CN116516138A - Pipe joint intermediate frequency induction heating post-heat treatment device and control method of heat treatment temperature field - Google Patents

Abstract

The invention discloses a pipeline joint intermediate frequency induction heating post-heat treatment device which comprises a coil change-over switch, an intermediate frequency induction heat treatment machine, a first induction coil, a second induction coil, a first thermocouple and a second thermocouple which are respectively arranged on pipelines corresponding to the first induction coil and the second induction coil, and a third thermocouple which is arranged on a welding seam, wherein two ends of the first induction coil and two ends of the second induction coil are respectively connected with the change-over switch and the intermediate frequency induction heat treatment machine, and the change-over switch is used for controlling connection and disconnection between the first induction coil and the second induction coil. The heat treatment device can heat the pipeline with low temperature at one side when the temperature difference at two sides of the welding line exceeds a certain degree, so that the temperature fields at two sides of the welding line are symmetrically distributed, the highest temperature point of the heating area is always positioned on the welding line, the deviation of the highest temperature point of the heating area from the welding line is effectively avoided, the adverse effect of the traditional post-welding heat treatment process on the joint performance is overcome, and the technical requirement of post-welding heat treatment of the joint is met.

Description

Pipe joint intermediate frequency induction heating post-heat treatment device and control method of heat treatment temperature field

Technical Field

The invention belongs to the technical field of heat-resistant steel welding, and particularly relates to a local postweld heat treatment device during medium-frequency induction heating of a pipeline welding joint and a control method for a heat treatment temperature field by adopting the heat treatment device, which are applicable to control of novel 9% Cr steel pipeline medium-frequency induction postheat treatment temperature fields such as medium-low alloy steel, T/P91, T/P92 and the like in different specifications.

Background

Post-weld heat treatment is a heat treatment that is performed to eliminate residual stress of the welded joint, improve the structure and performance of the welded joint. When the medium frequency induction heating is adopted, the general process flow is as follows: installing a thermocouple, wrapping heat preservation cotton, arranging and connecting heating coils, setting heat treatment parameters and carrying out heat treatment.

When the welded joint of the pipeline is subjected to postweld heat treatment, due to structural reasons (such as different structures at two sides of a welding line), environmental influences (such as air flow in the pipeline) and operational reasons (such as inconsistent thickness of heat insulation cotton and nonuniform winding interval of an induction coil), the highest temperature in a heating area can deviate from the welding line and be positioned at a certain position of the pipeline, and meanwhile, the temperature difference between the longitudinal direction and the axial direction of the heating area and the inner wall and the outer wall of the welding line is increased. The maximum temperature deviation and the local temperature gradient are related to various factors such as the pipeline structure, the post-welding heat treatment process and the like. The rationality of the temperature field of the heating area is damaged by the deviation of the highest temperature from the welding line, the increase of the temperature gradients in different directions and the like, the residual stress eliminating effect is reduced, and particularly, the deviation of the highest temperature from the welding line can cause irreversible damage to the material performance even directly caused by the fact that the highest temperature exceeds the material phase change point.

Disclosure of Invention

In view of the above, in order to overcome the defects of the prior art, the invention aims to provide a device for performing intermediate frequency induction heating on a pipeline joint and then performing heat treatment on the pipeline joint, which can obtain a reasonable temperature field, so that the highest temperature is positioned on a welding line, and the temperature gradient of the axial direction, the circumferential direction and the inner wall and the outer wall of the welding line of the pipeline is within a required range.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

the utility model provides a pipeline joint intermediate frequency induction heating heat post heat treatment device, includes coil change over switch (coil open and shut controller), intermediate frequency induction heat treatment machine, first induction coil, second induction coil, arranges respectively first thermocouple and the second thermocouple on first induction coil and second induction coil correspond the pipeline, arranges the third thermocouple on the welding seam, the both ends of first induction coil, second induction coil are connected with change over switch and intermediate frequency induction heat treatment machine respectively, the change over switch is used for controlling connect and disconnection between first induction coil and the second induction coil, still be provided with the connecting wire between change over switch and the intermediate frequency induction heat treatment machine.

