Patent Publication Number: US-2022236232-A1

Title: Ultrasonic inspection device and inspection method

Description:
TECHNICAL FIELD 
     The present disclosure relates to an ultrasonic inspection device and an inspection method. 
     BACKGROUND ART 
     Turbine rotors of steam turbines in power plants are operated under high-temperature conditions. Therefore, SCC (stress corrosion cracking) may occur at sites that receive stresses when the turbine rotors are used for long periods of time. Since large stresses act on blade groove portions of rotor discs where blade root portions of moving blades are embedded, in particular, SCC is likely to occur. Non-destructive inspection of SCC occurring at the blade groove portions is thus conducted. As a method of the non-destructive inspection for the blade groove portions, an ultrasonic flaw detection method may satisfactorily be applied in terms of versatility and on-site workability. 
     Patent Literature 1 describes an ultrasonic inspection apparatus for ultrasonically inspecting a blade embedded portion of a rotor disc. The device includes a probe and a carriage for relatively moving the probe in a circumferential direction of the rotor disc along the rotor disc. The carriage includes a plurality of rotor disc traveling rollers for traveling on a disc surface of the rotor disc, a plurality of rotor shaft traveling rollers for traveling on a circumferential surface of a rotor shaft provided concentrically with the rotor disc, a holder assembly that includes a holder for holding the probe in a state in which the probe faces the disc surface, and at least one guide rail for guiding the holder in a radial direction of the rotor shaft. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] Japanese Unexamined Patent Application, Publication No. 2016-206049 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     A disc surface of a large-sized turbine rotor is provided with a flange such that a steam flow from a rotor blade is caused to efficiently flows toward a stationary blade (casing). Therefore, a portion where the flange projecting from the other regions serves as a narrow portion with a narrow gap from an adjacent disc. The device in Patent Literature 1 includes the carriage for causing the probe to move in the circumferential direction of the disc and is thus relatively large. Therefore, there is a probability that traveling of the probe in the circumferential direction becomes unstable at the narrow portion for some reasons such as an interference between the ultrasonic inspection device and the adjacent turbine rotor. 
     Also, in a case in which flaw detection is performed on the blade groove portion from the disc surface where the flange is provided in ultrasonic inspection, it is necessary to dispose the ultrasonic probe on the curved surface of the flange. According to the device in Patent Literature 1, the disposition on the curved surface of the flange is not taken into consideration, and there is thus a probability that the ultrasonic wave cannot effectively be incident because for example, it is not possible to physically dispose an device with the ultrasonic probe set thereon between discs of the turbine rotors, or because an air layer or the like is formed between the ultrasonic probe and the curved disc surface, in a case in which the flaw detection is performed on the blade groove portion from the curved surface of the flange of the disc surface. 
     Also, according to the device in Patent Literature 1, it is necessary to prepare a probe with an element alignment following the curved shape in accordance with the shape (curvature) of the curved portion or a wedge or the like that serves as an intermediate medium for causing an ultrasonic wave to be incident on the curved surface from elements typically smoothly aligned in order to cause ultrasonic waves to be focused on a blade groove range that serves as a flaw detection region when the flaw detection is performed from the curved disc surface in the ultrasonic inspection. Therefore, it is not possible to use the elements for several purposes, and preparation for the inspection may become complicated. 
     From such viewpoints, there is a probability that the device in Patent Literature 1 cannot suitably inspect the large-size turbine rotor in which the disc surface of the turbine rotor is curved. 
     The present disclosure was made in view of such circumstances, and an object thereof is to provide an ultrasonic inspection device and an inspection method capable of suitably inspecting a large-sized turbine rotor in which a disc surface of the turbine rotor is curved. 
     Solution to Problem 
     In order to solve the aforementioned problem, an ultrasonic inspection device and an inspection method according to the present disclosure employ the following means. 
     An ultrasonic inspection device according to a first aspect of the present disclosure is an ultrasonic inspection device for ultrasonically inspecting a rotor disc, the device including: an ultrasonic probe that transmits an ultrasonic wave to a disc surface of the rotor disc; a holding portion that movably holds the ultrasonic probe relative to the disc surface of the rotor disc; a moving portion that causes the ultrasonic probe to move in a direction that intersects a radial direction of the rotor disc; an adjustment portion that adjusts a moving direction of the moving portion; a position detecting portion that detects a radial position of the ultrasonic probe being held relative to the disc surface; and a control portion that controls the adjustment portion on the basis of information detected by the position detecting portion such that the radial position of the ultrasonic probe fails within a predetermined range. 
