Stainless Steel Coil Tube for Reformer Furnace High-Pressure Steam Generation
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
Product Reference No.: 940
Category: Industrial Heat-Exchange Coil Tubes (Reformer Furnace Application)
1. Product Overview
The stainless steel coil tube (盘管) described herein is a specialized heat-exchange component designed for integration into first-stage reformer furnaces (一段炉) operating within petrochemical and natural gas processing facilities. This product is specifically engineered for high-pressure steam generation, serving as a critical element in energy-saving technical transformations (节能技术改造) of existing reformer furnace systems.
In the context of natural gas steam reforming (NGSR), the coil tube is positioned within the furnace radiant zone to absorb radiant heat from the combustion process and transfer thermal energy to the working fluid — typically high-pressure water/steam. The coil tube design maximizes the heat-transfer surface area while maintaining structural integrity under extreme thermal cycling conditions. The energy-saving retrofit application focuses on improving thermal efficiency by optimizing coil geometry, material selection, and installation configuration to reduce fuel consumption while maintaining or increasing steam output capacity.
The coil tube assembly is wound into a helical configuration to facilitate compact installation within the furnace radiant section, ensuring uniform heat distribution and minimizing thermal stress concentrations that could lead to premature failure.
2. Material & Properties
Given the demanding operating environment of reformer furnaces — characterized by high temperatures, oxidizing atmospheres, and thermal fatigue — the coil tube material selection is critical for long-term reliability and performance.
2.1 Base Alloy Composition
The coil tube is fabricated from austenitic stainless steel grades optimized for high-temperature oxidation resistance and thermal stability. The primary material grades employed include:
- 310S (UNS S31008): A high-temperature austenitic stainless steel with enhanced chromium and nickel content, providing superior resistance to oxidation and scaling at temperatures up to 1150°C (2094°F).
- 309S (UNS S30908): A general-purpose high-temperature stainless steel offering excellent resistance to thermal cycling and thermal cracking.
- 321H (UNS S32109): A stabilized austenitic stainless steel with titanium stabilization, providing enhanced resistance to intergranular corrosion and stress corrosion cracking at elevated temperatures.
- 347H (UNS S34709): A niobium-stabilized austenitic stainless steel offering improved creep strength and resistance to intergranular attack at elevated temperatures.
2.2 Mechanical Properties
The material properties at operating temperature are designed to meet or exceed the following requirements:
- Tensile Strength (at 900°C): ≥ 200 MPa
- Yield Strength (at 900°C): ≥ 100 MPa
- Elongation (at 900°C): ≥ 30%
- Cyclic Oxidation Resistance: ≥ 10,000 thermal cycles without significant scale spalling
- Thermal Conductivity (at 800°C): ≈ 33 W/(m·K)
- Coefficient of Thermal Expansion (20–900°C): ≈ 18.5 × 10⁻⁶ /°C
2.3 Chemical Composition (Typical — Grade 310S)
| Element | Specification (wt%) | Function |
|---|---|---|
| C (Carbon) | ≤ 0.08 | Low carbon to prevent sensitization and intergranular corrosion |
| Cr (Chromium) | 24.0 – 26.0 | Primary oxidation and scaling resistance element |
| Ni (Nickel) | 19.0 – 22.0 | Austenite stabilizer; enhances high-temperature strength |
| Mn (Manganese) | ≤ 2.00 | Deoxidizer and mild strength contributor |
| S (Sulfur) | ≤ 0.030 | Limited to prevent sulfidation |
| P (Phosphorus) | ≤ 0.045 | Limited to prevent hot shortness |
| Si (Silicon) | ≤ 1.50 | Deoxidizer; supports scale adhesion |
| Fe (Iron) | Balance | Base metal |
3. Specifications
3.1 Geometric Dimensions
| Parameter | Specification | Notes |
|---|---|---|
| Outer Diameter (OD) | 50.8 – 114.3 mm (2" – 4½") | Standard sizes; custom dimensions available |
| Wall Thickness (WT) | 3.0 – 6.35 mm (1/8" – 1/4") | Selected based on design pressure and temperature |
| Coil Mean Diameter (CMD) | 600 – 2,000 mm | Determined by furnace geometry and heat-transfer requirements |
| Number of Turns | 8 – 30 turns | Varies by furnace configuration |
| Coil Height (Total Developed Length) | 12,000 – 80,000 mm | Dependent on required heat-transfer area |
| Pitch (Turn-to-Turn Spacing) | 15 – 40 mm | Optimized for radiant heat absorption |
| End Preparation | Beveled ends (37°) or plain ends | For welding to header/riser connections |
3.2 Operating Conditions
| Parameter | Design Value | Operating Range |
|---|---|---|
| Maximum Operating Temperature | 1,100°C | 800 – 1,050°C |
| Design Pressure | 4.0 – 6.0 MPa (g) | 3.5 – 5.5 MPa (g) |
| Operating Medium | — | High-pressure water / saturated steam |
| Steam Output Temperature | — | 480 – 540°C |
| Furnace Atmosphere | — | Hydrogen-rich (reformate gas) / Combustion products |
| Design Life | — | ≥ 10 years continuous operation |
3.3 Applicable Standards
| Standard | Title / Scope |
|---|---|
| ASTM A213 / A213M | Standard Specification for Seamless Austenitic Stainless Steel Tubing for Heat-Transfer and Exothermic Reactions |
| ASTM A790 / A790M | Standard Specification for Seamless Ferritic and Austenitic Chromium-Stainless Steel Tubing for High-Temperature Service |
| ASME B31.3 | Process Piping (design and construction) |
| EN 10216-5 | Seamless Steel Tubes for Technical Purposes — Part 5: Heat-Resistant Grades |
| GB/T 14976 | Chinese National Standard — Fluid Transport Seamless Stainless Steel Tubes |
| GB/T 5310 | Chinese National Standard — Seamless Steel Tubes for High-Temperature Boilers and Overheaters |
4. Manufacturing Process
The manufacturing of the stainless steel coil tube involves a multi-stage process chain that ensures dimensional accuracy, metallurgical quality, and mechanical integrity. The process flow is as follows:
- Raw Material Procurement and Inspection: Seamless stainless steel tubes (pre-wound or straight) are procured from certified mills. Incoming inspection includes chemical composition verification (spectrographic analysis), mechanical testing (tensile, hardness), and dimensional verification.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050–1100°C followed by rapid water quenching to achieve a fully austenitic microstructure free of carbide precipitation. This ensures maximum corrosion resistance and ductility.
