JPS63233363A - Detecting method for flaw by eddy current - Google Patents

Abstract

PURPOSE:To enable the detection of the exact flaw depth by determining the kind of a flaw and by assuming the flaw depth thereafter from the relationship between flaw depths and phase angles which is found beforehand in regard to flaws of said kind. CONSTITUTION:A ternary figure showing the relationships among an amplitude (s) of a flaw detection signal, a flaw depth (d), an inter-peak time difference DELTAt and the kinds of a flaw and a graph of the relationship between a phase angle theta of the flaw detection signal and the flaw depth which is found beforehand in accordance with the kind of each flaw, are prepared. Then, the flaw detection signal is obtained from a metal tube to be inspected, the kinds of a flaw is determined from the result of detection, and the depth of the flaw is assumed. In this way, the depth of the flaw can be detected accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an eddy current flaw detection method for detecting defects (IE1 cracks, dents, etc.) in metal pipes and the like.

[Prior art]

For example, eddy current flaw detection is used to inspect heat exchanger tubes in heat exchangers. As shown schematically in FIG. 4, a coil 2 is inserted into a metal tube 1 to be detected, and while an alternating current is applied to the coil 2, a signal cable 6 is swept by a coil sweeper 3. to move the coil 2 within the tube 1.

An alternating magnetic field is generated from the coil 2, and as this moves within the tube 1 together with the coil 2, eddy currents are induced in the portion of the tube 1 to be detected. If the tube 1 has a defect such as thinning or cracking, the eddy current will be disturbed, and the impedance of the coil 2 will change. Therefore, defects in the tube 1 can be detected by analyzing the change in impedance of the coil 2 as a flaw detection signal.

The impedance change of the coil 2 described above is given to the eddy current flaw detector 4 as a flaw detection signal, and is displayed on the CRT display 40 as a vector waveform.

FIG. 5 shows an example of the CRT waveform of the flaw detection signal displayed on the CRT display 40, starting from the origin 0, which is the intersection of the X-axis in the horizontal direction of the screen and the Y-axis in the vertical direction,
Draw a trajectory in the order of b, c, and d in a figure-eight pattern.

The waveform of the flaw detection signal displayed in a figure 8 shape on the CRT display 40, with time plotted on the horizontal axis, is the waveform of the X component and Y component, respectively, as shown in the graph of FIG. The graph of FIG. 6 shows the inter-peak time difference ΔT of the Y component.

By the way, defect evaluation by the eddy current flaw detection method is generally performed based on the amplitude S and phase angle θ of the figure-8 pattern of the CRT waveform shown in FIG. Specifically, it is as follows.

The width S tends to correspond to the volume of the defect rather than the depth of the defect. Therefore, shallow, wide, groove-like defects and deep, narrow, crack-like defects often have almost the same amplitude, making it difficult to distinguish between the two. Evaluation is not so important at present.On the other hand, since the phase angle θ has a higher correlation with the depth of the defect than the amplitude S, it is now possible to evaluate the defect based on this phase angle θ. There are many things to do.

Now, defect evaluation based on the phase angle θ is performed by machining artificial defects simulating natural defects on a reference metal pipe at various depths in advance and measuring these artificial defects, for example, as shown in Fig. 7. As shown in the figure, a calibration curve showing the relationship between the defect depth and the phase angle θ of the flaw detection signal (in the example shown in Fig. 7, defects on the inner and outer surfaces and through-hole defects are categorized) is created, and it is determined by the actual inspection. The defect depth corresponding to the phase angle θ is estimated for a signal showing an amplitude S above a certain level among the obtained flaw detection signals.

[Problem that the invention seeks to solve]

However, in the conventional defect evaluation method based on the phase angle θ in the eddy current flaw detection method described above, it is difficult to evaluate the type of defect, such as a groove-like defect, a concave defect such as thinning, and an extremely narrow width such as a single crack. It is not possible to determine the types of defects such as deep defects or through holes, so it is necessary to determine the relationship between the amplitude S and the defect depth in advance. There was a problem that it was not possible to obtain

The present invention was made with the aim of solving the above-mentioned problems, and by first determining the type of defect and then estimating the depth of the defect accordingly, it is possible to identify defects more accurately than before. The purpose is to provide an eddy current flaw detection method that can estimate the depth of

Means for Solving Problem c] The eddy current flaw detection method of the present invention estimates the approximate depth of a defect based on the phase angle of the obtained flaw detection signal, and uses this estimated value, amplitude, and peak-to-peak time difference. The defect type is determined from the above, and the defect depth is estimated from the relationship between the defect depth and phase angle, which are determined in advance for each defect type.

