JP4636967B2 - Ultrasonic flaw detection method - Google Patents

Description

  The present invention relates to ultrasonic flaw detection for detecting a defect by causing an ultrasonic wave to enter an inspection object made of a metal material or an inorganic material and detecting a reflected echo reflected from the defect inside the inspection object. Regarding the law. In particular, this is an ultrasonic flaw detection technique suitable for use when the ultrasonic irradiation cross section of the object to be inspected is thin and the defect to be flawed is in a deep part.

  In order to detect defects in the object to be inspected, such as inclusions in metal materials and inorganic materials such as steel and aluminum, and defects in welds when welding steel materials, ultrasonic waves are incident on the object to be inspected. Thus, it is widely performed to examine the presence or absence of a reflection echo due to the defect. For example, there are a vertical flaw detection method in which an ultrasonic wave is vertically incident on the surface of an object to be inspected and an oblique flaw detection method in which the ultrasonic wave is incident obliquely. In addition, in order to stabilize the acoustic coupling between the contact medium and the object to be inspected and perform precise flaw detection, an ultrasonic probe that transmits and receives ultrasonic waves and the object to be inspected are placed in water. A water immersion type ultrasonic flaw detection method is generally used (Non-Patent Document 1).

  FIG. 2 is a diagram for explaining an ultrasonic flaw detection method.

When detecting defects 41 (inclusions, voids, etc.) inside the object to be inspected of the metal plate 11 having a larger surface than the ultrasonic probe 21, as shown in FIG. 2 (a). The focusing probe 21 may be measured by two-dimensional scanning in the in-plane direction of the metal plate 11. Here, 31 is an ultrasonic wave. On the other hand, the detection of the defect 41 in the deep part of the thin metal plate material 12 as compared with the size of the ultrasonic probe 21 as shown in FIG. 2B, or on the metal plate 14 shown in FIG. When inspecting the joint portion 51 when another thin metal plate 15 is joined by brazing or welding, most of the ultrasonic waves emitted from the ultrasonic probe are incident on the thin metal plate, Since it is difficult to propagate in the vertical direction, it is difficult to detect defects with high sensitivity by the vertical flaw detection method. That is, there are the following problems when inspecting the inside of an inspection object having a thin plate thickness perpendicular to the incident direction or the inside of a rod-shaped inspection object with respect to the depth at which the ultrasonic waves are incident.
(A) Since the effective ultrasonic beam divergence differs between the case where the defect is in the center and the end of the object, the sensitivity of the defect is greatly different, and it is difficult to detect both with the same threshold value. It is.
(B) When SN is poor, a defect at the end may be missed.

  For this reason, it is common practice to perform flaw detection inspection by making ultrasonic waves incident on the wide surface of the plate or the side surface of the bar. When the defect is detected by the oblique flaw detection method shown in FIG. 3, two ultrasonic probes 6 and 7 are required for transmission and reception. When a receiving probe could not be installed due to the shape of the part to be inspected, it was necessary to measure with one probe.

  However, depending on the shape of the object to be inspected and the environment around the object to be inspected, it is necessary to make ultrasonic waves incident on a narrow surface of the plate-shaped or bar-shaped object to be inspected.

New Nondestructive Inspection Handbook (Nikkan Kogyo Shimbun, published October 15, 1992), P295 Figure 2.379, P297 Figure 2.280, P307 Figure 2.392

  When detecting the reflected echo by making the ultrasonic wave incident on a narrow surface (incident surface) such as the end face of a plate-like, rod-like, or tubular object, when the ultrasonic probe is at the center of the incident surface In some cases, the intensity of the reflected echo due to the defect is greatly different from that at the end. In many cases, a large error is included when the height of the reflected echo is automatically discriminated by scanning the ultrasonic probe. Further, when the defect size to be detected is small or the like, the SN ratio is lowered, so there is a possibility of overlooking the defect at the end.

  In view of such a situation, the first object of the present invention is to detect a defect in a thin plate-like, thin rod-like, or thin tubular inspection object with high sensitivity as compared with the size of an ultrasonic probe. And It is a second object of the present invention to detect a defect with as uniform sensitivity as possible over the entire cross section of the object to be inspected that is orthogonal to the ultrasonic propagation direction.

