JP6364280B2 - Evaluation method of thread defect - Google Patents

Description

  The present invention relates to a method for evaluating a defect of a screwed portion.

  Conventionally, a laser sensor for irradiating a laser beam to a screw thread and detecting its reflected light, an elevating mechanism for raising and lowering the laser sensor, and checking for the presence or absence of a thread chip based on a signal sent from the laser sensor. 2. Description of the Related Art There is known a thread missing detection device that includes a determination unit for determination (see, for example, Patent Document 1).

JP 2006-71303 A

  Since the above-described chipping detection device for a thread is intended to directly irradiate the thread with laser light, the target thread must be exposed to the outside. For this reason, when the screw used as the detection object of a chip | tip is screwed together, you have to remove a screw.

  In addition, the internal steam is high temperature and high pressure, and the integrity of the studs used in valve chambers such as main valves of steam turbines, which tend to deteriorate over time, and the threaded parts of the implant parts are checked so that high temperature and high pressure steam does not leak. However, when using the above-mentioned chipping detection device for a thread, it takes a lot of time and labor to confirm the safety after reattaching the exposed female screw part by removing the screwed part. There is a problem that must be spent.

  This invention is made | formed in view of such a situation, The objective is to provide the defect | deletion evaluation method of the internal thread part which can evaluate the defect | deletion of the threaded part of the screwed state.

In order to achieve the above-described object, the screw part defect evaluation method of the present invention propagates through a threaded member provided with a threaded part to be evaluated, and is reflected by the ultrasonic waves reflected on the surface of the threaded part of the threaded member. Based on the target screw part echo intensity for which the echo intensity was measured, and the master curve indicated by the graph in which the echo intensity indicating the plurality of screw parts having different defect degrees and the defect degree are associated with each other, the defect of the screw part is determined. A method for evaluating a defect of a screw part to be evaluated, wherein the master curve is a simulated screw part echo obtained by measuring a simulated screw part formed so that cross sections of a plurality of types of screw threads having different defect degrees are connected in a straight line. A simulated screw graph that correlates the strength with the degree of defect of each simulated screw part, and a healthy screw that measures the echo intensity of the healthy thread part that is different in size and has no defect Obtained based on the echo intensity is a correction factor, defect evaluation method of the threaded portion, characterized in that it is generated based on correcting the simulated screw graph based on the curvature of the threads.

  According to such a defect evaluation method for a threaded portion, the ultrasonic wave used for measuring the echo intensity is reflected on the surface of the threaded portion that becomes a boundary between the screwing member and the outside, for example, a space or another adjacent member. Therefore, by propagating through the screwing member and measuring the target screw part echo intensity with the ultrasonic wave reflected on the surface of the screw part to be evaluated, without exposing the screw part to be evaluated to the outside, It is possible to measure the echo intensity more accurately. For this reason, even if it is the screw part of the screwed state, since the target screw part echo intensity can be measured without removing the screwing, it is possible to measure easily and in a short time.

  Further, since the master curve indicated by the graph in which the echo intensity indicating the plurality of screw parts having different degrees of defect and the degree of the defect are associated with each other and the target screw part echo intensity are evaluated, the defect of the screw part is evaluated. By simply measuring the echo intensity of the thread part to be evaluated, it is possible to easily evaluate the defect of the thread part to be evaluated.

  According to such a defect evaluation method for a threaded portion, the simulated screw is formed so that the cross sections of the threads having different degrees of defect are connected in a straight line, so that the threads having different degrees of defect can be more accurately identified. It is easy to form. Then, since the echo intensity of the simulated screw portions formed with different degrees of defects more accurately is measured, a more stable value can be obtained more easily than when measuring a state where a curved thread is missing. For this reason, it is possible to more accurately measure the echo intensity of threads having different degrees of defect.

In addition, the screw portions having different sizes measure the echo intensity in a healthy state with no defect, so that the difference in echo intensity depending on the size appears more accurately. For this reason, it is possible to more clearly grasp the influence on the echo intensity due to the difference in size, that is, the difference in curvature, and it is possible to obtain a more accurate correction coefficient.
And since the defect | deletion of a thread part is evaluated using the master curve with which the graph and the curvature of the thread part were matched by the more exact correction coefficient, it is possible to obtain a more exact evaluation result.

In this method for evaluating a defect in a threaded portion, it is preferable that the echo intensity is measured using an array probe.
According to such a defect evaluation method for a threaded portion, since the echo intensity in a wide range can be measured at once by the array probe, it is possible to evaluate the threaded portion defect earlier.

