JPS6250761B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring the circumferential and longitudinal wall thickness and thickness unevenness of a metal tube using electromagnetic ultrasound.

When manufacturing metal tubes by hot pressing, perforation, rolling, etc., the thickness of the material may deteriorate due to operational conditions such as uneven heating of the material, fluctuations in the position of perforation bars and rolling rolls, bending, and distortion. The thickness is not uniform and uneven thickness occurs. Therefore, there is a strong need for automatic measurement of the uneven thickness of metal pipes during operation or in a cold state.

Conventionally, the ultrasonic flaw detection method and the present inventors proposed a patent application in 1972.
There is a measurement method disclosed in No. 98458, but the former uses a couplant such as water or oil to penetrate and detect ultrasonic waves from an ultrasonic probe made of crystal, barium titanate, etc., into a metal tube. If necessary, and the surface condition of the metal pipe is poor (scale, dirt, unevenness, etc.),
Alternatively, if the metal tube is at a high temperature, it becomes impossible to maintain the couplant in a constant state, making measurement difficult.

In addition, in the latter case, it is necessary to rotate the detection end for measuring the wall thickness of the metal tube in the entire circumferential direction of the metal tube, which makes the rotation and holding mechanism of the detection end complicated, which makes it difficult to maintain equipment. There are also many practical difficulties. Furthermore, since the tube in the rough rolling process is not a perfect circle and has a poor shape, it may be impossible to make the detection end follow the circumferential direction of the tube.

The present invention focuses on the fact that the inner and outer diameters of metal tubes are set mechanically in advance during the manufacturing process, and detecting ends are placed at two appropriate locations on the surface of the metal tube in the circumferential direction. It is an object of the present invention to provide a method and a device that make it possible to measure the wall thickness unevenness over the entire length of a pipe based on the wall thickness signal at each position of the pipe obtained by scanning in the same direction.

Hereinafter, it will be explained in detail using examples. FIG. 1 shows a principle diagram when measuring the wall thickness of a metal tube using a longitudinal wave electromagnetic ultrasonic generation detector. In this, an electromagnetic ultrasonic generation detector 3 is placed opposite the metal tube 1 with a certain gap 2 provided therebetween. The electromagnetic ultrasonic generation detector 3 includes an ultrasonic generation coil 5, a detection coil 6, a magnetic field generation coil 7, and a magnet 8.
and a protective cover 9. When a voltage is applied to the magnetic field generating coil 7 from the magnetic field generating power supply 10, a magnetic field 11 is generated in the surface layer region of the metal tube 1. On the other hand, when a high frequency pulse current is passed from the high frequency pulse power source 12 to the ultrasonic generation coil 5, an eddy current 13 is generated by induction in the surface layer region of the metal tube 1, and at the same time a magnetic field 14 is generated. This eddy current 13 and magnetic field 1
4 produces a pulsed vibration force 15 shown by an arrow according to Fleming's left-hand rule. This vibration force 15 then travels in the direction of an arrow 16 as an electromagnetic ultrasonic wave. When this electromagnetic ultrasonic wave reaches the inner wall of the metal tube 1, it is reflected and returns in the direction of the arrow 17.
When reaching the surface layer of the metal tube 1, the vibration force 18
As a result of the interaction between the magnetic field 11 and the magnetic field 11, an eddy current 19 is generated according to Fleming's right-hand rule. This eddy current 19 is detected by the detection coil 6. The detection signal is amplified by an amplifier 20 and sent to a thickness calculation processor 21. A synchronization signal at the moment when an ultrasonic wave is generated in the metal tube 1 is sent from the high-frequency pulse power source 12 to the wall thickness calculation processor 21. Based on the synchronization signal, the processor 21 calculates a detection signal using the detection coil 6. Calculate the time interval t until the detection of
It is calculated by v×t, and the display device 21 is energized for display.

FIG. 2 shows a diagram of the principle of measuring the uneven thickness of a metal pipe according to the present invention. In order _to measure the wall thickness at _two appropriate locations in the circumferential direction of the metal tube 1 as described in FIG. electromagnetic ultrasonic generation detector 3,
Let d ₁ and d ₂ be the wall thicknesses measured at 3', and θ be the supplementary angle of the angle between the two electromagnetic ultrasonic generation detectors 3 and 3'. Here, the thickness unevenness rate of the metal tube 1 is defined by equation (1). Considering the X-Y coordinates with the center point of the outer circle as the origin 0, the outer circle is expressed by equation (2). Considering that the center point of the inner circle moves within the outer circle according to the uneven thickness of the metal tube 1,
If it is expressed by the coordinates (p, q) of this center point, then
The inner circle can be expressed by equation (3).

