JP5468408B2 - Inspection method of bolt screw part in use - Google Patents

Description

  The present invention relates to a method for inspecting corrosion or thinning of a bolt screw portion, which has a screw portion covered with concrete, grout material or the like, without disassembling in a use state. More specifically, the present invention relates to a method capable of quantitatively estimating the progress of corrosion or thinning of a bolt screw part.

  It has been confirmed that the embedded foundation bolts embedded in concrete cause thinning due to corrosion. From the viewpoint of maintaining the seismic resistance of the equipment, it is necessary to reliably detect foundation bolts with reduced thickness. As inspection of the foundation bolt, visual inspection and percussion inspection are performed. The visual inspection has a problem that the portion embedded in the foundation cannot be confirmed. In the percussion examination, it is difficult to set an objective standard because it is influenced by the surrounding environment and individual differences. Thus, the method of detecting the thinning in the foundation bolt has not been established yet.

  Among various non-destructive inspection methods, an ultrasonic inspection method that is a volume inspection method is preferable as an inspection method that can be applied to the detection of the thinning of a bolt hidden in the foundation of a concrete building or equipment. The pulse echo method in the ultrasonic flaw detection method is a method of scanning a probe on the surface of an inspection object and receiving an echo from a defect. It is considered that invisible bolt thinning can be detected using this method. However, in the conventional ultrasonic flaw detection method, one probe can transmit and receive only one direction of ultrasonic waves with high sensitivity. Unless the inclination of the defect in the bolt is grasped in advance, it is difficult to determine the propagation direction of the ultrasonic wave that can detect the defect well. Therefore, the conventional ultrasonic flaw detection method sometimes cannot detect a defect in the bolt. In the conventional ultrasonic flaw detection method, the presence or absence of a defect is determined using a flaw detection waveform. At that time, since the echo from the screw part or the echo by the mode conversion overlaps with the defect echo, it is difficult to determine the presence or absence of the defect in the bolt. In contrast, the phased array ultrasonic flaw detection method uses a single probe to control a plurality of transducers by electrically controlling transmission / reception timing for each transducer composed of a plurality of transducers. This is a technology that can utilize ultrasonic waves propagating in the direction. Further, in this method, the flaw detection result can be displayed as a cross-sectional image instead of the flaw detection waveform. From these facts, it is considered that the defect in the bolt can be measured with high accuracy by using the phased array ultrasonic flaw detection method.

  For example, a phased array type probe is brought into close contact with the end face of a bolt in use, an ultrasonic beam is incident in the diameter direction passing through the bolt center while continuously changing the refraction angle by sector scanning the probe, The ultrasonic echo reflected from the screw part of the bolt is received, and a cross-sectional image in the diameter direction of the bolt screw part is displayed from the ultrasonic echo. From this cross-sectional image, the ultrasonic echo from the bolt screw part is regularly arranged in the bolt length direction. There has been proposed a method for inspecting a bolt screw part in use that is judged to be a healthy part when it is displayed and is judged to be a defective part when there is a missing ultrasonic echo from the bolt screw part (Patent Document 1).

JP 2007-132908 A

  However, in the bolt screw portion inspection method described in Patent Document 1, it is only possible to determine whether the ultrasonic echo from the bolt screw portion is regularly displayed in the length direction of the bolt, whether it is sound or defective. It is impossible to estimate the progress of the thinning and the like, that is, the quantitative inspection of the amount and the depth, the area of the thinning, and the like.

  That is, there is a problem that it is not possible to accurately determine whether or not the thinning depth can be safely used because the depth of thinning cannot be quantitatively evaluated. In fact, a safety factor is expected for a bolt that supports a structure such as a foundation bolt. For example, safety tolerances are expected for embedded foundation bolts such as tanks and pumps in nuclear power plants so that they can withstand thinning to half the cross-sectional area. That is, if the thinning is uniformly generated on the entire circumference, it can be safely used up to 30% of the diameter. Moreover, even if the thickness is locally reduced or corroded, there is no safety problem until the thickness is reduced to 1/2. For this reason, even if the presence or absence of thinning can be simply detected, if it is not possible to determine whether the cross-sectional area is ½ or less, it is necessary to replace the foundation bolt until the foundation is destroyed. It is difficult to determine whether or not there is a problem, and it is not a practical inspection method.

  Furthermore, even if the screw portion is thinned or cracked, there is a situation in which the ultrasonic echo from the screw portion does not disappear so much that the local thinning or crack of the screw portion is overlooked and may not be detected. In addition, it is impossible to respond to the case where it is desired to reduce the thickness of the screw portion and identify the crack after investigating the cause of the bolt breakage or the like.

  Furthermore, an effective judgment about the safety of the foundation bolt can be obtained only by determining the depth of the thinning, but if the thinning area is obtained, a more accurate judgment can be made on the safety. It is desired.

  An object of the present invention is to provide an inspection method capable of quantitatively estimating the progress of corrosion or thinning of a bolt screw part.

In order to achieve such an object, the present invention changes the refraction angle continuously in the diameter direction passing through the center of the bolt while the phased array probe is brought into close contact with the end face of the bolt in use and rotated once. A sector scan that receives an ultrasonic echo that is incident and reflects an ultrasonic echo reflected from the screw part of the bolt is performed to create a categorical view and a side view of the bolt screw part from the screw part echo. In the inspection method of the bolt screw part in use that detects the thinned part using disappearance, the part where the indication of the screw part disappeared from the side view is identified as the thinned part, and the position of the maximum width part of the indication disappearing part Is determined as the position of the thinned portion in the axial direction from the end surface of the bolt to the thinned portion, and the axial distance l from the bolt end surface of the thinned portion is obtained, and the thinning error appearing in the side view is obtained. The maximum amplitude value of the thinning echo for each ultrasonic propagation direction is read from the instruction of-, the largest maximum amplitude value is obtained from the maximum amplitude values for each ultrasonic propagation direction, and the largest maximum amplitude value is obtained. The half angle is obtained as the refraction angle θ, and the radius r of the thinned portion is obtained from r = l · tan θ using the refraction angle θ and the axial distance l from the bolt end face of the thinned portion, and then the thinned portion The depth d of the thinned portion is determined from the difference between the radius r of the bolt and the diameter R of the bolt determined in advance.

