JPS5940264B2 - Eddy current flaw detection method - Google Patents

Description

[Detailed description of the invention] This invention relates to an eddy current flaw detection method for steel pipes and the like.

Conventionally, in an eddy current flaw detection device, a phase discrimination circuit converts the signal voltage from the detection coil into two signals that are orthogonal to each other.
By extracting two DC voltage signals (X signal, Y signal) and applying them to the horizontal and vertical deflection plates of the CRT display device, the Spot display is being carried out.

When evaluating defects, a signal having only an X component or a Y component is extracted and evaluated based on its magnitude. Furthermore, as shown in FIG. 2, for example, an apparatus has been developed that evaluates only signals within a selected fan-shaped area symmetrical about the Y axis as defect signals. However, the trajectory of the defect display spot often draws a figure 8 shape, but there are various signals such as signals from defects and signals due to dimensional changes in the inspected material, and in many cases, the trajectory is shaped like a figure 8 as shown in Figure 3. draws a wide loop.

Therefore, even if the phase is adjusted optimally, the trajectory moves inside and outside the fan-shaped area, making it difficult to separate them, making it impossible to determine or only making a rough distinction.By the way, the figure-eight spot display trajectory is a sign of a defect. This is the basis of well-known eddy current flaw detection; conceptually, the amplitude corresponds to the defect size, and the slope and phase correspond to the defect size as well as the depth from the defect surface. Corresponds to location and type respectively.

This invention was proposed in view of the above-mentioned circumstances, and it is possible to subdivide a fan-shaped area into two or more parts, and to determine which sub-divided fan-shaped area the phase at the maximum amplitude and the point giving the amplitude at that time are located. By comprehensively considering patterns with different flaw detection frequencies as necessary, various miscellaneous variables in this type of flaw detection can be properly handled, and accurate defect determination can be achieved. We hope that it is possible.

Next, the present invention will be explained with reference to FIGS. 4 to 9. Two mutually orthogonal DC voltage signals are extracted from the signal voltage from the detection coil using a phase discrimination circuit,
Let the DC output at a certain moment of the Y component be VX, VY,
When this is displayed on a CRT display, assuming that the spot at that instant is P, its locus will draw a figure-eight loop as shown in FIG.

(a) Calculate V2-Vx2+VY2 under the conditions that Y>0 and Vx2+VY2≧α (reference value).

Therefore, V gives the amplitude L at a certain instant. (b) Then, find the maximum value 2max of V2.

Therefore, 2max gives the maximum amplitude Lmax. (c) Also, the time to provide V2max (at maximum amplitude) is Yt-
Let t1 be the one at t-T, and find Vx.

Since the angle θt-t1 formed with the X axis at that time has the relationship VY tanθ1=t1-1, it can be calculated by 1X as VxY θ1-1 - Tan-1 -.

If these θ1-11 and V2max are used as elements and are classified according to combinations as shown in FIG. 7, they can be classified as partially cut out fan-shaped regions Sl, S2, and S3 as shown in FIG. 6.

It goes without saying that these areas can be further subdivided. When the defect determination area is divided into two or more areas in this manner, defects are determined based on which area Vmax and θ are displayed on the CRT display device based on the output from the material to be inspected.

For example, as shown in FIG. 8, the type and depth of the flaw are determined, and the size thereof is determined based on the level of Vmax. On the other hand, FIG. 9 shows an example of a different mode, in which two detection coils 3 with different flaw detection frequencies are placed at a predetermined proximity interval α on the line of the test material 2 sent by the feed roller 1.
3' is provided, and each signal voltage is passed through a phase discrimination circuit to obtain separate flaw information based on each frequency.

Then, considering the relative movement speed of the specimen 2 with respect to the detection coils 3 and 3', the time required for the flaw located under the detection coil 3 to come under the detection coil 3' is delayed by a cyst register 1 having the necessary resolution. By matching the flaw information from the detection coil 3 and the detection coil 3' and making a comprehensive judgment, it is possible to make an accurate judgment by effectively utilizing the fact that the characteristics of the defect signal differ depending on the flaw detection frequency. . Note that a larger number of detection coil-flaw detection device systems may be prepared. As described above, according to the present invention, it is possible to accurately determine not only the presence or absence of a defect, but also the type, size, and depth.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the phase and amplitude in the display device, Figures 2 and 3 are spot trajectory diagrams for explaining the conventional method, and Figure 4 is a diagram showing the phase and amplitude at the maximum amplitude. , Fig. 5 is a correlation diagram between the output voltage from the detection coil and time, Fig. 6 is a diagram showing an example of subdivision, Fig. 7 is a diagram showing the classification method, and Fig. 8 is an explanatory diagram of the flaw determination method. , FIG. 9 is a configuration diagram of a detection example with different modes. 1...Feed roller, 2...Test material, 3
, 3'...Detection coil.

Claims (1)

[Claims] 1. X and Y signals that are orthogonal to each other are extracted from the signal voltage from the detection coil using a phase discrimination circuit, and the magnitudes of the X and Y signals at a certain time are determined as V_X, V_Y.
As, (a) V_Y>0 and V_X_^2+V_Y
Under the condition that ＿＾2≧α (reference value), V＾2=V_X
Calculate _^2+V_Y_2^, (b) find the maximum value V^2max of that V^2, (c) find V_Y/V_X at the time to give that V^2max, and Θ=tan^
-^1 (V_Y/V_X) is calculated and displayed in the coordinate system, and the center side is deleted due to the combination of the angle between the first and second quadrants of V_Y>0 and the X axis and the amplitude radius from the origin. An eddy current flaw detection method characterized in that the defect is divided into at least two or more determination regions in a sector-like shape with a partial cutout, and the state of the defect is determined based on which determination region the calculated Vmax and Θ are in. 2. A plurality of detection coils with different detection frequencies are provided at intervals in the direction of transport of the material to be detected, and the output signals from each detection coil are extracted by a phase discrimination circuit into X and Y signals that are orthogonal to each other. Assuming that the magnitudes of the X signal and Y signal are V_X and V_Y, (a) V
Under the conditions of _Y>0 and V_X_^2+V_Y_^2≧α (reference value), V^2=V_X_^2+V_Y_
Calculate ^2, and (b) find the maximum value of V^2, V^2max.
(c) Find V_Y/V_X at the time that gives V^2max, and calculate Θ=tan^-^1(V_Y/
V_X) when calculated and displayed in the coordinate system
Divide the first and second quadrants where Y>0 into at least two or more determination regions in a partially-deleted sector shape with the center side deleted by a combination of the angle formed with the X axis and the amplitude radius from the origin,
An eddy current flaw detection method characterized in that the condition of a defect is determined by determining in which determination region the Vmax and Θ are located and by comprehensively determining the results of each detection flaw detection system.