JPH06294748A - Surface flaw inspection method at welded part of uo steel pipe - Google Patents

Abstract

PURPOSE:To detect surface flaw at a welded part of a UO steel pipe with high reliability. CONSTITUTION:A welded part 2 of UO steel pipe and the vicinity thereof are irradiated with light to form a slit light 4 in the vicinity of the welded part 2. The slit light 4 is then picked up by means of an image pickup unit 5 which produces an optical cut image 22 being employed in the flaw detection at the welded part 2. The optical cut image 22 is subjected to fine line processing to produce a fine line data S(X) which is then subjected to difference processing and flaw emphasis processing to produce a flaw detection data E(X) being employed in the decision of flaw. When a decision is made that a flaw is present, the fine line data S(X) is operated in order to detect the flaw and to decide the size of the flaw thus detecting the surface flaw highly accurately while attaining the information relevant to the size of the flaw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting the surface of a welded portion of a UO steel pipe, for example, it is suitable for use in a method for determining the presence or absence of a flaw by imaging the surface defect of the welded portion of the UO steel pipe by an optical cutting method. It is something.

[0002]

2. Description of the Related Art Conventionally, various methods have been used to inspect the surface of welds of UO steel pipes for defects. Current U
The surface flaw inspection of the welded portion of the O steel pipe is performed by a human visual inspection.

By the way, as a general surface flaw inspection method, for example, an optical method, an eddy current method, a leakage magnetic flux method and the like can be mentioned. Among these surface flaw inspection methods, the optical method is to scan and irradiate the object to be inspected with a laser spot or the like, and process a time-series reception signal obtained by receiving specular reflection light or scattered light. It is used for flaw detection and is used as a surface flaw inspection means for steel plates.

In the eddy current method, a high frequency magnetic field excites an eddy current on the surface of the object to be inspected, a detection coil is brought close to the object to be inspected, and a magnetic flux value interlinking with the detection coil is detected to detect a flaw. Is to be inspected,
It is used as a surface flaw inspection means for various inspection objects.

The leakage magnetic flux method is a method for inspecting a flaw by detecting a change in leakage magnetic flux by moving a magnetic sensor in the vicinity of an object to be inspected and allowing the magnetic flux to permeate and moving a magnetic sensor in proximity to the object to be inspected. Yes, it is generally used as a surface defect detection method for steel sheets.

[0006]

In the above-mentioned conventional flaw detection method, generally, the object to be inspected has a uniform shape. However, FIGS. 10 to 12 show a schematic shape of an undercut flaw, which is an example of a flaw generated at an end portion of a welded portion, but in the welded portion of the UO steel pipe 1, the steel pipe base metal portion is provided with a buildup. Therefore, in order to inspect the fine undercut flaw 21 generated at the weld end portion, an inspection method capable of precisely inspecting the welded portion having undulations and the vicinity thereof is necessary.

When the surface of the object to be inspected has undulations, for example, in the optical method, the crossing angle between the plane including the optical axis of the light projecting and receiving system and the surface of the object to be inspected changes, so that the received light intensity varies. Therefore, it becomes difficult to inspect fine defects.

Further, in order to obtain the detection accuracy by the method such as the eddy current method or the leakage magnetic flux method, it is necessary to shorten the gap between the sensor and the surface of the object to be inspected and keep it constant. Defects on the surface are difficult to detect.

Further, there is a light cutting method as a method for measuring the shape. In FIG. 10, the shape of the undercut flaw 21 is
Although it is shown in a large size for easy understanding, it is necessary to detect even very fine things because it is harmful, and since the shape of the welded part is not constant, it is possible to reliably detect flaws. No treatment method was proposed.

In view of the above problems, it is an object of the present invention to make it possible to detect a surface flaw in a welded portion of a UO steel pipe with high reliability.

[0011]

A method for inspecting a weld surface flaw of a UO steel pipe according to the present invention is a light obtained by irradiating a UO steel pipe weld portion and its vicinity with a slit light and imaging the slit light by an image pickup device. In a method of detecting a flaw in a welded portion using a cut image, a first process of thinning the light cut image to obtain thinned data, and a difference process of the thinned data to obtain difference data The second process, the third process for obtaining flaw detection data by performing flaw enhancement processing on the difference data, and the presence / absence of a flaw are determined using the flaw detection data, and a thin line is used when it is determined that there is a flaw. And a fourth process for detecting a flaw and determining the size of the flaw by calculating the digitized data.

