Circumferential seam heat treatment method for large-diameter thick-wall martensitic heat-resistant steel pressure vessel

Abstract

The invention relates to a heat treatment method for a circular seam of a large-diameter thick-wall martensitic heat-resistant steel pressure vessel, which is characterized in that an electromagnetic induction heater is arranged outside the vessel, a ceramic heating sheet is arranged inside the vessel along the circular seam, and the circular seam is subjected to heat treatment by adopting an internal and external simultaneous heating mode; an induction cable of the electromagnetic induction heater is wound outside the container at the circular seam part, and the heating range is the axial 550mm width range of the container; a plurality of thermocouples are circumferentially and uniformly distributed on the inner wall and the outer wall of the circular seam respectively, and the thermocouples on the outer side of the circular seam directly face the thermocouples on the inner side one by one; in the heat treatment process, the temperature difference between the inner and outer sides of the circular seam is controlled to be less than 50 DEG C through An electromagnetic induction heating range with a large width is arranged outside a container, a ceramic heating piece is arranged inside the container, meanwhile, a circular seam is heated, the heat dissipation efficiency of the deep portion of the circular seam is reduced, the temperature areas of the inner wall, the outer wall and the thickness center of the circular seam are consistent and all reach the target heat treatment temperature, and the whole circular seam metallographic structure is basically the same.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology, specifically relating to a method for heat treatment of circumferential seams in pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel. Background Technology

[0002] The latest type of high-pressure serpentine tube heater equipment for power plants in China is typically equipped with one high-pressure heater and two steam coolers per unit. The steam cooler is designed to operate at a temperature of 575℃. The shell material is SA-336 F91 (martensitic heat-resistant alloy steel), with an inner diameter of 2500mm, a cylinder wall thickness of 110mm, and a head wall thickness of 11mm. Due to assembly requirements, the head and cylinder are required to be joined together and circumferentially welded. After welding, the circumferential seam is heat-treated, and the weld hardness is required to reach 180~270HB. The metallographic structure of the inner and outer wall welds is tempered martensite or sorbite.

[0003] Due to the large wall thickness of the container, and the requirement for local heat treatment of 760±10℃×8h for the weld of martensitic heat-resistant alloy steel, the conventional method of heating with single or double-sided ceramic heating plates causes excessive heat dissipation during heat treatment of the circumferential weld due to the large wall thickness. This results in a large temperature difference along the thickness direction of the circumferential weld, making it difficult for the temperature at the center of the wall to meet the heat treatment requirements. Consequently, the weld hardness is unqualified, which ultimately leads to cracks in the circumferential weld.

[0004] Therefore, it is necessary to provide a heat treatment method for circumferential seams of pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel to solve the technical problem of excessive temperature difference between the weld thickness center and the outer wall, and difficulty in meeting the heat treatment requirements at the thickness center. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a heat treatment method for circumferential seams of pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel, which solves the technical problem of excessive temperature difference between the center of the weld thickness and the outer wall, and difficulty in meeting the heat treatment requirements at the center of the thickness.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a heat treatment method for the circumferential seam of a pressure vessel made of large-diameter thick-walled martensitic heat-resistant steel, wherein an electromagnetic induction heater is set outside the vessel and a ceramic heating plate is set inside the vessel along the circumferential seam, and the circumferential seam is heat treated by heating both inside and outside simultaneously. The induction cable of the electromagnetic induction heater is spirally wound at equal intervals on the outer wall of the container at the annular seam. The heating range is a 550mm width range along the axial direction of the container, and the annular seam is located at the center of the heating range. Multiple thermocouples are evenly distributed circumferentially on the inner and outer walls of the annular seam, with the thermocouples on the outer side of the annular seam facing each other on the inner side. During the heat treatment process, the power of the electromagnetic induction heater and the ceramic heating element are controlled according to the temperature information fed back by the thermocouple, so that the temperature difference between the inside and outside of the circumferential seam is less than 50℃.

[0007] As a preferred embodiment, the outer wall of the container is wrapped with two layers of 60mm thick and 1200mm wide aluminum silicate insulation blankets along the circumferential seam. At least two layers of high silica cloth are wrapped around the outside of the aluminum silicate insulation blankets. The induction cable is spirally wound around the outside of the high silica cloth. A layer of 60mm thick insulation cotton is wrapped around the outer wall of the container within a 1200mm range on both sides of the aluminum silicate insulation blankets. A layer of insulation cotton with a width of 1200mm is laid on the inner wall of the container on both sides of the ceramic heating element.

