GB2546371A - Ultrasonic inspection method and apparatus - Google Patents

Ultrasonic inspection method and apparatus Download PDF

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Publication number
GB2546371A
GB2546371A GB1619378.1A GB201619378A GB2546371A GB 2546371 A GB2546371 A GB 2546371A GB 201619378 A GB201619378 A GB 201619378A GB 2546371 A GB2546371 A GB 2546371A
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reception
transmission
oblique probe
probe
point
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GB2546371B (en
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Ohshima Yuki
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Hitachi GE Nuclear Energy Ltd
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Hitachi GE Nuclear Energy Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
    • B23K31/02—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to soldering or welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
    • B23K31/12—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to investigating the properties, e.g. the weldability, of materials
    • B23K31/125—Weld quality monitoring
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/043—Analysing solids in the interior, e.g. by shear waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/221—Arrangements for directing or focusing the acoustical waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/24—Probes
    • G01N29/2487—Directing probes, e.g. angle probes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/26—Arrangements for orientation or scanning by relative movement of the head and the sensor
    • G01N29/265—Arrangements for orientation or scanning by relative movement of the head and the sensor by moving the sensor relative to a stationary material
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C17/00—Monitoring; Testing ; Maintaining
    • G21C17/003—Remote inspection of vessels, e.g. pressure vessels
    • G21C17/01—Inspection of the inner surfaces of vessels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/04—Tubular or hollow articles
    • B23K2101/12—Vessels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/02—Iron or ferrous alloys
    • B23K2103/04—Steel or steel alloys
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/10—Number of transducers
    • G01N2291/102—Number of transducers one emitter, one receiver
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/26—Scanned objects
    • G01N2291/267—Welds
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Immunology (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Pathology (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Acoustics & Sound (AREA)
  • Mechanical Engineering (AREA)
  • Quality & Reliability (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Plasma & Fusion (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
  • Monitoring And Testing Of Nuclear Reactors (AREA)

Abstract

Provided are an ultrasonic inspection method and apparatus for detecting an internal defect 17 along a welding boundary surface 13a in an object, which is inclined with respect to a direction perpendicular to a surface 12 of the object. The object may be a nuclear reactor pressure vessel (RPV). A transmission oblique probe 21 and a reception oblique probe 22 are disposed by a probe movement mechanism so that a transmission point P1 of probe 21 and a reception point P2 of probe 22 are located on an intersection line E between two planes, the planes being (i) a virtual plane including a scanning point and a normal vector of surface 13a, and (ii) a surface 12 of the object. The probes 21 and 22 thereby avoid a portion 15, which may be a pump casing, which causes interference in the measurement. A point of the welding boundary surface 13a is thereby scanned, and the scanning point moves deeper into the object along the surface 13a. The method includes transmitting an ultrasonic wave with probe 21 and receiving the wave with probe 22, wherein both the transmission and reception paths S1, S2 are in the virtual plane.

Description

DESCRIPTION
Title of Invention: ULTRASONIC INSPECTION METHOD AND APPARATUS
Technical Field [0001]
The present invention relates to an ultrasonic inspection method and an ultrasonic inspection apparatus capable of detecting an internal defect generated along a welding boundary surface when detecting a welding portion having the welding boundary surface inclined in a thickness direction perpendicular to a surface of a subject. Background Art [0002]
Maintenance of constituent apparatuses in a power generation plant is necessary in order to maintain a normal operation, and a nondestructive inspection technique plays a highly important role. Particularly, in a nuclear power plant, it is important to ensure soundness of reactor primary apparatuses such as a reactor pressure vessel (RPV) or a recirculation system pipe, and thus an ultrasonic test (UT) is performed on a welding portion in which a defect is easily generated as a volume inspection, so that a defect is detected or a size thereof is evaluated.
[0003]
As an example of inspection targets, there is a welding portion of a reactor pressure vessel lower mirror part. The reactor pressure vessel lower mirror part includes, as illustrated in Figs. 1 and 2, a substantially spherical crown-shaped dome portion 11 and a substantially cone strip-shaped lower mirror petal portion 12, and the two portions are joined to each other via a welding portion 13. The dome portion 11 is provided with a plurality of control rod driving mechanism housings (CRD housings) 14, and the lower mirror petal portion 12 is provided with a plurality of internal pump casings (RIP casings) 15.
