JPH02105054A - Ultrasonic flaw detecting method - Google Patents

Abstract

PURPOSE:To improve S/N fetching plural pieces of waves in an area where the difference of frequency components of a defective echo and a noise echo obtained by an ultrasonic flaw detection is the largest, so that a beam path to a defect does not generate a shift exceeding a half-wave of an ultrasonic wave, bringing the waves to addition average by the same phase, and thereafter, bringing its result to integer multiple or exponent multiple. CONSTITUTION:The result of analysis of frequencies of a defective echo and a noise echo of waveforms obtained by an ultrasonic flaw detection of a body to be inspected is shown in a graph, and as for a specific frequency area for executing an addition average, an area A where the difference of frequency components of the defective echo and the noise echo is the largest is selected. Thereafter, plural pieces of waves consisting of the frequency component peculiar to the defective echo in the area A are fetched after the A/D conversion, brought to addition average, and thereafter, brought to integer multiple or exponent multiple. In such a manner, the small S/N of the defective echo and the noise echo obtained by bringing a probe to tremor can be increased, and for instance, with regard to a minute defect generated by hydrogen attack, as well, whether it exists or not can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrasonic flaw detection method, and particularly to an ultrasonic flaw detection method that improves the S/N ratio between defect echoes and noise echoes.

(Conventional technology) The waveform obtained by ultrasonic flaw detection of rope contains not only defect echoes but also noise echoes such as forest echoes and delayed echoes. Techniques have been taken to detect defects early and accurately by detecting defects.

In the conventional method, flaw detection waveforms are captured in the same phase and averaged.

(Problems to be Solved by the Invention) However, with conventional methods, it is difficult to effectively improve the S/N ratio to a sufficiently satisfactory level, and micro defects, such as welded parts of austenitic stainless steel and cast steel products, It is not possible to obtain sufficient detection ability for defects associated with hydrogen attack, and it is difficult to sufficiently ensure quality reliability of products in which the presence or absence of such minute defects is a problem.

This invention was made in view of the above problems, and uses ultrasonic waves that can effectively improve the S/N ratio between defect echoes and noise echoes while capturing and averaging the flaw detection waveforms in the same phase. The purpose is to provide a flaw detection method.

(Means for Solving the Problems) The ultrasonic flaw detection method according to the present invention detects waves consisting of frequency components in a region where the difference in frequency components between a defect echo and a noise echo obtained by ultrasonic flaw detection is the largest. A plurality of waves are taken out so that the beam path to the defect does not deviate by more than a half wavelength of the ultrasonic waves, and the waves are averaged in the same phase and multiplied by an integer or an exponential.

(Operation) According to the present invention, since the plurality of waves to be averaged are in the region where the difference in frequency components between the defect echo and the noise echo is the largest, even before the wave is averaged, the defect echo and the noise The echo ratio has the effect of increasing, and by limiting the frequency domain, noise is generated with almost random phase during averaging.
Their canceling rate is high, but on the other hand, since the beam path to the defect is less than half the wavelength of the ultrasonic wave, the canceling effect is small, so the averaged defect echo and noise echo O3N The ratio increases synergistically, and by multiplying it by an integer or an exponential, the S/N ratio is significantly improved.

In addition, if the frequency component is extracted after AD conversion, it is possible to extract the frequency component from any region where the defective echo is most prominent, without being affected by the frequency characteristics inherent in a circuit such as a frequency filter for an analog signal. This allows the S/N ratio to be improved even more effectively.

(Example) Figure 1 is a graph showing the frequency analysis results of defect echoes and noise echoes in the waveform obtained by ultrasonic flaw detection of the inspected object. The region A in which the difference in frequency components is the largest is selected. Then, a plurality of waves composed of frequency components unique to the defect echo in the region A selected in this manner are extracted after AD conversion. By extracting specific frequency components after AD conversion, it is possible to determine the region A where the difference between the frequency components of defective echoes and noise echoes is the largest, depending on the frequency characteristics specific to the circuit, such as the analog signal frequency filter. It is possible to arbitrarily select one. In addition, when extracting frequency components, it is necessary to ensure that the beam path to the defect does not deviate by more than half the wavelength of the ultrasonic wave. To do this, it is necessary to move the probe slightly or
Alternatively, perform ultrasonic flaw detection with the probe set in the fixed position. When the probe is slightly moved, there is an advantage that the effect of canceling out noise echoes, which will be described later, is improved.

FIGS. 2(a) and 2(b) show waveforms of frequency components peculiar to defect echoes in the region A extracted by slightly moving the probe. Also, the same figure (C)
shows a waveform obtained by averaging the frequency components in FIGS. 3A and 3B with the same phase. As is clear from these, the defect echo to noise echo O3N ratio is relatively small for the frequency components in Figures (a) and (B), but for the averaged frequency component in Figure (C), The signal-to-noise ratio is increasing. this is,
Since there is a large phase variation between the noise echoes in the frequency components in Figures (a) and (b), the noise echoes are canceled out and reduced by averaging, whereas the defective echoes have a phase difference. This is because the fluctuations are small and cannot be canceled out.

By multiplying the averaged waveform by an integral number or an exponential number, the defect signal can be increased to an arbitrary size. Therefore, sufficient detection ability is ensured even for minute defects such as defects caused by hydrogen erosion. In addition, the effect of this method is
In addition to detecting minute defects, S
It is clear that this can be obtained in all cases where N-ratio duty is required.

(Effects of the Invention) As described above, the method of this invention extracts only a plurality of waves consisting of frequency components in the region where defective echoes are most prominent, so these frequency components are averaged. This improves the SN ratio, and since the waveform is multiplied by an integral number or an exponential number after averaging, the defect signal can be increased to an arbitrary size. Therefore, it becomes possible to sufficiently ensure the quality reliability of products in which the presence or absence of minute defects such as defects caused by hydrogen attack is a problem.

[Brief explanation of the drawing]

Figure 1 is a graph substituted for a drawing to explain the method of selecting a specific frequency region for averaging, and Figure 2 (a) (b) (
C) is a waveform diagram showing the effect of averaging. A: Area 9■ where the difference in frequency components between defect echo and noise echo is greatest. Patent applicant: Idemitsu Engineering Co., Ltd.
Kawasaki Heavy Industries Inspection Service Co., Ltd. Kawasaki Heavy Industries Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] 1. A wave composed of frequency components in the region where the difference between the frequency components of the defect echo and the noise echo obtained by ultrasonic flaw detection is the largest is detected when the beam path to the defect deviates by more than half the wavelength of the ultrasonic wave. An ultrasonic flaw detection method characterized by taking out a plurality of flaws and averaging the waves made up of those frequency components in the same phase and multiplying by an integer or an exponential.