Stainless Steel Coil Tube for Catalytic Regenerator Heat Extraction Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a specialized heat-transfer component engineered for high-temperature, high-pressure environments within catalytic regenerator units in petrochemical and refining operations. This product is designed to serve as an internal heat extraction element, transferring thermal energy from catalytic cracking or regeneration processes to a working fluid (typically boiler feedwater or thermal oil), thereby recovering waste heat and improving overall plant energy efficiency.
Catalytic regenerator environments present extreme operational challenges, including temperatures ranging from 650°C to 850°C, cyclic thermal loading, abrasive catalyst particle erosion, and corrosive flue gas constituents. The coil tube product from Wenzhou Jixing Metal Materials Co., Ltd. is specifically engineered to withstand these demanding conditions while maintaining structural integrity and thermal performance over extended service intervals.
Material & Properties
The coil tube is fabricated from high-grade austenitic and super-austenitic stainless steels selected for exceptional oxidation resistance, thermal stability, and mechanical strength at elevated temperatures.
Primary Material Grades
- SAE 310 / S31008 (CF8M): Chromium-Nickel austenitic stainless steel with minimum 24% Cr and 19% Ni content, offering superior resistance to high-temperature oxidation and scaling up to 1150°C. This grade is the preferred selection for the outer tube surface directly exposed to regenerator flue gas.
- SAE 309 / S30908: High-temperature austenitic stainless steel with 34–38% Cr and 19–22% Ni, providing excellent resistance to thermal fatigue and creep deformation under cyclic loading conditions.
- SAE 321 / S32108 (Heat-Resistant): Stabilized austenitic stainless steel containing titanium (Ti ≥ 5× C), offering resistance to intergranular corrosion and improved creep strength at temperatures up to 870°C.
- SAE 347 / S34708 (Heat-Resistant): Stabilized with niobium (Nb ≥ 10× C), providing enhanced resistance to sensitization and improved high-temperature mechanical properties.
Key Mechanical Properties (Typical at Elevated Temperature)
- Yield Strength at 650°C: ≥ 120 MPa (for Grade 310)
- Tensile Strength at 650°C: ≥ 220 MPa (for Grade 310)
- Creep Rupture Life at 800°C / 50 MPa: ≥ 10,000 hours
- Thermal Conductivity at 800°C: 30–35 W/(m·K)
- Linear Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–800°C)
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ50.8 mm – Φ88.9 mm (2" – 3.5") | ASTM A213 / A269 |
| Wall Thickness (WT) | 4.0 mm – 12.7 mm (5/32" – 1/2") | ASME B36.19M |
| Coil Bend Radius (R) | 150 mm – 600 mm (configurable) | Custom per drawing |
| Maximum Operating Temperature | 850°C (continuous), 1150°C (intermittent) | Grade-dependent |
| Maximum Operating Pressure | 15.0 MPa (2175 psi) | ASME BPV Code Section I |
| Surface Finish | Ra ≤ 0.8 μm (inner), Ra ≤ 1.6 μm (outer) | ASTM A478 |
| Heat Treatment | Solution Annealing at 1050–1150°C followed by water quench | ASTM A213 |
| Acceptable Deviation (OD) | ±0.5% of nominal | ASTM A213 |
| Acceptable Deviation (WT) | −0.1 mm / +0.1 mm | ASME B36.19M |
| Length per Coil | Up to 120 m (continuous) | Custom per order |
| End Condition | Beveled ends per ASME B1.20.1, or flat-cut with deburred | ASME B1.20.1 |
Manufacturing Process
1. Material Selection and Incoming Inspection
Raw material is procured from certified mills with full material traceability. Each heat of stainless steel tubing undergoes rigorous incoming inspection including chemical composition analysis (per ASTM E415 / E1251), mechanical property verification, and visual surface inspection for defects.
2. Straightening and Cutting
As-received tubing is cold-straightened to achieve straightness tolerance of ≤ 1 mm/m. Lengths are cut to specified dimensions using precision cutting equipment to prevent work hardening and surface damage.
3. Cold Bending / Coil Forming
The coil tube is formed using specialized mandrel-assisted cold bending machinery. The bending process is carefully controlled to prevent:
- Wall thinning exceeding 10% at the bend apex
- Surface wrinkling or folding on the inner radius
- Excessive work hardening that compromises creep resistance
The bending process is performed at controlled speeds with appropriate mandrel support to maintain dimensional accuracy throughout the coil geometry.
4. Solution Heat Treatment (Post-Forming)
Following coil forming, the entire assembly undergoes solution annealing at 1050–1150°C in a protective atmosphere (argon or vacuum) to relieve residual stresses induced during bending. This treatment restores full austenitic microstructure, eliminates strain hardening, and ensures uniform mechanical properties throughout the coil.