Now, calculate the coordinates p, q of the center point of the inner circle from equations (3-1) and (3-2), in which the coordinate values of the wall thickness measurement point of the inner circle are substituted for x, y in equation (3). and can be expressed by equations (4) and (5), respectively. A of both these expressions,
B is replaced by equations (6) and (7), respectively.

The distance between the center points of the outer circle and the inner circle can be expressed as δ in equation (8). Therefore, by using this δ, the uneven thickness of the metal pipe can be determined as ε in equation (9).

Thickness unevenness rate (%) = Maximum wall thickness - Minimum wall thickness / Average wall thickness x 100 (
1) x ² + y ² = r ² ₁ (2) (x-p) ² + (y-q) ² = r ² ₂ (3) {(r ₁ − d ₁ )cosθ−p} ² + {(r ₁ −d ₁ ) sinθ−q} ² = r ² ₂
(3-1) {(-r ₁ +d ₂ )-P} ² +q ² = r ² ₂ (3-2) q=Ap+B (5) A=-{(r ₁ - d ₁ ) cos θ+(r ₁ - d ₂ )}
/(r ₁ - d ₁ ) sin θ(6) B={(r ₁ - d ₁ ) ² -(r ₁ - d ₂ ) ² }/2(
r ₁ − d ₁ ) sin θ(7) δ=√ ₂ − ₂ (8) ε=2δ/r ₁ − r ₂ (9) FIG. Figure 3a shows a side view as seen from a direction parallel to the direction of travel of the metal tube, and b of Figure 3 shows a front view seen from a direction perpendicular to the direction of travel of the metal tube. It shows.

In a and b of FIG. 3, the high temperature metal tube 2
3 moves in the direction of the arrow 24 by the conveyance roller, the metal tube 23 is detected by the high temperature metal detector 25.
The tip of the is detected. This detection signal is transmitted to the control device 2.
Sent to 6. Upon receiving the detection signal, the control device 26 controls the holding and holding of the electromagnetic ultrasonic generation detectors 3 and 3'.
The copying devices 27 and 27' are driven to supply cooling water to the electromagnetic ultrasonic generation detectors 3 and 3' from the cooling water pipes 28 and 28', and then the metal pipe 23 is connected to the cooling water. At the same time, a start signal is sent to the high-frequency pulse power supply 29 and the magnetic field generation power supply 30, and each power supply is started. Based on the principle described in FIG. 1, two of the metal tubes 23 are
A detection signal corresponding to the thickness of the wall can be obtained. At this time, since the high frequency pulse currents sent from the high frequency pulse power supply 29 to the two electromagnetic ultrasonic generation detectors 3 and 3' are generated alternately, the detection signals according to the wall thickness are also alternately sent to the dedicated amplifiers 31 and 3'. 31'. These signals are added by an adder 32 and sent to a thick signal processor 33. Thick signal processor 3
3 identifies the instantaneous synchronization signal in the ultrasonic generation of each electromagnetic ultrasonic generation detector 3, 3' sent from the high frequency pulse power source 29, detects the corresponding detection signal, and detects the two positions of the metal tube 23. The wall thickness is calculated based on the principle described in FIG.

When such measurements are repeated up to the vicinity of the rear end of the metal pipe 23 and the high temperature metal detector 25 detects the rear end of all the metal pipes 23, the detection signal is sent to the control device 2 again.
Sent to 6. When the control device 26 receives the detection signal, it drives the holding/copying devices 27 and 27'.
The electromagnetic ultrasonic generation detectors 3 and 3' are separated from the tube 23. After separation, each power supply will stop starting and the supply of cooling water will also stop. During this time, the wall thickness calculation processor 33
The thickness signals calculated by are sequentially sent to the thickness deviation calculator 34. The thickness deviation calculator 34 is a metal tube 23
Based on the wall thickness signals at two locations in the circumferential direction, the wall thickness deviation rate of the metal tube 23 is calculated based on the principle explained using FIG. At the same time, electromagnetic ultrasonic generation detectors 3, 3' are sent from a measuring device 35 attached to a conveying roller that is started and stopped by the control device 26.
Metal pipe 2 receives a length measurement signal from the connecting pipe to the separating pipe.
The calculation result of the thickness unevenness ratio corresponding to the longitudinal position of No. 3 is output to the display 36.

