Pipeline joint medium frequency induction heating post-weld heat treatment device and heat treatment temperature field control method

Abstract

The present invention discloses a medium frequency induction heating post-weld heat treatment device for pipe joints, comprising a coil switching switch, a medium frequency induction heat treatment machine, a first induction coil, a second induction coil, a first thermocouple and a second thermocouple respectively arranged on the pipes corresponding to the first induction coil and the second induction coil, and a third thermocouple arranged on the weld, wherein the two ends of the first induction coil and the second induction coil are respectively connected to the switching switch and the medium frequency induction heat treatment machine, and the switching switch is used to control the connection and disconnection between the first induction coil and the second induction coil. The heat treatment device of the present invention can heat the pipe on the side with lower temperature when the temperature difference on both sides of the weld exceeds a certain degree, so that the temperature field on both sides of the weld is symmetrically distributed, so that the highest temperature point of the heating area is always located on the weld, effectively avoiding the highest temperature point of the heating area from deviating from the weld, overcoming the adverse effects of the traditional post-weld heat treatment process on the joint performance, and meeting the technical requirements for post-weld heat treatment of the joint.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat-resistant steel welding, and specifically relates to a local post-weld heat treatment device during medium-frequency induction heating of a pipeline welding joint and a method for controlling a heat treatment temperature field using the heat treatment device. The present invention can be applied to controlling a post-weld heat treatment temperature field of medium-frequency induction heating of new 9% Cr steel pipelines such as medium- and low-alloy steels of different specifications, T / P91, T / P92, etc. Background Art

[0002] Post-weld heat treatment is a heat treatment to eliminate residual stress in welded joints and improve the structure and performance of welded joints. When medium-frequency induction heating is used, the general process is: install thermocouples → wrap insulation cotton → arrange and connect heating coils → set heat treatment parameters → perform heat treatment.

[0003] During the post-weld heat treatment of pipeline welding joints, due to pipeline structural reasons (such as different structures on both sides of the weld), environmental influences (such as air flow in the pipeline) and operational reasons (such as inconsistent thickness of insulation cotton, uneven winding spacing of induction coils, etc.), the maximum temperature in the heating area may deviate from the weld and be located at a certain position in the pipeline. At the same time, the temperature difference between the longitudinal and axial directions of the heating area and the inner and outer walls of the weld increases. The maximum temperature deviation and excessive local temperature gradient are related to many factors such as pipeline structure and post-weld heat treatment process. The maximum temperature deviation from the weld and the increase in temperature gradients in different directions destroy the rationality of the temperature field in the heating area and reduce the residual stress elimination effect. In particular, the maximum temperature deviation from the weld may cause the maximum temperature to exceed the phase change point of the material, causing irreversible damage to the material properties, and even directly leading to the scrapping of the joint. Summary of the invention

[0004] In view of this, in order to overcome the defects of the prior art, the purpose of the present invention is to provide a medium-frequency induction heating post-weld heat treatment device for a pipe joint, which can obtain a reasonable temperature field so that the highest temperature is located on the weld, and the axial, circumferential and inner and outer wall temperature gradients of the pipe weld are within the required range.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A medium-frequency induction heating post-weld heat treatment device for a pipe joint comprises a coil switching switch (coil opening and closing controller), a medium-frequency induction heat treatment machine, a first induction coil, a second induction coil, a first thermocouple and a second thermocouple respectively arranged on the pipes corresponding to the first induction coil and the second induction coil, and a third thermocouple arranged on the weld. The two ends of the first induction coil and the second induction coil are respectively connected to the switching switch and the medium-frequency induction heat treatment machine. The switching switch is used to control the connection and disconnection between the first induction coil and the second induction coil. A connecting line is also arranged between the switching switch and the medium-frequency induction heat treatment machine.

[0007] According to some preferred implementation aspects of the present invention, the weld is located in the heating area corresponding to the first induction coil or the second induction coil, and the second induction coil is located at one end of the winding length of the first induction coil. Preferably, the weld is located in the heating area corresponding to the first induction coil.

[0008] According to some preferred implementation aspects of the present invention, the distances between the first thermocouple, the second thermocouple and the third thermocouple are LA and LB respectively, and the ratio between LA and LB is 0.9 to 1.1, that is, the distances between the first thermocouple, the second thermocouple and the third thermocouple are equal or similar, preferably equal.

