Stainless Steel Coil Tube for Regenerator Heat Transfer (Coiltube)
1. Product Overview
The Stainless Steel Coil Tube (盘管/Coiltube) is a precision-engineered tubular product designed for use as an internal heat extraction coil in fluid catalytic cracking (FCC) regenerators and similar high-temperature industrial processes. These coil tubes serve as critical heat transfer elements, extracting excess thermal energy from hot flue gas or catalyst streams to control regenerator bed temperatures and improve overall process efficiency.
Based on extensive failure analysis studies of regenerator heat extraction coil tubes, Wenzhou Jixing Metal Materials Co., Ltd. has developed a specialized product line that addresses the primary degradation mechanisms encountered in service—including thermal fatigue (热疲劳), intergranular corrosion (晶间腐蚀), oxidative scaling (氧化结垢), and creep rupture (蠕变断裂). The coil tube design incorporates material selection, geometric optimization, and advanced manufacturing processes to maximize service life under extreme operating conditions.
2. Material & Properties
2.1 Available Material Grades
- 310S / UNS S31008 — Austenitic stainless steel with excellent resistance to thermal cycling and high-temperature oxidation up to 1150°C (2100°F). Preferred for regenerator applications with peak tube wall temperatures exceeding 900°C.
- 309S / UNS S30908 — Austenitic stainless steel offering good thermal fatigue resistance and moderate creep strength, suitable for moderate-temperature regenerator zones.
- 316L / UNS S31603 — Low-carbon austenitic stainless steel with enhanced resistance to intergranular corrosion due to reduced carbon content (≤0.03% C), ideal where sulfur and chloride exposure is a concern.
- 321H / UNS S32168 — Titanium-stabilized austenitic stainless steel providing superior resistance to intergranular corrosion in the temperature range of 425–870°C (800–1600°F).
- 347H / UNS S34768 — Niobium-stabilized austenitic stainless steel with excellent resistance to thermal cracking and carburization.
2.2 Key Mechanical & Physical Properties (Typical for Grade 310S)
- Tensile Strength (拉伸强度): ≥515 MPa at 20°C; ≥170 MPa at 900°C
- Yield Strength (屈服强度): ≥205 MPa at 20°C (0.2% offset)
- Elongation (延伸率): ≥35% at 20°C (50 mm gauge length)
- Thermal Conductivity (导热系数): 24 W/(m·K) at 100°C; 34 W/(m·K) at 900°C
- Thermal Expansion Coefficient (热膨胀系数): 16.3 × 10⁻⁶ /K (20–1000°C)
- Maximum Continuous Service Temperature (最高连续使用温度): 1150°C
- Carburization Resistance (抗渗碳性): Excellent above 900°C
2.3 Chemical Composition Requirements (Grade 310S, wt%)
| Element | Specification | Element | Specification |
|---|---|---|---|
| C (Carbon) | ≤ 0.08 | Ni (Nickel) | 19.0 – 25.0 |
| Mn (Manganese) | ≤ 2.00 | Cr (Chromium) | 24.0 – 26.0 |
| P (Phosphorus) | ≤ 0.045 | S (Sulfur) | ≤ 0.030 |
| S (Sulfur) | ≤ 0.030 | N (Nitrogen) | ≤ 0.10 |
| Si (Silicon) | ≤ 1.50 | Fe (Iron) | Balance |
3. Specifications
| Parameter | Specification | Unit | Standard / Reference |
|---|---|---|---|
| Outer Diameter (OD) Range | 19.05 – 76.20 | mm | ASTM A213 / ASME SA-213 |
| Wall Thickness Range | 1.50 – 6.35 | mm | ASTM A213 / ASME SA-213 | OD Tolerance | ± 0.10 (OD ≤ 38.1 mm); ± 0.15 (OD > 38.1 mm) | mm | ASTM A213 |
| Wall Thickness Tolerance | ± 10% of nominal | — | ASTM A213 |
| Coil Winding Diameter | 300 – 3000 | mm | Custom / Project Specification |
| Coil Length (as supplied) | 5 – 50 | m | Custom / Project Specification |
| Surface Finish (Internal) | RA ≤ 1.6 μm (polished); RA ≤ 0.8 μm (electropolished) | μm | ASTM A269 / Custom |
| Surface Finish (External) | Mill finish / Pickled & Passivated | — | ASTM A473 |
| Heat Treatment | Solution Annealing (1010–1150°C) + Water Quench | — | ASTM A213 |
| End Form | Plain / Beveled / Threaded / Flanged | — | ASME B16.11 / Custom |
| Maximum Operating Temperature | 1100 | °C | Material-dependent |
| Maximum Operating Pressure | 15 | MPa | ASME B31.3 / Material-dependent |
| Coil Straightness (after unwinding) | ≤ 1.5 mm/m | mm/m | Custom / Project Specification |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection — Incoming stainless steel seamless pipe or welded pipe undergoes full material verification including mill test certificates (MTC), spectrographic analysis (PMI), and visual surface inspection per ASTM E394 (spark test) or ASTM E1426 (XRF).
- Cutting & End Preparation — Raw pipe is cut to required lengths with precision shearing or plasma cutting. Ends are deburred, chamfered, and cleaned to remove oxide scale.
