Soft structure detection method, residual life estimation method and test object selection method

Abstract

To provide a soft structure detection method that can determine whether or not there is soft structure within weld metal.SOLUTION: A soft structure detection method for detecting soft structure in a test object of weld metal using ultrasonic testing comprises: a first testing step for conducting ultrasonic testing on the test object by transmitting a first ultrasonic beam along an inclination direction from at least one oblique transducer and acquiring a reflection wave of the first ultrasonic beam returning to the oblique transducer; a second testing step for conducting ultrasonic testing on the test object by transmitting a second ultrasonic beam along an oblique direction from a transmitting transducer and acquiring a reflection wave of the second ultrasonic beam received by a receiving transducer arranged between the same and the transmitting transducer; and a determination step for determining whether or not there is soft structure in the test object based on the ultrasonic testing results of the first testing step and the ultrasonic inspection results of the second testing step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for detecting softened structure in a weld metal, a method for estimating remaining life, and a method for selecting a weld metal to be inspected. [Background technology]

[0002] In recent years, it has been known that softened structures occur in the heat-affected zones of welds and base metals of high-temperature steam piping (high chromium steel piping) used in thermal power plants, for example (see Patent Document 1, for example). The softened structures that occur in metal components used under high-temperature and high-pressure conditions have significantly lower hardness than normal regions (base metal and weld metal), and the crystal grains also become coarse. Therefore, the presence of this softened structure may reduce the strength of the metal components, and it is expected that the need for non-destructive detection of softened structures will increase in the future.

[0003] Ultrasonic testing (UT) has been known as a method for non-destructively inspecting metal members (see Patent Document 1). In ultrasonic inspection, a short pulse signal of ultrasonic waves is transmitted (transmitted) from a flaw detector to an object to be inspected, such as a welded part of a high-temperature steam pipe, and the reflected wave (echo signal) is received and analyzed. This makes it possible to estimate the presence or absence and location of defects in the object to be inspected. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-169935 Summary of the Invention [Problem to be solved by the invention]

[0005] Although it is possible to distinguish between softened structure and weld flaws (defects) in a weld metal by ultrasonic inspection using known techniques, there is a problem in that it is difficult to distinguish between softened structure and columnar crystals (dendrite grains) in a weld metal by ultrasonic inspection. Note that Patent Document 1 attempts to determine the presence or absence of softened structure in an inspection object by performing ultrasonic inspection on the inspection object using ultrasonic waves having a set frequency according to the expected grain size of the crystal grains that form the softened structure.

[0006] In view of the above circumstances, an object of at least one embodiment of the present disclosure is to provide a softened tissue detection method capable of determining the presence or absence of softened tissue in a weld metal. [Means for solving the problem]

[0007] A method for detecting soft tissue according to at least one embodiment of the present disclosure includes: A softened tissue detection method for detecting softened tissue in an inspection object of a weld metal by ultrasonic testing, comprising: a first inspection step of performing ultrasonic inspection in which a first ultrasonic beam is incident on the inspection object from at least one angle probe along an inclination direction and a reflected wave of the first ultrasonic beam returning to the angle probe is obtained; a second inspection step of performing ultrasonic inspection in which a second ultrasonic beam is irradiated from a transmitting probe along an inclined direction to the inspection object, and a reflected wave of the second ultrasonic beam is acquired by a receiving probe disposed with the weld metal sandwiched between the transmitting probe and the receiving probe; The method further includes a determination step of determining the presence or absence of the softened tissue in the inspection object based on the ultrasonic inspection results of the first inspection step and the ultrasonic inspection results of the second inspection step.

[0008] A remaining life estimation method according to at least one embodiment of the present disclosure includes: A remaining life estimation method for estimating a remaining life of a weld metal, comprising the steps of: The method further includes a remaining life estimation step of estimating a remaining life of the weld metal from the determination result of the determination step obtained by the softened structure detection method, by utilizing a relationship between the determination result of the determination step and a reduction rate of the remaining life of the weld metal.

[0009] A method for selecting an inspection target according to at least one embodiment of the present disclosure includes: An inspection object selection method for selecting a weld metal to be inspected for the presence or absence of softened tissue in the softened tissue detection method, comprising: a welding pass distance acquisition step of acquiring a welding pass distance of a plurality of weld metals which are candidates for the inspection object; and a weld metal selection step of selecting the weld metal to be the inspection object in consideration of the weld pass distances of the plurality of weld metals acquired in the weld pass distance acquisition step. Effect of the Invention

[0010] According to at least one embodiment of the present disclosure, a soft tissue detection method capable of determining the presence or absence of soft tissue in a weld metal is provided. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a flow diagram illustrating an example of a method for soft tissue assessment including a soft tissue detection method according to an embodiment of the present disclosure. [Diagram 2] FIG. 1 is a flow diagram illustrating an example of a method for soft tissue detection according to an embodiment of the present disclosure. [Diagram 3] 1 is a diagram illustrating a schematic configuration of an ultrasonic inspection system according to an embodiment of the present disclosure. [Figure 4] 1A to 1C are diagrams for explaining ultrasonic testing in a first testing step of a soft tissue detection method according to an embodiment of the present disclosure. [Diagram 5] 1A to 1C are diagrams for explaining ultrasonic testing in a first testing step of a soft tissue detection method according to an embodiment of the present disclosure. [Figure 6]1A to 1C are diagrams for explaining ultrasonic testing in a second testing step of a soft tissue detection method according to an embodiment of the present disclosure. [Figure 7] 1A to 1C are diagrams for explaining ultrasonic inspection results of a first inspection step and ultrasonic inspection results of a second inspection step in a soft tissue detection method according to an embodiment of the present disclosure. [Figure 8] FIG. 13 is a diagram for explaining a determination step in a soft tissue detection method according to an embodiment of the present disclosure. [Figure 9] 11A to 11C are diagrams for explaining a probe moving step in a soft tissue detection method according to an embodiment of the present disclosure. [Figure 10] FIG. 2 is a diagram for explaining a remaining life estimation method according to an embodiment of the present disclosure. [Figure 11] FIG. 2 is a flow diagram illustrating an example of a remaining life estimation method according to an embodiment of the present disclosure. [Figure 12] FIG. 1 is a diagram for explaining an inspection target selection method according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as the embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure.

[0013] (Soft tissue evaluation method) FIG. 1 is a flow diagram showing an example of a softened tissue evaluation method M including a softened tissue detection method M2 according to an embodiment of the present disclosure. The softened tissue evaluation method M according to some embodiments is a method for non-destructively evaluating softened tissue 21, which is abnormal metal structure that may precipitate in a part of a weld metal 2. As shown in FIG. 1, the method can be broadly divided into three methods: an inspection target selection method M1, a softened tissue detection method M2, and a remaining life estimation method M3. That is, the softened tissue evaluation method M includes the inspection target selection method M1, the softened tissue detection method M2, and the remaining life estimation method M3. Note that each of the inspection target selection method M1, the softened tissue detection method M2, and the remaining life estimation method M3 according to the present disclosure can be performed independently of the other methods of the softened tissue evaluation method M.