[0009] According to some preferred implementation aspects of the present invention, the third thermocouple is located at the center of the weld. When the wall thickness of the corresponding pipeline is thicker, the weld is wider. At this time, the influence of the weld size should be considered, that is, the third thermocouple is located at the center of the weld width. And preferably, the first thermocouple and the second thermocouple are located on the same straight line. In some embodiments, it is preferred that the straight line where the first thermocouple and the second thermocouple are located is equal to the straight line where the third thermocouple is located from the vertical plane where the axis of the pipeline is located, and as close to the vertical plane as possible, so as to achieve more accurate measurement and control of the temperature. The straight line where the first thermocouple and the second thermocouple are located and the straight line where the third thermocouple is located are located on the same side of the vertical plane (that is, the three thermocouples are located on the same straight line) or on both sides.

[0010] According to some preferred implementation aspects of the present invention, the first thermocouple and the second thermocouple are respectively located at 2 / 3 to 4 / 5 of the winding length of the induction coil. That is, the first thermocouple and the second thermocouple are respectively located on both sides of the weld, and are preferably located at 3 / 4 of the distance from the weld to the winding length of the coil on both sides.

[0011] According to some preferred implementation aspects of the present invention, the length direction of the thermocouple arrangement is parallel to the axis of the pipeline to avoid damaging the thermal insulation cotton.

[0012] According to some preferred implementation aspects of the present invention, when the temperature difference measured by the first thermocouple and the second thermocouple is less than 30°C, the switching switch controls the first induction coil and the second induction coil to be connected in series, the third thermocouple serves as a temperature control thermocouple, and the first thermocouple and the second thermocouple serve as temperature measuring thermocouples to perform post-weld heat treatment on the pipeline weld.

[0013] According to some preferred implementation aspects of the present invention, when the temperature difference measured by the first thermocouple and the second thermocouple is equal to or higher than 30°C, the switching switch controls the first induction coil to disconnect from the second induction coil, controls the induction coil of the pipe on the side with low temperature to heat, and the corresponding thermocouple is used as a temperature control thermocouple until the temperature of the pipe on this side is equal to the temperature of the pipe on the other side, and then the switching switch controls the first induction coil and the second induction coil to heat simultaneously after being connected in series. The average temperature range of post-weld heat treatment is generally specified as 30°C. If the heat treatment temperature is required to be 750°C, 720-750°C is considered to be the average temperature range, that is, during the average temperature stage, 720~750°C are considered to be the average temperature.

[0014] According to some preferred implementation aspects of the present invention, the first induction coil and the second induction coil are wound in the same direction.

[0015] According to some preferred implementation aspects of the present invention, the winding length of the first induction coil is greater than 2 / 3 of the length of the pipeline heating area, and the remainder is the length of the second induction coil. Preferably, the winding length of the first induction coil is 3 / 4 of the length of the pipeline heating area, and the winding length of the second induction coil is 1 / 4 of the length of the pipeline heating area, so as to achieve zoned heating. When the temperature field is offset and the temperature fields on both sides of the weld are asymmetric, the first or second induction coil is used for separate heating to correct the offset temperature field.

[0016] According to some preferred implementation aspects of the present invention, the pipeline is wrapped with a thermal insulation layer, the induction coil is wound around the thermal insulation layer, and the thermocouple is located between the thermal insulation layer and the pipeline.

[0017] According to some preferred embodiments of the present invention, the coverage area of ​​the thermal insulation layer extends outward by at least 300 mm along the length of the pipeline heating range.

[0018] The present invention also provides a method for controlling the temperature field of heat treatment according to the above-mentioned medium frequency induction heating post-weld heat treatment device for pipe joints, comprising the following steps:

[0019] Installing the post-weld heat treatment device;

[0020] When the temperature difference measured by the first thermocouple and the second thermocouple is less than 30°C, the switch controls the first induction coil and the second induction coil to be connected in series, the third thermocouple is used as a temperature control thermocouple, and the first thermocouple and the second thermocouple are used as temperature measuring thermocouples to perform post-weld heat treatment on the pipeline weld; and / or,

[0021] When the temperature difference measured by the first thermocouple and the second thermocouple is equal to or higher than 30°C, the switching switch controls the first induction coil to be disconnected from the second induction coil, controls the induction coil of the pipe on the side with the lower temperature to be heated, and the corresponding thermocouple is used as a temperature control thermocouple until the temperature of the pipe on this side is equal to the temperature of the pipe on the other side. Then, the switching switch controls the first induction coil and the second induction coil to be connected in series and heated simultaneously.

