Ultrasonic inspection method, ultrasonic inspection device, and program

Abstract

To appropriately evaluate a joint state in the boundary surface of a parent material and a build-up weld zone.SOLUTION: This ultrasonic inspection method includes: a reference signal acquisition step (SA2) for transmitting an ultrasonic signal to a test piece in which a defect of a size that serves as a criterion for determining the acceptability of joints to the boundary surface of a parent material and a build-up weld zone applied to the parent material and acquiring an echo signal reflected therefrom; a threshold setting step (SA5) for setting a threshold on the basis of the peak value of the reflected echo signal; an inspection signal acquisition step (SA8) for transmitting an ultrasonic signal to an inspection object having the build-up weld zone applied to the parent material and acquiring an echo signal reflected therefrom, as an inspection echo signal; and an evaluation step for evaluating a joint state in the boundary surface of the parent material and the build-up weld zone, on the basis of the comparison of the peak value of the inspection echo signal with the threshold.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present disclosure relates to an ultrasonic inspection method, an ultrasonic inspection device, and a program. [Background technology]

[0002] It has been known to overlay weld a cobalt-based hard alloy, which has a harder material than the base material of the valve, onto the valve seats and valve bodies of main valves such as steam control valves used in steam turbines. This type of overlay welding makes it possible to make the valves less susceptible to damage caused by thermal shock due to the inflow and outflow of high-temperature, high-pressure superheated steam, and by wear such as erosion and corrosion.

[0003] However, if there is a defect in the overlay welding, the overlay weld may peel off during operation of the steam turbine, damaging the valve. In addition, as the operation of the steam turbine progresses, the overlay weld may be damaged and peel off, so it is necessary to inspect the overlay weld periodically.

[0004] Patent Document 1 discloses a method for determining whether the strength of a joint of an object to be inspected satisfies a required strength using ultrasonic waves. For example, Patent Document 1 discloses an inspection method in which ultrasonic waves are transmitted to the joint of the object to be inspected, reflected echoes from the joint are received, and heights of the reflected echoes are calculated at predetermined intervals around the entire circumference of the joint, and heights of the calculated reflected echoes that are equal to or greater than a threshold are integrated, and whether the joint satisfies the required strength is determined based on the integrated value. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-202292 Summary of the Invention [Problem to be solved by the invention]

[0006] The method disclosed in Patent Document 1 is intended to inspect a joint when different members are joined by brazing, welding, etc. Therefore, it is difficult to directly use this method to detect defects (such as peeling) at the boundary surface of an overlay weld. Furthermore, Patent Document 1 does not disclose a specific method for setting a threshold value.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide an ultrasonic inspection method, an ultrasonic inspection device, and a program that can appropriately evaluate the bonding condition at the boundary between the base material and the overlay weld. [Means for solving the problem]

[0008] A first aspect of the present disclosure is an ultrasonic inspection method comprising: a reference signal acquisition step of transmitting ultrasonic waves to a test piece having a defect of a size that serves as an evaluation standard for determining the quality of the bond at the interface between a buildup weld applied to a base material and the base material, and acquiring the reflected echo signal; a threshold setting step of setting a threshold based on the peak value of the reflected echo signal; an inspection signal acquisition step of transmitting ultrasonic waves to an object to be inspected having a buildup weld applied to the base material and acquiring the reflected echo signal as an inspection echo signal; and an evaluation step of evaluating the bonding condition at the interface between the base material and the buildup weld based on a comparison between the peak value of the inspection echo signal and the threshold.

[0009] A second aspect of the present disclosure is an ultrasonic inspection device that includes a threshold setting unit that sets a threshold based on the peak value of the reflected echo when ultrasonic waves are transmitted to a test piece that has a defect of a size that serves as an evaluation criterion for determining whether the joint is good or bad at the interface between a buildup weld applied to a base material and the base material, and an evaluation unit that transmits ultrasonic waves to an object to be inspected that has a buildup weld applied to the base material and evaluates the bonding condition at the interface between the base material and the buildup weld based on a comparison of the reflected echo signal with the threshold.

[0010] A third aspect of the present disclosure is a program for causing a computer to function as the ultrasonic inspection device. [Effects of the Invention]