[0014] The inspection object selection method M1 is a method for selecting a weld metal 2 that is an object to be inspected for the presence or absence of softened tissue 21. The softened tissue detection method M2 is a method for detecting softened tissue 21 in an inspection object 3 in the weld metal 2 that is an object to be inspected by ultrasonic testing (UT). The remaining life estimation method M3 is a method for estimating the remaining life of the weld metal 2 in consideration of the softened tissue 21 in the inspection object 3 in the weld metal 2 detected in the softened tissue detection method M2. The inspection object selection method M1 may be performed before the softened tissue detection method M2, and the weld metal 2 selected in the inspection object selection method M1 may be used as the inspection object in the softened tissue detection method M2. The remaining life estimation method M3 is performed after the softened tissue detection method M2.

[0015] (Soft tissue detection method) Fig. 2 is a flow diagram showing an example of a soft tissue detection method M2 according to an embodiment of the present disclosure. Fig. 3 is a diagram showing a schematic configuration of an ultrasonic inspection system 1 according to an embodiment of the present disclosure. As shown in Figs. 1 and 2, the soft tissue detection method M2 according to some embodiments includes a first inspection step S21, a second inspection step S22, and a determination step S23.

[0016] (First inspection step) 4 and 5 are diagrams for explaining ultrasonic testing in a first testing step S21 of a soft tissue detection method M2 according to an embodiment of the present disclosure. In the first testing step S21, as shown in Fig. 4 and Fig. 5, ultrasonic testing (first ultrasonic testing) is performed in which a first ultrasonic beam is incident on an inspection target 3 of a weld metal 2 from at least one angle probe 41 along an inclination direction and a reflected wave of the first ultrasonic beam returning to the angle probe 41 is obtained. In the first ultrasonic testing, ultrasonic testing may be performed by a pulse-echo method.

[0017] The weld metal 2 is a metal that melts and solidifies during welding. As shown in Fig. 3, the welded portion 20 includes the weld metal 2 and a heat affected zone (HAZ) 202 of a base metal 201, which is the metal material to be welded. The weld metal 2 does not include the heat affected zone 202 of the base metal 201.

[0018] The inspection object 3 includes at least one weld cross section 31 along a direction perpendicular to a depth direction (welding direction) DD of the weld metal 2. Hereinafter, as shown in Fig. 3, a direction away from an outer surface 203 of the weld metal 2 (downward in the figure) is defined as a height direction (thickness direction) HD of the weld metal 2, and a direction perpendicular to the height direction HD in the weld cross section 31 (left-right direction in the figure) is defined as a width direction WD of the weld metal 2. One side of the center (width direction center position CP) of the width direction WD of the weld metal 2 is defined as a first side FS, and the other side of the center (width direction center position CP) of the width direction WD of the weld metal 2 is defined as a second side SS.

[0019] In the illustrated embodiment, the at least one angle beam probe 41 includes a plurality of angle beam probes 41 (41A, 41B). The plurality of angle beam probes 41 includes a first angle beam probe 41A and a second angle beam probe 41B arranged with the weld metal 2 sandwiched between the first angle beam probe 41A and the second angle beam probe 41B. In the first flaw detection step S21, ultrasonic flaw detection is performed to obtain reflected waves of the first ultrasonic beam returning to each of the first angle beam probe 41A and the second angle beam probe 41B. Note that in other embodiments, ultrasonic flaw detection may be performed by a single angle beam probe 41 in the first flaw detection step S21.

[0020] In the embodiment shown in FIG. 4 and FIG. 5, the first angled probe 41A is attached to the outer surface 204 of the base metal 201 adjacent to the first side FS of the weld metal 2. The second angled probe 41B is attached to the outer surface 205 of the base metal 201 adjacent to the second side SS of the weld metal 2. The first angled probe 41A is adapted to make the first ultrasonic beam incident along a direction inclined toward the other side (right side in the figure) of the width direction WD with respect to the height direction HD. The first angled probe 41A is adapted to receive a reflected wave of the first ultrasonic beam that bounces back along a direction inclined toward the other side (right side in the figure) of the width direction WD with respect to the height direction HD. The second angled probe is adapted to make the first ultrasonic beam incident along a direction inclined toward the one side (left side in the figure) of the width direction WD with respect to the height direction HD. In addition, the second oblique angle probe is configured to receive the reflected wave of the first ultrasonic beam that bounces back along an inclined direction inclined to one side (the left side in the figure) in the width direction WD with respect to the height direction HD described above.

[0021] Each of the multiple angle beam probes 41 (41A, 41B) has a transmitter 411 for transmitting a first ultrasonic beam (first ultrasonic incident wave IW1) and a receiver 412 for receiving a reflected wave (echo signal) RW1 of the first ultrasonic beam transmitted by the transmitter 411. The transmitter 411 incorporates a transmitting side transducer for generating the first ultrasonic beam, and the receiver 412 incorporates a receiving side transducer for receiving the first ultrasonic beam.

[0022] (Second inspection step) FIG. 6 is a diagram for explaining ultrasonic testing in the second testing step S22 of the softened tissue detection method M2 according to an embodiment of the present disclosure. In the second testing step S22, as shown in FIG. 6, a second ultrasonic beam is irradiated from a transmitting probe 42 along an inclination direction to an inspection target 3 of a weld metal 2, and a reflected wave of the second ultrasonic beam received by a receiving probe 43 arranged with the weld metal 2 sandwiched between the transmitting probe 42 and the receiving probe 43 is acquired (second ultrasonic testing). In the second ultrasonic testing, ultrasonic testing may be performed by a catch-up method. The above-mentioned inspection target 3 includes at least one weld cross section 31 along a direction perpendicular to the depth direction of the weld metal 2. It is preferable that the weld cross section 31 that is the inspection target 3 in the second testing step S22 is the same as the weld cross section 31 that is the inspection target 3 in the first testing step S21.

[0023] 6, the transmitting probe 42 is attached to an outer surface 204 of the base metal 201 adjacent to a first side FS of the weld metal 2. The receiving probe 43 is attached to an outer surface 205 of the base metal 201 adjacent to a second side SS of the weld metal 2. The transmitting probe 42 is adapted to emit a second ultrasonic beam along a direction inclined toward the other side (right side in the figure) of the width direction WD with respect to the height direction HD. The receiving probe 43 is adapted to receive a reflected wave of the second ultrasonic beam that bounces back along a direction inclined toward the one side (left side in the figure) of the width direction WD with respect to the height direction HD.

[0024] The transmitting probe 42 has a transmitter 421 for transmitting a second ultrasonic beam (second ultrasonic incident wave IW2). The receiving probe 43 has a receiver 431 for receiving a reflected wave (echo signal) RW2 of the second ultrasonic beam transmitted by the transmitter 421. The transmitter 421 incorporates a transmitting transducer for generating the second ultrasonic beam, and the receiver 431 incorporates a receiving transducer for receiving the second ultrasonic beam.