[0004]
Generally, in an inspection before services or an inspection during services, an ultrasonic inspection is performed according to a single-probe method in order to detect a defect (crack) which is opened on an inner surface side of the lower mirror part (refer to PTL 1). Specifically, for example, as illustrated in Fig. 3, an oblique probe 20 for transmission and reception is disposed on an outer surface side (the lower side in Fig. 3) of the lower mirror petal portion 12 so as to avoid an interference portion formed of the RIP casing 15 and an R portion 15a in the vicinity thereof, and ultrasonic waves are transmitted from the oblique probe 20 for transmission and reception toward the vicinity of an opening of a defect 16 (crack) . The oblique probe 20 for transmission and reception receives ultrasonic waves (corner echo) reflected at a corner formed between the defect 16 and the inner surface of the lower mirror petal portion 12. Consequently, the defect 16 which is opened on the inner surface side (the upper side in Fig. 3) of the lower mirror part is detected. Citation List Patent Literature [0005] PTL 1: JP-A-6-11595 Summary of Invention Technical Problem [0006]
On the other hand, as an inspection in the final manufacturing stage, the welding portion 13 may be required to be inspected over the entire depth direction of the lower mirror part in order to detect a planar internal defect (specifically, inherent breakage or uneven melting of the welding portion 13) generated along the welding boundary surface of the welding portion 13.
[0007]
Here, as illustrated in Fig. 4, since a welding boundary surface 13a of the welding portion 13 on the outer circumferential side (the right side in Fig. 4) is inclined with respect to the thickness direction perpendicular to the surface of the lower mirror petal portion 12, transmission and reception angles (refraction angles) of the oblique probe 20 for transmission and reception can be set so that an ultrasonic wave is incident to the welding boundary surface 13a in a normal direction (that is, in a direction perpendicular to an internal defect 17 generated along the welding boundary surface 13a). Consequently, an ultrasonic wave can be transmitted from the oblique probe 20 for transmission and reception to the internal defect 17, and the ultrasonic wave reflected at the internal defect 17 can be received by the oblique probe 20 for transmission and reception. The amplitude of the ultrasonic wave reflected at the internal defect 17, that is, the amplitude of the ultrasonic wave received by the oblique probe 20 for transmission and reception can be increased, and thus the internal defect 17 can be detected with high sensitivity.
[0008]
However, as a scanning point (that is, a point for detecting the internal defect 17) on the welding boundary surface 13a comes closer to the inner surface of the lower mirror part, the oblique probe 20 for transmission and reception is required to be separated from the welding boundary surface 13a (refer to virtual arrangement indicated by a two-dot chain line in Fig. 4), and thus the oblique probe 20 for transmission and reception interferes with the interference portion such as the RIP casing 15. Thus, in the single-probe method using the oblique probe 20 for transmission and reception, it is difficult to detect, for example, an internal defect 17 in a depth range U illustrated in Fig. 4.
[0009]
An object of the present invention is to provide an ultrasonic inspection method and an ultrasonic inspection apparatus, capable of avoiding interference between an oblique probe and an interference portion of a subject and also detecting an internal defect with high sensitivity. Solution to Problem [0010]
In order to achieve the object, according to the present invention, there is provided an ultrasonic inspection method of inspecting a welding portion having a welding boundary surface inclined with respect to a thickness direction perpendicular to a surface of a subject, and detecting an internal defect generated along the welding boundary surface by using a transmission oblique probe and a reception oblique probe disposed on the surface of the subject, the method including disposing the transmission oblique probe and the reception oblique probe so that a transmission point of the transmission oblique probe and a reception point of the reception oblique probe are located on an intersection line at which a virtual plane including a scanning point of the welding boundary surface and a normal vector of the welding boundary surface on the scanning point intersects the surface of the subject, and the transmission oblique probe and the reception oblique probe avoid interference with an interference portion of the subject, so as to correspond to the scanning point of the welding boundary surface, moved in a depth direction of the subject; and causing the transmission oblique probe to transmit an ultrasonic wave through a transmission path in the virtual plane, and causing the reception oblique probe to receive the ultrasonic wave through a reception path in the virtual plane.
Advantageous Effects of Invention [0011]
According to the present invention, it is possible to avoid interference between an oblique probe and an interference portion of a subject and also detect an internal defect with high sensitivity.
Brief Description of Drawings [0012] [Fig. 1] Fig. 1 is a bottom view of a reactor pressure vessel lower mirror part which is an example of a subject.
[Fig. 2] Fig. 2 is a vertical sectional view of the lower mirror part taken along the line II-II in Fig. 1.
[Fig. 3] Fig. 3 is a vertical sectional view of the lower mirror part for explaining a single-probe method of detecting a defect which is opened on an inner surface side of the reactor pressure vessel lower mirror part.
[Fig. 4] Fig. 4 is a vertical sectional view of the lower mirror part for explaining a single-probe method of detecting an internal defect which is generated at a welding portion of the reactor pressure vessel lower mirror part.
