Stainless Steel Preheater Coil Tube for Heat Exchange Reforming Furnaces
Product Overview
The Coil Tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered stainless steel tube product specifically designed for use in heat exchange type reforming furnaces (换热式转化炉), particularly as preheater coil tubes in natural gas and hydrocarbon processing applications. These coil tubes serve as critical heat transfer elements within the preheating section of catalytic reforming systems, where process gases are heated to required temperatures prior to entering the catalytic reformer tubes.
This product line addresses one of the most challenging operational issues in reforming furnace technology: carbon deposition (析炭) on the inner and outer surfaces of preheater coil tubes. Through advanced metallurgical formulations and manufacturing processes, Wenzhou Jixing's coil tubes are engineered to minimize carbon accumulation, extend service life, and maintain optimal thermal efficiency throughout the operating cycle.
Material & Properties
The coil tubes are fabricated from high-grade austenitic and austenitic-ferritic stainless steel alloys selected for exceptional resistance to carbon deposition, high-temperature oxidation, and thermal cycling fatigue. The material selection is guided by the operating conditions within the preheater zone, where temperatures typically range from 400 °C to 750 °C.
Key Material Grades Available
- 310S / 310H (UNS S31008 / S31054) — High-temperature austenitic stainless steel with superior resistance to carbon deposition and scaling at temperatures up to 1100 °C. The elevated carbon content in 310H provides enhanced creep strength at elevated service temperatures.
- 304H (UNS S30409) — General-purpose austenitic stainless steel with improved high-temperature strength, suitable for preheater sections operating at moderate temperatures.
- 321H (UNS S32109) — Titanium-stabilized austenitic stainless steel offering excellent resistance to intergranular corrosion and carbon deposition in reducing atmospheres.
- HP-Nb (UNS N08825) — Nickel-based alloy with exceptional resistance to carburization in hydrogen-rich and hydrocarbon environments.
- HP-40 (UNS N06625) — Nickel-iron-chromium alloy providing outstanding resistance to carbon deposition in severe service conditions.
Typical Chemical Composition (310S Grade)
| Element | C | Si | Mn | P | S | Cr | Ni | N |
|---|---|---|---|---|---|---|---|---|
| Composition (%) | ≤0.08 | ≤1.50 | ≤2.00 | ≤0.035 | ≤0.030 | 24.0–26.0 | 19.0–22.0 | ≤0.10 |
Mechanical Properties (Annealed Condition, 310S)
| Property | Value | Test Temperature |
|---|---|---|
| Tensile Strength (Rm) | ≥520 MPa | 20 °C |
| Yield Strength (Rp0.2) | ≥205 MPa | 20 °C |
| Elongation (A) | ≥35 % | 20 °C |
| Thermal Conductivity | ~22 W/(m·K) | 100 °C |
| Linear Thermal Expansion | ~16.4 × 10−6 /K | 20–1000 °C |
| Maximum Service Temperature | 1100 °C | — |
Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | Φ19 mm – Φ60 mm (custom sizes available) |
| Wall Thickness (WT) | 1.0 mm – 4.5 mm |
| Coil Bundle Length | Up to 500 m per continuous coil |
| Bend Radius | 3D – 6D (minimum bend radius, where D = OD) |
| Surface Finish | Pickled and Passivated (2B finish); Ra ≤ 0.8 μm on inner surface upon request |
| Welding | Continuous TIG (Tungsten Inert Gas) welded; full radiographic inspection available |
| Applicable Standards | ASTM A312 / A213, ASME SB310, EN 10216-5, GB/T 14976 |
| Design Pressure | Up to 2.5 MPa (custom designs available) |
| Design Temperature | Up to 750 °C (preheater operating range) |
| Coil Configuration | Spiral coil, serpentine coil, or helical coil arrangements |
Manufacturing Process
The manufacturing of high-performance preheater coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage process designed to ensure metallurgical integrity, dimensional accuracy, and resistance to carbon deposition.
- Material Selection and Incoming Inspection — High-grade stainless steel seamless tubes are procured from certified mills. Each batch undergoes spectroscopic analysis (OES), chemical composition verification, and mechanical property testing to ensure conformance with specified standards.
- Dimensional Preparation and Annealing — Tubes are cut to required lengths and solution-annealed at 1050–1150 °C followed by controlled air or water quenching. This step eliminates residual stresses from prior cold working and establishes the required austenitic microstructure with uniform grain size (ASTM grain size 6–8).
- Coil Forming and Bending — Precision CNC-controlled bending equipment is used to form the coil tubes into the required geometry (spiral, serpentine, or helical configurations). Bending is performed at controlled temperatures (typically 600–800 °C for hot bending) to prevent work hardening and microstructural degradation at bend locations.
- Welding — All weld joints are fabricated using continuous TIG welding with inert gas (argon or argon-helium mixture) shielding. Weld parameters are optimized for each material grade to ensure full penetration, minimum heat-affected zone (HAZ) width, and proper grain growth control.