[0011] This has the effect of making it possible to appropriately evaluate the bonding state at the boundary surface between the base material and the overlay weld. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram for explaining an example of an object to be inspected according to an embodiment of the present disclosure, and is a vertical cross-sectional view showing an example of the internal structure of a steam valve used in a steam turbine. [Figure 2] FIG. 2 is a perspective view of a valve seat portion shown in FIG. [Figure 3] FIG. 2 is a schematic vertical cross-sectional view of a valve seat portion. [Figure 4] 4 is an enlarged longitudinal cross-sectional view of a portion A of the valve seat portion 10 shown in FIG. 3. FIG. [Figure 5] 1 is a diagram illustrating an overall configuration of an ultrasonic inspection system according to an embodiment of the present disclosure. [Figure 6] 1 is a schematic configuration diagram illustrating an example of a hardware configuration of an ultrasonic inspection device according to an embodiment of the present disclosure. [Figure 7] FIG. 2 is a functional block diagram showing an example of functions of an ultrasonic inspection device according to an embodiment of the present disclosure. [Figure 8] FIG. 10 is a longitudinal sectional view showing an example of a test piece when a vertical probe is used as a probe. [Figure 9] FIG. 10 is a longitudinal sectional view showing an example of a test piece when a vertical probe is used as a probe. [Figure 10] FIG. 10 is a longitudinal sectional view showing an example of a test piece when a vertical probe is used as a probe. [Figure 11] 1 is a flowchart illustrating an example of the procedure of an ultrasonic inspection method performed during new construction according to an embodiment of the present disclosure. [Figure 12] 1 is a flowchart illustrating an example of the procedure of an ultrasonic inspection method performed during new construction according to an embodiment of the present disclosure. [Figure 13] 10A and 10B are diagrams for explaining an ultrasonic inspection method using a test piece. [Figure 14] FIG. 10 is a diagram illustrating setting of a threshold value according to an embodiment of the present disclosure. [Figure 15] 1 is a flowchart illustrating an example of a procedure of an ultrasonic inspection method performed during a periodic inspection according to an embodiment of the present disclosure. [Figure 16] 10 is a diagram showing an A-scope of an inspection echo signal when a defect that is determined to result in a poor bonding state is present in the evaluation process. FIG. [Figure 17] FIG. 10 is a diagram showing an example of an A-scan of an inspection echo signal when the test result is determined to be pass in the evaluation process. [Figure 18] FIG. 10 is a diagram showing an example of an A-scan of an inspection echo signal when it is determined in the evaluation process that there is a progressive defect. [Figure 19] FIG. 10 is a diagram showing an example of a C-scope based on an inspection echo signal obtained by inspecting an object to be inspected. [Figure 20] FIG. 10 is a longitudinal sectional view showing an example of a test piece when an elevation angle probe is used as a probe. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of an ultrasonic inspection method, an ultrasonic inspection device, and a program according to the present disclosure will be described below with reference to the drawings. The following description will be given by way of example of inspecting the bonding condition (e.g., welding defects, peeling, etc.) of an overlay weld in a steam valve used in a steam turbine, but the present disclosure is not limited to this. For example, the ultrasonic inspection method, the ultrasonic inspection device, and the program according to the present disclosure can be widely applied to evaluating the bonding condition of an overlay weld applied to a base material.

[0014] 1 to 4 are diagrams illustrating an example of an object to be inspected according to an embodiment of the present disclosure. FIG. 1 is a longitudinal cross-sectional view showing an example of the internal structure of a steam valve used in a steam turbine. In FIG. 1, a casing 4 of a regulator valve serving as a pressure vessel is formed by fastening a valve cover 2 to a valve body 1 of the steam valve with bolts 3. A valve element 7 that moves toward and away from a valve seat 6 via a valve stem 5 is disposed within the casing 4, and a strainer 8 that retains foreign matter in the steam is provided on the outer periphery of the valve element 7. The valve stem 5 is held by a guide member 9, and a drive device (not shown) that moves the valve element 7 up and down is provided at its end.

[0015] Steam in the steam valve flows into the casing 4 from, for example, a steam pipe (not shown) as indicated by the arrow IN, passes through a flow path formed between the valve element 7 and the valve seat 6 by the upward movement of the valve element 7 shown in Fig. 1, and flows out as indicated by the arrow OUT. A valve seat portion 10 (see Figs. 2 to 4) is formed at the contact point between the valve element 7 and the valve seat 6.

[0016] Fig. 2 is a perspective view of the valve seat 10 shown in Fig. 1, Fig. 3 is a schematic longitudinal cross-sectional view of the valve seat 10, and Fig. 4 is an enlarged longitudinal cross-sectional view of part A of the valve seat 10 shown in Fig. 3. As shown in Figs. 2 to 4, the valve seat 10 has an overlay weld 11 formed by overlay welding performed over the entire circumferential direction of the base metal. As an example, a stellite material, which is a cobalt-based corrosion-resistant and heat-resistant alloy, is overlay welded. Examples of overlay welding methods for such stellite material include an oxyacetylene method using a cobalt-based hard alloy welding wire, a TIG (tungsten inert gas) method, a PTA (plasma transferred arc) method, and a method of thermally spraying a cobalt-based alloy powder. The base material is not particularly limited, but an example thereof is a forged material.

[0017] In this embodiment, an example will be described in which the bonding condition (defective welding, peeling, etc.) between the base material and the overlay weld 11 formed on the valve seat portion 10 of the valve seat 6 is evaluated.

[0018] 5 is a diagram showing the overall configuration of an ultrasonic inspection system 50 according to an embodiment of the present disclosure. In FIG. 5, the ultrasonic inspection system 50 includes an ultrasonic probe (hereinafter simply referred to as "probe") 20 and an ultrasonic inspection device 30.

