JPH095304A - Ultrasonic flaw detection method in welded part between straight pipe and elbow - Google Patents

Abstract

PURPOSE: To detect a flaw in a weld between a straight pipe and an elbow by arrang ing two probes so that a horizontal isosceles triangle whose base line is composed of the line connecting the probes to each other and vortex is at the intersection of the perpendicular bisector of the base line and a surface to be inspected can be formed. CONSTITUTION: A transmitting probe 1 and a receiving probe 2 are arranged so that, a transmitting beam LT and a receiving beam LR can be propagated through the vicinity of the internal surface of a section to be inspected in nearly the same line when the beams LT and LR are viewed from the side face in the axial direction. Consequently, both the beam LT from the probe 1 and the beam LR of reflected echoes from a defect F are propagated in parallel with the internal surface of a plate in the longitudinal section of the section to be inspected at the position where the defect exists and the noise of reflected echoes, etc., from penetration beads can be reduced remarkably, because the defect can be detected without making ultrasonic waves to incident to the penetration beads. Therefore, since the noise of reflected echoes, etc., from the penetration beads of the weld of an austenitic stainless steel pipe are remarkably reduced, the defect can be detected with high accuracy through a weld metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for ultrasonic flaw detection of a welded portion between a straight pipe and an elbow, which is suitable for flaw detection testing of a welded portion of a stainless steel pipe.

[0002]

2. Description of the Related Art In a nuclear power plant, an ultrasonic flaw detection test is conducted on a welded portion of a pipe during its operation. In the conventional flaw detection procedure, ultrasonic waves are incident from both directions across the welded portion of the subject with a vertical angle of 0 ° and transverse wave oblique angles of 45 ° and 60 °, which is effective for flaw detection of carbon steel pipes. . By the way, as shown in the partial longitudinal sectional view of FIG. 2, for example, in the case where the subject 11 is composed of the welded portion 12 of the straight pipe 11a and the elbow 11b, when the radius of curvature of the elbow 11b is small, the flaw detection on the ventral side is performed. At some time, since a gap d is created between the surface to be inspected and the contact surface of the transverse wave probe 21, ultrasonic waves do not penetrate,
An undetectable range occurs as shown by the diagonal lines. In order to avoid this, it is desirable to detect flaws from the straight pipe 11a side to the elbow 11b side. However, when the specimen 11 is the welded portion 12 of the stainless steel pipe, as will be described later, in transverse wave flaw detection, attenuation and forest-like echo in the weld metal are large, and therefore the transverse wave probe 21 is used for flaw detection from the straight pipe 11a side. Not applicable. Further, when the test object is austenitic stainless steel, the anisotropy of sound velocity occurs due to the fact that the weld metal becomes columnar crystals, and the anisotropy is particularly remarkable in flaw detection by transverse waves. Therefore, in the transverse wave flaw detection, a pseudo echo is generated from the vicinity of the back wave portion of the weld metal, and it is generally difficult to distinguish it from the defect echo. Further, in transverse wave flaw detection, since attenuation and forest-like echo in the weld metal are large, transverse wave flaw detection is not necessarily effective for flaw detection of the welded portion of the stainless steel pipe.
As a countermeasure against this, it is conceivable to apply a longitudinal wave probe instead of the transverse wave probe, and the conventional longitudinal wave probe is used in order to reduce the noise due to the forest-like echo. A split type and a left and right split type shown in the perspective view of FIG. 4 have been proposed.

[0003]

First, in the longitudinal wave type probe 22 of front and rear division type shown in FIG. 3, the refraction angles θ _T and θ _R of the transmitting oscillator 23 and the receiving oscillator 24 are set appropriately. As a result, the transmission beam L _T and the reception beam L _R are focused at the beam intersection at the position of the depth D in the subject 11. Further, in the left-right split type longitudinal wave probe 22 of FIG.
3 and the reception transducer 24 are arranged on the left and right, and the transmission beam L _T and the reception beam L _R are focused at the beam intersection D in the subject 11. However, when the split type longitudinal wave probe 22 is used for flaw detection via weld metal, as shown in the explanatory view of FIG. 5, the longitudinal wave probe 22 is provided on the surface of the subject 11.
When a longitudinal wave is applied to the welding portion 12 by hitting, the reflected echo N from the back wave 14 appears as noise, and therefore there is a problem that it is not always easy to distinguish the defect F from the echo S. It is not easy to detect flaws on the elbow side from the straight pipe side through the weld metal with respect to the welded portion of the straight pipe and the elbow.