[0012]

According to the above-described flaw detection method, since the processing is performed by emphasizing and detecting only the flaw portion, it is highly reliable even for fine flaws in a UO steel pipe welded portion having undulations such as padding. It becomes possible to detect, and when it is determined that there is a flaw, the depth of the flaw is measured so that information on the flaw depth can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for inspecting the surface of a welded portion of a UO steel pipe according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an example of a flaw inspection apparatus for explaining an embodiment of the present invention.

In FIG. 1, 1 is a UO steel pipe and 2 is a welded portion thereof. When the surface flaw of the UO steel pipe 1 is inspected as described above, the slit light projector 3 emits light to form the slit light 4 at and near the welded portion. Further, the image pickup device 5 is arranged at a position where the slit light 4 is captured.
Although the case where the welded portion on the inner surface of the UO steel pipe is inspected is shown here, in the case of the outer surface as well, slit light may be formed on the welded portion on the outer surface and in the vicinity thereof by the same method to perform imaging. .

An example of the slit light projector 3 is shown in FIG.
As shown in, the laser diode 13 is caused to emit light, and the laser light is condensed by the collimator lens 14. Then, a device is used that spreads the laser light into a fan shape by the cylindrical lens 15 to form the slit light 4. As a result, the slit light 4 having a half width of, for example, about 0.1 mm is formed.

The image pickup device 5 is, for example, a CCD.
A camera is used. In a normal case, one image pickup device may be used, but since it is desired that the image pickup device 5 has sufficient resolution in the case of detecting a minute flaw, for example, a plurality of image pickup devices may be provided with a limited field of view. It is possible to deal with this by disposing it. FIG. 1 shows an example in which two image pickup devices are used.

By the way, welding defects called undercut often occur in the skirt of the welded portion 2 as indicated by reference numeral 21 in FIG. The shape thereof is generally V-shaped as shown in FIG. 4 which is a sectional view taken along the line AA ′ of FIG.

Therefore, when the image pickup device 5 photographs the slit light 4 between BB 'in FIG. 3, a light section image 22 as shown in FIG. 5 is obtained. The light section image 22 thus obtained is input to the flaw detection processing unit 6.

In the flaw detection processing unit 6, first, the light section image 22 is A / D converted in the image storage unit 7 and stored as a two-dimensional digital value (x, y). The thinning is performed by the unit 8. The thinning processing performed here is shown in detail in FIG.

As shown in FIG. 6, here, for the two-dimensional image data p (x, y), the process of selecting the point having the maximum brightness on one line in the screen y direction shown in FIG. 6 is performed. To the y of the maximum brightness point corresponding to the x coordinate.
A thinned data string S (x) in which coordinate values are arranged is obtained.

At this time, if the luminance of the point selected as the maximum luminance does not reach the luminance threshold value so as to prevent noise outside the slit image from being erroneously selected for a portion where the luminance of the slit image is small, the maximum in x _n-1 is obtained. Y coordinate of luminance point S (x
_The same value as ( _n-1 ) is used to prevent the thinned data from deviating from the slit image.

Next, in the difference processing unit 9, the thinning processing unit 8
The difference data string D (x) is calculated for the thinned data string S (x) output by FIG. 7 shows the details of the calculation method. By setting an appropriate number of pixels dx, the thinned data string S
For some point B (x _n, y _B ) on (x), the point A (x _n
-Dx, y _A ) and the point C (x _n + dx, y _c ) are taken, and for these y coordinates, dy = (y _c −y _B ) − (y _B −y _A ) ... (Equation 1) The element dy is calculated.

This operation is performed over the entire x coordinate to create a difference data string D (x) in which the difference elements dy are arranged in correspondence with the x coordinate. In the difference data string D (x) thus obtained, as shown in FIG. 7, the non-flaw part has a value close to 0, and the thinned data sequence S (x) has a V-shaped flaw. Only the part has a large value.

Defects may be judged using this difference data string D (x). However, in order to improve the judgment accuracy, the defect emphasizing processing unit 10 makes a difference data string D as shown in FIG. The moving sum operation of k continuous data of (x) is performed by the following two equations.

[0025]

[Equation 1]

Then, a flaw detection data string E (x) in which the flaw portion is further emphasized is created. In the flaw presence / absence determination unit 11,
The size of the flaw detection data string E (x) is compared with a preset flaw detection threshold value. Then, when all the elements of the flaw detection data string E (x) do not exceed the flaw detection threshold value, it is detected that there is no flaw, and the flaw detection processing for the image is finished.

Further, as shown in FIG. 8, when there is an element that exceeds the flaw detection threshold value in the flaw detection data string E (x), it is detected that there is a flaw, and the flaw depth determination unit 12 At, the flaw depth is determined.