     In the aforementioned configuration, the ultrasonic probe is movably held relative to the disc surface of the rotor disc, and the ultrasonic probe is moved by the moving portion. In this manner, the ultrasonic inspection device travels on the disc surface of the rotor disc. Also, in the aforementioned configuration, the control portion controls the adjustment portion such that the radial position of the ultrasonic probe falls within the predetermined range. It is thus possible to cause the radial position of the ultrasonic probe to fall within the predetermined direction when the ultrasonic probe moves in the direction that intersects the radial direction of the rotor disc. In other words, it is possible to cause the ultrasonic probe to move in the circumferential direction while maintaining the predetermined radial position. 
     In this manner, in the aforementioned configuration, the ultrasonic inspection device can travel in the circumferential direction on the disc surface of the rotor disc. As compared with a configuration in which a carriage and the like secured to a rotor shaft, for example, is provided to fix the radial position of the ultrasonic probe, the ultrasonic inspection device can be reduced in size by not being provided with the carriage and the like. It is thus possible to easily mount the ultrasonic inspection device on the disc surface of the rotor disc even in a case of a rotor disc at a short distance from an adjacent rotor disc, like a large-sized rotor disc, for example. 
     Also, the ultrasonic inspection device according to the first aspect of the present disclosure may include a drive portion that drives the moving portion. 
     In the aforementioned configuration, the ultrasonic inspection device includes the drive portion that drives the moving portion. In this manner, there is no need to obtain power from outside, and the ultrasonic inspection device can travel by itself on the disc surface of the rotor disc. Therefore, wiring of a power line is not needed, and it is possible to secure a degree of freedom in movement of the ultrasonic inspection device, as compared with a structure in which the ultrasonic inspection device obtains power from the outside. 
     Also, since the ultrasonic inspection device travels by itself, and there is no need for an operator to manually move the ultrasonic inspection device, it is also possible to apply the ultrasonic inspection device to inspection of a large- sized rotor disc that some portion of which is difficult for the operator to reach. 
     In addition, the ultrasonic inspection device according to the first aspect of the present disclosure may include a magnet that sticks to the disc surface, and the magnet may be separated from the disc surface. 
     In the aforementioned configuration, the magnet is separated from the disc surface. It is thus possible to reduce a traveling resistance when the ultrasonic inspection device moves. 
     Moreover, the ultrasonic inspection device according to the first aspect of the present disclosure may include a moving distance detecting portion that detects a distance of the movement caused by the moving portion. 
     The aforementioned configuration includes the moving distance detecting portion that detects the distance of the movement. It is thus possible to grasp the position of the ultrasonic inspection device in the circumferential direction. Therefore, it is possible to associate an inspection result of the ultrasonic probe and the position in the circumferential direction. Accordingly, it is possible to specify the position of a damage that has occurred in the rotor disc. 
     An ultrasonic inspection device according to a second aspect of the present disclosure is an ultrasonic inspection device for ultrasonically inspecting a rotor disc, the device including: an ultrasonic probe that transmits an ultrasonic wave to a disc surface of the rotor disc; a probe-side holder to which the ultrasonic probe is secured; a deformation portion that is provided between the ultrasonic probe and the disc surface, allows the ultrasonic wave to pass therethrough, and is deformable by being pressed against the disc surface; a rotor disc-side holder that includes a sticking portion sticking to the disc surface, is provided closer to the rotor disc than the probe-side holder, and holds the deformation portion; and a biasing portion that biases the probe-side holder toward the rotor disc. 
     The aforementioned configuration includes the deformation portion that is deformed by being pressed against the rotor disc between the ultrasonic probe and the rotor disc. In this manner, the deformation portion is deformed in accordance with the surface of the rotor disc by the deformation portion being pressed against the rotor disc, an air layer between the ultrasonic probe and the rotor disc is thus removed, and it is possible to suitably deliver the ultrasonic wave from the ultrasonic probe to the rotor disc. Therefore, it is also possible to suitably inspect a rotor disc with a curved disc surface such as a large-sized rotor disc, for example, by causing the deformation portion to be deformed. 
