JP2012242233A - Pipe inner surface inspection method and pipe inner surface inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pipe inner surface inspection method whose detection accuracy of a flaw on a pipe inner surface is high and which requires less labor and cost, and a pipe inner surface inspection device.SOLUTION: An annular lighting 3 is placed opposite an end surface 21 of a steel pipe 2 to nearly match a central shaft 32 of the annular lighting 3 and a pipe shaft 22 of the steel pipe 2, illumination light is emitted to an inner surface 23 of the steel pipe 2, a camera 4 is placed opposite the end surface 21 of the steel pipe 2 to nearly match a light axis of the camera 4 the pipe shaft 22 of the steel pipe 2, and images of the end surface 21 and the inner surface 23 are picked up. An inner surface image is extracted from the picked up images, and the inner surface image is divided into a plurality of annular areas in a radial direction. A reference range of density is set every divided annular area, and a group of pixels whose density deviates from the reference range is extracted as a group of flaw candidate pixels. Prescribed density defined for every annular area is subtracted from the density of pixel in the prescribed pixel including the group of flaw candidate pixels, a pixel area where density is subtracted is converted into a pixel area when viewed from the radial direction of the pipe inner surface, and it is determined on the basis of the converted pixel area whether or not there is a flaw.

Description

  The present invention relates to a pipe inner surface inspection method and a pipe inner surface inspection apparatus. In particular, the present invention relates to a pipe inner surface inspection method and an in-pipe inspection apparatus with good detection accuracy of flaws on the pipe inner surface.

Conventionally, it is common to emit illumination light from the outside to the inside of a steel pipe and visually inspect the flaws on the inside.
However, a bright area and a dark area are formed in the circumferential direction of the inner surface depending on the position of illumination. Moreover, even if the illumination is arranged so that there is little variation in the brightness in the circumferential direction, a great variation in the brightness occurs in the tube axis direction of the steel pipe.
As described above, when the brightness varies greatly, it becomes difficult to see the flaw depending on the position of the flaw, and the flaw may be overlooked.
Also, when the diameter of the steel pipe is small or when the flaw is in the back of the pipe axis direction, the flaw is viewed from an oblique direction. It may be difficult to determine whether.
In addition, the inner surface is also contaminated, and the detection accuracy of flaws depends greatly on the ability of the inspector.
Therefore, the flaw detection accuracy varies depending on the ability of the inspector, the diameter of the steel pipe, etc., and there is a risk of missing the flaw.

Also known is a method of detecting flaws on the surface of a steel sheet by irradiating the surface of the steel sheet with a linear laser beam, imaging the surface of the steel sheet with a delay integration type imaging means, and outputting a light cut image. (For example, refer to Patent Document 1). However, when the diameter of the steel pipe is small, it is difficult to detect flaws by this method because the imaging means cannot be put in the steel pipe. In addition, when the unevenness of the flaw is small or when the difference in color density between the flaw and the surrounding is small, it is difficult to detect the flaw by this method.
Also, a method for detecting flaws on the surface by combining eddy current flaw detection or leakage magnetic flaw detection and flaw detection using an image is known (for example, see Patent Document 2). However, in this method, both eddy current testing or leakage magnetic flux testing and image testing must be performed, which is laborious and expensive.

JP 2010-91514 A JP 2009-8659 A

  The present invention has been made to solve the problems of the prior art, and provides a pipe inner surface inspection method and an in-pipe inspection apparatus that are highly accurate in detecting defects on the inner surface of the pipe and that do not require labor and cost. This is the issue.

In order to solve the above problems, the inventors of the present invention have made extensive studies and as a result, obtained the following findings (1) to (4).
(1) By making the annular illumination face the end face of the tube and making the central axis of the annular illumination substantially coincide with the tube axis of the tube, fluctuations in the circumferential brightness of the inner surface of the tube can be reduced.
(2) When the inner surface of the tube is imaged from the tube axis direction by the imaging means, the inner surface image has a lower inner surface concentration as it is closer to the annular illumination, and a higher concentration at a position farther from the annular illumination, and the concentration in the tube axis direction. Fluctuations occur. Therefore, the inner surface image is divided into a plurality of annular regions in the radial direction, and a density reference range for discriminating defect candidates is provided for each annular region, so that density fluctuations in the tube axis direction are not affected by defect detection accuracy. The effect on it can be reduced.
(3) By converting an annular region including a defect candidate into an annular region when viewed from the radial direction of the pipe, the exact shape of the defect can be known, so that the detection accuracy of the defect is improved.
(4) If all the annular regions constituting the inner surface image of the tube are converted to the annular region when viewed from the radial direction of the tube, the amount of data processing increases, which requires cost and labor. Therefore, cost and labor can be reduced by converting only the annular region including the flaw candidate into the annular region when viewed from the radial direction of the pipe.

