PAUT Inspection Method for Crevice Corrosion Monitoring in HNR Maintenance Department of Operating Nuclear Power Plant

Abstract

The method for inspecting gap corrosion in a repair section according to the present invention comprises, in a PAUT inspection method for monitoring gap corrosion in a repair section of an operating nuclear power plant HNR, the steps of: attaching a scanner to a predetermined location in the head section of the nuclear power plant; setting a scan center around the penetration pipe of the head section; and operating the scanner to move a probe based on the scan center and performing an ultrasonic inspection.

Description

Technology Field

[0001] The present invention relates to a PAUT inspection method for monitoring corrosion in gaps of HNR repair sections in an operating nuclear power plant, and more specifically, to a repair section gap corrosion inspection method that can easily and accurately ultrasonically inspect the internal area of ​​the base material surrounding the gap of a half nozzle repair (HNR) penetration pipe in the head section of an operating nuclear power plant. Background Technology

[0002] Generally, the Control Rod Drive Mechanism (CRDM) of a nuclear power plant's reactor head serves to regulate the plant's electrical output by controlling the nuclear reaction within the reactor through the use of electromagnetic force to extend or retract control rods.

[0003] Control rods are withdrawn or inserted in steps, and to move one step, a series of sequence operations typically consisting of 6 to 7 steps must be performed sequentially. If any of the sequence operations fail to be performed properly mechanically or electrically, the control rod may fail to move or fall down.

[0004] The containment building of a nuclear power plant is installed such that a plurality of penetration pipes pass vertically through the upper head section and the lower head section. The internal flow path of these penetration pipes forms a nozzle through which boric acid flows.

[0005] Boric acid is an important means for controlling the rate of nuclear fission reactions in pressurized water reactors, but it has the property of corroding carbon steel.

[0006] Boric acid flows through the penetration tube of the control rod drive unit (CRDM), and this boric acid can corrode the base material of the head part.

[0007] In particular, Half Nozzle Repair (HNR) technology is a maintenance technique that involves removing only about half of a cooling system's penetration pipe and joining a new nozzle. In this case, a gap is formed between the existing and new penetration pipes to account for thermal expansion; however, since there is a possibility of corrosion occurring in the base material of the head adjacent to this gap, an inspection method is required to easily and accurately monitor such corrosion. Prior art literature

[0008] Registered Patent Publication No. 10-0680482 (Registered on Feb. 1, 2007) The problem to be solved

[0009] The present invention aims to provide a method for inspecting corrosion in a repair gap, which can easily and accurately ultrasonically inspect the internal area of ​​the base material surrounding the gap of a half-nozzle repair (HNR) penetration pipe. means of solving the problem

[0010] The method for inspecting gap corrosion in a repair section according to the present invention for achieving the above objective comprises, in a PAUT inspection method for monitoring gap corrosion in a repair section of an operating nuclear power plant HNR, the steps of: attaching a scanner to a predetermined location in the head section of the nuclear power plant; setting a scan center around the penetration pipe of the head section; and operating the scanner to move a probe based on the scan center and performing an ultrasonic inspection.

[0011] During the ultrasound examination stage, the scanner can perform the ultrasound examination by moving the probe radially around the scan center.

[0012] The ultrasonic inspection step can perform an ultrasonic inspection at every predetermined angle position centered on the scan center and store shape indications as data.

[0013] Ultrasonic inspection can focus on the internal area of ​​the base material of the head section adjacent to the gap formed between the existing penetration tube and the new penetration tube.

[0014] Ultrasonic inspection can determine the presence of corrosion by analyzing signals corresponding to the location of the base material area adjacent to the gap, based on the wall signals of the existing and new penetration pipes, the weld signals of the existing penetration pipes, and the base material clad surface signals of the head section.

[0015] For each of the multiple penetration tubes mounted in the head, the relative installation angle with respect to the head can be stored in advance.

[0016] During the ultrasound examination phase, the scanner may perform the ultrasound examination by moving the transducer circumferentially around the scan center.

[0017] A scanner according to the first embodiment may include a base portion to which three arm portions are combined, an attachment portion each provided at the lower end of the three arm portions and attached to a head portion, a rotary middle portion rotatably coupled to the lower part of the base portion, a guide rail coupled to the lower part of the rotary middle portion, and a probe holder portion mounted to be movable along the guide rail.

