Production method of high-temperature and high-pressure resistant large-diameter iron-nickel-based alloy pipe

Abstract

The application discloses a production method of a high-temperature and high-pressure resistant large-diameter iron-nickel-based alloy pipe, which comprises the following steps: a vacuum melting step, a hot deformation processing step and a heat treatment step; wherein the solid solution treatment in the heat treatment step comprises the following steps: a heating step, a heat preservation step and a cooling step; the cooling step adopts a double cooling mode of early water cooling and later polymer quenching liquid cooling; when the cooling time of the large-diameter alloy pipe blank is less than the conversion time, the large-diameter alloy pipe blank is cooled in the water cooling mode; and when the cooling time of the large-diameter alloy pipe blank is equal to or greater than the conversion time, the large-diameter alloy pipe blank is cooled in the polymer quenching liquid. The application has a faster cooling speed, thereby effectively inhibiting the precipitation of the gamma prime phase in the cooling process, and simultaneously significantly reducing the stress in the low-temperature stage, which is beneficial to the control of deformation and cracking.

Description

Technical Field

[0001] This invention relates to the field of iron-nickel-based alloy pipe production technology, specifically to a method for producing large-diameter iron-nickel-based alloy pipes resistant to high temperature and high pressure. Background Technology

[0002] Advanced ultra-supercritical power generation technology is a key path to improving the efficiency of coal-fired power plants and reducing carbon emissions. Its core lies in continuously improving the steam parameters (temperature and pressure) of the boiler. When steam temperatures reach 650℃ and above, traditional austenitic heat-resistant steels can no longer meet the stringent requirements for high-temperature endurance strength and creep resistance. High-performance iron-nickel-based superalloys, such as HT700P (or GH2070P) alloys, must be used. These alloys are strengthened through γ' phase precipitation and possess excellent high-temperature mechanical properties, making them ideal candidate materials for manufacturing large-diameter superheaters, reheater pipes, and headers.

[0003] However, the high alloying composition of iron-nickel-based alloys also presents significant manufacturing challenges. In the crucial stage of tube fabrication—solution treatment—rapid cooling of the workpiece is necessary to obtain a supersaturated solid solution to ensure the effectiveness of subsequent aging precipitation strengthening. Currently, the commonly used cooling methods in the industry include:

[0004] Water quenching offers the fastest cooling rate and effectively suppresses the precipitation of the γ' phase during cooling, ensuring strength. However, for large-diameter thin-walled pipes, the enormous thermal stress generated by water quenching can easily lead to uncontrollable deformation (such as bending or ellipticization) or even cracking of the workpiece, resulting in low yield and extremely high risk.

[0005] Oil quenching or polymer quenching fluid cooling: Compared to water quenching, its cooling intensity is lower, especially at low temperatures where it can significantly reduce stress, which is beneficial for controlling deformation and cracking. However, at high temperatures, its cooling capacity may be insufficient, posing a risk of inadequate suppression of the γ' phase, resulting in the final product failing to meet strength performance standards.

[0006] Therefore, neither water cooling, oil cooling, nor polymer quenching fluid cooling can effectively meet the requirements of solution treatment for large-diameter iron-nickel-based alloys. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a method for producing large-diameter iron-nickel-based alloy tubes that are resistant to high temperature and high pressure. This method has a fast cooling rate, which effectively suppresses the precipitation of γ' phase during the cooling process, and at the same time can significantly reduce stress at low temperature, which is beneficial to controlling deformation and cracking.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for producing a large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure includes the following steps:

[0010] Vacuum melting step: The raw materials are processed using a double vacuum melting process to prepare ingots;

[0011] Hot deformation processing steps: The ingot is homogenized to obtain an ingot with homogenized structure, and then the homogenized ingot is hot deformed to obtain a large-diameter alloy tube blank.

[0012] Heat treatment steps: The large-diameter alloy tube blank is subjected to solution treatment and aging treatment;

[0013] The heat treatment step, specifically the solution treatment of the large-diameter alloy tube blank, includes the following steps:

[0014] Heating step: The large-diameter alloy tube blank is heated to raise its temperature to a first set temperature.

[0015] Insulation step: Insulate the heated large-diameter alloy tube blank.

[0016] Cooling step: The large-diameter alloy tube blank, after the heat preservation step, is cooled in a quenching tank.