     Also, in the aforementioned configuration, the deformation portion changes in accordance with the curved form of the disc surface, and it is thus possible to remove the air layer in any curved form. Therefore, the curved form of the disc surface that is an inspection target may change in accordance with movement in a case in which the ultrasonic inspection device moves, for example. Even in such a case, the deformation portion changes in accordance with a change in curved form of the disc surface. Therefore, it is possible to suitably perform inspection while causing the ultrasonic inspection device to move. 
     Also, in the aforementioned configuration, the probe-side holder is biased toward the rotor disc by the biasing portion. In this manner, it is possible to press the deformation portion against the rotor disc via the probe-side holder. Therefore, it is possible to more suitably press the deformation portion against the rotor disc. Accordingly, it is possible to more suitably cause the deformation portion to be deformed in accordance with the disc surface of the rotor disc and to remove the air layer. 
     Also, the ultrasonic inspection device according to the second aspect of the present disclosure may further include an angle adjustment portion that changes an angle of the ultrasonic probe relative to the disc surface. 
     The aforementioned configuration includes the angle adjustment portion that changes the angle of the ultrasonic probe relative to the disc surface of the rotor disc. It is thus possible to appropriately transmit the ultrasonic wave to a target location (inspection target location) through the adjustment cf the angle of the ultrasonic probe. 
     An ultrasonic inspection device according to a third aspect of the present disclosure is an ultrasonic inspection device for ultrasonically inspecting a rotor disc, the device including: a first ultrasonic probe that transmits an ultrasonic wave to a disc surface of the rotor disc; a second ultrasonic probe that transmits the ultrasonic wave to the disc surface and is provided to be adjacent to the first ultrasonic probe; a first inclination means that causes the first ultrasonic probe to be inclined on an opposite side of the second ultrasonic probe; and a second inclination means that causes the second ultrasonic probe to be inclined on an opposite side of the first ultrasonic probe. 
     The aforementioned configuration includes the first inclination means that causes the first ultrasonic probe to be inclined on the opposite side of the second ultrasonic probe and the second inclination means that causes the second ultrasonic probe to be inclined on the opposite side of the first ultrasonic probe. It is thus possible to cause an ultrasonic wave transmitted from the first ultrasonic probe and an ultrasonic wave transmitted from the second ultrasonic probe to be focused inside the rotor disc by transmitting the ultrasonic waves from the first ultrasonic probe and the second ultrasonic probe in the state in which the first ultrasonic probe and the second ultrasonic probe are inclined. Also, it is possible to adjust the depth of the focusing position of the ultrasonic waves (the distance from the disc surface of the rotor disc) through the adjustment of the inclination angles. Therefore, it is possible to cause the ultrasonic waves to be focused at a desired position through the adjustment of the first ultrasonic probe and the second ultrasonic probe in accordance with the shape of the curved portion even in a case of a turbine with a curved disc surface such as a large-sized rotor disc, for example. Accordingly, it is possible to easily perform inspection because there is no need to prepare an element and the like with a refraction angle calculated in accordance with the shape (curvature) of the curved portion. 
     Also, it is possible to locate the focusing position of the ultrasonic waves on the first ultrasonic probe or on the second ultrasonic probe by setting the inclination angle of the first ultrasonic probe and the inclination angle of the second ultrasonic probe to be different inclination angles. In other words, in a case in which the inclination angle of the first ultrasonic probe is set to be larger than the inclination angle of the second ultrasonic probe, the focusing position of the ultrasonic waves is located on the second ultrasonic probe. On the contrary, in a case in which the inclination angle of the second ultrasonic probe is set to be larger than the inclination angle of the first ultrasonic probe, the focusing position of the ultrasonic waves is located on the first ultrasonic probe. It is thus possible to cause the ultrasonic waves to be focused in a wider range. 
