JPH0242411B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the cold thickness of a steel pipe with extremely high accuracy.

In recent years, as demand for steel pipes such as oil country tubular goods has increased, higher quality has been required. In order to meet this demand, it is desirable to measure the thickness, etc. during steel pipe manufacturing and reflect the measurement results on the manufacturing line. A method using electromagnetic ultrasound is known as a method for measuring the thickness of steel pipes during manufacture. In this method, a DC magnetic field is applied to the steel pipe, and a high-frequency current is instantaneously applied to a coil facing the surface of the pipe to generate eddy currents on the surface, causing distortion due to the Lorentz force with the DC magnetic field. The ultrasonic waves thus generated are propagated toward the inner surface of the steel pipe, and the time T from the time the ultrasonic waves are generated to the time an echo is detected from the inner surface is measured, and this T value is substituted into the following equation (1). This is a method for measuring the thickness D.

D=T・V/2...(1) However, V: Sound velocity inside a steel pipe However, when using this method to measure the thickness of hot material, such as during the steel pipe manufacturing process, the following There was a problem. In other words, the sound velocity V varies depending on the measuring section due to temperature unevenness of the material to be measured, and this sound velocity V
When a fixed value is used as the value of , the measurement error is large. Furthermore, it is necessary to measure with a hot tube in order to reflect it on the manufacturing line, but the quality control dimensions of the finished product are for when it is cold, and for the same reason, sufficient temperature correction cannot be performed and it is not effective control information. I wasn't getting it.

The present invention has been made in view of the above circumstances, and its purpose is to measure the thickness of the material to be measured in the heat tube using electromagnetic ultrasonic waves at the exit side of the stretching reducer mill, and at the same time measure the surface temperature of the steel tube. To accurately measure the thickness of the steel pipe when it is hot and when it is cold at the exit side of the stretch reducer mill by measuring the sound velocity that depends on the temperature of the steel pipe and correcting the thickness due to contraction. It is an object of the present invention to provide a thickness measuring method that makes it possible to eliminate steps such as dimension measurement and material arrangement/distribution in a subsequent finishing line.

The thickness measuring method according to the present invention is a method of measuring the thickness of a steel pipe at the exit side of a stretching reduction mill that performs diameter reduction rolling of the steel pipe, wherein the steel pipe temperature at the exit side of the stretching reduction mill is 720°C. ~880
℃, an eddy current is generated by electromagnetic induction in the steel pipe to which a DC magnetic field is applied, and longitudinal ultrasonic vibration is generated by the Lorentz force with the DC magnetic field, and this vibration or its reflected wave is applied to the surface of the steel pipe. The propagation time of the ultrasonic vibration is determined by detecting the ultrasonic vibration with a coil placed in front of it, while the surface temperature of the steel pipe is measured, and the ultrasonic wave in the steel pipe is determined by the measured temperature S corresponding to the position of the steel pipe where the propagation time is determined. The propagation speed of vibration Vs is determined as Vs = b-a・S, where a and b are constants. Using Vs, the amount of thermal expansion of the steel pipe, and the propagation time, calculate the thickness of the steel pipe when it is cold. It is characterized by seeking.

Next, the present invention will be specifically explained based on the drawings.
FIG. 1 is a schematic diagram showing an implementation state of the present invention, and FIG. 2 is a schematic sectional view taken along the - line in FIG. 1.
In the figure, 1 indicates an electromagnetic ultrasonic generator. The electromagnetic ultrasonic generator 1 magnetizes a steel pipe P with a surface temperature of 720 to 880°C with direct current and propagates the ultrasonic wave inside the steel pipe P according to the above-mentioned principle. It has a cylindrical shape as a whole, and the steel pipe P is inserted into the inside and moved in the axial direction.

A radiation thermometer 10 is disposed in the generating section 1 so as to be as close as possible to a thickness measuring section, that is, coils 51 and 52, which will be described later.

The electromagnetic ultrasonic wave generator 1 has the following configuration. That is, the iron cores 2a and 2b are 2 in the axial direction.
It is divided into cylindrical parts, each having a U-shaped cross section with a notch in the center (the drawing shows a cross section of one side of the axis line, so it appears as an L-shape), and the iron core 2
Cylindrical iron cores 2'a and 2'b each having a tapered tip are inserted into the notches a and 2b, respectively. Excitation coils 3a, 3b are fixed inside the respective iron cores 2a, 2'a, 2b, 2'b. A coil storage block 4 is interposed at the tapered tip of the iron cores 2'a, 2'b. This block 4 is a cylindrical object made of a non-magnetic material, and a transmitting coil 51 and a receiving coil 52 are arranged concentrically at six equally spaced positions on the inner circumferential side, that is, facing the outer circumference of the steel pipe P. The coils 51 and 52 are assembled and arranged so that the axial direction thereof is the radial direction of the steel pipe P, and the coils 51 and 52 are covered with a non-conductive cover 6 without being exposed to the inner peripheral side of the block 4. Cooling water is passed through the iron cores 2'a, 2'b and block 4, which are close to the hot steel pipe P, through water conduit pipes 7 and 8, respectively, for cooling. Coils 51 and 52 are installed along the water conduit 7 formed in the
The cable to is inserted. The excitation coil 3 of the electromagnetic ultrasonic generator 1 configured in this way
A DC power supply (not shown) is connected to a and 3b, and a pulse current generating circuit 11 and an amplifier 13 are connected to the coils 51 and 52, respectively.

