JPH0198952A - Defect detecting device for electric welded tube - Google Patents

Abstract

PURPOSE:To detect a flaw generated at the seam part of the title electric welded tube with a good S/N and high accuracy by performing flaw detection operation while performing follow-up control automatically so that a probe type coil is arranged at the center position of a high-temperature area. CONSTITUTION:A center position detecting device 1 for the high-temperature area outputs an electric signal indicating the deviation quantity between the center position of the high-temperature area and a reference position. A servo amplifier 5 is applied with the analog output generated by the detector and the output of a potentiometer 4 which operates associatively with a follow-up mechanism 2 having a through-hole 7. A servo motor 3 driven with the output of this servo amplifier 5 drives the follow-up mechanism 2 and performs control so that the reference position is aligned with the center of the high-temperature area. Then the probe type coil 6 provided at the reference position of the follow-up mechanism 2 is moved relatively to makes a flaw detecting scan on the seam part 41 and thus local variation is detected to know the presence of a defect. Further, a marking device marks a part nearby the position where the defect is present.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an apparatus for inspecting defects in the joint portion of an electric resistance welded pipe made by rolling a band-shaped steel plate and welding the joint using high-frequency power.

(Prior Art) As shown in FIG. 5, an electric resistance welded pipe manufacturing apparatus includes a work coil 50 connected to the output side of a high frequency power source 48.
In the work coil 50, a steel strip 48 is rolled up and a high frequency current is induced in the seam part opened in a figure 7 shape.The seam part 41 is heated by the induced high frequency current, and the seam part 41 is butted and welded. The sewing tube 40 is manufactured continuously.

The electric resistance welded pipe 40 made in this way is likely to have defects at the seam 41 due to poor adjustment of the pipe-making equipment or defects in the raw material steel plate.
1 needs to be inspected.

Therefore, as one of the devices for inspecting such defects in the seam portion 41, an eddy current flaw detection device (electromagnetic induction flaw detection device) using a probe-shaped coil is conventionally known.

Eddy current flaw detection equipment using a probe-shaped coil scans the material to be inspected by moving the material to be inspected and the probe-shaped coil relative to each other, and the electromagnetic coupling state between the coil and the material to be inspected indicates whether a defect exists. Then, it will fluctuate locally, so
By detecting this variation, the presence of a defect is known.

(Problem to be solved by the invention) In an eddy current flaw detection device that uses such a probe-shaped coil, increasing the size of the coil increases the flaw detection range, but it is difficult to detect small flaws unless the sensitivity is increased. Yes, increasing sensitivity tends to pick up noise, lowering the S/N ratio and worsening detection accuracy. On the other hand, if the coil is made smaller, small flaws can be easily detected without increasing the sensitivity, but there is a problem in that the flaw detection range becomes narrower and small flaws are easily overlooked.

(Means for Solving the Problems) Therefore, the present invention was devised to solve such problems, and is based on the temperature distribution of welding residual heat in the seam portion 41 generated during welding. Then, the center position of the high temperature region is found, and noting that the center position of this high temperature region coincides with the joint portion 41, the probe-shaped coil of the eddy current flaw detection device is placed above the center position of the high temperature region. The structure is such that flaw detection can be performed while automatically following control.

(Embodiment) As shown in the schematic diagram of FIG. 1, the ERW pipe defect detection device of the present invention outputs the deviation amount between the center position of the high temperature region of the ERW pipe 40 and the reference position as an electrical signal. a servo motor 3 whose control signal is an electric signal corresponding to the deviation amount, and a follow-up mechanism having a sector gear driven by the servo motor 3 and a through hole 7. 2, a probe type attached to this tracking mechanism 2, a coil 6, a device connected to this probe type coil 6 to generate an output when detecting a defect, and a device that generates an output when detecting a defect by the output of this device. It consists of a marking device and a marking device.

[High-temperature region center position detection device] The high-temperature region center position detection device W1 includes a double-sided mirror 4 rotated by a motor 42, as shown in FIG.
3, the photoelectric conversion element converts light rays incident from an angle range θ including the seam portion 41 of the electric resistance welded tube 40 into a photoelectric conversion element! It is equipped with a sweeping device that sequentially makes the light enter the lottery starting point. It includes a start pulse generator 46 that generates a pulse output at θ1 and a center pulse generator 47 that generates a pulse output at the center point 02 of the sweep.

