JP3077793B2 - Automatic magnetic particle inspection equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic particle flaw detection apparatus for analyzing magnetic image data obtained by a television camera by attaching magnetic powder to a magnetized test object and detecting defects on the surface and near the surface of the test object. For example, the present invention relates to a magnetic particle flaw detector capable of detecting even a minute welding defect called a penetrator in a welded portion of an electric resistance welded steel pipe.

[0002]

2. Description of the Related Art Inspection of surface flaws such as cracks generated in a metal material is performed by, for example, an ultrasonic flaw detector. For example, in the case of an ERW steel pipe, a cold weld, Since defects such as penetrators, burn-through and hook cracks occur, quality control is performed by ultrasonic testing for ERW welds. The penetrator, which is a minute welding defect generated in the electric resistance welded portion, is difficult to detect by the ultrasonic testing. For this reason, as shown in FIG. 7A, the inspection of the surface flaw of the ERW pipe is performed by cutting out the ERW pipe 71 by a predetermined length and setting the ERW welded part 72 to 3 o'clock or 9 o'clock of the watch.
As shown in FIG. 7B, the ERW steel pipe 71 is pressed to a specified height, and then inspected by a flat test to observe whether the ERW weld 72 has a defect or not. I have.

Since the flattening test is performed by human means, the welded portion does not bend accurately due to the displacement of the ERW welded portion, and the test cannot be performed. Has a problem that a personal error occurs in the determination result because the observation is also performed visually.

As a method for solving the above-mentioned problem, a magnetic powder pattern group attached to an inspection object is converted into an electric image signal by an image pickup tube, and the electric image signal is converted into a bright and dark image signal.
Classify the signals into different types, and separately obtain a sweep voltage synchronized with the scanning electron beam of the image pickup tube to show the coordinates on the screen,
The coordinates on the screen and the output value of the video signal at the position corresponding to the coordinates are stored by light and dark, and the coordinates corresponding to light belong to a coordinate point set or an isolated bright point belonging to any bright point set part on the screen. Classify as coordinates, measure the area and perimeter or perimeter and length of each magnetic powder pattern at the same time for each classification, and (area) / (perimeter) ² or (perimeter) / ( Length), and only those for which the measured value is larger than the reference value and the calculated value is smaller than the reference value are determined to be surface flaws (Japanese Patent Publication No. 58-57705). The video signal is sampled and converted into a large number of digital signals in the width direction, and then, for each of a plurality of digital signals in the width direction and the length direction, the digital signals are subtracted to obtain representative values, respectively. These representative values correspond to the required number of scan lines. It is stored for each scanning line, and the stored representative values are added by a required number in the direction of a predetermined line segment on the surface of the inspection object, and a flaw signal when the added value exceeds a threshold value is used. A magnetic particle flaw detection method and device for inspecting surface flaws (Japanese Patent Publication No. 59-22895) has been proposed.

When binarizing and analyzing image data obtained by a television camera, a pixel dividing means for obtaining a luminance signal for each pixel from the image data, and a pixel number for each luminance based on the luminance signal for each pixel. Luminance distribution converting means for obtaining a distribution, peak detecting means for obtaining a luminance having the maximum number of pixels from the distribution of the number of pixels for each luminance, and binarizing the image data by a threshold determined from the maximum pixel number luminance A device provided with a digitizing means (Japanese Patent Laid-Open No. 55948/1990), for binarizing image data obtained by a television camera and detecting surface flaws, for each screen of image data of the surface of an inspection object; After obtaining the pixel number distribution for each luminance in one arbitrary line, the lowest luminance at which the number of pixels becomes zero is obtained from the pixel number distribution for each luminance in one line, and a threshold determined by the lowest luminance is obtained. Apparatus for binarizing the image data (JP-A-6-43120) have been proposed Ri.

[0006]

In the magnetic particle flaw detection method and apparatus disclosed in the above-mentioned conventional publication, although the magnetizing current is DC, the penetrator existing on the surface of the inspection object and in the vicinity of the surface can be detected in principle. A penetrator at a position deeper than the surface or a minute penetrator has a problem that it is difficult for a leakage magnetic flux to appear on the surface of the inspection object and is difficult to detect by magnetic particle flaw detection.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to greatly improve the defect detection capability of magnetic particle flaw detection, and to automatically remove magnetic particle patterns other than defects in automatically inspecting magnetic particle flaw detection. It is to provide a device.

