A medium frequency induction heating post-weld heat treatment device and heat treatment method for membrane wall welding joints

Abstract

The present invention discloses a post-weld heat treatment device for a membrane wall welded joint by medium-frequency induction heating. The membrane wall includes tubes and fins, and there are fin welds between adjacent fins. There are welded joints on the tubes. The heat treatment device includes a temperature control thermocouple, two induction coils respectively arranged on both sides of the membrane wall, and a medium-frequency induction heat treatment machine. The induction coils are connected to the medium-frequency induction heat treatment machine; the uniform temperature width W of the heating area of the membrane wall E is 6 times the wall thickness of the membrane wall tubes on each side of the welded joint to 2 times the outer diameter of the membrane wall tubes. The heat treatment device of the present invention can obtain a reasonable uniform temperature range, overcome the phenomenon of large uniform temperature range when the heating area is large, but large thermal expansion and large shrinkage during cooling of the membrane wall, resulting in large residual stress and large deformation, and also overcome the small uniform temperature range when the heating area is small, low heat treatment efficiency and poor residual stress elimination effect, and solves the adverse effects of traditional post-weld heat treatment processes on the performance of the joints.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding heat treatment, and specifically relates to a medium-frequency induction heating local post-weld heat treatment device for membrane wall welding joints and a method for post-weld heat treatment using the heat treatment device, which can be applied to medium-frequency induction heating local post-weld heat treatment of welding joints on the heating surface of water-cooled wall tubes in power station boilers. 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] The heating surface of the water-cooled wall of a power station boiler mostly adopts a membrane wall structure. The membrane wall is welded by small-diameter tubes and fins, with low rigidity and easy deformation. When the membrane wall is composed of small screens to form a large screen, it is generally assembled, welded and partially heat-treated after welding on site. Due to the structural characteristics of the membrane wall, its temperature field after welding heat treatment is approximately a two-dimensional temperature field. When the heating area of ​​the membrane wall structure after welding heat treatment is small, not only is the heat treatment efficiency low, but also due to the heat transfer characteristics of the two-dimensional temperature field, the uniform temperature area of ​​the heat treatment area is small, and the effect of eliminating welding residual stress is not good; when the heating area of ​​the membrane wall structure after welding heat treatment is large, the expansion of the heating area is large. Due to the constraint of the non-heated area around the two-dimensional temperature field, not only the deformation of the membrane wall after welding heat treatment is large, but also the effect of eliminating welding residual stress is poor, which seriously affects the quality and service life of the membrane wall. 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 membrane wall welding joints, which can obtain a reasonable uniform temperature zone through the arrangement of induction heating coils, thereby effectively reducing welding residual stress and controlling the deformation of the heated area.

[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 membrane wall welded joint, the membrane wall comprising a tube and fins, a fin weld between adjacent fins, a welding joint on the tube, the heat treatment device comprising a temperature-controlled thermocouple, a medium-frequency induction heat treatment machine and two induction coils respectively arranged on both sides of the membrane wall, the induction coils being connected to the medium-frequency induction heat treatment machine; the uniform temperature width W of the heating area of ​​the membrane wall E The length of the heating time is 6 times the wall thickness of the membrane wall pipe on each side of the welding joint (the wall thickness is generally 5-16mm) to 2 times the outer diameter of the membrane wall pipe (the outer diameter is generally 32-76mm); when the membrane wall fins in the heating area are not welded, the heating length LE Not more than 2000mm; when the membrane wall fins in the heating area are welded, the heating length L E Butt joints of not more than 10 membrane wall pipes.

[0007] According to some preferred implementation aspects of the present invention, the winding length L of the induction coil R =L E +2~4 turns; the winding width W of the induction coil R =W E +2~4 turns, each turn is close together to ensure a reasonable temperature range.

