JP3389599B2 - Ultrasonic flaw detection method for steel pipe and ultrasonic flaw detection apparatus for steel pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for ultrasonically detecting a welded portion of a longitudinal joint welded steel pipe having acoustic anisotropy, and an ultrasonic flaw detector used for the method.

[0002]

2. Description of the Related Art There is a method disclosed in JIS Z 3060 as a conventional technique for manually detecting a welded portion of a welded steel pipe having acoustic anisotropy. In JIS Z 3060, when the two transverse wave sound velocity ratios with different polarization planes propagating in the thickness direction exceed 1.02,
Or, if the flaw detection refraction angle deviates from the nominal refraction angle by 2 ° or more when the V transmission method is performed with two probes having a nominal refraction angle of 60 °, it is said that there is acoustic anisotropy. There, it is instructed to perform flaw detection using the probe shown in Table 1 (t
Is the wall thickness of the steel pipe and D is the width of the vibrator.

[0003]

[Table 1]

It is instructed that the flaw detection refraction angle when these probes are used is calculated as follows.

First, as shown in FIG. 14, 0.5 skip,
Detects slit defects on the inner and outer surfaces with 1.0 skip and
Position Y from the defect obtained at the time to the probe_Q, Y_PTo 0.5
Skip probe distance Y_LTo Y_L= Y_Q-Y_P Ask as. Next, Y for which the wall thickness t has been previously obtained_LDivided by
15, vertical axis t / Y _L, Horizontal axis t / D (D is the oscillator
The flaw detection refraction angle θ is obtained using the value of (width).

As described above, in manual flaw detection, it takes a great deal of time to determine the flaw detection refraction angle of the acoustically anisotropic material,
Through these steps, the probe can be arranged so that ultrasonic waves can be incident on the flaw detection site for the first time.

Therefore, JIS G 0584, which specifies ultrasonic flaw detection of the welded portion of the long joint welded steel pipe during the manufacturing process, does not have a guideline for having acoustic anisotropy. At present, flaw detection is performed using the same probe as in the case where there is no acoustic anisotropy, and the flaw detection refraction angle at that time is measured off-line in advance. Further, the problem of the deviation of the flaw detection position caused by the deviation between the nominal refraction angle and the flaw detection refraction angle due to acoustic anisotropy is solved by changing the probe position to cover the flaw detection site widely. .

[0008]

However, such a method has the following problems. First,
Since flaw detection is performed using the same probe as when the object to be inspected has no acoustic anisotropy, the refraction angle changes depending on the magnitude of acoustic anisotropy, and the desired flaw detection position / refraction angle It is impossible to carry out flaw detection. That is, flaw detection cannot be performed due to the desired round-trip transmissivity / beam divergence of ultrasonic waves, and even a defect with the same size / shape / direction will change the defect echo height depending on the acoustic anisotropy. There is a problem that leads to overestimation and underestimation of. This problem will be specifically described.

For example, a certain probe is made so that the refraction angle is 60 ° when there is no acoustic anisotropy, and the refraction angle is 60 °.
At this time, it is assumed that the ultrasonic beam is designed to have a divergence angle φ within the body to be inspected. The divergence of the beam is caused by the wave diffraction phenomenon and depends on the size of the vibration source. If the size of the vibration source is D ′ and the wavelength of the ultrasonic wave is λ, the spread angle φ is expressed by the following equation.

Φ = sin ⁻¹ (λ / D ′) (1) However, in the case of oblique flaw detection, the size D ′ of the vibration source is not the width D of the vibrator but the apparent width D ′ of the vibrator. become. The apparent oscillator width D ′ and the oscillator width D are related by the reduction factor F as in the following equation (2), and the reduction factor F is
When the incident angle is i and the refraction angle is θ, it is expressed as in Expression (3).

D ′ = F · D (2) F = cosi / cosθ (3) That is, when the relationship between the incident angle and the refraction angle changes due to the presence of acoustic anisotropy, the reduction ratio F is calculated by the equation (3). As a result, the apparent transducer width D ′ also changes according to equation (2), so that the divergence angle φ of the ultrasonic beam also changes depending on equation (1).

From the above, when a probe with a nominal refraction angle of 60 ° is used at a flaw detection refraction angle other than 60 °, the divergence of the beam changes, so the reflection echo from the defect causes
There is a problem that it is different from the case of 60 ° flaw detection. in short,
When the beam divergence is diverged due to acoustic anisotropy, not only the position uncertainty becomes large, but also the defect echo becomes small and the defect is underestimated. On the other hand, if the beam becomes narrow due to acoustic anisotropy, the uncertainty of the position will be small, but the echo from the defect will be strong and the defect will be overestimated. Happens.

Further, when such a method is used, it is usual to carry out flaw detection with a probe having a different nominal refraction angle for each flaw detection on the inner surface, outer surface and central portion. If two probes are made to face each other in order to obtain V, then there is a problem that the flaw detection efficiency of the line is also reduced.

On the other hand, in flaw detection of an acoustically anisotropic material, there is a method for accurately measuring the flaw detection refraction angle and flaw detection position by obtaining the change in sound velocity in the flaw detection direction.
It is disclosed in Japanese Patent No. 261992. In the present invention, as shown in FIG. 16, one of the bevel probes 41 and 42 facing each other is moved to obtain the propagation time within the detection range of the transmission echo, and further, from the shape of the inspected object. The beam path length at the position is calculated, the sound velocity is obtained from the beam path and the propagation time, the actual refraction angle is obtained from the sound velocity using a graph as shown in FIG. 17, and the flaw detection position is obtained from this.