The present invention has been proposed in view of the above circumstances, and the noise of the reflection echo from the back wave is significantly reduced, and the welded portion between the straight pipe and the elbow which enables highly accurate flaw detection. An object is to provide an ultrasonic flaw detection method.

[0005]

In order to achieve such an object, the invention of claim 1 coaxially welds the rear end of an elbow to the front end of a straight pipe in the front-rear direction made of austenitic stainless steel. When ultrasonic flaw detection is performed on the annular welded portion of the subject, the transmitting probe and the receiving probe are symmetrically arranged on the upper surface of the front end of the straight pipe with respect to the longitudinal center line thereof. A pair of probes consisting of a child is provided, and each probe is transmitted to the intersection of the vertical bisector in the front-rear direction of the line connecting both probes with the elbow side test surface of the welded part. When the reflected beam from the surface to be inspected of the transmission beam is received by the reception probe by directing the beam and the reception beam, the pair of left and right probes are set to the left and right ends of the bottom, and the intersection point is set. Set both probes so that a horizontal isosceles triangle with And it said that it has set.

According to a second aspect of the present invention, in the first aspect, a longitudinal wave probe is used in which the pair of left and right probes has a transmission beam and a reception beam having a refraction angle of 60 ° to 80 ° with respect to the surface to be inspected. Characterized by being a child.

[0007]

According to this structure, as shown in FIG.
A longitudinal wave transmitted from the transmission probe 1 having a longitudinal wave of 60 ° to 80 ° arranged for transmission on the left side is the subject at the intersection of the transmission beam L _T and the reception beam L _R , which is the subject. The light is incident on the surface of the defect F so as to be in contact with the surface, and the reflection echo from the defect F is detected by the receiving probe 2 having a longitudinal wave of 60 ° to 80 ° arranged on the right side. Therefore, according to such a flaw detection method, a defect can be detected without injecting an ultrasonic wave into the backside wave of the welded portion to be inspected, so that noise such as a reflection echo from the backside wave is significantly reduced. .

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the method of the present invention is applied to flaw detection of a coaxial weld between a straight pipe and an elbow will be described with reference to the drawings.
FIG. 1 shows its three-view drawing, FIG. 1 (A) is a top view thereof, FIG. 1 (B) is a front view in the pipe axis direction of FIG.
[Fig. 4] is a vertical cross-sectional view taken along line CC of Figs.

In the above figure, the same reference numerals as in FIG. 2 denote the same members as in the same figure, respectively, 1 is a transmitting probe, 2 is a receiving probe, and the refraction angles are longitudinal waves 60. ° ~ 80
°. F is an inner surface defect near the weld. The probes 1 and 2 are arranged such that the incident point of each beam and the defect F are substantially on the same plane, and the transmission probe 1 transmits the transmission beam L _T and the reflection from the defect F occurs. The reception beam L _{R of the} echo is received by the reception probe 2. Here, as shown in FIG. 3A, the defect F is a vertical bisector of both the probes 1 and 2, and is on the center line of the straight pipe 11a. F, 1, on the intersection of the line and the elbow-side groove surface of the welded member (hereinafter referred to as the test surface)
2 has a relationship of three vertices of an isosceles triangle that is close to a horizontal equilateral triangle having F as a vertex.

At this time, as shown in FIG. 1B, the transmission beam L _T and the reception beam L when viewed from the side in the tube axis direction.
Both probes are arranged so that _R is substantially on the same straight line and passes near the inner surface of the member 11 to be tested. With such an arrangement, the angle of refraction of both probes and the distance Y to the defect of the probes are
_This is possible by setting _b appropriately. For example, in a 4-inch pipe having a plate thickness of 13.5 mm, if Y _b is 80 mm, the distance L _b between both probes is 70 mm, and the refraction angle is 78 °. In such a device, the test part 11
While gently rotating around the center line, the inner surface of the weld of the elbow is scanned, and the received wave is received each time. Further, at that time, if necessary, the subject is stationary, the probe 1 and the probe 2 are held in the same mutual relation position, and the overall arrangement is kept unchanged, so that the subject is placed on the center line of the subject. It can also be rotated around.