  Here, it is preferable to use a probe having a frequency of 5 MHz for the phased array probe. It is also possible to qualitatively determine the depth of thinning in relation to the delay in the appearance position of the thinning echo with respect to the maximum width position of the disappearance portion of the screw portion echo.

  According to the bolt thinning inspection method of the present invention, not only the axial position and the circumferential position of the thinning of the screw portion of the bolt that is not exposed can be detected, but also the maximum depth of the thinning can be estimated. Progress can be estimated quantitatively, such as the amount of meat, the depth, and the area of thinning. For this reason, it is possible to accurately determine whether or not the bolt to be inspected can be used safely in the future. According to experiments by the present inventors, it has been clarified that the thinning position is estimated with an error within 3.6% from the depth corresponding to the maximum disappearance width of the screw portion echo. This estimation accuracy is quite accurate in the ultrasonic flaw detection method.

  Further, when a probe having a frequency of 5 MHz is used, when the thinning is in the screw portion, a phenomenon that a part of the echo of the screw portion disappears can be observed without fail, and all the thinning can be detected. In addition, in the case of a frequency of 5 MHz, even if there is a crack in the screw part, the screw part echo does not disappear and appears overlapping with the defect echo from the crack, so using the difference in the screw part echo due to thinning and cracking, It is possible to identify thinning and cracks in the threaded portion.

  In addition, since the relationship between the delay in the appearance position of the thinning echo with respect to the maximum width position of the disappearance part of the screw part echo has a correlation with the thinning depth, only by judging the appearance position of the thinning echo on the image, It is possible to judge the thickness of the thinning depth qualitatively.

  Furthermore, according to the bolt thinning inspection method of the present invention, it is possible to measure the maximum depth not only in the local thinning but also in the entire circumferential thinning.

In the principle diagram of the bolt thinning inspection method of the present invention, it is shown by ultrasonic wave propagation analysis that longitudinal waves excited by the probe are received as thinning echoes after being mode-converted twice by thinning. It is a thing. It is a flowchart figure which shows one Embodiment of the bolt thinning inspection method of this invention. It is a figure which shows an example of the flaw detection result by the bolt thinning test | inspection method of this invention, (A) shows a tactical view, (B) shows a side view. It is a perspective view which shows one Embodiment of a measurement jig. It is a graph which shows the correlation with the estimation result of the thinning depth of the bolt by the bolt thinning inspection method of the present invention, and the thinning depth measured by the racer. The (A) side view and (B) the merged side view when the axial thinning position is read from the side view using the disappearance of the screw part echoes are respectively shown. It is a figure explaining the method to set the ultrasonic propagation direction (alpha) in a sectial view, (A) shows a sectial view and (B) shows a side view. It is a figure explaining the process of reading the maximum amplitude value of a thinning echo in the side view corresponding to the ultrasonic propagation direction (alpha), (A) shows a sectional view and (B) shows a side view. It is a figure explaining the process of reading the maximum amplitude value of a thinning echo in the side view corresponding to the ultrasonic propagation direction (alpha), (A) shows a sectional view and (B) shows a side view. It is a figure explaining the estimation method of a thinning area, (A) is the case of fan-shaped thinning of an angle of less than 180 °, (B) ~ (D) is the case of fan-shaped thinning of an angle of 180 ° or more (C) shows the cross section of the bolt remaining after thinning, and (D) shows the semicircular cross section that it approximated. (A)-(h) shows eight types of bolt test bodies used in the confirmation experiment of the bolt thinning inspection method of the present invention. (A)-(c) shows the three types of embedded bolt test bodies used in the confirmation experiment of the bolt thinning inspection method of the present invention. Specimen No. The measurement result in 1 is shown, (a) is a result using a probe with a frequency of 5 MHz, and (b) is a result using a probe with a frequency of 2 MHz. The measurement result in test body RB-1 is shown, (a) is a result using a probe with a frequency of 5 MHz, and (b) is a result using a probe with a frequency of 2 MHz. The measurement result in test body RB-2 is shown, (a) is a result using a probe with a frequency of 5 MHz, and (b) is a result using a probe with a frequency of 2 MHz. Specimen No. The measurement result in 4-2 is shown, (a) is a result using a probe having a frequency of 5 MHz, and (b) is a result using a probe having a frequency of 2 MHz. Specimen No. The measurement result in 5-1, is shown, (a) is the result using the probe of frequency 5MHz, (b) is the result of using the probe of frequency 2MHz. Specimen No. The measurement result in 5-2 is shown, (a) is a result using a probe with a frequency of 5 MHz, and (b) is a result using a probe with a frequency of 2 MHz. Specimen No. 8A and 8B show the measurement results in FIG. 8, where (a) shows the results using a probe with a frequency of 5 MHz, and (b) shows the results using a probe with a frequency of 2 MHz. Specimen No. The measurement results in 8-2 are shown. (A) is a result using a probe with a frequency of 5 MHz, and (b) is a result using a probe with a frequency of 2 MHz. Specimen No. 10A and 10B show the measurement results in FIG. 10, where (a) shows the results using a probe with a frequency of 5 MHz, and (b) shows the results using a probe with a frequency of 2 MHz. Specimen No. 4A and 4B show measurement results, where (a) shows a result using a probe with a frequency of 5 MHz, and (b) shows a result using a probe with a frequency of 2 MHz. Specimen No. Fig. 5 shows the measurement results in Fig. 5, where (a) shows the results using a probe with a frequency of 5 MHz, and (b) shows the results using a probe with a frequency of 2 MHz. Specimen No. It is explanatory drawing which shows the analysis model which made 8 thinning object. Specimen No. predicted by analysis 8 A scopes. It is a figure explaining the state of propagation of the ultrasonic wave in a bolt. It is explanatory drawing which shows the path | route of a thinning echo.

  Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.

  FIG. 1 shows the principle of the bolt thinning inspection method of the present invention. In this bolt thinning inspection method, a phased array probe 3 is brought into close contact with the end face 2 of the bolt 1 in use, and an ultrasonic beam is incident in a diameter direction passing through the bolt center while continuously changing the refraction angle. Then, by performing a sector scan to receive the ultrasonic echo reflected from the screw part 4 of the bolt 1, when the thinned part 5 exists in the screw part 4, the screw part echo 8 is displayed in the sectional view or the side view. The existence of the thinned portion 5 is confirmed by utilizing the disappearance. As a result of the sector scan, the present inventors have found that the axial position where the circumferential disappearance width of the echo from the screw portion 4 is maximum corresponds to the position where the thickness is thinned most. At the same time, in the bolt thinning inspection method, the present inventors show that the thinning echo 7 appears after the disappearance of the screw portion echo 8, that is, the thinning echo position 7 is far from the actual thinning position. We found that it was observed. Moreover, the present inventors have found that the amplitude value of the received signal varies depending on the thickness of the thinning echo 7 observed at a position far from the disappearance portion 6 of the screw portion echo 8 indicating the actual thinning position. In other words, when the image processing is performed so that the display color is changed in accordance with the amplitude value, it has been found that the scale of the thinning can be displayed as a change in the display color. And this phenomenon is that the longitudinal wave excited by the probe is subjected to mode conversion twice by thinning and is received as a thinning echo by ultrasonic propagation analysis by the present inventors. Was revealed.

  The method of inspecting a bolt screw portion in use according to the present invention is based on such knowledge, and the phase of the phased array probe 3 is brought into close contact with the end surface 2 of the bolt 1 in use and is rotated once. A sector scan is performed in which an ultrasonic beam is incident from a probe with a frequency of preferably 5 MHz and an ultrasonic echo reflected from the screw part of the bolt is received while continuously changing the refraction angle in the diameter direction passing through The position of the thinned portion 5 is specified by using the disappeared portion 6 of the screw portion echo 8 that appears in the sectional view and side view of the screw portion 4 created from the sound wave echo, and attention is paid to the thinned echo by the mode conversion. The maximum depth d of the thinned portion 5 is estimated from the geometric relationship using the propagation direction in which the half value of the maximum amplitude is obtained.

  That is, the position of the maximum width portion of the portion (disappearance portion) 6 where the indication of the screw portion 4 disappears from the side view (the portion where the circumferential disappearance width of the screw portion echo 8 is maximum) is specified as the position of the thinning portion 5. The axial distance l from the bolt end surface 2 to the thinned portion 5 is obtained with the position of the maximum width portion of the indication disappearance portion 6 as the thinning position. Read the maximum amplitude value of the thinning echo for each sound wave propagation direction, find the largest maximum amplitude value from the maximum amplitude values for each ultrasonic wave propagation direction, and refract half the angle of this largest maximum amplitude value. The angle θ is obtained, and the refraction angle θ is assumed to be an angle with respect to the bolt axis up to the deepest portion of the thinned portion 5, and is reduced using the refraction angle θ and the axial distance l from the bolt end surface of the thinned portion. The radius r of the bolt of the meat part is r Determined from l · tan .theta, and requests the maximum depth d of the reduced thickness portion 5 from the difference between the diameter R of the previously sought-bolt with radius r of thinning sites.

  Specifically, as shown in FIG. 1, the phased array probe 3 is brought into close contact with the end face 2 of the bolt 1 in use, and is rotated once while performing sector scanning, so that the entire screw portion of the bolt is Collect circumference data, construct at least sectial and side views, and in some cases merge side views, whether or not there is thinning, its axial position and axial thinning length, thinning depth and necessary The thickness reduction range in the circumferential direction is determined according to

  Here, the sectional view (hereinafter referred to as SS) is an image composed of flaw detection waveforms corresponding to different ultrasonic wave propagation directions at a certain probe position, that is, an A scope of each refraction angle at a certain probe position. This is a luminance-modulated (reception echo-intensity and ultrasonic wave propagation distance display method with rectangular coordinates). For example, FIG. 3A is a categorical view at a certain position composed of a flaw detection waveform corresponding to an ultrasonic wave propagation direction from −30 ° to 30 °. Therefore, for example, if the probe is rotated at an interval of 1 ° from 0 ° to 360 °, 360 categorical views can be obtained in one rotation. The side view (hereinafter referred to as BS) is a flaw detection image composed of flaw detection waveforms at different probe positions corresponding to a certain ultrasonic wave propagation direction, that is, a luminance modulation of each A scope in the scan direction. It is. For example, the side view illustrated in FIG. 3B includes a flaw detection waveform in which the probe position is 0 ° to 360 ° in the case of the ultrasonic propagation direction 9 °. Furthermore, the merged side view (hereinafter referred to as “MBS”) is obtained by overlapping side views corresponding to different ultrasonic propagation directions, that is, by superposing B scopes having a plurality of refraction angle components.

  Hereinafter, the thinning inspection method for the bolt screw portion in use according to the present invention will be described in more detail based on the flowchart shown in FIG.