  In this thread portion defect evaluation method, the echo intensity is measured by the ultrasonic wave propagated from a direction orthogonal to the surface of the thread portion to be measured in a healthy state without a defect. desirable.

  According to such a defect evaluation method for a screw part, the echo intensity of a screw part that has been lost can be compared with a maximum value of the echo intensity in a healthy state with no defect, so that a clearer evaluation can be performed. It is.

  In this thread portion defect evaluation method, the thread portion to be evaluated is a female screw. Such a defect evaluation method for a threaded portion is particularly suitable for a female screw that is formed inside a hole or the like and is difficult to measure and confirm from the surface side.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the defect | deletion evaluation method of the internal thread part which can evaluate the defect | deletion of the screw part of the screwed state.

It is a perspective view which shows the state which measures object thread part echo intensity in the evaluation method of the thread part which concerns on this invention. It is a figure which shows the influence on the echo intensity by the difference in the attachment surface of an array probe. It is a figure which shows the difference in the reflective state of the echo of the healthy screw part and the missing screw part. It is a figure which shows the example by which the echo intensity of the healthy screw part and the missing screw part was mapped and shown. It is a figure which shows the relationship between the defect | deletion state of a test piece, and echo intensity. It is a figure which shows the relationship between the curvature of a thread part, and echo intensity. It is a figure which shows the produced | generated master curve.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the present embodiment, a description will be given of a thread portion defect evaluation method for evaluating a thread portion defect in which a stud bolt used for a steam turbine main valve or the like is screwed.

  The thread portion defect evaluation method of the present embodiment is based on the strength of the ultrasonic wave transmitted from the external boundary of the female screw with respect to the female screw as the screw portion into which the implanted bolt is screwed. The deficiency of the thread portion is evaluated based on the measured value of the target thread portion echo intensity to be shown and the master curve generated in advance. Here, the internal thread into which the implanted bolt is screwed is a threaded portion to be evaluated, and the member provided with this internal thread corresponds to the threaded member.

  As shown in FIG. 1, the target thread portion echo intensity of the female screw is that of the main body 2 (screwing member) having the screwing hole 2 b provided with the female screw 2 a into which the stud bolt 1 is screwed. An array probe 3 in which a plurality of transducers are arranged in the vicinity is attached and measured. In addition, in FIG. 1, since the female screw used as evaluation object is hidden by the implantation bolt 1, the code | symbol is attached | subjected to the female screw 2a of the adjacent screwing hole 2b.

  The measurement using the array probe is based on the same principle as the phased array method of the so-called ultrasonic flaw detection test in which a flaw inside the object is inspected using ultrasonic waves. More specifically, an ultrasonic echo transmitted from the transducer, propagated in the main body 2 to which the array probe 3 is attached, and reflected by the surface of the female screw 2a (boundary with the outside) is converted into the array probe. 3 is received and converted into an electrical signal, and is calculated by a computer or the like, whereby the target screw portion echo intensity is measured as a value corresponding to the missing state of the female screw 2a, and the result is displayed.

  At this time, ultrasonic waves are transmitted from a direction orthogonal to the surface so that the echo intensity of the echo reflected on the surface (flank) of a healthy female screw without a defect is maximized. Also, rust may have occurred on the mounting surface of the array probe 3, and as shown in FIG. 2, the echo intensity before polishing the mounting surface is lower than the echo height after polishing. When the array probe is attached, it is desirable to perform a surface treatment such as polishing to remove rust and scale on the attachment surface.

  More specifically, by transmitting ultrasonic waves from the attached array probe in a direction perpendicular to the surface of the female screw in a healthy state without any defect, as shown in FIG. The echo is reflected so as to bounce back to the array probe, and the echo is reflected in a direction different from the direction of the transmitted array probe in accordance with the defect state in the defect portion. Here, the general screw thread angle of the female screw is 60 degrees (flank angle 30 degrees), and the threading is performed perpendicularly to the surface or the like on which the female screw is formed. When the incident angle is set to 30 degrees with respect to the penetration direction of the processed hole, it is possible to emit ultrasonic waves perpendicular to the measurement surface (flank).

