Stainless Steel Coiltube for Catalytic Regenerator Heat Extraction — Technical Specification
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product Catalog No. 1586), this coiltube (盘管, Coiled Tube) is engineered for extreme-duty thermal management in petrochemical catalytic regenerator systems. The product specification is informed by rigorous failure analysis studies conducted on industrial coiltube assemblies in refining operations, ensuring that every design parameter addresses the root causes of degradation observed in real-world service.
Product Overview
The Coiltube product line is designed as a helically wound, continuous-length tubing solution intended for heat extraction and heat transfer applications within catalytic cracking units (CCU) and fluid catalytic cracking (FCC) regenerators. Unlike straight pipe segments, coiltubes are formed into helical coils, which provide exceptional heat transfer efficiency due to enhanced turbulence and compact spatial footprint. These coils are typically installed inside the regenerator vessel, where they absorb radiant heat from the catalyst bed and transfer it to process water or steam, thereby controlling the operating temperature of the regenerator and recovering thermal energy.
The design philosophy of this coiltube incorporates lessons learned from documented failure analyses, including those involving oxidative scaling, creep rupture, thermal fatigue cracking, and high-temperature hydrogen attack (HTHA) observed in refinery coiltube assemblies. Each manufacturing parameter is calibrated to mitigate these known failure modes, extending service life and reducing unplanned shutdown events.
Material & Properties
Base Material Grades
The coiltube is fabricated from austenitic stainless steel and high-temperature alloy grades selected for their resistance to oxidation, carburization, and thermal cycling in regenerator environments:
- ASTM A318 / A318M — Stainless Steel Coil Tubing for High-Temperature Service (grades including TP304, TP304L, TP316, TP316L, TP310, TP310S)
- ASTM A269 — Seamless Austenitic Stainless Steel Tubing for Boilers, Heaters, and Exchangers
- ASTM A335 — Seamless Ferritic Alloy-Steel and Stainless Steel Boilers, Heaters, and Exchangers Tubing (for specific ferritic applications)
- SAE 310S / 310 — High-chromium, high-nickel austenitic grade for maximum oxidation resistance above 1000 °C
Key Mechanical and Thermal Properties
| Property | Typical Value (310S Grade) | Test Standard |
|---|---|---|
| Tensile Strength (RT) | ≥ 515 MPa | ASTM E8 |
| Yield Strength (0.2% offset, RT) | ≥ 205 MPa | ASTM E8 |
| Elongation (minimum, 50 mm gauge) | ≥ 35% | ASTM E8 |
| Creep Strength (1100 °C, 1000 h) | ≥ 45 MPa | ASTM E139 |
| Thermal Conductivity (100 °C) | 16.3 W/(m·K) | ASTM E153 |
| Linear Thermal Expansion (20–1000 °C) | 17.2 × 10⁻⁶ /K | ASTM E228 |
| Maximum Continuous Service Temperature | 1150 °C (oxidizing atmosphere) | Manufacturer's Data |
| Oxidation Scale Growth Rate (1000 °C) | ≤ 0.15 mm/year | ASTM G32 |
Chemical Composition (310S — Typical)
| Element | Minimum (%) | Maximum (%) |
|---|---|---|
| Carbon (C) | — | 0.08 |
| Chromium (Cr) | 24.0 | 26.0 |
| Nickel (Ni) | 19.0 | 22.0 |
| Manganese (Mn) | — | 2.0 |
| Silicon (Si) | — | 1.5 |
| Sulfur (S) | — | 0.03 |
| Phosphorus (P) | — | 0.035 |
Specifications
| Parameter | Specification | Reference Standard |
|---|---|---|
| Tube Outer Diameter (OD) | Φ25 mm – Φ159 mm (custom sizes available) | ASTM A318 / ASME B36.19M |
| Tube Wall Thickness | 1.5 mm – 8.0 mm | ASME B36.19M |
| Coil Diameter (CD) | 600 mm – 3000 mm (as per design requirement) | ASME B31.1 |
| Coil Length (per assembly) | Up to 150 m continuous coil | Manufacturer's Specification |
| Surface Finish | Mill finish (Ra ≤ 3.2 μm) or pickled & passivated (Ra ≤ 1.6 μm) | ASTM A380 |
| Heat Treatment Condition | Solution annealed (1050–1150 °C) + water/quench cooled | ASTM A318 §6.4 |
| Design Pressure | Up to 4.0 MPa (gas side) | ASME BPV Section I / B31.1 |
| Design Temperature | Up to 950 °C (catalyst bed interface) | ASME BPV Section I |
| Corrosion Allowance | 1.0 – 1.5 mm (design margin) | API 579 |
| End Forming | Plain end, beveled (37.5°), or threaded per ASME B1.20.1 | ASME B1.20.1 |
| Welding Method (if applicable) | GTAW (Gas Tungsten Arc Welding) with filler matching base grade | ASME Section IX QW-451 |
Manufacturing Process
The manufacturing of coiltube for catalytic regenerator heat extraction follows a multi-stage process designed to ensure metallurgical integrity, dimensional accuracy, and resistance to the severe degradation mechanisms identified in failure analyses:
- Material Procurement & Incoming Inspection — Raw bar stock or seamless pipe blanks are sourced from certified mills. Each heat lot is verified through mill test reports (MTR) covering chemical composition (ASTM E415 / E1251), mechanical properties, and non-destructive testing (NDT) results. Spectroscopic analysis confirms trace element control, particularly sulfur and phosphorus limits critical for hot short resistance during coiling.