[Fig. 5] Fig. 5 is a bottom view of the lower mirror part illustrating a transmission oblique probe and a reception oblique probe used for an ultrasonic inspection method of an embodiment of the present invention, and corresponds to a view which is viewed from an arrow V direction in Fig. 6.
[Fig. 6] Fig. 6 is a diagram illustrated by projecting the transmission oblique probe, the reception oblique probe, an ultrasonic wave transmission path, and an ultrasonic wave reception path onto a vertical section of the lower mirror part taken along the line VI-VI in Fig. 5.
[Fig. 7] Fig. 7 is a view which is viewed from an arrow VII direction in Fig. 6, and illustrates arrangement of the transmission oblique probe and the reception oblique probe on an outer surface of a lower mirror petal portion.
[Fig. 8] Fig. 8 is a bottom view of a lower mirror part model for computing a defect detection condition.
[Fig. 9] Fig. 9 is a vertical sectional view of the lower mirror part model taken along the line IX-IX in Fig. 8, and illustrates an example of an application limit depth of the single-probe method.
[Fig. 10] Fig. 10 is a horizontal sectional view of the lower mirror part model taken along the line X-X in Fig. 9, and illustrates a range in which the application limit depth of the single-probe method occurs, that is, a range in which the ultrasonic inspection method of the embodiment of the present invention is to be applied.
[Fig. 11] Fig. 11 is a horizontal sectional view of the lower mirror part model, and is a view for explaining a method of setting an incidence angle and a reflection angle of ultrasonic waves for a defect in the ultrasonic inspection method of the embodiment of the present invention.
[Fig. 12] Fig. 12 is a horizontal sectional view of the lower mirror part model, and illustrates an example of an ultrasonic wave one-way propagation distance in the ultrasonic inspection method of the embodiment of the present invention.
[Fig. 13] Fig. 13 is a conceptual diagram illustrating positional relationships among a scanning point of a welding boundary surface, and a starting point, a transmission point, and a reception point on an outer surface of the lower mirror petal portion in the ultrasonic inspection method of the embodiment of the present invention.
[Fig. 14] Fig. 14 is a diagram illustrating various defect detection conditions in the ultrasonic inspection method of the embodiment of the present invention.
[Fig. 15] Fig. 15 is a block diagram illustrating a configuration of an ultrasonic inspection apparatus of the embodiment of the present invention.
Description of Embodiments [0013]
For example, the above-described welding portion 13 of the reactor pressure vessel lower mirror part is an inspection target in the present invention, and a description will be made of an ultrasonic inspection method of detecting the planar internal defect 17 generated along the welding boundary surface 13a of the welding portion 13 on the outer circumferential side. The same portions as the portions described with reference to Figs. 1 to 4 are given the same reference numerals, and a description thereof will be omitted as appropriate.
[0014]
In the single-probe method using the oblique probe 20 for transmission and reception, for example, it is difficult to detect the internal defect 17 in the depth range U illustrated in Fig. 4. Thus, in the ultrasonic inspection method of the embodiment of the present invention, a two-probe method using a transmission oblique probe and a reception oblique probe is performed.
[0015]
Fig. 5 is a bottom view of the lower mirror part illustrating a transmission oblique probe and a reception oblique probe used for an ultrasonic inspection method of an embodiment of the present invention, and corresponds to a view which is viewed from an arrow V direction in Fig. 6. Fig. 6 is a diagram illustrated by horizontally projecting the transmission oblique probe, the reception oblique probe, an ultrasonic wave transmission path, and an ultrasonic wave reception path onto a vertical section of the lower mirror part taken along the line VI-VI in Fig. 5. Fig. 7 is a view which is viewed from an arrow VII direction (that is, a thickness direction of the lower mirror petal portion 12) in Fig. 6, and illustrates arrangement of the transmission oblique probe and the reception oblique probe on an outer surface of the lower mirror petal portion 12.
[0016] A transmission oblique probe 21 and a reception oblique probe 22 are disposed on the outer surface of the lower mirror petal portion 12 in a substantially V shape with the interference portion interposed therebetween, so as to avoid the interference portion formed of the RIP casing 15 and the R portion 15a in the vicinity thereof. Specifically, a scanning point D of the welding boundary surface 13a is moved in the depth direction of the lower mirror part, and the transmission oblique probe 21 and the reception oblique probe 22 are disposed so that a transmission point Pi of the transmission oblique probe 21 and a reception point P2 of the reception oblique probe 22 are located on an intersection line E ( in the present embodiment, a circle) at which a virtual plane (in the present embodiment, a substantially horizontal plane) including the scanning point D of the welding boundary surface 13a and a normal vector of the welding boundary surface 13a on the scanning point D intersects the outer surface of the lower mirror petal portion 12, and the transmission oblique probe 21 and the reception oblique probe 22 avoid interference with the interference portion of the lower mirror petal portion 12, so as to correspond to the scanning point D of the welding boundary surface 13a.