  First, the phased array probe 3 is brought into close contact with the end surface 2 (upper surface in this example) of the bolt 1 in use as shown in FIG. 1 using, for example, a rotating jig as shown in FIG. The rotating jig includes a base disk 17 fixed by screw tightening using the screw 4 of the bolt 1 to be inspected, a rotating disk 12 with external teeth that are rotatably supported around the disk 17, A portal-type probe mounting frame 13 fixed to the upper surface of the toothed rotating disk 12 and supporting the phased array probe 3 so as to be movable up and down, and meshing with the outer teeth on the peripheral surface of the rotating disk 12, the rotating disk 12 A rotary handle 14 that can rotate at an arbitrary angle and an encoder 15 that detects the rotation angle are mainly configured. The faced array probe 3 is elastically pressed against the end surface 2 of the bolt 1 by the pressing spring 16 and is rotated about the central axis of the bolt 1 by rotating the rotating disk 12 with the rotary handle 14. Attached to. At this time, the plurality of transducers constituting the probe 3 are positioned on a straight line passing through the center of the bolt 1. The probe position is input to the computer by the rotary encoder 15. The faced array probe 3 is connected to a phased array flaw detector (not shown).

  It is preferable to measure the radius R of the bolt in advance (S1) as a stage before the mounting of the phased array probe 3 to the end face 2 of the bolt 1 in use. Of course, the design value may be used for the radius R of the bolt without actually measuring it, and it may be obtained when calculating the depth of the thinned portion 5 and input to the computer from the input means. .

  Next, the axial thinning position from the side view, that is, the axial length 1 from the bolt end surface 2 to the thinning portion 5 is read from the side view using the disappearing portion 6 of the screw portion echo 8 (S2: FIG. 3B). (See FIG. 6A). At this time, the position of the maximum width portion of the indicated portion of the disappearing portion 6 of the screw portion echo 8 appearing in the side view is regarded as the position of the thinning portion 5, and the axial length l from the bolt end surface 2 to the thinning portion 5. Is read.

  Here, as a method of observing the disappearing portion 6 of the screw portion echo 8, it is preferable to employ, for example, either a method of observing a sector real view or a method of observing a side view.

  According to the method of observing the sector real view, in the sector real view, while moving the ultrasonic wave propagation direction cursor from the minimum value (for example, −30 °) to the maximum value (for example, 30 °), the screw portion echo 8 is displayed on the side view. It is observed whether or not the disappearing part 6 and the thinning echo 7 appear. Subsequently, the ultrasonic wave propagation direction cursor 9 is moved back and forth so that the thinning echo 7 is observed most clearly.

  According to the method of observing the side view, the disappearance portion 6 of the thinning echo 7 and the screw portion echo 8 appears in the sector real view while moving the probe position cursor 10 from 0 ° to 360 °. Observe whether or not. When the disappearing portion 6 of the thinning echo 7 and the screw portion echo 8 is observed, the ultrasonic wave propagation direction cursor 9 is moved so as to pass through the thinning echo 7 in the sector real view, and the screw portion echo 8 disappears in the side view. The part 6 and the thinning echo 7 are made to appear. Subsequently, the ultrasonic wave propagation direction cursor 9 is moved back and forth in the sector real view so that the thinning echo 7 is observed most clearly. If the ultrasonic propagation direction cursor 9 is moved in the sectoral view so as to be decreased by one step, for example, by 1 °, in accordance with the step size of the refraction angle set in the sector scan, the side corresponding to the ultrasonic propagation direction θ is set. The view appears automatically.

  Note that when the merged side view shown in FIG. 6B is used, it is not necessary to move the ultrasonic wave propagation direction cursor 9 as described above. This is because the side views corresponding to different ultrasonic propagation directions overlap to form a merged side view. That is, the disappearing portion 6 of the screw portion echo 8 suddenly appears in the merged side view. Moreover, the observation using the merged side view may clearly observe the disappearing portion 6 of the screw portion echo 8 even when the disappearing portion 6 of the screw portion echo 8 is unclear in the side view. At that time, it is necessary to observe the merged side view. However, in both the side view and the merged side view, if the disappearing portion 6 of the screw portion echo 8 is clear, it is sufficient to observe only the side view. Therefore, when the disappearing portion 6 of the screw portion echo 8 can be clearly observed in the side view, the observation in the merged side view is not necessary. If the value of the axial position corresponding to the maximum width of the disappearing portion 6 of the screw portion echo 8 obtained from the side view and the merged side view is different, the average value of the two is used as the axial direction position of thinning. .

Next, the ultrasonic wave propagation direction α ₀ at the disappearance position of the thinning echo 7 is determined (S3: see FIGS. 3A and 7). As for the ultrasonic wave propagation direction α ₀ , accuracy is not particularly a problem, and it is sufficient that the angle is larger than the ultrasonic wave propagation direction in which the thinning echo 7 is not observed in the sector real view. For example, as shown in FIG. 7, when the thinning echo 7 appears in the sectional view by moving the probe position cursor 10 in the side view from left to right, that is, by changing the probe rotation angle. The ultrasonic wave propagation direction cursor 9 is shaken in the sectional view to observe the thinning echo 7 appearing in the side view. Then, from the situation where the thinning echo 7 appears only in the cereal view and the thinning echo does not appear in the side view, the ultrasonic wave propagation direction 9 is decreased by 1 ° and the thinning echo appears in the side view. the position of the propagation direction cursor 9 is determined as the ultrasonic propagation direction alpha _0.

Therefore, the ultrasonic wave propagation direction is set to α (= α ₀ ) in the sectional view (step 4).

  Next, as shown in FIG. 8, the maximum amplitude value MaxAmp (α) of the thinning echo 7 is read in the side view corresponding to the ultrasonic wave propagation direction α (step 5). For example, as shown in FIG. 8B, when reading the thinning echo 7 appearing in the side view with a cursor frame 11, the maximum amplitude value corresponding to the echo is loaded in the phased array device. Automatically calculated by the software (for example, TomoView installed in TomoScan 3 manufactured by Zetec), and the value is displayed. Therefore, the value is read and input to the computer via the input means as the maximum amplitude value of the thinning echo 7 corresponding to the current ultrasonic wave propagation direction α, and stored in the memory.