  The present invention has been completed based on the above findings obtained by the present inventors. That is, the annular illumination is made to face one of the end faces of the tube, the center axis of the annular illumination and the tube axis of the tube are substantially coincided, and the illumination light of the annular illumination is emitted toward the inner surface of the tube. And an imaging step in which the imaging means is made to face either one of the end surfaces, the optical axis of the imaging means and the tube axis of the tube are substantially matched, and the end surface and the inner surface of the tube are imaged by the imaging means; And extracting an inner surface image from a position corresponding to the inner peripheral edge of one of the end faces to a position corresponding to the inner peripheral edge of the other end face from the image captured in the imaging step, A division step for dividing the annular region into a plurality of annular regions, and a density reference range for each of the annular regions divided by the division step, and a pixel group whose density deviates from the reference range is extracted as a candidate pixel group. A determination step; The predetermined density determined for each of the annular areas is subtracted from the density of the pixels in the predetermined pixel area including the flaw candidate pixel group extracted in the primary discrimination step, and the pixel area on which the density has been subtracted is There is provided a tube inner surface inspection method characterized by comprising a secondary determination step of converting into a pixel area when viewed from the radial direction and determining the presence or absence of a flaw from the converted pixel area.

Here, the annular illumination means illumination in which a light source is formed in an annular shape or a plurality of light sources are arranged in an annular shape. Specifically, for example, illumination in which a plurality of light sources such as LEDs and light bulbs are annularly arranged, and illumination such as an annular fluorescent lamp can be exemplified.
In the above division step, the number of divisions of the annular region may be determined to be a constant number regardless of the fluctuation range of the density of the inner surface image, or when the fluctuation range of the density of the inner surface image is large. The number of divisions may be increased, and may be decreased when it is small.
The reference range of the density for each annular region in the primary determination step may be determined based on, for example, the representative value of the density of each annular region. Representative values include maximum density, minimum density, and average density.
The density to be subtracted in the secondary discrimination step may be determined based on the representative value of the density of each annular region. Representative values include maximum density, minimum density, and average density. Specifically, for example, the concentration to be subtracted may be the average concentration of each annular region. Further, the density to be subtracted may not be the average density of the annular area to which the pixel area belongs, but may be the lowest density of the annular area.
When subtracting the density determined for each annular area, if the pixel area to be subtracted straddles a plurality of annular areas, the same density is subtracted over the entire pixel area to be subtracted. Instead, the density determined for each annular region to which each pixel constituting the subtracted pixel region belongs is subtracted.

According to the present invention, since the central axis of the annular illumination and the tube axis of the tube are substantially coincided with each other, fluctuations in the circumferential direction of the density of the inner surface image can be reduced.
Further, since the reference range of the density for extracting the defect candidate pixel group is defined and the pixel group outside the reference range is set as the defect candidate pixel group, the reference to be extracted becomes constant, and the missing of the defect can be reduced.
Even if the central axis of the annular illumination and the tube axis of the tube are substantially coincided as described above, the imaged inner surface image has a lower inner surface concentration as it is closer to the annular illumination, and a higher concentration as it is farther from the annular illumination. As described above, the concentration varies in the tube axis direction. Therefore, in the present invention, the inner surface image is divided into a plurality of annular regions in the radial direction, and a reference range of the density of the candidate pixel group is determined for each annular region. For example, the density of the reference range is lowered in the annular area near the annular illumination, and the density of the reference range is increased in the annular area far from the annular illumination. In this way, by setting the reference range of the density of the flaw candidate pixel group for each annular region in accordance with the fluctuation of the density in the tube axis direction, regardless of the brightness fluctuation due to the position in the pipe axis direction on the inner surface of the pipe. Therefore, the flaw candidate pixel group can be extracted with the same accuracy.

In the second determination step, the density determined for each annular area is subtracted. For example, if the average density for each annular area is subtracted, the density of each annular area after the subtraction is set to an equivalent density level. Can do. By making the density levels of the respective annular regions equal, the appearance of the flaws becomes equal, and variations in flaw detection accuracy between the annular regions can be reduced. In particular, a flaw candidate pixel group extending in the tube axis direction and straddling a plurality of annular regions has less variation in density in the tube axis direction, so that it is easy to see and detection accuracy is improved.
In the second determination step, the pixel area including the flaw candidate pixel group is converted into a pixel area when viewed from the radial direction of the inner surface of the tube, so that the exact shape of the flaw is known and the flaw candidate pixel group is obtained. A flaw can be detected from the pixel group with high accuracy. As a result, it is possible to reduce errors in determining what is not a flaw as a flaw.
In particular, if the person determines whether or not there is a flaw in the second discrimination step, the flaw pixel area is converted into a pixel area when viewed from the radial direction of the tube inner surface while maintaining the density difference in the area. Since it becomes the same state as in the case of visual observation, the flaw detection accuracy is improved.

In the present invention, if only the first determination step cannot be detected without performing the second determination step, there is a high possibility that a non-flaw is determined as a defect, and the detection accuracy of the defect is deteriorated.
Further, if only the second determination step is performed without performing the first determination step, the inner surface image of the entire area of the inner surface of the tube must be converted into an inner surface image when viewed from the radial direction of the tube. In addition, since the amount of data processing increases, cost and labor are required.
Therefore, as in the present invention, by combining the first determination step and the second determination step, it is possible to improve the flaw detection accuracy without cost and effort.