- Post-Weld Heat Treatment (PWHT) — Welded assemblies undergo post-weld annealing at 1050–1150 °C for stress relief and grain boundary stabilization. This is critical for preventing intergranular corrosion and ensuring uniform mechanical properties at weld locations.
- Pickling and Passivation — The final surface treatment involves acid pickling (mixed acid: HNO3/H2SO4 or citric acid) followed by passivation to remove scale, decarburization layers, and to form a stable chromium oxide passive film. This step is essential for minimizing initial carbon deposition sites.
- Quality Control and Testing — Comprehensive testing includes hydrostatic pressure testing (1.5× design pressure), radiographic inspection (RT) of welds, dimensional verification, surface roughness measurement, and optional intergranular corrosion testing (ASTM A923 Practice E).
Carbon Deposition Mitigation — Technical Solutions
A defining technical advantage of Wenzhou Jixing's preheater coil tubes is the systematic approach to carbon deposition (析炭) prevention, based on in-depth analysis of the mechanisms governing carbon accumulation in reforming furnace preheaters:
Root Causes of Carbon Deposition
- Excessive wall temperature — Local hot spots exceeding the carbon deposition threshold temperature (typically 720–780 °C for most austenitic grades) due to uneven heat flux distribution or insufficient process gas velocity.
- Inadequate gas flow velocity — Low Reynolds number (Re) in the preheater tubes leads to laminar flow conditions, reducing convective heat transfer and creating localized high-temperature zones.
- Surface roughness and scale formation — Internal oxide scales and surface defects serve as nucleation sites for carbon deposition, accelerating the process.
- Hydrogen partial pressure reduction — Decreased hydrogen partial pressure (PH₂) in the process gas shifts the equilibrium toward carbon formation (Boudouard reaction: 2CO ⇌ C + CO2).
- Material selection mismatch — Use of lower-grade materials (e.g., 304) in high-temperature preheater zones where 310S or nickel-based alloys are required.
Engineering Solutions Implemented
- Optimized tube geometry — Spiral coil configurations with calculated pitch-to-diameter ratios that ensure turbulent flow (Re > 4000) throughout the operating range, promoting uniform heat distribution and enhanced convective cooling of the tube walls.
- Enhanced surface finish — Internal surface roughness controlled to Ra ≤ 0.8 μm through mechanical honing or electrolytic polishing, reducing nucleation sites for carbon deposition by up to 60 %.
- Grade-specific material selection — 310S/310H for zones above 700 °C; 321H for moderate temperature zones; HP-Nb or HP-40 for critical high-carbon-deposition-risk applications.
- Wall thickness optimization — Calculated wall thickness profiles that balance thermal resistance with structural integrity, preventing excessive wall temperature while maintaining pressure containment.
- Anti-scaling surface treatments — Available upon request: aluminum oxide (Al2O3) diffusion coating or ceramic thermal barrier coating to further inhibit carbon nucleation.
Applications
- Catalytic Reforming Units — Preheater coil tubes in heat exchange type reforming furnaces (HETR) for naphtha reforming in petroleum refining and petrochemical plants.
- Steam Methane Reforming (SMR) — Preheating sections of reforming furnaces for hydrogen production and syngas generation.
- Ammonia Synthesis — Process gas preheating in ammonia converters and synthesis loops.
- Ethylene Cracking — Preheater coils in ethylene crackers for hydrocarbon feedstock heating.
- Hydrocracking — High-temperature process gas preheating in hydrocracker units.
- Coating Furnaces — Thermal processing furnaces for continuous coating lines requiring high-temperature heat transfer elements.
Quality Certifications
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 14001:2015 | Environmental Management System certification |
| ISO 45001:2018 | Occupational Health and Safety Management System certification |
| ASME Section I / VIII | Pressure vessel and component certification (where applicable) |
| EN 10204 Type 3.1 | Third-party inspection and test certification for material compliance |
| API 5L / API 5CT | Petroleum and natural gas industry product specifications (where applicable) |
| CE Marking (PED 2014/68/EU) | European Pressure Equipment Directive compliance |
Unique Selling Points
- Anti-Carbon Deposition Engineering — Industry-leading understanding and mitigation of carbon deposition mechanisms in reforming furnace preheaters, with validated solutions that extend coil tube service life by 40–60 % compared to conventional designs.
- Custom Geometry Optimization — CFD (Computational Fluid Dynamics)-driven coil geometry design to ensure uniform heat flux distribution and prevent local hot spots.
- Premium Material Availability — Full range of austenitic stainless steels and nickel-based alloys (310S, 310H, 321H, HP-Nb, HP-40) for grade-specific application matching.
- Superior Surface Finish — Internal surface roughness of Ra ≤ 0.8 μm achievable, significantly reducing carbon nucleation sites.
- End-to-End Traceability — Full material traceability from mill certificates through manufacturing, with EN 10204 Type 3.1 third-party inspection available for each batch.
- Technical Consulting — Dedicated engineering support for carbon deposition analysis, material selection, and coil design optimization based on specific operating conditions.
Note: All specifications, dimensions, and material grades listed above are representative values. Wenzhou Jixing Metal Materials