JPS5942261B2 - Steel pipe joint position detection method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting the joint position of steel pipes, such as electric resistance welded pipes, forge-welded pipes, etc., by electromagnetic induction.

When performing eddy current flaw detection, ultrasonic flaw detection, or post-annealing on steel pipe joints, if the joint moves from side to side, the distance between the flaw detection probe and the flaw detection probe will vary, causing a large variation in flaw detection sensitivity. A problem was occurring that caused a decrease in sensitivity.

In addition, in the case of post-annealing, there is a problem in that there is a large misalignment between the center of the post-annealer and the position of the joint, making it impossible to perform appropriate annealing. A common countermeasure against this problem was to manually maintain the position of the flaw detection probe or post annealer and the joint by visual inspection. A device for detecting the joint position is installed in front of the annealer, and the detection signal allows the position of the flaw detection probe or post annealer to automatically follow the joint position. Conventionally, a method for detecting the position of the joint (hereinafter referred to as seam) is to scan a seam detection coil (hereinafter referred to as detection coil) over the seam in a direction perpendicular to the seam line, and An electromagnetic induction method is used to detect the seam portion as a change in impedance, but there is a problem in that the distance between the object to be measured and the detection coil must always be kept constant when scanning the detection coil. In other words, when the distance between the detection coil and the steel pipe changes, a pseudo signal (hereinafter referred to as a lift-off signal) is generated, and the detection sensitivity also changes.
The detection coil 1 can be oscillated at a constant frequency across the seam 3 in the direction of the arrow A and the mouth at a constant interval 11 according to the curvature of the steel pipe, or as shown in FIG. A method was used in which the steel pipe 2 was rotated at a constant interval 1 on the circumference in the direction of arrow C or in the opposite direction at a constant period. However, according to the method shown in Fig. 1, the scanning mechanism becomes complicated due to the oscillation, and if the drive source is in sinusoidal motion, the oscillation of the detection coil 1 is not constant, so if the position of the seam part changes, the detection The signal is not constant.

Also, the scanning speed cannot be increased. According to the method shown in Figure 2, when changing the outer diameter of the steel pipe, laborious work such as changing the rotation radius, correcting the circumferential speed, and centering is required, and measures are taken to prevent bending of the ends of the steel pipe. is necessary. In contrast to the conventional methods described above, the method of the present invention uses the electromagnetic induction method to detect the position of the seam of a steel pipe. This method is based on the fact that a stable seam position can be detected by selecting the first frequency band of the filter.

This method enables easy operation, high scanning speed, high response speed, and highly accurate detection. Next, the principle of the present invention will be explained with reference to FIGS. 3 and 4.

On the line of the seam part 3 of the steel pipe 2, set the central axis to O (seam part 3
When the detection coil 1 is rotated in a circle as shown in FIG. 3 and FIG. The distance between the coil 1 and the outer surface of the steel pipe changes to 11, 12, and 13, and a lift-off signal generated by this change in distance is detected. The inventors discovered that there is a difference in frequency between the seam signal and the lift-off signal, and that they each have a frequency band and are different, and solved the problem by frequency-discriminating the detection signal. It is. In other words, the electric conductivity and magnetic permeability of the seam portion are locally changed due to the joint state of the steel pipe or other causes, and these changes extend along the seam line in the pipe axis direction.

When the rotating detection coil traverses this band-like region of the order of mm at a substantially right angle, a seam signal that allows the seam position to be recognized in the form of a differential signal is generated. On the other hand, since the rotating detection coil rotates on a flat plate, the distance relationship between the detection coil and the steel pipe should be such that the minimum distance is directly above the steel pipe and the maximum distance is at the end of the rotation in the left and right direction with respect to the pipe axis of the steel pipe. Each rotation is sensed, and the smaller the radius of curvature of the steel pipe, that is, the smaller the diameter of the steel pipe, the larger the output amplitude of the distance fluctuation signal. However, the distance variation signal changes slowly with the rotation speed as a parameter, regardless of the curvature of the steel pipe. On the other hand, since the seam signal is generated by crossing a narrow band-like transition band approximately corresponding to the seam width, its signal period is shorter than that of the lift-off signal, and this causes the above-mentioned frequency difference. FIG. 5 shows the relationship between this seam signal and the lift-off pseudo seam signal when the rotation speed is changed. In this figure, W1 is the frequency band of the seam signal, and W2 is the frequency band of the lift-off signal. It can be seen from FIG. 5 that as the number of rotations on the horizontal axis increases, the difference in frequency (energy distribution) between the two becomes larger, and separation by the band filter tends to become easier.

