JP3021265B2 - Ultrasonic testing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection method suitable for flaw detection of piping, equipment, containers and the like made of austenitic stainless steel castings in nuclear power plants.

[0002]

2. Description of the Related Art Conventionally, various non-destructive inspections have been performed as inspections during service of pipes of nuclear power plants and welded parts of equipment. One of the nondestructive inspections is an ultrasonic inspection test. In the ultrasonic flaw detection test, it is difficult to perform sufficient flaw detection for welded parts such as pipes made of cast austenitic stainless steel because the base material has coarse grains and the ultrasonic waves are greatly attenuated. And has been.

However, in recent years, application of a longitudinal wave, a low frequency (for example, 1 MHz), and a high damping type flaw detector has been proposed as an appropriate flaw detection condition. As a result, it is becoming possible to perform an effective level of inspection on welds such as pipes made of austenitic stainless steel castings.

The noise scattered at crystal grain boundaries and detected as a so-called forest-like echo increases as the material becomes more attenuated, and it is difficult to discriminate this from a defect echo (flaw echo). Signal processing method in the frequency domain,
For example, by applying the split spectrum processing (SSP),
S / N is being improved.

[0005]

However, even when appropriate flaw detection conditions are applied, in flaw detection of welds such as pipes made of cast austenitic stainless steel, the weld metal must have a columnar crystal structure. In addition, since the sound velocity has anisotropy, a noise echo (a so-called pseudo echo) such as a defect echo existing on the inner surface is generated from the vicinity of the back wave part, separately from the forest echo. In this case, it has been difficult to distinguish between a defective echo and a pseudo echo since there is almost no difference between the echo heights of the two and the SSP has no effect.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and can easily identify a defect echo / pseudo echo in a flaw detection of a welded portion such as a pipe made of austenitic stainless steel casting. An object of the present invention is to provide an ultrasonic inspection method.

[0007]

SUMMARY OF THE INVENTION The present invention is to flaw detection based on a predetermined inspection conditions, after analyzing the frequency of the original testing signals obtained in this case, signal from the distribution of the original testing signals
Detecting whether the first peak of the signal waveform is lower than the second peak, and determining that the first peak is lower than the second peak as a pseudo echo; When the first peak is on the higher frequency side than the second peak , a reference line indicating a value lowered by a predetermined value from the second peak and a signal of the original flaw detection signal
It is detected whether or not there are two intersections with the waveform.
The ultrasonic flaw detection method is characterized in that a defect echo is determined when there are a plurality of points, and a pseudo echo is determined when the number of the intersections is more than two.

[0008]

The flaw detection conditions are, for example, 36 degrees longitudinal wave and 1M frequency.
By performing the flaw detection at Hz, the transmittance of the ultrasonic wave is improved, and the beam path can be suppressed short by reducing the refraction angle to 36 degrees in order to reduce the attenuation. Accordingly, ultrasonic flaw detection can be performed even on a material having a large attenuation, such as an austenitic stainless steel cast material.

Also, the detected original flaw detection signal (RF signal)
For, the difference in the reflection characteristics of the defective echo and the pseudo echo results in a difference in the frequency distribution, which is characterized by the number of intersections with the line 6 dB down from the second peak. Therefore, by focusing on the difference in the frequency distribution, it is possible to easily identify a defect echo / pseudo echo in a flaw detection of a welded portion such as a pipe made of an austenitic stainless steel casting.

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing the procedure of the ultrasonic flaw detection method according to the present invention. First, in the present invention, flaw detection is performed under predetermined flaw detection conditions, that is, a longitudinal wave of 36 degrees and a frequency of 1 MHz (preferably a split flaw detector) (step S1). In this case, by setting the flaw detection conditions to a longitudinal wave of 36 degrees and a frequency of 1 MHz, the transmission of the ultrasonic waves is improved, and the refraction angle is reduced to 36 degrees to reduce the attenuation.
The beam path can be kept short. Accordingly, ultrasonic flaw detection can be performed even on a material having a large attenuation, such as an austenitic stainless steel cast material.

Next, in order to determine whether the detected echo is a defective echo (flaw echo) or a pseudo echo, a frequency analysis of the detected original signal (RF signal) is performed (step S2). At this time, the time width to be analyzed is within a range of ± 3 μsec from the peak position of the waveform.

Next, from the distribution state, it is detected whether or not the first peak P1 is on the lower frequency side than the second peak P2 . As a result, as shown in FIG. Is lower than the second peak P2 (Yes in step S3), a pseudo echo is set (step S4).

On the other hand, when the first peak P1 is on the higher frequency side than the second peak P2 (N in step S3)
o) 6 dB down from the second peak P2
The line L is drawn as a reference line, and it is detected whether or not there are two intersections with the line L. As a result, as shown in FIG. 3 , the intersection with the line L (indicated by “x” in the figure) If there are more than two (No in step S5), a pseudo echo is set (step S6). As shown in FIG. 4 , when the number of intersections with the line L is two (Yes in step S5), a defect echo is set (step S7).

Such a determination is based on experimentally confirming from a large number of data that a difference in the reflection characteristics between the defective echo and the pseudo echo results in a difference in the frequency distribution, and the classification is performed as described above. Things.

FIGS. 2 to 4 show examples of experimental data of the frequency distribution of the defective echo and the pseudo echo determined by the above-described procedure. FIG. 2 shows the frequency distribution of the pseudo echo in the first determination. FIG. 3 shows an example of a frequency distribution determined as a pseudo echo in the second determination, and FIG. 4 shows an example of a frequency distribution determined as a defective echo in the first and second determinations. As can be seen from these figures, the difference between the frequency distributions of the defective echo and the pseudo echo is clear, and the difference makes it possible to distinguish between the two.

[0016]

As described above, according to the present invention, flaws are detected at a longitudinal wave of 36 degrees and a frequency of 1 MMz, and defects are detected by focusing on the difference in the frequency distribution of the original flaw detection signal (RF signal) of the detected echo. Echo and pseudo-echo are determined, so that it has excellent effects such as easy detection of defect echo / pseudo-echo in flaw detection of welds such as pipes made of cast austenitic stainless steel. Can be done.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of an ultrasonic flaw detection method according to one embodiment of the present invention.

FIG. 2 is a diagram showing an example of a frequency distribution that is regarded as a pseudo echo in the first determination of the embodiment.

FIG. 3 is a view showing an example of a frequency distribution that is regarded as a pseudo echo in the second determination of the embodiment.

FIG. 4 is a view showing an example of a frequency distribution that is determined as a defect echo in the first and second determinations of the embodiment.

[Explanation of symbols]

P1: first peak; P2: second peak; L: line 3 dB down from the second peak.

Claims (1)

(57) [Claims] 1. A flaw detection is performed based on predetermined flaw detection conditions. After frequency analysis of an original flaw detection signal obtained at this time, a first peak of the signal waveform of the original flaw detection signal is shifted from a second peak based on a distribution state thereof. Detecting whether or not it is on the low frequency side, if the first peak is on the lower frequency side than the second peak, it is determined to be a pseudo echo, and the first peak is higher than the second peak If it is on the side, it is detected whether or not there are two intersections between a reference line indicating a value lowered by a predetermined value from the second peak and the signal waveform of the original flaw detection signal , An ultrasonic flaw detection method, wherein a defect echo is determined when there are two intersections, and a pseudo echo is determined when there are more than two intersections.