JPS63221239A - Leak magnetic flux flaw detecting method - Google Patents

Abstract

PURPOSE:To improve the detection ability of surface flaw detection for an iron or steel product by applying simultaneously a horizontal and a vertical magnetic field to the surface of a steel material and comparing the amplitude of sensor output components based upon the magnetic fields with each other. CONSTITUTION:A horizontal magnetic field magnetizer 11 formed by arranging magnetic poles opposite each other in one diameter direction of a material 10 to be inspected such as a steel pipe magnetizes the surface of the material 10 to be inspected horizontally, i.e. in a peripheral direction and a vertical magnetic field magnetizer 12 which is arranged at a position shifting from the magnetic poles in the peripheral direction magnetizes the surface of the material 10 to be inspected vertically. The detection signal of a sensor 13 arranged in the vicinity of the vertical magnetic field magnetizer 12 is separated by synchronization detectors 23 and 24 of two systems into a signal component SV based upon the vertical magnetic field V and a signal component SH based upon the horizontal magnetic field H and a comparator 25 performs arithmetic processing to decide a scratch and abrasion when (2) SV>=SH or a crack when (2) SV<SH.

Description

[Detailed Description of the Invention] The second invention in the industrial field of application relates to the improvement of a leakage magnetic flux flaw detection method, which applies two kinds of magnetic fields in required directions to a material to be inspected, and detects unnecessary signals such as scratches and scratches and cracks. It enables discrimination from harmful defect signals such as
This invention relates to a leakage magnetic flux flaw detection method that reduces the overdetection rate and improves the ability to detect minute defects, thereby simultaneously improving the detection ability and reliability of surface flaw detection for steel products.

Background technology Ultrasonic flaw detection, magnetic particle flaw detection, and
Application of various flaw detection methods such as leakage magnetic flux flaw detection and eddy current flaw detection is essential, and reliable flaw detection equipment with high detection ability is required.

However, in general, in any flaw detection method, by improving the detection ability, the defect tends to be easily influenced by signals other than the defects to be detected, that is, noise and unnecessary signals.

The leakage magnetic flux flaw detection method that is the subject of this invention is a method in which when a ferromagnetic material is magnetized, the magnetic flux leaking from surface flaws is detected using a magnetic sensing element such as a Hall element. Defects are detected by applying an alternating magnetic field in the circumferential direction of the material to be inspected (1), detecting magnetic flux leaking from defects with a sensor (2), and synchronously detecting the detected signals.

The causes of unnecessary signals and noise in such leakage magnetic flux flaw detection can be divided into two types: (1) those caused by the material such as non-uniform magnetic permeability, and (2) those caused by surface properties such as scale and scratches.

Leakage magnetic flux flaw detection detects leakage magnetic flux caused by the presence of flaws on the material surface, so by improving the detection ability, it is possible to detect signals caused by the above-mentioned surface properties, and when introduced into the production process. , the so-called overdetection rate increases.

Therefore, in order to improve the detection ability and reduce the overdetection rate, it is necessary to improve the surface properties of the inspected material, and measures are being taken to remove scale.

However, although scratches and scratches that occur during the transportation of inspected materials do not pose a problem in terms of product quality, they remain because they are difficult to remove, and are the main cause of overdetection in magnetic flux leakage testing. It has become.

In addition, to improve the detection ability of open defects, there is a method of applying a magnetic field to the inspected material from multiple directions to detect open defects (Japanese Patent Application Laid-open No. 58-218644). Since both were detected at the same time, over-detection could not be prevented.

Problems with the conventional technology In short, if the detection sensitivity of target flaws is improved in leakage magnetic flux flaw detection, in addition to harmful defects such as cracks and burrs that pose problems in terms of product quality assurance, there will be problems such as abrasions during transportation and scratches. In order to detect flaws that do not pose a problem for product use, this can cause over-detection or false detection, and it is necessary to lower the detection sensitivity for flaw detection.

Purpose of the Invention The present invention makes it possible to distinguish between unnecessary signals such as scratches and scratches and harmful defect signals such as cracks in magnetic flux leakage detection, thereby reducing the overdetection rate and improving the ability to detect minute defects. The purpose of this research is to develop a leakage magnetic flux flaw detection method that simultaneously improves the detection ability and reliability of surface flaw detection for steel products.