[0017] The cooling process employs a dual cooling method: initial water cooling followed by polymer quenching. When the cooling time of the large-diameter alloy tube blank is less than the conversion time, water cooling is used. When the cooling time of the large-diameter alloy tube blank reaches or exceeds the conversion time, polymer quenching is used to cool the large-diameter alloy tube blank.

[0018] Preferably, the conversion time is determined in the following way:

[0019] A large-diameter alloy tube blank was taken as the test workpiece. A thermocouple was embedded in the test workpiece, and the test workpiece was cooled by water cooling. The curve of the relationship between the cooling time and the temperature of the test workpiece in the cooling step of the solution treatment was measured.

[0020] Based on the γ' phase precipitation kinetic model of the test workpiece, a critical temperature for the complete precipitation of the γ' phase of the test workpiece is determined as the conversion temperature. At the same time, based on the obtained curve of the relationship between cooling time and test workpiece temperature, the cooling time corresponding to the conversion temperature is obtained as the conversion time.

[0021] In this way, by measuring the cooling time and temperature relationship curve of the test workpiece, the temperature, which is difficult to monitor online, is converted into time, which is easy to control precisely. This is because, under fixed working conditions (workpiece, medium, initial temperature), the cooling process of the workpiece is highly repetitive. Therefore, by measuring a test workpiece, the actual cooling process of large-diameter alloy tube blanks can be obtained relatively accurately. Time is also the easiest physical quantity to measure and control precisely. It is not only low in measurement cost but also highly reliable. The time measurement method perfectly avoids the technical difficulties of directly measuring temperature in harsh quenching environments, ensures the consistency of switching timing in mass production, and ensures the stability of product performance.

[0022] Preferably, the dual cooling method of the cooling step is implemented through a control system, the control system comprising:

[0023] The first media supply unit is used for supplying and spraying water;

[0024] The second medium supply unit is used to supply and spray polymer quenching fluid of the target concentration;

[0025] The controller, which is communicatively connected to the first medium supply unit and the second medium supply unit, is configured to control the opening and closing of the first medium supply unit and the second medium supply unit based on the comparison result of the cooling time and the switching time, so as to perform the switching of the cooling medium.

[0026] In this way, the controller controls the opening and closing of the first medium supply unit and the second medium supply unit according to the relationship between the cooling time and the conversion time, ensuring that when the cooling time is less than the conversion time, the first medium supply unit water-cools the workpiece, while when the cooling time reaches or exceeds the conversion time, the second medium supply unit cools the workpiece with polymer quenching liquid.

[0027] Preferably, the first medium supply unit includes a first medium supply pipe and a first medium spray pipe, and a first control valve is provided at the connection between the first medium supply pipe and the first medium spray pipe;

[0028] The second medium supply unit includes a second medium supply pipe and a second medium spray pipe, and a second control valve is provided at the connection between the second medium supply pipe and the second medium spray pipe;

[0029] The controller is communicatively connected to the first control valve and the second control valve, respectively. The controller is configured to switch the cooling medium by controlling the opening and closing of the first control valve and the second control valve, respectively, based on the comparison result of the cooling time and the switching time.

[0030] In this way, the controller achieves the switching effect of the cooling medium through the first control valve and the second control valve respectively, which is precise and has a short switching time.

[0031] Preferably, a drain valve is also provided at the bottom of the quenching tank, and the controller is communicatively connected to the drain valve;

[0032] The controller is further configured to open the drain valve at the same time as opening the second control valve, and the drain valve automatically closes after a set time.

[0033] In this way, by setting up a drain valve, the water at the bottom of the quenching tank can be drained in time during the initial stage of switching from water cooling to polymer quenching liquid cooling. This can effectively prevent the presence of water from interfering with the concentration of polymer quenching liquid and the subsequent cooling process. It ensures that the concentration of the medium sprayed onto the workpiece surface is always within the target range throughout the entire polymer quenching liquid cooling stage, thereby ensuring the uniformity and stability of the low-temperature cooling effect.

[0034] Preferably, the second medium supply unit further includes a second medium mixing pipe and a water supply pipe. The second medium conveying pipe and the water supply pipe are both connected to the second medium mixing pipe. The second medium mixing pipe is connected to the second medium spraying pipe. The polymer quenching liquid stock solution conveyed by the second medium conveying pipe and the water conveyed by the water supply pipe are fully mixed at the second medium mixing pipe to form a polymer quenching liquid of the target concentration. The second medium mixing pipe conveys the polymer quenching liquid of the target concentration to the second medium spraying pipe. The second control valve is located at the position where the second medium mixing pipe and the second medium spraying pipe are connected.

