Metal pipe defect detection device and defect detection method

Abstract

To provide a technique capable of more accurately detecting harmful defects on a surface of a metal pipe.SOLUTION: A metal pipe defect determination device, which determines the presence / absence of defects on a metal pipe surface, comprises: a thickness expansion data acquisition unit 11A which acquires thickness expansion data in the two-dimensional direction made of thickness data for each unit area aligned in the circumferential direction and the longitudinal direction of the metal pipe from flaw detection data of the ultrasonic flaw detection of the metal pipe surface; an area setting unit 11C which sets a determination area consisting of regions where the unit areas are continuous in at least m or more (m: an integer of 2 or more) in the circumferential direction and n or more (n: an integer of 2 or more) in the longitudinal direction in the thickness expansion data; a determination criterion setting unit 11D which sets a determination criterion value for determining defects on the basis of the thickness data within the determination area; and a defect determination unit 11E which compares each thickness data in the determination area set with the determination criterion value with the determination criterion value to determine whether or not there is a defect.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for determining the presence or absence of minute defects on the surface of a metal pipe, such as a steel pipe, using the results of ultrasonic flaw detection on the surface of the metal pipe. The present invention is particularly effective for determining (detecting) the presence or absence of defects on the inner surface of a metal pipe, which are difficult to detect visually. [Background technology]

[0002] Some steel pipes are required by standards to have their wall thickness measured. Wall thickness measurements for such steel pipes are primarily performed using ultrasonic testing. Ultrasonic testing involves measuring the entire circumference of the steel pipe in both the circumferential direction (also called the pipe circumferential direction) and the longitudinal direction (also called the pipe axial direction). There is an allowable range for the wall thickness of a steel pipe. In other words, there are upper and lower limit values ​​for the measured wall thickness. The pass / fail judgment of the wall thickness of the steel pipe is made, for example, depending on whether the measured wall thickness data is thicker than the upper limit or thinner than the lower limit.

[0003] Here, there are cases where minute defects (also simply called micro defects) are present on the inner surface of a steel pipe. These micro defects can be confirmed as a sudden (local) decrease in wall thickness on the steel pipe surface. If the depth of the micro defect is greater than the allowable range, the micro defect must be detected as a harmful defect. However, the wall thickness of the part where such a micro defect exists may not fall below the minimum wall thickness. In other words, such micro defects cannot be detected by determining whether or not the wall thickness is within the allowable range as described above. In the past, such harmful micro-flaws were detected by visual inspection by an operator, but because it was a visual inspection, there was a risk that steel pipes with harmful defects on the inside surface would be shipped out.

[0004] In response to this, methods for detecting such harmful micro defects include those described in Patent Documents 1 and 2, for example. In Patent Document 1, the change in wall thickness in the circumferential direction of the pipe and the steepness are monitored to determine pass / fail, while in Patent Document 2, it is determined to be harmful if there are consecutive points exceeding a threshold value. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-153974 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-222617 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method described in Patent Document 1 detects flaws from a group of information arranged one-dimensionally in the circumferential or longitudinal direction, which may make it impossible to detect flaws that are continuous diagonally. Similarly, the method described in Patent Document 2 also detects flaws using information arranged one-dimensionally in the circumferential or longitudinal direction. Therefore, it may not be possible to detect flaws that are continuous diagonally. Furthermore, flaws are recognized as abrupt changes in thickness relative to the surface surrounding the flaw. Therefore, when flaws are determined using a fixed threshold, as in Patent Document 2, there is a problem in that the detection accuracy of harmful flaws is poor.

[0007] The present invention has been made in light of the above-mentioned points, and aims to provide a technique that can more accurately detect harmful defects on the surface of a metal pipe. [Means for solving the problem]

[0008] In order to solve the problems, one aspect of the present invention is a metal pipe defect detection device that determines the presence or absence of defects on the surface of a metal pipe, and includes: a thickness development data acquisition unit that acquires two-dimensional expanded wall thickness data consisting of thickness data for each unit area arranged in the circumferential and longitudinal directions of the metal pipe from flaw detection data acquired by performing ultrasonic flaw detection in two dimensions, that is, in the longitudinal and circumferential directions, along the surface of the metal pipe; an area setting unit that sets, from the expanded wall thickness data, a determination area where the unit areas are continuous for m or more in the circumferential direction (m: an integer of 2 or more) and n or more in the longitudinal direction (n: an integer of 2 or more); a determination criterion setting unit that sets a determination reference value for determining defects based on the thickness data present in the determination area; and a flaw detection unit that determines whether or not a defect exists by comparing each piece of thickness data in the determination area, for which the determination reference value has been set, with the determination reference value. [Effects of the Invention]