However, this method has the following problems. That is, at the time of measurement, since V scanning is performed using a set of probes with a constant incident angle, the emission point of ultrasonic waves in the probe cannot be known at a position other than the center of the ultrasonic beam. However, it is not possible to obtain an accurate propagation distance in the body under test. Furthermore, since the propagation distance in the wedge is not known and the propagation time is not known, it is not possible to accurately obtain the propagation time in the inspected body. Therefore, the accurate sound velocity distribution cannot be measured, and as a result, the flaw detection refraction angle and flaw detection position cannot be accurately obtained.

Further, since the V-scan method uses bottom reflection, it is impossible to measure a refraction angle region where bottom reflection does not occur due to the curvature of the steel pipe. Therefore, when a flaw is detected by the direct method that does not use the reflection on the bottom surface, the incident angle cannot be determined because the sound velocity in the propagation direction is unknown.

The present invention has been made in view of the above circumstances, and when ultrasonically inspects a welded portion of a longitudinal joint welded steel pipe having acoustic anisotropy, the inner surface /
An object of the present invention is to provide an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus used for the flaw detection, which enable flaw detection on the outer surface / central portion at a desired refraction angle or a predetermined position.

[0018]

The first means for solving the above-mentioned problems is a method of ultrasonically detecting the welded portion of a longitudinal joint welded steel pipe having acoustic anisotropy, in advance for each steel type and rolling condition. The refractive angle dependence of the sound velocity is measured, and the data is stored in a storage device, and at the time of flaw detection, the incident angle corresponding to the refraction angle used for flaw detection is automatically calculated using these refraction angle dependence data. The ultrasonic flaw detection method (claim 1) is characterized in that a probe having a calculated incident angle is selected and used.

The incident angle means the angle formed by the traveling direction of the ultrasonic wave in the probe and the normal line direction of the steel pipe at the incident point of the ultrasonic wave. The flaw detection refraction angle is an angle formed by a direction in which an ultrasonic wave immediately after entering the steel pipe travels and a normal line direction of the steel pipe at an incident point of the ultrasonic wave.

Since the acoustic anisotropy of a material to be inspected is almost uniquely determined by its crystal form or a process step during manufacturing, for example, processing and heat treatment, the dependence of the sound velocity on the refraction angle is previously determined for each material lot, that is, It is measured for each steel type and rolling condition, and it is stored in a table or a formulation. When it is necessary to perform flaw detection with a predetermined flaw detection refraction angle, the incident angle that gives the predetermined flaw detection refraction angle is immediately determined by Snell's law from the corresponding sound velocity and the sound velocity in the probe. You can ask. Then, by selecting and using a probe having the obtained incident angle, it is possible to perform ultrasonic flaw detection at a target flaw detection refraction angle.

A second means for solving the above problems is
In the method of ultrasonically detecting a welded portion of a longitudinal joint welded steel pipe having acoustic anisotropy, the refractive angle dependence of the sound velocity is measured in advance for each steel type and rolling condition, and the data is stored in a storage device. At the time of flaw detection, the incident angle of the probe to be used and the flaw detection refraction angle according to the medium sound velocity of the probe are automatically calculated using these refraction angle dependence data, and from the calculated flaw detection refraction angle, The ultrasonic flaw detection method (claim 2) is characterized in that the set position of the probe is automatically calculated.

As in the case of the first means, the dependence of the sound velocity on the refraction angle is measured in advance for each material lot, that is, for each steel type and rolling condition, and is stored as a table or formulation. Then, at the time of flaw detection, a probe having a predetermined incident angle and a medium acoustic velocity of the probe is selected and used. The probe normally selected has an incident angle corresponding to a defined nominal refraction angle. The incident angle of the probe and the sound velocity in the probe are determined, and the flaw detection refraction angle is calculated from these values and the stored refractive index dependence of the sound velocity.

In general, the dependence of the sound velocity on the refraction angle is described so as to obtain the sound velocity corresponding to the refraction angle. Therefore, in order to obtain the flaw detection refraction angle, a convergence calculation is performed, and Snell's law and the refraction of the sound velocity are calculated. The refraction angle that satisfies both of the angular dependence relations is obtained and used as the flaw detection refraction angle. When the flaw detection refraction angle is obtained, the set position of the probe necessary for irradiating the target flaw detection position with ultrasonic waves can be obtained from the size of the steel pipe.

Since the incident angle and the nominal refraction angle have a one-to-one relationship and are uniform, the method of using the nominal refractive index instead of the incident angle is also included in the scope of the present invention as a uniform method. .

A third means for solving the above-mentioned problems is as follows:
The first or second means, wherein two variable-angle probes or array-type oblique-angle probes are used, and the probes are arranged facing each other on an object to be inspected with the same incident angle. , V scan,
A method for measuring the speed of sound in a test object at a position where a maximum echo is detected by measuring the refractive angle dependence of the speed of sound by changing the incident angle a number of times (claim 3). is there.

The position where the maximum echo is detected corresponds to the center position of the ultrasonic wave. In the variable angle probe or the array type oblique angle probe, it is possible to know from which position of the probe the beam center is emitted when ultrasonic waves are generated at an arbitrary angle. Therefore, the propagation distance in the inspection object can be accurately obtained. Further, it is possible to accurately know the propagation path and the propagation time in the wedge. Therefore, by performing V-scanning using these probes and measuring the sound velocity at the position where the maximum echo is detected, the propagation path of the ultrasonic wave in the body under test,
The propagation time can be measured accurately. Thereby, the dependence of the sound velocity on the refraction angle can be accurately measured.