[0008]

The magnetic particle flaw detector according to the present invention has flattening means for flattening in the direction in which defects of the inspection object spread before magnetizing the inspection object. As described above, prior to magnetizing the inspection target, the inspection target is flattened in a direction in which the defect spreads by the flattening means, so that the defect is at a position deeper than the surface, and even a minute defect. Since the defect becomes larger and more magnetic flux leaks out on the surface, the detectability of magnetic particle flaw detection is greatly improved.

Further, the magnetic particle flaw detector according to the present invention has a flattening means for flattening in a direction in which a defect of the inspection object spreads before magnetizing the inspection object, and an inspection object obtained by a television camera. An inspection area is set from the surface image data, the image data in the area is converted into a binarized image by a predetermined threshold, (vertical length / horizontal length) of the binarized image is calculated, and the calculated value is calculated. And a defect judging means for judging a defect only when is smaller than the reference value. As described above, prior to magnetizing the inspection target, the inspection target is flattened in a direction in which the defect spreads by the flattening means, so that the defect is at a position deeper than the surface, and even a minute defect. Since the defect becomes larger and more magnetic flux leaks out on the surface, the detectability of magnetic particle flaw detection is greatly improved. Further, an inspection area is set from image data of the surface of the inspection object obtained by the television camera, and the image data in the area is binarized by a predetermined threshold value. In addition, images other than defects, such as a lump of magnetic particles and accumulation of magnetic particles due to surface defects of the inspection object, are also included. Since the defective image is long horizontally and these noise images are also long vertically, the (vertical length) / (horizontal length) of the binarized image is calculated, and when the value is smaller than the reference value, that is, By detecting a defect only when it is long horizontally, noise is removed and only the defect can be automatically inspected.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The flattening means in the magnetic particle flaw detector of the present invention comprises a flat cylinder, a flat metal fitting, and a flat tip metal fitting. The flattening of the inspection object is performed by pushing out a flat metal fitting by a flat cylinder and flattening the inspection object. The extrusion size in this case is adjusted by replacing the flat tip metal fitting. The optimum flattening amount is, for example, in the case of an electric resistance welded steel pipe, 80 to 95% of the outer diameter D after the flattening with respect to the outer diameter D. The flattening amount is an effective value for securing the detectability of the subsequent magnetic particle flaw detection and preventing deterioration of the visibility of defects due to excessive flattening. For example, when there is a penetrator at the welded portion of the electric resistance welded steel pipe, the flattening makes the defect larger, and can greatly improve the detection ability in magnetic particle flaw detection.

The setting of the inspection area from the image data of the surface of the inspection object obtained by the television camera in the magnetic particle inspection apparatus of the present invention is determined by the shape and size of the inspection object, the direction and type of the defect to be detected. For example, in the case of detecting a weld defect of an ERW steel pipe, the welding line of the ERW weld is specified, and the inspection area is limited to a predetermined width centering on the welding line and only a welded portion obtained by cutting a bead. Thus, the background is always constant, erroneous detection can be prevented, and a defect in the welded portion of the ERW steel pipe can be determined with high accuracy.

The defect determining means of the present invention converts the image data in the inspection area into a binary image by a predetermined threshold value,
The (vertical length / horizontal length) of the binarized image is calculated, and a defect is determined only when the calculated value is smaller than the reference value. That is, in the image obtained by converting the image data in the inspection area into a binarized image based on a predetermined threshold value, in addition to the image due to the defect, there is a mass of magnetic powder or a surface flaw of the inspection object that is not a problem as a product. Images other than defects such as accumulation of magnetic particles are also included. For example, as shown in FIG. 5, the images of the penetrator defects F ₁ and F ₂ of the welded portion 51 of the electric resistance welded steel pipe are long horizontally if the imaging direction is horizontal and the direction perpendicular to the imaging direction is vertical. Lumps of magnetic powder M ₁ and accumulation of magnetic powder M ₂ due to surface defects of the inspection object to the extent that they are not a problem as a product,
Since noise images other than welding defects, such as M ₃ and M ₄ , have the feature of being elongated vertically, the (vertical length) / (horizontal length) of the binarized image is calculated, and when the value is smaller than the reference value, That is, it is detected as a defect only when it is long horizontally. As shown in FIG. 6, the reference value r of (vertical length) / (horizontal length) of the binarized image is (vertical length) / (horizontal length), for example, in the case of a penetrator defect at the welded portion of the ERW steel pipe. = 0.4 or less,
In the case of noise other than welding defects, the distribution is (vertical length) / (horizontal length) = 0.6 to 1. Therefore, in the case of detecting a weld defect of the ERW steel pipe, the (vertical length) /
(Horizontal length) is calculated, and the calculated value is used as a reference value, for example, r ≦ 0.
By comparing with No. 5, it is possible to remove noises other than welding defects and detect only welding portion defects.