[0009] According to one aspect of the present invention, a two-dimensional region along the surface of a metal pipe, i.e., a region consisting of two or more consecutive unit areas in both the circumferential and longitudinal directions, is set as a judgment area. Then, a judgment reference value is set based on the wall thickness within the judgment area. Therefore, a judgment reference value is set for each area depending on the state of change in wall thickness around the position where the presence or absence of a flaw is to be judged. Therefore, according to this aspect of the present invention, it is possible to more accurately detect harmful defects on the surface of a metal pipe by avoiding the influence of electrical noise and ensuring the detection of oblique defects. Furthermore, according to this aspect of the present invention, each determination area is a two-dimensional area, so even harmful flaws that are diagonally continuous can be detected. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing an example of the configuration of a flaw detection facility including a flaw determination device according to an embodiment based on the present invention; [Figure 2] FIG. 10 is a diagram showing an example of expanded wall thickness data. [Figure 3] 10A and 10B are diagrams showing examples of judgment areas and examples of minute flaws; [Figure 4]FIG. 10 is a diagram illustrating an example of a method for setting a plurality of determination areas. [Figure 5] FIG. 10 is a diagram showing an example of actual flaw thickness data. [Figure 6] FIG. 10 is a diagram showing an analysis image of actual flaw thickness data. [Figure 7] FIG. 10 is a diagram showing an example of thickness data when actual noise occurs. [Figure 8] This is an image of the analysis of thickness data when actual noise occurs. [Figure 9] FIG. 10 is a diagram showing examples of variables to be set and the determination results at that time. DETAILED DESCRIPTION OF THE INVENTION

[0011] Next, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an oil well tubular good and other steel pipes are used as examples of metal pipes to be evaluated for the presence or absence of flaws. However, the metal pipes that are the subject of the present invention are not limited to steel pipes.

[0012] (composition) The equipment is equipped with flaw detection equipment 1 as equipment for evaluating steel pipes. As shown in FIG. 1, the flaw detection equipment 1 of this embodiment includes a flaw detection device 10 and an evaluation device 11.

[0013] <Flaw detection device 10> The flaw detection device 10 uses an ultrasonic flaw detector placed close to the surface (outer surface) of the steel pipe to scan the surface of the steel pipe to be inspected in the circumferential and longitudinal (axial) directions, continuously detecting flaws around the entire surface of the steel pipe. The above scan is performed, for example, in a spiral pattern along the surface of the steel pipe. Also, for example, detection signals from the flaw detector are continuously acquired at a predetermined sampling period in synchronization with the relative movement of the flaw detector with respect to the outer surface of the steel plate, and output information is continuously calculated at predetermined scanning intervals based on the acquired detection signals and sequentially stored in a memory unit. Here, the method is not particularly limited as long as it is possible to detect flaws in the entire circumference of the surface portion of the steel pipe. That is, as long as it is possible to obtain wall thickness data in the circumferential and longitudinal directions of the steel pipe surface, i.e., in two-dimensional directions, any known means may be applied to the equipment and flaw detection method of the flaw detection device 10. In addition, each piece of flaw detection data includes circumferential and longitudinal coordinates, that is, two-dimensional position information on the surface of the steel pipe, in addition to wall thickness information.

[0014] <Evaluation Device 11> The evaluation device 11 of this embodiment includes a wall thickness developed data acquisition unit 11A, a wall thickness determination unit 11B, an area setting unit 11C, a determination criterion setting unit 11D, and a flaw determination unit 11E. The wall thickness developed data acquisition unit 11A, the area setting unit 11C, the determination criterion setting unit 11D, and the flaw determination unit 11E constitute the metal pipe flaw determination device of this embodiment.

[0015] [Wall thickness development data acquisition unit 11A] The wall thickness expansion data acquisition unit 11A acquires two-dimensional wall thickness expansion data tDATA from the flaw detection data obtained by the flaw detection device 10, which consists of a group of wall thickness data arranged in the circumferential direction (pipe circumferential direction) and longitudinal direction (pipe axial direction) of the steel pipe. As shown in FIG. 2, the expanded thickness data tDATA is two-dimensional data in which thickness data, which is data on thickness values, is arranged continuously in the circumferential direction and also in the longitudinal direction for each unit area TA.

[0016] In Figure 2, each square corresponds to a unit area TA. The pitch of the unit areas TA should be the same as the measurement pitch of the flaw detection in the circumferential and longitudinal directions. In this way, the expanded wall thickness data tDATA is a group of wall thickness data in which the wall thickness data for the entire length of the steel pipe and for each position around the entire circumferential direction are expanded onto a two-dimensional plane. Here, Figure 2 shows an image of the expanded wall thickness data tDATA. In Figure 2(c), the vertical direction is the longitudinal direction of the pipe, and the horizontal direction is the circumferential direction of the pipe. The numbers 1 to 9 in the first row of the top row and the leftmost column in Figures 2 to 4 indicate the coordinates of the measurement points. The other numbers written on the matrix are actually the measured thickness values. However, in this figure, to show the principle of flaw determination, the numbers are shown as integers from 1 to 5, and the larger the number, the thicker the thickness.

[0017] [Thickness determination section 11B] The thickness determination unit 11B compares the thickness of each flaw detection data with the preset upper and lower limit thicknesses to determine whether there is any thickness data that falls outside the allowable thickness range between the upper limit thickness and the lower limit thickness. The thickness determination unit 11B makes a determination based on the thickness itself.

[0018] [Area setting section 11C] The area setting unit 11C sets a determination area DA consisting of unit areas TA that are continuous in the circumferential direction by m or more (m: an integer of 2 or more) and in the longitudinal direction by n or more (n: an integer of 2 or more) from the thickness expanded data tDATA. The determination area DA is configured as a two-dimensional area of ​​"m x n" unit areas TA. In the following description, the case where m=3 and n=3 will be described as an example.