Further, from FIG. 5, it can be seen that when the rotation speed of the detection coil is 600 rpm, the seam signal is within the frequency pass band of 85 to 220 Hz. On the other hand, since the lift signal is distributed in the range of 25 to 55 Hz, the lift-off signal can be removed by a band filter, and the seam portion signal can be extracted. The extraction of seam signals according to the present invention will be explained with reference to FIG. 6a.

An oscillator 22 oscillates a constant frequency, which is applied to the steel pipe 2 from an excitation coil via a bridge 23, that is, the steel pipe is energized. A detection coil 1 for detecting electromagnetic changes in the steel pipe undergoes a change, and the output of the coil is amplified by an amplifier 4. The method for excitation and detection of the steel pipe 2 may be any of the comparative electromagnetic induction method, orthogonal excitation electromagnetic induction method, adjacent electromagnetic induction method, and single coil detection electromagnetic method. Further, reference numeral 5 indicates pest control for suppressing the influence of foreign substances so that the bridge 23 functions normally, and is inputted into the bridge 23 via the output signal of the amplifier 4 to suppress the influence of foreign substances.

The amplified signal is given to the phase detector 6, which improves the ratio of the seam signal to the noise signal due to other factors. A phase shifter 7 is capable of arbitrarily shifting the phase from the phase of the oscillator waveform, and supplies this output to the phase detector 6 as a reference waveform.

Reference numeral 8 designates a band filter 1, which detects a seam part signal generated when the detection coil 1 rotates on the steel pipe 2 and passes the seam part to be detected, and a detection coil 1 and steel pipe 2 generated due to the influence of the curvature of the steel pipe. This filter outputs only the seam part signal from the signal mixed with the lift-off signal, that is, the signal due to the variation in distance between the seam part and the lift-off signal.

Reference numeral 9 denotes a calculation circuit that calculates the deviation in the position of the detection coil 1, which calculates the direction and amount of deviation by associating the detector 24 for extracting the rotational position of the detection coil 1 with the seam deviation position.

Using the deviation amount output of the calculation circuit 9 that calculates the seam deviation amount at the seam detection position, three post annealers 10A, 10B, and 10C are arranged as shown in FIG. Explain how to always anneal on the seam.

10a, 10b, and 10c are composed of a deviation amount proportional coefficient setter and an operational amplifier, and store the distance from the seam detection position to the post annealer position and, for example, the distance from the welding position 26 to the seam detection device 27. , From the transfer speed 25 of the steel pipe 2 and the amount of seam deviation at the seam detection position, the seam deviation amount 10Aa, 10Bb, 10Cc at the post annealer position is determined based on the welding position, seam detection position, and post annealer positional relationship. Compute, amplify,
By these signals, the post-annealer controller 101a,
101b and 101c, post annealer 10A~
10C to move the post annealer 1 so that it always anneals the seam portion of the steel pipe.

In this example, 13 post annealers were used, but it goes without saying that it can be done with just one post annealer, and it can also be used as a flaw detector. In Figure 6b, O is the reference line of the steel pipe seam and is 0.
1 represents the amount of deviation. FIG. 7 shows an example of an apparatus for carrying out the present invention.

Reference numeral 11 denotes a base, and the end of an arm 13 fits into a screw screw 12 provided on the base 11. The arm 13 is driven by a motor 14 connected to the screw screw 12, and the arm 13 is driven by a motor 14 connected to the screw screw 12. It is possible to move up and down in the direction.