[0013]

【Example】

Embodiment 1 Hereinafter, details of a magnetic particle flaw detector according to the present invention will be described with reference to FIGS. 1 and 2 showing an embodiment. FIGS. 1A and 1B show the flattening operation of the magnetic particle flaw detector according to the present invention by the flattening device, wherein FIG. 1A shows a flattened state, FIG. 1B shows a flattened state, and FIG. Schematic diagram at the time of magnetic particle flaw detection after completion of flattening,
FIG. 2 is an explanatory view of the entire configuration of the magnetic particle flaw detector according to the present invention.

1 and 2, reference numeral 1 denotes an electric resistance welded steel pipe which is a 1 m-long sample to be inspected, and 2 denotes an electric resistance welded steel pipe 1.
The welded portions 3, 4 are electrodes for magnetizing the ERW pipe 1. The ERW pipe 1 is cleaned and removed of oil on the surface, and then the welding line W is set at 12:00 of the timepiece, and the longitudinal direction is at both ends. It is set between the electrodes 3 and 4. 5, 6 are flat cylinders 7, 8, flat metal fittings 9, 10, flat flat metal fittings 11, provided at horizontal opposing positions in a direction orthogonal to the longitudinal direction of the ERW steel pipe 1.
The flattening device 12 is used to operate the flattening cylinders 7 and 8 to push out the flattening fittings 9 and 10, and to flatten the ERW steel pipe 1 from both sides by the flattening fittings 9 and 10. The flattening dimensions at this time are the flattened tip fittings 11, 1
Adjust by replacing 2. Therefore, FIG.
When flattening to the P dimension shown in (b), the length of the flat end metal fittings 11 and 12 in the direction orthogonal to the longitudinal direction of the ERW steel pipe 1 is P / 2.

Reference numerals 13 and 14 denote screw shafts arranged in parallel above the ERW steel pipe 1 along the ERW pipe 1, 15 and 16 motors for rotating the screw shafts 13 and 14, and 17 a rotation of the screw shaft 13. The magnetized liquid spraying device is movable along the ERW steel pipe 1 in parallel, and a predetermined current value and a predetermined time are supplied to the flattened ERW pipe 1 set between the electrodes 3 and 4 to magnetize the magnet. After that, the motor 15 is driven to rotate the screw shaft 13 so that the magnetic powder liquid spraying device 17 is rotated.
Is moved to spray a magnetic powder solution having a predetermined concentration over the entire length of the welded portion 2 of the ERW steel pipe 1.

Reference numeral 18 denotes a television camera which is movable in parallel along the electric resistance welded steel pipe 1 by rotation of the screw shaft 14, 19,
Reference numeral 20 denotes an ultraviolet lamp which is movable in parallel along the electric resistance welded steel pipe 1 by rotating the screw shaft 14 together with the television camera 18. The ultraviolet lamps 19 and 20 emit ultraviolet light while driving the motor 16 to drive the screw shaft 14. By rotating the TV camera 18 and the ultraviolet lamps 19 and 20, the entire length of the welded portion 2 of the ERW steel pipe 1 is moved by the TV camera 18.
It is configured to shoot. Reference numeral 21 denotes a television monitor for displaying an image captured by the television camera 18 and converted by the A / D converter 22; 23, a signal processing device for the image signal converted by the A / D converter 22;
An inspection area setting unit 24 for specifying a window as an inspection area by coordinates from a raw image converted and displayed on the television monitor 21, a binarization processing unit 25 for binarizing the image of the inspection area by its luminance, binary The defect determination unit 26 performs a defect determination of the welded portion 2 of the electric resistance welded steel pipe 1 from the digitized image, and a defect counting unit 27 that counts welding defects determined as defects by the defect determination unit 26. Reference numeral 28 denotes a console for inputting and setting an inspection area, a threshold value, and an r value to the inspection area setting unit 24, the binarization processing unit 25, and the defect determination unit 26, and 29 denotes the number of defects measured by the defect counting unit 27. It is a printer that outputs.