  In order to solve the above-mentioned problem, the present invention is opposed to any one end surface of the tube, and is opposed to any one of the end surfaces, annular illumination for emitting illumination light toward the inner surface of the tube, Imaging means for imaging an end face and an inner surface of the tube, and defect candidate display means for extracting and displaying a defect candidate pixel group from an image of the tube imaged by the imaging means, and the annular illumination has a central axis The tube is arranged so as to substantially coincide with the tube axis of the tube, the imaging means is arranged so that its optical axis substantially coincides with the tube axis of the tube, and the flaw candidate display means is imaged by the imaging means. An inner surface image from a position corresponding to the inner peripheral edge of either one of the end surfaces to a position corresponding to the inner peripheral edge of the other end surface is extracted from the images of the end surface and the inner surface of the tube, and the inner surface image is radially Divided into a plurality of annular regions, and A density reference range is provided, a pixel group whose density deviates from the reference range is extracted as a defect pixel group, and a predetermined pixel area is determined for each annular area from the density of pixels in a predetermined pixel area including the defect candidate pixel group. The tube inner surface inspection apparatus is characterized in that the pixel area from which the density is subtracted is converted into a pixel region when viewed from the radial direction of the tube inner surface.

  Preferably, the tube inner surface inspection device is capable of abutting against any one of the end surfaces, and is emitted from the annular illumination toward the inner surface of the tube when abutting against any one of the end surfaces. A contact plate through which the illumination light passes, and a fixed frame to which the imaging means, the annular illumination, and the contact plate are attached. The imaging means and the contact plate are optical axes of the imaging means. And the corresponding illumination plate are fixed to the fixed frame so that they are perpendicular to each other, and the annular illumination is mounted so as to be movable between the imaging means and the contact plate in parallel with the optical axis of the imaging means. It is done.

Since the abutment plate allows the illumination light emitted from the annular illumination to the inner surface of the tube to pass through, it is possible to image the end surface and the inner surface of the tube with the end surface of the tube abutting against the abutment plate.
Here, the contact plate is, for example, a plate made of a transparent material such as glass or resin, or a plate made of metal or resin having a mesh structure. Further, it may be a plate having a hole having a diameter larger than the inner diameter of the tube and smaller than the outer diameter of the tube so that the end surface of the tube is brought into contact with the periphery of the hole.

When imaging the inner surface of the tube, it is desirable that the inner surface of the tube is brightly illuminated over the entire length in the tube axis direction. Therefore, the annular illumination is preferably a position where the illumination light can be illuminated over the entire length of the inner surface in the tube axis direction and as close to the end surface of the tube as possible.
On the other hand, in order to image the inner surface extending in the tube axis direction, the depth of field must be increased, so that the imaging means is separated from the contact plate within the range of the distance that can be imaged in consideration of the magnification of the lens. Position is preferred.
As described above, since the preferred position of the annular illumination and the preferred position of the imaging means are independent of each other, the appropriate positions cannot be obtained if the annular illumination and the imaging means are determined as a unit. Therefore, it becomes difficult to detect flaws.
Therefore, the imaging conditions can be optimized by allowing the annular illumination to move separately from the imaging means, as in the preferred tube inner surface inspection apparatus described above. Further, since the annular illumination moves in parallel with the optical axis of the image pickup means, the uniformity of the density of the inner surface image in the circumferential direction can be maintained even if the annular illumination is moved.

  By using a fixed frame, when performing inner surface inspection of a plurality of tubes having the same tube inner diameter and length, if the abutment plate is brought into contact with the end surface of the tube, there is no gap between the imaging means and the abutment plate. Since the distance and the distance between the annular illumination and the abutting plate are constant, it does not take time to adjust the imaging conditions even if the tubes are sequentially inspected.

  According to the present invention, it is possible to increase the accuracy of detection of flaws on the inner surface of a pipe without labor and cost.

FIG. 1 is a configuration diagram illustrating an example of a pipe inner surface inspection apparatus used in the pipe inner surface inspection method according to the present embodiment. FIG. 2 is a diagram for explaining an inner surface image extraction method. FIG. 2A is a captured image of the end surface and the inner surface of the steel pipe, FIG. 2B is a captured image obtained by binarizing the captured image of FIG. 2A, and FIG. It is a schematic diagram of the outer periphery and inner periphery of a near side end surface extracted from a captured image, and the inner periphery of a back side end surface. FIG. 3 is a diagram for explaining a method for measuring the density distribution of the inner surface image. Fig.3 (a) is a figure which shows the center position of a steel pipe, FIG.3 (b) is a figure which shows the measurement line which measures density | concentration distribution. FIG. 4 is a diagram for explaining a method of dividing the fluctuation range of the average density. FIG. 5 is a diagram illustrating a method of dividing the inner surface image into a plurality of annular regions. FIG. 6 is a diagram for explaining a method of selecting a pixel region including a flaw candidate pixel group from the inner surface image. FIG. 6A is a diagram illustrating a state in which four points for selecting a pixel region including a flaw candidate pixel group are plotted, and FIG. 6C illustrates a pixel region including a flaw candidate pixel group with a line. It is a figure which shows the state enclosed. FIG. 7 is a diagram illustrating a state in which a predetermined density determined for each pixel area is subtracted from the flaw pixel area. FIG. 7A is an inner surface image before the predetermined density is subtracted, FIG. 7B is a diagram showing the density to be subtracted, and FIG. 7C is a diagram in which the predetermined density is subtracted. It is an inner surface image after. FIG. 8 is a diagram for explaining a method of converting a flaw pixel area from a sector shape to a rectangle. FIG. 8A is a diagram illustrating coordinates before conversion, and FIG. 8B is a diagram illustrating coordinates after conversion. FIG. 9 is a diagram for explaining a method of converting the length in the tube axis direction. FIG. 9A is a schematic diagram illustrating a state in which the inner surface is being imaged, and FIG. 9B is a diagram illustrating a relationship between L and R ′ in the schematic diagram of FIG. FIG. 9C is a diagram showing the relationship between L and r ′ in the schematic diagram of FIG. 9A, and FIG. 9D is a diagram showing the coordinates after conversion. FIG. 10 is a photograph of each stage in which a pixel region having a flaw candidate pixel group is converted into a pixel region when viewed from the radial direction of the tube inner surface. FIG. 10A shows a pixel region after the density is subtracted, FIG. 10B shows a pixel region after conversion into a rectangle, and FIG. 10C shows the length in the tube axis direction. This is a pixel area after the height is converted.

