JP7263806B2 - Welding method for cast steel members - Google Patents

Description

The present invention relates to a method for welding cast steel members.

For example, in facilities of a thermal power plant, facilities made of cast steel such as steam turbine casings and valves for generating power are installed. However, since these facilities made of cast steel are operated in a high-temperature environment, repeated start-up and stoppage will cause cracks under the influence of thermal stress.

Therefore, when cracks occur in cast steel equipment, for example, the following countermeasures are appropriately implemented.

First, as a first coping method, there is a method of removing cracks by grinding or the like, and replacing the equipment with new equipment when the wall thickness after removing the cracks reaches a predetermined minimum wall thickness. .

In addition, as a second coping method, the crack is removed by grinding or the like to form a groove, a welding material is supplied to the groove to form an overlay, and heat treatment is performed after welding to restore the thickness of the equipment. method.

JP 2016-112574 A

However, in the case of the first coping method, there is a risk that it will take a long time to replace large cast steel equipment such as steam turbine casings and valves with new equipment.

In the case of the second coping method, there are a method of transporting cast steel equipment to a factory and performing post-weld heat treatment, and a method of performing post-weld heat treatment in the facility (site) of the power plant. In the former case, the cast steel equipment must be brought back to the factory, but since the post-weld heat treatment is performed on the entire cast steel equipment in the factory furnace, welding residual stress can be effectively reduced. On the other hand, in the latter case, post-weld heat treatment can be performed on site, but since the post-weld heat treatment is a process of partially heating the welded location in cast steel equipment with a heater or the like, the weld residual stress is reduced as in the former case. you can't. In particular, when the crack is deep and the amount of welding material used is large, post-weld heat treatment becomes even more insufficient, resulting in welding deformation due to welding residual stress. Even if the temper beat method is used as an alternative to the post-weld heat treatment, the same problem occurs.

Therefore, an object of the present invention is to provide a welding method that checks the amount of welding deformation caused by welding residual stress in a facility where cast steel equipment is installed and does not exceed the allowable amount of deformation of cast steel members. do.

The main aspect of the present invention that solves the above-described problems is a method for welding cast steel members, wherein a first position on the cast steel member, which is a position near a groove formed by removing a crack that has occurred in the cast steel member, is specified. and a second position on the cast steel member that is a predetermined distance away from the first position as a position that is not affected by deformation due to welding with respect to welding of the groove. 2 step, and a third step of specifying a third position between the first position and the second position on the cast steel member, which is a position where deformation due to welding is confirmed with respect to welding of the groove. , the height of the overlay to be formed in the groove based on a master curve showing the relationship between the height of the overlay formed by supplying the welding material to the groove and the contraction rate of the groove a fourth step of predicting the deformation amount of the first position corresponding to the distance between the first position and the second position and the distance between the second position and the third position a fifth step of predicting the deformation amount at the third position from the predicted deformation amount at the first position based on the ratio; and when the predicted deformation amount at the third position does not exceed the allowable deformation amount. and a sixth step of forming the overlay on the groove.

Other features of the present invention will become apparent from the accompanying drawings and the description herein.

According to the present invention, it is possible to check the amount of welding deformation caused by welding residual stress in a facility where cast steel equipment is installed, and perform welding that does not exceed the allowable amount of deformation of cast steel members.

FIG. 2 is a cross-sectional view schematically showing a valve device of a steam turbine casing; FIG. 4 is a top view showing a groove formed in the cast steel member; FIG. 4 is a side cross-sectional view showing a groove formed in the cast steel member; FIG. 11 is another side cross-sectional view showing a groove formed in the cast steel member; FIG. 4 is a characteristic diagram obtained by measuring the height of a build-up formed on a groove and the contraction rate of the groove. 5 is a master curve showing the relationship between the height of the overlay formed on the groove and the contraction rate of the groove obtained with reference to FIG. 4 ; It is a flow chart which shows the welding method of the cast steel member concerning this embodiment. It is a block diagram which shows the welding propriety judgment apparatus used for the welding method which concerns on this embodiment.

At least the following matters will become apparent from the description of the present specification and the accompanying drawings.

A steam turbine casing installed in a facility of a thermal power plant is manufactured using cast steel members. In the present embodiment, for example, a valve device for adjusting the flow rate of steam in a steam turbine compartment will be described below as an object to be welded.

===Steam Turbine Casing Valve Device===
FIG. 1 is a cross-sectional view schematically showing a valve device of a steam turbine casing.

