 / GB/T 12771 requirements.
- Cold Drawing (for seamless tube stock): Tubes are cold-drawn through precision dies to achieve the target outer diameter and wall thickness with tight tolerances. This process improves surface finish, reduces grain size, and enhances mechanical properties.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at temperatures between 1050 °C and 1150 °C followed by rapid cooling (water quench or controlled air cool) to dissolve carbide precipitates, restore full austenitic microstructure, and maximize corrosion and high-temperature resistance.
- Pickling & Passivation: The tube surface is cleaned by acid pickling (nitric/hydrofluoric acid blend) to remove oxide scale, followed by passivation treatment to establish a uniform chromium-rich passive film. This is critical for preventing premature oxidation initiation.
- Coil Bending / Forming: Tubes are cold-bent or warm-bent into the specified coil geometry using CNC-controlled bending machinery. Bend radii are carefully controlled (typically ≥ 5D) to minimize residual stresses and avoid work-hardening-induced cracking. Internal bending mandrels or tooling are used to prevent tube ovalization and wrinkling.
- Welding (if applicable): Tube-to-header connections are welded using GTAW (Gas Tungsten Arc Welding) or orbital welding with inert gas (argon) shielding. Weld procedures are qualified per ASME Section IX / ISO 15614. Welds are subjected to 100 % visual inspection and selected radiographic testing (RT) or ultrasonic testing (UT).
- Post-Weld Heat Treatment (PWHT): Welded assemblies undergo post-weld annealing to relieve welding residual stresses and restore the solution-annealed microstructure in the heat-affected zone (HAZ).
- Final Inspection & Testing: Completed coil tubes undergo dimensional inspection, surface quality verification, hydrostatic pressure testing (1.5× design pressure per ASTM A213), and non-destructive testing (NDT) including eddy current testing (ECT) for wall thickness verification and surface defect detection.
- Marking, Packaging & Delivery: Each coil tube is marked with material grade, heat number, dimensions, and lot identification. Tubes are packaged with protective end caps and wrapped in moisture-proof material for shipment.
Applications
Wenzhou Jixing Metal Materials Co., Ltd. stainless steel coil tubes are engineered for the most demanding heat recovery and process heating applications in the petroleum refining, petrochemical, and power generation industries.
Primary Application Areas
- Catalytic Cracking Unit (FCCU) Regenerator Heat Recovery: Coil tubes installed within the FCC regenerator to extract heat from the hot catalyst stream (typically 650 °C – 800 °C), recovering energy for steam generation or feed preheating. This is the primary application addressed by the Luoyang Refinery failure study, where improved material selection and design have been shown to extend service life significantly.
- Crude Oil Distillation Unit (CDU) Heat Integration: High-temperature heat exchange coils for recovering thermal energy from overhead vapor streams and hot process streams.
- Visbreaking and Delay Coking Unit Heat Recovery: Coil tubes exposed to severe coking and thermal degradation conditions in high-temperature visbreaking and coking processes.
- Hydrocracker and Reforming Unit Heat Recovery: Integration of heat recovery coils in hydrogen-rich, high-temperature process streams.
- Boiler Fired Heaters and Waste Heat Boilers: Tubular heating coils for waste heat boiler (WHB) applications in refinery and petrochemical complexes.
- Petrochemical Polymerization Reactors: Heat removal coils in exothermic polymerization reactors (e.g., polypropylene, polyethylene production).
- Power Generation Boiler Economizers and Air Preheaters: Stainless steel coil tubes in ultra-supercritical boiler systems for improved efficiency and reduced NOx emissions.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that every coil tube product meets or exceeds international and national standards.
Quality Management System
- ISO 9001:2015 — Quality Management Systems certification for consistent product quality and customer satisfaction.
- ISO 14001:2015 — Environmental Management Systems certification for environmentally responsible manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
Product Standards & Codes
- ASTM A213 / ASME SA-213 — Standard Specification for Seamless and Welded Austenistic Stainless Steel and Heat-Resisting Alloy Tubes for High-Temperature Service.
- GB/T 12771 — Technical requirements for stainless steel seamless tubes for general use (Chinese National Standard).
- GB/T 14976 — Technical requirements for stainless steel welded tubes for fluid transport (Chinese National Standard).
- ASME BPV Code Section VIII, Division 1 — Rules for Construction of Pressure Vessels (applicable to pressure-containing coil tube assemblies).
- API 5CT / API 5L — For coil tubes used in oil and gas industry applications requiring API certification.
- NACE MR0175 / ISO 15156 — For coil tubes used in sour service environments containing H₂S.
- EN 10216-5 — European standard for technical delivery conditions for seamless and welded stainless steel tubes.
Testing & Inspection Capabilities
- Chemical Analysis: Optical emission spectrometry (OES) for full chemical composition verification per ASTM E415.
- Mechanical Testing: Tensile testing per ASTM A370; hardness testing per ASTM E92 (Rockwell B/C scales).
- Hydrostatic Testing: 100 % hydrostatic pressure testing at 1.5× design pressure per ASTM A213, with no leakage or permanent deformation.
- Non-Destructive Testing (NDT): Eddy current testing (ECT) per ASTM