The arm 13 may be moved up and down by a cylinder or the like. On the other hand, at the other end of the arm 13 is a holder 1 for the detection coil 1.
A shaft 1-5 is fixedly installed, and the holder is equipped with a signal transmission mechanism such as a slip ring or a rotary transformer 16 with the rotating body.
7 passes through the shaft 17, and the lower part of the shaft 17 can be rotated by a belt 19 passed between the shaft 17 and a motor 18, thereby forming a rotation device for the detection coil 1. Reference numeral 20 denotes an air cylinder connected to the upper end of the shaft 17, and the operation of this cylinder allows the detection coil 1 to move up and down in the direction of arrow H.

This is a device that makes slight movements, and for example, moves up and down when there is an abnormality in the seam of a steel pipe. Further, the terminal of the detection coil 1 is connected to an electromagnetic induction detector (not shown) via a slip ring 16. 2 is a steel pipe fed on rollers 21, and 3 is a seam portion.

When detecting a seam of a steel pipe, first drive the motor 14 to move the arm 13 and holder 15 up and down in the direction of the arrow H, and adjust the distance between the detection coil 1 and the seam 3 at the upper end of the steel pipe 2 appropriately. After setting, operate the air cylinder 20 in the direction of arrow E to lift the detection coil 1.

That is, the ends of the steel pipe usually have many defects in shape, and this prevents the ends of the steel pipe 2 from colliding with the detection coil 1. Next, the steel pipe 2 is sent toward the detection coil 1, and the motor 18 is driven to rotate the detection coil 1 in a circle. The rotation of the detection coil 1 only needs to block the steel pipe seam portion 3, and therefore, either circular rotation, circular rotation, or oscillating rotation may be used. Steel pipe 2
At the same time as the tip of the steel tube passes through the detection coil 1, the air cylinder 20 is operated in the direction of the arrow to start detecting the position of the steel pipe seam portion 3. In addition, in the above, the air cylinder 20 is not installed and the steel pipe 2 is operated only by the motor 14.
It is also possible to adjust the distance between the detection coil 1 and the detection coil 1. Further, the holding table 15 is provided with a detector 24 for detecting the rotational position of the detection coil 1, so that the rotational position of the detection coil 1 can be known. As the detector 24, a limit switch, an angle meter, a non-contact type detector, etc. may be used. Note that the detector 24
is for detecting the position of the detection coil 1, and therefore the location where the detector 24 is installed is not limited to the holding base 15. Since the present invention uses a scanning method that rotates the detection coil regardless of the diameter of the steel pipe, when changing the size, it is only necessary to adjust the distance between the detection coil and the steel pipe, which not only improves workability but also simplifies the mechanism. Since the scanning is rotary and the diameter is small, it is easy to increase the scanning processing capacity.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams of the conventional seam position detection method;
Figures 3 and 4 are explanatory diagrams of rotation of the detection coil of the present invention.
The figure shows the frequency bands of the seam part and lift part of the detection coil of the present invention, Figures 6A and b are explanatory diagrams of an embodiment for implementing the present invention, and Figure 7 shows the device of the present invention. This is an example for explanation. 1: Detection coil, 2: Steel pipe, 3: Steel pipe seam, 8: Filter 11: Base, 13: Arm.

Claims (1)

[Claims] 1. A method for detecting a steel pipe joint by electromagnetic induction, in which a steel pipe joint detection coil is rotated in a plane parallel to the axis of the steel pipe and located above the steel pipe joint. Further, a detector is provided for detecting the rotation of the detection coil, and a filter is provided to pass a frequency band higher than the frequency band of the lift-off signal for the detection signal from the detection coil to discriminate the frequency, and the signal passed through the filter is provided. A method for detecting the position of a steel pipe joint, characterized in that the position of the steel pipe joint is detected from an output and a detection signal obtained by detecting rotation of the detection coil. 2. An arm that can be raised and lowered is provided on the base, and a detection coil is provided at one end of the arm for detecting a steel pipe joint in a plane parallel to the axis of the steel pipe and located above the steel pipe joint by electromagnetic induction. A rotation device is provided to rotate the detection coil, and a detector is provided to detect the rotation of the detection coil. Among the detection signals of the detection coil, which are the steel pipe joint signal and the lift-off signal, only the steel pipe joint signal is detected at a frequency. A steel pipe joint position detection device characterized by being provided with a filter that is extracted by discrimination.