JPS60117134A - Method and apparatus for detecting spot defect of electro-united steel pipe - Google Patents

Abstract

PURPOSE:To detect a spot defect accurately by detecting the bead width of a welded part with an optical sensor to make judgment that a spot defect exists when the difference between the detection signal and a delay signal exceeds a specified value. CONSTITUTION:In the manufacture of a electro-united steel pipe 11, the width of the bead 14 is measured with an image sensor camera 12 immediately after it passes between squeeze rolls 13. The detection signal E1 of the bead width is inputted into a subtraction circuit 16 directly and through a delay circuit 15 (by the detection signal E2) for subtraction processing and the subtraction signal E0 is inputted into a level discrimination circuit 17. As the subtraction signal E0 exceeds a specified level, a delay circuit 20 is driven to delay the operation by a required time until the welded part involved reaches a marking device 19 and a marking device operating circit 18 is actuated to mark the welded part with the marking device 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting spot defects in electric resistance welded steel pipes for heat welding edge portions of steel strips formed into tubular shapes.

In the conventional welding process for ERW steel pipes, welding inputs are determined manually by the operator based on the operator's visual observation of the molten steel temperature at the weld zone, the measurement of the discharge bead temperature of the V-shave edge on the exit side (squeeze throw), etc. It's being adjusted.

However, when adjusting the welding input by the operator, there are individual differences and limitations between operators in how they perceive the color of the molten steel, and in how responsive they are to changes in the surface temperature and color of the molten steel due to changes in plate thickness, pipe forming speed, etc. Therefore, if the welding input is varied depending on the operator, if the joint surface temperature is low, it will result in incomplete cold welding, and if the joint surface temperature is too high, welding will drop due to the pressure drop at the joint surface, or penetrators will occur. This may result in welding defects called .

Therefore, in order to prevent the occurrence of welding defects as described above, welding conditions such as the outer diameter of the pipe, wall thickness, material, welding speed,
Many heat input control methods have been proposed for managing the amount of upset and the like.

However, even with these heat input control methods, it is currently impossible to prevent so-called spot defects that occur due to sudden causes such as coil edge flaws, scale entrainment, and steam back. In addition, it is difficult to detect this spot defect using an ultrasonic flaw detector in an online inspection process, and it is desired to develop a reliable detection method for spot defects.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for detecting spot defects in electric resistance welded steel pipes, which make it possible to reliably detect the occurrence of spot defects.

In order to achieve the above object, the spot defect detection method for electric resistance welded steel pipes according to the present invention detects the bead width of the welded part using an optical sensor, and detects the detection signal E by the optical sensor.
1 and a delayed signal E2 obtained by delaying the detection signal El, and when the subtracted signal EO obtained by the subtraction process exceeds a predetermined level, the occurrence of a spot defect in the weld is detected; The welded part is marked.

Further, the spot defect detection device for electric resistance welded steel pipes according to the present invention includes an optical sensor that detects the bead width of a welded portion and outputs a detection signal E1 thereof, and a detection signal El from the optical sensor that is delayed. a delay circuit that outputs a signal E2; a subtraction circuit that performs subtraction processing on the detection signal El and the delayed signal E2 and outputs a subtraction signal EO; and a subtraction circuit that discriminates whether or not the subtraction signal EO exceeds a predetermined level, The present invention includes a level discrimination circuit that detects the occurrence of a spot defect in the weld when the EO exceeds a predetermined level, and a marking device that marks the weld where the spot defect has occurred.

The present invention will be explained in detail below.

The present invention continuously measures the bead width immediately after welding using a non-contact optical sensor, and detects spot defects based on the detection of abnormal fluctuations in the bead width. That is, it is recognized that the bead width immediately after welding undergoes relatively long-period fluctuations due to heat input, upset amount, changes in plate thickness, etc. Furthermore, it is recognized that the bead width in the vicinity of a spot defect caused by an unexpected cause such as a short circuit of the V-shaped coil edge due to scale or a scratch on the coil edge fluctuates for a very short period of time. In order to detect this extremely short-term bead width variation, it is necessary to continuously measure the bead width without contact and to exclude the long-period bead width variation.

