JP2015017883A - Ultrasonic flaw detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flaw detection method capable of certainly detecting the presence or absence of a flaw such as an internal defect immediately below a surface of a steel material even if a disturbance reflected wave exists.SOLUTION: An ultrasonic wave B is made to enter a circular cross section at each point in the circumferential direction of the circular cross section of a round steel material M, an intensity distribution diagram is obtained in which the lateral axis shows each point and the longitudinal axis shows time change of reflected wave intensity in the ultrasonic wave at each point. When, of the regions (high intensity regions) in which the reflected wave intensity is a certain value or higher in the intensity distribution diagram, at least one region is inclined in the lateral axis direction, it is determined that a flaw F occurs in the round steel material M.

Description

  The present invention relates to an ultrasonic flaw detection method, and in particular, relates to an ultrasonic flaw detection method that can favorably detect internal defects and surface defects immediately below the surface of a round steel material.

  Patent Document 1 discloses an ultrasonic flaw detection method for a round steel material using an array probe. An array probe is an ultrasonic emission surface by providing a number of ultrasonic transducers on a circular arc surface concentric with the outer peripheral surface of a round steel material. By driving the required number of ultrasonic transducers, An ultrasonic beam is emitted toward the round steel material so that the transverse wave refraction angle becomes a predetermined angle. By rotating the round steel material as appropriate or by providing a plurality of array probes of the same kind adjacent to the entire circumference of the round steel material, the entire surface of the round steel material can be scanned with an ultrasonic beam to detect surface defects.

JP 2009-150679 A

  By the way, in the conventional ultrasonic flaw detection method described above, when an array probe is used, in addition to the reflected wave of the refracted transverse wave flaw detection beam that is effective for detecting internal defects directly under the surface, the straight wave travels straight into the round steel material and is on the opposite side. There is a problem that the internal defects and surface flaws cannot be reliably detected because a reflected wave such as a reflected wave that is reflected and returned from the inner surface of the steel material or a reflected wave that is repeatedly reflected in the round steel material is generated.

  Therefore, the present invention solves such a problem, and provides an ultrasonic flaw detection method capable of reliably detecting the presence or absence of defects such as internal defects directly under the surface of a steel material even in the presence of disturbing reflected waves. For the purpose.

  In order to achieve the above object, in the first aspect of the present invention, ultrasonic waves (B) are incident on the circular cross section at each point in the circumferential direction of the circular cross section of the round steel material (M), Obtain an intensity distribution map taking the time change of the reflected wave intensity of the ultrasonic wave at each point as the other axis, and at least one of the areas (high intensity areas) where the reflected wave intensity in the intensity distribution map is a certain level or higher. When the region is inclined in the uniaxial direction, it is determined that wrinkles (F) are generated in the round steel material (M).

  In the first invention, the reflected path of the disturbing reflected wave is constant even if the ultrasonic incident point changes. Accordingly, the high intensity region of the disturbing reflected wave is parallel to the uniaxial direction on the intensity distribution diagram and does not tilt. On the other hand, when a flaw such as an internal defect directly under the surface is present in the round steel material, the reflection path of the flaw detection reflected wave from the flaw changes with a change in the ultrasonic incident point. Therefore, the high intensity region of the flaw detection reflected wave is inclined in the uniaxial direction on the intensity distribution diagram. Thereby, the presence or absence of wrinkles in the round steel material can be reliably determined depending on whether the high-strength region is inclined in the uniaxial direction.

  In the second invention, a strength distribution map of a normal round steel material (M) having no flaw (F) is acquired in advance, and the difference between the strength distribution map and the strength distribution map of the round steel material (M) to be flawed is obtained. The determination is performed based on the intensity distribution chart obtained by taking

  In the second invention, since the influence of the disturbing reflected wave is removed in the intensity distribution diagram taking the difference, it is possible to more reliably determine whether or not there is a flaw in the round steel material.

  The reference numerals in the parentheses indicate the correspondence with specific means described in the embodiments described later.

  As described above, according to the ultrasonic flaw detection method of the present invention, it is possible to reliably detect an internal defect or the like directly under the surface of a steel material even if an interference reflected wave exists.