A fourth means for solving the above-mentioned problems is as follows.
In the first or second means, two variable-angle probes or array-type oblique-angle probes are used, and the incident angles of the probes are the same, and the flaw detection refraction angle is set on the object to be inspected. Detecting the angle of incidence at which the maximum echo is detected by changing the angle of incidence, and locating the sound velocity in the inspected object using Snell's law. The present invention is characterized in that the dependence of the sound velocity on the refraction angle is measured by changing the refraction angle and performing a large number of times.

The distance corresponding to the flaw detection refraction angle means that when an ultrasonic wave is incident on the object to be inspected at the flaw detection refraction angle, the incident point of the ultrasonic wave and the ultrasonic wave reflected on the back surface are returned to the front surface again. It is the distance from the point. The two variable angle probes or the array type probe are separated by this distance, and the incident angles of the two probes are changed while being the same, and the incident angle at which the maximum echo is detected is obtained. This incident angle is an incident angle corresponding to the flaw detection refraction angle. Since the speed of sound in the probe is known, the speed of sound in the pair to be inspected can be obtained from Snell's law from this incident angle and flaw detection refraction angle. By repeating this operation while changing the flaw detection refraction angle, the relationship between the flaw detection refraction angle and the sound velocity, that is, the dependence of the sound velocity on the refraction angle can be obtained.

The fifth means for solving the above-mentioned problems is as follows.
In the first means or the second means, a line focus type bevel probe in which a transducer is attached on the circumference of a semi-circular wedge and the emission point of the ultrasonic wave of the probe is a focal point Two of them are arranged facing each other on the object to be inspected, V scanning is performed, and the sound velocity in the object to be inspected is measured at a position where a transmitted echo can be detected, thereby measuring the dependence of the sound velocity on the refraction angle. What is characterized is (Claim 5).

In a line focus type bevel probe in which a transducer is attached on the circumference of a semi-circular wedge and the emission point of the ultrasonic wave of the probe is the focus, any portion of the transducer is inspected. The distance to the body incidence point is the same. Therefore,
By using such a probe, the position of the ultrasonic wave emitted from the probe becomes constant regardless of the direction in which the ultrasonic wave propagates in the body to be inspected. It is possible to accurately calculate the ultrasonic wave propagation path and propagation time. Other functions are the same as those of the third means.

A sixth means for solving the above-mentioned problems is as follows.
The first means or the second means, wherein the sound velocity ratio of two transverse waves propagating in the thickness direction and having different polarization planes and the refraction angle of the sound velocity of the SV wave propagating in the L direction (rolling direction). From the dependence, the dependence of the sound velocity in the C direction (direction perpendicular to the rolling direction) on the refraction angle is measured (claim 6).

Although the flaw detection refraction angle differs from the nominal refraction angle due to the acoustic anisotropy, the refraction angles in the L direction (rolling direction) and the C direction (direction orthogonal to the rolling direction) (testing refraction angle and nominal refraction angle). ), There is a certain relationship depending on the magnitude of acoustic anisotropy. Utilizing this, the refraction angle in the C direction can be estimated from the refraction angle in the L direction, and the refraction index dependence of the sound speed in the C direction can be calculated from the refraction index dependence of the sound speed in the L direction.

In the case of automating the measurement of the sound velocity distribution in the C direction of the welded steel pipe, the method of using two beveled probes and arranging them facing each other on the object to be inspected and performing V scanning is as follows. Since V scanning must follow the curvature of the steel pipe,
The device becomes a two-dimensional moving mechanism and becomes complicated. But,
With this means, it is sufficient to measure only the refractive index dependence of the sound velocity in the L direction. Therefore, since only V scanning in the longitudinal direction of the steel pipe is required, a one-dimensional movement of the measuring device is sufficient, and the mechanism is simple.

The seventh means for solving the above-mentioned problems is as follows.
Any one of the first to sixth means is characterized in that the refraction angle dependence of the sound velocity is regressed by a periodic function with a period of π / 2 or π and stored in a storage device as a functional form. (Claim 7).

In order to measure the dependence of sound velocity on the refraction angle,
It is necessary to measure the incident angle-sound velocity a finite number of times, but it is difficult to perform the measurement evenly at even refraction angle intervals. Therefore, by reducing the number of measurements and regressing the relationship between the refraction angle and the sound velocity with a periodic function of period π / 2 or π,
The relationship between the refraction angle and the speed of sound can be continuously determined even at a place other than the measured value, and the relationship between the refraction angle and the speed of sound can be determined with a small number of parameters.

A simple periodic function of the period π / 2 is V (θ) = (a + b) / 2 + (ab) cos (4θ) / 2 (4). Here, a and b are arbitrary constants ,? Is the refraction angle, and V (?) Is the speed of sound when the refraction angle is?. In addition, regression accuracy can be improved by adding a higher-order periodic function as in the following expressions (5) and (6). V (θ) = (a + b) / 2 + (ab) cos (4θ) / 2 + c ・ cos (8θ) (5) V (θ) = (a + b) / 2 + (ab) cos (4θ) / 2 + c · cos (8θ) + d · cos (16θ) (6) Here, a, b, c, and d are arbitrary constants.

