JP3568084B2 - Detection method of vertical seam position of pipe using leakage magnetic flux pig - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for detecting a vertical seam position of a tube using a leakage magnetic flux pig.
[0002]
[Prior art]
As a conventional method for detecting a vertical seam of a steel pipe constituting a pipeline, a nondestructive inspection method using ultrasonic waves is applied, and a method using a dedicated ultrasonic pig is generally performed.
That is, as shown in FIG. 1, the vertical seam 1 is formed, for example, in the case of a pipe 1 of a high pressure main line of city gas or the like, with a thick part having a width of about several cm along the axial direction of the pipe 2. Since non-destructive inspection using an ultrasonic pig can directly detect the wall thickness of the pipe, it is possible to detect a thick part in the axial direction of the pipe and detect that part as a vertical seam. it can. In addition, in FIG. 1, the code | symbol 3 is a welding line.
[0003]
[Problems to be solved by the invention]
The above method has the following problems.
a. The ultrasonic pig is not preferable when the pipeline is a gas supply pipe or the like because the inner surface of the steel pipe of the pipeline is wet.
b. In such a pipeline, soundness inspection (presence of thinned portion) is performed using leakage magnetic flux pigs. However, since vertical seam detection is performed separately from such inspection, double inspection is required. Has become.
An object of the present invention is to solve such a problem.
[0004]
[Means for Solving the Problems]
In order to solve the above-described problems, according to the present invention, a large number of magnets and magnetic sensors are arranged at predetermined intervals while moving a leakage magnetic flux pig, which is disposed corresponding to the inner periphery of a tube to be inspected, in the axial direction of the tube. Collect the data corresponding to the leakage magnetic flux output by the magnetic sensors, compare the variance of the data for each magnetic sensor, and detect the position of the magnetic sensor corresponding to the data with the largest variance as the vertical seam position. suggest.
[0005]
Further, in the present invention, in the above configuration, the data for which the dispersion is to be calculated is a narrow section of 20 to 200 points upstream from the end of the vertical seam near the weld line where the thick part is formed in the circumferential direction of the pipe. We propose to use the data of
[0006]
According to the present invention described above, the position of the vertical seam where the wall thickness of the pipe is increasing is determined from the collected data by the leakage magnetic flux pig in the inspection of the soundness of the pipe, and the dispersion of the data due to the increase in the wall thickness is increased. Can be detected.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described together with embodiments with reference to the drawings.
As described above, FIG. 1 shows a part of a pipe to be inspected for soundness (the presence or absence of a thinned portion) by applying the present invention, and this pipe 2 has a thick wall along the axial direction. A vertical seam 1 is formed as a part, and a welding line 3 is formed in a circumferential direction. As shown in the figure, the welding line 3 has a thick portion formed in the circumferential direction of the pipe.
[0008]
A large number of magnets and magnetic sensors are arranged in the axial direction of such a tube 2 while moving a leakage magnetic flux pig arranged in correspondence with the inner periphery of the tube at each predetermined interval while moving the leakage magnetic flux pig. A quantity of data is collected and a check of the integrity of the tube 2 is performed.
[0009]
In the data collected by such a leakage magnetic flux pig, in the vertical seam 1, the leakage magnetic flux decreases because the thickness of the tube 2 is increased. Therefore, if the decrease of the leakage magnetic flux is detected by appropriate data processing from the collected data, the position of the magnetic sensor having the data can be detected as the vertical seam 1 position.
[0010]
As this data processing method, for example, as shown in FIG. 1, the average value of the leakage magnetic flux data of the sound portion of each magnetic sensor in each of the pipe portions before and after the welding line 1 is obtained, and By comparing this value with the tube, it is possible to detect that the position of the magnetic sensor where the value of the leakage magnetic flux has decreased most is the position of the vertical seam 1. This method utilizes the fact that the position of the vertical seam 1 is shifted before and after the welding line 3.
[0011]
As described above, in the method of detecting the longitudinal seam 1 by reducing the leakage magnetic flux, the moving speed of the leakage magnetic flux pig requires relatively strict management in order to accurately measure the leakage magnetic flux. Therefore, the present invention proposes a method of detecting the position of the vertical seam 1 that is easy to manage without depending on the moving speed of the leakage magnetic flux pig.
[0012]