According to some preferred embodiments of the invention, the weld is located in a heated region corresponding to a first induction coil or a second induction coil located at one end of the length of the first induction coil. Preferably, the weld is located in the corresponding heating zone of the first induction coil.

According to some preferred embodiments 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 0.9-1.1. I.e. the distances between the first thermocouple, the second thermocouple and the third thermocouple are equal or close, preferably equal.

According to some preferred embodiments of the present invention, the third thermocouple is located at the center of the weld, and the weld is wider when the wall thickness of the corresponding pipe is thicker, and the effect of the size of the weld should be considered, that is, the third thermocouple is located at the center of the width of the weld. And preferably the first thermocouple and the second thermocouple are located on the same straight line. In some embodiments, it is preferable 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 is as close to the vertical plane as possible, so as to achieve more accurate measurement and control of temperature. The straight line where the first thermocouple and the second thermocouple are located is located on the same side (i.e. three thermocouples are located on the same straight line) or on both sides of the vertical plane as the straight line where the third thermocouple is located.

According to some preferred embodiments of the invention, the first thermocouple and the second thermocouple are located at 2/3 to 4/5 of the winding length of the induction coil as a whole. I.e. the first thermocouple and the second thermocouple are located on both sides of the weld, respectively, and preferably at 3/4 of the coil winding length of both sides from the weld.

According to some preferred embodiments of the invention, the length direction of the thermocouple arrangement is parallel to the axis of the pipeline, so that damage to the insulation cotton is avoided.

According to some preferred embodiments of the present invention, when the temperature difference measured by the first thermocouple and the second thermocouple is less than 30 ℃, the change-over switch controls the first induction coil to be connected in series with the second induction coil, 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 postweld heat treatment on the welding seam of the pipeline.

According to some preferred embodiments of the present invention, when the temperature difference measured by the first thermocouple and the second thermocouple is equal to or higher than 30 ℃, the switch controls the first induction coil to be disconnected from the second induction coil, controls the induction coil of the low-temperature one-side pipeline to heat, and the corresponding thermocouple is used as a temperature control thermocouple until the temperature of the one-side pipeline is equal to the temperature of the other-side pipeline, and controls the first induction coil to be connected in series with the second induction coil and then to heat simultaneously. The post-weld heat treatment soaking temperature range is generally specified to be 30 ℃. If the heat treatment temperature is required to be 750 ℃, the temperature of 720-750 ℃ is considered as the temperature equalizing range, namely, the temperature equalizing temperature is considered as the temperature equalizing temperature of 720-750 ℃ in the temperature equalizing stage.

According to some preferred embodiments of the invention, the first induction coil and the second induction coil are wound in the same direction.

According to some preferred embodiments of the invention, the length of the first induction coil is greater than 2/3 of the length of the heating zone of the pipe, the remainder being the length of the second induction coil wound. Preferably, the winding length of the first induction coil is 3/4 of the length of the pipeline heating area, the winding length of the second induction coil is 1/4 of the length of the pipeline heating area, so that zone heating is realized, when the temperature field is deviated, and when the temperature fields on two sides of the welding seam are asymmetric, the temperature field is independently heated through the first induction coil or the second induction coil, and the deviated temperature field is corrected.

According to some preferred embodiments of the invention, the pipe 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 pipe.

According to some preferred embodiments of the invention, the insulation cover area extends outwardly by at least 300mm over the length of the heating zone of the conduit.

The invention also provides a control method for the heat treatment temperature field of the heat treatment device after the intermediate frequency induction heating welding of the pipeline joint, which comprises the following steps:

installing the post-weld heat treatment device;

when the temperature difference measured by the first thermocouple and the second thermocouple is less than 30 ℃, the change-over 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 postweld heat treatment on the pipeline weld joints; and/or the number of the groups of groups,

when the temperature difference measured by the first thermocouple and the second thermocouple is equal to or higher than 30 ℃, the change-over switch controls the first induction coil and the second induction coil to be disconnected, controls the induction coil of the pipeline with low temperature to heat, and the corresponding thermocouple is used as a thermocouple for controlling temperature, until the temperature of the pipeline with low temperature is equal to the temperature of the pipeline with low temperature, and controls the first induction coil and the second induction coil to be connected in series and then heated simultaneously.

Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages: the intermediate frequency induction heating post-heat treatment device for the pipeline joint can heat the pipeline with low temperature when the temperature difference at two sides of the welding line exceeds a certain degree, so that the temperature fields at two sides of the welding line are symmetrically distributed, the highest temperature point of a heating area is always positioned on the welding line, the deviation of the highest temperature point of the heating area from the welding line is effectively avoided, the adverse effect of the traditional post-heat treatment process on the joint performance is overcome, and the technical requirement of post-heat treatment of the joint is met.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic view showing the structure of a heat treatment apparatus after induction heating welding of pipe joints in accordance with a preferred embodiment of the present invention;

in the drawing, a pipeline-1, a welding line-2, an insulating layer-3, a coil change-over switch-4, an intermediate frequency induction heat processor-5, a connecting wire-6, a first induction coil-A, a second induction coil-B, a first thermocouple-TA, a second thermocouple-TB and a third thermocouple-T0.

Detailed Description

In order to make the technical solution of the present invention better understood by those skilled in the art, the technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

Example 1 intermediate frequency induction post-heating welding heat treatment device for pipe joint

As shown in fig. 1, the intermediate frequency induction heating post-heat treatment device for the pipeline joint in the embodiment comprises a heat insulation layer 3, a coil change-over switch 4, an intermediate 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 which are respectively arranged on the first induction coil a and the second induction coil B and correspond to the pipeline 1, and a third thermocouple T0 which is arranged on a welding seam 2, wherein the heat insulation layer 3 is wrapped by the induction coils, and the thermocouples are positioned between the heat insulation layer 3 and the pipeline 1. The coverage area of the insulation 3 extends outwardly for at least 300mm over the length of the heating range of the pipe 1. The pipeline 1 can be a small-diameter pipe or a medium-large-diameter pipe; can be medium-low alloy steel or novel heat-resistant steel with 9 percent of Cr.

The welding line 2 is positioned in the heating area corresponding to the first induction coil A, the second induction coil B is positioned at one end of the winding length of the first induction coil A, namely, the welding line 2 is wound by the first induction coil A, and the second induction coil B is positioned at one side of the welding line 2. The two end joints of the first induction coil A and the second induction coil B are respectively connected with the change-over switch 4 and the intermediate frequency induction heat treatment machine 5, and the coil change-over switch 4 can connect or disconnect the first induction coil A and the second induction coil B in series according to the instruction of the intermediate frequency induction heat treatment machine 5. A connecting wire 6 is also arranged between the change-over switch 4 and the medium frequency induction heat treatment machine 5.

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.

The length direction of the thermocouple arrangement is parallel to the axis of the pipe 1. As shown in fig. 1, 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 positioned on the same straight line; more preferably, 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 surface where the axis of the pipeline is located, and the straight line is as close to the vertical surface as possible, so that more accurate measurement and control of temperature are realized. The straight line where the first thermocouple and the second thermocouple are located is located on the same side (i.e. three thermocouples are located on the same straight line) or on both sides of the vertical plane as the straight line where the third thermocouple is located.

The distances among the first thermocouple TA, the second thermocouple TB and the third thermocouple T0 are LA and LB, respectively, la= (0.9-1.1) LB. I.e. the distances between the first thermocouple TA, the second thermocouple TB and the third thermocouple T0 are equal or close, preferably equal. The distances between the first thermocouple and the welding line are equal as far as possible, so that the temperatures at the left side and the right side of the welding line are symmetrically distributed.

The first thermocouple TA and the second thermocouple TB are positioned at 2/3 to 3/4 of the winding length of the entire induction coil inward, respectively. I.e. the first thermocouple TA and the second thermocouple TB are located on both sides of the weld 2, respectively, and preferably at 3/4 of the coil winding length of both sides from the weld 2.