When a DC current is passed through the excitation coils 3a and 3b, a DC magnetic field is applied to the surface of the steel pipe P facing the iron cores 2'a and 2'b, that is, the block 4, in the axial direction of the steel pipe. On the other hand, the pulse current generation circuit 11 emits a pulse current based on a trigger signal from the synchronous pulse generation circuit 12, and by passing this through the transmitting coil 51, the magnetic flux in the radial direction of the steel pipe P changes, and due to this magnetic flux change. Accordingly, an eddy current is generated on the surface of the steel pipe P. The Lorentz force caused by this eddy current and the magnetic field generates a strain (Fleming's left-hand rule) that changes in a direction perpendicular to the surface of the steel pipe P, and the strain propagates in a direction perpendicular to the surface of the steel pipe P. That is, longitudinal ultrasonic waves are generated from the surface of the steel pipe P. This ultrasonic wave is a steel pipe P
The reflected ultrasonic wave propagates through the inside and is reflected by its inner circumferential surface, and this reflected ultrasonic wave reaches the outer surface and generates an eddy current by the process opposite to the above (Fleming's right-hand rule), which is generated by the eddy current in the receiving coil 52. Detected as induced voltage. The detected signal is sent to amplifier 13.

The amplifier 13 amplifies the input signal, and the amplified signal is subjected to envelope detection by the synchronous detector 14 and sent to the gate circuit 16. At this time, the peak value of the output of the amplifier 13 is adjusted by the sensitivity correction circuit 15 so that it becomes approximately a predetermined value.

The gate circuit 16 includes a synchronous pulse generation circuit 1
2, the gate circuit 16 sends a pulse current to the transmitting coil 5.
The time counting circuit 1 generates a signal that should be counted from the time when the circuit 1 is energized to the time when the first echo is detected.
I am sending it to 7.

A clock pulse of a constant frequency is supplied to the time counting circuit 17 from a clock pulse generation circuit 18, and the clock pulse is applied to the time counting circuit 17 from the period when the signal from the gate circuit 16 is supplied, that is, from the time when the ultrasonic wave is generated on the surface of the steel pipe P. The number of clock pulses until the echo from the inner surface is detected is determined and this value is provided to the arithmetic circuit 19.

The radiation thermometer 10 detects the surface temperature of the steel pipe P, and a detection signal is given to the arithmetic circuit 19 via the A/D converter 20.

Figure 3 shows the experimental results showing the relationship between the surface temperature of the steel pipe P and the longitudinal sound velocity, which was measured using electromagnetic ultrasound and a radiation thermometer, similar to the method of the present invention, and the measurement results have good reproducibility. It has been obtained. Although it changes irregularly near the transformation point, it shows good linearity in other temperature ranges, especially in the temperature range of 720°C to 880°C for hot-worked steel pipes.

The calculation circuit 19 is set with the following equation (2) that indicates the relationship between the steel pipe surface temperature and the sound speed in this temperature range, Vs = b - a · S ... (2) where, S: steel pipe surface temperature Vs: Sound velocity a and b in the steel pipe at the steel pipe surface temperature S: Constant The sound velocity Vs in the steel pipe at the steel pipe surface temperature S is calculated using the input S from the A/D converter 20, and then according to the following (3). Calculate the thickness Ds using the sound speed Vs.

Ds=T·Vs/2 (3) Note that the difference between the position where T is measured and the position where S is measured is corrected by the arithmetic circuit 19.

Further, the arithmetic circuit 19 is set with a thermal expansion coefficient αs in the temperature range, and calculates the thickness D's at the cold room temperature S ₀ according to the following equation (4).

D′s=Ds−Ds・∫ ^S _S0 α(S)dS (4) This D′s is displayed on the display 21.

Note that the arithmetic circuit 19 may be provided in common to the six sets of coils around the steel pipe P, and information may be taken in sequentially for each set of coils. Six indicators 21 may be provided to display the measured values of each coil separately, or only one may be provided to selectively display the values. Also, display 2
1 or in place of the display 21, a recorder may be provided. Furthermore, the arithmetic circuit 19 may be a calculator such as a minicomputer, and the results may be stored in a floppy disk or the like. Of course, calculations can be performed both online and offline.