[0019] The probe 20 irradiates ultrasonic waves into the interior of the object under inspection, receives reflected echoes returning from the object under inspection, and outputs an output signal related to the received reflected echoes (hereinafter referred to as a "reflected echo signal") to the ultrasonic inspection device 30. In this embodiment, the probe 20 uses a single-transducer vertical probe that transmits an ultrasonic beam that is perpendicularly incident on the surface (flaw detection surface) of the object under inspection. The vertical probe may be configured, for example, by a single sensor, or may be a phased array probe configured by multiple sensors. It is also possible to use a wheel-type (tire-type) probe or the like. In this embodiment, a case where the probe is configured by a single sensor will be described as an example. The size of the probe 20 should be appropriate to suit the defect size that is the evaluation standard for determining poor bonding and the curved surface shape of the overlay weld. The appropriate contact medium can be used depending on the test, such as clean machine oil, castor oil, sonicote, or grease.

[0020] Furthermore, the probe 20 according to this embodiment is equipped with a probe movement distance measuring device (not shown) for creating an internal scope image (for example, a B-scope, a C-scope, etc., which will be described later). This probe movement distance measuring device is composed of an encoder attached to the probe 20. The encoder outputs pulses according to the amount of movement of the probe 20, allowing the ultrasonic inspection device 30 to associate the inspection position in the object to be inspected with the reflected echo signal.

[0021] The ultrasonic inspection device 30 inspects the inside of the object to be inspected based on the reflected echo signals received from the probe 20, and notifies the inspector of the inspection results by displaying them on a display unit or the like.

[0022] FIG. 6 is a schematic diagram showing an example of the hardware configuration of an ultrasonic inspection device 30 according to an embodiment of the present disclosure. As shown in FIG. 6, the ultrasonic inspection device 30 is, for example, a computer system. The ultrasonic inspection device 30 includes, for example, a CPU (Central Processing Unit: processor) 31, a main memory 32, a secondary storage 33, and a communication interface 35. These components are interconnected directly or indirectly via a bus, and cooperate with each other to execute various processes. The ultrasonic inspection device 30 may also include an input device 36 and an output device 37.

[0023] The CPU 31 controls the ultrasonic inspection device 30 using, for example, an OS (Operating System) stored in a secondary storage device 33 connected via a bus, and performs various processes by executing various programs stored in the secondary storage device 33. One or more CPUs 31 may be provided, and they may work together to realize processes.

[0024] The main memory device 32 is composed of writable memory such as cache memory, RAM (Random Access Memory), etc., and is used as a working area for reading out the execution program of the CPU 31 and writing the processing data by the execution program.

[0025] The secondary storage device 33 is a non-transitory computer-readable storage medium. Examples of the secondary storage device 33 include a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, and a semiconductor memory. Examples of the secondary storage device 33 include a read-only memory (ROM), a hard disk drive (HDD), and a solid-state drive (SSD) flash memory. The secondary storage device 33 stores, for example, an operating system (OS) for controlling the entire ultrasound inspection device 30, such as Windows (registered trademark), iOS (registered trademark), or Android (registered trademark), a basic input / output system (BIOS), various device drivers for operating peripheral devices, various application software, and various data and files. The secondary storage device 33 also stores programs for implementing various processes and various data required for implementing the various processes. A plurality of secondary storage devices 33 may be provided, and the programs and data described above may be stored separately in each secondary storage device 33.

[0026] The communication interface 35 functions as an interface for connecting to a network to communicate with other devices and transmitting and receiving information. For example, the communication interface 35 communicates with other devices via a wired or wireless connection. Examples of wireless communication include communication via lines such as Bluetooth (registered trademark), Wi-Fi, mobile communication systems (3G, 4G, 5G, 6G, LTE, etc.), and wireless LAN. An example of wired communication is communication via lines such as a wired LAN (Local Area Network).

[0027] Examples of the input device 36 include a keyboard, a touchpad, a pointing device, etc. Examples of the pointing device include a mouse, a touch panel, a pen tablet, a trackpad, a trackball, etc. Examples of the output device 37 include a display, a projector, and a printer.

[0028] Next, an example of the functions of the ultrasonic inspection device 30 according to this embodiment will be described with reference to the drawings. Fig. 7 is a functional block diagram showing an example of the functions of the ultrasonic inspection device 30 according to this embodiment. A series of processes for realizing the various functions described below is stored in the secondary storage device 33 in the form of a program, for example, and the CPU (processor) 11 reads this program into the main storage device 32 and executes information processing and arithmetic processing to realize the various functions. Note that the program may be pre-installed in the secondary storage device 33, provided in a state stored in a non-transitory computer-readable storage medium, or distributed via wired or wireless communication means. Examples of non-transitory computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0029] As shown in FIG. 7, the ultrasonic inspection device 30 includes, for example, a signal acquisition unit 41, a threshold setting unit 42, a storage unit 43, an evaluation unit 44, a progression estimation unit 45, and a display control unit 46.

[0030] The signal acquisition unit 41 receives the reflected echo signal output from the probe 20 .

[0031] The threshold setting unit 42 sets a threshold for evaluating defects at the boundary between the base metal and the overlay weld applied to the base metal, based on the inspection results using the test piece.