Depending on how the inspection object is rolled, the period π
Component may appear, and a component with a phase shift of π / 2 may also appear, so that accurate regression may be possible by the following equation. V (θ) = (a + b) / 2 + (ab) cos (4θ) / 2 + e ・ cos (2θ)… (7) V (θ) ＝ (a + b) / 2 + (ab) cos (4θ) / 2 + e · cos (2θ) + f · sin (4θ) (8) Here, a to f are arbitrary constants. More unknowns require more measurements, but other higher order term combinations are possible.

In this way, the dependence of the speed of sound on the refraction angle is
The capacity of the storage device can be reduced by regressing with a periodic function of the period π / 2 or π and storing the function form in the storage device.

The eighth means for solving the above-mentioned problems is as follows.
Sonic velocity distribution storage means for storing the refraction angle dependence of the sound velocity for each steel type and rolling conditions of the steel pipe, flaw detection refraction angle, means for inputting the steel type and rolling conditions, and the flaw detection refraction angle that has been input, the steel type and rolling conditions, An ultrasonic flaw detector for a steel pipe, comprising: an incident angle calculating means for calculating an incident angle by using the data of the refractive angle dependence of the sound velocity stored in the sound velocity distribution storage means (claim 8). ).

In the present means, when the flaw detection refraction angle, the steel type and the rolling condition are input, the incident angle calculation means determines the refraction angle dependence of the sound velocity stored in the sound velocity distribution storage means corresponding to these input values. The incident angle is calculated using the data, and this is used to calculate the incident angle according to Snell's law. The data of the refraction angle dependence of the sound velocity stored in the sound velocity distribution storage means may be in the form of a table or a regression equation.

According to the present means, it is possible to immediately select the probe that can obtain the required flaw detection refraction angle, and therefore the time required for flaw detection can be shortened.

The ninth means for solving the above-mentioned problems is as follows.
Sound velocity distribution storage means for storing the refraction angle dependence of the sound velocity of each steel type and rolling condition of the steel pipe, and means for inputting the steel type, rolling condition, incident angle or nominal refraction angle of the probe, and sound velocity in the probe. , The means to enter the size of the steel pipe, the type of steel entered,
A refraction angle calculation for calculating a flaw detection refraction angle from the rolling condition, the incident angle or nominal refraction angle of the probe, and the medium sound velocity of the probe using the data of the refraction angle dependency of the sound velocity stored in the sound velocity distribution storage means. And an ultrasonic flaw detection device for a steel pipe, comprising: a means and a probe position calculation means for calculating the set position of the probe from the calculated flaw detection refraction angle and the input size of the steel pipe. (Claim 9)

This means is a device for performing flaw detection after selecting a probe in advance, and selects and uses a probe having a predetermined incident angle and a medium acoustic velocity of the probe. The probe normally selected has an incident angle corresponding to a fixed nominal refraction angle. In this case, since the actual flaw detection refraction angle deviates from the nominal bending angle, the probe position for irradiating ultrasonic waves to the location to be flaw-detected cannot be calculated using the nominal refraction angle.

Therefore, in the present means, when the steel type, rolling conditions, the incident angle of the probe (or the nominal refraction angle may be used), and the sound velocity in the probe are input, the refraction angle calculation means causes the sound velocity distribution storage means. The flaw detection refraction angle is calculated using the data of the dependence of the sound velocity on the refraction angle. In general, the refraction angle dependence of the sound velocity is described so as to obtain the sound velocity corresponding to the refraction angle. Therefore, in order to obtain the flaw detection refraction angle, a convergence calculation is performed.
The refraction angle that satisfies both Snell's law and the relationship of the dependence of sound velocity on the refraction angle is determined and used as the flaw detection refraction angle. Then, the probe position calculation means calculates the set position of the probe for irradiating the target flaw detection position with ultrasonic waves from the calculated flaw detection refraction angle and the input size of the steel pipe. This calculation can be easily performed due to the geometrical relationship. Then, by setting the probe at the calculated probe setting position, it is possible to perform flaw detection at the target flaw detection position. The probe position may be set automatically or manually.

[0045]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of the present invention.
It is a block diagram which shows an example. The sonic velocity distribution storage means 12 stores data indicating the relationship between the refraction angle and the sonic velocity, which is measured by a method described later, for each steel type and rolling condition of the steel pipe. The storage method may be in the form of a correspondence table of the refraction angle and the sound velocity, or may be the one in which the sound velocity is expressed as a function of the refraction angle.

Upon flaw detection, when the flaw detection refraction angle used for flaw detection, the steel type of the steel pipe, and the rolling conditions are determined, the flaw detection refraction angle, steel type, and rolling condition input means 11 are input. The input method may be set by a person or may be preset from a host computer or the like. When these values are input, the incident angle calculation means 13 causes the sound velocity distribution storage means 12
Among the data stored in (1), the data corresponding to these are searched, and the medium acoustic velocity of the steel pipe corresponding to the flaw detection refraction angle is calculated. Then, the incident angle is calculated using the Snell's law from the medium sound velocity of the steel pipe, the medium sound velocity of the probe, and the flaw detection refraction angle.

The calculated incident angle is displayed to the operator, and the operator selects a probe having a corresponding incident angle and an ultrasonic spread angle required for flaw detection and sets it on the flaw detector. An automatic probe replacement device may be installed to automatically set the probe having the calculated incident angle on the flaw detector. The spread angle of ultrasonic waves required for flaw detection may be automatically calculated by a known method.