The present invention applies an alternating current to a coil facing a conductive object to be inspected, and obtains a change in the generated eddy current due to a defect in the conductive object as a flaw detection signal. In the eddy current flaw detection method for detecting defects, the relationship between the phase angle of the flaw detection signal and the defect depth is determined in advance according to each of multiple defect types, and the phase angle, amplitude, and maximum of the flaw detection signal obtained are determined in advance. Determine the type of defect based on a combination of the time difference between the value and the minimum value, and estimate the depth of the defect in the conductive object based on the relationship between the phase angle of the determined defect type and the defect depth. It is characterized by

[Effect]

In the eddy current flaw detection method of the present invention, the type of defect is first determined, and then the defect depth is estimated from the relationship between the defect depth and the phase angle that have been determined in advance for that type of defect.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof.

The present invention deals with various types of eddy currents generated by applying an alternating current to a coil 2 inserted and moved within a conductive object to be detected, for example a metal tube 1 such as a heat exchanger tube. The amplitude S of the flaw detection signal obtained as a change in the impedance of the coil 2 caused by the change corresponding to the defect has a high correlation with the volume of the defect, the phase angle θ also has a correlation with the depth of the defect, and the peak of the Y component. Since the time difference ΔT is correlated with the length of the defect in the axial direction (the axial direction of the tube to be detected), it is possible to almost accurately determine the type of defect by comprehensively evaluating these specifications. This was done with this in mind.

Specifically, first, the defect depth d is roughly estimated using the phase angle θ of the vector waveform of the flaw detection signal shown in FIG. As mentioned above, this method is similar to the conventional method,
For example, a standard calibration curve as shown in FIG. 7 may be prepared in advance, and the measurement may be performed based on this.

Next, the type of defect is determined from the amplitude S, the defect depth d, and the inter-peak time difference ΔT of the Y component shown in FIG.

This defect type can be easily determined using a ternary diagram in which three elements, amplitude S, defect depth d, and peak-to-peak time difference ΔT, are each placed at the apex of an equilateral triangle, as shown in FIG. 1, for example. Specifically, it can be classified into the following five groups.

1st group...Concave defect amplitude S like thinning...Large defect depth d...Small to medium peak time difference ΔT...Large 2nd group...Crack in circumferential direction, i-shaped defect amplitude S...
Large defect depth d... Time difference between medium and large peaks ΔT... Small to medium Group ■... Pitting-like defect vibration f@S... Medium defect depth d... Between large peaks Time difference ΔT...Small group ■...Crack-like defect amplitude S...Small to medium defect depth d...Large peak-to-peak time difference ΔT...Small to medium Group V...-Noise number Adding notes for all groups except group ① to group ①, in group 1, the defect volume is large (amplitude S is large) and the defect depth d is small to medium.

The axial length of the defect is large (the peak-to-peak time difference ΔT is large), and this is a relatively shallow but large defect, that is, a shallow concave defect, specifically a defect such as thinning.

Group ■ has a large defect volume (large amplitude S), medium to large defect depth d, and small to medium defect axial length (peak-to-peak time difference Δ
T is small to medium), and this is a defect that is relatively deep but narrow, and the axial length of the tube 1 is not very long, that is, a defect that is long, narrow, and deep in the circumferential direction of the tube 1. This is a crack or groove-like defect that extends in the circumferential direction. .

Group ■ has a medium defect volume (medium amplitude S), a large defect depth d, and a small axial length of the defect (small inter-peak time difference ΔT).
This is a defect that is relatively deep, narrow in width, and small in volume, that is, a pitting-like defect extending in the thickness direction of the pipe 1, specifically, a pitting-like defect before reaching the through hole.

Group (2) has a small to medium defect volume (small to medium amplitude S).