[0032] FIG. 8 is a diagram showing a longitudinal cross section of a test piece as an example according to this embodiment. As shown in FIG. 8, the test piece has an overlay weld 61 formed by applying overlay welding to a base material 60. This test piece simulates the test piece, and is made using the same material as the test piece, and the thickness of the overlay weld is also set to be the same as that of the test piece. The test piece may also be made by cutting out from an actual product. Furthermore, as long as the influence of the material and shape is small or can be compensated for, the test piece may be made of a material and shape different from those of the test piece.

[0033] In this test piece, a defect of a size that serves as an evaluation criterion for determining whether a joint is good or bad is provided at the interface S between the base material 60 and the overlay weld 61 applied to the base material 60. Specifically, a flat-bottom hole 62 having a bottom is provided at the interface S between the base material 60 and the overlay weld 61. This flat-bottom hole 62 simulates, for example, a space (a gap caused by delamination) between the base material and the overlay weld. The diameter of the flat-bottom hole 62 is set to the defect size that serves as the evaluation criterion for determining whether a joint is good or bad. For example, if a defect of α [mm] or more is detected and is determined to be defective, a flat-bottom hole of α [mm] in size is provided. Note that, in FIG. 8, the flat-bottom hole 62 is provided at the center in the width direction of the interface, but this example is not limited to this. For example, as shown in FIGS. 9 and 10, the flat-bottom hole 62 may be provided at a position shifted from the center in the width direction.

[0034] The threshold setting unit 42 sets the threshold using, for example, the peak value of a reflected echo signal (hereinafter referred to as a "reference echo signal") reflected from a defect when ultrasonic waves are transmitted to the above-mentioned test piece. For example, the threshold setting unit 42 sets the peak value (maximum signal strength) of the reference echo signal as the threshold.

[0035] The memory unit 43 stores various data related to ultrasonic testing, such as information on the threshold set by the threshold setting unit 42, a reference echo signal which is a reflected echo signal obtained in testing using a test piece, and a reflected echo signal obtained during testing of the test object (hereinafter referred to as the "test echo signal").

[0036] The evaluation unit 44 evaluates the bonding condition of the object to be inspected based on the inspection echo signal, which is a reflected echo signal of the object to be inspected acquired by the signal acquisition unit 41 during inspection of the object to be inspected. For example, the evaluation unit 44 evaluates the bonding condition at the boundary surface between the base material and the overlay weld based on a comparison between the peak value (maximum signal strength) of the inspection echo signal and a threshold value. Specifically, the evaluation unit 44 determines that the bonding condition is defective when the peak value of the inspection echo signal is equal to or greater than the threshold value.

[0037] During the periodic inspection, the evaluation unit 44 may further evaluate the bonding state of the boundary surface based on a predetermined first reference value that is set to be less than the threshold value. For example, during the periodic inspection, the evaluation unit 44 determines that there is a progressable defect when the peak value of the inspection echo signal is equal to or greater than the first reference value and less than the threshold value.

[0038] Furthermore, the evaluation unit 44 may further evaluate the bonding condition of the interface based on the S / N ratio during regular inspection. For example, the evaluation unit 44 may determine that a progressive defect exists if the S / N ratio during regular inspection is equal to or greater than a predetermined second reference value. The S / N ratio is a value indicating the ratio of the peak value of the signal intensity of the inspection echo signal to the signal intensity of the background noise. The signal intensity of the background noise may be calculated based on the noise of a reference echo signal acquired during an inspection using a test piece, or may be calculated using an inspection echo signal acquired during regular inspection of the object under inspection. For example, the signal intensity of the background noise may be calculated by acquiring the peak value of the background noise contained in the inspection echo signal at each position obtained during inspection of the object under inspection and statistically processing the acquired peak value.

[0039] When the evaluation unit 44 determines that there is a progressive defect, the progression estimation unit 45 uses the defect progression speed to estimate the cumulative operating load until the defect size reaches the evaluation criterion. For example, the defect progression speed can be calculated using the Paris Law. For example, the progression estimation unit 45 uses the following calculation formula to calculate the cumulative operating load until the defect size reaches the evaluation criterion.

[0040] da / dN=C(△K)m (1)

[0041] In the above equation (1), da / dN is the defect growth rate (the size of the defect growth per load cycle), C and m are constants determined by the material, and △K is the stress intensity factor range, which is the range of variation of the stress intensity factor with respect to the load.

[0042] The amount of defect growth per load cycle can be calculated using equation (1), which allows us to calculate how much more load the detected defect needs to be subjected to before it reaches the evaluation standard defect size α [mm].

[0043] The display control unit 46 creates a display screen for notifying the inspector of the inspection results, for example, and displays it on the output device 37 such as a display. For example, the display control unit 46 causes the display to display a reflected echo image (A-scope) of the inspected object acquired during the inspection, a cross-sectional scan image (B-scope) created based on the reflected echo signals of the inspected object, a planar image (C-scope) created based on the reflected echo signals of the inspected object, and the like. Note that, since many known techniques have been proposed for displaying the results of the ultrasonic inspection, it is only necessary to adopt any of these techniques to create appropriate images and display them based on various input instructions input from the input device 36.