[0019] Figure 3 shows an example of a unit area TA as the area within the bold frame. Figure 3 also shows an image of flaw determination. The example in Figure 3(a) shows a case where a decrease in wall thickness occurs in only one area if the measurement results are taken at face value. However, upon closer examination, it is likely that the wall thickness is not significantly different from other areas, and this is due to electrical noise. On the other hand, depending on the tolerance setting for the wall thickness of the steel pipe, the wall thickness may be reduced in only one area. Data shown as such a flaw may also be mistaken for a harmful flaw. Figure 3(b) shows an example where the flaw extends circumferentially. Figure 3(c) shows an example where the flaw extends longitudinally. Note that in Figure 3, the shaded area represents the unit area TA, and the flaw occurs there. From the viewpoint of detecting locally present harmful minute defects (hereinafter also simply referred to as defects), m and n are each preferably 3 or more and 10 or less, and more preferably 3 or more and 5 or less.

[0020] The area setting unit 11C sets a determination area DA each time the thickness developed data tDATA is displaced from a predetermined position along the development direction of the thickness developed data tDATA. "In the development direction" refers to at least one of the circumferential direction and the longitudinal direction. This allows the area setting unit 11C to set multiple determination areas DA within the thickness developed data tDATA. In this case, the amount of displacement in the circumferential direction is preferably smaller than the above m and is an integer value equal to or greater than 1. Furthermore, the amount of displacement in the longitudinal direction is preferably smaller than the above n and is an integer value equal to or greater than 1. It is particularly preferable that the above m and n are 1. In this case, there is an overlap between adjacent determination areas DA.

[0021] In the area setting unit 11C of this embodiment, for example, as shown in FIG. 4, the initial position of the determination area DA is set so that the upper left end of the determination area DA is the first row in the longitudinal direction and the first column in the circumferential direction of the wall-thickness expanded data tDATA. Then, each time the determination area DA is shifted by one square (one unit area TA) in the circumferential direction, a determination area DA is set sequentially. When it is determined that the right end of the determination area DA in the circumferential direction is at the right end position of the wall-thickness expanded data tDATA, the determination area DA is shifted downward by one square in the longitudinal direction and set so that the left end of the determination area DA is at the left end position of the wall-thickness expanded data tDATA. Then, as described above, each time the determination area DA is shifted by one square (one unit area TA) in the circumferential direction, a determination area DA is set sequentially. The above process is repeated until the lower right position of the determination area DA is at the left end and bottom end of the wall-thickness expanded data tDATA, thereby sequentially setting multiple determination areas DA. As a result, a plurality of determination areas DA are set so as to cover the entire area of ​​the thickness development data tDATA. The determination areas DA may be set so that there is no overlap between them. Although it is preferable that the sizes of the determination areas DA are uniform, they may be different.

[0022] [Judgment criteria setting section 11D] The judgment criterion setting unit 11D sets, for each judgment area DA, a judgment criterion value DS for judging the presence or absence of minute defects of a harmful depth from the wall thickness data present in the judgment area DA. The judgment criterion setting unit 11D of this embodiment includes a reference value calculation unit 11Da and a thickness steepness correction unit 11Db.

[0023] [Reference value calculation unit 11Da] The reference value calculation unit 11Da calculates the average or median value of the thickness data within the target determination area DA, and sets the calculated value as the reference value. Here, it is preferable to set the number of minimum value exclusion points and the number of maximum value exclusion points based on the measurement noise (measurement accuracy) estimated from the accuracy of ultrasonic flaw detection. In this case, the reference value calculation unit 11Da performs preprocessing to calculate the reference value. The preprocessing uses the minimum value exclusion points and the maximum value exclusion points to remove thickness data that may be measurement noise from the thickness data within the determination area DA. For example, the preprocessing sorts the thickness data within the target determination area DA in order of thickness, e.g., ascending order. Then, the minimum value exclusion points are removed from the minimum value side of the thickness data, and the maximum value exclusion points are removed from the maximum value side. Furthermore, the reference value calculation unit 11Da calculates the average or median of the remaining thickness data to determine the reference value.

[0024] The minimum value exclusion score and the maximum value exclusion score may simply be set to a value equal to or less than 1 / 4 of the number of unit areas TA present in one judgment area DA. For example, when m=3 and n=3, the number of unit areas TA present in the judgment area DA is 9, so the minimum value exclusion score and the maximum value exclusion score are set to 1 or 2. Strictly speaking, the frequency of noise varies depending on the wall thickness measurement settings (testing speed, frequency, etc.) and the characteristics of the steel pipe (dimensions, shape, surface contamination, etc.). For this reason, it may be difficult to uniquely determine the minimum and maximum exclusion points.