[0022] Due to the adoption of the above technical scheme, compared with the prior art, the advantages of the present invention are as follows: the medium-frequency induction heating post-weld heat treatment device for pipe joints of the present invention can heat the pipe on the lower temperature side when the temperature difference on both sides of the weld exceeds a certain degree, so that the temperature field on both sides of the weld is symmetrically distributed, so that the highest temperature point in the heating area is always located on the weld, effectively avoiding the highest temperature point in the heating area from deviating from the weld, overcoming the adverse effects of traditional post-weld heat treatment processes on joint performance, and meeting the technical requirements for post-weld heat treatment of joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 It is a schematic diagram of the structure of a medium frequency induction heating post-weld heat treatment device for a pipe joint in a preferred embodiment of the present invention;

[0025] In the attached drawings, pipeline-1, weld-2, insulation layer-3, coil switching switch-4, medium frequency induction heat treatment machine-5, connecting line-6, first induction coil-A, second induction coil-B, first thermocouple-TA, second thermocouple-TB, third thermocouple-T0. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0027] Example 1: Pipeline joint medium frequency induction heating post-weld heat treatment device

[0028] like Figure 1As shown, the medium frequency induction heating post-weld heat treatment device for pipe joints in this embodiment includes an insulation layer 3 wrapped outside the pipe 1, a coil switching switch 4, a medium frequency induction heat treatment machine 5, a first induction coil A, a second induction coil B, a first thermocouple TA and a second thermocouple TB arranged on the pipe 1 corresponding to the first induction coil A and the second induction coil B, respectively, and a third thermocouple T0 arranged on the weld 2. The induction coil is wrapped outside the insulation layer 3, and the thermocouple is located between the insulation layer 3 and the pipe 1. The coverage area of ​​the insulation layer 3 extends outward by at least 300 mm on the length of the heating range of the pipe 1. The pipe 1 can be a small diameter pipe or a medium or large diameter pipe; it can be a medium and low alloy steel or a 9% Cr new heat-resistant steel.

[0029] The weld 2 is located in the heating area corresponding to the first induction coil A, and the second induction coil B is located at one end of the winding length of the first induction coil A, that is, the weld 2 is wound inside by the first induction coil A, and the second induction coil B is located on one side of the weld 2. The two end connectors of the first induction coil A and the second induction coil B are respectively connected to the switch 4 and the medium frequency induction heat treatment machine 5. The coil switch 4 can connect or disconnect the first induction coil A and the second induction coil B in series according to the instructions of the medium frequency induction heat treatment machine 5. A connecting line 6 is also provided between the switch 4 and the medium frequency induction heat treatment machine 5.

[0030] The winding direction of the first induction coil A is the same as that of the second induction coil B. In this embodiment, the winding length of the first induction coil A is 3 / 4 of the winding length of the whole coil, and the winding length of the second induction coil B is 1 / 4 of the winding length of the whole coil, so as to realize zone heating. When the temperature field is offset and the temperature fields on both sides of the weld are asymmetric, the first or second induction coil is used for heating separately to correct the offset temperature field.

[0031] The length direction of the thermocouple arrangement is parallel to the axis of the pipeline 1. Figure 1 As shown, the third thermocouple T0 is located at the center of the width of the weld 2. Preferably, the first thermocouple and the second thermocouple are located on the same straight line; more preferably, the straight line where the first thermocouple and the second thermocouple are located and the straight line where the third thermocouple is located are equidistant from the vertical plane where the axis of the pipeline is located, and are as close to the vertical plane as possible, so as to achieve more accurate measurement and control of the temperature. The straight line where the first thermocouple and the second thermocouple are located and the straight line where the third thermocouple is located are located on the same side of the vertical plane (that is, the three thermocouples are located on the same straight line) or on both sides.

[0032] The distances between the first thermocouple TA, the second thermocouple TB and the third thermocouple T0 are LA and LB respectively, LA = (0.9-1.1) LB. That is, the distances between the first thermocouple TA, the second thermocouple TB and the third thermocouple T0 are equal or close, preferably equal. That is, the distances between the first thermocouple, the second thermocouple and the weld are made equal as much as possible, so that the temperature on the left and right sides of the weld is symmetrically distributed.