[0008] As a preferred embodiment, the circumferential seam is the connection seam between the container's end cap and the cylinder body. A support cylinder with the same outer diameter as the cylinder body is connected to the end cap. The circumferential seam is located outside the support cylinder. The aluminum silicate insulation blanket, high silica cloth, and insulation cotton are wrapped around the outer wall of the container and the outer wall of the support cylinder. Part of the induction cable is wrapped around the outer wall of the support cylinder. The outer wall of the end cap is insulated with insulation cotton.

[0009] As a preferred method, heating the container is divided into five stages, including: The first stage heating rate is 35℃ / h, heating to 200℃; The second stage heating rate is 30℃ / h, heating to 00℃; The third stage heating rate is 25℃ / h, heating to 550℃; The fourth stage heating rate is 20℃ / h, heating to 690℃; The fifth stage heating rate is 15℃ / h, heating to 750~770℃; Then it enters the cooling stage, with a cooling rate of ≤55℃ / h, cooling down to 200℃; After the fourth stage is completed, the temperature is maintained for 3 hours before the fifth stage of heating begins. After the fifth stage is completed, the temperature is maintained for 8 hours before the cooling stage begins.

[0010] As a preferred option, the temperature difference between the inside and outside of the circumferential seam is less than 10°C at the end of the fifth stage.

[0011] As a preferred embodiment, the ceramic heating element is supported by a support fixture and attached to the inner wall of the container, completely covering the circumferential seam. The support fixture includes multiple arc-shaped support plates connected end to end to form a complete circle. At least one ceramic heating element is connected to the outer arc surface of each support plate, and all ceramic heating elements are evenly distributed around the circumference.

[0012] As a preferred embodiment, a connecting plate and two stiffening plates are respectively connected to the inner arc surfaces at both ends of any of the support plates. The two stiffening plates are respectively vertically connected to both sides of the connecting plate. The connecting plates on the adjacent ends of the two support plates are arranged opposite each other and connected to each other by bolts.

[0013] As a preferred embodiment, a pre-compressed spring is provided between the two interconnected connecting plates. The spring is sleeved on the bolt, and both ends of the spring abut against the two connecting plates respectively. The stiffener is connected to the opposite sides of the two interconnected connecting plates, and the opposite sides of the two connecting plates are used for adjusting nuts.

[0014] As a preferred embodiment, each support plate is provided with multiple elongated holes arranged along its length direction. The long diameter direction of the elongated holes is consistent with the length direction of the support plate. Each ceramic heating element on the support plate corresponds to two adjacent elongated holes. Two screws are connected to the ceramic heating element and inserted into the corresponding elongated holes. One end of the screw passes through the elongated hole and is locked by a lock nut. When the lock nut is loosened, the screw can slide along the long diameter direction of the elongated hole to finely adjust the position of the ceramic heating element.

[0015] The beneficial effects of this invention are as follows: By setting a wide electromagnetic induction heating range outside the container and setting ceramic heating plates inside, the invention simultaneously heats the circumferential seam, reducing the heat dissipation efficiency deep within the circumferential seam, and making the temperature of the inner and outer walls and the thickness center of the circumferential seam consistent, all reaching the target heat treatment temperature, and making the metallographic structure of the entire circumferential seam basically the same, this invention solves the technical problem of local heat treatment of the circumferential seam of large-diameter thick-walled martensitic heat-resistant steel pressure vessels.