Hereinafter, a pipe inner surface inspection method according to an embodiment of the present invention will be described with reference to the accompanying drawings as appropriate.
FIG. 1 is a configuration diagram illustrating an example of a pipe inner surface inspection apparatus used in the pipe inner surface inspection method according to the present embodiment.
The pipe inner surface inspection apparatus 1 includes an annular illumination 3 that emits illumination light to the steel pipe 2, a camera (imaging means) 4 that images the steel pipe 2, and a flaw candidate display means 5 that displays a flaw candidate pixel group. .
The annular illumination 3 is disposed so as to face the end surface 21 of the steel pipe 2 so that the central axis 32 of the annular illumination 3 and the tube axis 22 of the steel pipe 2 substantially coincide with each other.
The annular illumination 3 has, for example, a configuration in which a plurality of LEDs 31 are attached at equal intervals in the circumferential direction on a base material such as a synthetic resin formed in an annular shape. The LED 31 faces the central axis side of the annular illumination 3 and emits illumination light inclined with respect to the central axis 32 of the annular illumination 3.
The camera 4 is disposed so as to face the end surface 21 of the steel pipe 2 so that the optical axis 41 of the camera 4 and the pipe axis 22 of the steel pipe 2 substantially coincide.
The camera 4 is a CCD camera, for example, and transmits the captured image data to the candidate display means 5.
The flaw candidate display means 5 is a personal computer (hereinafter referred to as PC as appropriate) 51 and a program for detecting a candidate pixel group that is not installed in the PC 51 and displaying a pixel area including the flaw candidate pixel group on the monitor of the PC 51. With.
The pipe inner surface inspection apparatus 1 preferably includes a contact plate 6 that contacts the end surface 21 of the steel pipe 2 and a fixed frame 7 to which the contact plate 6 and the like are attached. An annular illumination 3, a camera 4 and a contact plate 6 are attached to the fixed frame 7.
Hereinafter, a case where the pipe inner surface inspection apparatus 1 includes the contact plate 6 and the fixed frame 7 will be described as an example.
The contact plate 6 is made of, for example, a transparent resin.
The fixed frame 7 includes a camera mounting plate 71 to which the camera 4 is mounted, and a plurality of parallel guide bars 73 that connect the camera mounting plate 71 and the contact plate 6. The guide rod 73 is configured to be perpendicular to the camera mounting plate 71.
The contact plate 6 is fixed vertically to the guide rod 73.
The camera mounting plate 71 has a hole for mounting the camera 4 at the center.
The camera mounting plate 71 is configured to be movable along the guide rod 73. Specifically, for example, the camera mounting plate 71 includes a plurality of through holes through which the plurality of guide rods 73 penetrate, and the penetrating guide rod 73 is fixed with screws. By moving the camera mounting plate 71 along the guide rod 73, the distance between the camera mounting plate 71 and the contact plate 6 can be changed, and thereby the distance between the camera 4 and the contact plate 6 can be changed. it can.

The annular illumination 3 includes a plurality of through holes that allow the plurality of guide bars 73 to pass through, and is attached to the fixed frame 7 by allowing the guide bars 73 to pass through the through holes.
The annular illumination 3 is formed so that its central axis 32 is parallel to the guide rod 73, and can move in parallel to the guide rod 73.
The camera 4 is attached to the camera mounting plate 71 so that the optical axis 41 thereof substantially coincides with the central axis 32 of the annular illumination 3.

Since the abutment plate 6 allows the illumination light emitted from the annular illumination 3 to the inner surface 23 of the steel pipe 2 to pass through, the end surface 21 of the steel pipe 2 and the end surface 21 of the steel pipe 2 are in contact with the abutment plate 6. The inner surface 23 can be imaged.
By allowing the annular illumination 3 to move separately from the camera 4, the imaging conditions can be optimized. Further, since the annular illumination 3 moves in parallel with the optical axis of the camera 4, evenness of the inner surface image density can be maintained even if the annular illumination 3 is moved.
When the inner surface of a plurality of steel pipes 2 having the same inner diameter and length of the steel pipe 2 is to be inspected by using the fixed frame 7, the abutment plate 6 is brought into contact with the end face 21 of the steel pipe 2 so Since the distance between the contact plate 6 and the distance between the annular illumination 3 and the contact plate 6 are constant, it is not time-consuming to adjust the imaging conditions even if the steel pipe 2 is inspected sequentially.