As shown in FIG. 3, there is an amplifier 12 that amplifies the output of the photoelectric conversion element 11, a peak value detection circuit 13 that detects the peak value of the output of the amplifier 12, and a peak value detection circuit 13 that detects the peak value of the output of the amplifier 12. A hold circuit 14 that holds the peak value output until the next peak value output occurs, a voltage divider 15 that divides the output of the hold circuit 14, and the output of the amplifier 12 and the voltage divider 15.
The high-temperature region signal generation circuit includes a comparator 16 that compares the outputs of the voltage divider 15 and generates an output when the output of the amplifier 12 is larger than the output of the voltage divider 15.

The pulse output a of the start pulse generator 46 is differentiated by the differentiating circuit 18, and the first pulse b generated at the leading edge of the pulse output a and the negative pulse generated at the trailing edge of the pulse output a are converted by the inverter circuit 17. A circuit for obtaining the inverted second pulse C and a pulse output d of the center pulse generator 47.
A differentiating circuit 18 differentiates the pulse output d to obtain a third pulse e generated at the leading edge of the pulse output d.

A clock pulse generator 20 is provided, and the pulse output of this clock pulse generator 20 is sent to the comparator 1.
6 and the two inputs of the AND circuit 21, respectively. The output of this AND circuit 21 is led directly to the first counter circuit 23 and also to the second counter circuit 25 via the l/2 frequency dividing circuit 22. A second pulse C generated by the inverter circuit 17 is guided to each clear terminal.

The counting output of the second counter circuit 25 is led to the input terminal of the first latch circuit 24, and the output of the first latch circuit 24 is led to the two input terminals of the matching circuit 26 together with the counting output of the first counter circuit 23. are applied to each.

Note that the first pulse b generated by the differentiating circuit 18 is applied to the strobe terminal of the first latch circuit 24.

The output of this coincidence circuit 2B is applied to two inputs of an OR circuit 27 together with the pulse output e of the differentiating circuit 18, and the output of this OR circuit 27 is applied to the clock pulse of the T-flip-flop circuit 28. It is led to the input terminal. Note that this T-flip-flop circuit 2B
A second pulse C generated by the inverter circuit 17 is applied to the reset terminal of the inverter circuit 17 .

The output j of the T-flip-flop circuit 28 and the pulse output of the clock pulse generator 20 are led to a third counter circuit 31 via an AND circuit 30.

Note that the clear terminal of this third counter circuit 31 is
A second pulse C generated in the inverter circuit I7 is guided.

The output of the third counter circuit 31 is transmitted to the second latch circuit 3.
2, and the output of the second latch circuit 32 is applied to the digital input terminal of the D/A conversion circuit 33.

The first pulse b generated by the differentiating circuit 18 is applied to the strobe terminal of the second latch circuit 32 via the inhibiting circuit 29 . The prohibition input terminal A of this prohibition circuit 29 has
The output j of the T-flip-flop circuit 28 is led.

The third pulse e generated in the differentiating circuit 18 is applied to the set terminal, and the second pulse C generated in the inverter circuit 17 is applied to the set terminal.
is applied to the reset terminal of the R-3 flip-flop circuit 35, the output Q of this R-S flip-flop circuit 35 is applied to the data input terminal, and the output of the matching circuit 26 is applied to the clock pulse input terminal. A polarity determination circuit is provided, which includes a D-flip-flop circuit 3B to which voltage is applied, and a comparator 34 to which an output i of this D-flip-flop circuit 36 is applied. A reference voltage Es is applied to this comparator 34.

The output of this comparator 34 is then transmitted to the D/A conversion circuit 33.
is applied to the reference voltage input terminal ref of.

This comparator 34 produces a positive output when its input voltage is higher than the reference voltage Es applied to the reference voltage input terminal ref, and produces a negative output when it is lower than the reference voltage Es. The converter circuit 33 converts the digital output of the second latch circuit 32 into an analog voltage based on the output voltage of the comparator 34, and outputs it as a position signal.

Next, the operation of the center position detection device 1 in the high temperature region will be explained.