[0033] The first thermocouple TA and the second thermocouple TB are located at 2 / 3 to 3 / 4 of the winding length of the induction coil, that is, the first thermocouple TA and the second thermocouple TB are located on both sides of the weld 2, and preferably at 3 / 4 of the distance from the weld 2 to the winding length of the coil on both sides.

[0034] During on-site heat treatment, when the temperature difference measured by the first thermocouple TA and the second thermocouple TB is less than 30°C, the switching switch 4 controls the first induction coil A and the second induction coil B to be connected in series, the third thermocouple T0 is used as a temperature control thermocouple, the first thermocouple TA and the second thermocouple TB are used as temperature measuring thermocouples, and post-weld heat treatment is performed on the weld 2 of the pipeline 1 according to the set post-weld heat treatment process.

[0035] When the temperature difference measured by the first thermocouple TA and the second thermocouple TB is equal to or higher than 30°C, the switching switch 4 controls the first induction coil A and the second induction coil B to be disconnected, and controls the induction coil of the pipeline 1 on the side with low temperature to be heated. The corresponding thermocouple is used as a temperature control thermocouple to control the temperature according to the heating / cooling rate of the post-weld heat treatment until the temperature of the pipeline 1 on this side is equal to the temperature of the pipeline 1 on the other side. The switching switch 4 controls the first induction coil A and the second induction coil B to be connected in series and heated simultaneously.

[0036] Example 2 Control method for temperature field of medium frequency induction heating post-weld heat treatment of pipeline joints

[0037] This embodiment provides a method for controlling the temperature field of heat treatment performed by the medium frequency induction heating post-weld heat treatment device for pipe joints in Embodiment 1, specifically comprising the following steps:

[0038] (1) Determine the winding length of the induction coil

[0039] The heating area of ​​the pipeline 1 and the winding length of the induction coil are determined according to relevant standards or technical requirements.

[0040] (2) Install the thermocouple

[0041] The third thermocouple T0 is spot welded or tied on the weld 2, and the first thermocouple TA and the second thermocouple TB are spot welded or tied on both sides of the weld 2. The first thermocouple TA and the second thermocouple TB are respectively located at 3 / 4 of the coil winding length on both sides from the weld 2, and are equal or close to the third thermocouple T0. The arrangement direction of the thermocouple is parallel to the axial direction of the pipeline 1.

[0042] (3) Wrap with thermal insulation cotton

[0043] The heating coil winding area and the outer side thereof within a range of at least 300 mm are covered with thermal insulation cotton to form a thermal insulation layer 3.

[0044] (4) Winding induction coil

[0045] The first induction coil A and the second induction coil B are wound in the same direction; the winding length of the first induction coil A is 3 / 4 of the overall winding length of the induction coil, and the winding length of the second induction coil B is 1 / 4 of the overall winding length of the induction coil.

[0046] (5) Connect the induction coil to the switch 4 and the medium frequency induction heat treatment machine 5. The switch 4 and the medium frequency induction heat treatment machine 5 are connected via a connecting line 6.

[0047] (6) Set a heat treatment process curve and perform post-weld heat treatment. Preferably, the pipe hole of the pipeline 1 is blocked to reduce the air flow inside the pipeline 1.

[0048] During heat treatment, when the temperature difference measured by the first thermocouple TA and the second thermocouple TB is less than 30°C, the switch 4 controls the first induction coil A and the second induction coil B to be connected in series, the third thermocouple T0 is used as a temperature control thermocouple, and the first thermocouple TA and the second thermocouple TB are used as temperature measuring thermocouples to perform post-weld heat treatment on the pipeline weld.

[0049] When the temperature difference measured by the first thermocouple TA and the second thermocouple TB is equal to or higher than 30°C, the switching switch 4 controls the first induction coil A and the second induction coil B to be disconnected, controls the induction coil of the pipe on the side with the lower temperature to be heated, and the corresponding thermocouple is used as a temperature control thermocouple until the temperature of the pipe on this side is equal to the temperature of the pipe on the other side. Then, the switching switch 4 controls the first induction coil A and the second induction coil B to be connected in series and heated simultaneously.