     An inspection method according t.o a first aspect of the present disclosure is an inspection method for ultrasonically inspecting a rotor disc using the ultrasonic inspection device according to the aforementioned first aspect, the method including: an ultrasonic wave transmission process of transmitting an ultrasonic wave from the ultrasonic probe to the disc surface of the rotor disc; a holding process of movably holding the ultrasonic probe relative to the disc surface, by the holding portion; a moving process of causing the ultrasonic probe to move in a direction that intersects the radial direction of the rotor disc, by the moving portion; an adjustment process of adjusting a moving direction of the moving portion, by the adjustment portion; a position detecting process of detecting a radial position of the ultrasonic probe being held relative to the disc surface, by the position detecting portion; and a control process of controlling the adjustment portion on the basis of information detected in the position detecting process, by the control portion such that the radial position of the ultrasonic probe fails within a predetermined range. 
     In the aforementioned configuration, it is possible to inspect the rotor disc while causing the ultrasonic inspection device to travel in the circumferential direction on the disc surface of the rotor disc. It is thus possible to reduce the size of the ultrasonic inspection device corresponding to non- provision of a carriage and the like as compared with a configuration in which the radial position of the ultrasonic probe is fixed, by providing the carriage and the like secured to a rotor shaft, for example. It is thus possible to easily mount the ultrasonic inspection device or. the disc surface of the rotor disc and to easily perform the inspection even in a case of a rotor disc at a short distance from an adjacent rotor disc, like a large-sized rotor disc, for example. 
     In the inspection method according to the first aspect of the present disclosure, in the holding process, the ultrasonic probe may be held relative to a curved surface of the disc surface. 
     In the aforementioned configuration, it is possible to cause the ultrasonic probe to be held on the curved surface of the rotor disc. 
     Also, the inspection method according to the first aspect of the present disclosure may include: a recording process of recording inspection data obtained by the ultrasonic wave transmitted from the ultrasonic probe; and a determination process of determining whether or not the rotor disc has been damaged on the basis of the inspection data recorded in the recording process. 
     In the aforementioned configuration, it is possible to suitably determine whether or not the rotor disc has been damaged. 
     Advantageous Effects of Invention 
     It is possible to suitably inspect a large-sized turbine rotor in which a disc surface of the turbine rotor is curved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a vertical sectional view of a turbine rotor and a rotor blade according to an embodiment of the present disclosure. 
         FIG. 2  is a view of a disc surface of a rotor disc according to the embodiment of the present disclosure when seen from a front side. 
         FIG. 3  is a top view of the rotor disc according to the embodiment of the present disclosure. 
         FIG. 4  is a schematic perspective view of an ultrasonic inspection device according to the embodiment of the present disclosure. 
         FIG. 5  is a side view of the ultrasonic inspection device in  FIG. 4 . 
         FIG. 6  is a perspective view of the ultrasonic inspection device according to the embodiment of the present disclosure. 
         FIG. 7  is a perspective view of the ultrasonic inspection device according to the embodiment of the present disclosure and is a diagram illustrating a state in which the ultrasonic inspection device is mounted on the rotor disc. 
         FIG. 8  is a block diagram of a control device according to the embodiment of the present disclosure. 
         FIG. 9  is a perspective view of an inspecting portion according to the embodiment of the present disclosure. 
         FIG. 10  is a perspective view of the inspecting portion according to the embodiment of the present disclosure and is a diagram in which an arm portion is emitted. 
         FIG. 11  is a perspective view of the inspecting portion according to the embodiment of the present disclosure and is a diagram in which the arm portion and an angle adjustment portion are omitted. 
         FIG. 12  is a perspective view illustrating a section of the inspecting portion according to the embodiment of the present disclosure. 
         FIG. 13  is a schematic diagram illustrating a second magnet and a rolling roller provided at the inspecting portion according to the embodiment of the present disclosure. 
         FIG. 14  is a schematic side view of the inspecting portion according to the embodiment of the present disclosure. 
         FIG. 15A  is a schematic diagram illustrating an inclination adjustment mechanism according to the embodiment of the present disclosure. 
         FIG. 15B  is a schematic diagram illustrating the inclination adjustment mechanism according to the embodiment of the present disclosure. 
         FIG. 15C  is a schematic diagram illustrating the inclination adjustment mechanism according to the embodiment of the present disclosure. 