The valve device 100 is a device for adjusting the flow rate of steam supplied to a steam turbine casing, and includes a valve body 110 , a valve seat 120 , a valve body 130 and a valve body cover 170 . The valve box 110 is formed using a cast steel member.

The valve box 110 internally forms a steam flow path 112 communicating between a steam inlet 111 connected to a steam generating means such as a boiler and a steam outlet (not shown) connected to a steam turbine casing. It is a box. A valve seat 120 and a valve body 130 are accommodated in the valve box 110 .

The valve seat 120 has an annular shape and is installed so that the steam flow path 112 is formed.

The valve body 130 is a steam stop valve that shuts off steam flowing through the steam flow path 112 by being seated on or separated from the seat surface 121 of the valve seat 120 . The valve body 130 is installed so as to be able to advance and retreat in the up and down arrow directions in FIG. 1 with respect to the valve seat 120 .

Since the steam turbine casing is operated in a high-temperature environment, repeated starting and stopping may cause cracks due to thermal stress. In this embodiment, for convenience of explanation, it is assumed that a crack occurs inside the valve box 110 .

=== master curve ===
FIG. 2 is a top view showing a groove formed in a cast steel member. 3A and 3B are side cross-sectional views showing grooves formed in cast steel members. FIG. 4 is a characteristic diagram obtained by measuring the build-up height of the groove and the contraction rate of the groove. FIG. 5 is a master curve showing the relationship between the build-up height of the groove and the contraction rate of the groove obtained with reference to FIG. Note that FIG. 3A shows a cross section obtained by cutting the groove in half along a plane defined by the X-axis and the Z-axis, viewed in the + direction of the Y-axis. FIG. 3B shows a cross section obtained by cutting the groove in half along a plane defined by the Y-axis and the Z-axis, viewed in the + direction of the X-axis. 4 and 5, the horizontal axis indicates the ratio (%) of the height of the overlay to the height from the bottom of the groove to the surface of the cast steel member, and the vertical axis indicates the groove in the height of the overlay. The amount of shrinkage (μm) per 1 mm is shown as the shrinkage rate of .

The process of creating a master curve will be described below.

First, a cast steel member 200 made of the same material as that of the valve body 110 is prepared.

Next, a groove 210 is formed in the cast steel member 200 . The groove 210 has the shape of a truncated square pyramid whose diameter decreases in the thickness direction (−Z direction) of the cast steel member 200 . The groove 210 has an opening 220 that is flush with the surface of the cast steel member 200, and the length L1 of the opening 220 in the direction along the X axis and the length L2 in the direction along the Y axis are , are set to several tens of mm.

Next, molten welding material is supplied to the groove 210 so that the ratio of the height of the overlay 230 to the height from the bottom surface 240 of the groove 210 to the surface of the cast steel member 200 approaches 100% at a constant rate. Then, the build-up 230 is formed step by step. For example, a molten welding material is supplied to the groove 210 so that the ratio of the height of the overlay to the height from the bottom surface 240 of the groove 210 to the surface of the cast steel member 200 approaches 100% by 1%. A build-up 230 is formed step by step. The welding material is, for example, a nickel alloy that does not require heat treatment, and the welding method is, for example, TIG welding, MIG welding, arc welding, or the like.

Next, after the build-up 230 is formed on the groove 210, the lengths of the groove 210 in the X-axis and Y-axis directions at the height of the build-up 230 are measured. On the other hand, before forming the overlay 230 on the groove 210, the lengths of the groove 210 in the X-axis and Y-axis directions at the height of the overlay 230 to be formed are measured in advance. Then, the lengths of both before and after forming the build-up 230 are compared, and the amount of shrinkage per mm in the direction along the X-axis and Y-axis of the groove 210 at the height of the build-up 230 is calculated. A digital caliper, for example, is used to measure the length of the groove 210 in the directions along the X-axis and the Y-axis.

Next, the ratio (%) of the height of the overlay 230 formed on the groove 210 is plotted on the horizontal axis, and the contraction rate (μm /mm) on the vertical axis to create a graph (characteristic diagram) of FIG. The solid line indicates the shrinkage rate of the groove 210 in the X-axis direction, and the dashed line indicates the shrinkage rate of the groove 210 in the Y-axis direction.