Next, a pipe inner surface inspection method using the above-described pipe inner surface inspection apparatus 1 will be described.
First, the next imaging step is performed.
The annular illumination 3 is made to face one of the end faces 21 of the steel pipe 2 and the central axis 32 of the annular illumination 3 and the tube axis 22 of the steel pipe 2 are substantially aligned so that the illumination light of the annular illumination 3 is directed to the inner surface of the steel pipe 2. The optical axis 41 of the camera 4 and the tube axis 22 of the steel pipe 2 are substantially aligned with each other, and the end face 21 and the inner surface of the steel pipe 2 are aligned with the camera 4. Imaging is performed (imaging step).
In the present embodiment, the annular illumination 3 is already arranged so as to face the end surface 21 of the steel pipe 2 so that the central axis 32 substantially coincides with the pipe axis 22 of the steel pipe 2, and the camera 4 has an optical axis 41 of the steel pipe. Since it arrange | positions facing the end surface 21 of the steel pipe 2 so that it may correspond with the 2 pipe axis 22 substantially, an imaging step is performed as follows, for example.
The annular illumination 3 is moved along the guide rod 73 so that the illumination light of the annular illumination 3 is emitted to the entire inner surface of the steel pipe 2. At this time, for example, the illumination light emitted from the annular illumination 3 may have an incident angle α on the inner surface of the end surface 21 of the steel pipe 2 of approximately 80 °.
Subsequently, the camera mounting plate 71 is slid along the guide rod 73 to move the camera 4 to the imaging position. And the end surface 21 and the inner surface 23 of the steel pipe 2 are imaged by the camera 4.
Since the central axis of the annular illumination 3 and the tube axis of the steel pipe 2 are substantially coincident with each other, fluctuations in the circumferential direction of the density of the inner surface image can be reduced.

Next, from the image captured in the imaging step, from the position corresponding to the inner peripheral edge of the end surface 21 of the steel pipe 2 on the side where the camera 4 is located (hereinafter referred to as the near side), the side opposite to the near side (hereinafter referred to as the back side). The inner surface image up to a position corresponding to the inner peripheral edge of the end surface 21 of the steel pipe 2 is extracted, and the extracted inner surface image is divided into a plurality of annular regions in the radial direction (division step).
The dividing step is performed as follows, for example.
FIG. 2 is a diagram for explaining an inner surface image extraction method. 2A is a captured image of the end surface 21 and the inner surface 23 of the steel pipe 2, and FIG. 2B is a captured image obtained by binarizing the captured image of FIG. 2A. (c) is a schematic diagram of the outer periphery and inner periphery of the front side end surface extracted from the captured image, and the inner periphery of the back side end surface. 2A and 2B, the contact plate 6 is a resin plate having a mesh structure, and the mesh line of the contact plate 6 is shown in the vertical direction and the horizontal direction passing through the center of the image.
The camera 4 sends the image data of the captured inner surface image to the flaw candidate display means 5. Then, the flaw candidate display means 5 performs binarization processing or the like on the inner surface image (see FIG. 2A) according to the installed program (see FIG. 2B), and the outer peripheral edge C1 and the inner edge of the end surface 21 The peripheral edge C2 is extracted. Since the illumination light is emitted to the end face 21, the density of the portion of the end face 21 is low. On the other hand, since the density is higher on the outer side and the inner side of the end face 21 than on the end face 21, there is a density boundary with the end face 21. The flaw candidate display means 5 extracts the density boundaries as the outer peripheral edge C1 and the inner peripheral edge C2. Similarly, the inner peripheral edge C3 of the end surface 21 of the steel pipe 2 on the back side is extracted (see FIG. 2 (c)).
Then, the flaw candidate display means 5 extracts a region surrounded by the inner peripheral edge C3 on the back side and the inner peripheral edge C2 on the near side as an inner surface image in accordance with the installed program.

FIG. 3 is a diagram for explaining a method for measuring the density distribution of the inner surface image. Fig.3 (a) is a figure which shows the center position of a steel pipe, FIG.3 (b) is a figure which shows the measurement line which measures density | concentration distribution.
The flaw candidate display means 5 calculates the center of gravity of the area surrounded by the outer periphery C1 on the near side in accordance with the installed program, and calculates the position of the calculated center of gravity as the tube axis position G (hereinafter, the position of the tube axis in the image). (Referred to as the center position as appropriate) (see FIG. 3A).
Subsequently, the flaw candidate display means 5 measures the density distribution from the center position G to the front inner periphery C2 along a straight line from the center position G to the front inner periphery C2 according to the installed program. To do. Straight lines from the center position G toward the inner peripheral edge C2 on the near side are provided at an angular pitch set in advance in the circumferential direction. In the present embodiment, the density distribution on the measurement lines D1, D2, D3, and D4 extending in four directions from the center position G with an angular pitch of 90 ° is measured (see FIG. 3B).