[0044] The ultrasonic inspection device 30 may also include a signal processing unit for performing various processes required to evaluate the bonding state on the reflected echo signals received by the signal acquisition unit 41. The signal processing unit performs, for example, a time axis adjustment process, an evaluation gate setting process, and the like. Furthermore, when an inspection echo signal is acquired, a process for determining whether or not it is a false echo signal may be provided. For example, in the A-scope, it is possible to determine whether or not it is a false echo signal by determining whether or not a reflected echo exceeding a predetermined value is generated continuously for a predetermined period of time.

[0045] Next, an ultrasonic inspection method using the ultrasonic inspection system 50 having the above configuration will be described with reference to the drawings.

[0046] First, an ultrasonic inspection method performed when new buildup welding is performed will be described with reference to Figures 11 and 12. Figures 11 and 12 are flowcharts showing an example of the procedure of the ultrasonic inspection method performed when new buildup welding is performed.

[0047] First, as shown in FIG. 13, the inspector brings the probe 20 into contact with the surface of the test piece and moves the probe 20 along the surface of the overlay weld 61 of the test piece (SA1). As a result, ultrasonic waves are irradiated into the interior of the test piece at each inspection position. The irradiated ultrasonic waves are reflected in the area where the flat-bottom hole 62 is provided, and the reflected waves are received by the probe 20 as reflected echoes. As a result, reflected echoes are obtained from the area where the defect (flat-bottom hole 62) is provided. Furthermore, in areas where the flat-bottom hole 62 is not provided and the joint is good, most of the echoes are not reflected by the boundary surface S. For this reason, the signal intensity of the reflected echo reflected from the good boundary surface S is very small.

[0048] The reflected echo received by the probe 20 undergoes predetermined processing such as signal conversion and is then output as a reference echo signal to the ultrasonic inspection device 30. When the ultrasonic inspection device 30 acquires the reference echo signal at each inspection position (SA2), it obtains a reflected echo image (A-scan) at each inspection position. As shown in FIG. 14, for example, the A-scan indicates the relationship between the signal intensity of the reflected echo and the elapsed time since the ultrasonic wave was emitted, in other words, the distance from the incident surface of the ultrasonic wave along the propagation direction of the ultrasonic wave.

[0049] 14, the ultrasonic inspection device 30 sets an evaluation gate G based on the distance from the surface of the overlay weld 61 to the boundary surface S in the A-scope obtained at each inspection position (SA3), and identifies the peak value (maximum signal intensity) in the time range of the evaluation gate G (SA4). At this time, the ultrasonic inspection device 30 may adjust the scale of the time axis based on the distance from the surface of the overlay weld 61 to the boundary surface S, as shown in FIG.

[0050] Then, the maximum value is identified from the peak values ​​identified at each inspection position, and this maximum value is set as a threshold value (SA5). This threshold value corresponds to the signal strength of the reflected echo signal obtained when a defect that determines that the bonding state is poor occurs.

[0051] Next, the gain of the ultrasonic inspection device 30 is adjusted so that the peak value set as the threshold value becomes 100% (SA6). This adjustment may be performed by an inspector or may be performed automatically by the ultrasonic inspection device 30.

[0052] Next, the object to be inspected is inspected. In the inspection of the object to be inspected, the probe 20 is moved along the surface of the object to be inspected (SA7). In this embodiment, for example, the probe 20 scans along the circumferential direction of the valve seat portion 10 shown in FIG. 2. Note that the scanning of the probe 20 may be performed manually by an inspector, or the probe 20 may be automatically moved along a preset scanning route.

[0053] As a result, ultrasonic waves are irradiated into the interior of the object at each inspection position, and the reflected echoes are sequentially received. The reflected echoes from the object thus obtained are subjected to predetermined processing, correlated with position information, and sequentially output to the ultrasonic inspection device 30.

[0054] In the ultrasonic inspection device 30, when an inspection echo signal is acquired at each inspection position (SA8), an evaluation gate G is set on the A-scope at each inspection position based on the distance from the surface of the overlay weld to the boundary surface S (SA9). At this time, the scale of the time axis may be adjusted, as in the case of an inspection using a test piece.

[0055] Then, for each inspection echo signal acquired at each inspection position, the peak value of the inspection echo signal is compared with a threshold value (100%) within the time range of evaluation gate G to determine whether the peak value is equal to or greater than the threshold value (SA10). As a result, if the peak value is equal to or greater than the threshold value (SA10: YES), as in the A-scope shown in Fig. 16, for example, the system determines that the test is defective (SA11) and proceeds to step SA13. On the other hand, if the peak value is less than the threshold value (SA10: NO), as in the A-scope shown in Fig. 17, for example, the system determines that the test is acceptable (SA12) and proceeds to step SA13.

[0056] In step SA13, the inspection results are displayed on the display (SA13), and the process ends. Note that when displaying the inspection results, A-scope, B-scope, C-scope, etc. based on the inspection echo signal acquired during the inspection may be displayed on the display together with the inspection results. This makes it possible to notify the inspector of the location and size of the peeling when a defect is determined.