- Coil Winding (盘管成型) — The straight pipe is wound into the specified coil geometry using a CNC-controlled coil winding machine. The winding process is carefully controlled to maintain uniform bend radius, avoid plastic deformation, and prevent surface damage. Typical minimum bend radius is 3× OD for seamless pipe and 4× OD for welded pipe.
- Post-Winding Annealing — Coiled tubes undergo stress-relief annealing at 800–900°C in a protective atmosphere (nitrogen or vacuum) to eliminate residual stresses introduced during the winding process, thereby improving resistance to thermal fatigue and stress corrosion cracking.
- Pickling & Passivation — The coil surface is treated with a controlled acid pickling solution (HNO₃/HF mixture) to remove oxide scale and contamination, followed by passivation to restore the protective chromium oxide film per ASTM A967.
- Dimensional & Non-Destructive Testing (NDT) — Each coil is subjected to hydrostatic pressure testing (per ASTM A213), dimensional verification, and optional eddy current testing (ASTM E309) or ultrasonic testing (ASTM E213) for internal defect detection.
- Final Inspection & Packaging — Coils are inspected for surface quality, marked with product identification, wrapped in protective material, and packaged for shipment.
4.2 Critical Process Controls for Regenerator Applications
Failure analysis of regenerator heat extraction coil tubes has identified that thermal fatigue cracking (热疲劳开裂) initiates preferentially at coil bend regions and tube-to-header weld joints. To mitigate this, the following controls are implemented:
- Bend region microstructure verification via metallographic examination (ASTM E3) to confirm austenitic grain structure and absence of delta ferrite or carbide precipitation at grain boundaries.
- Residual stress measurement (X-ray diffraction method, ASTM E975) at coil bend zones to confirm stress levels below 50% of yield strength.
- Intergranular corrosion testing (ASTM A262 Practice E / 1C) to verify resistance to sensitization-induced degradation.
5. Applications
5.1 Primary Applications
- FCC Regenerator Heat Extraction (催化裂化再生器取热) — The principal application. Coil tubes extract heat from the hot catalyst/flue gas stream in the regenerator of a Fluid Catalytic Cracking unit to maintain optimal regeneration temperature (typically 700–750°C) and recover process heat.
- Flue Gas Heat Recovery (烟气余热回收) — Coil tubes immersed in high-temperature flue gas streams to preheat process feed water or generate steam.
- Crude Oil Heater Coils (原油加热盘管) — Immersed coil configurations for preheating crude oil or process streams.
- Styrene Monomer Reactor Coils (苯乙烯单体反应器盘管) — Heat transfer coils in polymerization reactors operating at elevated temperatures.
- Hydrocracker Quench Coils (加氢裂化急冷盘管) — Emergency quench systems requiring rapid heat absorption.
- Boiler and Heat Exchanger Coils (锅炉及换热器盘管) — General industrial heat exchange applications requiring high-temperature stainless steel.
5.2 Operating Environment Characteristics
- Temperature range: 400°C – 1100°C (intermittent peaks up to 1150°C)
- Thermal cycling frequency: 10–50 cycles per year (startup/shutdown)
- Exposure to: SO₂, H₂S, HCl, CO₂, and particulate catalyst fines
- Internal medium: Flue gas, process water, or steam (depending on design)
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
- ASTM A213 / ASME SA-213 — Standard Specification for Seamless Ferritic and Austenitic Stainless Steel Tubing for High Temperature Service
- ASTM A269 / ASME SA-269 — Standard Specification for Austenitic Stainless Steel Seamless, Welded, and Heavy-Walled Tubing
- ASTM A967 — Standard Practice for Chemical Cleaning and Passivation of Stainless Steel Parts
- ASTM A262 — Standard Practices for Detecting Susceptibility of Stainless Steels to Intergranular Corrosion
- ASME B31.3 — Process Piping (design and code compliance)
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubing for Fluid Transport
- GB/T 24511 — Chinese National Standard for General Rules for Pressure Parts
6.2 Testing & Certification
- Mechanical Testing — Tensile testing per ASTM E8/E8M; hardness testing per ASTM E92 (Rockwell B scale)
- Chemical Analysis — Spectrometric analysis per ASTM E100 or ASTM E415; verified by independent third-party laboratory (e.g., SGS, BV, or Intertek)
- Hydrostatic Testing — Per ASTM A213, at 1.5× design pressure with minimum hold time of 20 seconds per 100 mm of tube length
- Non-Destructive Examination — Eddy current testing per ASTM E309; visual inspection per ASTM E165
- Material Traceability — Full heat-to-heat traceability from raw material mill through final product, with documentation per EN 10204 3.1 or 3.2 certification
7. Unique Selling Points
- Failure-Informed Design — Product specifications are directly informed by documented failure analysis of regenerator coil tubes (再生器取热盘管失效分析), incorporating lessons learned from thermal fatigue, intergranular corrosion, and oxidative degradation mechanisms.
- Stabilized Material Grades — Availability of low-carbon (L-grade) and stabilized (Ti/Nb) austenitic grades specifically selected to resist intergranular carbide precipitation during prolonged exposure at 425–870°C.
- Post-Winding Stress Relief — Mandatory post-winding annealing eliminates residual stresses that would otherwise accelerate thermal fatigue crack initiation at coil bends.
- Full Traceability — Complete material traceability from mill heat number to final coil identification, enabling rapid root-cause analysis in the event of field performance issues.
- Custom Coil Geometry — CNC-controlled winding capability supports a wide range