[0025] An example of a method for determining the minimum value exclusion points and the maximum value exclusion points is shown below. For example, consider a case where the number of unit areas TA is 159 in the circumferential direction and 557 in the longitudinal direction, for a total of 88,563, and noise occurs in an average of 99 locations based on previously acquired data. Also consider a case where the determination area DA is set to approximately 0.1% of the total number of unit areas (88,563). In this example, the determination area DA can be expressed as a 3 x 3 area. In this case, since the probability of picking up noise in each determination area DA exceeds 1, it can be determined that the minimum value exclusion points and the maximum value exclusion points should be set to 2.

[0026] [Thickness steepness correction part 11Db] The thickness steepness correction unit 11Db performs processing to reduce the reference value calculated by the reference value calculation unit 11Da by a thickness correction amount (steepness judgment value) corresponding to the thickness steepness amount due to harmful defects, and the corrected value is set as the judgment reference value DS for the judgment area DA. The thickness correction amount (steepness judgment value) is set in advance according to the depth of the flaw to be evaluated, etc. In the thickness steepness correction unit 11Db of this embodiment, the judgment reference value DS is calculated by the following formula. Judgment standard value DS = standard value - steepness judgment value (1) The steepness judgment value (thickness correction amount) is set to a value that is set as the steepness of the thickness based on, for example, the depth of the harmful flaw being evaluated. For example, if the minimum depth of the harmful flaw to be detected is set to 0.3 mm, the steepness judgment value is set to 0.3 mm. In other words, this is the case when the steepness of the thickness due to the harmful flaw is 0.3 mm.

[0027] The wall thickness correction amount may be set, for example, as a value obtained by multiplying the wall thickness of the metal pipe by a steep judgment rate set based on the ratio of the depth of the flaw to be evaluated. This steep judgment rate is expressed as "(minimum depth of harmful flaw to be detected) ÷ wall thickness of the steel pipe." The wall thickness of the steel pipe may be the minimum wall thickness allowable for the steel pipe, or may be the average wall thickness in the judgment area DA to be evaluated. When the steepness determination rate is used, the thickness correction amount is "reference value x steepness determination rate". Then, the thickness steepness correction section 11Db calculates the judgment reference value DS by the following formula. Judgment standard value DS = standard value - standard value × steepness judgment rate (2) = Reference value × (1 - steepness judgment rate)

[0028] Here, it is preferable to use formula (1) for thick-walled steel pipes (thickness ≧ 5 mm), whereas it is preferable to use formula (2) for thin-walled steel pipes (thickness < 5 mm), since applying formula (1) may result in the threshold value for steepness determination becoming too strict. The steepness determination ratio is, for example, a value in the range greater than 0.0 and equal to or less than 0.10. In addition, the steepness judgment value and steepness judgment rate for setting the thickness correction amount may be optimized by repeatedly calculating using flaw detection data obtained when harmful flaws actually occur so as to increase the detection accuracy.

[0029] Defects that occur in steel pipes are generally divided into those that occur during rolling and those that occur at other times. Examples of defects that occur during rolling include those shown in Figure 3(b) and (c) due to friction between the steel pipe being rolled and tools such as rolls. In some cases, defects may occur diagonally. In addition, cracks may occur along grain boundaries. An example of defects that occur due to reasons other than rolling is a dent made during transportation. The inventors have found that, although there are various types of defects that typically occur, even if they have directional characteristics or have little directional characteristics like dents, they are unlikely to become extremely deep holes locally. From the above, it has been found that a localized decrease in thickness at only one point, as shown in Figure 3(a), i.e., a thickness distribution that varies locally relative to the surrounding area, is unlikely to occur in actual manufacturing processes.

[0030] For example, one measurement area can be set to 1 mm circumferentially and 10 mm axially, and the measurement location can be moved in a spiral pattern at intervals of 1 mm circumferentially and 5 mm axially. If the difference between adjacent wall thickness measurements results in a localized overthickness, or if the measurement location is locally thinned by 20% or more of the nominal wall thickness, these are not considered defects in the manufacturing process. Therefore, these can be considered noise. Conversely, if the variation is less than 20%, the measurement value can be used to detect defects regardless of whether it is noise or a defect. This determination method requires measuring the entire circumference of the pipe. It is also possible to set the wall thickness measurement area to, for example, 8 mm circumferentially and 20 mm axially, and adjust the measurement location accordingly.

[0031] When determining whether or not a flaw exists or the type of flaw based on these criteria in more detail, the determination can be supplemented with data accumulated during the manufacturing process. For example, a large amount of data on the occurrence of actual flaws in the target steel pipe is acquired. Then, from the acquired data, a correlation between the flaw depth and the steepness determination value or steepness determination rate, which makes the above formulas (1) and (2) valid, is found, and the steepness determination value or steepness determination rate is found and set from that correlation.

[0032] [Defect determination unit 11E] The flaw determination unit 11E determines whether or not a flaw exists by comparing each thickness data in the determination area DA for which the determination standard value DS has been determined by the determination standard setting unit 11D with the determined determination standard value DS. That is, the flaw determination unit 11E compares each thickness data in the target determination area DA with the above-obtained determination standard value DS, and performs processing to determine that there is a harmful flaw in the unit area TA where "thickness data < determination standard value DS".