The defect depth d is large, the axial length of the defect is small to medium (the peak-to-peak time difference ΔT is small to medium), which is relatively deep, but the width is not very wide, and the axial length of the pipe is small to medium. This is a defect that is not very long, that is, a deep and somewhat long defect, specifically a crack-like defect.

As described above, since the type of defect can be determined based on the three elements of amplitude S, defect depth d, and peak-to-peak time difference ΔT, the ft class of the defect can be determined from the obtained flaw detection signal. . Then, the depth of the defect is estimated based on the phase angle θ according to a calibration curve corresponding to each determined defect type.

FIG. 2 is a graph showing the relationship between the phase angle θ and the defect depth depending on the type of defect.
Types of defects, namely internal pitting defects■, external pitting defects■
, shows the relationship between the phase angle θ of the flaw detection signal and the defect depth for each of the outer circumferential ring-shaped defects. Note that pitting defects (■) and (■) on the inner and outer surfaces are both 10% of the wall thickness of tube 1.
When the depth reaches 0%, it becomes a through hole (■).

From the graph in Figure 2, for example, even if the defect is on the same outer surface, the pitting-like defect ■ and the circumferential ring-like defect ■ have a defect depth of 40" when the phase angle θ of the flaw detection signal is 90".
% and 5%. In this case, in the conventional defect evaluation method, as is clear from FIG.
The defect depth was estimated to be 5%.

Therefore, when carrying out the method of the present invention, first, the amplitude S of the flaw detection signal, the defect depth d, the time difference between peaks ΔT, and the value of the defect as shown in FIG. A ternary diagram showing the relationship between the defects and the defect depth, and a graph showing the relationship between the phase angle θ of the flaw detection signal and the defect depth according to each defect type as shown in FIG. 2 are prepared. Then, a flaw detection signal is obtained from the pipe to be inspected using a device as shown in Fig. 4, the type of defect is determined from the results based on Fig. 1, and the defect depth is estimated based on Fig. 2. .

In addition, although the above-mentioned embodiment inspects metal tubes such as heat exchanger tubes, the present invention is applicable not only to tubes but also to defect inspections of various metal objects, more specifically conductive objects. be.

〔effect〕

As described above, according to the present invention, the type of defect is determined from the phase angle, amplitude, and time difference between peaks of the obtained flaw detection signal,
Since the defect depth can be estimated according to the determined defect type, the defect depth can be detected more accurately than in the past.

[Brief explanation of the drawing]

Figure 1 is a ternary diagram showing the relationship between the amplitude S of the flaw detection signal, the defect depth d, the time difference ΔT between peaks, and the defect type, and Figure 2 is the relationship between the phase angle θ and the defect for each of the various defect types. A graph showing an example of a calibration curve with depth, Fig. 3 is an explanatory diagram of each defect whose calibration curve is shown in the graph of Fig. 2, and Fig. 4 is a schematic diagram showing the implementation state of a general eddy current flaw detection method. , Fig. 5 is a schematic diagram showing the vector waveform of the flaw detection signal, Fig. 6 is a chart showing the vector waveform of Fig. 5 over time for each of the X and Y components, and Fig. 7 is used in the conventional method. It is a graph showing a calibration curve between the depth of an artificial defect and the phase angle θ of a flaw detection signal. 1...Pipe 2...Coil S...Amplitude θ...Phase angle ΔT...Time difference between peaks d...(estimated) defect depth Patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Noboru Kono also has 1 figure and 3 figures missing. Circle) Figure 7 Figure 6

Claims (1)

[Claims] 1. By applying an alternating current to a coil facing a conductive object to be inspected and obtaining a change in the generated eddy current due to a defect in the conductive object as a flaw detection signal, In the eddy current flaw detection method for detecting defects in a conductive object, the relationship between the phase angle of the flaw detection signal and the defect depth is determined in advance according to each of a plurality of defect types, and the phase angle of the obtained flaw detection signal and Determine the type of defect based on a combination of the amplitude and the time difference between the maximum value and the minimum value, and determine the type of defect in the conductive object based on the relationship between the phase angle of the determined defect type and the defect depth. An eddy current flaw detection method characterized by estimating depth.