[0035] In this way, by setting up a second medium mixing pipe, the water and polymer quenching liquid stock solution can be mixed in real time, so that the polymer quenching liquid sprayed from the second medium spray pipe is always within the target concentration range, further ensuring the uniformity and stability of the low temperature cooling effect.

[0036] Preferably, an online concentration detector is provided at the outlet of the second medium spray pipe. The online concentration detector is used to detect the concentration of the polymer quenching liquid at the outlet of the second medium spray pipe. A third control valve is provided on the second medium conveying pipe, and a fourth control valve is provided on the water supply pipe. The online concentration detector, the third control valve, and the fourth control valve are all communicatively connected to the controller.

[0037] The controller is further configured to: control the opening of the third control valve and the fourth control valve respectively by using the concentration signal detected by the online concentration detector, so as to adjust the mixing ratio of water and polymer quenching liquid stock solution to obtain polymer quenching liquid of target concentration.

[0038] In this way, by setting up an online concentration detector, the concentration fluctuation of the polymer quenching fluid sprayed from the outlet of the second medium spray pipe is detected in real time and fed back to the controller. The controller then adjusts the opening of the third and fourth control valves according to the concentration signal detected by the online concentration detector, thereby adjusting the mixing ratio of water and polymer quenching fluid stock solution. This can dynamically compensate for the concentration deviation of polymer quenching fluid caused by factors such as stock solution viscosity and water pressure fluctuation, thereby controlling the concentration fluctuation of polymer quenching fluid within a very small range and greatly improving the stability of cooling performance.

[0039] Preferably, the online concentration detector is an online refractometer or an online density meter.

[0040] Preferably, the target concentration range of the polymer quenching fluid is 5% to 20%.

[0041] Preferably, the polymer quenching fluid comprises PAG polyether with alkyl ends.

[0042] In this way, PAG polyethers with alkyl ends have good chemical stability, strong corrosion resistance, and long service life.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] 1. This invention employs highly efficient water cooling in the initial cooling stage (high-temperature phase), enabling rapid cooling across the sensitive temperature range (e.g., above 600°C) where the γ' strengthening phase is most likely to precipitate. This significantly suppresses premature and coarse precipitation of the γ' phase during cooling. This ensures that alloying elements are fully retained in the supersaturated solid solution, providing an ideal precursor structure for subsequent aging treatment, ultimately resulting in excellent high-temperature creep strength and creep resistance. In the later cooling stage (low-temperature phase), polymer quenching fluid cooling is switched to utilize its "reverse solubility" to form a uniform polymer film on the workpiece surface, significantly reducing the cooling rate in and around the martensitic transformation temperature range (typically below 300°C). This greatly alleviates the thermal and structural stresses generated within the workpiece due to rapid cooling, fundamentally preventing common quenching deformations (such as bending and excessive ellipticity) and cracking problems in large-diameter thin-walled pipes. This ensures product integrity and service safety, significantly reduces scrap rates and subsequent straightening costs, and directly improves production efficiency.

[0045] 2. This invention uses cooling time, a physical quantity that is easy to monitor and control accurately online, as the switching time to control the switching of the cooling medium. This cleverly avoids the extreme difficulty and impracticality of directly measuring the surface temperature of the workpiece in the harsh quenching environment of high-speed spraying and steam diffusion.

[0046] 3. This invention obtains a scientifically reasonable conversion time through experimental workpieces and strictly adheres to a fixed time parameter in mass production, making this complex process highly repeatable and stable. It reduces over-reliance on operator experience, ensuring that each batch and each pipe undergoes the exact same cooling process, thereby achieving highly consistent mechanical properties.

[0047] 4. All cooling processes of the present invention are completed in a single quenching tank by switching media, eliminating the need for complex, time-consuming transfer operations between multiple tanks that pose a risk of temperature runaway. This simplifies the process, shortens the production cycle, and improves equipment utilization and production efficiency.