That is, when moving the leakage magnetic flux pig into the tube 2 in the inspection, each magnetic sensor is usually in close contact with the inner surface of the tube 2, but cannot be completely adhered at the position of the vertical seam 1, and the lift-off varies with the movement. I do. Therefore, since the leakage magnetic flux fluctuates with the movement of the leakage magnetic flux pig, the variance of the leakage magnetic flux data corresponding to the fluctuation also increases. Accordingly, if the increase in the variance of the data is detected from the collected data by appropriate data processing, the position of the magnetic sensor having the data can be detected as the vertical seam 1 position.
[0013]
FIG. 2 schematically shows the detection operation of the vertical seam 1 by this method. That is, FIG. 2 schematically shows data collected by the leakage magnetic flux pig, and eight magnetic sensors S14 to S21 are arranged along the circumferential direction of the tube in FIG. Among them, since the variance of the data of the magnetic sensor S19 is the largest, it can be detected that the position of the magnetic sensor S19 is the vertical seam 1 position.
[0014]
FIG. 3 shows an example of the state of dispersion in actually collected data. The horizontal axis of the figure shows the magnetic sensor numbers (1 to 200), and the vertical axis shows the distribution of data. In this example, a steep peak of data variance appears around the sensor S148, and therefore, it can be clearly seen that there is the vertical seam 1 in this sensor 148 and its vicinity.
[0015]
However, depending on the pipe to be measured, if the section in the axial direction of the data for which dispersion is to be obtained is too wide, the increase in data dispersion due to the vertical seam 1 will be buried in the increase in data dispersion due to factors other than the vertical seam 1. There are cases.
In such a case, in the present invention, the section of the data for which the variance is to be calculated is defined as the section in which the variance of the data by the vertical seam 1 appears most remarkably, that is, in the vicinity of the welding line 3, the upstream side from the end E of the vertical seam 1. , The identifiability of an increase in data dispersion due to the vertical seam 1 is improved.
That is, FIG. 4 shows an example of the state of dispersion in the actually collected data. FIG. 4 (a) shows a measurement section L of 20 points from the end E of the vertical seam 1 which is appropriately separated from the welding line 3 to the upstream side. (B) is the variance calculated from the data for 200 measurement sections L from the end E to the upstream side, and (c) is the 1000 variance measured from the end E to the upstream side. This shows the variance calculated based on the data for the section L.
From this figure, it can be seen that in the case of (c), where the axial section of the data for which the variance is to be determined is wide, the increase in the variance due to the vertical seam 1 that could not be clearly identified, but in (b) the identification is somewhat possible, and (a) ) Indicates that it can be clearly identified.
[0016]
As described above, in the method of detecting the longitudinal seam 1 by reducing the leakage magnetic flux, the moving speed of the leakage magnetic flux pig requires relatively strict control in order to accurately measure the leakage magnetic flux. In the method of the present invention for detecting the vertical seam 1 by the increase, the management is easy because the method does not depend on the moving speed of the leakage magnetic flux pig.
[0017]
【The invention's effect】
As described above, the present invention has the following effects.
a. Since the longitudinal seam can be detected based on the collected data of the leakage magnetic flux pig in the inspection of the soundness of the pipeline, labor saving of the pipeline inspection can be realized.
b. There is no need to make the inside of the tube wet unlike an ultrasonic pig.
c. Vertical seam detection can be automated.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a part of a pipe to be inspected by applying the present invention.
FIG. 2 is an explanatory diagram schematically showing an example of a vertical seam detection operation to which the present invention is applied.
FIG. 3 is an explanatory diagram showing an example of a state of dispersion in actually collected data.
FIG. 4 is an explanatory diagram showing the dependence of the variance state in actually collected data on the data section.
[Explanation of symbols]
1 vertical seam 2 pipe 3 welding line

Claims (2)

Data corresponding to the leakage magnetic flux output by each magnetic sensor at predetermined intervals while moving the leakage magnetic flux pig in which a number of magnets and magnetic sensors are arranged corresponding to the inner circumference of the pipe to be inspected in the axial direction of the pipe Variance of data is compared for each magnetic sensor, and the position of the magnetic sensor corresponding to the data having the largest variance is detected as a vertical seam position. Seam position detection method The data for obtaining the variance is characterized by using data of a narrow section of 20 to 200 points upstream from the end of the vertical seam near the weld line where the thick part is formed in the circumferential direction of the pipe. A method for detecting a vertical seam position of a pipe using the leakage magnetic flux pig according to claim 1.

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