[0050] Implementation Cases

[0051] The material of the suspension pipe of the boiler superheater of a power station is T91, with an outer diameter of 63.5mm and a wall thickness of 18.0mm. The welding process in the installation project requires the use of medium-frequency induction heating method to perform local post-weld heat treatment on the butt joint. The post-weld heat treatment constant temperature is 740℃, the constant temperature time is 120min, the temperature rise and fall speed is 300℃ / h, the heating area is not less than 90mm on each side of the weld 2, and the insulation cotton coverage is not less than 300mm on each side of the weld 2.

[0052] The method of the present invention is used to perform local post-weld heat treatment on the weld joint, and the specific implementation steps are as follows:

[0053] (1) Determine the winding length of the induction coil

[0054] According to the post-weld heat treatment process requirements, the heating area is not less than 90 mm on each side of weld 2. Considering the heating power and heating coil size, the coil winding length is determined to be 120 mm on each side of weld 2.

[0055] (2) Arrangement of thermocouples

[0056] A thermocouple, namely the third thermocouple T0, is installed on the weld 2, and a thermocouple, namely the first thermocouple TA and the second thermocouple TB, is installed on both sides of the weld 2 at a distance of 90 mm from the center line of the weld 2. The thermocouples are fixed by spot welding, and the direction is consistent with the length direction of the pipeline 1.

[0057] (3) Coated with thermal insulation cotton

[0058] The insulation range is 400mm on each side of weld 2. Use a piece of insulation cotton as much as possible, and cover both sides of weld 2 with equal length.

[0059] (4) Winding heating induction coil

[0060] Since the joint is in the horizontal welding position during heat treatment, Figure 1 As shown, the first induction coil A is wound with a length of 180 mm; the second induction coil B is wound with a length of 60 mm, the weld 2 is wound inside the first induction coil A, and the second induction coil B is located at the lower end of the first induction coil A and at the lower side of the weld 2.

[0061] (5) Connect the thermocouple and heating coil.

[0062] The thermocouple is connected to the medium frequency induction heat treatment machine 5 , the induction coil is connected to the switching switch 4 and the medium frequency induction heat treatment machine 5 , and the switching switch 4 and the medium frequency induction heat treatment machine 5 are connected via a connecting line 6 .

[0063] (6) Set the post-weld heat treatment process parameters and temperature field control start conditions, and perform post-weld heat treatment.

[0064] Set the post-weld heat treatment process parameters according to the welding heat treatment process requirements; set the switch 4 to disconnect the A and B induction coils when the temperature difference between the first thermocouple TA and the second thermocouple TB exceeds 30°C, and heat with one coil alone; when the temperature difference between the first thermocouple TA and the second thermocouple TB is less than 5°C, coils A and B are connected in series, and the two coils are heated at the same time. The temperature of the switch opening and closing can be set on the medium frequency induction heat treatment machine, such as 20°C, 30°C, etc., and it is set to 30°C here.

[0065] Temperature measurements during implementation show that, with the above post-weld heat treatment method, the temperature at the weld is the highest temperature in the heating area, and the temperatures on both sides of the weld are basically equal at equal distances from the weld center, that is, the temperature field on both sides of the weld is symmetrical. This method obtains the required temperature field and meets the strict requirements of post-weld heat treatment of T91 steel joints.

[0066] In the present invention, the given post-weld heat treatment process and the required heating range are known and determined for a specific pipe joint. Calculating the power required for heating the pipe joint according to the given post-weld heat treatment process and the required heating range is common knowledge in the art and will not be described in detail here.

[0067] For local post-weld heat treatment of pipe butt joints, the ideal temperature field is centered on the weld, with the temperature field on both sides of the weld distributed symmetrically, the highest temperature is located on the weld, and the temperature gradients of the pipe axial, circumferential and inner and outer walls are within the required range. However, in actual engineering, due to the influence of structure, environment and operation, the ideal temperature field is often not obtained, resulting in poor stress relief effect, and even overheating of the heating area causing irreversible damage to the material.