5. Surface Treatment and Passivation
The inner and outer surfaces undergo acid pickling and passivation treatment to remove any heat scale, oxidation, or surface contaminants. The passivation layer (chromium oxide film) is verified per ASTM A967 to ensure corrosion resistance is fully restored.
6. Non-Destructive Testing (NDT)
- Eddy Current Testing (ECT): 100% coverage of the coil tube to detect surface and near-surface defects per ASTM E169.
- Helium Leak Testing: Performed at 1.5× design pressure to verify weld integrity and tube wall continuity per ASTM F2126.
- Dimensional Verification: CMM (Coordinate Measuring Machine) inspection of coil geometry, bend radii, and straight sections.
Applications
Primary Application: Catalytic Regenerator Heat Extraction
The coil tube is installed internally within fluid catalytic cracking (FCC) regenerator units and other catalytic regeneration systems. Its primary function is to extract waste heat from the hot flue gas (typically 650–850°C) generated during catalyst regeneration. The extracted heat is used to generate high-pressure steam, preheat process streams, or supply thermal energy to downstream units.
Design Considerations for Regenerator Service
- Erosion Resistance: The tube geometry and material selection account for abrasive catalyst particle impact, with wall thickness selected to ensure minimum 10-year erosion life at design velocity limits (typically ≤ 25 m/s gas velocity).
- Thermal Fatigue Resistance: The material and design accommodate cyclic temperature fluctuations between startup/shutdown conditions and steady-state operation.
- Creep Resistance: At sustained operating temperatures above 650°C, the Grade 310/309 material provides adequate creep strength to prevent progressive deformation over the design life.
- Corrosion Resistance: Resistance to sulfuric acid dew-point corrosion, chloride-induced pitting, and high-temperature sulfurization.
Secondary Applications
- Catalytic reformer heat recovery systems
- Coker heater coil tubes
- Hydrocracker overhead heat exchanger coil sections
- Industrial furnace heat transfer coils
- Power generation waste heat recovery systems
Quality Certifications
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing and supply chain |
| ISO 3834-2 | Quality requirements for welding of metallic products |
| ASME Section I | Boiler and Pressure Vessel Code compliance for pressure-containing components |
| API 5CT / API 5L | American Petroleum Institute standards for tubular products (where applicable) |
| NACE MR0175 / ISO 15156 | Material requirements for resistance to sulfide stress cracking in sour service |
| EN 10204 3.1 | Material test report with independent inspection certification |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for EU market |
| Mill Test Reports (MTR) | Full traceability from raw material mill through final product delivery |
Unique Selling Points
1. Specialized Regenerator-Service Engineering: Unlike generic heat exchanger tubing, this coil tube product is specifically engineered with lessons learned from catalytic regenerator failure analysis — addressing the root causes of tube rupture including erosion, thermal fatigue cracking, creep deformation, and high-temperature corrosion. The design incorporates enhanced wall thickness at high-erosion zones and optimized geometry to minimize flow-induced vibration.
2. Superior High-Temperature Performance: The selection of Grade 310/309 stainless steel provides a safety margin of ≥ 100°C above maximum operating temperature, ensuring long-term structural integrity even under transient over-temperature events.
3. Comprehensive Post-Forming Heat Treatment: Full solution annealing after coil forming eliminates residual stresses that would otherwise accelerate creep deformation and thermal fatigue cracking during service — a critical differentiator over products that skip this step to reduce cost.
4. Full Traceability and Third-Party Verification: Every coil tube is accompanied by complete material traceability documentation, with all critical dimensions and properties verified by independent third-party inspection agencies (e.g., SGS, Bureau Veritas, DNV).
5. Custom Geometry Engineering: The coil geometry is optimized per specific regenerator vessel dimensions and flow patterns, with CFD (Computational Fluid Dynamics) analysis available to ensure uniform heat transfer distribution and minimal erosion zones.
Failure Prevention Features
Informed by extensive analysis of catalytic regenerator coil tube failure modes, this product incorporates the following engineering safeguards:
- Enhanced Wall Thickness at Erosion Zones: Additional wall thickness (typically 15–25% above minimum code requirement) at locations exposed to highest catalyst particle impact velocity.
- Optimized Bend Geometry: Generous bend radii (≥ 4× tube OD) to minimize stress concentration and reduce susceptibility to thermal fatigue cracking at bend apex.
- Internal Support Ring Design: Engineered support structures to prevent tube sagging, vibration-induced fretting, and contact erosion between adjacent coil passes.
- Protective Coating Options: Optional ceramic or refractory coating on the outer surface to provide additional erosion and corrosion protection in aggressive service environments.