JPH08189919A - Ultrasonic flaw detection test method - Google Patents

Abstract

PURPOSE: To precisely find inclination and size of crack with a single sensor, relating to an ultrasonic flaw detection test method for a thin tube such as a heat-transfer pipe. CONSTITUTION: Water 3 is sealed in a testing body 2 such as a thin tube, and bidirectional ultrasonic probe 1 is disposed with eccentric quantity S from axis center of the tube. From the probe 1, ultrasonic waves 20 and 21 provided with the same characteristics are emitted in the A and B directions, different by 180 degrees from each other, and each ultrasonic wave 20 and 21 repeats reflection between on the inner and outer surfaces of the tube with an incident angle i and a refractive angle r, and advances in the clockwise direction F and the counterclokwise direction P, respectively, and reflected by a crack 4 to be returned, and the reflected waves are measured by the probe 1. By finding respective reflected wave ratios, inclination angle and size of the crack 4 are precisely detected, so that a plurality of probes are not required to be disposed, as conventionally did, and ultrasonic waves of the same characteristic are easily emitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection test method applied to defect inspection of heat transfer tubes and the like.

[0002]

2. Description of the Related Art An ultrasonic probe has electrodes attached to both sides of a piezoelectric element such as a crystal (an element which has a property of changing its size when a voltage is applied and generating a voltage when a force is applied to change its size). A sound absorbing material is provided on one surface so that ultrasonic waves can be transmitted from the opposite surface.

An example of a typical ultrasonic probe is shown in FIG. In the figure, electrodes 13, 14 are provided on both surfaces of the piezoelectric element 11.
Is provided and is housed in the case 12. Piezoelectric element 1
The sound absorbing material 15 (on the side of the electrode 14) is provided on one side of 1
The ultrasonic wave 17 is transmitted only in one direction through the protective film 16.

In the ultrasonic flaw detection test, it is important to find defects (scratches, cracks, etc.) in the object to be inspected and to determine their morphology. Particularly, for defects having a progressive property such as cracks leading to cracks. The need is particularly great.

A method for estimating the size, direction, etc. of a crack
As one of them, there is a method of obtaining these from the strength of ultrasonic waves reflected by a crack. Defects with crack-like directionality, which are usually estimated by comparison with the intensity of reflected ultrasonic waves from artificially created defects of known dimensions (for example, horizontal hole of drill, bottom of hole of drill, etc.) Then, the intensity of the reflected ultrasonic wave varies greatly depending on the incident direction of the ultrasonic wave. This is an example of a case such as fretting fatigue crack, and it is observed when the crack caused by this crack propagates with a large inclination rather than perpendicular to the surface of the subject. In order to know the size of such cracks, it is necessary to obtain the tilt angle of the cracks.

For this purpose, ultrasonic waves are incident on the crack from both the clockwise and counterclockwise directions, the ultrasonic wave reflection intensities are obtained for each, and the ratio is estimated from the ratio of the two (hereinafter referred to as the ultrasonic wave reflection intensity ratio R). There are possible ways to do this. In order to properly obtain the ultrasonic reflection intensity ratio R, it is necessary to perform measurement using an ultrasonic probe having the same ultrasonic characteristics (ultrasonic transmission strength, reception sensitivity, frequency characteristics, etc.). is there. However, since the conventional automatic ultrasonic flaw detection test is performed by a pair of probes arranged in opposite directions (that is, separate probes), completely identical ultrasonic characteristics cannot be transmitted simultaneously. is the current situation.

A technique similar to the present invention which meets the above-mentioned need is disclosed in Japanese Patent Laid-Open No. 58-34358. This outline relates to an ultrasonic flaw detector for a pipe, and includes a pair of bevel probes axially and in opposite directions to each other in a flaw detection head composed of five probes, and a circumferential and reverse direction. By providing a pair of facing angle beam probes and five vertical probes, a directional defect can be reliably detected by a single flaw detection operation.

However, in the method disclosed in Japanese Patent Laid-Open No. 58-34358, a pair of probes are arranged on the outer surface of the tube in opposite axial and circumferential directions. Two probes for each direction are indispensable, and it is almost impossible to perfectly match the ultrasonic characteristics of each probe.

[0009]

As described above, as one of the methods for estimating the size, direction, etc. of a crack, there is a method for obtaining it from the intensity of ultrasonic waves reflected by the crack. This is usually done by comparing the intensity of the reflected ultrasonic waves from artificially created defects of known dimensions (for example, the horizontal hole of a drill, the hole bottom of a drill, etc.), but for defects with a directional property such as a crack. The intensity of reflected ultrasonic waves varies greatly depending on the incident direction of ultrasonic waves. This is seen when the cracks due to the cracks are not perpendicular to the surface of the subject but propagate with a large inclination like the fretting fatigue cracks.

