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JP2007040906

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DESCRIPTION JP2007040906
PROBLEM TO BE SOLVED: To detect a defect of a thin plate-like, thin rod-like or thin-walled
tubular test object at high sensitivity as compared with the size of an ultrasonic probe, and to
check the cross section of the test object orthogonal to the ultrasonic wave propagation direction
The purpose is to detect defects with as uniform sensitivity as possible throughout. An ultrasonic
flaw detection method for detecting an echo echo due to a defect inside an inspection object by
making an ultrasonic probe face the plane (incident surface) of the inspection object and making
the ultrasonic wave perpendicularly incident on the plane 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, and the width
direction The ratio (E1 / E2) of the ultrasonic energy (E2) incident on the inside of the test object
when the center of the ultrasonic probe is at the center of the target is larger than a
predetermined value and not more than 2. The dimensions of the ultrasonic probe are
determined and measured. [Selected figure] Figure 1
Ultrasonic flaw detection method
[0001]
According to the present invention, ultrasonic flaws are detected by causing an ultrasonic wave
to be incident on the inside of an inspection object made of a metal material or an inorganic
material and detecting a reflection echo reflected from a defect inside the inspection object.
About the law. In particular, it 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.
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[0002]
In order to detect defects in the object to be inspected such as inclusions inside metal materials
such as steel and aluminum and inorganic materials, and defects in welded parts when steels are
welded to each other, ultrasonic waves are incident on the object to be inspected It is widely used
to check 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 an ultrasonic wave is
obliquely incident. In addition, in order to stabilize the acoustic coupling between the contact
medium and the test subject and perform precise flaw detection, an ultrasonic probe for
transmitting and receiving ultrasonic waves and the test subject are disposed in water. Usually, a
water-immersed ultrasonic flaw detection method is used (Non-patent Document 1).
[0003]
FIG. 2 is a view for explaining an ultrasonic flaw detection method.
[0004]
As shown in FIG. 2A, when detecting a defect 41 (inclusion, void, etc.) inside the inspected object
of the metal plate 11 having a large surface as compared with the ultrasonic probe 21 by the
vertical flaw detection method And the two-dimensional scan of the focusing probe 21 in the inplane direction of the metal plate 11 for measurement.
Here, 31 is an ultrasonic wave. On the other hand, as compared with the dimensions of the
ultrasonic probe 21 as shown in FIG. 2 (b), the detection of the defect 41 in the deep part of the
thin metal plate 12 or the metal plate 14 shown in FIG. 2 (c) When inspecting the joint 51 when
another thin metal plate 15 is joined by brazing or welding, most of the ultrasonic waves emitted
from the ultrasonic probe are made to enter the thin metal plate and It is difficult to detect
defects with high sensitivity in the vertical flaw detection method because it is difficult to
propagate in the longitudinal direction. That is, there are the following problems in inspecting
the inside of an inspection object or a rod-like inspection object having a thin plate thickness
perpendicular to the incident direction with respect to the depth at which the ultrasonic wave is
incident. (A) When the defect is at the center or at the end of the object, the effective ultrasound
beam spreads differently, so the sensitivity of the defect differs significantly, making it difficult to
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2
detect both with the same threshold value It is. (B) If the SN is bad, the defect at the end may be
missed.
[0005]
For this reason, it is common practice to carry out flaw detection inspection by making ultrasonic
waves incident on the wide surface of the plate or the side surface of the rod. When making a
defect in the oblique angle flaw detection method shown in FIG. 3, two ultrasonic probes 6, 7 are
required for transmission and reception. When the receiving probe can not be installed due to
the shape of the portion to be inspected, it is necessary to perform measurement with one probe.
[0006]
However, depending on the shape of the object to be inspected and the environment around the
object to be inspected, ultrasonic waves need to be incident on the narrow surface of the platelike or rod-like object to be inspected.
[0007]
New nondestructive inspection manual (Nichikan Kogyo Shimbun, published on October 15,
1992), P295 Figure 2.379, P297 Figure 2.280, P307 Figure 2.392
[0008]
When ultrasonic waves are incident on a narrow surface (incident surface) such as an end
surface of a plate-like, rod-like or tubular inspection object to detect a reflection echo, the
ultrasonic probe is located at the center of the incident surface The intensity of the reflection
echo due to the defect may be largely different from that at the end.