[0048] 5. This invention, through a unique time-controlled dual cooling process, not only perfectly balances the stringent requirements of iron-nickel-based alloy pipes for high-temperature strength and high structural integrity, but also transforms the process into a precise, reliable, and stable process suitable for large-scale industrial manufacturing, providing solid technical and quality assurance for the supply of key pipelines for advanced ultra-supercritical power plant boilers at 650℃ and above. Attached Figure Description

[0049] Appendix Figure 1 This is a flowchart of the production method of the high-temperature and high-pressure resistant large-diameter iron-nickel-based alloy pipe of the present invention;

[0050] Appendix Figure 2 This is a flowchart of the solution treatment step in the production method of the high-temperature and high-pressure resistant large-diameter iron-nickel-based alloy pipe of the present invention.

[0051] Appendix Figure 3 This is a system block diagram of the control system in the production method of large-diameter iron-nickel-based alloy pipes resistant to high temperature and high pressure according to the present invention. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0053] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0054] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation on the embodiments. Moreover, the method and / or process should not be limited to the steps performed in the written order; those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0055] Advanced ultra-supercritical power generation technology is a key path to improve the efficiency of coal-fired power plants and reduce carbon emissions. Its core lies in continuously improving the steam parameters (temperature and pressure) of the boiler. When the steam temperature is raised to 650°C and above, traditional austenitic heat-resistant steel can no longer meet the stringent requirements for high-temperature endurance strength and creep resistance. High-performance iron-nickel-based high-temperature alloys, such as HT700P (or GH2070P) alloy, must be used.

[0056] In a specific embodiment of the present invention, a method for manufacturing large-diameter iron-nickel-based alloy tubes for the aforementioned advanced ultra-supercritical boiler is provided, as shown in the attached figure. Figure 1 As shown, the method includes the following steps:

[0057] Step S1) Vacuum melting step: The raw materials are processed using a double vacuum melting process to prepare ingots.

[0058] Vacuum melting is the primary step in ensuring the purity and uniformity of the alloy's microstructure. A dual vacuum melting process is typically employed: vacuum induction melting (VIM) followed by electroslag remelting (ESR). VIM effectively removes gases and harmful impurities, allowing for precise control of the composition. ESR further purifies the metal, improving the ingot's crystal structure and density.

[0059] Vacuum induction melting (VIM) is a step performed in a vacuum environment. This effectively removes gases such as hydrogen, oxygen, and nitrogen from the raw materials and reduces the oxygen content through a carbon-oxygen reaction. Simultaneously, under vacuum conditions, harmful trace elements with boiling points lower than the base metal (such as lead, bismuth, tin, and antimony) are also effectively removed. The entire process utilizes electromagnetic stirring to ensure uniform alloy composition.

[0060] Electroslag Remelting (ESR): Ingots refined by VIM (Vacuum Insulation) are used as consumable electrodes for secondary refining in conductive slag. Current flowing through the slag pool generates heat, melting the metal at the electrode tip. As the molten droplets pass through the slag pool, an electrochemical reaction occurs, resulting in deep desulfurization, removal of non-metallic inclusions, and coarsening and flotation of these inclusions. The metal then rapidly solidifies in a water-cooled crystallizer, forming a dense, uniform, directional crystalline structure, significantly improving the material's hot working properties.

[0061] Step S2) Hot deformation processing step: The ingot is homogenized to obtain a homogenized ingot, and then the homogenized ingot is hot deformed to obtain a large-diameter alloy tube blank.

[0062] The purpose of hot deformation processing is to break up the as-cast structure, weld internal defects (such as porosity and pores), refine the grains, form a uniform processed structure, and create favorable conditions for subsequent heat treatment.

[0063] Preparation before hot deformation includes ingot casting and heating. Ingots obtained through double vacuum melting (VIM+VAR / ESR) may have surface defects such as cold shuts and cracks. These surface defects can propagate during deformation, leading to forging cracking or becoming sources of subsequent fatigue. Therefore, the outer surface of the ingot needs to be machined to remove surface defects. Then, the machined ingot undergoes homogenization treatment: the ingot is held at a high temperature of 1170-1200℃ for 20-50 hours (the specific holding time and temperature depend on the ingot diameter). Homogenization treatment eliminates dendritic segregation and compositional inhomogeneity within the ingot, allowing alloying elements (such as Al, Ti, Nb, etc.) to diffuse fully, creating conditions for subsequent uniform deformation.

[0064] The main methods of hot deformation are forging + rolling and hot extrusion.

[0065] The forging + rolling method first involves an upsetting process to break up the cast grains and improve transverse properties. Then, the material is drawn to obtain a solid bar or hollow cylindrical billet of the desired diameter. The forged solid bar is then punched on a specialized press to obtain a hollow tube. This tube is then fed into a skew rolling mill or a periodic rolling mill for further rolling to precisely control the wall thickness and diameter.

