Ultrasonic flaw detection method

Abstract

To provide an ultrasonic flaw detection method capable of more precisely and stably inspecting a bolt.SOLUTION: In an ultrasonic flaw detection method for detecting a defect in a bolt that fastens and fixes members to each other, the bolt has a rod-shaped shaft portion extending along an axis and a head portion provided at an end of the shaft portion on one side in an axial direction. The method includes a step of emitting an ultrasonic wave toward a target region in an under-neck portion, which is a connection portion between the head portion and the shaft portion, from a position separated in a radial direction with respect to the axis, and a step of receiving an ultrasonic wave reflected by a defect. In the step of emitting the ultrasonic wave, the ultrasonic wave is incident in an angle range of 30° to 65° with respect to the axis in a cross-sectional view including the axis.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an ultrasonic flaw detection method. [Background technology]

[0002] In nuclear power plants and the like, ultrasonic waves are commonly used to detect defects that occur in various components exposed to high temperatures and pressures. In particular, to check the soundness of bolts, a technique has been proposed in which ultrasonic waves are applied not on the bolt axis but from a position slightly spaced radially from the axis, as described in Patent Document 1 below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-240570 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above Patent Document 1, detailed relative positions with respect to the bolt are not considered or disclosed, and there is an issue that the inspection results vary depending on the worker.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an ultrasonic flaw detection method that can inspect bolts more precisely and stably. [Means for solving the problem]

[0006] In order to solve the above problems, the ultrasonic flaw detection method disclosed herein is an ultrasonic flaw detection method for detecting defects in a bolt that fastens components together, wherein the bolt has a rod-shaped shank extending along an axis and a head provided at one end of the shank in the axial direction, and includes the steps of: irradiating ultrasonic waves from a position radially spaced from the axis toward a target area in a neck portion that is a connection between the head and the shank; and receiving ultrasonic waves reflected by the defect, wherein in the irradiating step, the ultrasonic waves are irradiated at an angle range of 30° to 65° with respect to the axis in a cross-sectional view including the axis. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide an ultrasonic flaw detection method that enables more precise and stable bolt inspection. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of a bolt that is a target of ultrasonic flaw detection according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is an explanatory diagram showing the relative positions of a probe and a target area in the ultrasonic flaw detection method according to the first embodiment of the present disclosure, as viewed from a radial direction relative to the axis of the bolt. [Figure 3] 3 is a flowchart showing each step of the ultrasonic flaw detection method according to the first embodiment of the present disclosure. [Figure 4] FIG. 10 is an explanatory diagram showing the relative positions of a probe and a target area in an ultrasonic flaw detection method according to a second embodiment of the present disclosure, as viewed from a radial direction relative to the axis of the bolt. [Figure 5] FIG. 10 is an explanatory diagram showing the relative positions of a probe and a target area in an ultrasonic flaw detection method according to a second embodiment of the present disclosure, as viewed from the axial direction of the bolt. [Figure 6] FIG. 10 is an explanatory diagram showing the relative positions of a probe and a target area in an ultrasonic flaw detection method according to a third embodiment of the present disclosure, as viewed from a radial direction relative to the axis of the bolt. DETAILED DESCRIPTION OF THE INVENTION

[0009] First Embodiment An ultrasonic testing method according to a first embodiment of the present disclosure will be described below with reference to FIGS. 1 to 3. This ultrasonic testing method is used, as an example, to inspect the integrity of bolts 1 that are widely used in reactor internals of pressurized water reactors. In reactor internals, many bolts 1 are used to fasten plate-like members. The reactor internals are important members that adjoin fuel assemblies, which are the energy source for nuclear power generation, and form the boundary of the reactor core. Therefore, it is necessary for these bolts 1 to maintain their fastening function, i.e., to maintain the integrity of the bolts, over a long period of service.

[0010] (Bolt configuration) First, the shape of a bolt 1 having a target region for the ultrasonic flaw detection method will be described with reference to Fig. 1. As shown in Fig. 1, the bolt 1 has a shank 11, a head 12, and a neck portion 13. The shank 11 is cylindrical and has an axis O as its center, and has a male thread 14 cut on the outer circumferential surface at one end in the direction of the axis O. This male thread 14 is threaded into a female thread formed on another member, thereby fastening these members together.