When the temperature difference measured by the first thermocouple TA and the second thermocouple TB is less than 30 ℃ in the field heat treatment, the change-over switch 4 controls the first induction coil A to be connected in series with the second induction coil B, 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 the welding seam 2 of the pipeline 1 is subjected to the post-welding heat treatment according to a set post-welding heat treatment process.

When the temperature difference measured by the first thermocouple TA and the second thermocouple TB is equal to or higher than 30 ℃, the switch 4 controls the first induction coil a and the second induction coil B to be disconnected, controls the induction coil of the one-side pipeline 1 with low temperature to heat, and the corresponding thermocouple is used as a temperature control thermocouple to control the temperature according to the temperature rise/fall speed of the postweld heat treatment until the temperature of the one-side pipeline 1 is equal to the temperature of the other-side pipeline 1, and the switch 4 controls the first induction coil a and the second induction coil B to be connected in series and then heated simultaneously.

Example 2 control method of Heat treatment temperature field after Medium frequency induction heating welding of pipe Joint

The embodiment provides a control method for a heat treatment temperature field of a heat treatment device after intermediate frequency induction heating welding of a pipeline joint according to embodiment 1, which specifically comprises the following steps:

(1) Determining the winding length of an induction coil

The length of the winding of the induction coil and the heating area of the pipe 1 are determined according to relevant standards or specifications.

(2) Thermocouple installation

And a third thermocouple T0 is fixed on the welding line 2 by spot welding or binding, and the first thermocouple TA and the second thermocouple TB are fixed on two sides of the welding line 2 by spot welding or binding. The first thermocouple TA and the second thermocouple TB are respectively positioned at 3/4 of the winding length of the coils at the two sides and are equal to or close to the third thermocouple T0. The thermocouple is arranged in a direction parallel to the axial direction of the pipe 1.

(3) Thermal insulation cotton

And covering heat preservation cotton in the winding area of the heating coil and the outer side of the winding area by at least 300mm to form a heat preservation layer 3.

(4) Winding induction coil

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 whole winding length of the induction coil, and the winding length of the second induction coil B is 1/4 of the whole winding length of the induction coil.

(5) The induction coil is connected with a change-over switch 4 and an intermediate frequency induction heat treatment machine 5, and the change-over switch 4 is connected with the intermediate frequency induction heat treatment machine 5 through a connecting wire 6.

(6) Setting a heat treatment process curve, and performing postweld heat treatment. The tube holes of the tube 1 are preferably plugged to reduce the flow of air inside the tube 1.

When the temperature difference measured by the first thermocouple TA and the second thermocouple TB is less than 30 ℃, the change-over switch 4 controls the first induction coil A to be connected in series with the second induction coil B, 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 postweld heat treatment is carried out on the pipeline weld joints.

When the temperature difference measured by the first thermocouple TA and the second thermocouple TB is equal to or higher than 30 ℃, the change-over switch 4 controls the first induction coil A to be disconnected from the second induction coil B, controls the induction coil of the low-temperature one-side pipeline to be heated, and the corresponding thermocouple is used as a temperature control thermocouple until the temperature of the one-side pipeline is equal to the temperature of the other-side pipeline, and the change-over switch 4 controls the first induction coil A to be connected in series with the second induction coil B and then to be heated simultaneously.

Description of the preferred embodiments

The material of the superheater suspension tube of a certain power station boiler is T91, the outer diameter is 63.5mm, and the wall thickness is 18.0mm. The welding process in the installation engineering requires adopting an intermediate frequency induction heating method to carry out local postweld heat treatment on the butt joint. The constant temperature of the postweld heat treatment is 740 ℃, the constant temperature time is 120min, the temperature rising speed is 300 ℃/h, the heating area is not less than 90mm on each side of the welding seam 2, and the coverage area of the heat preservation cotton is not less than 300mm on each side of the welding seam 2.

The method of the invention is adopted to carry out local postweld heat treatment on the welded joint, and the specific implementation steps are as follows:

(1) Determining induction coil winding length

According to the requirements of the postweld heat treatment process, the heating area is not smaller than 90mm on each side of the welding line 2. The coil winding length was determined to be 120mm per side of the weld 2 in consideration of the heating power and the heating coil size.