  Then, it is determined whether or not (α−Δα) is smaller than 0 (step 6). If it is not smaller than 0 (step 7), the process returns to step 4 again, and steps 4 to 6 are repeated. At this time, the ultrasonic wave propagation direction cursor 9 is moved so as to decrease, for example, by 1 °, and the maximum amplitude value corresponding to each angle, that is, the ultrasonic wave propagation direction is read (see FIGS. 8 to 9). Into.

Then, it is determined whether or not (α−Δα) is smaller than 0 (step 6). When it is determined that (α−Δα) is smaller, the largest maximum value Max (MaxAmp) among the maximum amplitude values MaxAmp (α) of the thinning echo is determined. (Α)) is obtained, and then the ultrasonic propagation direction θ corresponding to the half value is obtained (step 8). When steps 4 to 6 described above are repeated, maximum thinning echo amplitude values corresponding to different ultrasonic propagation directions are obtained. Therefore, the largest maximum amplitude value Max (MaxAmp (α)) is obtained from these maximum amplitude values, and the ultrasonic wave propagation direction corresponding to the half value is obtained. If the ultrasonic wave propagation direction corresponding to the half value is between the refraction angle increments set in the sector scan, the ultrasonic propagation direction with the smaller half value and the smaller ultrasonic propagation direction The propagation direction corresponding to the half value is obtained by linear interpolation using the value of the ultrasonic propagation direction. Specifically, for example, the ultrasonic propagation direction θ corresponding to the half value is obtained from (yθ−y1) / (y2−y1) = (xθ−x1) / (x2−x1). Note that Δα is the step size of the refraction angle set in the sector scan. Here, the amplitude of the thinning echo becomes maximum in the ultrasonic wave propagation direction α in which the ultrasonic beam hits the corner from the reflection characteristics of the ultrasonic wave. As shown in FIG. 1, the ultrasonic propagation direction θ when the ultrasonic beam hits the deepest thinned portion is smaller than α. From this, an angle larger than α can be excluded as the ultrasonic wave propagation direction α ₀ .

When the ultrasonic wave propagation direction θ corresponding to the half value of the maximum value Max (MaxAmp (α)) of MaxAmp (α), that is, the refraction angle, is obtained, the refraction angle θ and the axial length l of the deepest portion of the thinned portion. Are used to determine the maximum depth d of the thinned portion 5 by the calculation of Formula 1 in the central processing unit (step 9).
[Equation 1]
d = RL−tan (θ)
Here, the radius R of the bolt is measured in advance in step 1, but a design value may be used in some cases. Then, the radius R of the bolt is read from the memory when calculating the thinning depth.

Here, if the maximum depth d of the thinned portion 5 is obtained, the thinned shape and the area can be further estimated. For example, in order to estimate the thinning area, as shown in FIG. 10, the start position Φ1 in the circumferential direction of the thinning 5 from the side view where the maximum width of the disappearing portion 6 of the screw portion echo 8 is obtained or from the merged side view. And the end position Φ2 are read. Then, the start position Φ1 and end position Φ2 obtained from the maximum width position of the disappearance portion 6 of the screw portion echo 8 and the length r from the bolt center of the maximum depth portion of the thinning portion 5 (thinning from the bolt radius). 10 (A) or 10 (B) is drawn using a value obtained by subtracting the maximum depth d). In the case of fan-shaped thinning with an angle of less than 180 ° as shown in FIG.
[Equation 2]
Thinning area = R ・ R ・ (Φ2-Φ1) / 2-R ・ r ・ sin [(Φ2-Φ1) / 2]
From this, the area of thinning is obtained.
Further, in the case of fan-shaped thinning at an angle of 180 ° or more as shown in FIG. 10 (B), it is considered that the cross section of the bolt left by the thinning is shown in FIG. 10 (C). Since it approximates to FIG.
[Equation 3]
Thinning area = R ・ R ・ (Φ2-Φ1) / 2-R ・ rl ・ sin [(Φ2-Φ1) / 2]
Where r1 = R ・ cos [(Φ2-Φ1) / 2]
It is requested from.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention.

  First, an experiment was conducted to determine whether or not there was any thinning of the threaded portion of the foundation bolt in the phased array ultrasonic flaw detection method and to identify the thinning position by the echo disappearance phenomenon. In this experiment, a total of 11 specimens were used, as shown in FIGS. The test body shown in FIG. 11 is only a bolt, whereas FIG. 12 shows a test body that simulates a bolt embedded in concrete. Hereinafter, they are called a bolt test body and an embedded bolt test body, respectively. The material of the bolt is carbon steel SS41-B, and the diameter, length, and length of the screw portion are 30 mm, 300 mm, and 120 mm, respectively. As shown in FIGS. A slit having a depth of 5 mm was processed in the bolt specimens RB-1 and RB-2 without giving any defects to 1. The other specimens were given artificial defects simulating local thinning and total thinning. Further, as shown in FIGS. 11 and 12, some of the defective portions are in the screw portion, and others are away from the screw portion. Table 1 shows the details of the defects given to each specimen. The defect position, defect length, and defect depth in the table indicate the distance from the upper end surface of the bolt to the defect center, the length in the bolt axial direction, and the maximum depth in the direction perpendicular to the axial direction.

(Measurement method and measurement conditions)
A phased array device called TomoScan 3 manufactured by Zetec was used for the measurement. Software called TomoView2.29 was used for setting measurement conditions, data acquisition and result analysis. Bolt specimens and embedded bolt specimens were measured using 32-element phased array probes with frequencies of 5 MHz and 2 MHz, respectively. The width and interval of the vibrators are 0.5 mm and 0.1 mm, respectively. The length of the vibrator is usually about 10 mm, but here it is determined to be 20 mm in consideration of the diameter of the bolt. In the ultrasonic flaw detection test, the phased array probe 3 is attached to the bolt to be inspected after being attached to the rotating jig shown in FIG. 4, and the probe 3 is attached to the central axis of the bolt by turning the rotary handle 14. This was done by rotating around. The probe position is sequentially input to the computer by a rotary encoder. The resolution of the rotary encoder is 0.1 °.

