Strain measurement method and strain measurement system

Abstract

To precisely diagnose the remaining life of piping by ensuring measurement precision of strain without causing re-welding to a welded part of piping.SOLUTION: A beam material is laid while straddling a welded part of piping, the beam material is supported by a mounting seat welded to a position not thermally affecting a thermal influence part of the welded part, a probe having a first member and a second member rotatably journaled to a common rotating shaft is fixed above the thermal influence part, a first measurement needle provided in one end of the first member is brought into contact with a part near a first boundary in one side of the thermal influence part, a second measurement needle provided in one end of the second member is brought into contact with a part near a second boundary in the other side of the thermal influence part, a first electrode is provided in the other end of the first member and a second electrode is provided in the other end of the second member while opposing the first electrode so as to form a capacitive element, and the amount of strain is measured based on a change in a capacitive element generated by a change in the distance between the first measurement needle and the second measurement needle by extension of the thermal influence part.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a strain measurement method and a strain measurement system.

Background Art

[0002] Conventionally, for the purpose of diagnosing the remaining life of pipes, etc., a strain gauge has been attached to the surface of a pipe to measure the amount of strain in a welded part.

[0003] For example, in Patent Document 1, as a method for measuring strain generated in a high-temperature environment, it includes a plurality of electrodes facing each other, a guard and a shield having conductivity that surround each of the plurality of electrodes with the facing surface side open, and a plurality of biaxial sheath cables that connect each of the plurality of electrodes to a measurement device. A capacitance-type strain gauge is described.

[0004] Also, for example, in Patent Document 2, a strain / crack measurement device configured for the purpose of measuring local large strain in a high-temperature environment and measuring the occurrence of cracks and the dimensions in the depth direction of cracks with the same sensor is described. The strain / crack measurement device is a clip-type capacitance-type strain gauge that detects the strain between two points of a measurement object as a change in capacitance between two electrode plates fixed inside an opposing mounting frame. A constant current source is provided to apply a constant current to the measurement object while sandwiching the capacitance-type strain gauge. The mounting frame of the capacitance-type strain gauge is electrically insulated and connected on the side contacting the measurement object and the fulcrum end side, and means for measuring the crack depth dimension from the change in potential difference between electrode wires attached to both sides contacting the measurement object is provided.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] For example, the heat-affected zone (HAZ) formed by welding of high-chromium steel used in large-diameter high-temperature steam pipes (hereinafter referred to as "piping") in thermal power plants may lose strength and be damaged due to prolonged use. Therefore, in thermal power plants, the amount of creep strain in the welded joint is continuously measured by attaching strain gauges to the surface of the piping to diagnose the remaining lifespan.

[0007] Incidentally, if re-welding occurs in a welded joint (hereinafter referred to as "re-welding"), an inspection to confirm the integrity of the welded joint becomes necessary for safety reasons, and the installation of instruments, including the inspection, will take several days. Therefore, for example, if a strain gauge disclosed in Patent Document 1 is used, as shown in Figure 4, it is necessary to prevent re-welding from occurring in the welded joint 3 by welding mounting seats 7a and 7b that support beam members 6a and 6b to positions that avoid the welded joint on the surface of the pipe wall 2a of the pipe 2 (sufficiently away from the welded joint) and attaching a capacitive strain gauge (hereinafter referred to as "strain gauge 40").

[0008] However, when the strain gauge 40 is attached to the pipe 2 in the manner shown in Figure 4, ensuring measurement accuracy becomes a problem. Specifically, in order to ensure measurement accuracy, it is preferable to directly measure the elongation of the strain in the HAZ 5a and 5b sections, which greatly affect the progression of life. However, if the strain gauge 40 is installed as shown in the figure, it becomes impossible to measure the strain of HAZ 5a and 5b individually, and it becomes difficult to properly diagnose the remaining life, especially if there is a difference in the progression of life of each HAZ 5a and 5b.

[0009] Patent Document 2 describes a clip-type capacitive strain gauge that detects the strain between two points on an object to be measured as a change in capacitance between two electrode plates fixed inside opposing mounting frames. Here, the clip-type capacitive strain gauge described in the document (hereinafter referred to as "strain gauge") can be used to measure individual HAZs 5a and 5b, for example, as shown in Figure 4, to measure the strain of each HAZ 5a and 5b individually. However, the document does not disclose a specific method for attaching the strain gauge to the pipe 2, in particular a method for fixing it to the pipe 2 while avoiding re-welding the welded joint 3.