Composition of the Invention The present invention is a leakage magnetic flux flaw detection method in which two types of magnetic fields are applied simultaneously, one along the surface of a material to be inspected and the other in a direction perpendicular to the surface, to detect defects caused by the presence of flaws on the surface of the material to be inspected. By separating the output of the sensor that detects the leakage magnetic flux into a leakage magnetic flux component due to the magnetic field applied in the direction along the surface and a leakage magnetic flux component due to the applied magnetic field in the direction perpendicular to the surface, and calculating the ratio of the amplitudes of the two types of flaw signals. , leakage magnetic flux flaw detection characterized by detecting target flaws that have a detrimental effect on the performance of the metal material to be tested by distinguishing and eliminating the effects of flaws or abnormal surface properties that are unrelated to the performance of the metal material to be tested. It's a method.

That is, this invention simultaneously applies a horizontal magnetic field and a vertical magnetic field to the steel surface, and separates the sensor output signal component (SH) due to the horizontal magnetic field and the sensor output signal component (SV) due to the vertical magnetic field. By comparing the amplitudes, it is possible to remove the crack/scratch signal (SV≧SH) and detect minute cracks without over-detecting, improving the detection ability and reliability of surface flaw detection for steel products. can be achieved at the same time.

Based on the Drawings (Disclosure of the Invention) FIG. 1 is a block diagram of a flaw detection apparatus for carrying out the flaw detection method of the present invention. FIG. 2 is a block diagram of a flaw detection device having two systems of detection circuits according to the present invention. FIG. 3 is an explanatory diagram showing a magnetizer and a sensor in a flaw detection apparatus for carrying out the flaw detection method of the present invention. FIG. 4 is a graph showing the relationship between the opening angle of a flaw and the detectability. FIG. 5 is a graph of detection phase angle and signal output showing the dependence of defect detection ability on detection phase angle.

In the method of this invention, as shown in FIG. ) In addition to imparting magnetization in the parallel direction, that is, in the circumferential direction, to the surface, the material to be inspected is (10
) is added to the surface perpendicular magnetization.

At this time, the magnetic field distribution near the surface of the material to be inspected (10) becomes a magnetic field that is a combination of a vertical magnetic field (V) and a horizontal magnetic field (H).

A sensor (1) placed near the vertical magnetic field magnetizer (12)
3), when leakage magnetic flux from the defect is detected, as shown in Figure 4, if the bottom width, that is, the flaw opening angle is small, the horizontal magnetic field (H) is not effective, and on the contrary, the vertical magnetic field (H) is not effective. V) has a large detectability at this time.

In general, scratches and scratches that occur on steel products have a shallow depth but a large base width, while cracks, which are harmful defects, have a small base width and close contact, i.e., the opening angle In many cases, the forest is 0.

Therefore, among the detected signals, there is a signal component (Sv) due to the vertical magnetic field (V) and a signal component (SH) due to the horizontal magnetic field (H).
), and ■Sv≧SR・・・・Oyster scratches, scratches ■SV<
SH...If arithmetic processing is performed for cracks, it becomes possible to distinguish unnecessary signals such as scratches and scratches from harmful defect signals such as cracks, reducing the overdetection rate and detecting minute defects. This makes it possible to improve performance.

Therefore, in order to separate the detection signal from the composite magnetic field into a signal component (SV) due to the vertical magnetic field (v) and a signal component (SH) due to the horizontal magnetic field (H), the following method is performed.

As shown in FIG. 2, the sensor (12) output signal is passed through two systems of synchronous detectors (23×24) to detect each signal component (SHXSV). The synchronous detector (23
A required frequency signal from the power supply (20) to the horizontal magnetic field magnetizer (11) and the vertical magnetic field magnetizer (12) is input to X24) via a phase shifter (21X22).

To be more specific, when the above-mentioned synchronous detector (23x24) detects the output signal of the sensor (13), if the detection phase angle is changed, the defect detection ability changes as shown in FIG. 5, for example. .

That is, the phase angle at which the detectability is maximum in the horizontal magnetic field (H) and the phase angle at which the detectability is maximum in the vertical magnetic field (V) are different.

When focusing on detecting cracks, the maximum detectability phase angle of the 0 mark in Fig. 5 is 150°, while when focusing on scratches and scratches, the maximum detectability phase angle of the mark is 90°. Become.

Therefore, the synchronous detector (23) is a channel that effectively detects the horizontal magnetic field (H), with a detection phase angle of 150°, while the synchronous detector (24) effectively detects the vertical magnetic field (V). channel, and the detection phase angle is set to 90°.

At this time, the amplitude of the signal detected by the synchronous detector (23) is changed to the amplitude of the signal detected by the SH1 synchronous detector (24).
Then, the comparator (25) can discriminate between the two types of flaw signals according to the above-mentioned discrimination formula, and the oyster flaw/scratch flaw signal (
By removing Sv≧SH), micro crack defects can be detected without over-detection, and such detection signals can be used, for example, with a marking device (
26).

In the example of the apparatus shown in FIG. 1 described above, a case is shown in which two magnetic fields are applied with excitation at the same frequency, but there is also a method of excitation at different frequencies.

