Stainless Steel Coil Tube for Steam Reforming Furnace Applications
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Code: JX-CT-1245 | Category: Process Coil Tubing for Petrochemical and Chemical Engineering
1. Product Overview
The JX-CT-1245 series Stainless Steel Coil Tube is a precision-engineered process tubing solution specifically designed for demanding high-temperature service environments within Primary Steam Reforming Furnaces (一段转化炉, Primary Reforming Furnace, PRF). These coil tubes serve dual critical functions: humidification coil tubes (增湿盘管, Moisture Addition Coil Tubes) for controlled steam injection and fuel gas preheating coil tubes (燃料气预热盘管, Fuel Gas Preheating Coil Tubes) for thermal conditioning of process gas streams.
Deployed in the furnace tube bank of primary reforming units, these coil tubes are integral to the hydrocarbon reforming process, where they facilitate the conversion of hydrocarbons (such as natural gas or naphtha) into synthesis gas (syngas) through controlled thermal and catalytic reactions. The coiled geometry provides maximum heat transfer surface area within a compact footprint, enabling efficient energy utilization and precise process temperature management.
Key Engineering Context: In a typical Primary Reforming Furnace (designated as Unit 101B in the referenced process configuration), the addition of humidification and fuel gas preheating coil tubes represents a critical process modification (改造, process retrofit) aimed at enhancing conversion efficiency, improving thermal distribution uniformity, and extending the operational life of the reforming catalyst bed.
2. Material & Properties
2.1 Base Material Grades
The JX-CT-1245 coil tubes are manufactured from high-performance austenitic stainless steel grades selected for exceptional resistance to high-temperature oxidation, carburization, and thermal fatigue. The primary material specifications are as follows:
- 310S (UNS S31008): Primary grade for fuel gas preheating coil tubes, offering outstanding hot strength and resistance to thermal cycling at temperatures up to 1150°C (2100°F).
- 309S (UNS S30908): Used for humidification coil tubes exposed to moisture-laden environments at elevated temperatures, providing superior resistance to intergranular corrosion and scaling.
- 310CbT (UNS S31025): Enhanced variant with titanium stabilization for applications requiring prolonged service in reducing atmospheres with periodic oxidative excursions.
2.2 Mechanical Properties (Annealed Condition, at 900°C)
| Property | 310S | 309S | 310CbT | Test Standard |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ASTM A213 / ASME SA-213 |
| Yield Strength (0.2% Offset, MPa) | ≥ 103 | ≥ 103 | ≥ 103 | ASTM A213 / ASME SA-213 |
| Elongation (%) | ≥ 30 | ≥ 30 | ≥ 30 | ASTM A213 / ASME SA-213 |
| Density (g/cm³) | 7.99 | 7.99 | 7.99 | — |
| Thermal Conductivity (W/m·K, 100°C) | 22.6 | 21.5 | 22.6 | ASTM E153 |
| Maximum Continuous Service Temperature (°C) | 1150 | 900 | 1150 | — |
2.3 Chemical Composition (wt%, Typical)
| Element | 310S | 309S | 310CbT |
|---|---|---|---|
| C (Carbon) | ≤ 0.08 | ≤ 0.08 | ≤ 0.08 |
| Cr (Chromium) | 24.0 – 26.0 | 22.0 – 24.0 | 24.0 – 26.0 |
| Ni (Nickel) | 19.0 – 22.0 | 12.0 – 15.0 | 19.0 – 22.0 |
| Ti (Titanium) | — | — | 5 – 8 × C |
| Si (Silicon) | ≤ 1.5 | ≤ 1.5 | ≤ 1.5 |
| Mn (Manganese) | ≤ 2.0 | ≤ 2.0 | ≤ 2.0 |
2.4 Physical & Corrosion Resistance Characteristics
- Hot Corrosion Resistance: The high chromium and nickel content provides exceptional resistance to sulfidation and carburization in reducing atmospheres typical of reforming furnace environments.
- Intergranular Corrosion Resistance: Ultra-low carbon (≤ 0.08% C) composition eliminates the risk of chromium carbide precipitation at grain boundaries during prolonged high-temperature exposure.
- Thermal Fatigue Performance: Superior resistance to cyclic thermal stress induced by repeated heating and cooling cycles during furnace startup, shutdown, and load variations.