In the ultrasonic flaw detection method of the present invention, an inspection object having at least one plane is placed in a water tank, and the ultrasonic probe is made to face the plane (incident surface) of the inspection object by the ultrasonic probe. An ultrasonic flaw detection method in which an ultrasonic wave is incident perpendicularly to the plane and a reflected echo due to a defect inside the inspection object is detected, and is detected at the end in the width direction of the inspection object perpendicular to the ultrasonic incident direction. The ratio (E1 /) of the ultrasonic energy (E1) incident on the inside of the inspection object when the center of the acoustic probe is located and the ultrasonic energy (E2) incident on the inside of the inspection object when located at the center The dimension of the ultrasonic probe is determined and measured so that E2) becomes −3 dB or more .

Further, in another ultrasonic flaw detection method according to the present invention, the transducer of the ultrasonic probe is a circular or elliptical focusing type, and the end in the width direction of the inspection object is perpendicular to the ultrasonic incident direction. The ultrasonic energy E1 when the center of the ultrasonic probe is in the part is evaluated by the ultrasonic spot area (S (a / 2)) on the incident surface, and the ultrasonic probe is centered in the width direction. The ultrasonic energy E2 when there is a child center is evaluated by an ultrasonic spot area (S (0)) on the incident surface, and the superposition is performed so that the ratio (E1 / E2) is −3 dB or more. It is characterized in that the dimensions of the acoustic probe are determined and measured.

  In the ultrasonic flaw detection method of the present invention, the center of an incident surface is detected when a reflected echo is detected by making an ultrasonic wave incident on a narrow incident surface for a plate-like, rod-like, or thin tubular inspection object having a small width. The ratio of the effective ultrasonic intensities at the time of incidence on the part or the end is set within a predetermined range, so that the defect can be detected almost uniformly and with high sensitivity over the entire cross section of the material to be inspected. .

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present invention, when the center of the transducer is located at the end of the incident surface of the object to be inspected and at the center, the diameter of the ultrasonic transducer is set so that the ratio of the respective effective beam areas becomes a predetermined value or more. Determine. A specific determination method in the water immersion flaw detection method of the present embodiment will be described below with reference to FIG. In FIG. 1, an ultrasonic wave 2 is generated by an ultrasonic probe 2 and is incident on an inspected object 1 having a width a, and a reflected echo from a defect is detected by the ultrasonic probe 2. The ultrasonic probe may be either a focusing type or a non-focusing type, but the focusing type will be described. It is assumed that the ultrasonic wave 3 emitted from the ultrasonic probe 2 is refracted when entering the object to be inspected from water and converges to a point P in the object to be inspected.

  The focal length F of the ultrasonic probe 2, the detection depth (inspection position) t in the inspection object 1, and the distance between the ultrasonic probe 2 and the inspection object 1 (hereinafter referred to as water distance). ) The relationship of equation (1) is established between L.

Here, C _s is a longitudinal wave sonic speed of the object to be inspected, the C _w longitudinal sound velocity of water, r ₀ is a vibrator radius of the probe.

On the other hand, the equation (2) is established between the transducer radius r ₀ and the radius r of the ultrasonic beam on the incident surface. Accordingly, when the ultrasonic wave is focused to a depth to be detected using the focusing type ultrasonic probe, the ultrasonic beam radius r on the incident surface of the object to be inspected is expressed by the equation (3).

  The ratio of the intensity incident on the object to be inspected out of the intensity of the entire ultrasonic wave emitted from the ultrasonic probe can be approximated by the ratio of the area (effective beam area) of the ultrasonic spot on the incident surface. Radius r of the ultrasonic beam on the incident surface, the width a of the object to be inspected, a diagram of the ultrasonic spot on the incident surface, the effective beam area when the transducer is at the center and at the end (S 0) and S (a / 2)) and the effective beam area ratio (S (a / 2) / S (0)) expressed in decibels are shown in Table 1 when the ultrasonic transducer is circular. Show. The effective beam area ratio is indicated by R, which is considered to represent the signal intensity when the defect is at the center and at the end. For example, when the vibrator is small and r ≦ (a / 2), the detection signal is reduced by 6 dB even if the defect has the same size at the edge of the inspection object. R is zero even if the radius of the ultrasonic transducer is infinite. By selecting the vibrator diameter so that R becomes a predetermined value (preferably −3 dB or more), defects can be detected with almost equal sensitivity over the entire area. Moreover, the defect of the end portion is not overlooked due to the deterioration of the SN ratio.

Using the ultrasonic beam diameter r on the incident surface obtained from Eq. (3) and the inspected object thickness a from F, L, r0, the ultrasonic beam diameter r is set so as to obtain a predetermined sensitivity difference according to Table 1. To decide. Further, the equation (3) is calculated in reverse to determine the ultrasonic transducer diameter r ₀ .