  At this time, by using an array probe, it is possible to instantaneously measure the echo intensity of a wide area, that is, a plurality of screw threads, and perform arithmetic processing to map faster and display as a color difference. It is possible. FIG. 4 shows a mapping of echo intensities measured at a healthy screw portion and a missing screw portion, and in the example of FIG. 4, the difference in echo intensity is represented by shading of colors. The reflection echo diagram shown in FIG. 4 shows the mapping of the reflection echo intensity at a plurality of threads of a female thread whose upper stage is healthy, and the color corresponding to the top of each thread is light, and the valley of the thread The color corresponding to is darker. Thus, since the change of density | concentration appears, it can grasp | ascertain that the thread protrudes highly. On the other hand, the lower row shows the reflected echo intensity at a plurality of threads of the deficient test piece (female screw), and the color appears dark even at the position corresponding to the top. Thus, since the change of density | concentration does not appear, the height of a screw thread is low and it can grasp | ascertain visually that the top part is missing. It is possible to grasp the degree of deficiency of a female screw measured with such a difference in density with respect to a healthy female screw.

  The measured target screw part echo intensity is quantitatively evaluated based on the master curve as described above. Here, the master curve is generated in advance as follows.

  In order to generate a master curve, first, a test piece having the same flank angle as the sound state of the screw to be evaluated and a plurality of test pieces (simulated screws) having different degrees of defect of the screw to be evaluated are formed. To do. The test piece to be formed at this time does not have a spiral shape provided on the outer periphery of the cylindrical member or the inner periphery of the hole, and is formed so that the cross section of the healthy screw thread or the missing screw thread is linearly connected. Has been.

  With respect to these test pieces, each simulated screw portion echo intensity is measured using the above-described array probe. In the present embodiment, a sound thread having no defect is assumed to have a residual thread thread ratio of 100%, and a simulated screw part echo intensity is measured using a specimen having a residual thread thread ratio of 62% and a residual thread thread ratio of 28%. Yes. The simulated thread portion echo intensity of the test piece measured at an echo incident angle of 30 degrees is as shown in FIG.

  The test piece is formed so that the cross section of the thread is continuous in a straight line, and is not curved like an actual male screw or female screw. On the other hand, since the ultrasonic wave transmitted from the array probe spreads three-dimensionally, even if the thread part has the same remaining thread rate, the simulated thread part echo intensity measured by the test piece and the actual The measured value is different from the echo intensity of the target screw portion measured for the male screw and the female screw.

  The curvature of the male screw and the female screw differs depending on the size. That is, even if the male screw and the female screw are healthy, the echo intensity differs depending on the outer diameter of a bolt or the like in which the male screw is formed or the inner diameter of the hole in which the female screw is formed. For this reason, if the defect | deletion of a thread part is evaluated based on the simulated thread part echo intensity | strength which measured the test piece, an error will arise and an exact evaluation result will not be obtained.

  Therefore, in order to make the simulated screw part echo intensity measured on the test piece correspond to the male screw and female screw formed in a spiral shape, the echo intensity of healthy screw parts of different sizes (healthy screw part echo intensity) was measured. Then, the correlation between the size, that is, the curvature and the sound screw part echo intensity was examined, and the correction coefficient y for making the simulated screw part echo intensity measured for the test piece correspond to the echo intensity of the male screw and the female screw was determined.

The correction coefficient y is obtained by first graphing the sound thread echo intensity of each thread using a test piece having a sound thread and nominal diameters M80, M52, and M24. The graphed result is shown in FIG. By obtaining a function (correction formula) indicating this graph, a correction coefficient y based on curvature is obtained as shown in (Formula 1).
y: Correction coefficient
r: Screw radius [m]
The error due to the curvature with respect to the bolt size or the diameter of the female screw hole is corrected by adding the obtained correction coefficient y to the simulated screw portion echo intensity obtained by measuring the test piece.

  Next, the echo intensity is measured for a plurality of studs used in the steam turbine casing, and a graph with the horizontal axis representing the degree of defect and the vertical axis representing the echo intensity is generated as shown in FIG. As shown in FIG. 7, in the actual machine, a correlation was observed between the defect level and the echo intensity, and the reliability was ensured.

  Next, the graph of FIG. 7 is used as a master curve as a reference for evaluation, and the defect of the female screw portion is evaluated. For example, when “remaining screw thread ratio 70%” is indicated as the recommended replacement value for the manufacturer of the implanted bolt to be evaluated, the echo of the screw thread when the remaining screw thread ratio is 70% from the master curve. Read the intensity. In the case of FIG. 7, it is shown that the echo intensity of the thread is about 55% when the remaining thread ratio is 70%. That is, when the target screw part echo intensity of the female thread to be evaluated is a value greater than 55%, it can be confirmed that the recommended replacement value of the manufacturer has not been reached, and a value of 55% or less. If it is, it can be confirmed that the replacement recommended value of the manufacturer has been reached.