Next, referring to FIG. 4, when the height ratio of the overlay 230 formed on the groove 210 is 25%, the amount of shrinkage of the groove 210 in the direction along the Y-axis direction changes the most at 2 μm. I know you are. Therefore, only the slope showing the change in the amount of contraction of the groove 210 in the direction along the Y axis when the height ratio of the overlay 230 formed on the groove 210 changes from 0% to 25% is used in the diagram. Create 5 master curves. Variations of the master curve of FIG. 5 may be prepared for grooves of various shapes and sizes in order to deal with cracks of various shapes and sizes.

The process of creating the master curve of FIG. 5 may be executed by computer software processing, and data of a plurality of master curves corresponding to grooves of various shapes and sizes may be stored in a storage device.

=== Welding method ===
FIG. 6 is a flowchart showing a welding method for cast steel members according to the present embodiment. As described above, the case where a crack occurs inside the valve box 110 will be described as an example with reference to FIG.

First, it is determined whether or not a crack has occurred inside the valve box 110 (step S1). When judging the presence or absence of cracks, for example, a penetrant inspection, which is one of non-destructive inspections, may be carried out at the time of overhaul inspection.

Next, if a crack has occurred inside the valve body 110 (step S1: YES), for example, by a crack growth prediction program, the degree of crack progress in the thickness direction of the valve body 110 is analyzed. When it is feared that the minimum required wall thickness of 110 is reached, the shape of the groove 140 is determined according to the depth of the crack (step S2). In this embodiment, the groove 140 has the shape of a truncated square pyramid whose diameter decreases from the inside to the outside of the valve body 110 . If no crack has occurred inside the valve body 110 (step S1: NO), the determination in step S1 is repeated.

Next, the groove 140 having the shape of a truncated square pyramid is formed while removing the crack by grinding (step S3). For example, a grinder (not shown) is used to form the groove 140 .

Next, a first position A is specified as a position near the groove 140 . The first position A is a position adjacent to one side forming the opening 150 of the groove 140 on the inner surface of the valve body 110, on the side of the groove 140 facing the valve body 130 (step S4 ).

Next, regarding welding of the groove 140, a second position B is specified as a position that is not affected by deformation due to welding. The second position B is a position on the inner surface of the valve body 110 opposite to the side of the valve body 130 facing the first position A. As shown in FIG. For example, the second position B is a position symmetrical to the first position A with respect to the valve element 130 (step S5).

Next, regarding welding of the groove 140, a third position C is specified as a position for confirming deformation due to welding. The third position C is a position on the seat surface 121 of the valve seat 120 that the valve body 130 comes into contact with when seated, on the side facing the groove 140 of the valve body 130 (step S6).

Next, regarding welding of the groove 140, a fourth position D is specified as a position for measuring deformation due to welding. The fourth position D is a position between the first position A and the third position D on the inner surface of the valve box 110 (step S7).

Next, the linear distance _DBD between the second position B and the fourth position D is measured. A digital vernier caliper, for example, is used to measure the linear distance _DBD (step S8).

Next, referring to the master curve of FIG. 5, the amount of deformation at the first position A at the height of the overlay 160 to be formed on the groove 140 is predicted. For example, if the height from the bottom surface of the groove 140 to the inner surface of the valve body 110 is 50 mm and the height of the overlay 160 to be formed on the groove 140 is 23 mm, the height of the overlay 160 to be formed on the groove 140 The ratio of the height of the overlay 160 is 46%. When the height ratio of the overlay 160 is 46%, the amount of shrinkage per 1 mm of the groove 140 is 3.7 μm. The amount of deformation at the first position A is predicted to be 89 μm (step S9).

Next, the ratio of the linear distance D-BC between the second position B and the third position C to the linear distance D- _AB between the first position A and the second position _B is used to predict the amount of deformation of the first position A. The amount of deformation at the third position C is predicted by multiplying the value. For example, when the linear distance D _AB between the first position A and the second position B is 620 mm, and the linear distance D _BC between the second position B and the third position C is 465 mm, the third position C The amount of deformation is estimated to be 67 μm (step S10).

Next, it is determined whether or not the predicted value of the amount of deformation at the third position C is less than a predetermined allowable amount of deformation. The allowable deformation amount is a limit value at which the flow rate of steam can be normally adjusted when the valve element 130 is seated on or separated from the valve seat 120, and is, for example, 100 μm ( step S11).

Next, since the predicted value of the deformation amount at the third position C is less than the allowable deformation amount (step S11: YES), the welding material in a molten state is supplied to the groove 140 height of 23 mm to form the overlay 160. form (step S12). If the predicted deformation amount at the third position C is greater than or equal to the allowable deformation amount (step S11: NO), a series of processing ends without forming the build-up 160 on the groove 140. FIG.