[0033] Here, if the number of flaws present within the judgment area DA (the number of unit areas TA judged to have flaws) is two or more (if the flaws are of a predetermined size or larger), it may be judged that there are harmful flaws within the judgment area DA. In this case, the number of detected flaws judged to be harmful flaws may be set in advance as a judgment score. The judgment score is set, for example, depending on the size of the harmful flaws to be detected, etc. In this embodiment, the presence or absence of a defect can be determined for each unit area TA individually. Therefore, based on the position coordinates of the unit area TA, unit areas TA determined to have defects may be determined to have harmful defects if the defects are continuous in the longitudinal direction, circumferential direction, or diagonal direction.

[0034] (Operation etc.) In this embodiment, when determining whether or not there is a flaw, a determination area DA consisting of a two-dimensional surface area is set. The determination area DA is set as an area in which two or more unit areas TA are consecutive in both the circumferential direction and the longitudinal direction. Then, for each determination area DA, a determination standard value DS is set based on the wall thickness within the determination area DA. For this reason, in this embodiment, the judgment reference value DS is set according to the state of change in wall thickness around the position where the presence or absence of a flaw is to be determined. That is, in this embodiment, it is possible to set a judgment reference value DS appropriate for each judgment area DA where flaw judgment is performed. As a result, in this embodiment, the judgment reference value DS can be set with greater accuracy. Therefore, in this embodiment, it is possible to detect harmful flaws on the surface of the metal pipe with greater accuracy.

[0035] In this embodiment, each determination area DA is a two-dimensional area, so even harmful defects that are continuous diagonally can be detected. In addition, in this embodiment, it is also possible to determine whether a defect is harmful or not from the number of defects present in a local area, such as within each determination area DA set as a two-dimensional area. In this embodiment, the presence or absence of defects on the inner surface of the steel pipe is determined from the relative value of the wall thickness, separately from the determination of whether the wall thickness is within the standard based on the absolute wall thickness measurement by the wall thickness determination unit 11B. In other words, the determination of defects is not an evaluation method that replaces the wall thickness measurement.

[0036] In this embodiment, each determination area DA is set so that adjacent determination areas DA overlap each other, which results in further improved accuracy in flaw detection. The reason for this will be explained below. The flaw to be detected is recognized as a portion where the thickness changes sharply relative to the surrounding surface. In other words, the recognition of the thickness change caused by the flaw differs depending on the flaw's location and the thickness of the area surrounding the flaw. For this reason, even if a flaw is present within one judgment area DA, it may not be recognized as a flaw depending on the thickness data for the same judgment area DA. However, in other judgment areas DA that contain the same flaw, the thickness around the flaw may be different, and the flaw may be detected as a flaw. As a result, the accuracy of flaw detection is further improved.

[0037] In particular, in this embodiment, the accuracy of flaw detection can be further improved by setting the judgment reference value DS for each judgment area DA based on the thickness data present in the judgment area DA. In this embodiment, there is a possibility that measurement noise estimated from the accuracy of ultrasonic flaw detection is contained in the thickness data present in the judgment area DA. For this reason, one or more minimum values ​​and one or more maximum values ​​are removed from the thickness data within the judgment area DA, and the judgment reference value DS is calculated from the remaining thickness data. This improves the accuracy of the judgment reference value DS.

[0038] (Example) Next, an example based on this embodiment will be described. When the wall thickness is measured over the entire length and circumference of a steel pipe using ultrasound, wall thickness data is obtained. The wall thickness data for each position is expanded to form the expanded wall thickness data tDATA. As mentioned above, the expanded wall thickness data tDATA is a two-dimensional display of the wall thickness data, as shown in Figure 2(c). As mentioned above, the case where m=3 and n=3 will be described as an example. Since the wall thickness of the steel pipe varies, in this embodiment, flaws are judged for each judgment area DA. By setting the judgment area DA to a partial area of ​​the entire area of ​​the entire length and circumference of the steel pipe, the effect of variations in the wall thickness of the entire steel pipe can be minimized.

[0039] If there are no flaws and all the areas within the determination area DA are the same thickness (for example, 5 mm), the reference value, which is the average or median value, will be a value equivalent to the thickness (for example, 5 mm).On the other hand, if there is a unit area TA with a flaw within it and its thickness is, for example, 3 mm, the reference value will be approximately 4.7 mm, and the unit area TA with a flaw can be detected. However, in reality, there is variation in the thickness of the flaw-free portion. For this reason, in this embodiment, a value obtained by subtracting the thickness correction amount from the reference value is used as the determination reference value DS for threshold determination.

[0040] Figure 5 shows an example of thickness data for actual harmful defects. The numbers in the figure represent the thickness value (mm) of each unit area TA. In this example, the judgment area DA was extracted at three points in the circumferential direction and three points in the axial direction of the tube. The steel pipe in question has an outer diameter of 139.8 mm (±0.8%) and a nominal wall thickness of 15.0 mm (±10%). In other words, the wall thickness tolerance is 13.5 mm ≦ wall thickness ≦ 16.5 mm. Therefore, the minimum wall thickness within the judgment area DA is 13.72 mm. Therefore, all wall thickness data within the judgment area DA will pass as a wall thickness tolerance.