[0057] Next, the ultrasonic inspection method performed during periodic inspection will be described with reference to Fig. 15. The ultrasonic inspection method performed during periodic inspection is the same as the ultrasonic inspection method performed when new overlay welding is performed as described above from step SA1 to step SA11, but differs in that some subsequent processing is added. Therefore, the processing from step SA11 onwards of the ultrasonic inspection method performed when new overlay welding is performed will be described below.

[0058] For each inspection echo signal acquired at each inspection position, the peak value is compared with a threshold value, and if it is determined that the peak value is less than the threshold value (SA10: NO in FIG. 15), the peak value is compared with a first reference value to determine whether the peak value is equal to or greater than the first reference value (SB12). The first reference value is calculated, for example, by multiplying the threshold value by a predetermined coefficient less than 1. For example, the first reference value is set to 50% of the threshold value.

[0059] As a result, if the peak value is less than the first reference value (SB12: NO), as in the A-scope shown in Fig. 17, it is determined whether the SN ratio is equal to or greater than the second reference value (SB13). As a result, if the SN ratio is less than the second reference value (SB13: NO), a pass determination is made (SB15), and the process proceeds to step SB18.

[0060] On the other hand, in step SB12, if the peak value is equal to or greater than the first reference value, for example, as in the A-scope shown in Figure 18 (SB12: YES), or if in step SB13 the SN ratio is equal to or greater than the second reference value (SB13: YES), it is determined that there is a progressive defect (SB16), and the operating load until the defect size reaches the evaluation criterion for defect determination (for example, α [mm]) is estimated (SB17), and the process proceeds to step SB18.

[0061] In step SB18, the inspection results are displayed on the display, and the process ends. Note that when displaying the inspection results, A-scope, B-scope, C-scope, etc. based on the inspection echo signal acquired during the inspection may be displayed on the display together with the inspection results. This makes it possible to notify the inspector of the location and size of the defect when a defect is determined to be defective.

[0062] Fig. 19 is a diagram showing an example of a C-scope of the valve seat portion 10 created based on an inspection echo signal acquired during a periodic inspection. The C-scope shown in Fig. 19 also displays the results of the PT inspection. The C-scope shown in FIG. 19 is divided into four regions according to the signal strength of the peak value. For example, the regions are divided into a region where the peak value is less than 25% of the threshold value, a region where the peak value is 25% to 50% of the threshold value, a region where the peak value is 50% or more of the threshold value, and a region where the S / N ratio is 3 or more. In FIG. 19, each region is indicated by different hatching, but the inspection results may also be displayed by different shades of color. For example, the greater the signal strength of the peak value, the higher the gradation (for example, a gradation closer to 255) that is displayed, allowing the inspector to intuitively grasp the bonding condition of the boundary surface. Furthermore, as shown in FIG. 19, penetrant testing (PT testing) can only detect defects that open on the surface, but the ultrasonic testing method according to this embodiment makes it possible to evaluate the bonding condition of the boundary surface inside the material that does not open on the surface.

[0063] In the ultrasonic inspection method described above, the case where the acquisition of inspection echo signals and the evaluation of defects are performed simultaneously during inspection has been described as an example, but the present invention is not limited to this example. For example, the acquisition of inspection echo signals (e.g., SA1 to SA8 in FIG. 11) and the evaluation process of the bonding state based on the inspection echo signals (e.g., SA9 in FIG. 11 to SA13 in FIG. 12, SA9 in FIG. 11 to SB18 in FIG. 15) may be performed separately. For example, an inspector may move the probe 20 along the surface of the object to be inspected, and the inspection echo signals obtained may be stored in the storage unit 43 (see FIG. 7) in association with the inspection positions. The inspection echo signals at each inspection position stored in the storage unit 43 may then be read out later, and the above-mentioned evaluation process may be performed using the read inspection echo signals.

[0064] The ultrasonic inspection method, ultrasonic inspection device, and program according to the present embodiment described above provide the following advantageous effects. In a test piece simulating an object to be inspected, a defect of a size that serves as an evaluation standard for determining the quality of the bond is provided at the interface between the base metal and the overlay weld, and a threshold is set based on the peak value of the reflected echo signal when ultrasonic testing is performed on this test piece. This makes it possible to set an appropriate threshold for evaluating the bond condition. The bond condition at the interface between the base metal and the overlay weld is then evaluated by comparing the set threshold with the peak value of the test echo signal, allowing for an appropriate evaluation of the bond condition at the interface between the base metal and the overlay weld.

[0065] Although the present disclosure has been described above using embodiments, the technical scope of the present disclosure is not limited to the scope described in the above embodiments. Various modifications or improvements can be made to the above embodiments without departing from the gist of the disclosure, and such modifications or improvements are also included in the technical scope of the present disclosure. Furthermore, the above embodiments may be combined as appropriate. Furthermore, the pre-processing procedures and the ultrasonic inspection method procedures described in the above embodiments are also examples, and unnecessary steps may be deleted, new steps may be added, or the processing order may be rearranged within the scope of the present disclosure.