[0025] As shown in FIG. 3, in the first flaw detection step S21 and the second flaw detection step S22, ultrasonic flaw detection may be performed using a first ultrasonic probe 4A(4) functioning as a first angle beam probe 41A and a transmitting probe 42, and a second ultrasonic probe 4B(4) functioning as a second angle beam probe 41B and a receiving probe 43. In the illustrated embodiment, the first ultrasonic probe 4A has the above-mentioned transmitter 411, receiver 412, and transmitter 421. The second ultrasonic probe 4B has the above-mentioned transmitter 411, receiver 412, and receiver 431. Note that the first ultrasonic probe 4A may further have a receiver 431, and the second ultrasonic probe 4B may further have a transmitter 421. That is, the first ultrasonic probe 4A may function as a receiving probe 43, and the second ultrasonic probe 4B may function as a transmitting probe 42. Each of the first ultrasonic probe 4A and the second ultrasonic probe 4B is an array probe incorporating at least a plurality of transmitting transducers and receiving transducers. By ultrasonic flaw detection using the first ultrasonic probe 4A and the second ultrasonic probe 4B, the first flaw detection step S21 and the second flaw detection step S22 can be performed simultaneously.

[0026] (Ultrasonic flaw detection system) In the illustrated embodiment, the above-mentioned softened tissue detection method M2 is performed by an ultrasonic inspection system 1 (see FIG. 3). The ultrasonic inspection system 1 includes a plurality of ultrasonic probes 4 (4A, 4B), a measuring device 11 that generates signal data of the reflected waves by measuring (observing) the intensity of the reflected waves of the ultrasonic beams (signal level of the echo signal) using receivers 412, 431 after transmitting ultrasonic beams from respective transmitters 411, 421 of the plurality of ultrasonic probes 4, and a determination device 12 that determines the presence or absence of softened tissue 21 in the inspection object 3 based on the signal data of the reflected waves generated by the measuring device 11.

[0027] After transmitting an ultrasonic beam from the transmitters 411, 421, the measuring device 11 measures the intensity of the reflected wave of the ultrasonic beam (signal level of the echo signal) using the receivers 412, 431, thereby generating intensity data (time series data) which is the time progression of the intensity of the reflected wave of the ultrasonic beam observed over a predetermined period from the time the ultrasonic beam is transmitted from the transmitters 411, 421.

[0028] 4 to 6, the position and size of the reflection source of the ultrasonic beam in the inspection object 3 can be estimated by the ultrasonic inspection in the above-mentioned first inspection step S21 and second inspection step S22. Examples of the reflection source of the ultrasonic beam detected in the above-mentioned first inspection step S21 and second inspection step S22 include softened tissue 21, columnar crystals (dendrite grains) 22 of the weld metal 2, and weld flaws (defects) 23. Since the ultrasonic beams transmitted from the transmitters 411 and 421 are reflected by the reflection sources and the reflected ultrasonic beams (reflected waves) are received by the receivers 412 and 431, there are locations (reflection source echoes) where the intensity of the reflected waves of the ultrasonic beams (signal level of the echo signal) changes significantly.

[0029] (Decision step) 7 is a diagram for explaining the ultrasonic inspection result of the first inspection step S21 and the ultrasonic inspection result of the second inspection step S22 in the softened tissue detection method according to an embodiment of the present disclosure. FIG. 8 is a diagram for explaining the judgment step S23 in the softened tissue detection method M2 according to an embodiment of the present disclosure. As shown in FIG. 7, the ultrasonic inspection in the first inspection step S21 obtains reflection source echoes from the softened tissue 21, the columnar crystals 22, and the welding flaw 23, and in particular, a relatively high reflection source echo from the columnar crystals 22 is obtained. The ultrasonic inspection in the second inspection step S22 obtains reflection source echoes from the softened tissue 21, the columnar crystals 22, and the welding flaw 23, but the reflection source echo from the columnar crystals 22 is relatively low.

[0030] In the ultrasonic inspection in the first inspection step S21, ultrasonic waves are strongly reflected in a direction perpendicular to the inclination of the columnar crystals 22, so that inspection may be performed under different ultrasonic inspection conditions for the surface layer side and the deep layer side of the weld metal 2. Here, the surface layer side of the weld metal 2 is a region that is within a predetermined distance from the outer surface 203 of the weld metal 2, and the deep layer side of the weld metal 2 is a region that is more than the predetermined distance from the outer surface 203 of the weld metal 2. The deep layer side of the weld metal 2 may have a larger distance in the width direction WD between the pair of angle beam probes 41 (41A, 41B) than the surface layer side, or the central refraction angle θ of each of the pair of ultrasonic probe angle beam probes 41 (41A, 41B) may be made smaller. The central refraction angle θ is the central angle of the angular range of the refraction angle of the ultrasonic beam incident from the incident point of the ultrasonic probe 4 in a cross section along a direction perpendicular to the welding direction of the weld metal 2, and is the angle with respect to a virtual line VL extending from the incident point of the ultrasonic probe 4 along the height direction HD of the weld metal 2.

[0031] In the ultrasonic inspection in the second inspection step S22, when a pair of ultrasonic probes 4A, 4B each functioning as both the transmitting probe 42 and the receiving probe 43 described above are used, inspection can be performed centering on the intersection point of the ultrasonic beam (central beam) extending along the central refraction angle θ of the pair of ultrasonic probes 4A, 4B, so that inspection may be performed under different ultrasonic inspection conditions for the surface layer side and the deep layer side of the weld metal 2. The distance in the width direction WD between the pair of ultrasonic probes 4A, 4B may be wider on the deep layer side of the weld metal 2 than on the surface layer side, or the central refraction angle θ of each of the pair of ultrasonic probes 4A, 4B may be smaller.

[0032] The inventors have found that the behavior (e.g., intensity) of the reflected waves of the first ultrasonic beam and the second ultrasonic beam differs between softened tissue 21 and columnar crystals 22, and that the difference in behavior makes it possible to identify whether the tissue is softened tissue 21 or columnar crystals 22.

[0033] In the judgment step S23, the presence or absence of softened tissue 21 in the inspection object 3 is judged based on the ultrasonic inspection result of the first inspection step S21 and the ultrasonic inspection result of the second inspection step S22. In the illustrated embodiment, the judgment step S23 is performed by the judgment device 12. Each step included in the judgment step S23 described later is also performed by the judgment device 12. In the ultrasonic inspection result of the first inspection step S21, a relatively high reflected source echo from the columnar crystal 22 is obtained, whereas in the ultrasonic inspection result of the second inspection step S22, a relatively low reflected source echo from the columnar crystal 22 is obtained. For this reason, the position and size of the columnar crystal 22 can be estimated from the ultrasonic inspection result of the first inspection step S21 and the ultrasonic inspection result of the second inspection step S22. In addition, since the welding flaw 23 is a void reflection different from the softened tissue 21 which is a tissue reflection, it is possible to distinguish the softened tissue 21 from the welding flaw 23 by a known method, for example, the waveform analysis described in Patent Document 1. This makes it possible to identify the softened structure 21, columnar crystals 22, and weld defects 23, which are reflection sources of the ultrasonic beam, and therefore makes it possible to estimate the presence or absence of the softened structure 21 in the inspection object 3.