[0011] The head 12 is provided on one side of the shaft portion 11 in the direction of the axis O. The head 12 has a flange portion 21 and an anti-rotation portion 22. The flange portion 21 has a cylindrical shape with the axis O as its center of gravity. The diameter of the circumscribing circle of the flange portion 21 is larger than the diameter of the shaft portion 11. The anti-rotation portion 22 is provided integrally with the flange portion 21. The anti-rotation portion 22 has a hexagonal shape that protrudes from the flange portion 21 on one side in the direction of the axis O. A notch 23 for locating a pin 30 is formed in a portion of the circumferential direction of the anti-rotation portion 22.

[0012] The neck portion 13 is provided between the head portion 12 and the shaft portion 11, thereby integrally connecting them. The diameter of the neck portion 13 gradually decreases from the lower end of the head portion 12 toward the other side in the direction of the axis O. The diameter of the end of the neck portion 13 on the other side in the direction of the axis O is equal to the diameter of the shaft portion 11.

[0013] As described above, since the head 12 of the bolt 1 is provided with a rotation prevention portion 22 and a pin 30 is inserted, if ultrasonic waves are incident directly from the direction of the axis O as in conventional flaw detection testing of the bolt 1, the ultrasonic waves are scattered by the pins 30, etc., and accurate flaw detection testing cannot be performed.

[0014] (Ultrasonic flaw detection method) An ultrasonic flaw detection method for solving these problems will be described with reference to Figures 2 and 3. As an example, as shown in Figure 2, a bolt 1 is formed by fastening together a first member 51 that extends flat and a second member 52 that extends in a direction perpendicular to the first member 51 (i.e., in the direction of the axis O of the bolt 1). A probe 40 is placed on the surface of the first member 51. The probe 40 is configured to be able to transmit ultrasonic waves and receive reflected waves. A flaw detection test is performed on the bolt 1 and the probe 40 with the bolt 1 and the probe 40 surrounded by a liquid such as water.

[0015] In this method, the probe 40 is placed at a position radially spaced from the axis O on the surface of the first member 51. The distance P between the ultrasonic wave incidence point of the probe 40 and the axis O is 10 mm to 40 mm, and most preferably, this distance P is 23±10 mm.

[0016] Furthermore, the range (angle range) of the angle θ1 between the incident direction of the ultrasonic waves and the axis O is from 30° to 65°. As long as the angle range of θ1 can be maintained, the probe 40 does not necessarily have to be disposed on the surface of the first member 51, and may be slightly spaced apart.

[0017] In this state, the steps shown in Figure 3 are executed. In step S1, the inspection target area of ​​the neck portion 13 of the bolt 1 as described above is determined. Based on this target area, the position of the probe 40 and the angle of incidence of the ultrasonic waves are set. In step S2, ultrasonic waves are emitted from the probe 40 toward the target area. If a defect is present in the target area in this state, the ultrasonic waves are reflected by the defective area. In step S3, this reflected wave is received by the probe 40. In step S4, the characteristics of the defect are determined by analysis based on the waveform and intensity of this reflected wave. This completes the steps of the ultrasonic flaw detection method.

[0018] (Action and effect) In conventional flaw detection testing of bolts 1, because the head 12 is provided with a rotation prevention portion 22 and has a pin 30 inserted therein, if ultrasonic waves are directly incident from the direction of the axis O, they are diffusely reflected by the pin 30, etc., making it impossible to perform accurate flaw detection testing. To solve this problem, the present embodiment employs the above-mentioned methods.

[0019] As shown in Fig. 1, defects occurring in the neck portion 13 of the bolt 1 often propagate within a range of 0° to 60° in angle θx relative to the radial direction of the axis O in a cross-sectional view including the axis O. According to the above method, ultrasonic waves can be stably incident on crack surfaces (defects) within this range, and can be incident at an angle close to 90°. This significantly improves the detection accuracy of the defect and significantly reduces the possibility of overlooking an inspection.