According to the ultrasonic flaw detection method in which the probe is arranged in this way, as shown in FIG. 1B, when viewed from the direction directly facing the horizontal vertical plane orthogonal to the straight pipe center line, Both the transmitted beam L _T from the tentacle and the received beam L _R of the reflected echo from the defect F propagate parallel to the inner surface of the plate in the longitudinal section at the position where the defect exists. Therefore, the defect can be detected without applying ultrasonic waves to the back wave, and thus noise such as reflected echo from the back wave is significantly reduced. Thus, according to such an ultrasonic flaw detection method, noise such as a reflection echo from the back wave of the welded portion of the austenitic stainless steel pipe is significantly reduced, so that the defect can be detected with high accuracy through the weld metal. It becomes possible.

[0012]

In summary, according to the first aspect of the present invention, the annular welded portion of the subject is formed by coaxially welding the rear end of the elbow to the front end of the straight pipe in the front-rear direction made of austenitic stainless steel. At the time of sonic flaw detection, a pair of probes consisting of a transmission probe and a reception probe are provided on the upper surface of the front end portion of the straight pipe symmetrically with respect to the longitudinal center line thereof. , Perpendicular to the front-back direction of the line connecting both transducers 2
The transmission beam and the reception beam of each probe are directed to the intersection of the bisector and the elbow side test surface of the welded portion, and the reflected wave from the test surface of the transmission beam is received by the reception probe. By receiving the probes, the probes are arranged so that the pair of left and right probes are at the left and right ends of the base and the horizontal isosceles triangle with the intersection as the apex is substantially formed. , The noise of the reflection echo from the back wave is greatly reduced,
The present invention is extremely useful industrially because an ultrasonic flaw detection method for a welded portion of a straight pipe and an elbow that enables flaw detection with high precision is obtained.

According to a second aspect of the present invention, in the first aspect, a longitudinal wave probe is used in which the pair of left and right probes has a transmission beam and a reception beam having a refraction angle of 60 ° to 80 ° with respect to the surface to be inspected. Since the noise of the reflection echo from the back wave is significantly reduced by using the child, an ultrasonic flaw detection method for a welded portion between a straight pipe and an elbow that enables flaw detection with high accuracy is obtained. It is extremely useful.

[Brief description of drawings]

FIG. 1 is a three-view drawing showing an embodiment of the present invention, in which FIG. 1 (A) is a top view thereof, and FIG. 1 (B) is a front view seen from the axial direction of FIG. 2C is a vertical sectional view taken along the line CC of FIG.

FIG. 2 is a partial vertical cross-sectional view showing a shear wave probe in a subject of a welded portion of a straight pipe and an elbow.

FIG. 3 is a vertical cross-sectional view showing a conventional front and rear split type probe.

FIG. 4 is a perspective view showing a conventional left and right split type probe.

FIG. 5 is an explanatory diagram of noise generation of a longitudinal wave probe in a conventional weld portion of a subject.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Transmitting probe 2 Receiving probe 10 Test object 11 Test part 11a Straight pipe 11b Elbow 12 Welded part 13 Test surface (elbow side groove surface) 14 Back wave L _T Transmit beam L _b Probe Distance L _R Received beam Y _b Distance between defect and probe

Claims (2)

[Claims] 1. A front end of a straight pipe, which is formed by coaxially welding a rear end of an elbow to a front end of a straight pipe in the front-rear direction made of austenitic stainless steel, by ultrasonic flaw detection. A pair of probes consisting of a transmitting probe and a receiving probe, which are arranged symmetrically with respect to the front-rear direction center line, are provided on the upper surface of the part, and the front and rear of the line connecting both the probes. The transmitted beam and the received beam of each probe are directed to the intersection of the perpendicular bisector of the probe with the elbow-side surface to be inspected, and a reflected wave of the transmission beam from the surface to be inspected is directed. When the probe for reception is received, the pair of left and right probes are used as left and right ends of the bottom side, and both probes are formed so that a horizontal isosceles triangle having the intersection as the apex is formed substantially. An ultrasonic flaw detection method for a welded portion between a straight pipe and an elbow, which is characterized by being provided. 2. The longitudinal wave probe according to claim 1, wherein the pair of left and right probes has a transmission beam and a reception beam having a refraction angle of 60 ° to 80 ° with respect to the test surface. Ultrasonic flaw detection method for welds between straight pipes and elbows.