[0008] According to some preferred embodiments of the present invention, the length direction of the induction coil winding is perpendicular to the longitudinal direction (length extension direction) of the membrane wall pipe, that is, the length direction of the induction coil winding is parallel to the arrangement direction of the membrane wall pipe welding joints.

[0009] According to some preferred implementation aspects of the present invention, the induction coils are wound and located on the same plane and are armored and fixed to the heating area of ​​the membrane wall.

[0010] According to some preferred implementation aspects of the present invention, the armor is a plastic plate that fixes the induction coil to the plastic plate that is non-heat-conductive, does not generate eddy currents under the action of a magnetic field, and is resistant to high temperatures (200° C. and above).

[0011] According to some preferred implementation aspects of the present invention, the temperature-controlling thermocouple is arranged on the pipe welding joint at the center position of the corresponding heating area.

[0012] According to some preferred implementation aspects of the present invention, a thermal insulation layer is provided outside the membrane wall, the temperature-controlling thermocouple is located between the thermal insulation layer and the membrane wall, and the coil is located outside the thermal insulation layer.

[0013] According to some preferred implementation aspects of the present invention, the coverage of the thermal insulation layer extends outward by at least 300 mm on each side of the upper, lower, left and right sides of the welding joint.

[0014] According to some preferred implementation aspects of the present invention, the winding directions of the two induction coils are consistent; the sizes of the two induction coils after winding are consistent. The induction coils include a first induction coil and a second induction coil respectively arranged on both sides of the membrane wall, the first induction coil and the second induction coil are wound in the same direction; and the length, width, and number of winding turns of the first induction coil and the second induction coil are completely consistent.

[0015] The present invention also provides a method for heat treatment according to the above-mentioned medium frequency induction heating post-weld heat treatment device for membrane wall welded joints, comprising the following steps: determining the uniform temperature width W of the membrane wall welded joint post-weld heat treatment E and heating length LE ; Install the heat treatment device, set the heat treatment process curve, and perform post-weld heat treatment.

[0016] Due to the adoption of the above technical scheme, compared with the prior art, the advantages of the present invention are: the medium-frequency induction heating post-weld heat treatment device for the membrane wall welding joint of the present invention can obtain a reasonable average temperature range, overcome the phenomenon that when the heating area is large, the average temperature range is large, but the membrane wall expands greatly when heated and contracts greatly when cooled, resulting in large residual stress and large deformation, and also overcome the problem that when the heating area is small, the average temperature range is small, the heat treatment efficiency is low, and the residual stress elimination effect is poor, solves the adverse effects of traditional post-weld heat treatment processes on joint performance, and meets the technical requirements of post-weld heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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.

[0018] Figure 1 It is a schematic diagram of the three-dimensional structure of a medium-frequency induction heating post-weld heat treatment device for a membrane-type wall welding joint in a preferred embodiment of the present invention;

[0019] Figure 2 It is a side view schematic diagram of a medium frequency induction heating post-weld heat treatment device for a membrane wall welding joint in a preferred embodiment of the present invention;

[0020] In the attached drawings, there are membrane wall-1, tube-2, fin-3, welding joint-4, temperature-control thermocouple-5, induction coil-6, first induction coil-61, second induction coil-62, medium frequency induction heat treatment machine-7, and insulation layer-8. DETAILED DESCRIPTION

[0021] 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.

[0022] Example 1: Medium frequency induction heating post-weld heat treatment device for membrane wall welding joint

[0023] like Figure 1-2As shown, the membrane wall 1 includes a tube 2 and fins 3, and there is a fin 3 weld (not shown) between adjacent fins 3 (fins between two tubes 2), and there is a weld joint 4 on the tube 2. The tube 2 is a small diameter tube, and the tube 2 is provided with fins 3 in the length direction, and the fins 3 are welded to form a heating surface. The small diameter tube of the tube 2 can be low alloy steel or 9% Cr new heat-resistant steel.