Subsequently, the average density at the same distance from the inner peripheral edge C2 to the center position G in the measurement lines D1, D2, D3, and D4 is calculated. Then, the fluctuation range of the average density is divided by a predetermined density range.
In this embodiment, the density is converted into an index called brightness, and the fluctuation range of the average density is divided. The density of the captured image is converted so that the brightest portion on the inner surface 23 has a brightness of 100% and the darkest portion of the captured portions has a brightness of 0%. Then, four reference values for dividing the inner surface image every 10% with respect to 100% brightness are provided. That is, the reference values are 90%, 80%, 70%, and 60% brightness.
FIG. 4 is a diagram for explaining a method of dividing the fluctuation range of the average density.
The horizontal axis in FIG. 4 indicates the distance from the inner peripheral edge C2, and the vertical axis indicates the brightness. FIG. 4 shows lines indicating the average distribution of brightness at the measurement lines D1, D2, D3, and D4.
Then, a point where the line indicating the average distribution of brightness intersects with the lines indicating the four reference values is obtained, and the distance from the inner peripheral edge C2 of each intersecting point is obtained. The obtained distance from the inner peripheral edge C2 is a position for dividing the inner surface image. In the example shown in FIG. 4, the inner surface image is divided into a plurality of annular regions at distances a, b, c, and d from the inner peripheral edge C2.

FIG. 5 is a diagram illustrating a method of dividing the inner surface image into a plurality of annular regions.
The flaw candidate display means 5 obtains the positions of the distances a, b, c, and d from the inner peripheral edge C2 on the measurement lines D1 to D4 according to the installed program. And the flaw candidate display means 5 calculates | requires four places whose distance is a from the inner periphery C2 by each line of the measurement lines D1-D4, and calculates | requires the circle nearest to the calculated | required four places by the least squares method. Similarly, a circle when the distance from the inner peripheral edge C2 is b, c, d is obtained by the least square method. Then, the inner face image is divided into a plurality of annular regions by the obtained circle.

Subsequently, the defect candidate display means 5 provides a density reference range for each annular area divided by the dividing step in accordance with the installed program, and extracts a pixel group whose density deviates from the reference range as a candidate pixel group. (Primary discrimination step).
The density reference range may be set by the candidate display means 5 without being based on the representative density value for each annular region, for example. Representative values include maximum density, minimum density, and average density.
In the present embodiment, the average brightness of each annular region is set to -5% to + 5%.
Then, the flaw candidate display means 5 extracts a pixel group that exceeds the reference range as a flaw candidate pixel group.
In this way, by determining the reference range of the density of the flaw candidate pixel group for each annular region in accordance with the fluctuation of the density in the tube axis direction, regardless of the brightness fluctuation due to the position in the pipe axis direction on the inner surface 23 of the steel pipe 2. In addition, the defect candidate pixel group can be extracted with the same accuracy.

Subsequently, the density determined for each annular area is subtracted from the density of the pixel in the predetermined pixel area including the flaw candidate pixel group extracted by the primary discrimination step, and the pixel area from which the density has been subtracted is determined from the radial direction of the tube inner surface. The pixel region is converted into a pixel region when viewed, and the presence or absence of a flaw is determined from the converted pixel region (secondary determination step).
The secondary determination step is performed as follows, for example.
FIG. 6 is a diagram for explaining a method of selecting a pixel region including a flaw candidate pixel group from the inner surface image. FIG. 6A is a diagram illustrating a state in which four points for selecting a pixel region including a flaw candidate pixel group are plotted, and FIG. 6C illustrates a pixel region including a flaw candidate pixel group with a line. It is a figure which shows the state enclosed.
The flaw candidate display means 5 displays the inner surface image on the monitor of the PC 51 according to the installed program, displays the extracted flaw candidate pixel group by marking, displays the coordinates of the position, etc. Be able to identify groups. Then, the operator selects a pixel area including the flaw candidate pixel group (hereinafter referred to as a flaw pixel area) from the inner surface image. For example, the operator plots four points (P1 to P4) surrounding the flaw candidate pixel group on the monitor of the PC 51 on which the flaw candidate pixel group is shown (see FIG. 6A). The flaw candidate display means 5 selects two points that are farthest from each other in the circumferential direction among the four points when viewed from the center position G according to the installed program (in the example of FIG. P2) From the center position G, straight lines M1 and M2 passing through the two points are drawn (see FIG. 6B). Further, the flaw candidate display means 5 is arranged in accordance with the installed program, and within the annular area to which the four points belong, the inner boundary line of the annular area closest to the center position and the outer side of the annular area farthest from the center position A boundary line is selected (in the example of FIG. 6B, boundary lines M3 and M4). A region surrounded by the two straight lines M1 and M2 and the two boundary lines M3 and M4 is a defect pixel region.

Subsequently, the flaw candidate display means 5 subtracts the density set for each annular area from the flaw pixel area according to the installed program, and displays the flaw pixel area from which the density has been subtracted on the monitor of the PC 51. The density to be subtracted may be set based on, for example, a representative value of density for each annular region. Representative values include maximum density, minimum density, and average density.
In the present embodiment, the average density for each annular region is subtracted from the entire inner surface image.
FIG. 7 is a diagram illustrating a state in which the density set for each annular region is subtracted from the flaw pixel region. FIG. 7A is an inner surface image before the density is subtracted, FIG. 7B is a diagram showing the density to be subtracted, and FIG. 7C is a diagram in which the set density is subtracted. It is a back inner surface image.
Since the average density for each annular area is subtracted, the density of each annular area after the subtraction can be set to an equivalent density level. If the candidate pixel group becomes difficult to see because of the pixel having a negative density value after subtraction, an appropriate density value may be added. By making the density levels of the respective annular regions equal, the appearance of the flaws becomes equal, and variations in flaw detection accuracy between the annular regions can be reduced. In particular, a flaw candidate pixel group extending in the tube axis direction and straddling a plurality of annular regions has less variation in density in the tube axis direction, so that it is easy to see and detection accuracy is improved.