[0066] For example, in the above-described embodiment, a vertical probe is used as the probe, but this is not limiting. For example, a vertical probe can also be used. In this case, instead of the flat-bottom hole 62, a slit 63 of a defect size based on the evaluation criteria may be provided at the end of the test piece, as shown in FIG. 20, and ultrasonic waves may be emitted into this slit 63, and the threshold value may be determined based on the reflected echo signal. Furthermore, with a vertical probe, as shown in FIG. 20, the probe is moved on a plane and ultrasonic waves are emitted from the base material side to receive the reflected echo. Note that the method for setting the threshold value from the received reference echo signal is the same as in the above-described inspection using a vertical probe. That is, the peak value of the reflected echo signal from the test piece is set as the threshold.

[0067] Furthermore, in the above embodiment, a single-transducer probe is used as the probe 20, but for example, a dual-transducer probe may be used as the probe 20. In this case, it is preferable to perform the inspection by scanning the probe 20 in the circumferential direction of the valve seat portion 10, which is the object to be inspected, and then scanning the probe 20 in a direction perpendicular to the circumferential direction (up-down direction). This is because a dual-transducer probe has directionality. Furthermore, even when a single-transducer probe is used, the inspection accuracy can be improved by performing the inspection in the circumferential direction and the up-down direction.

[0068] The ultrasonic inspection method, ultrasonic inspection device, and program according to the embodiment described above can be understood, for example, as follows.

[0069] The ultrasonic inspection method according to the present disclosure includes a reference signal acquisition step (SA2) of transmitting ultrasonic waves to a test piece having defects (62, 63) of a size that serves as an evaluation standard for determining the quality of the joint at the boundary surface (S) between an overlay weld (61) applied to a base material (60) and the base material (60) and acquiring the reflected echo signal; a threshold setting step (SA5) of setting a threshold based on the peak value of the reflected echo signal; an inspection signal acquisition step (SA8) of transmitting ultrasonic waves to an inspected object (10) having an overlay weld (11) applied to the base material (6) and acquiring the reflected echo signal as an inspection echo signal; and an evaluation step (SA10) of evaluating the bonding condition at the boundary surface between the base material (6) and the overlay weld (11) based on a comparison between the peak value of the inspection echo signal and the threshold value.

[0070] According to the ultrasonic inspection method, a defect of a size that serves as an evaluation criterion for determining whether the bond is good or bad is provided at the interface between the base metal and the overlay weld in a test piece simulating an object to be inspected, and a threshold is set based on the peak value of the reflected echo signal when ultrasonic inspection is performed on this test piece. This makes it possible to set an appropriate threshold for evaluating the bond condition. The bond condition at the interface between the base metal and the overlay weld is then evaluated by comparing the set threshold with the peak value of the inspection echo signal, thereby making it possible to appropriately evaluate the bond condition at the interface between the base metal and the overlay weld.

[0071] The ultrasonic inspection method according to the present disclosure is an ultrasonic inspection method using a vertical probe, wherein the test piece is provided with a flat-bottomed hole (62) having a diameter of a defect size that serves as an evaluation criterion for determining whether the joint is good or bad, the threshold setting step (SA5) sets the threshold based on the peak value of a reflected echo signal from the flat-bottomed hole (62), and the evaluation step (SA10) may determine (SA11) that the test piece is defective when the peak value of the inspection echo signal from the test piece is equal to or greater than the threshold.

[0072] According to the ultrasonic inspection method, when a vertical probe is used, the threshold value is set using a test piece provided with a flat-bottom hole having a diameter of the defect size that serves as the evaluation standard for determining the quality of the bond, which makes it possible to set an appropriate threshold value according to the probe used.

[0073] The ultrasonic inspection method according to the present disclosure is an ultrasonic inspection method using an incident angle probe, wherein the test piece is provided with a slit (63) of a defect size that serves as an evaluation criterion for determining whether the joint is good or bad, the threshold setting step (SA5) sets the threshold based on a peak value of a reflected echo signal from the slit, and the evaluation step (SA10) may determine that the test piece is defective when the peak value of the inspection echo signal from the test piece is equal to or greater than the threshold (SA11).

[0074] According to the ultrasonic inspection method, when a projection angle probe is used, the threshold value is set using a test piece provided with a slit of the defect size that serves as an evaluation standard for determining the quality of the bond, which makes it possible to set an appropriate threshold value according to the probe used.

[0075] In the ultrasonic inspection method according to the present disclosure, the evaluation process may determine that there is a progressive defect (SB16) if the peak value of the inspection echo signal from the object to be inspected is equal to or greater than a predetermined first reference value set below the threshold value but less than the threshold value (SB12: YES), or if the SN ratio is equal to or greater than a predetermined second reference value (SB13: YES).

[0076] According to the ultrasonic inspection method, it is possible to detect in advance defects that have progressed and may lead to peeling in the future.