[0016] The present invention also insulates the heating area and the container outside the heating area by setting up aluminum silicate insulation blankets, high silica cloth and insulation cotton to reduce the heat dissipation efficiency of the container, further reduce the heat dissipation efficiency at the center of the circumferential seam thickness, further reduce the temperature difference between different thicknesses of the circumferential seam, and ensure that the heat treatment effect of the circumferential seam meets the design requirements. Attached Figure Description

[0017] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the external structure of the container during the implementation of the heat treatment method described in this invention; Figure 2 yes Figure 1 AA section view in the middle; Figure 3 yes Figure 2 BB section view in the middle; Figure 4 yes Figure 3 The C-direction view in the middle; Figure 5 This is a schematic diagram of the connection structure between the support fixture and the ceramic sheet described in this invention; Figure 6 yes Figure 5 Enlarged view of part D in the image; Figures 1-6 In the middle: 1. Container; 101. Head; 102. Cylinder; 2. Circumferential seam; 3. Ceramic heating element; 4. Electromagnetic induction heater; 5. Induction cable; 6. Aluminum silicate insulation blanket; 7. High silicate cloth; 8. Insulation cotton; 9. Support fixture; 901. Support plate; 902. Connecting plate; 903. Rib plate; 904. Bolt; 905. Spring; 906. Long hole; 10. Support cylinder; 11. Screw; 12. Locking nut. Detailed Implementation

[0018] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] like Figures 1-4 As shown, a heat treatment method for the circumferential seam of a pressure vessel made of large-diameter thick-walled martensitic heat-resistant steel is used. An electromagnetic induction heater is set outside the vessel 1, and a ceramic heating element 3 is set inside the vessel 1 along the circumferential seam 2. The circumferential seam 2 is heat treated by heating both inside and outside at the same time. The induction cable 4 of the electromagnetic induction heater is spirally wound at equal intervals on the outer wall of the container 1 at the annular seam 2. The heating range is a 550mm axial width range of the container 1, and the annular seam 2 is located at the center of the heating range. Multiple dedicated K-type thermocouples 5 are evenly distributed circumferentially on the inner and outer walls of the annular seam 2, with the thermocouples 5 on the outer side of the annular seam 2 facing each other.

[0020] During the heat treatment process, based on the temperature information fed back by thermocouple 5, the power of electromagnetic induction heater and ceramic heating element 3 are controlled respectively to control the temperature difference between the inner and outer sides of the annular gap 2 to be less than 50℃.

[0021] The electromagnetic induction heater described in this embodiment is a medium-frequency heater. This device is an outsourced product and belongs to existing technology, so its specific structure will not be described in this embodiment.

[0022] Two layers of 60mm thick and 1200mm wide aluminum silicate insulation blankets 6 are wound around the outer wall of the container 1 along the circumferential seam 2. At least two layers of high silica cloth 7 are wrapped around the outside of the aluminum silicate insulation blankets 6. The induction cable 4 is spirally wound around the outside of the high silica cloth 7. A layer of 60mm thick glass fiber insulation cotton 8 is wound around the outer wall of the container 1 within a range of 1200mm on both sides of the aluminum silicate insulation blankets 6. When the axial length of the outer wall of the container covered by the insulation cotton 8 is less than 1200mm, the insulation cotton 8 is used to fully cover it.

[0023] A layer of insulation cotton 8 with a width of 1200mm is laid on the inner wall of the container 1 on both sides of the ceramic heating element 3.

[0024] The annular seam 2 is the connection seam between the end cap 101 of the container 1 and the cylinder 102. A support cylinder 10 with the same outer diameter as the cylinder 102 is connected to the end cap 101. The annular seam 2 is located outside the support cylinder 10. The aluminum silicate insulation blanket 6, the high silica cloth 7, and the insulation cotton 8 are wrapped around the outer wall of the container 1 and the outer wall of the support cylinder 10. Part of the induction cable 4 is wrapped around the outer wall of the support cylinder 10. The outer wall of the end cap 101 is insulated with insulation cotton 8.

[0025] Because the end cap 101 is curved, the induction cable 4 cannot be wound around the end cap 101. Therefore, a support cylinder 10 is provided for winding the induction cable 4. The support cylinder 10 serves as a tooling fixture and is removed after the heat treatment of the circumferential seam 2 is completed.

[0026] In this embodiment, the heating of container 1 is divided into five stages, wherein: The first stage heating rate is 35℃ / h, heating to 200℃; The second stage heating rate is 30℃ / h, heating to 00℃; The third stage heating rate is 25℃ / h, heating to 550℃; The fourth stage heating rate is 20℃ / h, heating to 690℃; The fifth stage heating rate is 15℃ / h, heating to 750~770℃; Then it enters the cooling stage, with a cooling rate of ≤55℃ / h, cooling down to 200℃; After the fourth stage is completed, the temperature is maintained for 3 hours before the fifth stage of heating begins. After the fifth stage is completed, the temperature is maintained for 8 hours before the cooling stage begins.