[0041] Also, Figure 6 shows an image of the analysis of the thickness data of the actual flaws, rather than the measured values. In Figure 6, the scans are (1), (2), and (3) in the circumferential direction, and (4), (5), and (6) in the longitudinal direction. Scans (1) and (6) in Figure 6 detect 13.72 mm, and scans (2) and (5) detect 13.92 mm. Figure 7 shows the thickness data obtained by measuring the same area, but with noise during measurement. In Figure 7, there is a data point of 13.72 mm at the center, but this is not the correct value due to noise; the correct value is 15.05. An image of the analysis of thickness data when actual noise occurs is shown in Figure 8. Scans (2) and (5) in Figure 8 detect 13.72 mm.

[0042] Here, in the method of Patent Document 1, in order to detect the flaw in Figure 6, it is necessary to set the threshold value for determining that the flaw is harmful at 13.72 mm. In that case, the noise in Figure 8 will also be determined to be harmful, which may make it impossible to determine that only the flaw is harmful. Furthermore, in the method described in Patent Document 2, since the defective portions are not continuous in any of the cases shown in FIG. 8, there is a risk that defects that cannot be determined to be harmful may not be detected. As described above, the methods described in Patent Documents 1 and 2 may not be able to detect a flaw (defective portion) if the flaw is oblique. In contrast to this, in this embodiment, the judgment standard value DS calculated from the thickness within the judgment area DA is used as a threshold value, and the defect judgment for each unit area TA is performed regardless of the scanning direction shown in Figure 8, etc., and if the defect (defective part) is slanted, the defect area can be judged to be a defect.

[0043] Next, a method for determining flaws in an embodiment based on this embodiment will be described. In this embodiment, the number of unit areas TA is expressed by points. Here, the setting of the judgment area DA is m: the number of points in the circumferential direction (points), and n: the number of points in the axial direction (points). Also, the allowable number of flaws within the judgment area DA is set as a: the number of points for judging steepness (points). Also, b: the number of points excluded from the minimum value (points), c: the number of points excluded from the maximum value (points), e: the steepness judgment value (%), and f: the steepness judgment value (mm). Here, a is an integer equal to or greater than 1, b and c are integers equal to or greater than 1, and e and f can be positive numbers.

[0044] These variables are set so that actual defects can be detected from the thickness data shown in Figure 5. Here, we assume that the values ​​of the variables are set as shown in Figure 7. In ultrasonic flaw detection, noise can occur when the flaw detection signal is sent from the probe to the flaw detector. This noise is transmitted as several abnormal values ​​in the maximum and minimum wall thickness directions. Since most of this noise is electrical, it is not continuous and only one abnormal value is transmitted, but noise caused by poor water film formation between the probe and steel pipe can be transmitted as several or more consecutive values. Therefore, depending on the equipment layout of the flaw detector and the properties of the steel pipe, noise may not occur, and excluding minimum and maximum values ​​may not be necessary. For this reason, by setting b: minimum value exclusion points (points) and c: maximum value exclusion points (points) to integers greater than or equal to 0, optimization can be performed depending on the equipment and situation.

[0045] In addition, depending on the rolling process of steel pipes, there are cases where the elongation rate is high or low, and accordingly, the shape of harmful defects to be detected, such as length, width, and depth, also differs. Therefore, a: number of steepness judgment points (points), e: steepness judgment value (%), f: steepness judgment value (mm) are appropriately set according to the steel pipe and defect to be evaluated. The data used in the calculation of this example are the actual flaw thickness data in Fig. 5 and the actual thickness data when noise occurs in Fig. 7. It was found that when the determination process is performed using the method of this embodiment, flaws can be detected and noise is not determined as a defect and is not over-detected. The calculation results for each level are shown below. Regarding the judgment method, calculations are made using formula 1 and formula 2, and if it is judged as poor by either formula, it is considered poor.

[0046] Next, specific calculation results for the settings shown in FIG. 7 will be shown. First, the calculation results for the actual flaw thickness data in Figure 5 are as follows: With b=1, 15.52 is excluded, and with c=1, 13.72 is excluded. If the above formula (2) is used to calculate the judgment reference value DS, the following calculation is obtained. Judgment criteria value DS = {14.96 + 15.04 + 14.96 + 13.92 + 15.10 + 15.02 + 15.07} ÷ 7 -{6.95+6.96+6.60+7.08+6.96+6.99+7.11}÷7×0.02 =14.87-0.30=14.57 5, out of the nine points, two points are equal to or less than the judgment standard value DS=14.57. In this example, the steep judgment score a is set to 2 (points) or more, and therefore the product is judged as defective.

[0047] Furthermore, if the above formula (1) is used to calculate the judgment reference value DS, the following calculation is obtained. Criterion value DS = {14.96 + 15.04 + 14.96 + 13.92 + 15.10 + 15.02 + 15.07} ÷ 7 -0.30 =14.87-0.30=14.57 5, two out of nine points are below the judgment standard value DS=14.57, and therefore are similarly judged as defective.