[0010] This invention was made in view of the above background, and aims to provide a strain measurement system and strain measurement method that can ensure the accuracy of strain measurement without causing re-welding of the welded joints of pipes, and that can accurately diagnose the remaining lifespan of pipes. [Means for solving the problem]

[0011] One of the present inventions for achieving the above objective is a strain measurement method for measuring strain in a welded joint of a pipe, comprising: a beam member spanning the welded joint; the beam member supported by one or more mounting seats welded to the heat-affected zone of the pipe formed around the welded joint in a position that does not have a thermal effect; a probe having a first member and a second member rotatably supported on a common rotation axis fixed to a position above the heat-affected zone of the beam member; and provided at one end of the first member A first measuring needle is brought into direct or indirect contact with the vicinity of the first boundary on one side of the heat-affected zone, and a second measuring needle provided at one end of the second member is brought into direct or indirect contact with the vicinity of the second boundary on the other side of the heat-affected zone. A first electrode is provided at the other end of the first member, and a second electrode is provided at the other end of the second member opposite to the first electrode, thereby forming a capacitive element. The capacitance of the element is generated when the distance between the first measuring needle and the second measuring needle changes as the heat-affected zone expands. Capacitance Based on the changes, the amount of strain in the heat-affected zone is measured.

[0012] As described above, in this invention, the beam member is supported by one or more mounting seats welded to a position that does not thermally affect the heat-affected zone formed around the welded joint of the pipe, and a probe is fixed above the heat-affected zone of the beam member. The first measuring needle provided at one end of the first member is brought into direct or indirect contact with the vicinity of the first boundary on one side of the heat-affected zone, and the second measuring needle provided at one end of the second member is brought into direct or indirect contact with the vicinity of the second boundary on the other side of the heat-affected zone. The amount of strain in the heat-affected zone is measured based on the change in the capacitance element caused by the change in the distance between the first and second measuring needles as the heat-affected zone expands, so that the strain in the heat-affected zone can be measured individually without causing re-welding of the welded joint. As a result, the accuracy of strain measurement can be ensured, and the remaining lifespan of the pipe can be accurately diagnosed.

[0013] Another aspect of the present invention is the strain measurement method described above, wherein the first measuring needle is brought into contact with the vicinity of the first boundary of the heat-affected zone via a first support fixed to the surface of the pipe, and the second measuring needle is brought into contact with the vicinity of the second boundary of the heat-affected zone via a second support fixed to the surface of the pipe.

[0014] Thus, in this invention, the first measuring needle is brought into contact with the vicinity of the first boundary of the heat-affected zone via a first support fixed to the surface of the pipe, and the second measuring needle is brought into contact with the vicinity of the second boundary of the heat-affected zone via a second support fixed to the surface of the pipe. As a result, the first and second measuring needles can be reliably brought into contact with the boundary of the heat-affected zone. Therefore, the accuracy of strain measurement can be ensured.

[0015] Another aspect of the present invention is the strain measurement method described above, wherein the first support portion has a recess on its upper surface, the first measuring needle contacts the bottom of the recess, and the second support portion has a recess on its upper surface, the second measuring needle contacts the bottom of the recess.

[0016] Thus, in this invention, the first measuring needle is brought into contact with the recess of the first support portion, and the second measuring needle is brought into contact with the recess of the second support portion. Therefore, the extension of the heat-affected zone can be reliably captured by the first and second measuring needles, and the strain can be measured with high accuracy.

[0017] Another aspect of the present invention is the strain measurement method described above, wherein the first support portion has an end face perpendicular to the piping on the side away from the heat-affected zone, and the first measuring needle abuts against the end face, and the second support portion has an end face perpendicular to the piping on the side away from the heat-affected zone, and the second measuring needle abuts against the end face.

[0018] Thus, in this invention, the first measuring needle is brought into contact with the end face of the first support portion, and the second measuring needle is brought into contact with the end face of the second support portion. As a result, the changes in the heat-affected zone can be reliably captured by the first and second measuring needles, and the strain can be measured with high accuracy.

[0019] Another aspect of the present invention is the strain measurement method described above, wherein the first support portion and the second support portion are fixed to the piping by welding.

[0020] In this way, by fixing the first and second support parts to the piping by welding, the first and second support parts can be reliably fixed near the boundary of the heat-affected zone without causing any thermal influence on the heat-affected zone.

[0021] Another aspect of the present invention is the strain measurement method described above, wherein the piping is a high-temperature steam pipe and the welded portion contains high-chromium steel.

[0022] Thus, the strain measurement method of the present invention can be applied to welded joints containing high-chromium steel in high-temperature steam pipes.