[0066] Hot extrusion is an efficient and mainstream method for producing high-performance, large-diameter pipes. It involves placing a heated ingot (or a pre-drilled billet) into an extrusion cylinder and forcing it through an annular die under immense pressure (thousands or even tens of thousands of tons) to form a hollow pipe in one pass.

[0067] Step S3) Heat treatment step: Perform solution treatment and aging treatment on the large-diameter alloy tube blank.

[0068] The purpose of heat treatment is to obtain the strengthening phase (γ' phase) with the best size, quantity and distribution by precisely controlling the heating, holding and cooling processes, while optimizing the grain boundary state, so that the material can achieve the best balance between strength and plasticity.

[0069] Solution treatment is a "reset" step in heat treatment, the purpose of which is to create an ideal initial state for subsequent aging precipitation.

[0070] In solution treatment, on the one hand, it is necessary to completely dissolve all the γ' phase (Ni3(Al, Ti)) and carbides present after hot deformation and precipitated during cooling into the austenitic matrix. Simultaneously, rapid cooling "fixes" this high-temperature state, resulting in a homogeneous, unstable single-phase austenitic microstructure. Furthermore, by controlling temperature and time, the growth of austenitic grains is controlled to obtain a suitable grain size.

[0071] Aging treatment is a "performance activation" step in heat treatment. Its purpose is to induce the precipitation of a dispersed strengthening phase in the supersaturated solid solution, thereby significantly improving its strength. Aging treatment requires, on the one hand, the uniform precipitation of the strengthening phase. This is achieved by promoting the uniform and dispersed precipitation of nanoscale, spherical, or cubic γ' phases within the supersaturated solid solution. These precipitated phases effectively hinder dislocation movement and are the primary strengthening mechanism. On the other hand, aging treatment also needs to stabilize grain boundaries, allowing carbides (such as M...) on the grain boundaries to... 23 C6 precipitates as discrete granules rather than a continuous film, thereby improving grain boundary strength, plasticity, and creep resistance. Furthermore, aging treatment can alleviate or eliminate residual micro-stress after solution cooling.

[0072] Specifically, the solution treatment of large-diameter alloy tube blanks in the heat treatment process includes the following steps, as shown in the appendix. Figure 2 As shown:

[0073] Step A1) Heating step: The large-diameter alloy tube blank is heated to raise its temperature to the first set temperature.

[0074] Specifically, the first setting temperature is determined as needed, typically using a box-type resistance furnace or a pit-type furnace. These furnaces must have a precise temperature control system (±5℃ or even higher accuracy) and good temperature uniformity. Secondly, the heating rate needs to be controlled, especially for large-diameter, thick-walled tubes, to avoid thermal stress caused by excessive internal and external temperature differences.

[0075] Step A2) Insulation step: Insulate the heated large-diameter alloy tube blank.

[0076] Specifically, the holding temperature must be higher than the total melting temperature of the γ' phase to ensure its complete dissolution. However, the temperature cannot be too high, otherwise it will lead to coarse grains and initial melting. Coarse grains will significantly reduce the toughness and fatigue strength of the material, while initial melting will cause the low-melting-point phases at the grain boundaries to melt, resulting in product scrap. The holding time depends on the cross-sectional thickness of the workpiece (such as the wall thickness of a pipe) and the furnace load. It is usually calculated as 1-2 minutes per millimeter of wall thickness, but the total time must have upper and lower limits (e.g., 30 minutes to 4 hours).

[0077] Step A3) Cooling step: Cool the large-diameter alloy tube blank that has been heat-preserved in the quenching tank.

[0078] The cooling stage is the "soul" of solution treatment and a decisive step in achieving a supersaturated solid solution.

[0079] The cooling process employs a dual cooling method: initial water cooling followed by polymer quenching. When the cooling time of the large-diameter alloy tube blank is less than the conversion time, water cooling is used. When the cooling time of the large-diameter alloy tube blank reaches or exceeds the conversion time, polymer quenching is used to cool the large-diameter alloy tube blank.

[0080] For example, the polymer quenching fluid uses PAG polyether with alkyl ends, which has good chemical stability, strong corrosion resistance and long service life.