[0048] Next, the calculation results for the thickness data when actual noise occurs in Figure 7 are as follows: With b=1, 15.04 is excluded, and with c=1, 13.72 is excluded. If the above formula (2) is used to calculate the judgment reference value DS, the following calculation is obtained. Judgment criteria value DS = {14.98 + 14.98 + 15.04 + 14.96 + 14.98 + 14.98 + 14.96} ÷ 7 -{6.95+6.96+6.60+7.08+6.96+6.99+7.11}÷7×0.02 =14.98-0.30=14.68 7, there is one point out of nine points that is equal to or less than the judgment standard value DS=14.68. In this example, the steep judgment score a is set to 2 (points) or more, so the product is judged as non-defective.

[0049] Furthermore, if the above formula (1) is used to calculate the judgment reference value DS, the following calculation is obtained. Criterion value DS = {14.98 + 14.98 + 15.04 + 14.96 + 14.98 + 14.98 + 14.96} ÷ 7 -0.30 =14.98-0.30 =14.68 7, there is one point out of nine points that is equal to or less than the judgment standard value DS=14.68. In this example, the steep judgment score a is set to 2 (points) or more, so the product is judged as non-defective.

[0050] The number of steepness judgment points (points) a is a value set depending on the condition of the flaw to be detected, and in this example, a=2 is set so that two consecutive points are evaluated as a flaw to be detected. As described above, according to the defect determination method of the present invention, defects can be detected more accurately by determining the surface (an area defined by an integer of 2 or more vertically and an integer of 2 or more horizontally) and by excluding one or more maximum and minimum values ​​within the determination area DA in order to separate noise from defects.

[0051] (others) The present disclosure may also have the following configuration. (1) A metal pipe defect detection device for determining the presence or absence of defects on the surface of a metal pipe, a wall-thickness development data acquisition unit that acquires two-dimensional wall-thickness development data consisting of wall-thickness data for each unit area arranged in the circumferential and longitudinal directions of the metal pipe from flaw detection data acquired by performing ultrasonic flaw detection in two dimensions along the surface of the metal pipe in the longitudinal and circumferential directions; an area setting unit that sets a determination area in the wall thickness development data, the unit area being a continuous area of ​​m or more in the circumferential direction (m: an integer of 2 or more) and n or more in the longitudinal direction (n: an integer of 2 or more); a judgment standard setting unit that sets a judgment standard value for judging flaws based on the thickness data present in the judgment area; a flaw determination unit that determines whether or not a flaw exists by comparing each thickness data within the determination area in which the determination reference value is set with the determination reference value; A metal pipe defect detection device comprising: (2) the area setting unit sets a determination area each time the sensor element is displaced in at least one of the circumferential direction and the longitudinal direction; The displacement in the circumferential direction is an integer value of 1 or greater that is smaller than m, The amount of displacement in the upper longitudinal direction is an integer value of 1 or more that is smaller than the above n. (3) The judgment standard setting unit sets the judgment standard value to a value obtained by subtracting a preset steep judgment value from a standard value consisting of the average or median value of the thickness data within the target judgment area. (4) The steepness judgment value is set based on the depth of the flaw to be evaluated. (5) The steepness judgment value is set as a value obtained by multiplying the reference value by a steepness judgment rate set based on the ratio of the depth of the flaw to be evaluated to the wall thickness of the metal pipe. (6) Based on the measurement noise estimated from the accuracy of the ultrasonic flaw detection, the minimum value exclusion point number and the maximum value exclusion point number are set, The above-mentioned judgment standard value is determined by arranging the thickness data within the target judgment area in thickness order, excluding the minimum value exclusion points from the minimum value side and the maximum value exclusion points from the maximum value side, and then determining the above-mentioned standard value from the remaining thickness data. (7) A flaw detection method for determining the presence or absence of flaws on the surface of a metal pipe, comprising: two-dimensional wall thickness development data consisting of wall thickness data for each unit area arranged in the circumferential and longitudinal directions of the metal pipe is obtained from the inspection data obtained by performing ultrasonic inspection in two dimensions along the surface of the metal pipe in the longitudinal and circumferential directions; In the thickness expansion data, a plurality of determination areas are set in the thickness expansion data, each of which is made up of a region in which the unit area is continuous for m or more in the circumferential direction (m: an integer of 2 or more) and n or more in the longitudinal direction (n: an integer of 2 or more); For each judgment area, a judgment reference value for judging flaws is set based on the thickness data present in that judgment area, and the presence or absence of flaws is judged by comparing the set judgment reference value with each thickness data in that judgment area. A method for determining defects in a metal pipe, comprising: (8) A determination area is set for each displacement in at least one of the circumferential direction and the longitudinal direction, thereby setting a plurality of determination areas in the wall thickness development data; The displacement in the circumferential direction is an integer value of 1 or greater that is smaller than m, The amount of displacement in the upper longitudinal direction is an integer value of 1 or more that is smaller than the above n. (9) The above-mentioned judgment reference value is determined by subtracting a predetermined steep judgment value from a reference value consisting of the average or median value of the thickness data within the target judgment area. (10) The steepness judgment value is set based on the depth of the flaw to be evaluated. (11) The steepness judgment value is set as a value obtained by multiplying the reference value by a steepness judgment rate set based on the ratio of the depth of the flaw to be evaluated to the wall thickness of the metal pipe. (12) In order to remove noise near the maximum and minimum thicknesses, one or more thickness data with minimum thickness values ​​are removed from the thickness data within the target judgment area based on the measurement noise estimated from the accuracy of the ultrasonic flaw detection, and one or more thickness data with maximum thickness values ​​are removed, and the above-mentioned reference value is determined from the remaining thickness data. [Explanation of symbols]