- Oxidation Behavior: Forms a stable, self-healing Cr₂O₃ oxide scale that provides protective barrier against further oxidation at service temperatures up to 1150°C.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification | Tolerance | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | 25 mm – 168 mm | ±0.5 mm | ASTM A213 |
| Wall Thickness | 1.5 mm – 8.0 mm | ±10% | ASTM A213 |
| Coil Bend Radius | 3× OD (minimum) | ±5% | Manufacturer Specification |
| Coil Length (per loop) | Up to 120 m (continuous) | ±1% | ASME B31.3 |
| End Condition | Plain end / Beveled end (45° ±2°) | — | Customer Specification |
| Surface Finish | Pickled and passivated (Ra ≤ 1.6 μm) | — | ASTM A967 |
3.2 Typical Coil Tube Configurations for Steam Reforming Furnace Applications
| Application | Material Grade | OD × WT (mm) | Bend Radius (mm) | Max. Operating Temp (°C) | Max. Operating Pressure (MPa) |
|---|---|---|---|---|---|
| Humidification Coil Tube (增湿盘管) | 309S | 57 × 3.0 | 171 | 850 | 2.5 |
| Fuel Gas Preheating Coil Tube (燃料气预热盘管) | 310S | 76 × 4.0 | 228 | 1050 | 1.6 |
| High-Temperature Fuel Gas Coil | 310CbT | 108 × 5.0 | 324 | 1150 | 1.2 |
3.3 Applicable Standards & Codes
- ASTM A213: Standard Specification for Austenitic Stainless Steel Seamless Tubing for High-temperature Service
- ASME SA-213: Specification for Stainless Steel Tubing for High-temperature Service
- ASME B31.3: Process Piping Code
- EN 10216-5: Tubes for Heat Exchangers and Heat Transfer Equipment — Technical Delivery Conditions
- GB/T 14976: Chinese National Standard for Stainless Steel Seamless Tubes for Fluid Transport
- ASTM A967: Standard Practice for Chemical Cleaning and Passivation of Stainless Steel Parts
- ISO 15530: Heat Exchangers — Welding of Tubes to Tube Plates
4. Manufacturing Process
4.1 Production Workflow
The manufacturing process for JX-CT-1245 stainless steel coil tubes follows a rigorous multi-stage workflow designed to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability:
- Raw Material Procurement & Inspection: Certified austenitic stainless steel seamless tubes are sourced from approved mills with full heat number traceability. Incoming material undergoes spectrographic analysis (PMI, Positive Material Identification), ultrasonic testing (UT), and hydrostatic pressure testing per ASTM A213 requirements.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050°C – 1150°C followed by rapid water quenching to achieve a fully austenitic, stress-free microstructure with optimal mechanical properties and maximum corrosion resistance.
- Precision Cutting: Tubes are cut to specified lengths using automated plasma or laser cutting systems to ensure square ends and minimal heat-affected zone (HAZ) distortion.
- Coil Forming (Roll Forming): The tube is fed through a series of progressive roll stations (typically 12–24 stations) to achieve the required coil geometry. The forming process is carefully controlled to prevent wall thinning, ovality, and residual stress concentration. A minimum bend radius of 3× OD is maintained to preserve structural integrity.
- Post-Forming Heat Treatment: Following coil forming, the tube may undergo a stress-relief annealing cycle at 850°C – 900°C to eliminate residual stresses introduced during the forming process, ensuring dimensional stability during subsequent welding and service.
- Pickling & Passivation: The formed coil tube is subjected to chemical pickling (nitric acid/hydrofluoric acid solution) to remove mill scale, oxide films, and surface contaminants. This is followed by passivation treatment per ASTM A967 to establish a protective chromium oxide layer.
- Non-Destructive Testing (NDT): Comprehensive NDT includes:
- Visual inspection (VT) for surface defects, discoloration, and geometric irregularities
- Eddy current testing (ET) for detection of surface and near-surface defects
- Ultrasonic testing (UT) for volumetric defect detection
- Helium or pneumatic leak testing for wall thickness verification and through-wall defect detection
- Dimensional Verification: Final dimensional inspection includes OD measurement, wall thickness measurement (ultrasonic), coil pitch measurement, and bend radius verification using calibrated instruments.
- Packaging & Shipping: Finished coil tubes are protected with moisture-absorbent desiccant packaging, wrapped in protective film, and secured on custom transport spools to prevent deformation during transit.
4.2 Process Control & Quality Assurance
Wenzhou Jixing Metal Materials Co., Ltd. implements a comprehensive Quality Management System (QMS) aligned with ISO 9001:2015 principles. Critical process parameters—including forming force, roll gap, coil speed, and heat treatment temperature profiles—are monitored in real-time using SCADA (Supervisory Control and Data Acquisition) systems. Each production lot is accompanied by a full mill test certificate (MTC) and a process traceability document linking the finished product to its raw material heat number and processing parameters.