[0024] like Figure 1-2 As shown, the medium-frequency induction heating post-weld heat treatment device for membrane wall welding joints in this embodiment includes a temperature-controlled thermocouple 5, two induction coils 6 respectively arranged on both sides of the membrane wall 1, a medium-frequency induction heat treatment machine 7, and a thermal insulation layer 8 wrapped outside the membrane wall 1, and the induction coil 6 is connected to the medium-frequency induction heat treatment machine 7. The coverage of the thermal insulation layer 8 is not less than 300 mm on each side of the upper and lower left and right extensions of the induction coil. The temperature-controlled thermocouple 5 is located between the thermal insulation layer 8 and the membrane wall 1, and the coil is located outside the thermal insulation layer 8. The temperature-controlled thermocouple 5 is arranged on the welding joint 4 of the pipe 2 at the center position of the corresponding heating area.

[0025] The uniform temperature width W of the heating area of ​​the membrane wall 1 E The welding joint 4 (upper and lower) of the pipe 2 is 6 times the wall thickness of the membrane wall 1 pipe to 2 times the outer diameter of the membrane wall 1 pipe on each side.

[0026] When the membrane wall 1 and fin 3 of the heating area are not welded, the heating length L E Not more than 2000mm; when the membrane wall 1 fin 3 of the heating area has been welded, the heating length L E Not more than 10 membrane wall 1 pipe butt joints.

[0027] The winding length L of the induction coil 6 R =L E +2~4 turns; winding width W of induction coil 6 R =W E +2 to 4 turns, with each turn set tightly together with no gap between them.

[0028] The length direction of the induction coil 6 is perpendicular to the longitudinal direction of the tube 2 in the membrane wall 1. That is, the length direction of the induction coil 6 is parallel to the arrangement direction of the welding joints 4 of the tube 2 on the membrane wall 1. After being wound, the induction coil 6 is located on the same plane and is armored and fixed to the heating area of ​​the membrane wall 1. The armoring is to fix the induction coil 6 on a plastic plate that is non-heat-conductive, does not generate eddy current under the action of a magnetic field, and is resistant to high temperatures.

[0029] The winding directions of the two induction coils 6 are consistent; the lengths, widths and turns of the two induction coils 6 after winding are consistent. The induction coils 6 include a first induction coil 61 and a second induction coil 62 respectively arranged on both sides of the membrane wall 1, the first induction coil 61 and the second induction coil 62 are wound in the same direction; and the sizes of the first induction coil 61 and the second induction coil 62 are completely consistent.

[0030] Example 2 Post-weld heat treatment method for membrane wall 1 welded joint 4 by medium frequency induction heating

[0031] This embodiment provides a method for heat treatment of the membrane wall 1 welded joint 4 according to the medium frequency induction heating post-weld heat treatment device of embodiment 1, comprising the following steps: determining the uniform temperature width W of the membrane wall 1 welded joint 4 after weld heat treatment E and heating length L E ; Install heat treatment equipment, set heat treatment process curve, and perform post-weld heat treatment.

[0032] The specific steps include:

[0033] (1) Determine the uniform temperature width W of the post-weld heat treatment of the membrane wall 1 welding joint 4 E and heating length L E

[0034] According to the tube size of the membrane wall 1 and the welding state of the fin 3, the uniform temperature width W of the post-weld heat treatment of the membrane wall 1 tube welding joint 4 is determined in combination with relevant standards or technical requirements. E and heating length L E .

[0035] (2) Install the thermocouple

[0036] The thermocouple is spot welded and fixed at the center of the heating range, and the thermocouple is located on the butt joint weld of the membrane wall 1 pipe.

[0037] (3) Wrap with thermal insulation cotton

[0038] 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 8.

[0039] (4) Winding induction coil 6

[0040] According to the average temperature width W E and heating length L E It is required to wind the induction coil 6. The winding length L of the induction coil 6 R =L E +2~4 turns, winding width W R =W E+2 to 4 turns, each turn is close together and there is no gap. That is, the insulation area covers the heating area of ​​the coil, and the heating area covers the uniform temperature (width) area.