         FIG. 15D  is a schematic diagram illustrating the inclination adjustment mechanism according to the embodiment of the present disclosure. 
         FIG. 16A  is a schematic diagram illustrating a modification of  FIG. 15A . 
         FIG. 16B  is a schematic diagram illustrating the modification of  FIG. 15A . 
         FIG. 16C  is a schematic diagram illustrating the modification of  FIG. 15A . 
         FIG. 17  is a schematic side view of the inspecting portion according to the embodiment of the present disclosure. 
         FIG. 18  is a flowchart illustrating an inspection method according to the embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of an ultrasonic inspection device and an inspection method according to the present disclosure will be described with reference to the drawings. Note that in the following description, the radial direction of a rotor disc will also be referred to as an X direction, the plate thickness direction of the rotor disc will also be referred to as a Y direction, and a tangential direction of the rotor disc (the direction that perpendicularly intersects the X direction and the Y direction) will also be referred to as a Z direction. 
       FIG. 1  is a vertical sectional view of a steam turbine. As illustrated in  FIG. 1 , a steam turbine  1  includes a turbine rotor  2  and a moving blade  3  secured to the turbine rotor  2 . The turbine rotor  2  includes a rotor shaft  4  and a plurality of rotor discs  5  provided concentrically with the rotor shaft  4 . The rotor discs  5  include a plurality of blade groove portions  6  with outer circumferential portions to which the moving blade  3  is fitted, as illustrated in  FIG. 2 . 
     An ultrasonic inspection device  100  according to the present embodiment is an device that is attached to a disc surface  5   a  of each rotor disc  5  to ultrasonically inspect the blade groove portion  6  as illustrated in  FIG. 1 . Specifically, the ultrasonic inspection device  100  is an device that inspects whether or not a damage such as SCC (stress corrosion cracking) has occurred in the blade groove portion  6  by transmitting an ultrasonic wave toward the blade groove portion  6 . In the present embodiment, an example in which a large-sized rotor disc  5  is defined as an inspection target from among the plurality of rotor discs  5  will be described. 
     As illustrate in  FIG. 1 , the disc surface  5   a  of the large-sized rotor disc  5  is not a flat surface. Specifically, the disc surface  5   a  is curved in the radius direction of the rotor disc  5 , is also curved in the circumferential direction of the rotor disc  5 , and has a two-dimensional curved surface shape. A simple expression of the “radial direction” in the following description means the radial direction of the rotor disc  5 . Also, a simple expression of the “circumferential direction” means the circumferential direction of the rotor disc  5 . Moreover, the curve of the disc surface  5   a  in the radial direction will also be referred to as a “small diameter R”, and the curve in the circumferential direction will also be referred to as a “large diameter R”. 
     As illustrated in  FIG. 2 , each blade groove portion  6  formed in the rotor disc  5  is a groove recessed from an outer circumferential surface of the rotor disc  5  and is a so-called side entry-type groove extending from the disc surface  5   a  on one side toward the disc surface  5   a  on the other side of the rotor disc  5 . Such a side entry-type groove requires identification between intermittent shape reflection echoes and cracking reflection echoes appearing in accordance with groove pitches worked in the circumferential direction, it is more difficult to perform inspection as compared with a groove extending in the circumferential direction. 
     Also, each blade groove portion  6  is a so-called skewed- type groove formed such that a linear groove is inclined relative to the plate thickness direction as illustrated in  FIG. 3 . The plurality of blade groove portions  6  are formed to be aligned at predetermined intervals in the circumferential direction. The moving blade  3  is a side entry-type moving blade including a blade root portion with a so-called Christmas tree shape. 
     Note that the shape of each blade groove portion  6  is not limited to the shape in the above description. For example, each blade groove portion  6  may be formed to be curved along the plate thickness direction (Y direction) or may be formed in parallel with the plate thickness direction (Y direction). 
     The ultrasonic inspection device  100  is attached to the curved surface which is closer to the rotor shaft  4  than a projecting portion formed between the blade groove portion  6  and the rotor shaft  4  and projecting from the disc surface  5   a , as illustrated in  FIG. 1 . Also, the ultrasonic inspection device  100  moves on the disc surface  5   a  of the rotor disc  5  in the circumferential direction of the rotor disc  5  as illustrated in  FIG. 2  as will be described later in detail (see the arrow in  FIG. 2 ). 