[0018] The attachment part is rotatably connected to the lower part of each of the three arm parts and may be equipped with a magnet.

[0019] It may further include an encoder unit installed in the base part to measure the rotation angle of the rotary middle part.

[0020] A scanner according to a second embodiment may include a base portion to which an arm portion is coupled, an attachment portion provided at the lower end of an arm portion and attached to a head portion, a rotary intermediate portion rotatably coupled to the lower end of the base portion, a guide rail coupled below the rotary intermediate portion, and a probe holder portion mounted to be movable along the guide rail.

[0021] The attachment part is rotatably connected to the lower part of one arm and may be equipped with three magnets.

[0022] It may further include an encoder unit installed in the base part to measure the rotation angle of the rotary middle part. Effects of the invention

[0023] According to the corrosion inspection method for gaps in the repair section of the present invention described above, the presence of corrosion in the internal area of ​​the base material surrounding the gap of a half-nozzle repair (HNR) penetration pipe can be easily and accurately inspected using ultrasonics. Brief explanation of the drawing

[0024] Figure 1 is a cross-sectional view showing the lower head section of a nuclear power plant containment building. Figure 2 is a cross-sectional view showing the inspection area around the gap in the HNR repair section of a nuclear power plant. Figure 3 is a cross-sectional view showing the ultrasonic beam in Figure 2. Figure 4 is a conceptual diagram illustrating the PAUT 2-axis inspection method. Figure 5 is a diagram showing the PAUT inspection screen. FIG. 6 is an upper perspective view showing a raster scanner according to a first embodiment of the present invention. FIG. 7 is a downward perspective view showing a raster scanner according to a first embodiment of the present invention. Figures 8 and 9 are conceptual diagrams illustrating scanning by moving a probe radially using a scanner. FIG. 10 is a conceptual diagram showing scanning by moving a probe in a circumferential direction using a scanner. FIG. 11 is an upward perspective view showing a 1-arm scanner according to a second embodiment of the present invention. FIG. 12 is a downward perspective view showing a 1-arm scanner according to a second embodiment of the present invention. Specific details for implementing the invention

[0025] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are illustrated and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0026] The terms used in this invention are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this invention, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that in the accompanying drawings, identical components are indicated by the same reference numerals whenever possible. Furthermore, detailed descriptions of known functions and configurations that may obscure the essence of the present invention will be omitted. For the same reason, some components in the accompanying drawings may be exaggerated, omitted, or schematically depicted.

[0028] FIG. 1 is a cross-sectional view showing the lower head section of a nuclear power plant containment building, FIG. 2 is a cross-sectional view showing the inspection area around the gap in the HNR repair section of a nuclear power plant, FIG. 3 is a cross-sectional view showing the ultrasonic beam in FIG. 2, and FIG. 4 is a conceptual diagram showing the PAUT 2-axis inspection method.

[0029] As shown in FIG. 1, a plurality of penetration pipes (120) are installed in the lower head portion (100) of the nuclear power plant (100) so as to penetrate each other in the vertical direction. The internal flow path of each penetration pipe (120) can form a nozzle (130) through which boric acid flows.

[0030] As shown in FIG. 2, the penetration pipe (120) can be composed of an existing penetration pipe (122) and a new penetration pipe (124) by Half Nozzle Repair (HNR).

[0031] The existing penetration tube (122) and the new penetration tube (124) can be spaced apart by a predetermined distance so that a gap (126) is formed between them to account for thermal expansion.

[0032] The new penetration tube (124) can be welded to form an outer weld (112) surrounding the new penetration tube (124) on a protrusion formed on the outer surface of the head portion (110).

[0033] The existing penetration tube (122) can be welded to the inner surface of the head portion (110) to form an inner weld (114) that surrounds the existing penetration tube (122). An inner clad surface (116) of a predetermined thickness can be coated and formed on the inner surface of the head portion (110). The inner weld (114) can pass through the inner clad surface (116) to form a weld with a J-shaped cross-section.

[0034] The method for inspecting corrosion in a gap of a repair section according to the present invention is a Phased Array Ultrasonic Testing (PAUT) method for monitoring corrosion around a gap (126) of a penetration pipe (120) formed in a repair section of an HNR of a nuclear power plant (100) in operation.