Next, the linear distance _DBD between the second position B and the fourth position D after forming the build-up 160 on the groove 140 is measured. A digital caliper in step S8 is used to measure the straight-line distance _DBD . Then, the difference between the linear distance _DBD measured in this step and the linear distance _DBD measured in step S8 is calculated as the deformation amount of the fourth position D (step S13).

Next, the deformation amount of the fourth position D is multiplied by the ratio of the linear distance _DBC between the second position B and the third position C to the linear distance _DBD between the second position B and the fourth position D. Thus, the deformation amount of the third position C is calculated. For example, if the deformation amount at the fourth position D is 90 μm and the linear distance D _BD between the second position B and the fourth position D is 550 mm, the deformation amount at the third position C is calculated as 76 μm (step S14).

Next, it is determined whether or not the amount of deformation at the third position C is less than the allowable amount of deformation (100 μm) (step S15).

Next, since the amount of deformation at the third position C is less than the allowable amount of deformation (step S15: YES), it is possible to form a higher overlay 160 on the groove 140 . Therefore, only when it is beneficial to form a higher build-up 160 on the groove 140, the processes after step S9 are executed. If the amount of deformation at the third position C is greater than or equal to the allowable amount of deformation (step S15: NO), a series of processes is terminated while the build-up 160 having a height of 23 mm is formed on the groove 140. FIG.

=== Weldability judgment device ===
At least part of the processing shown in FIG. 6 is realized by a device such as a computer.

FIG. 7 is a block diagram showing a weldability determination device used in the welding method according to this embodiment.

The weldability determination device 300 is a device that predicts the height of the overlay 160 that can be formed on the groove 140 when welding the groove 140, and includes a computer 310 and a storage device 320. there is

The storage device 320 stores a program for predicting the height of the overlay 160 that can be formed on the groove 140, and data representing the master curve of FIG.

Computer 310 receives information indicating first position A, second position B, third position C, fourth position D, linear distances D _AB , D _BC , and D _BD , and computer 310 receives information from storage device 320 . The welding method according to this embodiment is executed by referring to the table data while executing the read program.

===Summary===
As described above, the method for welding cast steel members according to the present embodiment includes the first step of specifying the first position A, which is the position near the groove 140 formed by removing the crack generated in the cast steel member; , with respect to the welding of the groove 140, a second step of identifying the second position B, which is a position not affected by deformation due to welding, and with respect to the welding of the groove 140, at a position where deformation due to welding is confirmed. a third step of specifying a third position C between the first position A and the second position B; A fourth step of predicting the deformation amount at the first position A corresponding to the height of the overlay 160 to be formed on the groove 140 based on the master curve showing the relationship with the amount of shrinkage per mm; Based on the ratio of the distance between the position A and the second position B and the distance between the second position B and the third position C, the deformation amount of the third position C from the deformation amount of the first position A and a sixth step of forming an overlay 160 on the groove 140 when the predicted value of the deformation amount at the third position C does not exceed the allowable deformation amount. As a result, it is possible to form the build-up 160 on the groove 140 within a range in which the predicted deformation amount at the third position C does not exceed the allowable deformation amount. In other words, welding deformation caused by welding residual stress can be confirmed, and welding can be performed without exceeding the allowable deformation amount of the cast steel member.

Further, in the welding method for cast steel members according to the present embodiment, when the predicted value of the amount of deformation at the third position C exceeds the allowable amount of deformation, the formation of the overlay 160 on the groove 140 is stopped. Including process. As a result, it is possible to prevent the build-up 160 from being excessively formed on the groove 140 .

Further, in the welding method for cast steel members according to the present embodiment, in the welding of the groove 140, in the eighth step of specifying the fourth position D between the first position A and the third position C, and in the sixth step When the build-up 160 is formed on the groove 140, the ninth step of measuring the deformation amount at the fourth position D, the distance between the second position B and the fourth position D, the second position B and the third a tenth step of calculating the deformation amount of the third position C from the deformation amount of the fourth position D based on the ratio of the distance to the position C, and the deformation amount of the third position C is allowed in the tenth step and an eleventh step of returning to the fourth step in order to further form the build-up 160 on the groove 140 if the deformation amount is not exceeded. As a result, it is possible to form the highest build-up 160 on the groove 140 within a range in which the predicted deformation amount at the third position C does not exceed the allowable deformation amount.