[0077] The ultrasonic inspection method according to the present disclosure may include a progression estimation process (SB17) for estimating, when the evaluation process determines that a progressive defect exists, the cumulative operating load at which the current defect size will be equal to or greater than the size that serves as the evaluation standard for determining whether the joint is good or bad, based on the progression rate of the defect and the usage status of the inspected object.

[0078] According to the ultrasonic inspection method described above, when it is determined that there is a progressive defect, the cumulative operating load until the current defect size reaches the evaluation standard size for determining whether the joint is good or bad is estimated, and therefore, it becomes possible to take appropriate measures (e.g., replacing the part, removing the overlay weld, reapplying the overlay weld, etc.) before the defect reaches peeling.

[0079] The ultrasonic inspection device (30) according to the present disclosure includes a threshold setting unit (42) that sets a threshold based on the peak value of the reflected echo when ultrasonic waves are transmitted to a test piece having defects (62, 63) of a size that serves as an evaluation criterion for determining whether the joint is good or bad at an interface (S) between an overlay weld (61) applied to a base material (60) and the base material (60), and an evaluation unit (44) that transmits ultrasonic waves to an inspected object (10) having an overlay weld (11) applied to the base material (6) and evaluates the bonding state at the interface between the base material (6) and the overlay weld (11) based on a comparison of the reflected echo signal with the threshold.

[0080] The program according to the present disclosure is a program for causing a computer to function as the ultrasonic inspection device (30). [Explanation of symbols]

[0081] 1: Valve body 2: Operculum 3: Bolt 4: Casing 5: Valve stem 6: Valve seat 7: Valve body 8: Strainer 9: Guide member 10: Valve seat (test object) 11: Overlay weld 20: Probe 30: Ultrasonic inspection equipment 31: CPU 32: Main memory 33:Secondary storage device 35: Communication interface 36: Input device 37: Output device 41: Signal acquisition unit 42: Threshold setting unit 43: Storage section 44: Evaluation section 45: Progress estimation part 46: Display control section 50: Ultrasonic inspection system 60: Base material 61: Overlay weld 62: Flat bottom hole 63: Slit

Claims

1. a reference signal acquisition step of transmitting ultrasonic waves to a test piece having a defect of a size that serves as an evaluation standard for determining whether a joint is good or bad at the interface between the overlay weld applied to the base material and the base material, and acquiring a reflected echo signal; a threshold setting step of setting a threshold based on a peak value of the reflected echo signal; an inspection signal acquisition step of transmitting ultrasonic waves to an object to be inspected having an overlay weld applied to a base material and acquiring a reflected echo signal as an inspection echo signal; an evaluation step of evaluating a bonding state at the boundary surface between the base material and the overlay weld based on a comparison between the peak value of the inspection echo signal and the threshold value; and The evaluation process is an ultrasonic inspection method in which a progressive defect is determined to be present when the peak value of the inspection echo signal from the object to be inspected is equal to or greater than a predetermined first reference value set below the threshold value but less than the threshold value, or when the signal-to-noise ratio is equal to or greater than a predetermined second reference value.

2. An ultrasonic inspection method using a vertical probe, The test piece is provided with a flat-bottom hole having a diameter of a defect size that serves as an evaluation standard for determining whether the joint is good or bad, the threshold setting step sets the threshold based on a peak value of the reflected echo signal from the flat-bottom hole; 2. The ultrasonic inspection method according to claim 1, wherein the evaluation step determines the object to be inspected as defective when a peak value of the inspection echo signal from the object to be inspected is equal to or greater than the threshold value.

3. An ultrasonic inspection method using an elevation angle probe, The test piece is provided with a slit of a defect size that serves as an evaluation standard for determining whether the joint is good or bad, the threshold value setting step sets the threshold value based on a peak value of a reflected echo signal from the slit; 2. The ultrasonic inspection method according to claim 1, wherein the evaluation step determines the object to be inspected as defective when a peak value of the inspection echo signal from the object to be inspected is equal to or greater than the threshold value.

4. The ultrasonic inspection method according to claim 1, further comprising a propagation estimation step of estimating, if the evaluation step determines that a propagation defect exists, a cumulative operating load at which the current defect size will be equal to or greater than the evaluation standard size for determining whether the joint is good or bad, based on the propagation speed of the defect and the usage status of the inspected object.

5. a threshold setting unit that sets a threshold based on the peak value of a reflected echo when ultrasonic waves are transmitted to a test piece having a defect of a size that serves as an evaluation standard for determining whether a joint is good or bad at a boundary between an overlay weld applied to a base material and the base material; an evaluation unit that transmits ultrasonic waves to an object to be inspected having an overlay weld applied to a base material, and evaluates the bonding condition at the boundary between the base material and the overlay weld based on a comparison between the reflected echo signal and the threshold value; Equipped with An ultrasonic inspection device that determines that there is a progressive defect when the peak value of the inspection echo signal from the object to be inspected is equal to or greater than a predetermined first reference value set below the threshold value but less than the threshold value, or when the signal-to-noise ratio is equal to or greater than a predetermined second reference value.

6. A program for causing a computer to function as the ultrasonic inspection apparatus according to claim 5.

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