[0035] The method for inspecting corrosion in a repair section according to the present invention includes the steps of attaching a scanner (200, see FIG. 6) to a predetermined location on the head section (110) of a nuclear power plant (100), setting a scan center around the penetration tube (120) of the head section (110), and operating the scanner (200) to move a probe based on the scan center and perform an ultrasonic inspection.

[0036] A scanner (200), as shown in FIG. 6, can be attached to the outer surface of the head portion (110) of the nuclear power plant (100) around the penetration tube (120) so as not to interfere with protruding parts such as the penetration tube (120). As shown in FIG. 3, a probe equipped in the scanner (200) can be movably mounted so as to inject ultrasound toward the gap (126) of the penetration tube (120).

[0037] As shown in FIG. 4, a scan center may be set on one side of the penetration tube (120) on the outer surface of the head portion (110). This scan center may be set as the center position of a probe suitable for ultrasonically inspecting the area around the internal gap (126) of the penetration tube (120) to be inspected.

[0038] Ultrasound examination can be performed by operating the scanner (200) and moving the probe radially around the scan center.

[0039] In the scanner (200), the probe can be rotatably provided so as to be movable in a horizontal direction relative to the outer surface of the head portion (110) and also to adjust the ultrasonic scanning angle.

[0040] As illustrated in FIG. 4, the probe can perform an ultrasonic examination by moving the probe radially inward or outward around the scan center on the outer surface of the head portion (110). At this time, the inner pad (PAD) area including the through tube (120) and the scan center on the outer surface of the head portion (110) becomes a non-scan area, and the area inside the circle surrounding the pad area can become a scan area.

[0041] The ultrasonic inspection step can perform an ultrasonic inspection at every predetermined angle position centered on the scan center and store shape indications as data.

[0042] For example, the scan area on the outer surface of the head portion (110) forms a total of 360 degrees, and the probe can move every 30 degrees around the scan center to perform ultrasonic scanning of the probe radially inward or outward. At this time, when the probe moves and performs ultrasonic scanning, multiple scan images can be stored in memory.

[0043] Ultrasonic inspection can be performed by focusing on the internal area of ​​the base material of the head portion (110) adjacent to the gap (126) formed between the existing penetration tube (122) and the new penetration tube (124).

[0044] In FIG. 2, the internal area of ​​the base material of the head portion (110) adjacent to the gap (126) is indicated as ①. This area ① is a region that is highly likely to be corroded by boric acid flowing into the penetration tube (120). Therefore, inspection can be performed mainly on the area ① inside the base material of the head portion (110) adjacent to the gap (126).

[0045] The gap (126) may vary depending on the total length of the penetration tube (120), but can be formed to be 3.0 to 6.0 mm. At this time, area ① can be an area 20 to 30 mm high on the inner surface of the base material in the longitudinal direction of the penetration tube (120).

[0046] ② The area is the end wall area on the gap (126) between the existing penetration pipe (122) and the new penetration pipe (124).

[0047] ③ The area refers to the inner weld area (114) of the head part (110).

[0048] ④ The area is the inner clad surface (116) area around the inner weld (114) on the inner side of the head portion (110).

[0049] Figure 5 is a diagram showing the PAUT inspection screen.

[0050] Ultrasonic inspection can determine whether corrosion has occurred by observing the signal corresponding to the location of the base material area adjacent to the gap from the wall signal of the existing penetration pipe (122) and the new penetration pipe (124), the weld signal of the existing penetration pipe (122), and the base material clad surface signal of the head part (110).

[0051] In FIG. 5, the wall signals of the existing penetration pipe (122) and the new penetration pipe (124) appear as signals in area ②, the weld signal of the existing penetration pipe (122) appears as signals in area ③, and the signal of the inner clad surface (116) around the inner weld (114) on the inner side of the head part (110) appears as signals in area ④.

[0052] ① The signal in the area may appear when the internal area of ​​the base material of the head part (110) adjacent to the gap (126) is corroded. In FIG. 5, no signal appeared in the area ①, in which case it can be determined that no corrosion occurred in the area ① of FIG. 2.

[0053] It is preferable that the relative installation angle with respect to the head portion (110) is stored in advance for each of the plurality of penetration tubes (120) mounted on the head portion (110).