[0081] For example, the conversion time is determined in the following way:

[0082] A large-diameter alloy tube blank was taken as the test workpiece. A thermocouple was embedded in the test workpiece, and the test workpiece was cooled by water cooling. The curve of the relationship between the cooling time and the temperature of the test workpiece in the cooling step of the solution treatment was measured.

[0083] Based on the γ' phase precipitation kinetic model of the test workpiece, a critical temperature for the complete precipitation of the γ' phase of the test workpiece is determined as the conversion temperature. At the same time, based on the obtained curve of the relationship between cooling time and test workpiece temperature, the cooling time corresponding to the conversion temperature is obtained as the conversion time.

[0084] In this way, by measuring the cooling time and temperature relationship curve of the test workpiece, the temperature, which is difficult to monitor online, is converted into time, which is easy to control precisely. This is because, under fixed working conditions (workpiece, medium, initial temperature), the cooling process of the workpiece is highly repetitive. Therefore, by measuring a test workpiece, the actual cooling process of large-diameter alloy tube blanks can be obtained relatively accurately. Time is also the easiest physical quantity to measure and control precisely. It is not only low in measurement cost but also highly reliable. The time measurement method perfectly avoids the technical difficulties of directly measuring temperature in harsh quenching environments, ensures the consistency of switching timing in mass production, and ensures the stability of product performance.

[0085] Specifically, the dual cooling method of the cooling process is implemented through a control system, as shown in the attached diagram. Figure 3 As shown, the control system includes:

[0086] A first medium supply unit is used for supplying and spraying water; the first medium supply unit includes a first medium supply pipeline and a first medium spraying pipeline, and a first control valve is provided at the connection between the first medium supply pipeline and the first medium spraying pipeline;

[0087] The second medium supply unit is used to supply and spray polymer quenching fluid of target concentration; the second medium supply unit includes a second medium supply pipe and a second medium spray pipe, and a second control valve is provided at the connection between the second medium supply pipe and the second medium spray pipe;

[0088] The controller is communicatively connected to the first medium supply unit and the second medium supply unit. Specifically, the controller is communicatively connected to the first control valve and the second control valve, respectively. The controller is configured to control the opening and closing of the first medium supply unit and the second medium supply unit based on the comparison result of the cooling time and the switching time, so as to perform the switching of the cooling medium. Specifically, the controller performs the switching of the cooling medium by controlling the opening and closing of the first control valve and the second control valve, respectively, based on the comparison result of the cooling time and the switching time.

[0089] In this way, the controller controls the opening and closing of the first and second media supply units based on the relationship between cooling time and switching time. This ensures that when the cooling time is less than the switching time, the first media supply unit cools the workpiece with water; when the cooling time reaches or exceeds the switching time, the second media supply unit cools the workpiece with polymer quenching fluid. Specifically, the controller achieves the switching effect of the cooling medium through the first and second control valves, providing precise control and a short switching time.

[0090] Specifically, a drain valve is installed at the bottom of the quenching tank, and the controller is connected to the drain valve.

[0091] The controller is also configured to open the drain valve at the same time as the second control valve, and the drain valve automatically closes after a set time.

[0092] In this way, by setting up a drain valve, the water at the bottom of the quenching tank can be drained in time during the initial stage of switching from water cooling to polymer quenching liquid cooling. This can effectively prevent the presence of water from interfering with the concentration of polymer quenching liquid and the subsequent cooling process. It ensures that the concentration of the medium sprayed onto the workpiece surface is always within the target range throughout the entire polymer quenching liquid cooling stage, thereby ensuring the uniformity and stability of the low-temperature cooling effect.

[0093] Specifically, the second medium supply unit further includes a second medium mixing pipe and a water supply pipe. Both the second medium conveying pipe and the water supply pipe are connected to the second medium mixing pipe, which is also connected to the second medium spraying pipe. The polymer quenching liquid stock solution conveyed by the second medium conveying pipe and the water conveyed by the water supply pipe are thoroughly mixed at the second medium mixing pipe to form a polymer quenching liquid of the target concentration. The second medium mixing pipe then conveys the polymer quenching liquid of the target concentration to the second medium spraying pipe. The second control valve is located at the connection point between the second medium mixing pipe and the second medium spraying pipe. For example, the target concentration range of the polymer quenching liquid is 5% to 20%.

[0094] In this way, by setting up a second medium mixing pipe, the water and polymer quenching liquid stock solution can be mixed in real time, so that the polymer quenching liquid sprayed from the second medium spray pipe is always within the target concentration range, further ensuring the uniformity and stability of the low temperature cooling effect.