In the flaw depth determination unit 12, the thinned data string S
The flaw depth is measured by using (x) to determine the flaw. Also,
As shown in FIG. 9, UO in the thinned data string S (x)
An approximate straight line of a portion corresponding to the base metal portion of the steel pipe is created, and the depth of the flaw portion is calculated as the maximum number of pixels in which the elements of the thinned data string S (x) are below the value on the base metal approximate straight line. Then, the maximum depth value of the flaw is calculated by taking the product of the length in the flaw depth direction corresponding to each pixel measured in advance.

Similarly, the above-described processing is performed over the entire length of the steel pipe, and the defect presence / absence information and the defect depth information obtained thereby are transmitted to an external device such as a product management computer.

Next, an example in which a specific numerical value is set and a flaw is inspected in the above-described embodiment will be described. In the slit light projector 3, two 20 mW laser diodes are used.
The pulse was lit in msec. Also, the image pickup device is a CCD
Images were taken with a camera in a field of view of 32 mm in the width direction and 45 mm in the depth direction, and then processed using an image processing device of 512 × 512 pixels.

When dx = 10 in the difference processing unit, k = 6 in the defect emphasis processing unit, the defect detection threshold value in the defect presence / absence determination unit was set to 30, and the longitudinal direction of the UO steel pipe was inspected at a pitch of 2 mm, the result was 0. Undercut flaws having a depth of 2 mm or more in the longitudinal direction of 3 mm or more were reliably detected, and the flaw depth was determined with an accuracy of about ± 0.05 mm.

[0032]

As described above, according to the present invention, the flaw detection method emphasizes and detects only the flaw portion. Therefore, it is possible to detect fine flaws in a UO steel pipe welded portion having undulations such as buildup. It is also possible to detect defects with high reliability. Further, when it is determined that there is a flaw, the depth of the flaw can be measured to obtain information on the flaw depth. Therefore, the method according to the present invention is suitable for automatic inspection of a welded portion of a UO steel pipe. Can be applied to.

[Brief description of drawings]

FIG. 1 is a block diagram of a flaw inspection apparatus for explaining an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an outline of an example of a slit light projector.

FIG. 3 is a partial perspective view of a UO steel pipe showing a schematic shape of an undercut flaw of a welded portion which is a flaw to be detected.

FIG. 4 is a cross-sectional view taken along the line A-A ′ in FIG.

5 is a diagram showing a light section image taken along line BB ′ in FIG.

FIG. 6 is an explanatory diagram showing the content of processing performed by a thinning processing unit.

FIG. 7 is an explanatory diagram showing contents of difference processing performed by a difference processing unit.

FIG. 8 is an explanatory diagram illustrating a process based on a moving sum of a plurality of pixels, which is performed by the defect emphasis processing unit.

FIG. 9 is an explanatory diagram showing a method of measuring a flaw depth performed by a flaw depth determination unit.

FIG. 10 is an explanatory diagram showing a schematic shape of an undercut flaw generated at an end portion of a welded portion.

11 is a cross-sectional view taken along the line A-A ′ in FIG.

FIG. 12 is a cross-sectional view taken along the line C-C ′ in FIG.

[Explanation of symbols]

 1 UO steel pipe 2 UO steel pipe welded portion 3 slit light projector 4 slit light 5 imaging device 6 flaw detection processing portion 7 image storage portion 8 thinning processing portion 9 difference processing portion 10 flaw enhancement processing portion 11 flaw presence / absence determination portion 12 flaw depth Judgment part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Takashima 8-1-1 Tsukaguchihonmachi, Amagasaki City Inside the Industrial Systems Research Center, Mitsubishi Electric Corporation (72) Inventor Katsuya Ueki 1-1-2 Wadazakicho, Hyogo-ku, Kobe Mitsubishi Electric Corporation Control Factory

Claims (1)

[Claims] 1. A method of irradiating slit light to a UO steel pipe welded portion and its vicinity and detecting a flaw in the welded portion by using a light cut image obtained by imaging the slit light with an imaging device, wherein the light cutting is performed. The first to obtain thinned data by thinning the image
And the difference processing of the thinned data to obtain difference data
And the third process for obtaining defect detection data by performing defect enhancement processing on the difference data, and determining the presence / absence of a defect using the defect detection data, and thinning the case when it is determined that there is a defect. A UO steel pipe welded portion surface flaw inspection method, comprising: a fourth process for detecting flaws and determining the size of flaws by calculating data.