[0041] The induction coil 6 includes a first induction coil 61 and a second induction coil 62 respectively arranged on both sides of the membrane wall 1. The first induction coil 61 and the second induction coil 62 are planar, wound in the same direction and have the same length, width and number of turns.

[0042] (5) Armor the wound induction coil 6

[0043] The coil is fixed on a plastic plate which is non-heat-conductive, does not generate eddy current under the action of a magnetic field and is resistant to high temperatures, and then fixed to the membrane wall.

[0044] (6) Connect the coil to the medium frequency induction heat treatment machine 7.

[0045] (7) Set the heat treatment process curve and perform post-weld heat treatment.

[0046] Implementation Cases

[0047] The water-cooled wall of a certain boiler adopts a membrane wall 1 structure, the tube material is 12Cr1MoVG, the outer diameter is 44.5mm, and the wall thickness is 9.0mm. The fin 3 material is P22, the width is 12mm, and the wall thickness is 6mm. 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 membrane wall 1 pipe welding joint 4. The constant temperature of the post-weld heat treatment is 720℃, the constant temperature time is 60min, the heating and cooling speed is 300℃ / h, the heating width of the welding joint 4 is not less than 60mm on each side, and the coverage of the insulation cotton is not less than 300mm on each side of the welding joint 4.

[0048] The heat treatment method of Example 2 is used to perform local post-weld heat treatment on the weld joint 4, and the specific implementation steps are as follows:

[0049] (1) Determine the winding width of the induction coil 6

[0050] According to the post-weld heat treatment process requirements, the heating width is not less than 60mm on each side of the weld joint 4. Considering the heating power and the size of the heating coil, the coil winding width is determined to be 90mm on each side of the weld.

[0051] (2) Determine the winding length of the induction coil 6

[0052] Since the weld seam of the fin 3 has not been welded yet, the number of heat treatment joints per furnace can be appropriately increased. According to the length of each induction coil 6, the winding length of each furnace is set to no more than 2000mm. The number of joints within the 2000mm length of the water-cooled wall is 11. The winding length of the induction coil 6 is to cover the 11 welded joints 4 plus 4 turns.

[0053] (3) Arrangement of thermocouples

[0054] A thermocouple is installed on the middle joint weld of the 11 joints. Multiple temperature measuring thermocouples are arranged in other areas. The thermocouples are fixed by spot welding, and the direction is consistent with the length direction of pipe 2.

[0055] (4) Coated with thermal insulation cotton

[0056] The insulation range is 400mm on both sides of the weld. The same specification of insulation cotton is used on both sides, and the coverage length on both sides of the weld is equal.

[0057] (5) Winding heating coil

[0058] The coil is wound according to the determined coil winding width and length, that is, the overall length and width of the coil are controlled. After completion, the heating coil is armored and fixed with a high temperature resistant plastic plate.

[0059] (6) Connect the thermocouple and heating coil

[0060] Connect the thermocouple and heating coil to the medium frequency induction heating machine.

[0061] (7) Setting post-weld heat treatment process parameters

[0062] Set post-weld heat treatment process parameters according to welding heat treatment process requirements.

[0063] (8) Start the machine for post-weld heat treatment.

[0064] Inspection after post-weld heat treatment shows that no obvious deformation is found in the heated area, and the temperature in the uniform temperature area is uniform. The method obtains the required temperature field and meets the quality requirements of post-weld heat treatment of the welded joint 4 of the membrane wall 1.

[0065] In the present invention, the given post-weld heat treatment process and the required heating range are known and determined for the specific membrane wall structure. The power required to heat the membrane wall pipe joint according to the given post-weld heat treatment process and the required heating range belongs to the common knowledge in the art and will not be described in detail here.