Then, when the ultrasonic probe is scanned and the reflected echo height is automatically
discriminated, a large error is often included.
In addition, when the size of the defect to be detected is small, etc., the SN ratio may be lowered,
so that the defect at the end may be missed.
03-05-2019
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[0009]
In view of such circumstances, the present invention has a first object to detect defects of a thin
plate-like, thin rod-like, or thin-walled tubular object to be inspected with high sensitivity as
compared with the size of an ultrasonic probe. I assume. Another object of the present invention
is to detect defects with as uniform sensitivity as possible over the entire cross section of the
inspection object orthogonal to the propagation direction of the ultrasonic waves.
[0010]
According to 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
ultrasonic probe to the plane (incident surface) of the inspection object. An ultrasonic flaw
detection method for making ultrasonic waves incident perpendicularly to the plane and
detecting a reflection echo due to a defect inside the object to be inspected, wherein the end in
the width direction of the object to be inspected perpendicular to the incident direction of The
ratio (E1 /) of the ultrasonic energy (E1) incident on the inside of the object under inspection
when the center of the acoustic probe is present and the ultrasonic energy (E2) incident on the
inside of the object under the center The ultrasonic probe is sized and measured such that E2) is
larger than a predetermined value and smaller than or equal to two.
[0011]
In the ultrasonic flaw detection method according to another aspect of 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 perpendicular to the ultrasonic incident direction The
ultrasonic energy E1 when the center of the ultrasonic probe is in the area is evaluated by the
ultrasonic spot area (S (a / 2)) on the incident surface, and the ultrasonic probe is detected at the
center in the width direction The ultrasonic energy E2 at the center of the child is evaluated by
the ultrasonic spot area (S (0)) on the incident surface, and the ratio (E1 / E2) is larger than a
predetermined value and 2 or less. And measuring and measuring the dimensions of the
ultrasonic probe so that
[0012]
In the ultrasonic flaw detection method according to the present invention, when an ultrasonic
wave is made incident on a narrow incident surface and a reflection echo is detected for a small
plate-like, rod-like or thin-walled tubular inspection object, the center of the incident surface is
detected. Since the ratio of the respective effective ultrasonic intensities when entering the part
03-05-2019
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or the end part is within the predetermined range, defects can be detected with high sensitivity
almost uniformly over the entire cross section of the inspection material .
[0013]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0014]
In the present invention, when the transducer center is at the end and at the center of the
incident surface of the inspection object, the diameter of the ultrasonic transducer is set so that
the ratio of the respective effective beam areas becomes equal to or more than a predetermined
value. Determined.
The specific determination method in the water immersion flaw detection method of this
embodiment is shown below using FIG.
In FIG. 1, an ultrasonic wave 3 is generated by an ultrasonic probe 2 and made to be incident on
an inspection object 1 of width a, and a reflection echo from a defect is detected by the ultrasonic
probe 2.
The ultrasound probe may be either focusing or non-focusing, but focusing will be described.
It is assumed that the ultrasonic wave 3 emitted from the ultrasonic probe 2 is refracted when it
is incident on the subject from water and converges to a point P in the subject.
[0015]
The focal distance F of the ultrasound probe 2 and the detection depth t (the position to be
inspected) t in the subject 1 and the distance between the ultrasound probe 2 and the subject 1
(hereinafter referred to as water distance The relationship of equation (1) is established between
L).
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[0016]
[0017]
Here, Cs is the longitudinal wave velocity of the test object, Cw is the longitudinal wave velocity
of water, and r0 is the transducer radius of the probe.
[0018]
On the other hand, the equation (2) is established between the transducer radius r0 and the
radius r of the ultrasonic beam at the incident surface.
Therefore, when an ultrasonic wave is focused to a depth to be detected using a focusing
ultrasonic probe, an ultrasonic beam radius r at the incident surface of the object to be inspected
is expressed by equation (3).