In order to obtain the inclination angle of such an inclined crack, ultrasonic waves are incident from both directions on the opposite side to the crack, the reflection intensity of the ultrasonic wave is calculated for each, and the ratio of the two (hereinafter There is a method of estimating from the sound wave reflection intensity ratio R).

In order to properly obtain this ultrasonic wave reflection intensity ratio R, as described above, the same ultrasonic wave characteristics (the ultrasonic wave transmission intensity,
Since it is necessary to perform measurement using an ultrasonic probe having reception sensitivity, frequency characteristics, etc.), a pair of probes (that is, Separate probes). Therefore, it was not possible to transmit completely the same ultrasonic characteristics at the same time.

It is an object of the present invention to detect a crack and to incline a crack by using a probe which emits ultrasonic waves having completely equal ultrasonic characteristics from one ultrasonic probe in both directions. Another object of the present invention is to provide a method for accurately estimating the crack size.

[0013]

Therefore, according to the present invention, an ultrasonic sensor for emitting ultrasonic waves having the same characteristics in opposite directions to each other is arranged eccentrically from the axial center of the thin tube inside the thin tube. Provided is a method of emitting ultrasonic waves from a sensor in opposite directions to a wall surface of a thin tube, measuring a reflected wave from a defective portion inside the wall of the thin tube, and detecting the defective portion from the ratio.

That is, according to the present invention, one ultrasonic sensor which emits ultrasonic waves having the same characteristics in mutually opposite directions is provided in a thin tube used in a heat exchanger, a steam generator, etc. Are eccentric to each other, and ultrasonic waves are emitted from the same ultrasonic sensor toward the inner wall surface of the same tube in opposite directions to each other, and ultrasonic waves of the same bidirectional direction are arranged inside the same tube in the circumferential direction. If there is a defective portion such as a crack that propagates to the inside of the thin tube wall, is reflected from the defective portion, the reflected waves that return are measured, and the ratio of the measured values is calculated to obtain the thin tube. There is provided an ultrasonic flaw detection test method characterized by detecting the presence, absence, direction, size, and the like of a defective portion that occurs in the.

[0015]

According to the present invention, when an ultrasonic wave is incident from the inner surface side of a thin tubular tube by such means, the ultrasonic wave propagates the entire circumference of the tube while being repeatedly reflected on the outer surface and the inner surface of the thin tube. At this time, when ultrasonic waves having the same characteristics such as transmission intensity, receiving sensitivity, frequency characteristics, etc. are incident on the wall surface of the thin tube from opposite directions of 180 °, the ultrasonic wave propagates around the entire circumference of the thin tube as described above. However, the propagation direction is the opposite direction. If there is a defect such as a crack in the thin tube, it means that ultrasonic waves are incident on both sides of the defect, and the ultrasonic characteristics are completely the same, so sensitivity calibration as an absolute value is not necessary. The size and inclination of the crack can be known from the ultrasonic reflection intensity ratio of the two.

According to such a method, a plurality of sensors have been conventionally required and the characteristics must be the same, but one ultrasonic sensor can be used for the test with high accuracy.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram in which an ultrasonic probe according to the ultrasonic flaw detection test method of the present invention is applied to a heat transfer tube. The figure shows a situation in which a bidirectional ultrasonic probe 1 (hereinafter, simply referred to as a probe) is used to inspect an object 2 to be inspected, which is a thin thin tube such as a heat transfer tube. Water 3 is injected into the inside of the device under test 2 in order to facilitate transmission of ultrasonic waves.
Here, 4 indicates an inclined crack inside the inspection object 2.

In this embodiment, the ultrasonic probe 1 is set eccentrically from the center of the object 2 to be inspected at a position which is substantially symmetrical with respect to the portion where the crack 4 is generated. The angle of incidence of ultrasonic waves on the device under test 2 due to this eccentricity is determined by the following equation.

[0019]

[Equation 1]

In FIG. 1, the ultrasonic waves 20 transmitted from the ultrasonic probe 1 in the A direction (clockwise direction F) are shown as 20a and 20b on the inner and outer surfaces of the inspection object 2 from the position A of the inspection object 2. While repeating the reflection, the crack 4 is reached in the clockwise direction F in the figure. Part of the ultrasonic waves is reflected by the crack 4, returns along the same path, and is received by the ultrasonic probe 1.

Similarly, the ultrasonic waves 21 having the same characteristics transmitted in the B direction (counterclockwise P) are repeatedly reflected from the B position of the inspection object 2 on the inner and outer surfaces of the inspection object 2 as shown by 21a and 21b. , Reaches the crack 4 in the counterclockwise direction P in the figure, is similarly reflected by the crack 4, and is received by the ultrasonic probe 1 again.