[0034] According to the above method, in the first flaw detection step S21 and the second flaw detection step S22, reflected waves of the first ultrasonic beam and reflected waves of the second ultrasonic beam are obtained, and in the judgment step S23, it is possible to identify whether these reflected waves are softened tissue 21 or columnar crystals 22 from the behavior of these reflected waves, thereby making it possible to judge the presence or absence of softened tissue 21 in the weld metal 2.

[0035] In the soft tissue detection method M2 according to some embodiments, as shown in Fig. 5, the at least one angle beam probe 41 includes the first angle beam probe 41A and the second angle beam probe 41B. In the first flaw detection step S21, ultrasonic flaw detection is performed to obtain a reflected wave of the first ultrasonic beam incident from the first angle beam probe 41A and returned to the first angle beam probe 41A, and ultrasonic flaw detection is performed to obtain a reflected wave of the first ultrasonic beam incident from the second angle beam probe 41B and returned to the second angle beam probe 41B.

[0036] The columnar crystals 22A formed on the first bevel probe 41A side, i.e., the first side FS, of the weld cross section 31 extend so as to incline toward the first side FS (the one side) as they move away from the outer surface 203 of the weld metal 2. The columnar crystals 22B formed on the second bevel probe 41B side, i.e., the second side SS of the weld cross section 31 extend so as to incline toward the second side SS (the other side) as they move away from the outer surface 203 of the weld metal 2.

[0037] According to the above method, the first ultrasonic beam from the first bevel probe 41A can be incident on the columnar crystal 22A formed on the first bevel probe 41A side at the weld cross section 31 along a direction perpendicular to the extending direction of the columnar crystal 22A, so that the position and size of the columnar crystal 22A, which is the reflection source, can be estimated with high accuracy. Similarly, the first ultrasonic beam from the second bevel probe 41B can be incident on the columnar crystal 22B formed on the second bevel probe 41B side at the weld cross section 31 along a direction perpendicular to the extending direction of the columnar crystal 22B, so that the position and size of the columnar crystal 22B, which is the reflection source, can be estimated with high accuracy.

[0038] In the soft tissue detection method M2 according to some embodiments, the above-mentioned inspection object 3 includes at least one weld cross section 31 along a direction perpendicular to the welding direction of the weld metal 2. The above-mentioned determination step S23 includes a first flaw detection image generating step S232 and a second flaw detection image generating step S233, as shown in FIG.

[0039] In the first inspection image generating step S232, a first inspection image DI1 (see FIG. 7) is generated which is an inspection image of at least one weld cross section 31 by the first ultrasonic beam based on the ultrasonic inspection result of the first inspection step S21 (e.g., intensity data of the reflected wave of the first ultrasonic beam). In the second inspection image generating step S233, a second inspection image DI2 (see FIG. 7) is generated which is an inspection image of at least one weld cross section 31 by the second ultrasonic beam based on the ultrasonic inspection result of the second inspection step S22 (e.g., intensity data of the reflected wave of the second ultrasonic beam).

[0040] The first inspection image DI1 and the second inspection image DI2 are generated by using a known inspection image generation technique, for example, TFM (Total Focusing Method) technique. The judgment device 12 outputs the generated inspection images (first inspection image DI1, second inspection image DI2, etc.) to a display device 13 capable of visualization, such as a display (see FIG. 3) or a printer, so that the above inspection images are displayed. The first inspection image DI1 and the second inspection image DI2 depict the position and size of the reflection source of the ultrasonic beam in the weld cross section 31. The first inspection image DI1 may be generated by integrating, for example, a flaw inspection image (left side in FIG. 5) generated from the first ultrasonic inspection result by the first angle probe 41A and a flaw inspection image (right side in FIG. 5) generated from the first ultrasonic inspection result by the second angle probe 41B.

[0041] According to the above method, the softened tissue 21 and the columnar crystals 22 are displayed in different states in the first inspection image DI1 and the second inspection image DI2, and therefore it is possible to easily identify whether the softened tissue 21 or the columnar crystals 22 exists from the first inspection image DI1 and the second inspection image DI2, and therefore it is possible to easily determine the presence or absence of the softened tissue 21 in the weld metal 2 using image analysis technology or the like. The identification of whether the softened tissue 21 or the columnar crystals 22 exists from the first inspection image DI1 and the second inspection image DI2 and the image analysis technology are performed, for example, by the above-mentioned determination device 12.

[0042] In the softened tissue detection method M2 according to some embodiments, the inspection object 3 includes at least one weld cross section 31 along a direction perpendicular to the welding direction of the weld metal 2. The determination step S23 includes the first flaw detection image generating step S232, the second flaw detection image generating step S233, and an image estimation step S234, as shown in FIG.

[0043] In the image estimation step S234, for each of a plurality of divided regions 32 each defined in the weld cross section 31, a first feature value corresponding to the intensity of the reflected wave of the first ultrasonic beam in the first flaw detection image DI1 is compared with a second feature value corresponding to the intensity of the reflected wave of the second ultrasonic beam in the second flaw detection image DI2 to estimate the position and size (length W in the width direction WD and length H in the height direction HD, see Figure 9) of the softened tissue 21 within the weld cross section 31.

[0044] Each of the divided regions 32 is a region constituting a part of the weld cross section 31, which is obtained by dividing the weld cross section 31 shown in the first inspection image DI1 and the second inspection image DI2 into a plurality of parts in the height direction HD and width direction WD of the weld metal 2. The first feature value may be any value that represents the intensity of the reflected wave of the first ultrasonic beam in the first inspection image DI1, and may be, for example, the brightness (echo height) of each divided region 32 in the first inspection image DI1. The second feature value may be any value that represents the intensity of the reflected wave of the second ultrasonic beam in the second inspection image DI2, and may be, for example, the brightness (echo height) of each divided region 32 in the second inspection image DI2.

[0045] Before comparing the first and second characteristic values, adjustments may be made, such as multiplying the first or second characteristic value by a predetermined correction value, taking into account the conditions of the first ultrasonic inspection and the second ultrasonic inspection.

[0046] According to the above method, the divided regions 32 in the weld cross section 31 in which the first feature value is higher than the second feature value can be identified as the columnar crystals 22, and the divided regions 32 in the weld cross section 31 in which the first feature value is lower than the second feature value can be identified as the softened tissue 21. From the divided regions 32 identified as the softened tissue 21 in the weld cross section 31, the position and size of the softened tissue 21 in the weld cross section 31 can be estimated. In addition, by setting the feature values ​​(brightness, echo height) of the divided regions 32 in the weld cross section 31 in which the first feature value is higher than the second feature value to zero, and setting the feature values ​​(brightness, echo height) of the divided regions 32 in the weld cross section 31 in which the second feature value is higher than the first feature value to the second feature value, a flaw detection image DI3 in which the softened tissue 21 is extracted can be generated as shown in FIG. 8.