[0095] Specifically, an online concentration detector is installed at the outlet of the second medium spray pipe. For example, the online concentration detector is an online refractometer or an online density meter. The online concentration detector is used to detect the concentration of the polymer quenching liquid at the outlet of the second medium spray pipe. A third control valve is installed on the second medium delivery pipe, and a fourth control valve is installed on the water supply pipe. The online concentration detector, the third control valve, and the fourth control valve are all communicatively connected to the controller.

[0096] The controller is also configured to control the opening of the third control valve and the fourth control valve respectively by using the concentration signal detected by the online concentration detector, so as to adjust the mixing ratio of water and polymer quenching liquid stock solution to obtain polymer quenching liquid of target concentration.

[0097] In this way, by setting up an online concentration detector, the concentration fluctuation of the polymer quenching fluid sprayed from the outlet of the second medium spray pipe is detected in real time and fed back to the controller. The controller then adjusts the opening of the third and fourth control valves according to the concentration signal detected by the online concentration detector, thereby adjusting the mixing ratio of water and polymer quenching fluid stock solution. This can dynamically compensate for the concentration deviation of polymer quenching fluid caused by factors such as stock solution viscosity and water pressure fluctuation, thereby controlling the concentration fluctuation of polymer quenching fluid within a very small range and greatly improving the stability of cooling performance.

[0098] Compared to existing technologies, this invention employs highly efficient water cooling in the initial cooling stage (high-temperature phase), enabling rapid cooling across the sensitive temperature range where the γ' strengthening phase is most likely to precipitate (e.g., above 600°C), thereby maximally suppressing premature and coarse precipitation of the γ' phase during cooling. This ensures that alloying elements are fully retained in the supersaturated solid solution, providing an ideal precursor structure for subsequent aging treatment, ultimately resulting in excellent high-temperature creep strength and creep resistance. In the later cooling stage (low-temperature phase), the process switches to polymer quenching fluid cooling, utilizing its "reverse solubility" to form a uniform polymer film on the workpiece surface, significantly reducing the cooling rate in and around the martensitic transformation temperature range (typically below 300°C). This significantly alleviates the thermal and structural stresses generated within the workpiece due to rapid cooling, thereby fundamentally and effectively eliminating common quenching deformations (such as bending and excessive ovality) and cracking problems in large-diameter thin-walled pipes. This ensures product integrity and service safety, significantly reduces scrap rates and subsequent straightening costs, and directly improves production efficiency. This invention uses cooling time—a physical quantity easily and accurately monitored and controlled online—as the switching time to control the switching of the cooling medium. This cleverly avoids the extreme difficulty and impracticality of directly measuring the workpiece surface temperature in the harsh quenching environment of high-speed spraying and steam permeation. This invention obtains a scientifically reasonable switching time through experimental workpieces and strictly adheres to a fixed time parameter in mass production, making this complex process highly repeatable and stable. It reduces over-reliance on operator experience, ensuring that each batch and each pipe undergoes the exact same cooling process, thus achieving highly consistent mechanical properties. All cooling processes in this invention are completed within a single quenching tank via medium switching, eliminating the need for complex, time-consuming, and temperature-runaway-risk transfer operations between multiple tanks. This simplifies the process, shortens the production cycle, and improves equipment utilization and production efficiency. Through a unique time-controlled dual-cooling process, this invention not only perfectly balances the stringent requirements of high-temperature strength and high structural integrity for iron-nickel-based alloy pipes, but also transforms the process into a precise, reliable, and stable flow suitable for large-scale industrial manufacturing. This provides a solid technical and quality guarantee for the supply of critical piping for advanced ultra-supercritical power plant boilers at 650℃ and above.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for producing a large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure, characterized in that, Includes the following steps: Vacuum melting step: The raw materials are processed using a double vacuum melting process to prepare ingots; Hot deformation processing steps: The ingot is homogenized to obtain an ingot with homogenized structure, and then the homogenized ingot is hot deformed to obtain a large-diameter alloy tube blank. Heat treatment steps: The large-diameter alloy tube blank is subjected to solution treatment and aging treatment; The heat treatment step, specifically the solution treatment of the large-diameter alloy tube blank, includes the following steps: Heating step: The large-diameter alloy tube blank is heated to raise its temperature to a first set temperature. Insulation step: Insulate the heated large-diameter alloy tube blank. Cooling step: The large-diameter alloy tube blank, after the heat preservation step, is cooled in a quenching tank. The cooling process employs a dual cooling method: initial water cooling followed by polymer quenching. When the cooling time of the large-diameter alloy tube blank is less than the conversion time, water cooling is used. When the cooling time of the large-diameter alloy tube blank reaches or exceeds the conversion time, polymer quenching is used to cool the large-diameter alloy tube blank.