[0027] At the end of the fifth stage, the temperature difference between the inside and outside of the circumferential seam was less than 10℃.

[0028] Using segmented slow heating can make the surface temperature of the circumferential seam 2 and the deep layer rise synchronously, reduce the temperature difference range, and improve the uniformity of heat treatment temperature in all parts of the circumferential seam wall thickness direction.

[0029] Combination Figure 2 and Figure 3 As shown, the ceramic heating element 3 is supported by a support fixture 9 and attached to the inner wall of the container 1, completely covering the circumferential seam 2. The support fixture 9 includes multiple arc-shaped support plates 901, which are connected end to end to form a complete circle. At least one ceramic heating element 3 is connected to the outer arc surface of each support plate 901, and all ceramic heating elements 3 are evenly distributed circumferentially. Figure 5 As shown, a connecting plate 902 and two stiffening plates 903 are respectively connected to the inner arc surfaces at both ends of any of the support plates 901. The two stiffening plates 903 are respectively vertically connected to both sides of the connecting plate 902. The connecting plates 902 on the adjacent ends of the two support plates 901 are arranged opposite each other and connected to each other by bolts 904.

[0030] like Figure 6 As shown, a pre-compressed spring 905 is provided between the two interconnected connecting plates 902. The spring 905 is sleeved on the bolt 904, and the two ends of the spring 905 abut against the two connecting plates 902 respectively. The stiffener 903 is connected to the opposite side of the two interconnected connecting plates 902, and the opposite side of the two connecting plates 902 is used for adjusting nuts.

[0031] The outer diameter of the support fixture 9 can be adjusted by using spring 905. When assembling each support plate 901, the spring 905 is compressed to make room for the installation of the last support plate 901. After all support plates 901 are installed, the pressure on each spring 905 is released, causing the spring 905 to push each support plate 901 to expand radially outward, pressing the ceramic heating element 3 tightly against the circumferential seam 2.

[0032] Each support plate 901 is provided with a plurality of elongated holes 906 arranged along its length direction. The long diameter direction of the elongated holes 906 is consistent with the length direction of the support plate 901. Each ceramic heating element 3 on the support plate 901 corresponds to two adjacent elongated holes 906. Two screws 11 are connected to the ceramic heating element 3 and inserted into the corresponding elongated holes 906. One end of the screw 11 passing through the elongated hole 906 is locked by a locking nut 12. When the locking nut 12 is loosened, the screw 11 can slide along the long diameter direction of the elongated hole 906 to finely adjust the position of the ceramic heating element 3.

[0033] The supporting fixture described in this invention has a simple structure, occupies little space, is easy to assemble and adjust, and can be applied to special working conditions where the internal space of a container is small.

[0034] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some examples of its application, and are not intended to limit the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A method for heat treatment of circumferential seams in pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel, characterized in that, An electromagnetic induction heater is installed outside the container (1), and a ceramic heating element (3) is installed inside the container (1) along the annular seam (2). The annular seam (2) is heat-treated by heating both inside and outside simultaneously. The induction cable (4) of the electromagnetic induction heater is spirally wound at equal intervals on the outer wall of the container (1) at the annular seam (2). The heating range is a 550mm width range along the axial direction of the container (1), and the annular seam (2) is located at the center of the heating range. Multiple thermocouples (5) are evenly distributed circumferentially on the inner and outer walls of the annular seam (2), with the thermocouples (5) on the outer side of the annular seam (2) and the thermocouples (5) on the inner side facing each other. During the heat treatment process, based on the temperature information fed back by the thermocouple (5), the power of the electromagnetic induction heater and the ceramic heating plate (3) are controlled respectively, and the temperature difference between the inside and outside of the annular gap (2) is controlled to be less than 50℃.