[0054] The placement angle of the multiple penetration tubes (120) with respect to the plane in contact with the outer surface of the head portion (110) varies depending on the installation location. This is because, since the head portion (110) is in a shape close to a hemisphere, the installation angle of the multiple penetration tubes (120) arranged vertically parallel to each other on the head portion (110) varies depending on the installation location.

[0055] If the relative installation angle of the head portion (110) for each penetration pipe (120) to be inspected is stored in memory in advance, the repair gap corrosion inspection system can easily determine the attachment position of the scanner (200). Thus, the scanner (200) can be quickly and accurately attached to a position adjacent to the specific penetration pipe (120) to be inspected from the head portion (110). Accordingly, the probe mounted on the scanner (200) can be accurately positioned to face the gap (126) of the penetration pipe (120).

[0056] FIG. 6 is an upward perspective view showing a raster scanner according to a first embodiment of the present invention, and FIG. 7 is a downward perspective view showing a raster scanner according to a first embodiment of the present invention.

[0057] A scanner (200) according to the first embodiment may include a base part (210) to which three arm parts (240) are combined, an attachment part (250) which is provided at the lower end of each of the three arm parts and attached to a head part (110), a rotary middle part (220) which is rotatably coupled to the lower part of the base part, a guide rail (230) which is coupled to the lower part of the rotary middle part, and a probe holder part (260) which is mounted so as to be movable along the guide rail.

[0058] The scanner (200) of this first embodiment can be called a raster scanner.

[0059] The base portion (210) is formed in the shape of a circular disc, and can be formed by combining a small diameter portion and a large diameter portion.

[0060] The three arm portions (240) can be joined by a plurality of bolts fastened to the upper surface of the large diameter portion of the base portion (210). The three arm portions (240) can be arranged at intervals of 120 degrees from each other. The three arm portions (240) may have an extension portion extending downward from the lower surface of the extended end.

[0061] The attachment part (250) is rotatably connected to the lower part of each of the three arm parts (240) and may be equipped with a magnet. Since the attachment part (250) is equipped with a magnet, the scanner (200) can be easily attached to or detached from the outer surface of the head part (110). In addition, since the outer surface of the head part (110) is a convex curved surface, the attachment part (250) can be mounted in close contact with the outer surface of the head part (110) by rotatably connecting the attachment part (250) to the arm part (240).

[0062] The rotary intermediate part (220) can be rotatably coupled to the lower surface of the base part (210). Additionally, the rotary intermediate part (220) may perform translational motion relative to the lower surface of the base part (210).

[0063] The guide rail (230) is coupled to a slider that moves translationally below the rotary middle section (220) and can move translationally together.

[0064] The probe holder portion (260) can be mounted so as to be movable along the guide rail (230). The probe holder portion (260) may be equipped with a motor that drives it to move along the guide rail (230). A probe can be detachably coupled to the probe holder portion (260). The probe holder portion (260) can be rotatably connected to a coupling portion that is slidably coupled to the guide rail (230). Thus, the probe can not only be moved relative to the outer surface of the head portion (110) but also the ultrasonic irradiation angle can be adjusted.

[0065] The scanner (200) may further include an encoder part (270) installed in the base part (210) to measure the rotation angle of the rotary intermediate part (220).

[0066] The encoder unit (270) is installed on one side of the large diameter portion of the base unit (210) and can measure the relative rotation angle position of the rotary intermediate portion (220) in real time. Based on the measurement value of this encoder unit (270), the position of the probe and the ultrasonic irradiation angle can be accurately adjusted in the scanner (200).

[0067] Figures 8 and 9 are conceptual diagrams illustrating scanning by moving a probe radially using a scanner.

[0068] First, as shown in FIG. 8, the rotary middle section (220) of the scanner can be positioned below the through tube (120), and the guide rail (230) can be positioned to the right of the rotary middle section (220).

[0069] The probe holder portion (260) equipped with the probe moves along the guide rail (230), and at the same time, the guide rail (230) can be rotated relative to the rotary middle portion (220). Accordingly, the probe scans while moving radially in the right area of ​​the scan center and can scan up to the rear area of ​​the penetration tube (120).

[0070] Next, as shown in FIG. 9, the rotary middle section (220) of the scanner can be positioned below the through tube (120), and the guide rail (230) can be positioned to the left of the rotary middle section (220).