[0019]
The ratio of the intensity incident on the inspection object to the intensity of the entire ultrasonic
wave emitted from the ultrasonic probe can be approximated by the ratio of the area of the
ultrasonic spot (effective beam area) on the incident surface.
The radius r of the ultrasonic beam on the incident surface, the width a of the object under
inspection, the figure of the ultrasonic spot on the incident surface, the effective beam area when
the transducer is at the center and at the end The relationship between 0) and S (a / 2)) and the
effective beam area ratio (S (a / 2) / S (0)) expressed in decibels is shown in Table 1 for the case
where the ultrasonic transducer is circular. Show.
The effective beam area ratio is indicated by R, where R is considered to represent the signal
strength when the defect is at the center and at the end. For example, when the transducer is
small and r ≦ (a / 2), the detection signal is reduced by 6 dB at the edge of the inspection object
even if the defect has the same size. R is zero even if the radius of the ultrasonic transducer is
infinite. By selecting the transducer diameter so that R is a predetermined value (preferably -3 dB
or more), defects can be detected with substantially uniform sensitivity over the entire area. In
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addition, it is possible to prevent the defect in the end from being missed due to the deterioration
of the SN ratio.
[0020]
[0021]
Using ultrasonic beam diameter r on the incident surface obtained from F, L, and r0 by the
equation (3) and test object thickness a, ultrasonic beam diameter r so as to have a
predetermined sensitivity difference according to Table 1 Decide.
Further, the equation (3) is calculated reversely to determine the ultrasonic transducer diameter
r0.
[0022]
From the ultrasonic wave propagation depth t of the object to be inspected, the required focal
length F and water distance L of the ultrasonic probe are determined. If L is made too large, then
F increases, and the spot diameter at a focusing depth proportional to (F · λ) / 2 r 0 (where λ is
the wavelength of the ultrasonic wave) increases, so care must be taken. Further, in determining
L, it is necessary to be careful that multiple reflection echoes generated between the ultrasonic
probe and the object to be examined do not get mixed in the inspection part. The distance L may
be determined appropriately at the time of measurement, and may be approximately zero. そのと
き、r0≒rとなる。
[0023]
Further, the effective beam area ratio when the ultrasonic transducer is elliptical can also be
derived as in the case of the above-mentioned circular case, and the results are shown in Table 2.
Compensating for vignetting at the entrance surface by orienting the major axis direction of the
elliptical ultrasonic transducer in the width direction of the entrance surface makes it possible to
make the shape of the ultrasound spot at the inspection position closer to a circle.
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[0024]
[0025]
The artificial defect was produced in the board of steel materials (SS400) as a to-be-inspected
object, and the sensitivity test of the ultrasonic probe was done.
An inspection object having a shape (plate material) shown in FIG. 4 in which the width
(thickness) in the direction perpendicular to the ultrasonic wave propagation path is thin was
used. As artificial defects, vertical holes with a diameter of 0.5 mm and a depth of 2 mm were
provided at two locations, the center of the lower surface (F1) and the place (F2) where the
defect end is 1 mm from the side of the inspection object.
[0026]
The probe used had a frequency of 15 MHz, an ultrasonic transducer diameter of 12 mm (radius
r0 = 6 mm), and a focal length F = 100 mm, and experiments were performed with a water
distance L = 4 mm from t = 24 mm. The width a of the inspection object 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 ratio of
echo intensities calculated in this case was R = −1.1 dB.
[0027]
The state of the reflected echo obtained from the F1 and F2 defects actually measured is shown
in FIG. When the height of the defect echo surrounded by the broken line in the figure is
measured at 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, close to the calculated value based on Table 1 above, and that two defects could be
detected with almost the same sensitivity.
[0028]
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It is explanatory drawing for determining by the dimension of an ultrasonic transducer | vibrator
in the ultrasonic flaw detection method of this invention. It is explanatory drawing of
arrangement | positioning with an ultrasonic probe and a to-be-tested object, (a) is a wide to-betested object, (b) is a narrow board material, (c) is a to-be-tested object which joined board
material. It is an arrangement. It is a layout of a bevel angle 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 sign
[0029]
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)
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