[0066] Due to the structural characteristics of the membrane wall, its post-weld heat treatment temperature field is similar to a two-dimensional temperature field. When the post-weld heat treatment heating area is small, not only is the heat treatment efficiency low, but due to the heat transfer characteristics of the two-dimensional temperature field, the uniform temperature area of ​​the heat treatment area is small, and the effect of eliminating welding residual stress is not good; when the post-weld heat treatment heating area is large, the expansion of the heating area is large. Due to the constraint of the non-heated area around the two-dimensional temperature field, not only is the deformation of the membrane wall after post-weld heat treatment large, but the effect of eliminating welding residual stress is poor, which seriously affects the quality and service life of the membrane wall.

[0067] The present invention aims at the temperature field characteristics of the post-weld heat treatment of medium-frequency induction heating of membrane wall, proposes the winding method and winding size of the induction coil, and designs it into an armored form to meet the requirements of the membrane wall structure. The device and method effectively avoid the adverse consequences caused by too small or too large average temperature range, successfully overcome the adverse effects of traditional post-weld heat treatment processes on joint performance, and meet the technical requirements for post-weld heat treatment of joints. The medium-frequency induction heating local post-weld heat treatment device and method of the membrane wall welding joint of the present application determine the appropriate heating range, and obtain a reasonable average temperature range through the arrangement of the induction heating coil, thereby effectively reducing welding residual stress and controlling the deformation of the heated area.

[0068] 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 method for post-weld heat treatment, characterized in that: The method comprises the following steps: Determine the uniform temperature width W of the membrane wall welding joint after welding heat treatment E and heating length L E ; Install the heat treatment device, set the heat treatment process curve, and perform post-weld heat treatment; A membrane wall welding joint medium frequency induction heating post-weld heat treatment device is used for post-weld heat treatment, the membrane wall includes a tube and a fin, there is a fin weld between adjacent fins, the tube has a welding joint, the heat treatment device includes a temperature-controlled thermocouple, a medium frequency induction heat treatment machine and two induction coils respectively arranged on both sides of the membrane wall, the induction coils are connected to the medium frequency induction heat treatment machine; the uniform temperature width W of the heating area of ​​the membrane wall E The length of the heating at one time is L, which is 6 times the wall thickness of the membrane wall pipe on each side of the welding joint to 2 times the outer diameter of the membrane wall pipe; when the membrane wall fins in the heating area are not welded, the length of the heating at one time is L E Not more than 2000mm; when the membrane wall fins in the heating area are welded, the heating length L E Not more than 10 welded joints of membrane wall pipes; The winding length L of the induction coil R =L E +2~4 turns; the winding width W of the induction coil R =W E +2 to 4 turns; the adjacent turns of the induction coil are fitted together; the length direction of the winding of the induction coil is perpendicular to the longitudinal direction of the membrane wall tube; after being wound, the induction coil is located on the same plane and fixed on the heating area of ​​the membrane wall.

2. The method according to claim 1, characterized in that After being wound, the induction coils are located on the same plane and are armored and fixed to the heating area of ​​the membrane wall.

3. The method according to claim 2, characterized in that The armor is to fix the induction coil on a plastic plate which is heat-proof, does not generate eddy current under the action of a magnetic field and is resistant to high temperatures.

4. The method according to claim 3, characterized in that The temperature-controlling thermocouple is arranged at the center of the heating area and on the welding joint of the membrane wall pipe.

5. The method according to claim 1, characterized in that A heat-insulating layer is arranged outside the membrane wall, the temperature-controlling thermocouple is located between the heat-insulating layer and the membrane wall, and the coil is located outside the heat-insulating layer.

6. The method according to claim 5, characterized in that The coverage of the thermal insulation layer extends at least 300 mm outward on each side of the upper and lower sides of the welding joint.

7. The method according to claim 1, characterized in that The winding directions of the two induction coils are consistent; the sizes of the two induction coils after winding are consistent.

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