[0047] In some of the above-described embodiments, the first flaw detection image DI1 and the second flaw detection image DI2 are generated, but the position and size of the softened tissue 21 in the weld cross section 31 (inspection object 3) may be estimated without generating the first flaw detection image DI1 and the second flaw detection image DI2. In a softened tissue detection method M2 according to some embodiments, the above-described inspection object 3 includes at least one weld cross section 31 along a direction perpendicular to the welding direction of the weld metal 2. The above-described determination step S23 includes an estimation step S231 as shown in FIG. 1.

[0048] In the estimation step S231, for each of a plurality of divided regions 32 each partitioned in the weld cross section 31 (test object 3), information regarding the intensity of the reflected wave of the first ultrasonic beam obtained from the ultrasonic inspection results of the first testing step S21 is compared with information regarding the intensity of the reflected wave of the second ultrasonic beam obtained from the ultrasonic inspection results of the second testing step S22, thereby estimating the position and size of the softened tissue 21 within the test object 3.

[0049] The information on the intensity of the reflected wave of the first ultrasonic beam and the information on the intensity of the reflected wave of the second ultrasonic beam to be compared in the estimation step S231 may be the intensity of the reflected wave of each divided region 32 (signal level of the echo signal), or may be a difference value of the intensity of the reflected wave of each divided region 32 relative to the incident wave, or may be a ratio (attenuation rate) of the intensity of the reflected wave of each divided region 32 relative to the incident wave. Before comparing the information on the intensity of the reflected wave of the first ultrasonic beam and the information on the intensity of the reflected wave of the second ultrasonic beam, adjustments such as multiplying these information by a predetermined correction value may be performed in consideration of the conditions of the first ultrasonic flaw detection and the second ultrasonic flaw detection.

[0050] According to the above method, the reflected wave of the first ultrasonic beam from the columnar crystals 22 has a relatively high intensity, whereas the reflected wave of the second ultrasonic beam from the columnar crystals 22 has a relatively low intensity. Therefore, the divided region 32 in which the intensity of the reflected wave of the first ultrasonic beam in the inspection object 3 is higher than the intensity of the reflected wave of the second ultrasonic beam can be specified as the columnar crystals 22, and the divided region 32 in which the intensity of the reflected wave of the first ultrasonic beam in the inspection object 3 is lower than the intensity of the reflected wave of the second ultrasonic beam can be specified as the softened tissue 21. From the divided region 32 specified as the softened tissue 21 in the inspection object 3, the position and size (length W in the width direction WD and length H in the height direction HD, see FIG. 9) of the softened tissue 21 in the inspection object 3 can be estimated.

[0051] (Probe movement steps) 9 is a diagram for explaining a probe moving step S24 in the softened tissue detection method M2 according to an embodiment of the present disclosure. As shown in FIG. 2, the softened tissue detection method M2 according to some embodiments further includes a probe moving step S24 in which at least one of the angle probes 41 (41A, 41B), the transmitting probe 42, and the receiving probe 43 are moved along the welding direction of the weld metal 2. As shown in FIG. 3, the above-mentioned inspection target 3 includes a plurality of weld cross sections 31 along a direction perpendicular to the welding direction of the weld metal 2 and spaced apart from each other along the welding direction. That is, the first flaw detection step S21, the second flaw detection step S22, and the determination step S23 are performed on each of the weld cross sections 31 at a plurality of locations within the range of the probe movement in the probe moving step S24.

[0052] In the embodiment shown in FIG. 2, the judgment step S23 is performed after the completion of the probe movement step S24, but it may also be performed promptly on the weld cross section 31 on which the first flaw detection step S21 and the second flaw detection step S22 have been performed while the probe movement step S24 is being performed.

[0053] The measuring device 11 measures (observes) the intensity of the reflected wave of the ultrasonic beam (signal level of the echo signal) at multiple locations within the above-mentioned probe movement range using receivers 412, 431, thereby generating signal data and intensity data (time series data) of the reflected wave at each of the multiple locations.

[0054] According to the above method, the presence or absence of softened tissue 21 can be determined in each of the multiple weld cross sections 31 by moving the bevel probe 41, the transmitting probe 42, and the receiving probe 43 along the welding direction of the weld metal 2. By determining the presence or absence of softened tissue 21 in each of the multiple weld cross sections 31, the position and size (length L in the welding direction, see FIG. 9) of the softened tissue 21 in the welding direction of the weld metal 2 can be estimated.

[0055] (Remaining life estimation method) FIG. 10 is a diagram for explaining a remaining life estimation method M3 according to an embodiment of the present disclosure. FIG. 11 is a flow diagram showing an example of the remaining life estimation method M3 according to an embodiment of the present disclosure. The remaining life estimation method M3 according to some embodiments is a method for estimating the remaining life of a weld metal 2. The weld metal 2 for which the remaining life is to be estimated is preferably the weld metal 2 for which the above-mentioned softened tissue detection method M2 has actually been performed. In the remaining life estimation method M3, the remaining life of the weld metal 2 is estimated from the determination result of the determination step S23 obtained in the softened tissue detection method M2 by utilizing the relationship between the determination result of the determination step S23 of the above-mentioned softened tissue detection method M2 and the reduction rate of the remaining life of the weld metal 2. The remaining life estimation method M3 may be performed by the above-mentioned determination device 12, or may be performed by another device (life expectancy evaluation device) different from the determination device 12.

[0056] In one embodiment, the life reduction amount of the weld metal 2 is calculated from the size information of the softened structure 21 based on first association information that associates size information of the softened structure 21, which is information regarding the position and size (lengths W, H, L, etc.) of the softened structure 21 in the weld metal 2 obtained by the judgment result of judgment step S23, with the life reduction amount of the weld metal 2.

[0057] The first association information indicates a correspondence relationship between the size information of the softened structure 21 and the life reduction amount of the weld metal 2, and may be any information that can acquire the life reduction amount of the weld metal 2 corresponding to the input information as output information when the size information of the softened structure 21 is input information. The first association information includes a list, a table, a map, a function, a machine learning model, a strength analysis model, and the like that indicate the correspondence relationship between the input information and the output information. The first association information may be created based on steady-state test data, or may be created based on past actual values, experimental values, numerical analysis results, and the like other than steady-state test data.

[0058] Fig. 10 shows an S (stress)-N (life) diagram of the weld metal 2. Curve C1 shown in Fig. 10 is a life evaluation curve when the softened structure 21 in the weld metal 2 is not taken into consideration, and curve C2 shown in Fig. 10 is a corrected life evaluation curve when the softened structure 21 in the weld metal 2 is taken into consideration, and is a curve corrected for curve C1 by the amount of reduction in life of the weld metal 2 calculated from the size information of the softened structure 21. The remaining life of the weld metal 2 under the evaluation temperature and stress conditions can be estimated using curve C2.

