A Method for Medium-Frequency Bending of Thick-Walled Pipes Made of GH4070P Nickel-Iron-Based Superalloy

Abstract

The invention discloses a method for bending medium-frequency pipes of GH4070P nickel-iron-based superalloy, including: the first step of preparation before pipe bending, the second step of medium-frequency bending, the bending temperature is 1050~1100°C, the starting bending temperature is 1080°C. When the temperature of the steel pipe reaches 600°C, keep it at a constant temperature until the temperature difference between the inner and outer walls of the pipeline is no more than 50°C, then quickly heat up to 950°C, keep it at a constant temperature again until the temperature difference between the inner and outer walls of the pipeline is no more than 50°C, then heat up to 1080°C and start pipe bending; when the bending angle of the pipeline meets the requirements, stop pipe bending, the third step of cooling, the fourth step of heat treatment and the fifth step of detection. The method for bending medium-frequency pipes of GH4070P nickel-iron-based superalloy of the invention can avoid staying too long in the temperature range where precipitation phases are easy to nucleate and grow, reducing the deformation resistance caused by precipitation strengthening in the core, thereby improving the structural strength and service life of the pipeline.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical component measurement, and particularly relates to a method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy. Background Art

[0002] With the development of thermal power generation technology, the development of 700°C advanced ultra-supercritical (A-USC) coal-fired power generation technology is of great strategic significance and practical application value for China to save energy, reduce pollutant and carbon dioxide emissions. The welding of high-temperature materials for power plants has always been a key technical link in power plant construction and production. With the continuous increase of steam parameters, the consumption of highly alloyed high-temperature materials used is also increasing. Especially the large use of nickel (iron)-based and nickel-cobalt-based superalloys in key components of power plant boilers has put forward new requirements for the medium-frequency elbow processing technology of pipelines.

[0003] The new nickel-iron-based GH4070P superalloy steel is a nickel-iron-based superalloy developed independently in China for use in ultra-supercritical boilers, and is mainly applied to the high-temperature section of boiler connecting pipelines and the main steam and reheated hot sections of boiler connecting pipes (the four major pipelines). The main alloy components of this alloy are Fe: 40 - 45%, Cr: 16 - 18%, Mo: 0.3 - 0.9%, Co: ≤2%, Ti: 2 - 2.5%, Al: 1.3 - 2%.

[0004] In the prior art, hot bending technology is generally used to manufacture elbows. For nickel-iron-based GH4070P superalloy steel, during the heating process, it is necessary to quickly pass through the temperature range where precipitation phases are prone to nucleation and growth to avoid the difficulty of pipe bending caused by insufficient re-dissolution of strengthening phases. This temperature range happens to be the temperature range of traditional hot bending technology. Therefore, traditional hot bending technology is not applicable to nickel-iron-based GH4070P superalloy steel. Summary of the Invention

[0005] The present invention aims to propose a method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy to solve the problem that the existing hot bending technology is not applicable to GH4070P nickel-iron-based superalloy.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy, comprising:

[0008] The first step, preparation before elbow bending. Use pipes with the same size as the connecting pipes for the process temporary openings and weld them to the GH4070P pipes;

[0009] Step 2, medium-frequency bending: Connect the power supply and heat the steel pipe. The bending temperature is 1050 - 1100 °C, and the starting bending temperature is 1080 °C. When the temperature of the steel pipe reaches 600 °C, keep it at a constant temperature until the temperature difference between the inner and outer walls of the pipe is no more than 50 °C, then quickly heat it up to 950 °C. After keeping it at a constant temperature again until the temperature difference between the inner and outer walls of the pipe is no more than 50 °C, heat it up to 1080 °C and start bending the pipe. When the bending angle of the pipe meets the requirements, stop bending the pipe.

[0010] Step 3, cooling: While bending the pipe, use cooling water to quickly cool the heated and deformed parts of the pipe. When the bending is completed, accelerate the cooling to room temperature and then take it out.

[0011] Step 4, heat treatment: Heat the cooled bent pipe to 600 °C, keep it at a constant temperature for a period of time, then heat it up again, quickly heat the bent pipe to 1050 °C, keep it at a constant temperature again. After the constant temperature is completed, perform water quenching, and let the bent pipe stand until it reaches room temperature.

[0012] Step 5, inspection: After the bent pipe is cooled, measure the angle, structural dimensions, wall thickness, and roundness of the bent pipe, and perform inspections on the bending radius, flatness, and waviness on the platform. Perform hardness and microscopic metallographic inspections on the surface of the bent pipe, and at the same time perform magnetic particle or penetrant inspections within the range of 45° above and below the center line of the outer arc of the bent pipe.

[0013] In some embodiments, the connecting pipe of the process temporary port in the first step uses a pipe with the same size but lower thickness.