In the present embodiment, since the flaw detection refraction angle is known in advance, the installation position of the probe for irradiating ultrasonic waves to the portion to be flaw-detected is geometrically determined from the flaw detection refraction angle and the size of the steel pipe. It can be easily determined by the relationship.

FIG. 2 is a block diagram showing another example of the embodiment of the present invention. In this embodiment, the probe to be used is predetermined, and therefore the incident angle and the speed of sound in the probe are known. As such a probe, a probe having an incident angle corresponding to a fixed nominal refraction angle is usually used.

As in the case of the first embodiment, the sound velocity distribution storage means 12 stores data indicating the relationship between the refraction angle and the sound velocity for each steel type and rolling condition of the steel pipe. At the time of flaw detection, the incident angle of the probe, the sound velocity in the probe, the steel type of the steel pipe and the rolling condition are input by the incident angle, the sonic velocity in the probe, the steel type, and the rolling condition input means 14. The refraction angle calculation means receives this input and uses the data stored in the sound velocity distribution storage means 12 to obtain the flaw detection refraction angle.

Since the data stored in the sound velocity distribution storage means 12 is the data showing the relationship between the refraction angle and the sound speed, in order to obtain the flaw detection refraction angle, the refraction angle satisfying this relationship and Snell's law at the same time is obtained. Iterative convergence calculation is used.

When the flaw detection refraction angle is obtained, the probe position calculation means 17 irradiates ultrasonic waves to the portion to be flaw-detected from the flaw detection refraction angle and the size of the steel pipe input from the steel pipe size input means 15. Calculate the required probe position. This calculation is simple because it can be performed based on a geometrical relationship.

Next, an example of a method of measuring the refractive angle dependence of the sound velocity of a test object having acoustic anisotropy in the embodiment of the present invention will be described with reference to FIG. In FIG.
Reference numeral 21 is an object to be inspected (steel pipe), 22 is a weld bead, 23 is a defect, 24 is a transmitting variable angle probe, and 25 is a receiving variable angle probe. The object to be inspected used in this embodiment has a wall thickness t.
= 22.2 mm, outer diameter D = 1320.8 mm UOE steel pipe.

First, the two variable-angle probes 24 and 25 whose wedges are acrylic are arranged to face each other as shown in FIG.
At this time, the distance Y between the variable angle probes 24 and 25 is the refraction angle.
Set to 1 skip position at 35 °. The refraction angle can be set to a position of less than 35 °, but a longitudinal wave and a transverse wave may occur at the same time, so a longitudinal wave critical angle or more is desirable.
It is also possible to set the position to two or more skips, but since the beam spread increases as the beam path length increases, in this case, the transducer width of the probe is increased to increase the beam directivity. It is desirable to raise it.

If the variable-angle probes 24 and 25 whose incident points do not change even when the incident angle is changed are used, the ultrasonic wave propagation path can be easily calculated and the refraction angle can be measured. Easy and accurate.

The distance between the probes for one skip is expressed by the following equation from the outer diameter D, the inner surface incident angle θ _i and the refraction angle θ. Y = 2πD (θ _i −θ) / 360 (9) Further, the inner surface incident angle θ _i is obtained by the following equation from the refraction angle θ, the outer diameter D and the wall thickness t. θ _i = sin ⁻¹ {sin θ / (1-2t / D)} (10) In the case of the present embodiment, t = 22.2 D = 1320.8 θ = 35
Substituting ° into equation (10) gives θ _i = 36.4 °. Further, from the equation (9), Y = 32.3 mm.

Next, at the position of the probe described above, ultrasonic waves are transmitted from the transmission variable angle probe 24, and while receiving ultrasonic waves at the reception variable angle probe 25, both the incident angle of the probe is changed simultaneously received echo to determine the incident angle theta ₂ of the probe is maximized.

Next, the speed of sound V (35 °) at this position is obtained using Snell's law (11). sin θ ₂ / V _wedge (= 2730) = sin (θ = 35) / V (35 °) (11) where V _wedge is the speed of sound in the transmission variable-angle probe 24. In the case of this embodiment, V (35 °) = 3295 m / s.

Similarly, V (36 °), V (37 °), V (38
°), it does not cause ... and examined continue the inner surface incident angle θ _lim
Repeat the measurement until the neighborhood. The angle that does not cause the internal incidence is obtained by substituting θ _i = 90 into the equation (10) and solving with θ, and is given by the following equation. θ _lim = sin ⁻¹ (1-2t / D) (12) In the case of the present embodiment, θ _lim = 75.1 °.

Then, it is possible to draw a sound velocity distribution map (dependence of the sound velocity on the refraction angle) as shown in FIG. The SV wave polarized in the thickness direction and propagating in the C direction has a minimum sound velocity V ₀ when propagating in the thickness direction and a sound velocity V ₄₅ when propagating in a direction forming 45 ° with the thickness direction. Since it becomes the maximum, it can be approximated by the following equation. V (θ) = (V ₀ + V ₄₅ ) / 2 + (V ₀ −V ₄₅ ) cos (4θ) / 2 (13) FIG. 5 is obtained by regressing the data shown in FIG. 4 by the equation (13). It is a representation. At this time, in addition to the above-described V-scan measurement, the acoustic velocity V ₀ of a transverse wave propagating in the wall thickness direction and polarized in the tube circumferential direction is investigated using a transverse wave probe and added to FIG.
The regression accuracy of equation 3) is improved. In this way, the sound velocity distribution (dependence of the sound velocity on the refraction angle) can be determined.