[0059] According to the above method, the remaining life of the weld metal 2 can be estimated from the position and size of the softened tissue 21 in the object 3 obtained from the determination result in the determination step S23 of the softened tissue detection method M2.

[0060] In a remaining life estimation method M3 according to some embodiments, as shown in Fig. 11, the above-mentioned remaining life estimation step S31 includes an area ratio calculation step S311 and a remaining life reduction rate calculation step S312. In the area ratio calculation step S311, the area ratio of the softened structure 21 is calculated based on the determination result of the above-mentioned determination step S23. In the area ratio calculation step S311, size information of the softened structure 21 obtained from a plurality of weld cross sections 31 of the weld metal 2 may be used as the determination result of the above-mentioned determination step S23, or size information of the softened structure 21 obtained from any representative weld cross section 31 of the weld metal 2 may be used. The area ratio of the weld metal 2 can be calculated from the size information of the softened structure 21.

[0061] In the remaining life reduction rate calculation step S312, the relationship between the area ratio of the softened structure 21 and the reduction rate of the remaining life of the weld metal 2 is utilized to calculate the reduction rate of the remaining life of the weld metal 2 from the area ratio of the softened structure 21 calculated in the area ratio calculation step S311.

[0062] In the illustrated embodiment, in the remaining life reduction rate calculation step S312, the reduction rate F of the remaining life of the weld metal 2 is calculated from the area ratio R of the softened structure 21 calculated in the area ratio calculation step S311 based on second association information that correlates the area ratio R of the softened structure 21 and the reduction rate F of the remaining life of the weld metal 2.

[0063] The second association information indicates the correspondence relationship between the area ratio R of the softened structure 21 and the reduction rate F of the remaining life of the weld metal 2, and may be any information that, when the area ratio R of the softened structure 21 is input information, can acquire the reduction rate F of the remaining life of the weld metal 2 corresponding to the input information as output information. The second association information includes a list, a table, a map, a function, a machine learning model, or the like that indicates the correspondence relationship between the input information and the output information. The second association information may be created based on steady-state test data, or may be created based on past actual values, experimental values, numerical analysis results, or the like other than steady-state test data.

[0064] In the illustrated embodiment, the remaining life estimation step S31 uses the life evaluation curve (curve C1) in the case where the softened structure 21 in the weld metal 2 is not taken into consideration to estimate the remaining life t r0 and a remaining life acquisition step S313 for acquiring the remaining life t r0 The remaining life t taking the softened tissue 21 into consideration is calculated by multiplying the remaining life by the remaining life reduction rate F calculated in the remaining life reduction rate calculation step S312. r and a remaining life calculation step S314 of calculating the remaining life.

[0065] According to the above method, there is a tendency that the higher the area ratio of the softened structure 21, the higher the reduction rate of the remaining life of the weld metal 2. By utilizing such a relationship between the area ratio of the softened structure 21 and the reduction rate of the remaining life of the weld metal 2, the reduction rate of the remaining life of the weld metal 2 can be calculated from the area ratio of the softened structure 21 calculated in the area ratio calculation step S311.

[0066] (Inspection subject selection method) 12 is a diagram for explaining an inspection object selection method M1 according to an embodiment of the present disclosure. The inspection object selection method M1 according to some embodiments is a method for selecting a weld metal 2 to be inspected for the presence or absence of softened tissue 21 in the above-mentioned softened tissue detection method M2. For example, in a power plant boiler, there are several thousand or more weld metals 2 that are candidates for the inspection object, so it is not realistic to perform the softened tissue detection method M2 on all of the weld metals 2.

[0067] 1, the inspection object selection method M1 includes a welding pass distance acquisition step S11 and a weld metal selection step S12. In the welding pass distance acquisition step S11, the welding pass distances DWP of a plurality of weld metals 2 that are candidates for the inspection object are acquired. In the weld metal selection step S12, the weld metal 2 to be the inspection object is selected in consideration of the welding pass distances of the plurality of weld metals 2 acquired in the welding pass distance acquisition step S11.

[0068] Since it is difficult to grasp the welding pass distance DWP from a drawing or the like, it is preferable to perform ultrasonic inspection on a plurality of weld metals 2 that are candidates for the inspection object, and obtain the welding pass distance DWP. In the welding pass distance acquisition step S11, as shown in FIG. 12, ultrasonic inspection is performed by irradiating an ultrasonic beam from an angle probe 44 along an inclination direction on an arbitrary welding cross section (representative welding cross section) 31 of the weld metal 2, and obtaining a reflected wave of the ultrasonic beam returning to the angle probe 44. The angle probe 44 has a transmitter 411 and a receiver 412, similar to the angle probe 41. The ultrasonic inspection by the angle probe 44 may be performed on a part of the representative welding cross section 31. For example, the target range of the ultrasonic inspection by the angle probe 44 may be either the first side FS or the second side SS, or may be either the surface side or the deep side described above.

[0069] The above-mentioned measuring device 11 generates signal data (intensity data) of the reflected wave, and the above-mentioned determining device 12 generates a flaw detection image DI4 of ultrasonic flaw detection by the angle probe 44. The flaw detection image DI4 depicts a plurality of welding passes 24 spaced apart from each other in the height direction HD in the representative welded cross section 31. The distance between a pair of welding passes 24 adjacent in the height direction HD in the flaw detection image DI4 (the distance in the height direction HD) can be acquired as the welding pass distance DWP.

[0070] According to the above method, the shorter the weld pass distance DWP of the weld metal 2, the greater the local heat input during welding, and therefore the higher the risk of softened tissue 21 occurring in the weld metal 2. Since the weld pass distance DWP of the weld metal 2 is strongly related to the risk of softened tissue 21 occurring, by using the weld pass distance DWP of the weld metal 2 as a parameter, the weld metal 2 having a high risk of softened tissue 21 occurring can be selected as the inspection object.

[0071] In this specification, expressions expressing relative or absolute configuration, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," do not only strictly represent such a configuration, but also represent a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions indicating that things are in an equal state, such as "identical," "equal," and "homogeneous," not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions describing shapes such as a rectangular shape or a cylindrical shape do not only refer to shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also refer to shapes that include uneven portions, chamfered portions, etc., to the extent that the same effect is obtained. In addition, in this specification, the expressions "comprise," "include," or "have" a certain element are not exclusive expressions that exclude the presence of other elements.

[0072] The present disclosure is not limited to the above-described embodiments, and includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0073] The contents described in the above-mentioned embodiments can be understood, for example, as follows.