Table 2 shows the flaw detection conditions. A pulse having a width of 100 ns (in the case of 5 MHz) or 250 ns (in the case of 2 MHz) and a voltage of 50 V was applied to each vibrator, and an ultrasonic wave was incident on the specimen. The ultrasonic echo received by the probe was A / D converted by a digitizer without applying a high-pass filter and a low-pass filter, and stored in a personal computer. The digitizer frequency, sensitivity (gain), and repetition frequency are 50 MHz, 35 dB, and 2000 Hz, respectively. The probe was rotated once around the central axis of the bolt at a pitch of 0.5 °. The measurement was performed as follows.

(1) Determine the flaw detection sensitivity. The flaw detection sensitivity was determined with reference to the bottom echo of the specimen to be measured. If the flaw detection sensitivity is low, adjust the soft gain in the analysis mode of the software (TomoView).
(2) The probe 3 is mounted on a probe mounting frame 13 of a jig shown in FIG. 4, and the jig is fixed to a specimen or bolt to be flawed. The probe position is adjusted so that the centers of the probe and the upper end surface of the bolt overlap.
(3) Set TomoScan 3 via TomoView. First, the flaw detection mode is set to the pulse echo of the phased array. Subsequently, the measurement conditions shown in Table 2 and the parameters described above are input. In order to calibrate the beam path during data analysis, the range of the beam path is set so that the bottom echo is observed.
(4) Mark the probe's flaw detection start position, measure it, and record the data.
(5) Analyze the data recorded in the analysis mode of TomoView.

(Measurement result)
The measurement result in each test body is shown in FIGS. The top and bottom of each figure correspond to probes with frequencies of 5 MHz and 2 MHz, respectively. In the figure, BE, DE, and RE represent a bottom echo, a delayed echo, and an echo of multiple reflections due to defects, respectively. The vertical axis of BS and MBS represents the beam path, and the horizontal axis represents the probe position. The meanings of the other symbols are as described above. The number in parentheses is the soft gain applied to that scope. The starting position of the probe is 0 °, and the position after one rotation is 360 °. Incidentally, mm on the horizontal scale label in BS and MBS is a software bug, and is an error of “°”.

  As shown in FIG. 13, screw echoes, bottom surface echoes, and delayed echoes are clearly observed in a sound embedded bolt specimen. However, when the frequency is 5 MHz, the screw echo is clearly seen from the frequency of 2 MHz. This is because the higher the frequency, the shorter the wavelength. On the other hand, as shown in FIGS. 14 to 23, when a probe having a frequency of 5 MHz is used, echoes from all the defects in the specimen are clearly observed. Comparing the results of the bolt specimen and the embedded bolt specimen, it was found that there was no influence of defect detection by embedding. On the other hand, in the case of the probe having a frequency of 2 MHz, although all defects in the bolt test specimen could be detected, the local thinning 2 of the embedded bolt test specimen No. 5 could not be detected.

  (1) The bottom echoes of specimens No.1, No.4-1, No.4-2, and No.8 appear at the vertical axis of 300 mm, while the bottom echoes of other specimens are 300 mm. Observed in the strong place. This is considered to be due to the difference in sound speed among the test specimens. In order to calibrate this difference, the measurement result is analyzed after regarding the appearance position of the bottom echo of each specimen as 300 mm.

  (2) As shown in FIGS. 14 and 15, not only a defect echo due to the slit but also an echo due to multiple reflection at the slit was detected.

  (3) In the case of thinning, a thinning echo appears far from the actual thinning position. As shown in FIGS. 17, 18, 19, 20, and 23, when the thinning at the screw portion is measured using a probe having a frequency of 5 MHz, a phenomenon in which part of the screw echo disappears is observed. Using this phenomenon, the length and position of the thinning can be estimated. Specifically, the disappearance length of the screw echo on the vertical axis of BS or MBS is the thinning length, and the beam path length corresponding to the maximum disappearance width on the horizontal axis is the thinning position. However, when the frequency is 2 MHz, the loss of screw echo is not clearly observed due to the long wavelength.

  (4) As shown in FIGS. 14 and 15, when the slit is in the screw portion, the screw echo does not disappear and the echo from the slit overlaps with the screw echo. It is considered possible to identify the thinning and cracking in the screw portion by utilizing the difference between the screw echo due to the thinning and the slit. Also, echoes from all-around thinning are observed over 0 to 360 ° in BS or MBS, whereas echoes from local thinning are observed only in a limited range.

  As an example, the measurement result of bolt specimen No. 5-1 is analyzed. Based on the above, it can be easily determined from FIG. 17 that there is one local thinning in the threaded portion of the specimen. In addition, the beam path lengths corresponding to the disappearance length and the maximum disappearance width of the screw echo can be read as 22.0 mm and 72.0 mm, respectively.

When the appearance position 310 mm 2 of the bottom echo is calibrated as 300 mm, the position and length of the local thinning can be estimated as 69.7 mm and 21.3 mm, respectively. Similarly, the property of the defect in each test body estimated from FIGS. 13 to 23 is shown in Table 3. The defect echo position and the defect position mean the defect position estimated from the beam path of the defect or the thinning echo and the measurement result.

