JP4736716B2 - Hot wall thickness measurement method for steel pipes - Google Patents

Description

  The present invention relates to a method for measuring the hot thickness of a steel pipe, and in particular, is an effective technique for measuring the thickness of a steel pipe in which a mandrel bar is still inserted in a seamless steel pipe production line. .

  The demand for automatic measurement of the outer diameter and wall thickness of steel pipes has been increasing in recent years in terms of quality control and speeding up of the inspection process.

  By the way, the method of measuring the thickness of a steel pipe has been conventionally measured directly by an operator using a measuring instrument such as a caliper or a micrometer, or manually or automatically by an ultrasonic thickness meter. . However, the method using a caliper or the like has a problem that only the both ends of the steel pipe can be measured. In addition, the ultrasonic thickness gauge can measure the entire length of the steel pipe, but the probe must be brought into contact with the surface of the steel pipe via a contact medium for the incidence of the ultrasonic wave on the pipe. Although it was possible to perform a cold measurement at, it was difficult to perform a hot measurement such as in a rolling process.

  For this reason, a technology has been developed that uses X-ray and γ-ray radiation and a TV camera to automatically measure the wall thickness over the entire length of the steel pipe, regardless of whether it is hot or cold, continuously and without contact ( For example, see Patent Document 1). In other words, when the radiation irradiated to the steel pipe is transmitted through the inner surface of the steel pipe, the attenuation is maximized, and the characteristic that is minimized when it is in contact with the outer surface is used to detect the maximum and minimum attenuation. The distance between the radiation source, the steel pipe to be measured, the moving distance of the detector, the time, or the image on the cathode ray tube is measured.

  Certainly, according to this technique, it is possible to automatically measure the wall thickness over the entire length of the steel pipe in a non-contact and continuous manner regardless of whether it is hot or cold. However, since radiation is transparent, it can be applied to measurements with a mandrel bar inserted into the steel pipe during rolling, as in the manufacturing process (also called a line) of Mannesmann mandrel mill type seamless steel pipe. difficult. That is, it is difficult to determine the boundary of the inner surface of the steel pipe by inserting the mandrel bar. Therefore, there is a problem that measurement on the entry side and the exit side of the mandrel mill cannot be performed.

  As such a non-contact measurement technique, there is a technique using a laser instead of the radiation. In other words, this is a technique for measuring the wall thickness by signal-processing multiple reflected echoes of ultrasonic waves generated in the steel pipe by laser irradiation to the steel pipe. For example, as recently published in the applicant's application, when measuring the thickness of a steel pipe hot using a laser ultrasonic thickness gauge, the temperature of the steel pipe is appropriately corrected to reduce the measurement error. Measurement technique (see Patent Document 2). According to this technique, the thickness of the steel pipe can be measured even when the mandrel bar is inserted hot.

  By the way, the principle of thickness measurement using this laser is as follows.

  First, as shown in FIGS. 3A and 3B, an ultrasonic wave generating laser 1 is applied to the outer surface 2 of a steel pipe (not shown). As a result, ultrasonic waves 3 are generated in the thickness direction as a reaction of ablation of the steel pipe outer surface 2. The ultrasonic wave 3 propagates in the thickness direction, is reflected on the inner surface, and when the reflected wave 5 reaches the outer surface 2 again, the outer surface 2 is slightly raised. The raised portion 6 of the outer surface 2 is separately irradiated with an echo detection laser 7, and a change in the waveform of the echo detection laser 7 due to the elevation of the outer surface 2 is detected by the optical interference device 8. In this detection, the time difference between the laser irradiation time for ultrasonic wave generation (ultrasonic wave generation time) and the rise detection time (echo detection time) of the outer surface due to the reflected wave from the inner surface becomes the ultrasonic wave advance time. The ultrasonic wave propagation speed is a physical property value determined by the steel type (composition) and temperature of the steel pipe. Therefore, this speed, the ultrasonic wave traveling time, and the geometric correction term (in the steel pipe wall thickness shown in FIG. 3B). The thickness of the steel pipe can be calculated by the following equation. In addition, since an ultrasonic wave generate | occur | produces at every angle (360 degrees) of a thickness direction, as shown in FIG.2 and FIG.3 (b), an echo is between the outer surface 2 and the inner surface 4 of a steel pipe. One reciprocating echo 9 (also referred to as a first echo) detected at the time of one reciprocation, second reciprocating second echo 10, three reciprocating third echo 11.