[0068] Therefore, the present application provides a medium frequency induction heating post-weld heat treatment device and a temperature field control method, which can make the highest temperature in the heating area located on the weld, and at the same time obtain a reasonable temperature gradient in the axial, circumferential and inner and outer walls of the pipeline weld, which can effectively avoid material damage and better eliminate welding residual stress. The present invention designs two induction coils according to the temperature field characteristics of medium frequency induction heating post-weld heat treatment. According to the temperature monitoring of the medium frequency induction heater, the two coils are connected in series or disconnected through a switching switch to heat the pipe section on the low temperature side, and the coils are automatically connected in series when the temperatures on both sides are equal, and the temperature is increased, constant and cooled according to the set post-weld heat treatment process curve. This technology effectively avoids the deviation of the highest temperature point in the heating area from the weld, successfully overcomes the adverse effects of traditional post-weld heat treatment processes on joint performance, and meets the technical requirements for post-weld heat treatment of joints.

[0069] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A medium frequency induction heating post-weld heat treatment device for pipe joints, characterized in that: It includes a coil switching switch, a medium frequency induction heat treatment machine, a first induction coil, a second induction coil, a first thermocouple and a second thermocouple respectively arranged on the pipes corresponding to the first induction coil and the second induction coil, and a third thermocouple arranged on the weld, wherein the two ends of the first induction coil and the second induction coil are respectively connected to the switching switch and the medium frequency induction heat treatment machine, the switching switch is used to control the series connection or disconnection between the first induction coil and the second induction coil, and a connecting line is also arranged between the switching switch and the medium frequency induction heat treatment machine; The weld is located in the heating area of ​​the first induction coil, and the second induction coil is located at one end of the winding length of the first induction coil; the winding directions of the first induction coil and the second induction coil are the same; the winding length of the first induction coil is greater than 2 / 3 of the length of the pipeline heating area, and the remainder is the winding length of the second induction coil; The distances between the first thermocouple, the second thermocouple and the third thermocouple are LA and LB respectively, and the ratio between LA and LB is 0.9-1.1; the first thermocouple and the second thermocouple are respectively located on both sides of the weld.

2. The heat treatment device according to claim 1, characterized in that The third thermocouple is located at the center of the weld width.

3. The heat treatment device according to any one of claims 1 to 2, characterized in that: The length direction of the thermocouple arrangement is parallel to the axial center line of the pipeline.

4. The heat treatment device according to claim 1, characterized in that When the temperature difference measured by the first thermocouple and the second thermocouple is less than 30°C, the switching switch controls the first induction coil and the second induction coil to be connected in series, the third thermocouple is used as a temperature control thermocouple, and the first thermocouple and the second thermocouple are used as temperature measuring thermocouples to perform post-weld heat treatment on the pipeline weld.

5. The heat treatment device according to claim 1 or 4, characterized in that: When the temperature difference measured by the first thermocouple and the second thermocouple is equal to or higher than 30°C, the switching switch controls the first induction coil to be disconnected from the second induction coil, controls the induction coil of the pipe on the side with the lower temperature to be heated, and the corresponding thermocouple is used as a temperature control thermocouple until the temperature of the pipe on this side is equal to the temperature of the pipe on the other side. Then, the switching switch controls the first induction coil and the second induction coil to be connected in series and heated simultaneously.

6. The heat treatment device according to claim 1, characterized in that: The pipeline is wrapped with a heat-insulating layer, the induction coil is wound outside the heat-insulating layer, and the thermocouple is located between the heat-insulating layer and the pipeline.

7. The heat treatment device according to claim 6, characterized in that The coverage area of ​​the thermal insulation layer extends outward by at least 300 mm along the length of the pipeline heating range.

8. A method for controlling the temperature field of heat treatment by the medium frequency induction heating post-weld heat treatment device for pipe joints according to any one of claims 1 to 7, characterized in that: The steps include: Installing the post-weld heat treatment device; When the temperature difference measured by the first thermocouple and the second thermocouple is less than 30°C, the switch controls the first induction coil and the second induction coil to be connected in series, the third thermocouple is used as a temperature control thermocouple, and the first thermocouple and the second thermocouple are used as temperature measuring thermocouples to perform post-weld heat treatment on the pipeline weld; and / or, When the temperature difference measured by the first thermocouple and the second thermocouple is equal to or higher than 30°C, the switching switch controls the first induction coil to be disconnected from the second induction coil, controls the induction coil of the pipe on the side with the lower temperature to be heated, and the corresponding thermocouple is used as a temperature control thermocouple until the temperature of the pipe on this side is equal to the temperature of the pipe on the other side. Then, the switching switch controls the first induction coil and the second induction coil to be connected in series and heated simultaneously.

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