[0023] Further issues disclosed in this application, and methods for solving them, will be made clear in the section on embodiments for carrying out the invention and in the drawings.

Advantages of the Invention

[0024] According to the present invention, it is possible to ensure the measurement accuracy of strain without causing rewelding to the welded part of the pipe, and it is possible to accurately diagnose the remaining life of the pipe.

Brief Description of the Drawings

[0025] [Figure 1] It is a diagram showing a schematic configuration of a strain measurement system. [Figure 2] It is a side view showing an enlarged view of a probe. [Figure 3A] It is a partially enlarged view showing the state near the measurement needle of the second member of the probe. [Figure 3B] It is a partially enlarged view showing the state near the measurement needle of the second member of the probe. [Figure 4] It is a diagram showing an example of a method for attaching a strain gauge to a pipe.

Modes for Carrying Out the Invention

[0026] Hereinafter, modes for carrying out the invention will be described. In the following description, the same or similar configurations may be denoted by common reference numerals and the description thereof may be omitted. Also, the same or similar configurations may be distinguished by attaching subscripts to the above common reference numerals and described.

[0027] FIG. 1 shows a schematic configuration of a strain measurement system 1 shown as an embodiment. The exemplified strain measurement system 1 is applied to the measurement of the amount of creep strain (hereinafter referred to as the "amount of strain") in a heat-affected zone (hereinafter referred to as "HAZ" (Heat-Affected Zone)) by welding of high-chromium steel used for large-diameter high-temperature steam pipes (hereinafter referred to as "pipes") in thermal power plants. Note that the application target of the strain measurement system 1 is not necessarily limited, and the strain measurement system 1 can also be applied to the measurement of the amount of strain of other types of pipes and the like.

[0028] In the figure, pipe 2 is shown as a cross-sectional view obtained by cutting its pipe wall 2a with a plane along the direction of extension of pipe 2. High-temperature steam V flows inside the pipe wall 2a, i.e., inside pipe 2. A welded joint 3 is formed on the pipe wall 2a by past repairs. The welded joint 3 includes weld metal 4 made of high-chromium steel or the like, and HAZs 5a and 5b formed around the weld metal 4.

[0029] As shown in the figure, the strain measurement system 1 includes a probe 10a for measuring the elongation (micro-strain) of HAZ 5a, a probe 10b for measuring the elongation (micro-strain) of HAZ 5b, a beam member 6 on which probes 10a and 10b are provided at predetermined positions, two mounting seats 7a and 7b welded to predetermined positions on the surface of the pipe wall 2a and supporting the beam member 6, and a transducer 8 that is electrically connected to probes 10a and 10b via cables 9a and 9b and determines the amount of strain based on the change in capacitance of capacitive elements provided on probes 10a and 10b (described later). The above predetermined positions are set at positions sufficiently far from the welded part 3 so as not to cause re-welding of the welded part 3.

[0030] Figure 2 is an enlarged side view of the probe 10 (common to probes 10a and 10b). The probe 10 has a scissor-like or clip-like structure, formed by combining two rod-shaped members (first member 11a, second member 11b) with parts that function as measuring needles 12a and 12b formed at their tips, which are rotatably supported on a common rotation axis 13. The materials of the first member 11a and the second member 11b are not necessarily limited, but it is preferable to use materials with a low coefficient of thermal expansion and high rigidity. In addition, although the measuring needles 12a and 12b shown in the example are depicted with sharp tips, the tips do not necessarily have to be sharp; for example, they may be spherical or approximately spherical.

[0031] A low electrode 15a is formed near the other end (the upper end of the paper) 111a of the first member 11a. A high electrode 15b and a guard electrode 15c are formed near the other end (the upper end of the paper) 111b of the second member 11b. The low electrode 15a and the high electrode 15b are provided facing each other, and a capacitive element (capacitor) is formed by the gap between them. The guard electrode 15c plays a role in correcting the stray capacitance (edge ​​capacitance) that occurs at the edge of the capacitive element. The form (shape, size, material, etc.) of the low electrode 15a, the high electrode 15b, and the guard electrode 15c is not necessarily limited.

[0032] Mounting seats 7a and 7b are welded to predetermined positions on the surface of the pipe wall 2a (pipe surface) such that the welded portion 3 is located between them. The beam member 6 is roughly rod-shaped (or roughly plate-shaped) and is fixed to the mounting seats 7a and 7b at a predetermined height so as to bridge them. The method of fixing the beam member 6 to the mounting seats 7a and 7b is not necessarily limited; for example, the beam member 6 may be fixed to the mounting seats 7 by cantilever support. It is preferable to use materials for the beam member 6 and mounting seats 7a and 7b that have a low coefficient of thermal expansion and high rigidity.