When detecting a defect in the welded portion 2 of the ERW pipe 1, prior to magnetizing the ERW pipe 1, the flat cylinders 7 and 8 are operated to flatten the flat pipe as shown in FIG. The metal fittings 9 and 10 are extruded, and the ERW steel pipe 1 is pressed from both sides by the flat metal fittings 9 and 10, and the outer diameter D of the ERW steel pipe 1 is 80 to 9
After flattening to 0%, the flat cylinders 7, 8 are operated to retract the flat metal fittings 9, 10 as shown in FIG. 1 (c). Defects in the welded portion 2 of the electric resistance welded steel pipe 1 are increased by the flattening process. Next, a predetermined magnetizing current is applied between the electrodes 3 and 4 for a predetermined time to magnetize the ERW steel pipe 1. Thereafter, the motor 15 is driven to move the magnetic powder liquid spraying device 17 along the magnetized ERW pipe 1, and the magnetic powder liquid having a predetermined concentration is sprayed over the entire length of the welded portion 2 of the ERW pipe 1. . The magnetic powder liquid sprayed over the entire length of the welded portion 2 of the magnetized electric resistance welded steel pipe 1 leaks magnetic flux from the welding line W on the surface of the welded portion 2 if the welding line W has a welding defect.
Magnetic powder liquid adheres more than other parts. In addition, the magnetic powder liquid adheres more to a material surface flaw portion which is not a problem as a lump or a product as compared with other portions.

Next, the television camera 18 is driven by the motor 16 while irradiating with the ultraviolet lamps 19 and 20, and
And photograph the entire length of the ERW steel pipe 1 including the welded portion 2. The welded portion 2 of the electric resistance welded steel pipe 1
When irradiation is performed at 9 and 20, welding defects, a lump of magnetic powder, and a material surface flaw portion that does not pose a problem as a product appear brighter than other portions.
Appears thinner in the raw image but slightly brighter than the other parts. The image signal photographed by the television camera 18 is transmitted to the A / D converter 2
After the conversion in 2, the signal is output to the signal processing device 23. The signal processing device 23 performs a predetermined process on the image signal input from the A / D converter 22 and determines whether or not there is a welding defect in the welded portion 2 of the ERW steel pipe 1.

The signal processing unit 23 includes an inspection area setting unit 24
(X ₁ , Y ₁ ), (X ₂ , Y ₂ ), (X ₃ , Y ₃ ), (X ₄ , Y ₃ )
Y ₄ ), the average luminance of each pixel line in the tube axis direction of the ERW pipe 1 is quantized at a predetermined period inputted from the A / D converter 22 and is based on the digitized luminance of each pixel. Calculated by the first threshold value for welding line W detection,
Value processing to specify the pixel line of the welding line W,
A window, which is an inspection area, is placed above and below the coordinates of four points (X ₁ , Y ₁ ), (X ₂ , Y ₂ ), (X ₃ , Y ₃ ),
(X ₄ , Y ₄ ).

Next, the signal processing unit 23 inputs the luminance of each pixel in the inspection area set as described above, that is, the window, into the second set for detecting the welding defect which is set in advance.
Is binarized by the binarization processing unit 25 according to the threshold value. In the window centering on the welding line W due to the binarization, in addition to the penetrator defect on the welding line W, a noise image of a magnetic particle pool due to a lump of magnetic particles and a material surface flaw that is not a problem as a product. Exists. The penetrator defect is elongated in the direction of the welding line W, and the noise of the lump of magnetic particles and the accumulation of the magnetic particles tends to be rounded. Therefore, for discrimination, the ratio (r) of the vertical dimension to the horizontal dimension in the welding line W direction, that is,
The defect determination unit 26 calculates r = (vertical length) / (horizontal length), and a reference value set in advance, for example, r = 0.
By selecting r ≦ 0.5 as compared with No. 5, the noise of the lump of the magnetic powder and the accumulation of the magnetic powder is removed, and only the penetrator defect can be extracted. The total number of the extracted penetrator defects is calculated by the defect counting unit 27 and the defect length is output to the printer 29.

Example 2 The magnetic particle flaw detector of Example 1 was used, and the outer diameter was 31.8 m.
A carbon steel ERW steel pipe having a thickness of 2.0 m, a thickness of 2.0 mm, and a length of 1 m was magnetized for 5 seconds with a DC current of 2000 A for each of the cases where the flattening treatment was performed before the magnetization and the case where the flattening treatment was not performed. Thereafter, a fluorescent magnetic powder having a particle diameter of 1 to 2 μm is sprinkled and adhered, and discrimination between a penetrator defect and noise is performed at a ratio r ≦ 0.5 of a vertical dimension to a horizontal dimension at a magnification of 10 times of a television camera. And the penetrator defect detection ability was compared. FIG. 4 shows the results. The defect length on the horizontal axis in FIG. 4 is the length L in the weld line W direction shown in FIG. 3, and the defect depth on the vertical axis is the depth D from the surface of the ERW steel pipe shown in FIG.
e, measured by a microscopic micrograph.