2. The method for heat treatment of circumferential seams in pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel according to claim 1, characterized in that, The outer wall of the container (1) is wrapped with two layers of 60mm thick and 1200mm wide aluminum silicate insulation blankets (6) along the annular seam (2). At least two layers of high silica cloth (7) are wrapped around the outside of the aluminum silicate insulation blankets (6). The induction cable (4) is spirally wound around the outside of the high silica cloth (7). A layer of 60mm thick insulation cotton (8) is wrapped around the outer wall of the container (1) within 1200mm on both sides of the aluminum silicate insulation blankets (6). A layer of insulation cotton (8) with a width of 1200mm is laid on the inner wall of the container (1) on both sides of the ceramic heating element (3).

3. The method for heat treatment of circumferential seams in pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel according to claim 2, characterized in that, The annular seam (2) is the connection seam between the end cap (101) of the container (1) and the cylinder (102). The end cap (101) is connected to a support cylinder (10) with the same outer diameter as the cylinder (102). The annular seam (2) is located outside the support cylinder (10). The aluminum silicate insulation blanket (6), high silica cloth (7) and insulation cotton (8) are wrapped around the outer wall of the container (1) and the outer wall of the support cylinder (10). Part of the induction cable (4) is wrapped around the outer wall of the support cylinder (10). The outer wall of the end cap (101) is insulated with insulation cotton (8).

4. The method for heat treatment of circumferential seams in large-diameter, thick-walled martensitic heat-resistant steel pressure vessels according to claim 3, characterized in that, Heating the container (1) is divided into five stages, among which: The first stage heating rate is 35℃ / h, heating to 200℃; The second stage heating rate is 30℃ / h, heating to 00℃; The third stage heating rate is 25℃ / h, heating to 550℃; The fourth stage heating rate is 20℃ / h, heating to 690℃; The fifth stage heating rate is 15℃ / h, heating to 750~770℃; Then it enters the cooling stage, with a cooling rate of ≤55℃ / h, cooling down to 200℃; After the fourth stage is completed, the temperature is maintained for 3 hours before the fifth stage of heating begins. After the fifth stage is completed, the temperature is maintained for 8 hours before the cooling stage begins.

5. The method for heat treatment of circumferential seams in large-diameter, thick-walled martensitic heat-resistant steel pressure vessels according to claim , characterized in that, At the end of the fifth stage, the temperature difference between the inside and outside of the circumferential seam was less than 10℃.

6. The method for heat treatment of circumferential seams in pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel according to claim 1, characterized in that, The ceramic heating element (3) is supported by a support fixture (9) and attached to the inner wall of the container (1) and completely covers the circumferential seam (2). The support fixture (9) includes multiple arc-shaped support plates (901), which are connected end to end to form a complete circle. At least one ceramic heating element (3) is connected to the outer arc surface of each support plate (901), and all ceramic heating elements (3) are evenly distributed around the circumference.

7. The method for heat treatment of circumferential seams in pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel according to claim 6, characterized in that, A connecting plate (902) and two stiffening plates (903) are respectively connected to the inner arc surfaces of both ends of any of the support plates (901). The two stiffening plates (903) are respectively vertically connected to both sides of the connecting plate (902). The connecting plates (902) on the adjacent ends of the two support plates (901) are arranged opposite each other and connected to each other by bolts (904).

8. The method for heat treatment of circumferential seams in pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel according to claim 7, characterized in that, A pre-compressed spring (905) is provided between two interconnected connecting plates (902). The spring (905) is sleeved on the bolt (904). The two ends of the spring (905) abut against the two connecting plates (902) respectively. The rib plate (903) is connected to the opposite side of the two interconnected connecting plates (902). The opposite side of the two connecting plates (902) is used for adjusting nuts.

9. The method for heat treatment of circumferential seams in pressure vessels made of large-diameter, thick-walled martensitic heat-resistant steel according to claim 6, characterized in that, Any support plate (901) is provided with multiple elongated holes (906) arranged along its length direction. The long diameter direction of the elongated holes (906) is consistent with the length direction of the support plate (901). Each ceramic heating element (3) on the support plate (901) corresponds to two adjacent elongated holes (906). Two screws (11) are connected to the ceramic heating element (3) and inserted into the corresponding elongated holes (906). One end of the screw (11) passing through the elongated hole (906) is locked by a lock nut (12). When the lock nut (12) is loosened, the screw (11) can slide along the long diameter direction of the elongated hole (906) to finely adjust the position of the ceramic heating element (3).

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