That is, the same ultrasonic probes 1 to 18
Ultrasonic waves having the same characteristics, which are transmitted in directions A and B different by 0 °, propagate in the inside of the device under test 2 in the clockwise direction and the counterclockwise direction and reach the crack 4, and the reflected waves thereof are broken. The ultrasonic wave reflection intensities from both directions are shown, and the ratio is the reflection intensity ratio R. The angle (refraction angle) when the ultrasonic wave propagates in the inspection object 2 is expressed by the following equation.

[0023]

[Equation 2]

FIG. 2 shows a structural diagram of a bidirectional ultrasonic probe having the same characteristics used for such a test. The outer edge of the piezoelectric element 5 is held by the case 6, and the thickness of the piezoelectric element 5 expands and contracts according to the change of the voltage by applying a voltage to the electrodes 7 and 8 on both surfaces thereof. Since both sides of the piezoelectric element 5 have a degree of freedom, the vibration is transmitted as ultrasonic waves in both directions A and B through the protective films 9 and 10 with the same characteristics.

FIG. 3 shows a pipe outer diameter of about 20 mm and a pipe wall pressure of about 1 mm.
When a crack with a tube surface length of 5 mm and a maximum depth of 0.5 mm is applied to the thin tube, the refraction angle is 45 degrees, and the ultrasonic wave wave mode is transverse wave, the ultrasonic reflection intensity ratio is The relationship with the inclination angle of the crack is shown.

From the characteristics shown in FIG. 3, the crack angle is 90
When the angle is °, the ultrasonic reflection intensity ratio is 1, and the crack inclination is 90 °.
It can be seen that the reflection intensity ratio also goes away from 1 as it goes away from.

In the above embodiment, the ultrasonic probe 1
Since the transducer of is expanded and contracted in the entire thickness direction, basically it is possible to transmit ultrasonic waves in both directions, and the characteristics of the ultrasonic waves transmitted in both directions are completely the same, so 4, the same ultrasonic waves 20 and 21 are emitted from both sides and reflected, and the inclination angle of an inclined crack such as a fretting crack can be clarified from the ultrasonic reflection intensity ratio. It is possible.

Further, if this characteristic is utilized, conventionally, a pair of probes also provided for the reverse direction was required, but this can be performed by one ultrasonic probe 1. Therefore, it is necessary to use a probe having a function of making the vibration direction free, and a structure in which the piezoelectric element 5 can be held by the outer edge of the case 6 is adopted.

Incidentally, the relationship between the ultrasonic reflection intensity ratio and the inclination of cracks described above is obtained by processing artificial slits of various inclination angles into thin tubes by means of electric discharge machining or a micro cutter and reflecting ultrasonic waves as described above. Characteristic data can be experimentally obtained by measuring the reflected wave.

[0030]

As described above in detail, in the present invention, an ultrasonic sensor for emitting ultrasonic waves having the same characteristics in mutually opposite directions is arranged eccentrically from the axial center of the thin tube in the present invention. Then, ultrasonic waves were emitted from the ultrasonic sensor in opposite directions to the wall surface of the thin tube, the reflected wave from the defective portion inside the wall of the thin tube was measured, and the defective portion was detected from the ratio. Therefore, it has the following effects.

(1) By transmitting ultrasonic waves bidirectionally, it becomes possible to inspect from both directions of the scratch at the same time, and the inclination angle direction of an inclined crack such as a fretting crack,
The size can be accurately detected.

(2) Since one probe can emit ultrasonic waves having the same characteristics without using a plurality of probes as in the prior art, the structure of the sensor itself can be simplified and its detection accuracy can be improved. It is a thing.

[Brief description of drawings]

FIG. 1 is a side view showing an inspection situation for implementing an ultrasonic flaw detection test method according to an embodiment of the present invention.

FIG. 2 is a side view of a bidirectional ultrasonic probe applied to the ultrasonic flaw detection test method of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a crack angle and an ultrasonic reflection intensity ratio R according to the ultrasonic flaw detection test method of the present invention.

FIG. 4 is a side view of a conventional ultrasonic probe.

[Explanation of symbols]

 1 Bidirectional ultrasonic probe 2 DUT 3 Water 4 Crack 5 Piezoelectric element 6 Case 7,8 Electrode 9,10 Protective film

Claims (1)

[Claims] 1. An ultrasonic sensor, which emits ultrasonic waves having the same characteristics in mutually opposite directions, is eccentric from the axis of the thin tube used in a heat exchanger, a steam generator or the like. The ultrasonic sensors emit ultrasonic waves from the same ultrasonic sensor toward the inner wall surfaces of the same tube in opposite directions, and ultrasonic waves in the same direction propagate in the circumferential direction inside the thin tube wall. If there is a defect such as a crack in the inside of the thin tube wall, the defect caused in the thin tube by measuring each reflected wave that is reflected from the defective part and returned and obtains the ratio of the measured values. An ultrasonic flaw detection test method characterized by detecting the presence, direction, size, etc.