The joint portion 41 of the ERW pipe is removed by the sweeping device shown in FIG.
When swept, an output f corresponding to the temperature distribution as shown in the waveform diagram of FIG. 4 is obtained from the amplifier 12 that amplifies the output of the photoelectric conversion element 11. is detected, and the peak value is held in the hold circuit 14 until the next peak value output is obtained.

After the peak value held by the hold circuit 14 is divided by the voltage divider 15, this divided voltage and the output voltage of the amplifier 12 are compared by the comparator 18. The comparator 16 generates an output g.

In this way, the voltage obtained by dividing the peak value and the output voltage of the amplifier 12 are compared to obtain the output g from the comparator IB, so no matter what the temperature is in the high temperature region, it is lower than the surroundings. Also, the output g can always be obtained in the high temperature region.

At the start of the sweep, the two counter circuits 23 and 25 are cleared by the second pulse C generated by the inverter circuit 17, and the count value is set to zero.

During the period when the comparator 16 is generating the output g, the pulse output of the clock pulse generator 20 is generated by the AND circuit 21.
The signal is counted by the first counter circuit 23, and after being frequency-divided by the 1/2 frequency divider circuit 22, it is also counted by the second counter circuit 25.

The first pulse b generated in the differentiator circuit 18 at the start of the next sweep
This causes the first latch circuit 24 to hold the count value of the second counter circuit 25, and the subsequent second pulse C clears the two counter circuits 23 and 25.

Then, the next output g of the comparator 16 determines the clock signal.
The pulse output from the pulse generator 20 is counted by the first counter circuit 23, and when the counted value reaches approximately 1/2 of the previous value, the second pulse output held by the first latch circuit 24 is counted.
coincides with the previous count value of the counter circuit 25, and when the coincidence occurs, pulse outputs h1 to h3 are generated from the coincidence circuit 26. These pulse outputs h1 to h3 represent the center of the high temperature region, and are applied to the T-flip-flop circuit 2B via the OR circuit 27 and to the clock pulse input terminal of the D-clip flop circuit 36. is also applied.

Two pulses, the pulse output h1 or h2 from the comparator 26 and the pulse output e from the differentiating circuit 18, are applied to the T-flip-flop circuit 28 via the OR circuit 27. The output shown in FIG. 3 jl or j2 is generated from the output Q of the T-flip-flop circuit 28 for one pulse period and is applied to the AND circuit 30.

The pulse width of the pulse jl or j2 generated from this T-flip-flop circuit 28 is the same as that between the center point of the sweep (corresponding to pulse e) and the center point of the high temperature region (pulse hl or h
2) shows the deviation value.

Only during the period when the T-flip prop circuit 28 is generating the pulse output j1 or j2, the pulse output from the clock pulse generator 20 is applied to the third counter circuit 31 via the AND circuit 30 and counted. Ru.

In this way, the count value corresponding to the deviation value counted by the third counter circuit 31 is transferred to the second latch circuit 32 by the first pulse b led from the differentiating circuit 18 via the inhibition circuit 28. The third counter circuit 31 is cleared by the subsequent second pulse C.

If the deviation value is zero and the pulse output h3 from the comparator 26 and the pulse output e from the differentiating circuit 18 occur simultaneously, the pulse output h3 from the T-flip-flop circuit 28 will rise. , the second pulse C produces an output j3 that falls, and the count value of the third counter circuit i 31 becomes abnormally large.

In this case, the output j3 of the T-flip-flop circuit 28 activates the +h circuit 28, and the differential circuit 18
The second latch circuit 32 is stopped from passing, and the count value of the third counter circuit 31 is not taken into the second latch circuit 32.

Therefore, the second latch circuit 32 continues to hold the previous count value as it is.

Since the pulse output e generated from the differentiating circuit 19 is applied to the set terminal of the R-S flip-flop circuit 35, the R-3 flip-flop circuit 35 is set by this pulse e, and the R-3 flip-flop circuit 35 is set by the second pulse C. It is reset to produce an output 511i from its output Q, and this output i is applied to the data input terminal of the D-flip-flop circuit 38.