[0020] When a liquid such as water is sealed in the gap between the head 12 of the bolt 1 and the first member 51, the difference in sound speed and density between the head 12, the first member 51, and the liquid causes propagation loss and refraction of ultrasonic waves between them. However, ultrasonic waves can propagate between these two members, and the constraints on the ultrasonic wave incidence conditions that were limited by the shape of the bolt 1 are eliminated, so that the ultrasonic waves are incident perpendicular to the crack surface (defect) that occurs in the neck portion 13.

[0021] According to the above method, by using a single probe 40, it is possible to easily and accurately perform ultrasonic flaw detection by simply adjusting the position of the single probe 40. This makes it possible to significantly reduce the cost and time required for inspection. As a result, it is possible to improve the plant's operating rate.

[0022] The first embodiment of the present disclosure has been described above. Note that various changes and modifications can be made to the above configuration without departing from the gist of the present disclosure.

[0023] Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to Figures 4 and 5. Note that the same components as those in the first embodiment above are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0024] As shown in Fig. 4, in this embodiment, two different probes (an incident-side probe 41 and a receiving-side probe 42) are used for the ultrasonic wave incident side and receiving side. The incident angle θ2 of the ultrasonic wave is preferably in the angle range of 30° to 65° with respect to the axis O. Most preferably, the angle range is 62±2°. The angle (receiving angle θ2) that the ultrasonic wave makes with the axis in the receiving-side probe 42 is also the same as above.

[0025] Furthermore, as shown in FIG. 5, when viewed from the direction of the axis O, it is desirable that the distance Q between the incident point A of the incident-side probe 41 and the axis O (or the neck portion 13) be set to be equal to the distance R between the reception point B of the receiving-side probe 42 and the axis O (or the neck portion 13). Also, it is desirable that the range of the angle θ3 formed by the first line L1 connecting the incident point A of the incident-side probe 41 and the axis O (or the neck portion 13) and the second line L2 connecting the incident point A of the incident-side probe 41 and the reception point B of the receiving-side probe 42 is 10° to 20°. Most desirably, this angle θ3 is 14°. Furthermore, it is desirable that the length S of the line L2 connecting the incident point A and the reception point B is 50 mm to 80 mm. Most desirably, the distance S is 64±10 mm.

[0026] The target area onto which the ultrasonic waves are incident may be located at a small radial distance X from the axis O. This is to detect defects that have developed at shallow positions near the surface of the neck portion 13.

[0027] (Action and effect) According to the above method, different probes (incident-side probe 41 and receiving-side probe 42) are used on the incident side and the receiving side. As a result, even if the incident angle and reflection angle of the ultrasonic waves are not symmetrical with respect to the axis O, it is possible to receive the reflected components with high accuracy by appropriately adjusting the position of the receiving-side probe 42. This further improves the accuracy of defect detection.

[0028] According to the above method, defects can be detected over a wide range in the circumferential direction of the bolt 1 with high accuracy.

[0029] The second embodiment of the present disclosure has been described above. Note that various changes and modifications can be made to the above configuration without departing from the spirit and scope of the present disclosure.

[0030] Third Embodiment Next, a third embodiment of the present disclosure will be described with reference to Fig. 6. Note that the same components as those in the above embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0031] As shown in FIG. 6, this embodiment uses a single phased array type probe 43. Unlike the probe 40 of the first embodiment, this probe 43 is capable of irradiating ultrasonic waves within an arbitrary angular range. In other words, ultrasonic waves are scanned within an arbitrary angular range by oscillating vertically. The angle θ4 ranges from 30° to 65°. The relative distance between the probe 43 and the axis O is 10 mm to 40 mm, as in the first embodiment, and most preferably, this distance is 23±10 mm.

[0032] (Action and effect) According to the above method, ultrasonic waves are incident on the target area within a given angular range. This allows for highly accurate detection of all defects within that angular range. Furthermore, since a wide angular range can be achieved using only a single probe 43, the time and cost required for inspection can be significantly reduced. This can improve the plant's operating rate.

[0033] (Other embodiments) The above describes in detail the embodiments of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present disclosure.

[0034] For example, the location where the bolt 1 is provided is not limited to between the first member 51 and the second member 52. Furthermore, the ultrasonic flaw detection method is not limited to applications in nuclear power plants.

[0035] <Additional Notes> The ultrasonic flaw detection method described in each embodiment can be understood, for example, as follows.