WT = (1 / 2n) × TOFn × V × f (n)
Here, WT: the thickness of the steel pipe, TOFn: the traveling time of the nth echo, V: the ultrasonic wave propagation velocity in the steel pipe, f (n): the geometric correction term of the nth echo However, the TOFn of the above equation is determined. It is difficult to accurately grasp the ultrasonic generation time and the echo detection time. This is because the detected waveform is complicated and the influence on the measurement value due to the degree of the steel pipe bulging is unavoidable. Therefore, in practice, TOFn = TOFm + δT
As described above, it is usual to provide an offset (correction) term δT for the measured value TOFm and tune it against the actual thickness (measured with calipers or the like). In this case, not only does the labor of the measurement take time, but there is a problem that the measurement cannot be performed with high accuracy and speed, and the measurement is often performed without providing an offset term.

In addition, when actually measuring the thickness of a steel pipe online, while measuring the steel pipe at a constant speed, measurements are made at about 400 points along the length of each pipe. The attenuation of ultrasonic waves in the steel pipe However, it is not always possible to obtain many after the second echo.
JP 54-114263 A JP 2005-134321 A

  In view of such circumstances, the present invention uses the three reciprocal echoes and four reciprocal echoes obtained at several locations among the reflected echoes of ultrasonic waves generated by laser irradiation, and the thickness of the steel pipe for measuring the thickness with high accuracy. The purpose is to provide a measurement method.

  The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.

That is, the present invention irradiates a laser on the outer surface of a steel pipe that travels on-line with heat, and generates a large number of echoes in which the generated ultrasonic waves are reflected and reciprocated within the thickness between the inner surface and the outer surface of the steel pipe In order to calculate the thickness from the values and the propagation speed of the ultrasonic wave, first of the detected echoes, 3 is detected. extract the reciprocating echo and 4 reciprocating echoes following each in each of the advance time (1), the offset value δT3 satisfying the following expression (2), set the .DELTA.t4, offset value of 3 round-trip echo traveling time δT3 And the offset value δT4 of the traveling time of the four reciprocating echoes are equal, and the following equations (4) and (5) are used simultaneously to obtain the wall thickness value WT from the equations (4) and (5). , then, the wall thickness value WT 1 are substituted into the following equation to give thickness from the measured value TOFm1 round-trip echo time to progression (6), determined by calculating back an offset value δTl of one round-trip echo time to progression, one round-trip echo traveling time which defines This is a hot wall thickness measurement method for a steel pipe, characterized in that the wall thickness WT of all measurement points is calculated from the following equation (6) using the offset value δT1 .
Record
TOF _actual 3 = TOF _measured 30 + δT3 (1)
TOF _actual 4 = TOF _measured 4 + δT4 (2)
WT = (1/6) × (TOFm3 + δT3) × V × f (3) (4)
WT = (1/8) × (TOFm4 + δT4) × V × f (4) (5)
WT = (1/2) × (TOFm1 + δT1) × V × f (1) (6)
Where TOF _actual 3 is the true third echo travel time
TOF _measured 3 is the measured travel time of the third echo
TOF _actual 4 is the true fourth echo time
TOF _measured 4 is the measured time of the 4th echo
V is the ultrasonic propagation velocity in the steel pipe,
TOFm3 is a measurement of the travel time of 3 reciprocating echoes.
f (3) is the geometric correction term of the third echo
TOFm4 is a measurement of the travel time of 4 reciprocating echoes.
f (4) is the geometric correction term of the fourth echo
TOFm1 is a measurement of the travel time of one round-trip echo
f (1) is the geometric correction term of the first echo

  In this case, if there are a plurality of the three reciprocating echoes and the four reciprocating echoes, it is preferable that the offset value of the traveling time is an average value thereof. Moreover, it is preferable that the temperature of the said steel pipe is 1200 degrees C or less, or the said steel pipe exists in the state which inserted the plug or the mandrel bar. Furthermore, it is more preferable if the thickness of the steel pipe is 3 to 35 mm.

  According to the present invention, even when traveling online at a temperature of 1200 ° C. or less, a steel pipe is irradiated with laser, and 3 reciprocal echoes and 4 reciprocal echoes are extracted from a large number of reflected echoes of the generated ultrasonic waves. It becomes possible to measure the wall thickness of the steel pipe with high accuracy.

  Hereinafter, the best embodiment of the present invention will be described based on the background of the invention.

  First, the inventor reviewed the conventional method for measuring the thickness of a steel pipe using a laser, and when actually measuring the thickness of a steel pipe on-line, the attenuation of ultrasonic waves in the steel pipe was significant, and always after 2 reciprocal echoes (3 reciprocal echoes). It was confirmed that a large number of 4 reciprocal echoes,. However, since the measurement is performed at a large number of about 400 points along the length direction while running the steel pipe at a constant speed, there is absolutely no more than two reciprocal echoes (hereinafter referred to as second echoes). It has also been found that the data can be obtained at several measurement positions in the case of the third echo and the fourth echo with few cases.