  It is also possible to set a criterion for determining whether or not to use the implanted bolt based on the evaluation result. For example, when the measured target screw part echo intensity is greater than 55%, it is determined that it can be used continuously, and when the target screw part echo intensity is greater than 40% and less than 55%, it is determined to be a follow-up observation. If it is less than 40%, it is possible to set a standard such as judging that it should be extracted and inspected.

  According to the thread defect evaluation method of the present embodiment, the echo intensity used for the defect evaluation is measured by an echo that propagates through the screwing member and is reflected at the boundary with the outside in the thread part to be evaluated. Therefore, even a screw portion that is not exposed to the outside can be evaluated. That is, since the target screw portion echo intensity can be measured even in a screwed screw portion, it is possible to evaluate without removing the screwed portion. For this reason, it is possible to measure and evaluate the target screw portion echo intensity easily and in a short time. At this time, since the ultrasonic wave is reflected at the boundary between the threaded member to be measured and the outside, for example, a space or another adjacent member, it is possible to accurately measure the defect state of the threaded portion.

  Evaluate screw thread defects based on the master curve that correlates the simulated screw part echo intensity and defect degree of multiple simulated screw parts formed with different defect degrees, and the target screw part echo intensity. Therefore, it is possible to easily grasp the defect state of the screw portion to be evaluated only by measuring the echo intensity of the screw portion to be evaluated.

  In addition, the master curve is a simulated screw part echo intensity obtained by measuring the echo intensity of the test piece formed so that the cross-sections of the threads having different defect degrees are connected in a straight line. It is possible to form the thread easily and more accurately. In other words, since the echo intensity of a test piece consisting of threads that are connected in a straight line is measured, a more stable value can be obtained more easily when measuring the state in which a curved thread is missing. is there.

  In addition, the screw portions having different sizes measure the echo intensity in a healthy state with no defect, so that the difference in echo intensity depending on the size appears more accurately. For this reason, it is possible to more clearly grasp the influence on the echo intensity due to the difference in size, that is, the difference in curvature, and it is possible to obtain a more accurate correction coefficient. Since the master curve shown in FIG. 7 in which the graph shown in FIG. 5 and the curvature of the screw portion are associated with each other by a more accurate correction coefficient is evaluated, a more accurate evaluation result is obtained. It is possible to obtain.

  In the above embodiment, the screw portion to be evaluated is a female screw that is provided on the inner peripheral side of the hole and is difficult to measure and confirm from the surface side. However, the present invention is not limited to this. For example, the defect of the male screw may be evaluated by measuring the intensity of the reflected echo reflected from the surface of the male screw by the ultrasonic wave propagated in the bolt. Moreover, in the said embodiment, although it demonstrated taking the case of the screwing member currently screwed together, it does not necessarily need to screw.

  The above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

1 Stud Bolt 2 Body (Screw member)
2a Female thread 2b Screw hole 3 Array probe

Claims (4)

The target screw portion echo intensity, which is propagated through the screwing member provided with the screw portion to be evaluated, and the echo intensity is measured by the ultrasonic wave reflected from the surface of the screw portion of the screwing member,
A master curve indicated by a graph in which the echo intensity indicating a plurality of screw portions having different defect degrees and the defect degree are associated with each other,
A method for evaluating the defect of a screw part for evaluating the defect of the screw part based on
The master curve is
Simulation in which simulated screw part echo intensity measured for simulated screw parts formed such that cross sections of plural types of screw threads having different defect degrees are connected in a straight line are associated with the degree of defect of each simulated screw part Screw graph, and
A correction coefficient that is obtained based on the sound screw part echo intensity measured by measuring the echo intensity of the healthy screw part that is different from each other in size, and that corrects the simulated screw graph based on the curvature of the screw part,
A defect evaluation method for a threaded portion, which is generated based on the above . 2. The thread defect evaluation method according to claim 1, wherein the echo intensity is measured using an array probe. The echo intensity of the threaded portion to be measured, according to claim 1 or 2, characterized in that it is measured by the ultrasonic wave propagated in a direction perpendicular to the surface in a healthy state without defect Defect evaluation method of screw part. The thread part evaluation method according to any one of claims 1 to 3 , wherein the thread part to be evaluated is a female thread.