[0036] (1) The ultrasonic flaw detection method according to the first aspect is an ultrasonic flaw detection method for detecting defects in a bolt 1 that fastens components together, wherein the bolt 1 has a rod-shaped shank 11 extending along an axis O and a head 12 provided at one end of the shank 11 in the direction of the axis O, and includes the steps of: irradiating ultrasonic waves from a position radially spaced apart from the axis O toward a target area in a neck portion 13 that is the connection between the head 12 and the shank 11; and receiving ultrasonic waves reflected by the defect, wherein in the irradiating step, the ultrasonic waves are irradiated at an angle range of 30° to 65° with respect to the axis O in a cross-sectional view including the axis O.

[0037] According to the above method, it is possible to significantly improve the accuracy of defect detection and to significantly reduce the possibility of inspection omissions.

[0038] (2) The ultrasonic flaw detection method according to a second aspect is the ultrasonic flaw detection method according to (1), in which the same probe 40 is used in the incident step and the receiving step.

[0039] According to the above method, once the position of one probe 40 is adjusted, ultrasonic flaw detection can be carried out easily and with high accuracy.

[0040] (3) The ultrasonic flaw detection method according to the third aspect is the ultrasonic flaw detection method of (1), in which an incident side probe 41 that incidents the ultrasonic waves is used in the incident step, and a receiving side probe 42 different from the incident side probe 41 that receives the reflected ultrasonic waves is used in the receiving step.

[0041] According to the above method, by appropriately adjusting the position of the receiving probe 42, it is possible to receive the reflected components with high accuracy.

[0042] (4) The ultrasonic flaw detection method according to the fourth aspect is the ultrasonic flaw detection method of (3), wherein, when viewed from the direction of the axis O, the distance between the incident side probe 41 and the axis O is set to be equal to the distance between the receiving side probe 42 and the axis O, and the angle formed by the first line connecting the incident side probe 41 and the axis O and the second line connecting the incident side probe 41 and the receiving side probe 42 is 10° to 20°.

[0043] According to the above method, defects can be detected over a wide range in the circumferential direction of the bolt 1 with high accuracy.

[0044] (5) The ultrasonic flaw detection method according to the fifth aspect is the ultrasonic flaw detection method of (1), wherein the step of injecting uses a phased array method in which the ultrasonic waves are injected toward the target area within the angle range.

[0045] According to the above method, defects included in the angle range can be detected with high accuracy without leaving any out. [Explanation of symbols]

[0046] 1...Bolt 11...Shaft 12...Head 13...Under the neck 14...Male thread 21...Flange 22...Stop 23...Notch 30...pin 40…Probe 41...Incidence side probe 42...Receiving probe 43…Probe 51...First member 52...Second member O…Axis line

Claims

1. An ultrasonic flaw detection method for detecting defects in a bolt that fastens members together, comprising: The bolt has a rod-shaped shaft portion extending along an axis and a head portion provided at one end of the shaft portion in the axial direction, irradiating an ultrasonic wave from a position spaced apart in a radial direction relative to the axis toward a target area in a lower neck portion, which is a connection portion between the head and the stem; receiving ultrasonic waves reflected by the defect; Including, In the step of irradiating, the ultrasonic waves are irradiated at an angle ranging from 30° to 65° with respect to the axis in a cross-sectional view including the axis.

2. The ultrasonic flaw detection method according to claim 1 , wherein the same probe is used in the incident step and the receiving step.

3. 2. The ultrasonic flaw detection method according to claim 1, wherein the step of injecting uses an incident side probe that injects the ultrasonic waves, and the step of receiving uses a receiving side probe different from the incident side probe that receives the reflected ultrasonic waves.

4. a distance between the incident-side probe and the axis when viewed from the axial direction is set to be equal to a distance between the receiving-side probe and the axis; 4. The ultrasonic flaw detection method according to claim 3, wherein an angle formed between a first line connecting the incident side probe and the axis and a second line connecting the incident side probe and the receiving side probe is 10° to 20°.

5. The ultrasonic flaw detection method according to claim 1 , wherein the step of irradiating the ultrasonic waves uses a phased array method in which the ultrasonic waves are irradiated toward the target area at any angle within the angle range.

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