[0017] A transmission angle θι (refraction angle) of the transmission oblique probe 21 is set so that an ultrasonic wave is transmitted through a transmission path Si in the above-described virtual plane, and a reception angle Θ2 (refraction angle) of the reception oblique probe 22 is set so that the ultrasonic wave is received through a reception path S2 in the virtual plane (details thereof will be described later). Consequently, an ultrasonic wave propagates in the virtual plane perpendicular to the internal defect 17 generated along the welding boundary surface 13a, and thus the amplitude of the ultrasonic wave reflected at the internal defect 17, that is, the amplitude of the ultrasonic wave received by the reception oblique probe 22 can be increased. Therefore, it is possible to detect the internal defect 17 with high sensitivity.
[0018]
The scanning point D of the welding boundary surface 13a is moved in the depth direction of the lower mirror part as follows. A starting point on the outer surface of the lower mirror petal portion 12 onto which the scanning point D of the welding boundary surface 13a is projected in the thickness direction of the lower mirror part is indicated by F, and an opening angle formed between two straight lines Gi and G2 respectively connecting the starting point F to the transmission point Pi of the transmission oblique probe 21 and the reception point P2 of the reception oblique probe 22 is indicated by γ. A position of the starting point F on the outer surface of the lower mirror petal portion 12 is changed in a state in which the opening angle y, the transmission angle θι of the transmission oblique probe 21, and the reception angle Θ2 of the reception oblique probe 22 are maintained to be constant. A gap between the starting point F and the transmission point Pi of the transmission oblique probe 21, and a gap between the starting point F and the reception point P2 of the reception oblique probe 22 are changed, and thus a gap Lpp between the transmission point Pi of the transmission oblique probe 21 and the reception point P2 of the reception oblique probe 22 is changed. Consequently, the scanning point D of the welding boundary surface 13a is moved in the depth direction of the lower mirror part. In the present embodiment, the gap between the starting point F and the transmission point Pi of the transmission oblique probe 21 is substantially the same as the gap between the starting point F and the reception point P2 of the reception oblique probe 22.
[0019]
In the above-described manner, in the ultrasonic inspection method of the present embodiment, it is possible to detect an internal defect with high sensitivity while avoiding interference between the oblique probes and the interference portion of the lower mirror petal portion.
[0020]
Next, a defect detection condition will be described. Fig. 8 is a bottom view of a lower mirror part model for computing a defect detection condition. Fig. 9 is a vertical sectional view of the lower mirror part model taken along the line IX-IX in Fig. 8, and illustrates an example of an application limit depth of the single-probe method. Fig. 10 is a horizontal sectional view of the lower mirror part model taken along the line X-X in Fig. 9, and illustrates a range in which the application limit depth of the single-probe method occurs, that is, a range in which the ultrasonic inspection method (two-probe method) of the present embodiment is to be applied. Fig. 11 is a horizontal sectional view of the lower mirror part model, and is a view for explaining a method of setting an incidence angle and a reflection angle of ultrasonic waves for a defect in the ultrasonic inspection method of the present embodiment. Fig. 12 is a horizontal sectional view of the lower mirror part model, and illustrates an example of an ultrasonic wave one-way propagation distance in the ultrasonic inspection method of the present embodiment. Fig. 13 is a conceptual diagram illustrating positional relationships among the scanning point of the welding boundary surface, and the starting point, the transmission point, and the reception point on the outer surface of the lower mirror petal portion in the ultrasonic inspection method of the present embodiment.
[0021]
In order to obtain a defect detection condition, the lower mirror part is modeled on the basis of representative numerical values of the reactor pressure vessel lower mirror part. In a lower mirror part model illustrated in Fig. 9, the welding boundary surface 13a is assumed to have a radius Rd and a cylindrical shape centering on a vertical central axis 0. The lower mirror petal portion 12 is assumed to have a half apex angle a and a cone strip shape centering on the central axis 0. A vertical central axis of the RIP casing 15 is indicated by 0r, and a horizontal distance (shortest distance) between the central axis 0r and the welding boundary surface 13a is indicated by Lrd.
[0022]
As illustrated in Fig. 9, an inclined angle of the welding boundary surface 13a with respect to the surface of the lower mirror petal portion 12 is a, and thus an inclined angle β of the welding boundary surface 13a with respect to the thickness direction perpendicular to the surface of the lower mirror petal portion 12 is expressed by the following equation (1) .