Next, the flaw candidate display means 5 converts the flaw pixel area from which the density has been subtracted into a flaw pixel area when viewed from the radial direction of the inner surface of the tube according to the installed program, and displays it on the monitor of the PC 51. This conversion is performed geometrically based not only on the camera 4 but also on the positional relationship of the pixel areas. The conversion is performed as follows, for example.
FIG. 8 is a diagram for explaining a method of converting a flaw pixel area from a sector shape to a rectangle. FIG. 8A is a diagram illustrating coordinates before conversion, and FIG. 8B is a diagram illustrating coordinates after conversion.
First, the flaw pixel area is converted from a fan shape to a rectangle. As an example, a method for converting a flaw pixel region K having vertices K1, K2, K3, and K4 as shown in FIG.
The center position G of the inner surface image is set as the origin of the XY coordinates. The vertices K1 and K2 are separated from the center position G by a distance r, and the vertices K3 and K4 are separated from the center position G by a distance R.
The vertex K3 is on a straight line passing through the center position G and the vertex K1, and the angle formed between the straight line passing through the center position G and the vertex K1 and the Y axis is θ. Similarly, there is a vertex K4 on a straight line passing through the center position G and the vertex K2, and the angle formed between the straight line passing through the center position G and the vertex K2 and the Y axis is θ.
Then, in order to change the arc shape of the flaw pixel region K into a linear shape and convert the distance from the vertex K1 to the vertex K2 into the rectangle having the same distance from the vertex K3 to the vertex K4, as shown in FIG. The coordinates of the respective vertices after conversion are represented by K1 (−R · sin θ, −r), K2 (R · sin θ, −r), K3 (−R · sin θ, −R), K4 (R · sin θ, −R). )And it is sufficient. Each pixel other than the vertex may be similarly converted from the distance from the center position G and the angle formed by the straight line connected to the center position G and the Y axis.

Subsequently, the flaw candidate display means 5 converts the length in the tube axis direction of the flaw pixel area converted into a rectangle according to the installed program, and displays it on the monitor of the PC 51.
In the inner surface image, even if the flaw is the same length in the tube axis direction, the flaw on the near side looks long and the flaw on the back side looks short, so that it looks the same length regardless of the position in the tube axis direction. The flaw pixel area converted into a rectangle is converted.
FIG. 9 is a diagram for explaining a method of converting the length in the tube axis direction. FIG. 9A is a schematic diagram illustrating a state in which the inner surface is being imaged, and FIG. 9B is a diagram illustrating a relationship between L and R ′ in the schematic diagram of FIG. FIG. 9C is a diagram showing the relationship between L and r ′ in the schematic diagram of FIG. 9A, and FIG. 9D is a diagram showing the coordinates after conversion.
A line segment K01 is an inner surface region corresponding to the flaw pixel region K (hereinafter referred to as a corresponding inner surface region). Looking at the correspondence between the flaw pixel area K and FIG. 9, the points G ′, K5 ′, and K6 ′ in FIG. 9 correspond to the center position G and the points K5 and K6 of the flaw pixel area K.
The distance r ′ from the tube axis to K5 ′ is obtained by multiplying the distance r from the center position G to the vertex K5 in the inner surface image by the ratio of the actual dimension and the dimension in the inner surface image.
Similarly, the distance R ′ from the tube axis to K6 ′ is obtained by multiplying the distance R from the center position G to the vertex K6 in the inner surface image by the ratio of the actual dimension to the dimension in the inner surface image.
What is necessary is just to calculate the ratio of the dimension in an actual dimension and an inner surface image from the internal diameter ID of the steel pipe 2, and the dimension of the internal diameter of the steel pipe 2 in a captured image, for example.
The contents of each symbol in the figure are as follows.
ID: inner diameter L of the steel pipe L: distance from the camera 4 to the end face 21 Y: distance from the end face 21 to the front end of the corresponding inner surface area K01 Z: distance from the end face 21 to the inner end of the corresponding inner face area K01 here Then, looking at the relationship between L and R ′, from FIG.
Since L: R ′ = Y: (ID / 2−R ′), Y = L (ID / 2−R ′) / R ′.
Also, looking at the relationship between L and r ′, from FIG.
Since L: r ′ = Z: (ID / 2−r ′), Z = L (ID / 2−r ′) / r ′.
The length Q when the corresponding inner surface region K01 corresponding to the flaw pixel region K is viewed from the radial direction of the inner surface 23 of the steel pipe 2 is Q = Z−Y = L (ID / 2−r ′) / r′−. L (ID / 2−R ′) / R ′.
Since the values of L, ID, r ′, and R ′ are known, they can be calculated.
In order to convert the length of the flaw pixel region K in the tube axis direction into the length when the flaw pixel region K is viewed from the radial direction of the tube inner surface, the length of the flaw pixel region K in the tube axis direction is changed. ,
(ZY) / (R'-r ') may be multiplied.
Therefore, in order to convert the length in the tube axis direction of the flaw pixel region K converted into the rectangle into the length when viewed from the radial direction of the tube inner surface, the coordinates of the vertices KI, K2, K3, and K4 are set as follows. Convert as follows.
KI: (−R · sin θ, −r)
K2: (R · sin θ, −r)
K3: (−R · sin θ, −R (ZY) / (R′−r ′))
K4: (R · sin θ, −R (ZY) / (R′−r ′))
Similar conversion may be performed for each pixel other than the vertex.
FIG. 10 is a photograph of each stage in which the flaw pixel area is converted into a pixel area when viewed from the radial direction of the inner surface of the tube. FIG. 10A shows a flaw pixel region after the density is subtracted, FIG. 10B shows a flaw pixel region after conversion into a rectangle, and FIG. 10C shows the tube axis direction. It is a flaw pixel area after the length of is converted.
The operator determines whether or not the flaw candidate pixel group is a flaw from the flaw pixel area after conversion displayed on the monitor of the PC 51.
In this way, the flaw pixel area including the flaw candidate pixel group is converted into a flaw pixel area when viewed from the radial direction of the inner surface of the tube while maintaining the density difference in the area, and the state is the same as in the case of visual observation. Therefore, the exact shape of the flaw can be known, and the flaw can be detected with high accuracy from the flaw candidate pixel group. As a result, it is possible to reduce errors in determining what is not a flaw as a flaw.
Note that the flaw candidate display means 5 determines whether the flaw candidate pixel group is flawed from the flaw pixel area after conversion displayed on the monitor of the PC 51. The flaw candidate display means 5 determines the density, length, and width of the flaw candidate pixel group. And based on the shape and the like.
As described above, the tube inner surface inspection method according to the present embodiment can increase the accuracy of detection of flaws on the tube inner surface without labor and cost.