2. The method for producing large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure according to claim 1, characterized in that, The conversion time is determined in the following way: A large-diameter alloy tube blank was taken as the test workpiece. A thermocouple was embedded in the test workpiece, and the test workpiece was cooled by water cooling. The curve of the relationship between the cooling time and the temperature of the test workpiece in the cooling step of the solution treatment was measured. Based on the γ' phase precipitation kinetic model of the test workpiece, a critical temperature for the complete precipitation of the γ' phase of the test workpiece is determined as the conversion temperature. At the same time, based on the obtained curve of the relationship between cooling time and test workpiece temperature, the cooling time corresponding to the conversion temperature is obtained as the conversion time.

3. The method for producing large-diameter iron-nickel-based alloy pipes resistant to high temperature and high pressure according to claim 2, characterized in that, The dual cooling method of the cooling step is implemented through a control system, which includes: The first media supply unit is used for supplying and spraying water; The second medium supply unit is used to supply and spray polymer quenching fluid of the target concentration; The controller, which is communicatively connected to the first medium supply unit and the second medium supply unit, is configured to control the opening and closing of the first medium supply unit and the second medium supply unit based on the comparison result of the cooling time and the switching time, so as to perform the switching of the cooling medium.

4. The method for producing large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure according to claim 3, characterized in that, The first medium supply unit includes a first medium supply pipe and a first medium spray pipe, and a first control valve is provided at the connection between the first medium supply pipe and the first medium spray pipe; The second medium supply unit includes a second medium supply pipe and a second medium spray pipe, and a second control valve is provided at the connection between the second medium supply pipe and the second medium spray pipe; The controller is communicatively connected to the first control valve and the second control valve, respectively. The controller is configured to switch the cooling medium by controlling the opening and closing of the first control valve and the second control valve, respectively, based on the comparison result of the cooling time and the switching time.

5. The method for producing large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure according to claim 4, characterized in that, A drain valve is also provided at the bottom of the quenching tank, and the controller is communicatively connected to the drain valve; The controller is further configured to open the drain valve at the same time as opening the second control valve, and the drain valve automatically closes after a set time.

6. The method for producing a large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure according to claim 5, characterized in that, The second medium supply unit further includes a second medium mixing pipe and a water supply pipe. The second medium conveying pipe and the water supply pipe are both connected to the second medium mixing pipe. The second medium mixing pipe is connected to the second medium spraying pipe. The polymer quenching liquid stock solution conveyed by the second medium conveying pipe and the water conveyed by the water supply pipe are fully mixed at the second medium mixing pipe to form a polymer quenching liquid of the target concentration. The second medium mixing pipe conveys the polymer quenching liquid of the target concentration to the second medium spraying pipe. The second control valve is located at the position where the second medium mixing pipe and the second medium spraying pipe are connected.

7. The method for producing a large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure according to claim 6, characterized in that, An online concentration detector is installed at the outlet of the second medium spray pipe. The online concentration detector is used to detect the concentration of the polymer quenching liquid at the outlet of the second medium spray pipe. A third control valve is installed on the second medium conveying pipe, and a fourth control valve is installed on the water supply pipe. The online concentration detector, the third control valve, and the fourth control valve are all communicatively connected to the controller. The controller is further configured to: control the opening of the third control valve and the fourth control valve respectively by using the concentration signal detected by the online concentration detector, so as to adjust the mixing ratio of water and polymer quenching liquid stock solution to obtain polymer quenching liquid of target concentration.

8. The method for producing a large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure according to claim 7, characterized in that, The online concentration detector is an online refractometer or an online density meter.

9. The method for producing a large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure according to claim 8, characterized in that, The target concentration range of the polymer quenching fluid is 5% to 20%.

10. The method for producing a large-diameter iron-nickel-based alloy pipe resistant to high temperature and high pressure according to claim 9, characterized in that, The polymer quenching fluid comprises PAG polyether with alkyl ends.

Images