As shown in FIG. 4, when the flattening process is performed before the magnetization, the detection limit of the penetrator defect is 0.1 mm, the defect depth is 0.1 mm, and the defect length is 0.1 mm.
In the case of 6 mm, the defect depth can be up to 1.2 mm, whereas when the flattening treatment is not performed before the magnetization, the defect length is limited to 0.35 mm. Even if it was a flaw, it could not be detected, and the defect depth was about 0.7 mm when the defect length was 0.6 mm. That is,
The penetrator defect detectability is determined by performing a flattening process on a defect length of 0.35 mm and a defect depth of approximately 0.7 mm, which are detectable limits when the flattening process is not performed.
Detection limit is defect length 0.1mm, defect depth 1.2m
m and greatly improved.

[0023]

According to the magnetic particle flaw detector of the present invention, prior to magnetizing the inspection object, the flattening means performs flattening processing in the direction in which the defect spreads, and automatically removes the magnetic particle pattern due to noise. Thereby, the detection capability of magnetic particle flaw detection can be greatly improved.

[Brief description of the drawings]

FIG. 1 shows a flattening operation by a flattening device of a magnetic particle flaw detector according to the present invention, wherein FIG.
(B) is a schematic diagram at the time of flattening, and (c) is a schematic diagram at the time of magnetic particle flaw detection after the flattening is completed. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of the entire configuration of a magnetic particle flaw detector of the present invention.

FIG. 2 is an explanatory diagram of the entire configuration of a magnetic particle flaw detector according to the present invention.

FIG. 3 is a partially cutaway perspective view for explaining a defect length and a defect depth of a welded portion of an electric resistance welded steel pipe in Example 2.

FIG. 4 shows penetrator defect detection ability (defect length and defect depth) depending on the presence or absence of flattening before magnetization in Example 2.
3 is a graph showing a comparison.

FIG. 5 is an example of image data after binarization.

FIG. 6 is a graph showing a relationship between a penetrator defect of the binarized image data, a lump of magnetic powder, a pool of magnetic powder, and a vertical and horizontal dimension distribution.

7A and 7B are explanatory views of a flattening test of a conventional welded portion of an electric resistance welded steel pipe. FIG. 7A shows a state before flattening, and FIG. 7B shows a state after flattening.

[Explanation of symbols]

1,71 ERW steel pipe 2,51 Weld 3,4 Electrode 5,6 Flattening device 7,8 Flat cylinder 9,10 Flat metal fitting 11,12 Flat metal tip 13,14 Screw shaft 15,16 Motor 17 Magnetic powder liquid spraying device 18 TV camera 19, 20 UV lamp 21 TV monitor 22 A / D converter 23 Signal processing device 24 Inspection area setting unit 25 Binarization processing unit 26 Defect judgment unit 27 Defect counting unit 28 Operation console 29 Printer 72 electric-resistance welded portion 73 flat W weld line F _1, F ₂ penetrator defect M ₁ mass magnetic powder M _2, M _3, M ₄ reservoir L defect length De defect depth of the magnetic powder

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 21/91 G01N 27/84 G06T 7/00

Claims (2)

(57) [Claims] 1. Means for magnetizing an inspection object, means for attaching a magnetic powder solution to the surface of the magnetized inspection object, means for irradiating light to the surface of the inspection object, and a portion irradiated by the means In a magnetic particle flaw detection device comprising a television camera for imaging the object and means for binarizing and analyzing image data of the surface of the inspection object obtained by the television camera and determining a defect of the inspection object, the inspection object is magnetized. An automatic magnetic particle flaw detection apparatus having flattening means for flattening in a direction in which a defect of an inspection object spreads before performing the inspection. 2. A means for magnetizing a test object, a means for attaching a magnetic powder solution to a surface of a magnetized test object, a means for irradiating light to the surface of the test object, and a portion irradiated by the means Magnetizing the inspection object in a magnetic particle flaw detection device comprising a television camera for imaging the object and means for binarizing and analyzing the image data of the surface of the inspection object obtained by the television camera to determine a defect of the inspection object Prior to this, an inspection area is set from flattening means for flattening in the direction in which the defect of the inspection object spreads, and image data of the surface of the inspection object obtained by the TV camera, and image data in the area is determined in advance. A binarized image based on the threshold value, calculate (vertical length) / (horizontal length) of the binarized image, and determine a defect only when the calculated value is smaller than a reference value. Specially Automatic magnetic particle inspection equipment.