The best way to continuously measure the bead width without contact is to use an optical sensor, i.e., an image sensor-1 camera. The length is about 1-1, and considering the maximum tube manufacturing speed of about 70 s/min, the time required for the defective part to pass through the scanning line of the image sensor and camera is 0.88 mm. sec, and in order to capture the defect with the image sensor-camera, the scanning time of the image sensor-camera is set to 0.sec.
It needs to be 8 seconds or less.

FIG. 1 and FIG. 2 are explanatory diagrams showing a state in which the width of the bead 14 immediately after passing through the squeeze roll 13 is measured by the image sensor-camera 12 when manufacturing the electric resistance welded steel pipe 11. The scanning direction of 12 is the second
As shown by X in the figure, it is arranged perpendicular to the weld line.

FIG. 3 shows an example of bead width fluctuations measured by the image sensor/camera 12, including a long-period bead width fluctuation 14A of about 1 sec and an extremely short-period bead width fluctuation 14B.
is recognized. The waveform shown in Fig. 3 is a waveform recorded by a high-speed electromagnetic oscilloscope, but it is not practical to find abnormalities during long-term pipe making using this method. Second, by removing long-period beat width fluctuations, only extremely short-term abnormal waveforms can be captured as electrical signals, which can be transmitted to an abnormality monitoring device and an abnormality marking device.

FIG. 4 is a block diagram showing an example of a control circuit used to implement the present invention. Beat width detection signal E shown in FIG. 5(A) obtained by the image sensor camera 12
1 is transmitted to the delay circuit (or delay line) 15, and the detected signal El is delayed by 10-510-50 to obtain the delayed signal E2 shown in FIG. 5(B). These detection signal E1 and delay signal E2 are subtracted in a subtraction circuit 16, and a subtraction signal EO is obtained.
(EO=El-, E2) is calculated. Since the waveform of the abnormal area changes rapidly over a very short period of time, the subtraction signal EO has a waveform as shown in Figure 5 (C), and the peak value and width of the waveform are thought to change depending on the condition of the weld. As a result of the study conducted by the present inventor, it has been found that if the wave height value is equal to or higher than the predetermined level A regardless of the abnormal waveform width, it is recognized that a harmful spot defect has occurred in the welded portion. Note that the above-mentioned predetermined level A is predetermined based on the pipe dimensions, pipe manufacturing speed, etc.

Therefore, in the present invention, when the subtraction signal EO is input to the level discrimination circuit 17 and the subtraction signal EO exceeds a predetermined level A, it is assumed that a harmful spot defect has occurred in the welded part, and the marking device operating circuit 18 is activated, and the marking device 19 marks the welded portion.

Note that the delay circuit 20 calculates the delay time from when the welded portion whose bead width was measured reaches the marking device 19 based on the distance between the bead width measurement position and the marking device 19 and the pipe manufacturing speed V. 1 (1=text/v), and the calculation result can be transmitted to the marking device operating circuit 18. The marking device operating circuit 18 operates the marking device 19 based on the calculation result of the delay circuit 20.
This makes it possible to mark welds where spot defects occur.

Further, the reason why the delay time of the R delay signal E2 with respect to the detection signal El in the delay circuit 15 is set to 10 to 50 m5ec is as follows. In other words, the above delay time is 0s
ec, the subtraction signal EO is not output at all, as shown in FIG. 6(A). Further, when the delay time becomes large, for example, 500+waec, the output waveform of the subtraction signal EO becomes complicated, as shown in t56 (B), and it may become impossible to detect spot defects. Therefore, in the delay circuit 15, it is necessary to delay the signal by a small amount of time, and 10 to 50 m5ec is preferable.