[0033] Probe 10a is positioned above HAZ 5a and mounted on beam member 6. More specifically, probe 10a is mounted on beam member 6 by fixing its rotation axis 13 to a predetermined position on beam member 6. Probe 10b is positioned above HAZ 5b and mounted on beam member 6. More specifically, probe 10b is mounted on beam member 6 by fixing its rotation axis 13 to beam member 6.

[0034] Furthermore, the method of fixing the probe 10 to the beam member 6 is not necessarily limited; for example, it may be provided on the side surface of the beam member 6, or it may be provided in a through-hole formed at a predetermined position in the beam member 6. In addition, the beam member 6 may be provided with a mechanism that allows the probe 10 to be fixed at any position along the extension direction of the beam member 6. This makes it possible to flexibly and easily set the position of the probe 10 according to the configuration of the welded joint 3 or the piping 2, for example.

[0035] Figure 3A is a partially enlarged view showing the vicinity of the measuring needle 12b of the second member 11b of the probe 10a. As shown in the figure, the measuring needle 12b is in contact with a predetermined pressure against a support portion 20b fixed near the boundary of the HAZ 5a on the surface of the pipe wall 2a. More specifically, the measuring needle 12b is in contact with the bottom 21 of an inverted conical recess formed on the upper part of the support portion 20b. In this way, since the measuring needle 12b is in contact with the bottom 21 of the recess of the support portion 20b, the displacement caused by the extension of the HAZ 5a can be reliably transmitted to the measuring needle 12b.

[0036] Furthermore, the form of the support portion 20b (outer shape, recess, and size and shape of the bottom portion 21) is not necessarily limited. For example, it may be shaped to match the shape of the tip of the measuring needle 12b (for example, the recess may have the same shape as the spherical tip shape of the measuring needle 12b). Alternatively, the support portion 20b may have a shape like that shown in Figure 3B. The support portion 20b illustrated in this figure has an end face 22 perpendicular to the pipe wall 2a, and the measuring needle 12b is in contact with the support portion 20b by its flat surface making surface contact with the end face 22. Even with this form of support portion 20b, the displacement caused by the extension of the HAZ 5a can be reliably transmitted to the measuring needle 12b.

[0037] The support portion 20b is made of a material such as ceramic and is fixed to the surface of the pipe wall 2a (pipe 2) by welding (oxidative welding) in a manner that does not have a thermal effect on the welded portion 3 (or a manner that reduces the thermal effect on the welded portion 3 to a negligible degree). Therefore, by providing the support portion 20b on the pipe 2, re-welding will not occur. Furthermore, a mechanism for adjusting the height of the probe 10a may be provided on the beam member 6 so that the measuring needle 12b contacts the support portion 20b with appropriate pressure.

[0038] In Figures 3A and 3B, the measuring needle 12b of the second member 11b of probe 10a is used as an example. However, the measuring needle 12a of the first member 11a of probe 10a also contacts the support portion 20a provided near the boundary of HAZ 5a, similar to the measuring needle 12b. Furthermore, the measuring needles 12a of the first member 11a and the measuring needles 12b of the second member 11b of probe 10b also contact the support portion 20c and support portion 20d provided near one boundary of HAZ 5b, respectively, similar to the case of probe 10a.

[0039] As described above, the measuring needle 12a of the first member 11a is in contact with the support portion 20a provided near one boundary of HAZ 5a, and the measuring needle 12b of the second member 11b is in contact with 20b provided near the other boundary of HAZ 5a. Therefore, when HAZ 5a extends (expands) along the longitudinal direction of the pipe 2, the distance between the measuring needles 12a and 12b increases, causing the first member 11a and the second member 11b to rotate (the probe 10 opens its legs around the rotation axis 13), and as a result, the distance (gap) between the Low electrode 15a and the High electrode 15b changes, and the capacitance of the capacitive element formed by them changes. The converter 8 is configured using a capacitance meter such as an LCR meter and an information processing device (computer), and measures the change in capacitance of the above-mentioned capacitive element using the function of the capacitance meter, and converts the measured value into a strain amount (amount of extension of HAZ 5a, 5b). The converter 8, for example, stores in advance the relationship between capacitance and strain obtained in a laboratory system (for example, as a mathematical formula, table, etc.), and converts the change in capacitance of a capacitive element into strain by comparing it with the above relationship, and outputs (displays, etc.) the obtained strain to a display device.