  Defect positions and defect length values estimated using the disappearance of screw echoes are underlined. X in the table indicates that it cannot be estimated. As shown in Table 3, although the defect in the screw part can be identified as cracking or thinning, it can only be determined whether or not other defects (defects not in the screw part) are over the entire circumference. All defects in the specimens RB-1 and RB-2 could be detected, and the position could be estimated accurately. For other specimens, comparing Tables 1 and 3, it can be seen that the value of the defect echo position is larger than the actual defect position. In specimens 4-1 and 4-2, although the actual defect positions are the same, the defect echo positions are greatly different from 165 mm and 140 mm, respectively. This is considered to be due to the fact that the respective defect depths are different from 5 mm and 10 mm. That is, it was found that the defect echo position greatly depends on the defect properties. For the thinning at the threaded portion, the maximum errors of the thinning position and length estimated from the measurement result at the frequency of 5 MHz are 3.6% and 14.3%, respectively. On the other hand, for the reason described above, in the case of a frequency of 2 MHz, the position and length of most thinning cannot be accurately estimated.

  From the above, (1) It is possible to identify thinning and cracking in the screw part based on whether or not the screw echo disappears. (2) Beam corresponding to the disappearance length and maximum disappearance width of the screw echo. From the path length, it is possible to estimate the length and position of the thinning in the screw part, (3) the echo position of the thinning largely depends on the nature of the defect, and (4) from the probe with a frequency of 2 MHz, It became clear that the frequency of 5 MHz is more suitable for thinning detection of the foundation embedded bolt specimen. Further, as described above, when the thinning is separated from the threaded portion, there is a problem that the thinning position cannot be estimated from the measurement result.

(Numerical analysis)
Using the analysis model shown in FIG. 24, ultrasonic propagation analysis by the finite element method was performed for the local thinning of specimen No. 8. For the sake of simplicity, it was assumed that it was a plane strain problem, and the screw part of the bolt was ignored. The bolt length and thickness reduction were 200 mm and 5 mm, respectively. With reference to FIGS. 11 and 12, the reduced thickness as shown in FIG. 24 was determined. Young's modulus, Poisson's ratio and mass density are 270 MPa / m, 0.285 and 7,900 kg / m, respectively. The element size is 0.05 mm and the time increment is 2 ns.

  A force having a center frequency of 2 MHz is applied to the upper end surface of the bolt to excite a longitudinal wave propagating through the bolt at a refraction angle of 10 °. FIG. 25 shows the A scope predicted by the analysis. As shown in the figure, the bottom echo and the thinning echo appear at 200 mm and 134 mm, respectively. A delayed echo is also observed after the bottom echo. This agrees well with the measurement results shown in FIG. FIG. 26 shows the state of ultrasonic propagation at different times after excitation in order to locate the defect echo. In the figure, L, RL, RS, MS, and ML represent a longitudinal wave, a longitudinal wave reflected wave, a transverse wave reflected wave, a transverse wave mode converted wave, and a longitudinal wave mode converted wave, respectively. As shown in the figure, when the excited longitudinal wave hits the thinning, a transverse mode converted wave is generated. This transverse wave hits the left side of the bolt, and a transverse reflected wave is generated. This transverse wave is mode-converted by thinning, and a longitudinal wave-mode converted wave is generated. This longitudinal wave propagates toward the upper end surface of the bolt and is received as a thinning echo. That is, it has been clarified that the thinning echo is received through a route as shown in FIG. 27 (FIG. 1). That is, the excited longitudinal wave is first subjected to mode conversion by thinning and then reflected by the opposite side surface. Subsequently, the transverse wave reflected wave is mode-converted again by thinning, so that the generated longitudinal wave mode conversion is observed as a thinning echo. Further, the N and M echoes shown in FIG. 25 are caused by different longitudinal waves generated by the longitudinal wave reflected wave RL and the longitudinal wave L hitting the left side surface and thinning of the bolt, respectively. In the case of the test body, those longitudinal waves are not observed as echoes because they are scattered by the screw portion.

(1) In the case of a probe having a frequency of 5 MHz, the bottom surface echo and the defect echo of each specimen were clearly observed, and it was found that there was no influence on the defect detection by the embedding. On the other hand, when the frequency was 2 MHz, all the defects in the bolt specimen could be detected, but one local thinning in the embedded bolt specimen could not be detected.
(2) Although the defect echo position from the crack agrees well with the actual defect position, the thinning echo position from the thinning appears farther than the actual defect position. It was clarified by ultrasonic wave propagation simulation that this is due to mode conversion in the thinning of the longitudinal wave excited by the probe.
(3) In the case of a frequency of 5 MHz, a phenomenon was observed in which part of the screw echo disappeared due to thinning in the screw portion. Using this phenomenon, the position and length of thinning could be estimated with errors within 3.6% and 14.3%, respectively. On the other hand, when the frequency is 2 MHz, the screw echo does not disappear so much even if the screw portion is thin.
(4) In the case of a frequency of 5 MHz, even if there is a slit in the screw part, the screw part echo does not disappear but appears overlapping with the defect echo from the slit. It is considered that the thinning and cracks in the screw portion can be identified by utilizing the difference between the thinning and the screw echo due to the slit. Further, in the case of all-around thinning, a thinning echo is observed over 0 to 360 ° in BS or MBS, whereas in the case of local thinning, only a limited range of thinning echo is observed.
(5) Although the thinning echo position varies greatly depending on the thinning depth even though the thinning position is the same, it became clear that the echo appearance position greatly depends on the thinning depth. .
(6) It became clear that the probe with a frequency of 5 MHz is more suitable for detecting the thinning of the foundation bolt than the probe with a frequency of 2 MHz.

Next, the thinning depth was estimated by the method of the present invention using a 36 mm diameter bolt that was artificially formed with thinning.
First, the radius R of the bolt is measured. Here, the diameter R of the bolt was 18 mm as measured with a caliper. Next, a phased array probe 3 is closely attached to the end face 2 of the bolt 1 via a jig so as to be rotatable, and an ultrasonic beam is passed through the bolt center while continuously changing the refraction angle. The sector scan for receiving the ultrasonic echo reflected from the screw portion 4 of the bolt 1 is performed, and the sectoral view, the side view, and the merged side view are configured as necessary.