[0071] The probe holder portion (260) equipped with the probe moves along the guide rail (230), and at the same time, the guide rail (230) can be rotated relative to the rotary middle portion (220). Accordingly, the probe scans while moving radially in the left area of ​​the scan center and can scan up to the rear area of ​​the penetration tube (120).

[0072] FIG. 10 is a conceptual diagram showing scanning by moving a probe in a circumferential direction using a scanner.

[0073] As illustrated in FIG. 10, during the ultrasonic examination step, the scanner may perform the ultrasonic examination by moving the probe circumferentially around the scan center.

[0074] As described above, the probe holder portion (260) equipped with the probe moves along the guide rail (230), and at the same time, the guide rail (230) can be rotated relative to the rotary intermediate portion (220). Accordingly, the probe can scan at predetermined angles while moving circumferentially on concentric circles centered on the scan center. The angle range relative to the scan center of the arc formed by the path along which the probe moves may all be the same, but the angle of some paths may be set differently from the angle of other paths.

[0075] In this case, the scanner attached to a predetermined position of the head unit (110) may scan while changing its attachment position.

[0076] FIG. 11 is an upward perspective view showing a single-arm scanner according to a second embodiment of the present invention, and FIG. 12 is a downward perspective view showing a single-arm scanner according to a second embodiment of the present invention.

[0077] A scanner (300) according to a second embodiment may include a base part (310) to which an arm part (340) is coupled, an attachment part (350) provided at the lower end of the arm part and attached to a head part (110), a rotary middle part (320) rotatably coupled to the lower end of the base part, a guide rail (330) coupled to the lower end of the rotary middle part, and a probe holder part (360) mounted to be movable along the guide rail.

[0078] In the second embodiment, the scanner (300) has one arm (340) coupled to the base part (310), so the scanner (300) of the second embodiment can be called a 1-arm scanner.

[0079] The base portion (310) is formed in the shape of a circular disc, and can be formed by combining a small diameter portion and a large diameter portion.

[0080] One arm (340) can be joined by a plurality of bolts fastened to the upper surface of the large diameter portion of the base portion (310). One arm (340) may have an extension portion extending downward from the lower surface of the extended end.

[0081] Since a plurality of parts, such as a plurality of through tubes (120), are arranged in the head portion (110), there may be cases where the scanner (200) of the first embodiment having three arm portions (240) cannot be installed without interfering with other parts. In such cases, the scanner (300) of the second embodiment having one arm portion (340) can be installed appropriately without interfering with other parts to perform an ultrasonic inspection.

[0082] The attachment part (350) is rotatably connected to the lower part of one arm part (340) and may be equipped with three magnets. Since the outer surface of the head part (110) is a convex curved surface, by rotatably connecting the attachment part (350) to the arm part (340), the attachment part (350) can be mounted in close contact with the outer surface of the head part (110). In addition, the scanner (300) of the second embodiment is equipped with one arm part (340), but since the attachment part (350) is equipped with three magnets, the scanner (300) can be easily and stably attached to or detached from the outer surface of the head part (110).

[0083] The rotary intermediate part (320) can be rotatably coupled to the lower surface of the base part (310). Additionally, the rotary intermediate part (320) can perform translational motion relative to the lower surface of the base part (310).

[0084] The guide rail (330) is coupled to a slider that moves translationally below the rotary middle section (320) so that they can move translationally together.

[0085] The probe holder portion (360) can be mounted so as to be movable along the guide rail (330). The probe holder portion (360) may be equipped with a motor that drives it to move along the guide rail (330). A probe can be detachably coupled to the probe holder portion (360). The probe holder portion (360) can be rotatably connected to a coupling portion that is slidably coupled to the guide rail (330). Thus, the probe can not only be moved relative to the outer surface of the head portion (110) but also the ultrasonic irradiation angle can be adjusted.

[0086] The scanner (300) may further include an encoder part (370) installed in the base part (310) to measure the rotation angle of the rotary intermediate part (320).

[0087] The encoder unit (370) is installed on one side of the large diameter portion of the base unit (310) and can measure the relative rotation angle position of the rotary intermediate portion (320) in real time. Based on the measurement value of this encoder unit (370), the position of the probe and the ultrasonic irradiation angle can be accurately adjusted in the scanner (300).