Next, concrete implementation results by the present inventor will be explained. This specific example uses a 1024-bit, MOS type, image sensor camera with a scan distance of 0.8 mm, an external diameter of 48.8 mm, and a wall thickness of 3.7 mm. I was involved in the manufacture of sewn steel pipes. That is, the change in the bead width immediately after passing through the squeeze throw is measured using a public image sensor camera, and the detected signal El is processed as described above, and a spray mark is placed on the side surface of the tube where the spot defect has occurred. After spraying and forming a pipe, a flattening test was conducted. Note that the analog output waveform after calculation processing was recorded using an electromagnetic oscilloscope. As a result, the analog output voltage of the detection signal El during normal operation was 2.3V on average, and no seam cracking occurred in the flattening test.
The analog output voltage of the subtraction signal EO during abnormality is 1.8 in instantaneous value. V (predetermined level A is 1.Ov),
Occurrence of seam cracking was observed in flattening test.

As described above, the spot defect detection method for electric resistance welded steel pipes according to the present invention detects the bead width of the welded part using an optical sensor and detects t33M? yE l
&1. Mmm. 1*mgz+t, ng signal E Q'', 1 is subtracted, and if the subtracted signal EO obtained by the subtraction process leaks below a predetermined level, detects the occurrence of a spot defect in the welded part, The welded portion is marked.Furthermore, the spot defect detection device for electric resistance welded steel pipes according to the present invention includes an optical sensor that detects the bead width of the welded portion and outputs a detection signal El. , a delay circuit that delays the detection signal El from the optical sensor and outputs the delayed signal E2; a subtraction circuit that performs subtraction processing on the detection signal El and the delayed signal E2 and outputs the subtracted signal EO; and a subtracted signal EO. a level discrimination circuit that discriminates whether or not EO exceeds a predetermined level, and detects the occurrence of a spot defect in the weld when the subtraction signal EO exceeds a predetermined level; and a marking device that marks the weld where the spot defect has occurred. Therefore, according to the present invention, it is possible to reliably detect the occurrence of spot defects.

[Brief explanation of drawings]

FIG. 1 is a side view showing a welding process in which the present invention is carried out, FIG. 2 is a front view of FIG. 1, and FIG. 3 is a waveform diagram showing a bead width detection signal measured by an image sensor-camera.
FIG. 4 is a block diagram showing an example of a control circuit used in implementing the present invention, FIG. 5(A) is a waveform diagram showing a detection signal,
Figure 5 (B) is a waveform diagram showing a delayed signal, Figure 5 (C) is a waveform diagram showing a subtraction signal, and Figure 6 (A) is a waveform diagram showing a delay time of 0v.
The waveform diagram in Fig. 6 (B) when ec is set is the delay time of 5.
It is a waveform diagram in the case of 00m5ec. DESCRIPTION OF SYMBOLS 1, 1... ERW steel pipe, 12... Image sensor camera, 14... Bead, 15... d extension circuit, 16...
...Subtraction circuit, 17...Level discrimination circuit, 19...
Marking device, El...detection signal, E2...delayed signal, EO...subtraction signal, A...predetermined level. Agent Patent Attorney Osamu Shiokawa Figure 6 (A) 1111111112---0 (B) 11th β and the next day

Claims (2)

[Claims] (1) A spot defect detection method for electric resistance welded steel pipes in which the edges of a steel band formed into a tubular shape are heat welded, in which the bead width of the welded part is detected by an optical sensor, and the detection signal El by the optical sensor is , subtracts the detected signal El from a delayed signal E2, and when the subtracted signal EO obtained by the subtraction process exceeds a predetermined level, detects the occurrence of a spot defect in the weld, and detects the occurrence of a spot defect in the weld. A method for detecting spot defects in ERW steel pipes. (2) A spot defect detection device for an electric resistance welded steel pipe that heat-welds the edge portion of a steel band formed into a tubular shape, an optical sensor that detects the bead width of the welded portion and outputs a detection signal E1; A delay circuit that delays the detection signal El applied to the optical sensor and outputs the delayed signal E2, and a delay circuit that performs subtraction processing on the detection signal E1 and the delayed signal E2, and outputs the subtracted signal EO.
a subtraction circuit that outputs a subtraction signal EO, a level discrimination circuit that discriminates whether or not the subtraction signal EO exceeds a predetermined level, and detects the occurrence of a spot defect in the weld when the subtraction signal EO exceeds a predetermined level; 1. A spot defect detection device for electric resistance welded steel pipes, comprising a marking device that marks a welded portion where the weld occurs.