It is a cross-sectional view of the round steel material which shows the path | route of a flaw detection reflected wave. It is a cross-sectional view of the round steel material which shows the path | route of a disturbance reflected wave. It is a cross-sectional view of the round steel material which shows the path | route of another disturbance reflected wave. It is a figure which shows the time relationship of each reflected wave signal. It is a cross-sectional view of the round steel material which shows the path | route of the disturbance reflected wave at the time of changing the launch point of an ultrasonic beam. It is a cross-sectional view of the round steel material which shows the path | route of the other disturbance reflected wave at the time of changing the launch point of an ultrasonic beam. It is a cross-sectional view of the round steel material which shows the path | route of a flaw detection reflected wave at the time of changing the launch point of an ultrasonic beam. It is an intensity distribution figure when there is an internal defect in a round steel material. It is an intensity distribution figure when there is no internal defect in a round steel material. It is a reflected wave intensity distribution figure after performing a difference process. It is a reflected wave intensity distribution figure after performing other processing.

  The embodiment described below is merely an example, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention. Details of the flaw detection method of the present invention will be described below.

  FIG. 1 shows a cross section of the round steel material M, and the array probe 1 is provided at a predetermined distance from the outer peripheral surface thereof. In the array probe 1, the ultrasonic wave emitting surface 11 facing the outer peripheral surface of the round steel material M is an arc surface substantially concentric with the outer peripheral surface of the round steel material M. The round steel material M and the array probe 1 are installed in water.

  A necessary number of ultrasonic transducers (not shown) of the array probe 1 are driven to emit an ultrasonic beam B, and a transverse wave is generated in the round steel material M so that the refraction angle θ is 40 to 45 °. This is a flaw detection beam D. When the flaw detection beam D is reflected by an internal defect (hereinafter simply referred to as “internal defect”) or a surface flaw immediately below the surface, it becomes a flaw detection reflected wave Rd, and returns to the array probe 1 again following the path when the flaw detection beam D is incident. . Whether the ultrasonic beam B output from the array probe 1 is scanned in a predetermined range in the circumferential direction of the round steel material M by sequentially driving the necessary number of ultrasonic transducers, and the round steel material M is appropriately rotated. By providing a plurality of array probes 1 of the same type adjacent to the entire circumference of the round steel material M, the entire circumference of the round steel material M can be scanned with the ultrasonic beam B.

  By the way, when the ultrasonic beam B enters the round steel material M, in addition to the refracting transverse wave flaw detection beam D, a straight traveling longitudinal wave beam B1 as shown in FIG. 2 is generated, which is reflected by the opposite steel surface. It returns to the array probe 1 again as an interference reflected wave Rb1. Further, as shown in FIG. 3, a longitudinal wave reflected wave R directed to the opposite steel surface is generated from the transverse wave flaw detection beam D, and this is reflected by the steel surface and again reflected to the array probe 1 as an interference reflected wave Rb2. Return.

  If the diameter D of the round steel material M is 28 mm and the radius of curvature of the ultrasonic emission surface 11 of the array probe 1 is 62.5 mm, the water distance WP from the array probe 1 to the round steel material M is 48.5 mm. When the refraction angle θ is 45 °, the water sound velocity Cw is 1480 m / s, the longitudinal wave sound velocity Ct is 5900 m / s, and the transverse wave sound velocity Cs is 3230 m / s, the time for reciprocating the water distance WP is 2 × (WP / Cw). ≈65.5 μs.

  Further, the time until the flaw detection beam D enters the round steel material M, is reflected by an internal defect, etc., and returns to the inner surface of the round steel material M again as a flaw detection reflected wave Rd is approximated by 2 × (D × Cosθ) / Cs). To about 12.2 μs. Further, the reciprocation time of the disturbing reflected wave Rb1 in the round steel material M is 2 × (D / Ct) ≈9.5 μs. The round trip time of the interference reflected wave Rb2 in the round steel M is approximately 14.2 μs as approximated by (D × Cos θ) / Cs + (D × Sin θ) / Ct + D / Ct.

  These time relationships are shown in FIG. In order to prevent unnecessary input of other reflected waves to the array probe 1, a pass gate W is set on the time axis, and this pass gate W generally has a path distance from the array probe 1 to the material surface of 1. The skip (S) is set in the range of 0.5 to 1.25 skip (S) as shown in FIG. However, also in this case, the disturbing reflected waves Rb1 and Rb2 are detected in addition to the flaw detection reflected wave Rd. Therefore, when the flaw detected reflected wave Rd overlaps the disturbing reflected waves Rb1 and Rb2, the presence of internal defects or the like is overlooked. Alternatively, when there is no internal defect or the like, the interference reflected waves Rb1 and Rb2 may be erroneously detected as the flaw detection reflected wave Rd.