[0023]
(i) [0024]
In order to determine interference between the interference portion formed of the RIP casing 15 and the R portion 15a in the vicinity thereof and an oblique probe 20 (or 21 or 22) on the basis of a position of a transmission/reception point Po (or the transmission point Pi or the reception point P2) of the oblique probe, a columnar interference region 30 having a radius Ri defined in the following Equation (2) centering on the central axis Or is assumed. Here, Rr is a radius of the RIP casing 15, and ARr is the maximum width of the R portion 15a. Rp is a radius of a virtual spherical plane circumscribing the oblique probe 20 (or 21 or 22) centering on the transmission/reception point Po (or the transmission point Pi or the reception point P2) .
[0025]
(2)
[0026]
If the transmission/reception point Po (or the transmission point Pi or the reception point P2) is present inside the interference region 30, it is determined that the interference portion formed of the RIP casing 15 and the R portion 15a in the vicinity thereof interferes with the oblique probe 20 (or 20 and 21). Thus, it is necessary to set the transmission/reception point Po (or the transmission point Pi or the reception point P2) outside the interference region 30.
[0027]
First, an application range of the single-probe method will be examined. In the single-probe method, as illustrated in Fig. 9, a transmission/reception angle θο of the oblique probe 20 for transmission and reception is set to β so that an ultrasonic wave is incident to the scanning point D of the welding boundary surface 13a in the normal direction (that is, in a direction perpendicular to the internal defect 17 ) . As the scanning point D (that is, the internal defect 17) of the welding boundary surface 13a comes closer to the inner surface of the lower mirror part, the transmission/reception point Po of the oblique probe 20 for transmission and reception is required to be separated from the welding boundary surface 13a. Thus, there is a probability that the transmission/reception point Po of the oblique probe 20 for transmission and reception may enter the interference region 30 in a circumferential range V (specifically, a range interposed between two straight lines respectively connecting the central axis 0 of the lower mirror petal portion 12 to contact points Qi and Q2 on an outer circumference of the interference region 30) of the welding boundary surface 13a illustrated in Fig. 10.
[0028]
For example, in a case where the scanning point D of the welding boundary surface 13a is present on a straight line connecting the central axis 0 of the lower mirror petal portion 12 to the central axis Or of the interference region 30, the following Expression (3) is required to be satisfied as a condition for the transmission/reception point Po of the oblique probe 20 for transmission and reception not entering the interference region 30. Here, W indicates a horizontal distance (shortest distance) between the scanning point D of the welding boundary surface 13a and the above-described intersection line E, and corresponds to a horizontal distance between the welding boundary surface 13a and the transmission/reception point Po of the oblique probe 20 for transmission and reception.
[0029]
(3) [0030]
The horizontal distance W changes depending on a depth
d of the scanning point D of the welding boundary surface 13a, and is expressed by the following Equation (4). Therefore, an application limit depth diim in this case is obtained according to the following Equation (5).
[0031]
(4) [0032]
(5) [0033]
Next, a defect detection condition in the ultrasonic inspection method of the present embodiment will be examined. As described above, it is difficult to apply the single-probe method in the circumferential range V of the welding boundary surface 13a depending on the depth d of the scanning point D of the welding boundary surface 13a, and thus the ultrasonic inspection method (two-probe method) of the present embodiment is applied. Thus, an incidence angle ξΞ (=reflected angle ξε) or the like of an ultrasonic wave to the internal defect 17 in the horizontal direction (skew direction) is set so that the transmission point Pi of the transmission oblique probe 21 and the reception point P2 of the reception oblique probe 22 do not enter the interference region 30 in the circumferential range V of the welding boundary surface 13a.
[0034]
As illustrated in Fig. 11, in a case where the scanning point D of the welding boundary surface 13a is present on the straight line connecting the central axis 0 of the lower mirror petal portion 12 to the contact point Qi (or Q2) on the outer circumference of the interference region 30, the incidence angle ξε required to avoid the interference region 30 becomes the maximum. Therefore, the incidence angle ξε is obtained according to the following Expression (6) which is derived on the basis of positional relationships illustrated in Fig. 11.
[0035]
(6) [0036] A one-way propagation distance LB of an ultrasonic wave (that is, a distance from the transmission point Pi of the transmission oblique probe 21 to the scanning point D of the welding boundary surface 13a, or a distance from the scanning point D of the welding boundary surface 13a to the reception point P2 of the reception oblique probe 22) is obtained according to the following Equation (7) which is derived on the basis of positional relationships illustrated in Fig. 12 (specifically, according to a cosine theorem regarding a triangle ODPi) .
[0037]
¢7) [0038]
The opening angle γ in the above-described probe arrangement is expressed by the following Equation (8) on the basis of positional relationships illustrated in Fig. 13. Here, a point M in Fig. 13 is a midpoint of a line segment connecting the transmission point Pi to the reception point P2, and y in Equation (8) indicates a length of a line segment connecting the starting point F to the midpoint M.