- Hot Rolling & Annealing — Billet or round bar is hot-rolled to the target diameter. The material is then solution-annealed at 1050–1150 °C followed by controlled cooling to achieve a fully austenitic, carbide-free microstructure. This step is critical for preventing intergranular corrosion and ensuring uniform grain structure resistant to creep deformation.
- Piercing & Seamless Tube Forming — For larger diameters, the material is pierced into seamless tubes using Mannesmann or plug-rolling technology. The seamless construction eliminates weld seams that would be vulnerable to intergranular cracking and stress corrosion in high-temperature service.
- Pilger Rolling / Cold Drawing — Tubes are cold-worked to achieve precise outer diameter and wall thickness tolerances (±0.05 mm for OD, ±0.05 mm for wall). This controlled cold work introduces beneficial compressive residual stresses on the outer surface, improving fatigue life.
- Intermediate Annealing — After cold working, tubes undergo intermediate annealing to relieve accumulated residual stresses and restore ductility for the subsequent coiling operation.
- Coiling (Helical Forming) — The tube is helically wound around a precision mandrel using a specialized coiling machine. The forming process is performed at controlled temperatures (ambient or warm-formed at 200–400 °C) to avoid work hardening and cracking. Coil geometry parameters (coil diameter, pitch, number of turns) are controlled to ±2 mm tolerance. The coiling speed and mandrel surface finish are optimized to minimize surface scratches and micro-cracking.
- Post-Coiling Stress Relief — Coiled assemblies are stress-relieved at 850–950 °C (below the sensitization range) for a minimum of 1 hour per 25 mm of wall thickness. This step is critical based on failure analysis findings that residual coiling stresses accelerate creep and thermal fatigue degradation.
- Surface Treatment — Pickling and passivation (ASTM A380) removes scale, oxide films, and processing residues. The resulting passive chromium oxide layer provides immediate corrosion resistance. For high-temperature service, an additional controlled oxide growth treatment (1000–1100 °C, 2–4 hours) may be applied to pre-form a stable, adherent Cr₂O₃ scale layer.
- Quality Control & Testing — Comprehensive NDT and destructive testing are performed per the Quality Certifications section below.
- Packaging & Shipping — Coils are wrapped in moisture-proof polyethylene film and secured on wooden or steel pallets with V-block supports to prevent deformation during transport.
Applications
This coiltube product is specifically engineered for the following industrial applications, with primary focus on petrochemical and oil refining sectors:
- Catalytic Regenerator Heat Extraction — Primary application. Installed within the catalyst bed of fluid catalytic cracking (FCC) units, catalytic reformers, and hydrocrackers. The coiltube absorbs radiant heat from the exothermic catalyst regeneration reaction (coking burn-off), transferring it to process water or steam on the tube side. Typical operating conditions: 700–950 °C on the gas side, 15–25 MPa on the water/steam side.
- Fluidized Bed Reactor Cooling — Heat extraction coils for fluidized bed catalytic cracking (FBCC) and fluidized bed combustion (FBC) systems where temperatures exceed conventional heat exchanger limits.
- Pyrolysis Furnace Coils — Ethylene cracking furnaces and steam cracking coil tubes operating at 800–1150 °C with hydrocarbon gas atmospheres.
- Catalytic Combustion Heat Recovery — Coils for waste heat recovery in catalytic incineration and regenerative thermal oxidizer (RTO) systems.
- High-Temperature Steam Superheaters — Superheater coils in power generation boilers and industrial steam systems.
- Hydrogenation & Hydrocracking Units — Heat extraction coils for exothermic hydrogenation reactors in refineries.
Case Study: Failure Analysis Informed Design Improvements
The design specifications for this coiltube product incorporate findings from the Shijiazhuang Refinery Catalytic Regenerator Heat Extraction Coiltube Failure Analysis (石家庄炼油厂催化再生器取热盘管失效分析). Key failure mechanisms identified in that study included:
- Oxidative scaling and scale spallation at the gas-side surface, leading to localized hot spots and accelerated wall thinning
- Thermal fatigue cracking at coil bends due to cyclic temperature differentials between the inner and outer surfaces of the helix
- Creep rupture at sustained high-temperature zones where local temperatures exceeded the design limit
- Residual stress effects from the coiling process that reduced creep-rupture life by 30–40%
Based on these findings, this product specification mandates: (a) post-coiling stress relief to eliminate forming-induced residual stresses; (b) minimum wall thickness with corrosion allowance of 1.5 mm; (c) material grade selection (310S or higher) for oxidation resistance at 950 °C; and (d) controlled coiling geometry to minimize thermal gradient across the wall section.
Quality Certifications
Every coiltube assembly produced by Wenzhou