In the present embodiment, the speed of sound is calculated by Snell's law (relationship between incident angle and refraction angle) at each position, but it can also be calculated from the propagation time and propagation distance of the ultrasonic wave in the subject. is there. However, also in this case, in order to make the incident point of the ultrasonic wave from the probe accurate, it is necessary to obtain the sound velocity for each position where the echo detected by the V-scan becomes maximum.

In this embodiment, a variable angle probe is used as the probe, but any probe can be used as long as it can change the incident angle. In addition, a linear array type probe can be used. The use of a probe is also possible. FIG. 6 is a schematic diagram of performing V scanning with the array type probe. In the following drawings, the same components as those shown in all the drawings are designated by the same reference numerals and the description thereof will be omitted. In FIG. 6, reference numerals 26, 26 'denote transmitting linear array type probes, 27, 27' denote receiving linear array type transducers, 26 and 26 ', 27 and 2'.
7's are the same thing only with different positions.

At the positions of 26 and 27, both linear array type probes are set so that the incident angle becomes small. At the positions of 26 'and 27', both linear array type probes are set so that the incident angle becomes large. In this way, the linear array type probe is used to perform the measurement while changing the incident angle. Only the method of changing the incident angle is different, and the measuring method and principle are shown in FIG. Is exactly the same as

Next, in the embodiment of the present invention, another example of the method for measuring the refraction angle dependence of the sound velocity of a test object having acoustic anisotropy will be described with reference to FIGS. 7 and 8. . Figure 7
In FIG. 8, 28 is a vertical shear wave probe, 29 is a transmission bevel probe, and 30 is a reception bevel probe.

First, as shown in FIG. 7, C propagates in the thickness direction t
Sound velocity V _{0C of} a transverse wave polarized in the direction t and thickness L
The sound velocity V _0L of the transverse wave polarized in the direction is obtained. Further, the sound velocity ratio R = V _0L / V _0C is determined from these two measured values. In the inspection object used in this embodiment, V _0L = 3218 m /
s, V _0C = 3065 m / s and R = 1.05.

Next, V-scanning is performed by using two probes with nominal refraction angles (STB refraction angles) of 70 ° and 60 °, facing each other in parallel in the L direction as shown in FIG. The transmission bevel probe 29 transmits ultrasonic waves, and the reception bevel probe 3
When the ultrasonic wave is received at 0, the inter-transducer distance Y'that maximizes the detected echo is determined. Then, the flaw detection refraction angles Θ _L70 and Θ _L60 of each probe are obtained from the equation (14). Θ = tan ⁻¹ {Y ′ / (2t)} (14)

In the present embodiment, the beam path lengths Y'are 186.4 mm and 101.2 mm, and the flaw detection refraction angles are Θ _L70 = 76.6 ° and Θ _L60 = 66.3 °, respectively. By the way, two probes with nominal refraction angles (STB refraction angles) of 70 ° and 60 ° are used, respectively, so that they are opposed to each other in parallel with the C direction and V
Differences between flaw detection refraction angles Θ _C70 and Θ _C60 and the above-mentioned Θ _L70 and Θ _{L60 which} can be stopped even after scanning Δ ₇₀ = Θ _L70 − Θ _C70 and Δ
₆₀ = Θ _L60 −Θ _C60 with the sound velocity ratio R as a variable.
There is a relationship like 0. In the case of this embodiment, since R = 1.05, Δ ₇₀ = 8.8 and Δ ₆₀ = 5.8 from FIGS. 9 and 10. These values and the measured refraction angle in the L direction Θ _L70 = 76.6 °,
Using θ _L60 = 66.3 °, Δ ₇₀ = θ _L70 −θ _C70 and Δ
_From the relation of ₆₀ = Θ _L60 -Θ _C60 , Θ _C70 = 67.8, Θ _C60 = 60.5
Becomes

From the flaw detection refraction angles Θ _C70 and Θ _{C60 in the} C direction, the incident angle θ _{wedge of the} probe, and the sound velocity V _{wedge of the} wedge, the sound velocity V _Θ in the flaw detection refraction angle direction is calculated using Snell's law of equation (15). You can ask. sin _Θ / V _Θ = sin θ _wedge / V _wedge (15) In equation (15), Θ = Θ _C70 = 67.8 °, θ _wedge = 52.58 °,
Substituting V _wedge = 2730m / s, V _67.8 = 3180m / s is obtained, and Θ = Θ _C60 = 60.5 °, θ _wedge = 52.58 °, V
_wedge = _2730m / s to assign and V _60.5 = 3245m / s is obtained. These two sound velocity values and the first obtained V _0C = 3065m /
If s is the speed of sound at a refraction angle of 0 °, it becomes as shown in FIG. As in the previous embodiment, FIG.
Regression by equation 3) results in Fig. 5.

The sound velocity distribution (the dependence of the sound velocity on the refraction angle) can be obtained by the above method.

In this embodiment, V scanning in the L direction is performed by the probe having two nominal refraction angles, but refraction in the L direction and the C direction as shown in FIGS. 9 and 10 is performed at other angles. If the relationship of the angular deviations is continuously obtained, all the deviations of the refraction angles in the L direction measured using the array type probe or the variable angle SV wave probe as described above in the C direction are obtained. It can be converted to a deviation and the accuracy of regression can be improved.