[0040] As described in detail above, the strain measurement system 1 of this embodiment supports the beam member 6 with mounting seats 7a, 7b that are positioned so as not to have a thermal effect on the heat-affected zones (HAZs) 5a, 5b formed around the welded joint 3. The measuring needles 12a, 12b of each probe 10a, 10b are brought into direct or indirect contact with the vicinity of the boundary between HAZs 5a, 5b, respectively, to individually measure the elongation of HAZs 5a, 5b. Therefore, the strain of HAZs 5a, 5b, which greatly affects the lifespan of the pipe 2, can be measured with high accuracy, and the remaining lifespan of the pipe 2 can be appropriately diagnosed.

[0041] The embodiments of the present invention have been described in detail above, but this description is for the purpose of facilitating understanding of the present invention and does not limit it. The present invention can be modified and improved without departing from its spirit, and of course, equivalents thereof are included in the present invention. For example, the above embodiments have been described in detail for the purpose of explaining the present invention in an easy-to-understand manner and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to add, delete, or replace some of the configurations of the above embodiments with other configurations. [Explanation of Symbols]

[0042] 1. Strain measurement system 2 Piping 2a pipe wall 3. Welded section 4. Weld metal 5a,5b HAZ 6 Beam material 7a, 7b Mounting base 8 Converters 9a, 9b cable 10a, 10b probes 11a First Member 11b Second member 12a Measuring needle 12b Measuring needle 15a Low electrode 15b High electrode 15c guard electrode 20a~20d Bearing part 21 Bottom 22 End face V High-temperature steam

Claims

1. A method for measuring strain in the welded joint of a pipe, A beam is placed across the aforementioned welded joint, The beam member is supported by one or more mounting seats welded to the heat-affected zone formed around the welded portion of the piping, in a position that does not cause thermal influence. A probe having a first member and a second member rotatably supported on a common axis of rotation is fixed above the heat-affected zone of the beam member. The first measuring needle, provided at one end of the first member, is brought into direct or indirect contact with the vicinity of the first boundary on one side of the heat-affected zone. The second measuring needle, provided at one end of the second member, is brought into direct or indirect contact with the vicinity of the second boundary on the other side of the heat-affected zone. A capacitive element is formed by providing a first electrode at the other end of the first member and a second electrode at the other end of the second member, facing the first electrode. The amount of strain in the heat-affected zone is measured based on the change in capacitance of the capacitive element caused by the extension of the heat-affected zone and the resulting change in the distance between the first measuring needle and the second measuring needle. Method for measuring strain.

2. A strain measurement method according to claim 1, The first measuring needle is brought into contact with the vicinity of the first boundary of the heat-affected zone via a first support fixed to the surface of the piping. The second measuring needle is brought into contact with the vicinity of the second boundary of the heat-affected zone via a second support fixed to the surface of the piping. Method for measuring strain.

3. A strain measurement method according to claim 2, The first support portion has a recess on its upper surface, and the first measuring needle contacts the bottom of the recess. The second support portion has a recess on its upper surface, and the second measuring needle contacts the bottom of the recess. Method for measuring strain.

4. A strain measurement method according to claim 2, The first support portion has an end face perpendicular to the piping on the side away from the heat-affected zone, and the first measuring needle contacts the end face. The second support portion has an end face perpendicular to the piping on the side away from the heat-affected zone, and the second measuring needle contacts the end face. Method for measuring strain.

5. A strain measurement method according to claim 2, The first support portion and the second support portion are fixed to the piping by welding. Method for measuring strain.

6. A strain measurement method according to claim 1, The aforementioned piping is a high-temperature steam pipe, and the welded portion contains high-chromium steel. Method for measuring strain.

7. A system for measuring strain in the welded joints of pipes, A beam member that spans across the aforementioned welded joint, One or more mounting seats supporting the beam member, welded to the piping at a position that does not affect the heat-affected zone formed around the welded portion, One or more probes having a first member and a second member fixed to a position above the heat-affected zone of the beam material and pivotally supported on a common rotation axis, Equipped with, The aforementioned probe A first measuring needle is provided at one end of the first member and is in direct or indirect contact with the vicinity of the first boundary on one side of the heat-affected zone, A second measuring needle is provided at one end of the second member and is in direct or indirect contact with the vicinity of the second boundary on the other side of the heat-affected zone, A capacitive element comprising: a first electrode provided at the other end of the first member; and a second electrode provided at the other end of the second member facing the first electrode; Equipped with, The device includes a transducer that measures the amount of strain in the heat-affected zone based on the change in capacitance of the capacitive element caused by the extension of the heat-affected zone and the resulting change in the distance between the first measuring needle and the second measuring needle. Strain measurement system.

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