Pulse outputs h1 to h3 from the comparator 26 are applied to the clock pulse input terminal of the D-flip-flop circuit 3B, and the generation timing of this pulse output h2 is longer than the pulse output e of the differentiator 19. In the above, when the output of the R-S flip-flop circuit 35 is between "0", the output Q of the D-flip 1 flop circuit 36 is "O", and the pulse output h from the comparator 2B is generated. When the timing is later than the pulse output e and the output Q of the R-S flip-flop circuit 35 is between "1", the output of the D-2 flip-flop circuit 38 is "1".

Therefore, depending on whether the center of the high temperature region is before or after the center of the sweep, the output of the D-flip-flop circuit 36 will be "
O" or "l 11, so this output is sent to comparator 3.
4, it is compared with the reference voltage Es.

The value of this reference voltage Es is selected to be an intermediate voltage between the output voltages of the D-flip-flop circuit 38 in the two states of "0" and "1", so that the operational amplifier operating as the comparator 34 A saturated positive or negative voltage from the output,
In other words, it generates constant voltages with different polarities.

In the D/A conversion circuit 33, when the output voltage of the comparator 34 is used as a reference voltage ref and the digital value held in the second latch circuit 32 is converted into an analog voltage, the absolute value of the deviation is a voltage, and the deviation An analog output whose direction is represented by polarity can be obtained at the terminal 37.

[Following Mechanism] A servo amplifier 5 to which the analog output generated at the terminal 37 of the circuit shown in FIG. 3, and the servo motor 3 moves the follow-up mechanism 2 and controls the reference position of the follow-up mechanism 2 to be aligned with the center of the high temperature region.

[Eddy current flaw detection device] 1st v! As shown in J, the following mechanism 2 is equipped with a probe-shaped coil 6 provided at a reference position, and the joint part 41 is detected for flaws by moving the probe-shaped coil relatively to the joint part 41 of the ERW tube. The presence of a defect is known by scanning and detecting local variations due to the defect in the electromagnetic coupling state between the probe-shaped coil 6 and the joint portion 41.

Then, when a defect is detected, an output is generated and the marking device is activated to place a mark in the vicinity of the portion where the defect exists.

(Other Embodiments) In the embodiments described above, the high temperature region center position detection device 1 is fixed and the probe-shaped coil 6 is attached to the follow-up mechanism 2, but the reference axis of the follow-up mechanism 2 ( The center position detecting device 1 of the high temperature region and the probe-shaped coil 6 are installed on the center line of the field of view of the center position detecting device 1, so that the center of the field of view of the center position detecting device 1 is aligned with the center of the high temperature region. The same operation can be performed by using follow-up control.

(Effects) As explained above, according to the defect detection device of the ERW pipe of the present invention, based on the fact that the center of the high temperature region corresponds to the seam of the ERW pipe, the probe is placed at the center of the high temperature region. Since eddy current flaw detection is performed while tracking control is performed to match the shaped coils, even flaws that tend to occur at seams can be detected with high precision and a good S/N ratio using the small probe shaped coil.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a defect detection device for electric resistance welded pipes according to the present invention, Fig. 2 is a perspective view showing a sweep device used in the device shown in Fig. A block diagram of a circuit that processes a signal to obtain an electrical signal corresponding to the center of a high temperature region, Figure 4 is a timing chart used to explain the operation, and Figure 5 is a diagram showing conventional ERW pipe manufacturing. It is a perspective view showing a process. l... High temperature region center position detection device 2... Tracking mechanism 3... Servo motor 4... Potentiometer 5... Servo amplifier 6... Probe type coil 7 of eddy current flaw detection device... Through hole 40...Erw tube 41...Joint part

Claims (1)

[Scope of Claims] Conversion means for sweeping the joint portion of the ERW pipe in a direction perpendicular to the ERW pipe and converting the temperature distribution into an electrical signal, and processing the output of the conversion means to convert the temperature distribution into a high temperature region. means for outputting an electrical signal corresponding to the center position of the high temperature region; a servo system controlled based on the amount of deviation between the electrical signal corresponding to the center position of the high temperature region and a reference position; and a flaw detection device operated by the servo system. 1. A defect detection device for an electric resistance welded pipe, comprising: a probe of the flaw detection device; and controlling the position of the probe of the flaw detection device to follow the center position of the high temperature region.