[0014] In some embodiments, the low-thickness pipe is connected to the GH4070P pipe by surfacing welding.

[0015] In some embodiments, the surfacing welding thickness is 6 - 8 mm. The surfacing welding layer thickness of 3 - 4 mm is alternately welded inside and outside the pipe, and the surfacing welding is carried out in multiple times.

[0016] In some embodiments, after the surfacing welding is completed, the surface of the weld layer is polished, and penetrant inspection of the weld layer is performed.

[0017] In some embodiments, when the bent pipe is heated from 600 °C to 1050 °C in the fourth step, the heating rate is not less than 200 °C per hour.

[0018] In some embodiments, when the pipe is heated from 600 °C to 950 °C in the second step, the heating rate is not less than 200 °C per hour.

[0019] The beneficial effects of the present invention are as follows:

[0020] The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to the present invention includes rapidly heating a pipeline at 600°C during the medium-frequency bending step, with a heating rate of not less than 200°C per hour. Immediately after the elbow is bent, the pipeline is rapidly cooled by water cooling to generate compounds that affect the structural strength. The heat treatment step is the same as the medium-frequency bending step. When the pipeline is heated from 600°C to 1050°C, it is rapidly heated, with a heating rate of not less than 200°C per hour. After the constant temperature is completed, water quenching is carried out. In both the medium-frequency bending step and the heat treatment step, rapid heating and rapid cooling are used for the pipeline during heating and cooling to avoid staying too long in the temperature range where the precipitation phase is prone to nucleation and growth, so as to prevent the decrease in deformation resistance caused by precipitation strengthening in the core, thereby improving the structural strength and service life of the pipeline.

[0021] Using a pipeline with the same size but lower thickness as the connecting pipeline for the process temporary port can reduce the consumption of GH4070P nickel-iron-based superalloy and welding materials and reduce costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a cross-sectional view of the inspection tool for the bottom diameter of the inner ring groove in the embodiment of the present invention;

[0023] Figure 2 It is a front cross-sectional view of the measuring part in the embodiment of the present invention;

[0024] Figure 3 It is a top view schematic diagram of the measuring part in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following further describes the present invention with reference to the drawings.

[0026] The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy in the embodiment of the present invention includes:

[0027] First step, preparation before bending. A steel pipe 1 is prepared from a solution-treated high-temperature heat-resistant nickel-iron-based GH4070P nickel-iron-based superalloy, with a specification of OD480*70mm and a length of L = 2125mm. The bending radius is set to 1380mm, the bending angle A is 75°, the bending arc length is 1806, and the straight sections at both ends are 159mm. Before bending, the steel pipe is subjected to inspections such as spectral detection, hardness, ultrasonic thickness measurement, and metallographic inspection.

[0028] As Figure 1As shown in the figure, the steel pipe 1 needs to be spliced with the straight pipe section of the jacking pipe 2 and the lead pipe 3. The jacking pipe 2 and the lead pipe 3 are made of 12Cr1MoVG steel pipes of the same specification. Double V-grooves are machined at both ends of the steel pipe 1, and one-end grooves are machined on the jacking pipe 2 and the lead pipe 3 respectively. Then, surfacing welding is carried out on the grooves, and the surfacing welding consumables are selected to be the same as the materials of the spliced straight section. The surfacing thickness should reach 6 - 8 mm, and the welding is carried out alternately from the inner and outer surfaces of the pipe. The surfacing layer thickness is 3 - 4 mm, and the surfacing is carried out in 2 - 3 times; after surfacing, the surface of the weld layer is polished clean, and after non-destructive testing, the assembly welding is carried out in the order of the jacking pipe 2 + the steel pipe 1 + the lead pipe 3.

[0029] The second step is medium-frequency bending. As Figure 2 shown in the figure, the assembled steel pipe combination is clamped on the pipe bender, the induction coil 4 and the cooling device are installed, and after connecting the water circuit and the circuit, the power supply is started for heating. When the temperature of the steel pipe 1 reaches 600 °C, the stable temperature is maintained for a period of time. When the temperature difference between the inner and outer walls of the steel pipe 1 is not greater than 50 °C, it is quickly heated to 950 °C, and the heating rate is greater than 200 °C per hour. The stable temperature is maintained for a period of time. When the temperature difference between the inner and outer walls of the steel pipe 1 is not greater than 50 °C, it is heated to 1080 °C to start bending the pipe. When the angle between the two ends of the steel pipe 1 reaches 75 °, the pipe bending is stopped. At this time, the steel pipe 1 is as Figure 3 shown in the figure. At this time, the steel pipe 1 is bent into a bent pipe, and the bending angle A is 75 °.

[0030] The third step is cooling. The steel pipe after leaving the position of the induction coil 4 is cooled with cooling water to quickly cool the bent pipe to room temperature.