The required focal length F and water distance L of the ultrasonic probe are determined from the ultrasonic propagation depth t of the object to be inspected. If L is made too large, F becomes large, and the spot diameter at the focusing depth proportional to (F · λ) / 2r ₀ (where λ is the wavelength of the ultrasonic wave) becomes large. Further, in determining L, care must be taken so that multiple reflection echoes generated between the ultrasonic probe and the object to be inspected do not enter the inspection part. The distance L may be appropriately determined at the time of measurement, and may be approximately zero. At that time, r ₀ ≈r.

  Further, the effective beam area ratio when the ultrasonic transducer is elliptical can be derived in the same manner as in the case of the circular shape, and the results are shown in Table 2. By compensating for vignetting on the incident surface by directing the major axis direction of the elliptical ultrasonic transducer in the width direction of the incident surface, the shape of the ultrasonic spot at the inspection position can be made closer to a circle.

  An artificial defect was produced on a steel (SS400) plate as an object to be inspected, and the sensitivity test of the ultrasonic probe was performed. A test object having a shape (plate material) shown in FIG. 4 having a thin width (thickness) in a direction perpendicular to the ultrasonic wave propagation path was used. As an artificial defect, vertical holes of φ0.5 mm and depth 2 mm were provided at two locations, the center portion of the lower surface (F1) and the location where the defect end portion was 1 mm from the side surface of the object to be inspected (F2).

The probe used had a frequency of 15 MHz, an ultrasonic transducer diameter of 12 mm (radius r ₀ = 6 mm), a focal length F = 100 mm, and an experiment was conducted from t = 24 mm to a water distance L = 4 mm. The width a of the object to be inspected is 5 mm and the radius r at the incident surface is 5.8 mm, which corresponds to the case of (c) in Table 1. The echo intensity ratio calculated in this case was R = −1.1 dB.

  FIG. 5 shows the reflected echo obtained from the actually measured F1 and F2 defects. When the defect echo height surrounded by a broken line in the figure is measured with the larger positive / negative amplitude, the F1 echo height is 95% from FIG. 5 (a), and the F2 echo height is 86% from FIG. 5 (b). is there. It was confirmed that R = 20 log (86/95) = − 0.85 dB, which is close to the calculated value based on Table 1 above, and that two defects can be detected with substantially the same sensitivity.

It is explanatory drawing for determining with the dimension of an ultrasonic transducer | vibrator in the ultrasonic flaw detection method of this invention. It is explanatory drawing of arrangement | positioning of an ultrasonic probe and a to-be-inspected object, (a) is a wide to-be-inspected object, (b) is a narrow board | plate material, (c) is a to-be-inspected object which joined the board | plate material. Arrangement. It is a layout view of the oblique flaw detection method. It is explanatory drawing of the sample of an Example. It is an example of the reflective echo of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test object 2 Ultrasonic probe 3 Ultrasonic wave 4 Defect 51 Joint part (brazing, welding part)
6 Ultrasonic probe (transmission)
7 Ultrasonic probe (Reception)

Claims (2)

An object to be inspected having at least one plane is placed in a water tank, and an ultrasonic probe is opposed to the plane (incident surface) of the object to be inspected by an ultrasonic probe, and ultrasonic waves are perpendicular to the plane. An ultrasonic flaw detection method for detecting incident echoes and reflection echoes caused by defects inside the inspection object,
Ultrasonic energy (E1) incident on the inside of the inspection object when the center of the ultrasonic probe is at the end in the width direction of the inspection object perpendicular to the ultrasonic incident direction;
When the ultrasonic probe center is in the center of the width direction, the ultrasonic probe (E1 / E2) ratio (E1 / E2) of the ultrasonic energy (E2) incident on the inside of the inspection object is −3 dB or more. An ultrasonic flaw detection method characterized by measuring a dimension of a touch element. The transducer of the ultrasonic probe is a circular or elliptical focusing type, and the ultrasonic probe has a center when the center of the ultrasonic probe is at the end in the width direction of the inspection object perpendicular to the ultrasonic incident direction. The ultrasonic energy E1 is evaluated by the ultrasonic spot area (S (a / 2)) on the incident surface,
The ultrasonic energy E2 when the center of the ultrasonic probe is at the center in the width direction is evaluated by the ultrasonic spot area (S (0)) on the incident surface,
The ultrasonic flaw detection method according to claim 1, wherein the ultrasonic probe is dimensioned and measured such that the ratio (E1 / E2) is −3 dB or more .

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