In the above description, the coils are used separately for transmission and reception, but only one coil may be provided for both transmission and reception. Further, as a device for DC magnetizing the steel pipe P, not only the electromagnet as described above but also a permanent magnet may be used. Furthermore, although the case where the thickness of the steel pipe P is measured is shown, measurements can also be made on other materials other than pipes. Further, although the case where a reflection method is used is shown, the method is not limited to this, and it goes without saying that a transmission method may also be used in which the coils are opposed to each other with the material to be measured interposed therebetween.

Next, examples of the present invention will be described. The electromagnetic ultrasonic wave generator 1 was placed upstream of the second roll from the outlet side of the stretching reduction mill, and the thickness of the steel pipe being processed in the mill was measured. The steel type of the pipe to be measured is
S50C carbon steel, outer diameter 42.7mmφ, 60.3mm
Three types: φ, 114.3mmφ, thickness 3.2~25mmt, length
Measurements were taken every 4 milliseconds (corresponding to a length of about 20 mm pitch) over the entire length of 400 pieces measuring 14 to 90 m. Note that the a value in the above equation (2) is 90 m/sec per 100°C temperature, and b
A value of 5600 m/sec was used.

Figure 4 is a graph showing the thickness D's (solid line) determined by the present invention, with the horizontal axis representing the length m from the tip of the steel pipe and the vertical axis representing the measured thickness mm. Also shown is the thickness D (dashed line) when no temperature-related correction is performed. From this figure, the thickness D'a obtained by the present invention is smaller than the thickness D without temperature correction, and since the amount of correction due to heat shrinkage is small in the low temperature part near the end of rolling, the thickness D′a obtained by the present invention is slightly corrected. It can be seen that the difference between 's~D is becoming smaller.

In FIG. 5, the horizontal axis shows the measured value D′s− by the method of the present invention.
Take the cold measurement value and plot the measured frequency on the vertical axis,
This is a graph showing the frequency distribution of the difference between the thickness D's determined by the present invention and the thickness actually measured in cold conditions.For comparison, FIG. The horizontal axis shows the measured value D without correction - the actual measured value in the cold, and the vertical axis shows the measured frequency. From these two figures, it can be seen that in the case of the present invention, the distribution approaches the actual measured value in the cold, and measurement can be performed with an accuracy of ±0.1 mm, thereby improving measurement accuracy.

Since the present invention employs the above-described method, it is possible to accurately measure the cold thickness of a steel pipe while hot at the exit side of a stretch reduction mill.

In particular, in the present invention, it is possible to determine the propagation velocity of ultrasonic vibration in the steel pipe at the exit side of the stretch reduction mill by simply measuring the surface temperature and using a linear equation that is easy to calculate. This can be done easily and quickly.

Therefore, it is possible to reflect the measurement results on the production line, and of course improve the dimensional accuracy of the product.
This has excellent effects, such as the ability to omit the steps of measuring dimensions, assembling and distributing materials, etc. on the finishing line later.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the implementation state of the present invention, Figure 2 is a schematic diagram showing the implementation state of the present invention.
The figure is a schematic sectional view taken along the - line in Figure 1.
The figure is a graph showing the relationship between steel pipe surface temperature and sound speed.
FIG. 4 is a graph showing measurement results according to the present invention.
Figure 5 is a graph showing the measurement error of the present invention, Figure 6 is a graph showing the measurement error of the present invention.
The figure is a graph showing measurement errors when no temperature correction is performed. P... Steel pipe, 3a, 3b... Excitation coil, 10
... Radiation thermometer, 19 ... Arithmetic circuit, 51 ... Transmission coil, 52 ... Receiving coil.

Claims (1)

[Claims] 1. A method for measuring the thickness of a steel pipe at the exit side of a stretching reduction mill that performs diameter reduction rolling of the steel pipe, wherein the steel pipe temperature at the exit side of the stretching reduction mill is 720°C to 880°C. ℃, an eddy current is generated by electromagnetic induction in the steel pipe to which a DC magnetic field is applied, and longitudinal ultrasonic vibration is generated by the Lorentz force with the DC magnetic field, and this vibration or its reflected wave is applied to the surface of the steel pipe. The propagation time of the ultrasonic vibration is determined by detecting the ultrasonic vibration with a coil placed in front of it, while the surface temperature of the steel pipe is measured, and the ultrasonic wave in the steel pipe is determined by the measured temperature S corresponding to the position of the steel pipe where the propagation time is determined. The propagation speed of vibration Vs is determined as Vs = b-a・S, where a and b are constants. Using Vs, the amount of thermal expansion of the steel pipe, and the propagation time, calculate the thickness of the steel pipe when it is cold. A thickness measurement method characterized by determining .