[0074] 1) A method for detecting soft tissue (M2) according to at least one embodiment of the present disclosure, comprising: A softened tissue detection method (M2) for detecting softened tissue (21) in an inspection object (3) of a weld metal (2) by ultrasonic testing, comprising: a first flaw detection step (S21) of performing ultrasonic flaw detection in which a first ultrasonic beam is incident on the inspection object (3) from at least one bevel probe (41) along an inclination direction and a reflected wave of the first ultrasonic beam returning to the bevel probe (41) is obtained; a second inspection step (S22) of performing ultrasonic inspection in which a second ultrasonic beam is irradiated from a transmitting probe (42) along an inclined direction to the inspection target (3) and a reflected wave of the second ultrasonic beam is acquired by a receiving probe (43) disposed between the transmitting probe (42) and a receiving probe (43) with the weld metal (2) sandwiched therebetween; and a determination step (S23) of determining the presence or absence of the softened tissue (21) in the inspection object (3) based on the ultrasonic inspection results of the first inspection step (S21) and the ultrasonic inspection results of the second inspection step (S22).

[0075] The inventors have found that the behavior (e.g., intensity) of the reflected waves of the first ultrasonic beam and the second ultrasonic beam differs between the softened structure (21) and the columnar crystals (22), and that the difference in behavior makes it possible to identify whether the structure is a softened structure (21) or a columnar crystal (22). According to the method of 1) above, the reflected waves of the first ultrasonic beam and the reflected waves of the second ultrasonic beam are obtained, and it is possible to identify whether the structure is a softened structure (21) or a columnar crystal (22) from the behavior of these reflected waves, so that the presence or absence of the softened structure (21) in the weld metal (2) can be determined.

[0076] 2) In some embodiments, the soft tissue detection method (M2) according to 1) above, In the determination step (S23), The method includes an estimation step (S231) of estimating the position and size of the softened tissue (21) within the test object (3) by comparing, for each of a plurality of divided regions (32) respectively partitioned in the test object (3), information regarding the intensity of the reflected wave of the first ultrasonic beam obtained from the ultrasonic inspection result of the first inspection step (S21) with information regarding the intensity of the reflected wave of the second ultrasonic beam obtained from the ultrasonic inspection result of the second inspection step (S22).

[0077] According to the method of 2) above, the reflected wave of the first ultrasonic beam from the columnar crystals (22) has a relatively high intensity, whereas the reflected wave of the second ultrasonic beam from the columnar crystals (22) has a relatively low intensity. Therefore, the divided region (32) in the inspection object (3) where the intensity of the reflected wave of the first ultrasonic beam is higher than the intensity of the reflected wave of the second ultrasonic beam can be identified as the columnar crystals (22), and the divided region (32) in the inspection object (3) where the intensity of the reflected wave of the first ultrasonic beam is lower than the intensity of the reflected wave of the second ultrasonic beam can be identified as the softened tissue (21). From the divided region (32) identified as the softened tissue (21) in the inspection object (3), the position and size of the softened tissue (21) in the inspection object (3) can be estimated.

[0078] 3) In some embodiments, the soft tissue detection method (M2) according to 2) above, The inspection object (3) includes at least one weld cross section (31) along a direction perpendicular to the welding direction of the weld metal (2), The determination step (S23) A first flaw detection image generating step (S232) of generating a first flaw detection image, which is a flaw detection image of the at least one weld cross section (31) by the first ultrasonic beam, based on the ultrasonic flaw detection result of the first flaw detection step (S21); The method includes a second inspection image generation step (S233) of generating a second inspection image, which is an inspection image of the at least one weld cross section (31) by the second ultrasonic beam, based on the ultrasonic inspection result of the second inspection step (S22).

[0079] According to the method of 3) above, the display states of the softened structure (21) and the columnar crystals (22) are different in the first and second flaw detection images. Therefore, it is possible to easily identify whether the structure is the softened structure (21) or the columnar crystals (22) from the first and second flaw detection images. Therefore, the presence or absence of the softened structure (21) in the weld metal (2) can be easily determined by using an image analysis technique or the like.

[0080] 4) In some embodiments, the soft tissue detection method (M2) according to 3) above, The determination step (S23) The method further includes an image estimation step (S234) of estimating the position and size of the softened tissue (21) within the weld cross section (31) by comparing a first feature value corresponding to the intensity of the reflected wave of the first ultrasonic beam in the first inspection image with a second feature value corresponding to the intensity of the reflected wave of the second ultrasonic beam in the second inspection image for each of a plurality of divided areas (32) defined in the weld cross section (31).

[0081] According to the method of 4) above, the divided regions (32) in the weld cross section (31) where the first characteristic value is higher than the second characteristic value can be identified as columnar crystals (22), and the divided regions (32) in the weld cross section (31) where the first characteristic value is lower than the second characteristic value can be identified as softened structures (21). From the divided regions (32) identified as the softened structures (21) in the weld cross section (31), the position and size of the softened structures (21) in the weld cross section (31) can be estimated.

[0082] 5) In some embodiments, the soft tissue detection method (M2) according to any one of 1) to 4) above, a probe moving step (S24) of moving the at least one angle probe (41), the transmitting probe (42), and the receiving probe (43) along a welding direction of the weld metal (2), The inspection object (3) includes a plurality of weld cross sections (31) along a direction perpendicular to the welding direction of the weld metal (2), the plurality of weld cross sections (31) being spaced apart from each other along the welding direction.

[0083] According to the method of (5) above, the presence or absence of softened tissue (21) can be determined in each of the multiple weld cross sections (31) by moving the bevel probe (41), the transmitting probe (42), and the receiving probe (43) along the welding direction of the weld metal (2). By determining the presence or absence of softened tissue (21) in each of the multiple weld cross sections (31), the position and size of the softened tissue (21) in the welding direction of the weld metal (2) can be estimated.

[0084] 6) In some embodiments, the soft tissue detection method (M2) according to any one of 1) to 5) above, The at least one angle probe (41) A first angle beam probe (41A); a second angle probe (41B) disposed between the first angle probe (41A) and the weld metal (2), In the first flaw detection step (S21), ultrasonic flaw detection is performed to obtain reflected waves of the first ultrasonic beam returning to each of the first angle beam probe (41A) and the second angle beam probe (41B).

[0085] According to the method of (6) above, the first ultrasonic beam from the first angle probe (41A) can be incident on the columnar crystal (22A) formed on the side of the first angle probe (41A) at the weld cross section (31) along a direction perpendicular to the extension direction of the columnar crystal (22A), so that the position and size of the columnar crystal (22A) that is the reflection source can be estimated with high accuracy. Similarly, the first ultrasonic beam from the second angle probe (41B) can be incident on the columnar crystal (22B) formed on the side of the second angle probe (41B) at the weld cross section (31) along a direction perpendicular to the extension direction of the columnar crystal (22B), so that the position and size of the columnar crystal (22B) that is the reflection source can be estimated with high accuracy.

[0086] 7) The remaining life estimation method (M3) according to at least one embodiment of the present disclosure includes: A method (M3) for estimating a remaining life of a weld metal (2), comprising: The present invention further includes a remaining life estimation step (S31) of estimating a remaining life of the weld metal (2) from the determination result of the determination step (S23) obtained in the softened tissue detection method (M2) described in 2) or 4) above, by utilizing a relationship between the determination result of the determination step (S23) of the softened tissue detection method (M2) described above and a reduction rate of a remaining life of the weld metal (2).