For example, in the case of excitation with a horizontal magnetic field of 10 KHz and a vertical magnetic field of 20 KHz, as shown in FIG. 2, the sensor output is separated by a filter and then synchronous detection is performed.

That is, the detection signal of the sensor (13) is completely passed through the bypass filter (34) and the low-pass filter C35;
After being separated, it is input to a synchronous detector (36x37).

The amplitude of the signal detected by the bypass filter (34) and the synchronous detector (36) is
), and if the amplitude of the signal detected by the synchronous detector (37) is SH, then the comparator (39) can discriminate between the two types of flaw signals according to the above-mentioned discrimination formula. It can be output to.

However, if a coil is used for the sensor (13), the SV output will be doubled, so the above-mentioned discrimination condition is
≧SH...Oyster scratches, scratches ■SV/2 <SH...
・Cracks occur.

Therefore, the signal component (SV
) is input to the calculator (38), divided and sent to the comparator (
39).

In addition, even if the sensor (13) is not an inductive type, it is necessary to consider the difference in frequency characteristics of each sensor, so as a discrimination condition, a required constant k is set, and ■Sv≧ks
H...Oyster cracks, scratches ■SV<ksH...May be cracks.

Effects of the Invention This invention simultaneously applies a horizontal magnetic field and a vertical magnetic field to the surface of a steel material, and separates the sensor output signal component (SH) due to the horizontal magnetic field and the sensor output signal component (SV) due to the vertical magnetic field. By comparing the amplitudes of the signals, it is possible to remove the crack/scratch signal (Sv≧SH) and detect minute cracks without over-detecting, improving the detection ability and reliability of surface flaw detection for steel products. Improvements can be achieved at the same time.

Example 200mmΦ,
Vertical and horizontal magnetic fields were applied at the same frequency of 2 kHz using a Hall element sensor to the seamless steel pipe and the inspected material with scale attached, and the results were separated by the detection phase angle. The results are shown in Figure 6. As shown, the magnetic field strength dependence of the signal for scratches and oyster scratches is different from the magnetic field strength dependence for cracks.
Discrimination according to the present invention became possible, and results were obtained with an overdetection rate of 10% and a micro crack defect detection rate of 90%.

On the other hand, under the same steel pipe, same frequency, and sensor conditions, as shown in Figure 7, flaw detection using only the horizontal magnetic field using conventional equipment resulted in an overdetection rate of 30% and a micro crack detection rate of 70%. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a flaw detection apparatus for carrying out the flaw detection method of the present invention. FIG. 2 is a block diagram of a flaw detection device having two systems of detection circuits according to the present invention. FIG. 3 is an explanatory diagram showing a magnetizer and a sensor in a flaw detection apparatus for carrying out the flaw detection method of the present invention. FIG. 4 is a graph showing the relationship between the opening angle of a flaw and the detectability. FIG. 5 is a graph of detection phase angle and signal output showing the dependence of defect detection ability on detection phase angle. FIGS. 6a and 6b are graphs of magnetic field strength and signal output showing the magnetic field strength dependence of the signals of scratches and scratches, and the magnetic field strength dependence of cracks. FIG. 7 is an explanatory diagram showing a magnetizer and a sensor in a flaw detection apparatus for carrying out a conventional flaw detection method. 10... Material to be inspected, 11.12... Magnetizer, 13.
...Sensor, 20.30,3i...Power supply, 21,2
2, 32, 33...phase shifter, 23.24, 36, 37
... Synchronous detector, 25.39 ... Comparator, 26.4
0...Marking device, 34.35...Filter, 38...Arithmetic unit. Patent applicant Sumitomo Metal Industries Co., Ltd. Applicant's agent Press 1) Yoshihisa tmjK Figure 4 Scratch Defect detection phase angle (0) Figure 6 (α) (b) Magnetic field strength (Oe) Magnetic field strength (Oe) 7th
figure

Claims (1)

[Claims] 1. In a leakage magnetic flux flaw detection method, two types of magnetic fields are applied simultaneously, one along the surface of a material to be inspected and the other in a direction perpendicular to the surface, to detect defects caused by the presence of flaws on the surface of the material to be inspected. By separating the output of the sensor that detects the leakage magnetic flux into a leakage magnetic flux component due to the magnetic field applied in the direction along the surface and a leakage magnetic flux component due to the applied magnetic field in the direction perpendicular to the surface, and calculating the ratio of the amplitudes of the two types of flaw signals. A leakage magnetic flux flaw detection method, characterized in that the target flaw is detected by distinguishing and eliminating the effects of flaws or abnormal surface properties that are unrelated to the performance of the inspected material.