  Then, the position of the maximum width of the disappearing portion 6 of the screw portion echo 8 is regarded as the axial position from the bolt end surface 2 of the thinned portion 5, and the axial length l is read from the side view or the merged side view. As shown in FIG. 6, since the axial position corresponding to the maximum width of the disappearing portion 6 of the screw portion echo 8 from the side view is 99 mm, the axial position of the deepest portion of the thinned portion 5 is set to 99 mm. . By the way, the same result was obtained from the merged side view. Therefore, the value (99 mm) of the axial length 1 read from the image is input to the computer using the input means.

  Next, the side view probe cursor 10 is moved from left to right (see FIG. 7B). When the thinning echo 7 appears in the sectional view, the ultrasonic propagation direction cursor 9 is shaken in the sectional view (see FIG. 7A), and the thinning echo appearing in the side view is observed. In the case of this experiment, when the ultrasonic wave propagation direction is 13 ° as shown in FIG. 7, the thinning echo 7 is observed in the side view, but when the propagation direction is smaller than that, the thinning echo is observed in the side view. 7 came to be observed. Therefore, the ultrasonic wave propagation direction α0 at the disappearance position of the thinning echo is set to 13.

  Since α = α0 at first, the ultrasonic wave propagation direction α is set to 13 ° in the sectional view.

  Then, the maximum amplitude value corresponding to the thinning echo 7 is sequentially read by swinging the ultrasonic wave propagation direction cursor 9 in the direction of decreasing the angle on the sectoral view with the step size of the refraction angle set by the sector scan. For example, when the ultrasonic propagation direction cursor is set to 10 °, a side view corresponding to the same direction automatically appears (see FIG. 10). As shown in FIG. 10B, the thinning echo 7 is surrounded by a frame 11, and the maximum amplitude value corresponding to the echo 7 is automatically calculated by software installed in the phased array device, and the value 46.5 is obtained. % Is displayed. Similarly, when the propagation direction was 9 °, the thinning echo maximum amplitude value was read as 70.3%.

When the reading of the maximum amplitude value described above is repeated, the thinning echo maximum amplitude values corresponding to different ultrasonic wave propagation directions are obtained as shown in Table 4.

According to Table 4, when the propagation direction is 8 °, the maximum amplitude is the maximum, and the value is 78.1%. The half value of 39.05% is between 6 ° and 7 ° in the propagation direction. The propagation direction corresponding to 39.05% is obtained by linear interpolation using the propagation directions of 6 ° and 7 °. Specifically, the half-value ultrasonic propagation direction is calculated from Equation 4. The half value of 39.05% was calculated as the corresponding ultrasonic propagation direction θ = 6.025 °.
[Equation 4]
(yθ-y1) / (y2-y1) = (xθ-x1) / (x2-x1)

  Therefore, the maximum depth d of the maximum thinned portion is calculated from d = R−L · tan (θ) from the ultrasonic wave propagation direction θ, the axial length l of the thinned portion, and the bolt radius R.

As a result,
d = RL ・ tan (θ)
= 18-99 ・ tan (6.025)
= 7.55mm
And obtained.

  Applying this technique, in addition to the above four specimens No.5-1, No.5-1, No.8-2 and No.8, it has simulated thinning at an axial length of 71 mm. The thickness reduction was estimated for a total of 8 bolts of a 36 mm bolt specimen having a simulated thickness reduction at a diameter of 30 mm and an axial length of 96 mm. At the same time, the depth of simulated thinning of these eight bolts was measured by laser measurement. The result is shown in FIG. From this result, it was proved that the thinning depth can be estimated with high accuracy with a maximum error of 1.84 mm and an average square error of 1.06 mm according to the bolt thinning inspection method of the present invention. This measurement accuracy can be said to be extremely high in ultrasonic flaw detection.

DESCRIPTION OF SYMBOLS 1 Foundation bolt 2 Bolt end face 3 Phased array probe 4 Screw part 5 Thinning part 6 Screw part echo disappearance part 7 Thinning echo 8 Screw part echo 9 Ultrasonic propagation direction cursor 10 Probe position cursor

Claims (3)

While the phased array probe is brought into close contact with the end face of the bolt in use and rotated once, an ultrasonic beam is incident while continuously changing the refraction angle in the diameter direction passing through the bolt center, and the bolt In the inspection method of the bolt screw part in use that detects the thinned part from the sector view and side view of the bolt screw part that is created from the ultrasonic echo by sector scanning to receive the ultrasonic echo reflected from the screw part,
The location where the indication of the screw portion disappeared from the side view is specified as the thinning portion, and the position of the maximum width portion of the indication disappearance portion is the position of the axial thinning portion from the end surface of the bolt to the thinning portion. Taking the axial distance l from the bolt end face of the thinned portion as a
Reading the maximum amplitude value of the thinning echo for each ultrasonic wave propagation direction from the instruction of the thinning echo appearing in the side view, and obtaining the largest maximum amplitude value from among the maximum amplitude values for each ultrasonic wave propagation direction And obtaining a half angle of the largest maximum amplitude value as the refraction angle θ,
Using the refraction angle θ and the axial distance l from the bolt end surface of the thinning portion to determine the radius r of the thinning portion from Equation 1;
A method for inspecting a bolt screw portion in use, comprising: obtaining a depth d of the thinned portion from a difference between a radius r of the thinned portion and a diameter R of the bolt obtained in advance.
r = l · tan θ (Formula 1)   The method for inspecting a bolt screw portion in use according to claim 1, wherein a probe having a frequency of 5 MHz is used for the phased array type probe.   3. The bolt screw portion in use according to claim 1, wherein the thickness of the thinned portion is qualitatively determined in relation to a delay in the appearance position of the thinning echo with respect to the maximum width position of the disappearance portion of the screw portion echo. Inspection method.