     [Ultrasonic Inspection Device] 
     Next, details of the ultrasonic inspection device  100  will be described using  FIGS. 4 to 8 . 
     The ultrasonic inspection device  100  includes an inspecting portion  10  that transmits an ultrasonic wave, a plurality of first magnets (holding portions)  11  that movably hold the inspecting portion  10  relative to the disc surface  5   a  of the rotor disc  5 , a drive wheel (moving portion)  12  that causes the inspecting portion  10  to move in a direction that intersects the radial direction of the rotor disc  5 , a steering wheel (adjustment portion)  13  that adjusts a traveling direction of the drive wheel  12 , two stroke sensors (position detecting portions)  14  that detect the position of the inspecting portion  10 , which is held relative to the disc surface  5   a , in the radial direction, and a control device (control portion)  15  that controls the steering wheel  13  on the basis of information detected by the stroke sensor  14 , as illustrated in  FIGS. 4 and 5 . The ultrasonic inspection device  100  detects data (UT data) in the entire region in the circumferential direction of the rotor disc  5  using the inspecting portion  10  while traveling on the rotor disc  5  in the circumferential direction using the drive wheel  12  and the like. 
     Also, the ultrasonic inspection device  100  includes a drive wheel support portion  16  that supports the drive wheel  12  and a steering wheel support portion  17  that supports the steering wheel  13 . The drive wheel support portion  16  and the steering wheel support portion  17  are plate-shaped members and are provided such that plate surfaces face the disc surface  5   a  of the rotor disc  5 . Hereinafter, the plate surfaces of the drive wheel support portion  16  and the steering wheel support portion  17  facing the disc surface  5   a  will be referred to as facing surfaces  16   a  and  17   a.    
     The inspecting portion  10  includes an ultrasonic probe  31  that transmits and receives ultrasonic waves to and from the disc surface  5   a  of the rotor disc  5 . The inspecting portion  10  acquires UT data obtained by the ultrasonic probe  31  and transmits the UT data to the control device  15 . The inspecting portion  10  is provided between the drive wheel support portion  16  and the steering wheel support portion  17 . As illustrated in  FIG. 6 , the inspecting portion  10  is adapted to be rotatable in a roll direction (see the arrow A 2  in  FIG. 6 ) relative to the drive wheel support portion  16  and the steering wheel support portion  17 . The roll direction is a rotational direction with the traveling direction (see the arrow A 1  in  FIG. 6 ) of the ultrasonic inspection device  100  defined as a central axis line Cl. A specific structure of the inspecting portion  10  will be described later. 
     Two first magnets  11  are provided at the drive wheel support portion  16 , and the two first magnets  11  are disposed to be aligned in the radial direction. In addition, two first magnets  11  are also provided at the steering wheel support portion  17 , and the two first magnets  11  are disposed to be aligned in the radial direction. Each first magnet  11  is secured to the facing surfaces  16   a  and  17   a  of the drive wheel support portion  16  and the steering wheel support portion  17 . Each first magnet  11  is provided to project in the direction of the rotor disc  5  from the facing surfaces  16   a  and  17   a . The four first magnets  11  hold the ultrasonic inspection device  100  on the disc surface  5   a  by sticking to the disc surface  5   a  of the rotor disc  5  with a magnetic force. However, the four first magnets  11  are disposed to be separated from the disc surface  5   a . This is because the drive wheel  12  and the steering wheel  13  project more toward the rotor disc than the first magnets  11  (see  FIG. 5 ). 
     The length of each first magnet  11  projecting from the facing surfaces  16   a  and  17   a  is adjusted by the stroke control device  18 . As illustrated in  FIG. 7 , the distances between the first magnets  11  and the disc surface  5   a  become constant by the stroke control device  13  setting the projecting length of each first magnet  11  to a length in accordance with the curved surface at the time of the sticking to the curved surface. The first magnets  11  can thus suitably attract the disc surface  5   a . Note that the stroke control device  18  is not essential and the magnet placement position may be set in advance on the basis of drawing information such that the distances between the first magnets  11  and the disc surface  5   a  become constant. 