In this way, the uneven thickness of the metal pipe is measured.
In the present invention, the degree of wall thickness unevenness is determined by how accurately the installation angles of the electromagnetic ultrasonic wave generation detectors 3 and 3' at two locations in the circumferential direction of the metal tube 23 can be maintained and followed during measurement. This has a significant impact on measurement accuracy.

FIG. 4 shows an example of the results of examining the variation of the measured value of the thickness unevenness with respect to the installation angle of the electromagnetic ultrasonic generation detector using the thickness unevenness as a parameter. Installation angle is 90°
135°, and the installation angle varies within a range of ±10° during measurement.
At 90°, 14% thickness deviation measurement value is approximately ±1.25%
However, at 135°, the measured value of thickness unevenness at 11% is approximately ±0.4%, and the measured value of thickness unevenness at 22% is approximately ±0.8. %
It can be seen that this is just a variation in

Therefore, it can be seen that the larger the installation angle is, the smaller the error in the thickness unevenness measurement value due to fluctuations in the installation angle is.

Also, as is clear from the explanation of the principle in Figure 2,
There may be two thickness unevenness ratio values calculated using wall thickness values at two points of the metal tube 23. Therefore,
It is necessary to determine which of these two values is correct. In other words, the value obtained by the discriminant in the radical in equation (4) may be a real root, a multiple root, or an imaginary root,
If it is an imaginary root, it is ignored as it cannot be calculated. With multiple roots, there is only one calculation value, so there is no problem. Therefore, the calculation of binary values in the case of real roots becomes a problem. However, regarding this, if a value that satisfies the following conditions is determined to be an appropriate value, it is possible to measure the thickness unevenness ratio without any practical problem.
That is, it has been found that depending on the design accuracy of the punching and rolling mill, the uneven thickness of the metal tube 23 never exceeds 50%. Also, one metal tube 2
Thickness unevenness rate at the starting point of drilling and rolling in step 3 is always 5%.
In addition, the thickness unevenness rate from the tip region to the rear end region of the metal tube 23 does not suddenly change locally.
Usually has a gradual increasing trend. Therefore, each metal tube 2
Only values that tend to gradually increase with respect to the thickness unevenness rate in the tip region of 3 are treated as appropriate values, and values that suddenly change by more than 50% are ignored. By repeating such calculations up to the rear end, it becomes possible to measure the thickness unevenness over the entire length of the metal tube 23.

FIG. 5 shows an example of the results of measuring the thickness unevenness in the length direction of a high-temperature seamless pipe. This is a measurement of the thickness unevenness rate over the entire length of a seamless pipe after drilling and rolling, which is the initial manufacturing process, in a hot online process. has been well measured. The installation angle of the two electromagnetic ultrasonic generators/detectors 3 and 3' is 135°, and the outer diameter of the pipe is 200 to 400 mm.
φ, wall thickness 50~100mm, pipe surface temperature 1150℃~
The temperature is 1200℃. The size of the electromagnetic ultrasonic generation detector used was 80 mm in diameter and 80 mm in height, and the surface facing the pipe had a curvature that matched the outer diameter of the pipe. The gap between the tip surfaces of the electromagnetic ultrasonic generators 3 and 3' and the pipe surface was set to 2.0 mm. Also,
The applicable frequency of electromagnetic ultrasound was 0.4-1.0MHz.

Such measurement results are sequentially fed back to the operation side and are used as control information to reduce uneven thickness in the product process from the early stage of manufacturing, and are also used for control in the heat treatment process of product pipes.

As described above, by using the method and device for measuring the thickness unevenness ratio of metal pipes according to the present invention, it is possible to appropriately measure the uneven thickness of metal pipes in various manufacturing processes, and the unevenness of thickness in each process can be measured. It can also produce significant results in terms of quality control, such as reducing wall thickness, improving yield, and improving dimensional accuracy.