Next, a transducer is attached on the circumference of a semi-circular wedge, and the ultrasonic wave emission point of the formula probe is used as a focal point, as shown in FIG.
A method of measuring the refraction angle dependence of the sound velocity by using two line focus type oblique angle probes 31 as shown in FIG.
Two line focus type bevel probes 31 are arranged on the steel plate 21 having a wall thickness Z as shown in FIG. 13, V scanning is performed, and a distance D between incident points at a position where transmission echo can be detected,
The propagation time t is measured and the sound velocity V is calculated by the following equation. V = {(2Z) ² + D ² } ^1/2 / t (16) The refraction angle indicating the propagation direction at this time is given by the following equation. θ = tan ⁻¹ {D / (2Z)} The refractive angle dependence of the sound velocity can be obtained by measuring the sound velocity at various positions by the above method.

[0072]

As described above, according to the first aspect of the present invention, the dependence of the sound velocity on the refraction angle is measured in advance for each steel type and rolling condition, and the data is stored in the storage device. In addition, at the time of flaw detection, the incident angle corresponding to the refraction angle used for flaw detection is automatically calculated using the data of these refraction angle dependences, and the probe having the calculated incidence angle is selected. Therefore, even when detecting a welded portion of a longitudinal joint welded steel pipe having acoustic anisotropy, it is possible to select a probe capable of injecting ultrasonic waves at the correct refraction angle, and therefore The ultrasonic wave having the determined incident angle on the inner surface can be accurately applied to the defect flaw detection portion.

In the invention according to claim 2, the dependence of the sound velocity on the refraction angle is measured in advance for each steel type and rolling condition, and the data is stored in a storage device. Angle and the probe refraction angle according to the medium sound velocity,
It is automatically calculated using these refraction angle dependence data, and the probe setting position is automatically calculated from the calculated flaw detection angle. The area can be illuminated.

In the invention according to claim 3, two variable-angle probes or array-type oblique-angle probes are used, and the probes are arranged facing each other on the object to be inspected at the same incident angle. However, the V-scan is performed, and the sound velocity is measured at the position where the maximum echo is detected. The refractive angle dependence of the sound velocity is measured by changing the incident angle many times and measuring the sound velocity. The dependency can be accurately measured.

According to the fourth aspect of the present invention, the incident angles of the probes are set to be the same, and the probes are arranged on the object to be inspected so as to face each other with a distance corresponding to the flaw refraction angle, and the incident angles are changed. Since the incident angle at which the maximum echo is detected is detected and the speed of sound in the object to be inspected is calculated by using Snell's law, it is possible to accurately measure the refraction angle dependence of the speed of sound.

In the invention according to claim 5, two line-focus type oblique-angle probes are used, and they are arranged on the object to be inspected so as to face each other, and V scanning is performed so that a transmission echo can be detected. Since the refraction angle dependency of the sound velocity is measured by measuring the sound velocity with, it is possible to accurately measure the refraction angle dependency of the sound velocity.

In the invention according to claim 6, from the sound velocity ratio of two transverse waves having different polarization planes and the refractive angle dependence of the sound velocity of the SV wave propagating in the L direction (rolling direction), C
Since the refractive angle dependence of the sound velocity in the direction (direction perpendicular to the rolling direction) is measured, the refractive index dependence of the sound speed in the C direction can be calculated from the refractive index dependence of the sound speed in the L direction. .

In the invention according to claim 7, the refraction angle dependence of the sound velocity is regressed by a periodic function of the period π / 2 or π and is stored in the storage device as a function form. And the sound velocity can be continuously determined, and the relationship between the refraction angle and the sound velocity can be determined with a small number of parameters.

The invention according to claim 8 has the same effect as the invention according to claim 1 and the invention according to claim 9 has the same effect as the invention according to claim 2.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of an embodiment of the present invention.

FIG. 2 is a block diagram showing another example of the embodiment of the present invention.

FIG. 3 is a diagram showing an example of a method for measuring the refractive angle dependence of the sound velocity of a test object having acoustic anisotropy.

FIG. 4 is a diagram showing a relationship between a refraction angle and a transverse wave sound velocity (dependence of a sound velocity on a refraction angle).

FIG. 5 is a diagram showing what is shown by regression of the data shown in FIG. 4 by a regression equation.

FIG. 6 is a schematic view showing a method of performing V scanning with an array type probe.

FIG. 7 is a diagram showing L-direction polarization and C-direction polarization of transverse waves propagating in the thickness direction.

FIG. 8 is a diagram showing a state in which a probe is opposed in parallel to the L direction and V scanning is performed.

FIG. 9 is a diagram showing a relationship between deviations of refraction angles in the L direction and the C direction at a flaw detection refraction angle of 70 °.

FIG. 10 is a diagram showing a relationship between deviations of refraction angles in the L direction and the C direction at a flaw detection refraction angle of 60 °.

FIG. 11 is a diagram showing a relationship between a refraction angle and a transverse wave sound velocity (dependence of a sound velocity on a refraction angle).

FIG. 12 is a diagram showing a line focus type bevel probe.

FIG. 13 is a diagram showing a state in which V scanning is performed using a line focus type bevel probe.

FIG. 14 is a diagram showing an example of a method for obtaining a flaw detection refraction angle in a conventional method.

FIG. 15 is an example of a graph for obtaining a flaw detection refraction angle.

FIG. 16 is a graph showing the change in sound velocity in the flaw detection direction.
It is a figure which shows the example of the prior art of the method of measuring a flaw detection refraction angle and a flaw detection position accurately.

17 is a diagram showing the relationship between the actual refraction angle and the speed of sound used in the method shown in FIG.