(2) Arranging thermocouples

And 1 thermocouple, namely a third thermocouple T0 is arranged on the welding seam 2, and 1 thermocouple, namely a first thermocouple TA and a second thermocouple TB, is respectively arranged at the positions which are 90mm away from the central line of the welding seam 2 on two sides of the welding seam 2. The thermocouple is fixed by spot welding, and the direction is consistent with the length direction of the pipeline 1.

(3) Coated heat-insulating cotton

The heat preservation range is 400mm each side of the welding line 2. A piece of heat-insulating cotton is used as much as possible, and the covering lengths of the two sides of the welding line 2 are equal.

(4) Winding heating induction coil

Since the joint is in a transverse welding position during heat treatment, as shown in fig. 1, the first induction coil A is wound for 180mm; the second induction coil B is wound with the length of 60mm, the welding line 2 is wound by the first induction coil A, the second induction coil B is positioned at the lower end of the first induction coil A, and the second induction coil B is positioned at the lower side of the welding line 2.

(5) A thermocouple and a heating coil are connected.

The thermocouple is connected to the intermediate frequency induction heat treatment machine 5, the induction coil is connected to the change-over switch 4 and the intermediate frequency induction heat treatment machine 5, and the change-over switch 4 is connected with the intermediate frequency induction heat treatment machine 5 through a connecting wire 6.

(6) And setting the post-welding heat treatment process parameters and the temperature field control starting conditions, and performing post-welding heat treatment.

Setting postweld heat treatment process parameters according to welding heat treatment process requirements; setting that when the temperature difference between the first thermocouple TA and the second thermocouple TB exceeds 30 ℃, the switching switch 4 turns off the A, B induction coil, and the coil is heated by a single coil; when the temperature difference between the first thermocouple TA and the second thermocouple TB is less than 5 ℃, the coils A, B are connected in series and 2 coils are simultaneously heated. The temperature at which the change-over switch is opened and closed, such as 20 ℃, 30 ℃ and the like, can be set on the medium-frequency induction heat treatment machine, and is set to be 30 ℃.

The temperature measurement in the implementation shows that by adopting the postweld heat treatment method, the temperature at the welding seam is the highest temperature of a heating area, the temperatures of the two sides of the welding seam, which are equidistant from the center of the welding seam, are basically equal, namely the temperature fields of the two sides of the welding seam are symmetrically analyzed. The method obtains a required temperature field and meets the strict requirements of post-welding heat treatment of the T91 steel joint.

In the present invention, a given post-weld heat treatment process and the required heating range are known and determined for a particular pipe joint. Calculating the power required to heat a pipe joint based on a given post-weld heat treatment process and the required heating range is well known in the art and will not be described in detail herein.

For the local postweld heat treatment of the butt joint of the pipeline, the ideal temperature field is that the welding line is taken as the center, the temperature fields at the two sides of the welding line are symmetrically distributed, the highest temperature is positioned on the welding line, and the temperature gradient of the axial direction, the circumferential direction and the inner wall and the outer wall of the pipeline is in the required range. However, in practical engineering, due to the influence of structure, environment and operation, an ideal temperature field is often not obtained, resulting in poor stress relief effect and even irreversible damage to the material caused by overheating of the heating area.

Therefore, the application provides a medium-frequency induction post-heating heat treatment device and a temperature field control method, which can enable the highest temperature of a heating area to be positioned on a welding line, and meanwhile, reasonable temperature gradients are obtained on the axial direction, the circumferential direction, the inner wall and the outer wall of the pipeline welding line, so that damage of materials can be effectively avoided, and meanwhile, welding residual stress is better eliminated. The invention designs two induction coils aiming at the characteristics of a heat treatment temperature field after medium-frequency induction heating welding. According to the temperature monitoring condition of the medium-frequency induction heater, the two coils are connected in series or disconnected through the change-over switch to heat the pipe section at the low temperature side, and the coils are automatically connected in series when the temperatures at the two sides are equal, so that the temperature is increased, the temperature is kept constant and the temperature is reduced according to the set post-welding heat treatment process curve. The technology effectively avoids the deviation of the highest temperature point of the heating area from the welding line, successfully overcomes the adverse effect of the traditional post-welding heat treatment technology on the joint performance, and meets the technical requirements of post-welding heat treatment of the joint.