[0039]
(8) [0040]
The gap Lpp between the transmission point Pi and the reception point P2 is expressed by the following Equation (9) on the basis of the positional relationships illustrated in Fig. 13. The length y is expressed by the following Equation (10) on the basis of the positional relationships illustrated in Fig. 13. Therefore, the following Equation (11) is derived from Equations (8) to (10) , and the opening angle γ is obtained according to Equation (11).
[0041]
(9) [0042]
( 1 ο) [0043]
(1 1) [0044]
The transmission angle θι of the transmission oblique probe 21 and the reception angle Θ2 of the reception oblique probe 22 are obtained according to the following Equation (12) which is derived on the basis of the positional relationships illustrated in Fig. 13.
[0045]
¢12) [0046]
The one-way propagation distance Lb of an ultrasonic wave in the above Equation (12) is nearly proportional to the depth d of the scanning point D of the welding boundary surface 13a. Thus, even if the transmission angle θι and the reception angle Θ2 are fixed, the depth d of the scanning point D of the welding boundary surface 13a can be changed. However, in a case where
the one-way propagation distance LB of an ultrasonic wave is the maximum (in other words, in a case where the depth d of the scanning point D of the welding boundary surface 13a becomes a thickness t of the lower mirror petal portion 12), errors of the transmission angle θι and the reception angle Θ2 have great influence on detection sensitivity. Therefore, the transmission angle θι and the reception angle Θ2 are obtained on the basis of the one-way propagation distance Lb of an ultrasonic wave and the depth d of the scanning point D of the welding boundary surface 13a which are obtained by using the above Equations (4) and (7), for example, in a condition in which the depth d of the scanning point D of the welding boundary surface 13a becomes the thickness t of the lower mirror petal portion 12. The above Equation (12) disregards a change in the probe in the normal direction due to a curvature change of the lower mirror petal portion 12, and thus is an approximate expression. However, since a curvature change of the lower mirror petal portion 12 is smooth, the transmission angle θι and the reception angle Θ2 obtained according to Equation (12) can be sufficiently put into practical use.
[0047]
In a case where the inclined angle β of the welding boundary surface 13a with respect to the thickness direction perpendicular to the surface of the lower mirror petal portion 12 is small, it is difficult to transmit an ultrasonic wave in the normal direction of the welding boundary surface 13a. In a case where the inclined angle β of the welding boundary surface 13a is large, the application limit depth dum of the single-probe method, obtained according to the following Equation (5), increases, and thus superiority of the ultrasonic inspection method (two-probe method) of the present embodiment disappears. Thus, taking into consideration the transmission/reception angle θο = 30 degrees to 75 degrees (that is, a = 30 degrees to 75 degrees) generally used in the single-probe method, and the above Equation (1), the inclined angle β of the welding boundary surface 13a is preferably within a range from 15 degrees to 60 degrees.
[0048]
Fig. 14 illustrates results of calculating the incidence angle ξε of an ultrasonic wave to the internal defect 17, the opening angle γin the probe arrangement, and the transmission angle θι and the reception angle Θ2 by using the above Equations (6), (11) and (12), and the like, in a case where the radius Ri of the interference region 30 and the curvature radius Rd of the welding boundary surface 13a are changed for each of three patterns in which the inclined angle β of the welding boundary surface 13a is 15 degrees, 35 degrees, and 60 degrees. In Fig. 14, each of the radius Ri of the interference region 30 and the curvature radius Rd of the welding boundary surface 13a is normalized as a ratio with a reference value Lrd by using the horizontal distance Lrd between the central axis 0r of the RIP casing 15 and the welding boundary surface 13a as the reference value. A ratio (t/Lrd) between the thickness t of the lower mirror petal portion and the reference value Lrd is fixed to 0.5.
[0049]
The inclined angle β of the welding boundary surface 13a in an actual reactor pressure vessel lower mirror part is about 35 degrees, the ratio (Ri/Lrd) between the radius Ri of the interference region 30 and the reference value Lrd is about 0.5 to 0.7, and the ratio (Rd/Lrd) between the curvature radius Rd of the welding boundary surface 13a and the reference value Lrd is about 5. In this condition, the incidence angle ξΞ of an ultrasonic wave is 55 degrees to 73 degrees, the opening angle γ is 122 degrees to 152 degrees, and each of the transmission angle θι and the reception angle Θ2 is 68 degrees to 75 degrees.