[Explanation of symbols] 11 Flaw detection angle, steel type, rolling condition input means 12 Sound velocity distribution storage means 13 Incidence angle calculation means 14 Incidence angle, probe sound velocity, steel grade, rolling condition input means 15 Steel pipe size input means 16 Refraction angle calculation means 17 Probe position calculation means 21 Inspection object (steel pipe) 22 Weld beads 23 defects 24 Variable angle probe for transmission 25 Variable angle probe for reception 26,26 'Transmitting linear array type probe 27, 27 'Receiving linear array type probe 28 Vertical Transverse Wave Transducer 29 Bevel probe for transmission 30 Bevel probe for reception 31 Line Focus Bevel Probe

Front page continuation (72) Inventor Takeo Shimizu Marunouchi 1-2-2, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) Reference JP-A-59-9554 (JP, A) JP-A-3-293559 ( JP, A) JP-A-8-220079 (JP, A) JP-A-8-261992 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 29/00-29/28

Claims (9)

(57) [Claims] 1. In a method of ultrasonically detecting a welded portion of a longitudinal joint welded steel pipe having acoustic anisotropy, the refractive angle dependence of the sound velocity is measured in advance for each steel type and rolling condition, and the data is stored in a storage device. Memorize and automatically calculate the incident angle corresponding to the refraction angle used for flaw detection using these refraction angle dependency data, and select the probe with the calculated incident angle. An ultrasonic flaw detection method, which is characterized by being used. 2. In a method of ultrasonically detecting a welded portion of a longitudinal joint welded steel pipe having acoustic anisotropy, the refractive angle dependence of the sound velocity is measured in advance for each steel type and rolling condition, and the data is stored in a storage device. It was memorized, and at the time of flaw detection, the flaw detection refraction angle according to the incident angle of the probe to be used and the sound velocity in the probe was automatically calculated using these refraction angle dependence data, and was calculated. An ultrasonic flaw detection method characterized in that a set position of a probe is automatically calculated from a flaw detection refraction angle. 3. The ultrasonic flaw detection method for a steel pipe according to claim 1 or 2, wherein two variable angle probes or array-type bevel angle probes are used, and an incident angle of the probe is changed. In the same manner, they are arranged facing each other on the object to be inspected, V scanning is performed, and the sound velocity in the object to be inspected is measured at the position where the maximum echo is detected.
An ultrasonic flaw detection method for a steel pipe, characterized in that the refractive angle dependence of sound velocity is measured by changing the incident angle many times. 4. The ultrasonic flaw detection method for a steel pipe according to claim 1 or 2, wherein two variable angle probes or array-type bevel angle probes are used, and an incident angle of the probe is changed. In the same way, on the object to be inspected, they are arranged facing each other with a distance corresponding to the flaw detection refraction angle, the incident angle is changed to detect the maximum echo, and Snell's law is used. An ultrasonic flaw detection method for a steel pipe, characterized in that the dependence of the sound velocity on the refraction angle is measured by calculating the sound velocity in the inspected object many times by changing the flaw detection refraction angle. 5. The ultrasonic flaw detection method for a steel pipe according to claim 1, wherein a transducer is attached on the circumference of a semi-circular wedge, and the ultrasonic wave emission point of the probe is focused. Two line-focusing type bevel probes are arranged facing each other on the object to be inspected, V scanning is performed, and the sound velocity in the object to be inspected is measured at a position where transmission echo can be detected. An ultrasonic flaw detection method for a steel pipe, characterized by measuring the dependence of sound velocity on the refraction angle. 6. The ultrasonic flaw detection method for a steel pipe according to claim 1 or 2, wherein the sound velocity ratio of two transverse waves propagating in the thickness direction and having different polarization planes and the L direction (rolling direction). ), The velocity of sound of the SV wave propagating to
An ultrasonic flaw detection method for a steel pipe, characterized by measuring the dependence of sound velocity in a direction (a direction perpendicular to the rolling direction) on the refraction angle. 7. Any one of claims 1 to 6
An ultrasonic flaw detection method for a steel pipe according to item 1, wherein the refractive angle dependence of the sound velocity is regressed with a periodic function of period π / 2 or π,
A method for ultrasonic flaw detection of a steel pipe, characterized by storing it in a storage device as a functional form. 8. A sound velocity distribution storage means for storing the refraction angle dependence of the sound velocity for each steel type and rolling condition of a steel pipe, and a flaw detection refraction angle,
A means for inputting the steel type and rolling conditions, and an incident angle for calculating the incident angle from the input flaw detection refraction angle, the steel type and rolling conditions, using the data of the refraction angle dependence of the sonic velocity stored in the sonic velocity distribution storage means. An ultrasonic flaw detector for a steel pipe, comprising: a calculating unit. 9. A sound velocity distribution storage means for storing the refraction angle dependence of the sound velocity for each steel type and rolling condition of the steel pipe, and the steel type, rolling condition, incident angle or nominal refraction angle of the probe, and medium sound velocity of the probe. From the input steel type, the means for inputting the size of the steel pipe, the input steel type, rolling conditions, the incident angle or nominal refraction angle of the probe, and the sonic velocity in the probe. A refraction angle calculating means for calculating a flaw detection refraction angle using data on the dependence of sound velocity on the refraction angle, and a probe for calculating a set position of the probe from the calculated flaw detection refraction angle and the input steel pipe size. An ultrasonic flaw detector for a steel pipe, comprising: a position calculating means.