[0088] According to the corrosion inspection method for gaps in a repair section of the present invention, the presence of corrosion in the internal area of ​​the base material surrounding the gap of a half-nozzle repair (HNR) penetration pipe can be easily and accurately inspected using ultrasonics.

[0089] Although an embodiment of the present invention has been described above, those skilled in the art may modify and change the present invention in various ways by adding, changing, deleting, or adding components, etc., without departing from the spirit of the present invention as described in the claims, and such modifications and changes are also to be considered to be included within the scope of the rights of the present invention. Explanation of the symbols

[0090] 100: Nuclear power plant 110: Head section 112: External weld 114: Inner weld 116: Inner clad surface 120: Penetrating tube 122: Existing penetration pipe 124: New Penetrating Pipe 126: Gaps 130: Nozzle 200: Raster Scanner 210: Bass section 220: Rotary middle section 230: Guide rail 240: Dark part 250: Attachment 260: Probe holder part 270: Encoder section 300: 1-arm scanner 310: Bass section 320: Rotary middle section 330: Guide rail 340: Dark part 350: Attachment 360: Probe holder section 370: Encoder section

Claims

Claim 1 A PAUT inspection method for monitoring gap corrosion in a maintenance section of an operating nuclear power plant, comprising the steps of: attaching a scanner to a predetermined location in the head section of the nuclear power plant; setting a scan center around the penetration pipe of the head section; and operating the scanner to move a probe based on the scan center and performing an ultrasonic inspection. Claim 2 A method for inspecting corrosion in a repair gap according to claim 1, wherein, in the ultrasonic inspection step, the scanner moves the probe radially around the scan center and performs an ultrasonic inspection. Claim 3 A method for inspecting corrosion in gaps of a repair part, wherein, in paragraph 2, the ultrasonic inspection step is characterized by performing an ultrasonic inspection at each predetermined angle position centered on the scan center and storing the shape indication as data. Claim 4 A method for inspecting corrosion in a repair gap according to claim 1, characterized in that the ultrasonic inspection is performed by focusing on the internal area of ​​the base material of the head part adjacent to the gap formed between the existing penetration pipe and the new penetration pipe. Claim 5 A method for inspecting corrosion in a repair gap according to claim 4, wherein the ultrasonic inspection determines whether corrosion is present by observing a signal corresponding to the location of the base material area adjacent to the gap from the existing penetration pipe and new penetration pipe wall signals, the welded part signal of the existing penetration pipe, and the base material clad surface signal of the head part. Claim 6 A method for inspecting corrosion in gaps of a repair section, characterized in that, in paragraph 4, the relative installation angle with respect to the head section is stored in advance for each of the plurality of penetration tubes mounted on the head section. Claim 7 A method for inspecting corrosion in a repair gap according to claim 1, wherein, in the ultrasonic inspection step, the scanner moves the probe in a circumferential direction around the scan center and performs an ultrasonic inspection. Claim 8 A method for inspecting corrosion in a repair gap according to claim 4, wherein the scanner comprises a base portion to which three arm portions are combined, an attachment portion each provided at the lower end of the three arm portions and attached to the head portion, a rotary intermediate portion rotatably coupled to the lower part of the base portion, a guide rail coupled below the rotary intermediate portion, and a probe holder portion mounted to be movable along the guide rail. Claim 9 A method for inspecting corrosion in gaps of a repair part, characterized in that, in claim 8, the attachment part is rotatably connected to the lower end of each of the three arm parts and is equipped with a magnet. Claim 10 A method for inspecting corrosion in a repair gap according to claim 8, further comprising an encoder unit installed in the base part to measure the rotation angle of the rotary intermediate part. Claim 11 A method for inspecting corrosion in a repair gap according to claim 4, wherein the scanner comprises a base portion to which a single arm portion is coupled, an attachment portion provided at the lower end of the single arm portion and attached to the head portion, a rotary intermediate portion rotatably coupled to the lower end of the base portion, a guide rail coupled below the rotary intermediate portion, and a probe holder portion mounted to be movable along the guide rail. Claim 12 A method for inspecting corrosion in a repair gap according to claim 11, characterized in that the attachment part is rotatably connected to the lower end of the one arm part and is equipped with three magnets. Claim 13 A method for inspecting corrosion in a repair gap according to claim 11, further comprising an encoder unit installed in the base part to measure the rotation angle of the rotary intermediate part.

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