  By the way, it is considered that the offset value δT related to the echo waveform and its detection time depends on the angle (θ) at which the ultrasonic waves are reflected (see FIG. 3B). That is, the offset values of the first echo and the second echo having a large difference in reflection angle are greatly different, but the difference between the angles becomes smaller as the third echo, the fourth echo, and the rear echo become smaller. Is expected to converge to a constant value and become almost the same value.

  Therefore, the inventor considers that the problem of the offset value as described above can be solved by utilizing the fact that the offset values of the third echo and the fourth echo are substantially equal, and as described below, The present invention was completed by improving the measurement method.

  As shown in FIGS. 3 (a) and 3 (b), the conventional measuring method includes an outer surface 2 of a steel pipe (not shown) that travels online at a constant speed (for example, 60 to 360 m / min). In addition, a number of echoes (measurement position is a steel pipe) which is irradiated with an ultrasonic wave generating laser 1 and ultrasonic waves 3 generated by plasma pressure are reflected and reciprocated within the wall thickness between the inner surface 4 and the outer surface 2 of the steel pipe. In this case, several hundred spots are detected by the optical interference device 8 by separately irradiating the laser 7 for detection. The detection result is obtained as an electric signal as shown in FIG. Therefore, the propagation time and reflection angle of the echoes traveling within the wall thickness are determined, and the wall thickness can be calculated from the values and the ultrasonic wave propagation velocity using the following formula. .

WT = (1 / 2n) × TOFn × V × f (n)
Here, WT: the thickness of the steel pipe, TOFn: the traveling time of the nth echo, V: the ultrasonic wave propagation velocity in the steel pipe, f (n): the geometric correction term of the nth echo First, in the present invention, Then, 3 reciprocal echoes and 4 reciprocal echoes are extracted from the detected echoes, and an offset value is set for each of the travel times.

That is, TOF _actual 3 = TOF _measured 3 + δT3 (1)
TOF _actual 4 = TOF _measured 4 + δT4 (2)
Here, TOF _actual 3: true (actual) third echo travel time TOF _measured 3: measured third echo travel time δT3: set third echo offset value TOF _actual 4: true (actual) ) Fourth echo travel time TOF _measured 4: Measured fourth echo travel time δT4: Set offset value of the fourth echo If a plurality of the three reciprocation and four reciprocation echoes can be extracted, the offset values are used. It is preferable to set it as the average value. This is because it is closer to the true value.

  Then, it is determined that those offset values are the same for 3 reciprocating echoes and 4 reciprocating echoes.

δT3 = δT4 (3)
Therefore, since the equations for calculating the thickness for the third echo and the fourth echo are the following (4) and (5), respectively, if (4) and (5) are combined under the condition (3), The wall thickness value WT is obtained.

WT = (1/6) × (TOFm3 + δT3) × V × f (3) (4)
WT = (1/8) × (TOFm4 + δT4) × V × f (4) (5)
Here, numerals 3 and 4 indicate the values of the third and fourth echoes, respectively, and m indicates a measured value.

  Next, when the thickness value WT obtained as described above is substituted into the following equation (6) that gives the thickness of one reciprocating echo, the offset value of one reciprocating echo is determined by back calculation.

WT = (1/2) × (TOFm1 + δT1) × V × f (1) (6)
The number 1 indicates the value of the first echo, and m indicates the measured value.

  Therefore, if the offset value δT1 of this one-way echo is used, it is possible to calculate the thickness of all other measurement points.

  The steel pipe to be measured according to the present invention may be any of a seamless steel pipe, an ERW steel pipe, a pressure welded steel pipe, etc., and is particularly effective when a plug, a mandrel bar or the like is inserted and rolled. . This is because the reflection of the ultrasonic wave between the inner surface and the outer surface of the steel tube by the laser is utilized, so that the problem of unclear boundaries as in the case of radiation does not occur. Further, the thickness range to be measured is desirably 3 to 35 mm. If it is less than 3 mm, it is too thin and difficult to measure, and if it exceeds 35 mm, the attenuation of the ultrasonic wave is remarkable, which is inconvenient. Furthermore, it is preferable that the temperature of the steel pipe at the time of measurement is 1200 degrees C or less. This is because if it exceeds 1200 ° C., it is too high and the attenuation of ultrasonic waves is remarkable. The reason why the lower limit was not set is that measurement is possible even at room temperature.