Further, in the welding method for cast steel members according to the present embodiment, when the amount of deformation at the third position C exceeds the allowable amount of deformation in the tenth step, further formation of the overlay 160 on the groove 140 is stopped. A twelfth step is included. As a result, it is possible to prevent the build-up 160 from being excessively formed on the groove 140 .

Further, in the ninth step, the amount of deformation at the fourth position D is the distance between the second position B and the fourth position D measured before forming the overlay 160 on the groove 140 and the groove 140 and the distance between the second position B and the fourth position D measured after forming the build-up 160 on the .

Also, in the ninth step, the amount of deformation at the fourth position D is measured by a digital caliper.

Also, the welding material is a nickel alloy that does not require heat treatment when welding the groove 140 . This makes it possible to effectively reduce welding residual stress.

Also, the shrinkage rate of the groove in the master curve is obtained as the amount of shrinkage per 1 mm of the groove with respect to the height of the build-up.

Further, the groove shrinkage ratio in the master curve is obtained from the largest slope among the slopes indicating the measured value of the shrinkage amount of the groove per 1 mm with respect to the build-up height.

Also, the cast steel member is a valve device 100 forming a steam turbine casing installed in a thermal power plant.

It should be noted that the above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit and interpret the present invention. The present invention may be modified and improved without departing from its spirit, and the present invention also includes equivalents thereof.

100 valve device 110 valve body 120 valve seat 121 seat surface 130 valve element 140, 210 groove 150, 220 opening 160, 230 overlay 170 valve body cover 200 cast steel member 300 weldability determination device 310 computer 320 storage device

Claims (10)

a first step of identifying a first position on the cast steel member, which is a position near the groove formed by removing the crack generated in the cast steel member;
A second step of identifying a second position on the cast steel member that is a predetermined distance away from the first position as a position that is not affected by deformation due to welding with respect to welding of the groove;
a third step of identifying a third position between the first position and the second position on the cast steel member, which is a position for confirming deformation due to welding, with respect to welding of the groove;
Based on a master curve showing the relationship between the height of the overlay formed by supplying the welding material to the groove and the contraction rate of the groove, the height of the overlay to be formed in the groove a fourth step of predicting the deformation amount of the corresponding first position;
Based on the ratio of the distance between the first position and the second position and the distance between the second position and the third position, the predicted value of the deformation amount at the first position is converted to the first position. a fifth step of predicting deformation amounts at three positions;
a sixth step of forming the overlay on the groove when the predicted value of the deformation amount at the third position does not exceed the allowable deformation amount;
A method for welding cast steel members, comprising: 2. The method according to claim 1, further comprising a seventh step of stopping forming the overlay on the groove when the predicted value of the deformation amount at the third position exceeds the allowable deformation amount. Welding method for cast steel members. an eighth step of identifying a fourth position between the first position and the third position for welding the groove;
a ninth step of measuring the amount of deformation at the fourth position when the build-up is formed on the groove in the sixth step;
Based on the ratio of the distance between the second position and the fourth position and the distance between the second position and the third position, the deformation amount of the fourth position is changed to the deformation amount of the third position. A tenth step of calculating the deformation amount;
an eleventh step of returning to the fourth step in order to further form the build-up on the groove when the amount of deformation at the third position does not exceed the allowable amount of deformation in the tenth step;
The method for welding a cast steel member according to claim 2, comprising : 4. A twelfth step of stopping further forming the build-up on the groove when the amount of deformation at the third position exceeds the allowable amount of deformation in the tenth step. The method for welding the cast steel member according to . In the ninth step,
The amount of deformation at the fourth position is the distance between the second position and the fourth position measured before forming the overlay on the groove, and the amount of deformation when the overlay is formed on the groove. and a distance between the second position and the fourth position measured later. In the ninth step,
The method for welding cast steel members according to claim 5, wherein the amount of deformation at the fourth position is measured by a digital caliper. The welding method for cast steel members according to claim 1, wherein the welding material is a nickel alloy that does not require heat treatment when welding the groove. The welding method for cast steel members according to claim 1, wherein the contraction rate of the groove in the master curve is obtained as a shrinkage amount per unit length of the groove with respect to the height of the overlay. The shrinkage rate of the groove in the master curve is obtained from the largest slope among the slopes indicating the measured value of the shrinkage amount per unit length of the groove with respect to the height of the overlay. The method for welding a cast steel member according to claim 8. The method of welding cast steel members according to claim 1, wherein the cast steel member is a member forming a steam turbine casing installed in a thermal power plant.

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