[0052] 1 Flaw detection equipment 10 Flaw detection equipment 11 Evaluation equipment 11A Wall thickness expansion data acquisition section 11B Thickness determination section 11C Area setting section 11D Judgment criteria installation section 11Da Reference value calculation unit 11Db Thickness steepness correction part 11E Defect detection section DA Judgment Area DS judgment criteria TA Unit Area tDATA Wall thickness expansion data

Claims

1. A metal pipe defect detection device that determines whether or not there is a defect on the surface of a metal pipe, a wall-thickness development data acquisition unit that acquires two-dimensional wall-thickness development data consisting of wall-thickness data for each unit area arranged in the circumferential direction and the longitudinal direction of the metal pipe from flaw detection data acquired by performing ultrasonic flaw detection in two dimensions, namely, the longitudinal direction and the circumferential direction, along the surface of the metal pipe; an area setting unit that sets a determination area in the wall thickness expanded data, the unit area being a continuous area of ​​m or more in the circumferential direction (m: an integer of 2 or more) and n or more in the longitudinal direction (n: an integer of 2 or more); a judgment standard setting unit that sets a judgment standard value for judging flaws based on the thickness data present in the judgment area; a flaw determination unit that determines whether or not a flaw exists by comparing each thickness data within the determination area in which the determination reference value is set with the determination reference value; A metal pipe defect detection device comprising:

2. the area setting unit sets a determination area each time the sensor element is displaced in at least one of the circumferential direction and the longitudinal direction, The displacement amount in the circumferential direction is an integer value of 1 or greater that is smaller than m, The amount of displacement in the upper longitudinal direction is an integer value of 1 or more that is smaller than the above n.

2. The metal pipe defect detection device according to claim 1.

3. The judgment standard setting unit sets the judgment standard value to a value obtained by subtracting a predetermined steep judgment value from a reference value consisting of an average value or a median value of the thickness data within the target judgment area.

2. The metal pipe defect detection device according to claim 1.

4. The steepness judgment value is set based on the depth of the flaw to be evaluated.

4. The metal pipe defect detection device according to claim 3.

5. The steepness judgment value is set as a value obtained by multiplying the reference value by a steepness judgment rate set based on the ratio of the depth of the flaw to be evaluated to the wall thickness of the metal pipe.

4. The metal pipe defect detection device according to claim 3.

6. Based on the measurement noise estimated from the accuracy of the ultrasonic flaw detection, the number of minimum value exclusion points and the number of maximum value exclusion points are set, The above-mentioned judgment reference value is determined by arranging the thickness data in the target judgment area in thickness order, excluding the minimum value exclusion points from the minimum value side and the maximum value exclusion points from the maximum value side, and then determining the above-mentioned reference value from the remaining thickness data. The metal pipe defect detection device according to any one of claims 3 to 5.

7. A flaw detection method for determining the presence or absence of flaws on the surface of a metal pipe, comprising: two-dimensional wall thickness development data consisting of wall thickness data for each unit area arranged in the circumferential and longitudinal directions of the metal pipe is obtained from the inspection data obtained by performing ultrasonic inspection in two dimensions along the surface of the metal pipe in the longitudinal and circumferential directions; In the thickness expansion data, a plurality of determination areas are set in the thickness expansion data, each of which is made up of a region in which the unit area is continuous for m or more in the circumferential direction (m: an integer of 2 or more) and n or more in the longitudinal direction (n: an integer of 2 or more); For each judgment area, a judgment reference value for judging flaws is set based on the thickness data present in that judgment area, and the presence or absence of flaws is judged by comparing the set judgment reference value with each thickness data in that judgment area. A method for determining defects in a metal pipe, comprising:

8. A determination area is set for each displacement in at least one of the circumferential direction and the longitudinal direction, thereby setting a plurality of determination areas in the wall thickness development data; The displacement amount in the circumferential direction is an integer value of 1 or greater that is smaller than m, The amount of displacement in the upper longitudinal direction is an integer value of 1 or more that is smaller than the above n.

8. A method for determining defects in a metal pipe according to claim 7.

9. The judgment reference value is determined by subtracting a predetermined steepness judgment value from a reference value consisting of the average or median value of the thickness data within the target judgment area.

8. A method for determining defects in a metal pipe according to claim 7.

10. The steepness judgment value is set based on the depth of the flaw to be evaluated.

10. The method for determining defects in a metal pipe according to claim 9.

11. The steepness judgment value is set as a value obtained by multiplying the reference value by a steepness judgment rate set based on the ratio of the depth of the flaw to be evaluated to the wall thickness of the metal pipe.

10. The method for determining defects in a metal pipe according to claim 9.

12. Based on the measurement noise estimated from the accuracy of the ultrasonic flaw detection, one or more thickness data on the minimum thickness side and one or more thickness data on the maximum thickness side are removed from the thickness data within the target judgment area, and the reference value is determined from the remaining thickness data. A method for determining defects in a metal pipe according to any one of claims 9 to 11.

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