  A small diameter seamless steel pipe (rolling target value: outer diameter 172 mm, wall thickness 5 mm, length 12600 mm) is drawn and rolled with a mandrel mill on the outlet side, before the mandrel bar is pulled out. The thickness was measured. The steel pipe temperature at the time of measurement was 1050 ° C. At that time, the measurement was performed in two ways: when the offset value according to the present invention was provided, and by the conventional method where no offset value was provided. Moreover, in order to confirm the reliability of this invention, about the steel pipe measured by this invention, the operator also performed the direct measurement using a measurement jig (gauge). In addition, the measurement with a gauge was performed by cutting the steel pipe extracted out of the line into a ring.

  The results are collectively shown in FIG. From FIG. 1, it is clear that the measured value according to the present invention almost coincides with the measured value by the gauge over the entire longitudinal direction of the steel pipe, and the accurate thickness measurement was performed. That is, compared with the conventional measuring method which does not provide an offset value, according to this invention, the measurement precision of steel pipe wall thickness is improved significantly.

It is a figure which shows the example of a wall thickness measurement in the mandrel mill exit side of a small diameter seamless steel pipe. It is a figure which shows the time change of the electrical signal of the reflective echo of the ultrasonic wave generate | occur | produced with the laser. It is a schematic diagram explaining the measurement principle of the steel pipe wall thickness by laser irradiation, (a) is a situation where a reflective echo advances within a steel pipe, (a) is generation | occurrence | production of an ultrasonic wave, and detection of a reflective echo.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser for ultrasonic generation 2 Outer surface 3 Ultrasonic wave 4 Inner surface 5 Reflected wave 6 Raised part 7 Laser for echo detection 8 Optical interference device 9 First echo 10 Second echo 11 Third echo

Claims (5)

A laser beam is applied to the outer surface of the steel pipe that runs online in the heat, and the generated ultrasonic waves detect and reciprocate a large number of echoes that are reflected and reciprocated within the wall thickness between the inner surface and the outer surface of the steel pipe. In determining the propagation time and reflection angle of echoes traveling within the thickness, and calculating the wall thickness from those values and the propagation speed of the ultrasonic wave,
First, 3 reciprocal echoes and 4 reciprocal echoes are extracted from the detected echoes, and offset values δT3 and δT4 satisfying the following equations (1) and (2) are set for the respective traveling times. By determining that the offset value δT3 of the traveling time of the three reciprocating echoes is equal to the offset value δT4 of the traveling time of the four reciprocating echoes, the following equations (4) and (5) are combined, The wall thickness value WT is obtained from the equation (5) , and then this wall thickness value WT is substituted into the following equation (6) that gives the wall thickness from the measured value TOFm1 of the traveling time of one round-trip echo. It is characterized in that the offset value δTl of the traveling time is calculated by back calculation, and the thickness WT of all the measurement points is calculated from the following equation (6) using the determined traveling time offset value δT1 of one reciprocating echo. Hot thickness of steel pipe Measuring method.
Record
TOF _actual 3 = TOF _measured 30 + δT3 (1)
TOF _actual 4 = TOF _measured 4 + δT4 (2)
WT = (1/6) × (TOFm3 + δT3) × V × f (3) (4)
WT = (1/8) × (TOFm4 + δT4) × V × f (4) (5)
WT = (1/2) × (TOFm1 + δT1) × V × f (1) (6)
Where TOF _actual 3 is the true third echo travel time
TOF _measured 3 is the measured travel time of the third echo
TOF _actual 4 is the true fourth echo time
TOF _measured 4 is the measured time of the 4th echo
V is the ultrasonic propagation velocity in the steel pipe,
TOFm3 is a measurement of the travel time of 3 reciprocating echoes.
f (3) is the geometric correction term of the third echo
TOFm4 is a measurement of the travel time of 4 reciprocating echoes.
f (4) is the geometric correction term of the fourth echo
TOFm1 is a measurement of the travel time of one round-trip echo
f (1) is the geometric correction term of the first echo   The method for measuring a hot thickness of a steel pipe according to claim 1, wherein if there are a plurality of the three reciprocating echoes and the four reciprocating echoes, the offset value of the traveling time is an average value thereof.   The method for measuring a hot thickness of a steel pipe according to claim 1 or 2, wherein the temperature of the steel pipe is 1200 ° C or lower.   The said steel pipe exists in the state which inserted the plug or the mandrel bar, The hot thickness measurement method of the steel pipe in any one of Claims 1-3 characterized by the above-mentioned.   The thickness of the said steel pipe is 3-35 mm, The hot thickness measurement method of the steel pipe in any one of Claims 1-3 characterized by the above-mentioned.

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