[0087] According to the above method (7), the remaining life of the weld metal (2) can be estimated from the position and size of the softened tissue (21) in the object (3) obtained from the judgment result in the judgment step (S23) of the softened tissue detection method (M2).

[0088] 8) In some embodiments, the remaining life estimation method (M3) according to 7) above, The remaining life estimation step (S31) includes: an area ratio calculation step (S311) of calculating an area ratio of the softened tissue (21) based on a result of the determination step (S23); and a remaining life reduction rate calculation step (S312) of calculating a reduction rate of a remaining life of the weld metal (2) from the area ratio of the softened structure (21) calculated in the area ratio calculation step (S311) by utilizing a relationship between the area ratio of the softened structure (21) and a reduction rate of a remaining life of the weld metal (2).

[0089] According to the above method (8), there is a tendency that the higher the area ratio of the softened structure (21), the higher the reduction rate of the remaining life of the weld metal (2). By utilizing such a relationship between the area ratio of the softened structure (21) and the reduction rate of the remaining life of the weld metal (2), the reduction rate of the remaining life of the weld metal (2) can be calculated from the area ratio of the softened structure (21) calculated in the area ratio calculation step (S311).

[0090] 9) At least one embodiment of the test object selection method (M1) according to the present disclosure includes: An inspection object selection method (M1) for selecting a weld metal (2) to be inspected for the presence or absence of softened tissue (21) in the softened tissue detection method (M2) according to any one of 1) to 6), comprising: A welding pass distance acquisition step (S11) for acquiring a welding pass distance of a plurality of weld metals (2) which are candidates for the inspection object; and a weld metal selection step (S12) of selecting the weld metal (2) to be inspected, taking into consideration the weld pass distance of the plurality of weld metals (2) acquired in the weld pass distance acquisition step (S11).

[0091] According to the method of (9) above, the shorter the weld pass distance of the weld metal (2), the greater the local heat input during welding, and therefore the higher the risk of softened tissue (21) occurring in the weld metal (2). Since the weld pass distance of the weld metal (2) is strongly related to the risk of softened tissue (21) occurring, by using the weld pass distance of the weld metal (2) as a parameter, the weld metal (2) having a high risk of softened tissue (21) occurring can be selected as the inspection target. [Explanation of symbols]

[0092] 1. Ultrasonic inspection system 2. Weld metal 3. Subjects of Inspection 4A,4B Ultrasonic probe 11 Measuring equipment 12 Judgment device 13 Display device 20 Welding 21 Soft tissue 22,22A,22B Columnar crystal 23 Welding flaws 24 Welding passes 31 Welding cross section 32 Split area 41,41A,41B,44 Angle angle probe 42 Transmitting transducer 43 Receiving transducer M Soft tissue evaluation method M1 Inspection target selection method M2 Soft tissue detection method M3 remaining life estimation method S11 Step for obtaining distance between welding paths S12 Welding metal selection step S21 First inspection step S22 Second inspection step S23 Judgment step S31 Remaining life estimation step

Claims

1. A softened tissue detection method for detecting softened tissue in an inspection object of a weld metal by ultrasonic testing, comprising: a first inspection step of performing ultrasonic inspection in which a first ultrasonic beam is incident on the inspection object from at least one angle probe along an inclination direction and a reflected wave of the first ultrasonic beam returning to the angle probe is obtained; a second inspection step of performing ultrasonic inspection in which a second ultrasonic beam is irradiated from a transmitting probe to the inspection object along an inclined direction, and a reflected wave of the second ultrasonic beam is acquired by a receiving probe disposed between the transmitting probe and the receiving probe and sandwiching the weld metal; A softened tissue detection method comprising: a determination step of determining the presence or absence of the softened tissue in the inspection object based on the ultrasonic inspection results of the first inspection step and the ultrasonic inspection results of the second inspection step.

2. In the determination step, and an estimation step of estimating the position and size of the softened tissue in the test object by comparing information on the intensity of the reflected wave of the first ultrasonic beam obtained from the ultrasonic inspection result of the first inspection step with information on the intensity of the reflected wave of the second ultrasonic beam obtained from the ultrasonic inspection result of the second inspection step for each of a plurality of divided regions in the test object. The method of claim 1 .

3. The inspection object includes at least one weld cross section along a direction perpendicular to the welding direction of the weld metal, The determining step includes: a first flaw detection image generating step of generating a first flaw detection image, which is a flaw detection image of the at least one weld cross section by the first ultrasonic beam, based on an ultrasonic flaw detection result of the first flaw detection step; A second inspection image generating step of generating a second inspection image which is an inspection image of the at least one weld cross section by the second ultrasonic beam based on the ultrasonic inspection result of the second inspection step. The method of claim 1 .

4. The determining step includes: The method further includes an image estimation step of estimating a position and a size of the softened tissue in the weld cross section by comparing a first feature value corresponding to an intensity of the reflected wave of the first ultrasonic beam in the first inspection image with a second feature value corresponding to an intensity of the reflected wave of the second ultrasonic beam in the second inspection image for each of a plurality of divided regions each defined in the weld cross section. The method of claim 3 .

5. a probe moving step of moving the at least one angle probe, the transmitting probe, and the receiving probe along a welding direction of the weld metal; The inspection object includes a plurality of weld cross sections along a direction perpendicular to the welding direction of the weld metal, the plurality of weld cross sections being spaced apart from each other along the welding direction. A method for detecting soft tissue according to any one of claims 1 to 4.

6. The at least one angle beam probe comprises: a first angle beam probe; a second angle beam probe disposed between the first angle beam probe and the weld metal, In the first flaw detection step, ultrasonic flaw detection is performed to obtain reflected waves of the first ultrasonic beam returning to each of the first angle beam probe and the second angle beam probe. A method for detecting soft tissue according to any one of claims 1 to 4.

7. A remaining life estimation method for estimating a remaining life of a weld metal, comprising the steps of: a remaining life estimation step of estimating a remaining life of the weld metal from the determination result of the determination step obtained by the softened structure detection method according to claim 2 or 4, by utilizing a relationship between the determination result of the determination step and a reduction rate of a remaining life of the weld metal. Remaining life estimation method.

8. The remaining life estimation step includes: an area ratio calculation step of calculating an area ratio of the softened tissue based on a result of the determination step; a remaining life reduction rate calculation step of calculating a reduction rate of a remaining life of the weld metal from the area rate of the softened structure calculated in the area rate calculation step, utilizing a relationship between the area rate of the softened structure and a reduction rate of a remaining life of the weld metal. The remaining life estimation method according to claim 7.

9. A method for selecting an inspection object for selecting a weld metal to be inspected for the presence or absence of softened tissue in the softened tissue detection method according to any one of claims 1 to 4, comprising: a welding pass distance acquisition step of acquiring a welding pass distance of a plurality of weld metals which are candidates for the inspection object; a weld metal selection step of selecting the weld metal to be the inspection object in consideration of the weld pass distances of the plurality of weld metals acquired in the weld pass distance acquisition step, Method of selecting test objects.

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