[0050]
In relation to reflection of an ultrasonic wave for the internal defect 17 of a steel material (assuming that a longitudinal wave sonic speed is 5.9 km/s, and a transverse wave sonic speed is 3.23 km/s), when taking into consideration that an incidence angle of a transverse wave is about 35 degrees or more, and reflectance of the transverse wave is 100%, it is preferable to use a propagation mode in which the transmission oblique probe 21 transmits the transverse wave to the internal defect 17, and the reception oblique probe 22 receives the transverse wave reflected at the internal defect 17. If the incidence angle ξε of the transverse wave to the internal defect 17 exceeds 80 degrees, there is a probability that the transverse wave from the transmission oblique probe 21 may directly arrive at the reception oblique probe 22 even in a case where the internal defect 17 is not present. Thus, the incidence angle ξε of the transverse wave to the internal defect 17 is preferably equal to or higher than 35 degrees and equal to or lower than 80 degrees.
[0051]
The ratio (Ri/Lrd) between the radius Ri of the interference region 30 and the reference value Lrd is 0.3 to 0.7 as a condition satisfying 35< ξε<80 on the basis of the calculation results illustrated in Fig. 14. Each of the transmission angle θι of the transmission oblique probe 21 and the reception angle Θ2 of the reception oblique probe 22 is equal to or higher than 40 degrees and lower than 90 degrees on the basis of the calculation results illustrated in Fig. 14 .
[0052]
Next, a description will be made of an ultrasonic inspection apparatus for performing the above-described ultrasonic inspection method with reference to Fig. 15. Fig. 15 is a block diagram illustrating a configuration of the ultrasonic inspection apparatus of the present embodiment.
[0053]
The ultrasonic inspection apparatus of the present embodiment includes the above-described transmission oblique probe 21 and reception oblique probe 22; a probe movement mechanism 4 0 which moves the transmission oblique probe 21 and the reception oblique probe 22 along the outer surface of the lower mirror petal portion 12; a transmission/reception device 41 which controls transmission and reception of ultrasonic waves in the transmission oblique probe 21 and the reception oblique probe 22; a control device 42 which controls the probe movement mechanism 40 and the transmission/reception device 41; a computation device 43 which performs various calculation processes; a storage device 44 which records various items of data; a display device 45 which displays various pieces of information on a screen; and an input device 46 via which various conditions are input and various operations are performed. The computation device 43 is formed of a computer, a board mounted with electronic components, or the like, and the storage device 44 is formed of a hard disk, a random access memory (RAM), or the like. The display device 45 is formed of a display, or the like, and the input device 46 is formed of a mouse, a keyboard, a touch panel, buttons, or the like.
[0054]
Although details are not illustrated, the probe movement mechanism 40 includes a probe unit, a circumferential movement mechanism which moves the probe unit in a circumferential direction along the outer surface of the lower mirror petal portion 12, and an axial movement mechanism which moves the probe unit in an axial direction along the outer surface of the lower mirror petal portion 12. The probe unit is provided with a first rail corresponding to the above-described straight line Gi; a first slider mechanism which moves the transmission oblique probe 21 along the first rail; a second rail corresponding to the above-described straight line G2; and a second slider mechanism which moves the reception oblique probe 22 along the second rail. The opening angle γ between the first rail and the second rail is fixed.
[0055]
The probe movement mechanism 40 disposes the transmission oblique probe 21 and the reception oblique probe 22 so that the transmission point Pi of the transmission oblique probe 21 and the reception point P2 of the reception oblique probe 22 are located on the intersection line E at which the virtual plane including the scanning point D of the welding boundary surface 13a and the normal vector of the welding boundary surface 13a on the scanning point D intersects the outer surface of the lower mirror petal portion 12, and the transmission oblique probe 21 and the reception oblique probe 22 avoid interference with the interference portion of the lower mirror petal portion 12, so as to correspond to the scanning point D of the welding boundary surface 13a. The transmission angle θι of the transmission oblique probe 21 is set so that an ultrasonic wave is transmitted through the transmission path Si in the above-described virtual plane, and the reception angle Θ2 of the reception oblique probe 22 is set so that the ultrasonic wave is received through the reception path S2 in the virtual plane.
[0056]
In a case where the scanning point D of the welding boundary surface 13a is moved in the depth direction of the lower mirror part, the probe unit (that is, the starting point F) is moved in the axial direction along the outer surface of the lower mirror petal portion 12. The gap Lpp between the transmission point Pi of the transmission oblique probe 21 and the reception point P2 of the reception oblique probe 22 is changed by moving the transmission oblique probe 21 along the first rail and also moving the reception oblique probe 22 along the second rail. Consequently, the scanning point D of the welding boundary surface 13a is moved in the depth direction of the lower mirror part.