  Therefore, in the present embodiment, further processing is performed based on the following knowledge. That is, considering the reflection path of the disturbing reflected wave Rb1, as shown in FIG. 5, the ultrasonic emission surface 11 is an arc surface substantially concentric with the outer peripheral surface of the round steel material M. Even if the launch point of the ultrasonic beam B (and hence each incident point of the ultrasonic beam B in the circumferential direction of the circular cross section of the round steel material M) changes from the Y point to the Z point, the reflection path of the disturbing reflected wave Rb1 is always Constant and unchanged. In addition, as shown in FIG. 6, the reflection path of the disturbing reflected wave Rb2 is always constant even if the launch point of the ultrasonic beam B is changed from the X point to the Y point to the Z point. Does not change.

  On the other hand, as shown in FIG. 7, when there is an internal defect F directly under the surface in the round steel material M, when the launch point of the ultrasonic beam B is changed from the X point to the Y point to the Z point, When the ultrasonic beam B is emitted, the reflection path of the flaw detection reflected wave Rd is the longest. From now on, the reflection path of the flaw detection reflected wave Rd gradually decreases as it moves to the Y point and the Z point, and the reflection path is the shortest at the Z point. Become.

  Therefore, when the distribution point of the ultrasonic beam B in the circumferential direction of the circular cross section of the round steel material M is plotted on the horizontal axis and the time variation of the reflected wave intensity at each point is plotted on the vertical axis, the intensity distribution diagram is drawn (FIG. 8). Since the reflection paths of the disturbing reflected waves Rb1 and Rb2 are always constant, the areas where the intensity of the disturbing reflected waves Rb1 and Rb2 is high (high brightness area, white area in FIG. 8) are emitted from the ultrasonic beam B. Even if the point changes, it always appears at a certain time, so the high luminance region extends in parallel to the horizontal axis direction. On the other hand, if there is an internal defect F or the like in the round steel material M, the flaw detection reflected wave Rd reflected here changes its reflection path according to each incident point of the ultrasonic beam B. The high luminance region in FIG. 8 where the intensity of Rd is high extends while being inclined in the horizontal axis direction.

  Further, in the present embodiment, with respect to a normal round steel material M having no internal defect F or the like, the intensity distribution of each launch point of the ultrasonic beam B on the horizontal axis and the time change of the reflected wave intensity of the ultrasonic wave at each point on the vertical axis. FIG. 9, that is, an intensity distribution diagram (FIG. 9) in which only the disturbing reflected waves Rb1 and Rb2 appear is acquired in advance, and this is an intensity distribution diagram (FIG. 8) of the round steel material M that is the target of wrinkle detection. Take the difference. Since the high-intensity areas of the disturbing reflected waves Rb1 and Rb2 are erased and only the high-intensity area of the flaw detection reflected wave Rd is left from the intensity distribution chart (FIG. 10) subjected to the difference processing, the differential with respect to the intensity distribution chart. FIG. 11 shows the high-luminance region clarified by performing processing, binarization processing, expansion processing, and contraction processing. Then, in the intensity distribution diagram after processing, it is determined that there is an internal defect when a high-luminance region extending in a horizontal axis direction that is longer than a certain length appears. Note that the reason for “more than a certain length” is that, in the case of a short length, there are many cases of simple noise. In this manner, it is possible to reliably detect the presence or absence of internal defects or the like in the round steel material.

  DESCRIPTION OF SYMBOLS 1 ... Array probe, B ... Ultrasonic beam (ultrasonic wave), F ... Internal defect (疵), M ... Round steel material.

Claims (2)

Intensity distribution in which ultrasonic waves are incident into the circular cross section at each point in the circumferential direction of the circular cross section of the round steel material, with each point as a single axis, and the time variation of the reflected wave intensity of the ultrasonic wave at each point as another axis. Obtaining a figure, it is determined that wrinkles have occurred in the round steel material when at least one region is inclined in the uniaxial direction among regions where the reflected wave intensity in the intensity distribution diagram is a certain level or more. Ultrasonic flaw detection method characterized by. Claims are obtained based on an intensity distribution chart obtained by obtaining in advance a strength distribution map of a normal round steel material without defects and taking a difference between the strength distribution chart and the strength distribution chart of a round steel material to be flawed. The ultrasonic flaw detection method according to 1.