[0031] The fourth step is heat treatment. After the bent pipe is cooled to room temperature, the angle, structural dimensions, wall thickness and pipe hardness are measured. After meeting the requirements, heat treatment is carried out. The heat treatment process adopts normalizing + quenching. First, the bent pipe is heated to 600 °C and kept at a constant temperature for 30 minutes, then it is heated to 1050 °C, and the heating rate is greater than 200 °C per hour, and it is kept at a constant temperature for 45 minutes. When the holding time is up, the furnace door is opened, and the steel pipe 1 is quickly placed in the cooling water tank for cooling. The bent pipe can be taken out after it is completely cooled.

[0032] The fifth step is inspection. The angle, structural dimensions, wall thickness and roundness of the bent pipe are measured, and the bending radius, flatness and waviness are detected on the platform. Hardness and microscopic metallographic inspections are carried out on the surface of the bent pipe. The inspection points should meet the requirements of the DL / T515 standard. At the same time, magnetic particle or penetrant inspection is carried out within the range of 45 ° above and below the center line of the outer arc of the bent pipe. After all inspections are qualified, the entire bending process is completed.

[0033] According to the method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to the embodiments of the present invention, in the medium-frequency bending and heat treatment steps, when the elbow is heated from 600°C, it is rapidly heated to the set temperature, and after bending or heat treatment is completed, it is rapidly cooled by water cooling, so as to avoid staying too long in the temperature range where the precipitation phase is easy to nucleate and grow, resulting in a decrease in the deformation resistance caused by precipitation strengthening in the core, thereby improving the structural strength and service life of the pipeline.

[0034] This embodiment does not impose any formal restrictions on the shape, material, structure, etc. of the present invention. Any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention all belong to the protection scope of the technical solution of the present invention.

[0035] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation on the protection content of the present invention.

[0036] If terms such as "first" and "second" are used in this article to limit components, those skilled in the art should be aware that the use of "first" and "second" is only for the convenience of describing the present invention and simplifying the description. Without additional statements, the above terms have no special meanings.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features, but these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy, characterized in that, it includes: The first step, preparation before bending. Use pipes with slightly different wall thicknesses but the same outer diameter as the connecting pipes of the process temporary opening, and weld them to the GH4070P pipes; The second step, medium-frequency bending. Connect the power supply and heat the steel pipe. The bending temperature is 1050~1100 °C, and the starting bending temperature is 1080 °C. When the temperature of the steel pipe reaches 600 °C, keep it at a constant temperature until the temperature difference between the inner and outer walls of the pipe is no more than 50 °C, then quickly heat it up to 950 °C, keep it at a constant temperature again until the temperature difference between the inner and outer walls of the pipe is no more than 50 °C, and then heat it up to 1080 °C to start bending the pipe; when the bending angle of the pipe meets the requirements, stop bending the pipe; The third step, cooling. While bending the pipe, use cooling water to quickly cool the heated and deformed parts of the pipe, and accelerate the cooling to room temperature and take it out at the end of bending; The fourth step, heat treatment. Heat the cooled elbow to 600 °C, keep it at a constant temperature for a period of time, then heat it up for the second time, quickly heat the elbow to 1030 °C, keep it at a constant temperature again, and perform water quenching after the constant temperature is completed, and let the elbow stand until it reaches room temperature; The fifth step, inspection. After the elbow is cooled, measure the angle, structural dimensions, wall thickness and roundness of the elbow, and detect the bending radius, flatness and waviness on the platform; Perform hardness and microscopic metallographic inspections on the surface of the elbow, and perform magnetic particle or penetrant inspections within the range of 45° above and below the center line of the outer arc of the elbow.

2. The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to claim 1, characterized in that, in the first step, the connecting pipes of the process temporary opening adopt pipes with slightly different wall thicknesses but the same outer diameter.

3. The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to claim 2, characterized in that, the connecting pipes are connected to the GH4070P pipes after surfacing.

4. The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to claim 3, characterized in that, the surfacing thickness is 6-8 mm, and the surfacing layer thickness of 3-4 mm is alternately welded inside and outside the pipe, and the surfacing is carried out in multiple times.

5. The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to claim 4, characterized in that, after the surfacing is completed, the surface of the weld layer is polished and magnetic particle inspection is carried out.

6. The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to claim 5, characterized in that, when the elbow is heated from 600 °C to 1030 °C in the fourth step, the heating rate is not less than 300 °C per hour.

7. The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to claim 6, characterized in that, the time of the second constant temperature in the fourth step is 45 minutes.

8. The method for bending medium-frequency elbows of GH4070P nickel-iron-based superalloy according to claim 7, characterized in that, when the pipe is heated from 600 °C to 950 °C in the second step, the heating rate is not less than 300 °C per hour.

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