Note that the present invention is applicable to both cold and hot processing of metal tubes. The outer diameter of the metal tube,
There are no restrictions on the wall thickness by changing the size and curvature of the electromagnetic ultrasonic generation detector and changing the frequency as appropriate. Further, although longitudinal electromagnetic ultrasonic waves are used in the explanation of the principles in the embodiments, there is no problem in applying transverse waves. Although there is no restriction on the installation angle of the electromagnetic ultrasonic generation detectors at two locations in the circumferential direction of the metal tube, the closer the installation angle is to 180°, the better the accuracy. Furthermore, the proper 3 in the circumferential direction of the metal tube
It is also possible to arrange electromagnetic ultrasonic generation detectors at these three points and measure the thickness unevenness rate based on the wall thickness values at those three points. Compared to the present invention, this method has the advantage that the measured value of the thickness unevenness rate is uniquely determined and the measurement accuracy is also good. Since it is necessary to increase the capacity of each necessary power source, there is a drawback that the equipment cost increases, and in this sense, the electromagnetic ultrasonic generation detector is
A pair is preferable.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a detector for explaining the principle of measuring the wall thickness of a metal tube using a longitudinal wave electromagnetic ultrasonic generation detector. FIG. 2 is a cross-sectional view of a metal tube for explaining the principle of measuring the uneven thickness of a metal tube according to the present invention. FIGS. 3a and 3b are block diagrams showing the configuration of a metal pipe thickness unevenness measuring device according to the present invention, and a is a side view seen from a direction parallel to the direction of movement of the metal pipe;
b is a front view seen from a direction perpendicular to the traveling direction of the metal tube. FIG. 4 is a graph showing the measured value of the thickness unevenness rate with respect to the installation angle of the electromagnetic ultrasonic generation detector using the thickness unevenness rate as a parameter. FIG. 5 is a graph showing the measurement results of the thickness unevenness ratio in the length direction of a high-temperature seamless pipe. 1, 23: metal tube, 2: gap, 3, 3': electromagnetic ultrasonic generation detector, 4: rotational symmetry axis, 5: ultrasonic generation coil, 6: detection coil, 7: magnetic field generation coil, 8: Magnet, 9: Protective cover, 10,
30: Magnetic field generation power supply, 11: Magnetic field, 12,2
9: High frequency pulse power supply, 13: Eddy current, 14: Magnetic field, 15: Vibration force, 16, 17, 24: Arrow, 1
8: Vibration force, 19: Eddy current, 20, 31, 3
1': Amplifier, 21, 33: Thickness arithmetic processor, 2
2, 36: Display, 25: High temperature metal detector, 2
6: Control device, 27, 27': Holding/copying device,
28, 28': Cooling water pipe, 32: Adder, 34:
Measuring device, 35: Measuring device.

Claims (1)

[Claims] 1. A magnetic field generating magnet, an ultrasonic generating coil that generates eddy currents on the outer circumferential surface of a metal tube, and a detection device that detects eddy currents generated by reflected ultrasonic waves from inside the metal tube. at least a pair of electromagnetic ultrasonic generators and detectors each comprising a coil, one of which is arranged so as to face the outer circumferential surface of the metal tube at a predetermined angle with the direction in which the other one faces the outer circumferential surface of the metal tube;
A method using electromagnetic ultrasound characterized in that the position and rate of uneven thickness of a metal tube in the circumferential direction are measured from the wall thickness values of the metal tube obtained by each electromagnetic ultrasonic detector. Method for measuring uneven wall thickness of metal pipes. 2. At least one pair consisting of a magnetic field generating magnet, an ultrasonic generating coil that generates eddy currents on the outer peripheral surface of the metal tube, and a detection coil that detects eddy currents generated by reflected ultrasonic waves from inside the metal tube. electromagnetic ultrasonic generators and detectors are disposed so that they can move forward and backward in the radial direction of the metal tube such that one of them faces the outer circumferential surface of the metal tube at a predetermined angle with the direction in which it faces the outer surface of the metal tube. In addition, a detector for detecting the approach of a metal tube is provided, and a signal corresponding to the wall thickness of the metal tube obtained by each electromagnetic ultrasonic generator and detector is sent to the electromagnetic ultrasonic generator coil by a high-frequency pulse. Thickness calculation that identifies each location in the circumferential direction of the metal tube as a detection signal based on a synchronized signal from a high-frequency pulse power supply that supplies current, and calculates the wall thickness value of each location based on the detection signal corresponding to the wall thickness. a metal tube length measuring device, a position signal in the axial direction of the metal tube from the length measuring device, and each wall thickness signal in the circumferential direction of the metal tube from the wall thickness calculation processor. An apparatus for measuring thickness unevenness of a metal pipe using electromagnetic ultrasonic waves, comprising a thickness unevenness calculator for calculating a thickness unevenness in the axial direction of a metal tube.