- Precision Boring and OD Grinding: Tubes are precision-bored to achieve uniform wall thickness (typically ±0.05 mm tolerance) and ground to exact outer diameter specifications. This step is critical for uniform heat-transfer performance and resistance to flow-accelerated corrosion.
- Coil Winding (Forming): Straight tubes are cold-formed or hot-formed into the helical coil geometry using a specialized coil-winding machine. The winding process is controlled to avoid excessive work hardening, plastic deformation, or residual stress that could compromise fatigue life. Hot-forming (at 600–800°C) is preferred for larger diameters and thicker walls.
- Post-Forming Stress Relief: Following coil formation, the assembly undergoes stress-relief annealing at 900–1000°C to eliminate residual stresses introduced during forming. This step is essential for preventing distortion during furnace operation and extending service life.
- End Beveling and Machining: Coil ends are beveled to 37° (ASME standard) or prepared per the applicable welding procedure specification (WPS) to facilitate butt-welding to riser tubes and headers.
- Surface Cleaning and Passivation: The coil tube interior and exterior surfaces are cleaned (pickling and passivation) to remove scale, oils, and contaminants. Acid pickling with a citric acid or nitric acid/hydrofluoric acid solution is followed by passivation to restore the protective chromium oxide film.
- Non-Destructive Testing (NDT): Comprehensive NDT is performed including:
- Eddy current testing (ECT) for surface and near-surface defect detection
- Hydrostatic pressure testing (1.5× design pressure) for leak integrity verification
- Visual inspection of welds and forming areas
- Dimensional verification of coil geometry (mean diameter, pitch, total length)
- Protective Coating and Packaging: The coil tube is coated with a high-temperature protective coating (silicon-based or ceramic-based) if required for the specific application, and packaged with moisture-absorbing desiccants for transportation and storage.
5. Applications
5.1 Primary Applications
- Natural Gas Steam Reforming (NGSR) Furnaces: The coil tube serves as a superheater or high-pressure steam generator within the radiant section of first-stage reformer furnaces. It absorbs radiant heat from the combustion of natural gas and converts feedwater into high-pressure steam, which is subsequently used for power generation or process heating.
- Energy-Saving Technical Retrofit (节能技术改造): In existing reformer furnace installations, the coil tube is deployed as part of an energy-efficiency upgrade program. By optimizing the coil geometry, increasing the heat-transfer surface area, and improving material performance, the retrofit achieves measurable reductions in fuel consumption (typically 5–12% improvement in thermal efficiency).
- Hydrogen Production Facilities: In dedicated hydrogen production plants (制氢装置), the coil tube is integral to the steam superheating process that provides the required high-temperature steam for the reforming reaction.
- Ammonia Synthesis Plants: In ammonia production (合成氨), the coil tube generates the high-pressure steam required for the water-gas shift reaction and process steam demands.
- Petrochemical Cracking Furnaces: In steam-cracking furnaces for ethylene production, similar coil tube configurations are employed for waste-heat recovery and steam generation.
5.2 Energy-Saving Retrofit Context
The energy-saving technical transformation of first-stage reformer furnace high-pressure steam coil tubes (一段炉高压蒸汽盘管节能技术改造) addresses the following optimization objectives:
- Reduction of furnace exit gas temperature (烟气出口温度) through improved heat absorption
- Minimization of heat losses through optimized coil spacing and insulation integration
- Extension of tube life through upgraded alloy selection, reducing unplanned shutdowns
- Enhancement of steam production capacity without proportional increase in fuel input
- Compliance with increasingly stringent environmental and energy-efficiency regulations
6. Quality Certifications and Compliance
The stainless steel coil tube product is manufactured and inspected in accordance with the following quality assurance frameworks and certifications:
- ISO 9001:2015: Quality Management System certification ensuring consistent product quality and process control throughout manufacturing.
- ISO 3834: Quality requirements for fusion welding of steel (applicable to coil-to-header weldments).
- EN 10204 Type 3.1 Certificate: Third-party inspection and testing certificate confirming compliance with specified requirements.
- ASME "S" Stamp: Sectional certification for heat-exchanger components where applicable.
- API 5CT / API 5L: American Petroleum Institute compliance for petroleum and natural gas industry applications (where relevant).
- GB/T 19001-2016: Chinese national equivalent of ISO 9001, ensuring compliance with domestic regulatory requirements.
- Material Traceability: Full heat-number traceability from raw material mill through final product delivery, including mill test certificates (MTC) for each lot.
7. Unique Selling Points
- Application-Specific Engineering: The coil tube is not a generic product but is engineered specifically for the demanding conditions of reformer furnace radiant sections, with geometry, material, and design parameters optimized for high-pressure steam generation under energy-saving retrofit scenarios.
- Extended Service Life Through Material Selection: The use of high-chromium, high-nickel austenitic grades (310S, 309S) provides exceptional resistance to thermal oxidation and cyclic fatigue