Reference Signs List [0057]
12 LOWER MIRROR PETAL PORTION
13 WELDING PORTION
13a WELDING BOUNDARY SURFACE
15 RIP CASING
15a R PORTION
17 INTERNAL DEFECT
21 TRANSMISSION OBLIQUE PROBE
22 RECEPTION OBLIQUE PROBE 40 PROBE MOVEMENT MECHANISM

Claims (1)

  1. CLAIMS [Claim 1] An ultrasonic inspection method of inspecting a welding portion having a welding boundary surface inclined with respect to a thickness direction perpendicular to a surface of a subj ect, and detecting an internal defect generated along the welding boundary surface by using a transmission oblique probe and a reception oblique probe disposed on the surface of the subject, the method comprising: disposing the transmission oblique probe and the reception oblique probe so that a transmission point of the transmission oblique probe and a reception point of the reception oblique probe are located on an intersection line at which a virtual plane including a scanning point of the welding boundary surface and a normal vector of the welding boundary surface on the scanning point intersects the surface of the subject, and the transmission oblique probe and the reception oblique probe avoid interference with an interference portion of the subject, so as to correspond to the scanning point of the welding boundary surface, moved in a depth direction of the subject; and causing the transmission oblique probe to transmit an ultrasonic wave through a transmission path in the virtual plane, and causing the reception oblique probe to receive the ultrasonic wave through a reception path in the virtual plane. [Claim 2] The ultrasonic inspection method according to claim 1, wherein the scanning point of the welding boundary surface is moved in the depth direction of the subject by maintaining an opening angle, a transmission angle of the transmission oblique probe, and a reception angle of the reception oblique probe to be constant, and changing a position of a starting point on the surface of the subject, and a gap between the transmission point of the transmission oblique probe and the reception point of the reception oblique probe, the starting point being located on the surface of the subject onto which the scanning point of the welding boundary surface is projected in the thickness direction of the subject, and the opening angle being formed between two straight lines respectively connecting the starting point to the transmission point of the transmission oblique probe and the reception point of the reception oblique probe. [Claim 3] The ultrasonic inspection method according to claim 1, wherein an inclined angle of the welding boundary surface with respect to the thickness direction of the subject is within a range from 15 degrees to 60 degrees. [Claim 4] The ultrasonic inspection method according to claim 1, wherein a propagation mode is used in which a transverse wave is transmitted from the transmission oblique probe to the internal defect, and the transverse wave reflected at the internal defect is received by the reception oblique probe, and wherein an incidence angle of the transverse wave to the internal defect is equal to or higher than 35 degrees and equal to or lower than 80 degrees. [Claim 5] The ultrasonic inspection method according to claim 1, wherein each of a transmission angle of the transmission oblique probe and a reception angle of the reception oblique probe is equal to or higher than 40 degrees and lower than 90 degrees . [Claim 6] The ultrasonic inspection method according to claim 1, wherein a welding portion having a welding boundary surface inclined with respect to a thickness direction perpendicular to a surface of a lower mirror petal portion of a reactor pressure vessel is inspected, and an internal defect generated along the welding boundary surface is detected by using a transmission oblique probe and a reception oblique probe disposed on the surface of the lower mirror petal portion. [Claim 7] An ultrasonic inspection apparatus which inspects a welding portion having a welding boundary surface inclined with respect to a thickness direction perpendicular to a surface of a subject, and detects an internal defect generated along the welding boundary surface by using a transmission oblique probe and a reception oblique probe disposed on the surface of the subject, the apparatus comprising: a probe movement mechanism that moves the transmission oblique probe and the reception oblique probe along the surface of the subject, wherein the probe movement mechanism disposes the transmission oblique probe and the reception oblique probe so that a transmission point of the transmission oblique probe and a reception point of the reception oblique probe are located on an intersection line at which a virtual plane including a scanning point of the welding boundary surface and a normal vector from the scanning point intersects the surface of the subject, and the transmission oblique probe and the reception oblique probe avoid interference with an interference portion of the subject, so as to correspond to the scanning point of the welding boundary surface, moved in a depth direction of the subject, wherein a transmission angle of the transmission oblique probe is set so that an ultrasonic wave is transmitted through a transmission path in the virtual plane, and wherein a reception angle of the reception oblique probe is set so that the ultrasonic wave is received through a reception path in the virtual plane. [Claim 8] The ultrasonic inspection apparatus according to claim 7, wherein the probe movement mechanism is configured to maintain an opening angle, the transmission angle of the transmission oblique probe, and the reception angle of the reception oblique probe to be constant, and to change a position of a starting point on the surface of the subject, and a gap between the transmission point of the transmission oblique probe and the reception point of the reception oblique probe, the starting point being located on the surface of the subject onto which the scanning point of the welding boundary surface is projected in the thickness direction of the subject, and the opening angle being formed between two straight lines respectively connecting the starting point to the transmission point of the transmission oblique probe and the reception point of the reception oblique probe.
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