The above embodiments are provided to illustrate the technical concept and features of the present invention and are intended to enable those skilled in the art to understand the content of the present invention and implement the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.

Claims (13)

1. The utility model provides a pipeline joint intermediate frequency induction heating heat post heat treatment device, its characterized in that, including coil change over switch, intermediate frequency induction heat treatment machine, first induction coil, second induction coil, arrange respectively first thermocouple and the second thermocouple on first induction coil and second induction coil correspond the pipeline, arrange the third thermocouple on the welding seam, the both ends of first induction coil, second induction coil are connected with change over switch and intermediate frequency induction heat treatment machine respectively, the change over switch is used for control connect and disconnection between first induction coil and the second induction coil, still be provided with the connecting wire between change over switch and the intermediate frequency induction heat treatment machine.

2. The heat treatment apparatus of claim 1, wherein the weld is located in a heated region corresponding to a first induction coil or a second induction coil located at one end of a winding length of the first induction coil.

3. The heat treatment apparatus according to claim 1, wherein distances between the first thermocouple, the second thermocouple and the third thermocouple are LA and LB, respectively, and a ratio between LA and LB is 0.9 to 1.1.

4. A heat treatment apparatus according to claim 3, wherein the third thermocouple is located at a central position of the width of the weld.

5. The heat treatment apparatus according to claim 1, wherein the first thermocouple and the second thermocouple are positioned at 2/3 to 4/5 of the winding length of the entire induction coil inward, respectively.

6. A heat treatment apparatus according to any one of claims 1-5, wherein the length direction of the thermocouple arrangement is parallel to the axis of the pipe.

7. The heat treatment apparatus according to claim 1, wherein the change-over switch controls the first induction coil and the second induction coil to be connected in series when the temperature difference measured by the first thermocouple and the second thermocouple is less than 30 ℃, the third thermocouple is used as a temperature control thermocouple, and the first thermocouple and the second thermocouple are used as temperature measurement thermocouples to perform post-weld heat treatment on the pipe weld.

8. The heat treatment apparatus according to claim 1 or 7, wherein when the temperature difference measured by the first thermocouple and the second thermocouple is equal to or higher than 30 ℃, the change-over switch controls the first induction coil and the second induction coil to be disconnected, controls the induction coil of the low-temperature one-side pipeline to be heated, and the corresponding thermocouple is used as a temperature control thermocouple until the temperature of the one-side pipeline is equal to the temperature of the other-side pipeline, and controls the first induction coil and the second induction coil to be connected in series and then heated simultaneously.

9. The heat treatment apparatus according to claim 1, wherein the first induction coil and the second induction coil are wound in the same direction.

10. The heat treatment apparatus of claim 1, wherein the first induction coil is wound to a length greater than 2/3 of the length of the heating region of the pipe, and the remainder is wound to a length of the second induction coil.

11. The heat treatment device of claim 1, wherein the pipe is surrounded by 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 pipe.

12. The thermal processing apparatus of claim 11, wherein the thermal layer has a footprint that extends outwardly at least 300mm of the length of the heating zone of the conduit.

13. A method for controlling a heat treatment temperature field of a heat treatment apparatus after induction heating welding of a pipe joint intermediate frequency according to any one of claims 1 to 12, comprising the steps of:

installing the post-weld heat treatment device;

when the temperature difference measured by the first thermocouple and the second thermocouple is less than 30 ℃, the change-over 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 postweld heat treatment on the pipeline weld joints; and/or the number of the groups of groups,

when the temperature difference measured by the first thermocouple and the second thermocouple is equal to or higher than 30 ℃, the change-over switch controls the first induction coil and the second induction coil to be disconnected, controls the induction coil of the pipeline with low temperature to heat, and the corresponding thermocouple is used as a thermocouple for controlling temperature, until the temperature of the pipeline with low temperature is equal to the temperature of the pipeline with low temperature, and controls the first induction coil and the second induction coil to be connected in series and then heated simultaneously.