DESCRIPTION OF SYMBOLS 1 ... Pipe inner surface inspection apparatus 2 ... Steel pipe (pipe)
21 ... End face 22 ... Tube axis 23 ... Inner surface 3 ... Annular illumination 32 ... Center axis 4 ... Camera (imaging means)
41 ... optical axis 5 ... flaw candidate display means 6 ... contact plate 7 ... fixed frame

Claims (3)

The annular illumination is opposed to one of the end faces of the tube, the central axis of the annular illumination and the tube axis of the tube are substantially aligned, and the illumination light of the annular illumination is emitted toward the inner surface of the tube; and An imaging step in which the imaging means is opposed to any one of the end faces, the optical axis of the imaging means and the tube axis of the tube are substantially coincided, and the end face and the inner surface of the tube are imaged by the imaging means;
From the image captured in the imaging step, an inner surface image is extracted from a position corresponding to the inner peripheral edge of either one of the end surfaces to a position corresponding to the inner peripheral edge of the other end surface, and the inner surface image is extracted in the radial direction. A dividing step of dividing into a plurality of annular regions;
A primary determination step in which a density reference range is provided for each of the annular regions divided by the division step, and a pixel group whose density deviates from the reference range is extracted as a candidate pixel group;
A predetermined density determined for each of the annular areas is subtracted from the density of the pixels in the predetermined pixel area including the flaw candidate pixel group extracted in the primary determination step, and the pixel area subtracted from the density is set on the inner surface of the tube. A tube inner surface inspection method comprising: a secondary determination step of converting into a pixel region when viewed from the radial direction and determining the presence or absence of a flaw from the converted pixel region. An annular illumination that faces one of the end faces of the tube and emits illumination light toward the inner surface of the tube;
An imaging means for imaging the end surface and the inner surface of the tube opposite to the one end surface;
Flaw candidate display means for extracting and displaying a flaw candidate pixel group from the tube image picked up by the image pickup means,
The annular illumination is arranged such that its central axis substantially coincides with the tube axis of the tube,
The imaging means is arranged so that its optical axis substantially coincides with the tube axis of the tube,
The flaw candidate display means, from the image of the end face and the inner face of the tube imaged by the imaging means, from the position corresponding to the inner peripheral edge of the one end face to the position corresponding to the inner peripheral edge of the other end face The inner surface image is extracted, the inner surface image is divided into a plurality of annular regions in the radial direction, a reference range of density is provided for each annular region, and a pixel group whose density is out of the reference range is used as a candidate pixel group. Extracted, subtracted a predetermined density determined for each annular area from the density of pixels in a predetermined pixel area including the flaw candidate pixel group, and viewed the pixel area from which the density was subtracted from the radial direction of the tube inner surface An apparatus for inspecting a tube inner surface, which is converted into a pixel area and displayed. An abutment plate that can abut against any one of the end faces and allows illumination light emitted from the annular illumination toward the inner surface of the tube to pass through when abutting against either one of the end faces. When,
The imaging means, the annular illumination, and a fixed frame to which the contact plate is attached,
The imaging means and the contact plate are fixed to the fixed frame so that the optical axis of the imaging means and the corresponding contact plate are perpendicular to each other,
3. The tube inner surface inspection apparatus according to claim 2, wherein the annular illumination is mounted so as to be movable between the imaging unit and the contact plate in parallel with the optical axis of the imaging unit. .