     The drive wheel  12  is provided at the facing surface I 6   a  of the drive wheel support portion  16 . The drive wheel  12  is disposed to come into contact with the disc surface  5   a  of the rotor disc  5 . The drive wheel  12  is driven and rotated by a drive force from a motor (not illustrated). Note that the motor may be incorporated in the drive wheel  12  or may be provided outside the drive wheel  12 . The ultrasonic inspection device  100  travels on the disc surface  5   a  by the drive wheel  12  being driven and rotated. An encoder (moving distance detecting portion) is incorporated in the drive wheel  12 . The encoder detects the amount of movement of the drive wheel  12 . The encoder transmits the detected information to the control device  15 . 
     The steering wheel  13  is provided at the facing surface  17   a  of the steering wheel support portion  17 . The steering wheel  13  is disposed to come into contact with the disc surface  5   a  of the rotor disc  5 . The steering wheel  13  is supported by the steering wheel support portion  17  such that the steering wheel  13  is rotatable about a central axis line C 2  that perpendicularly intersects the facing surface  17   a . The traveling direction of the ultrasonic inspection device  100  is adjusted by causing the steering wheel  13  to rotate about the central axis line C 2 . 
     One stroke sensor  14  is provided at each of the drive wheel support portion  16  and the steering wheel support portion  17 . The stroke sensor  14  detects the distance between a reference portion of the rotor disc  5  in the radial direction and the ultrasonic inspection device  100 . The stroke sensor  14  transmits the detected information to the control device  15 . In the example in  FIG. 7 , a shoulder portion  5   b  projecting from the disc surface  5   a  is applied as the reference portion in the radial direction. Specifically, the reference position is grasped by hooking a hook portion provided at a distal end of each stroke sensor  14  on the shoulder portion  5   b . Note that the reference portion may not be the shoulder portion  5   b . The reference portion may be any portion that can serve as a reference in the radial direction, and for example, an outer circumferential surface of the rotor shaft  4  may be used as the reference portion. 
     The control device  15  is configured with, for example, a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a computer-readable storage medium, and the like. Also, a series of processes to realize various functions are stored in the storage medium or the like in the form of a program in one example, and the various functions are realized by the CPU reading the program on the RAM or the like and executing information processing and arithmetic operations. Note that a mode in which the program is installed in advance in the ROM or another storage medium, a mode in which the program is provided in a state where the program is stored in a computer-readable storage medium, a mode in which the program is distributed via a wired or wireless communication means, or the like may be employed. The computer-readable storage medium is a magnetic disk, a magneto-optical disc, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like. 
     The control device  15  includes a storage portion  21  that stores a value (initial value) of the distance between the ultrasonic inspection device  100  and the shoulder portion (reference portion) when the ultrasonic inspection device  100  is mounted on the disc surface  5   a , a steering wheel control portion  22  that controls an orientation of the steering wheel  13  on the basis of information detected by the stroke sensor  14  such that the radial position of the ultrasonic inspection device  100  falls within a predetermined range, a self-position detecting portion (moving distance detecting portion)  23  that detects the self-position on the basis of information from the encoder, and a damage grasping portion  24  that grasps a damage of the rotor disc  5 , as illustrated in  FIG. 8 . 
     The steering wheel control portion  22  controls the angle by which the steering wheel  13  rotates such that the distance between the ultrasonic inspection device  100  and the shoulder portion (reference portion) becomes the initial value, on the basis of the initial value stored in the storage portion  21  and the information detected by the stroke sensor  14 . It is possible to travel in the circumferential direction while maintaining the predetermined radial position through such control of the steering wheel  13 . 
     The self-position detecting portion  23  calculates the traveling distance on the basis of information from the encoder and detects the self-position of the ultrasonic inspection device  100  in the circumferential direction. 
     The damage grasping portion  24  records the UT data on the rotor disc  5  detected by the inspecting portion  10  and the information regarding the self-position from the encoder in a temporally synchronous manner. In ether words, the UT data and the position in the circumferential direction where the UT data has been obtained are linked. It is thus possible to grasp what kind of damage has occurred and which part of the rotor disc  5  the damage has occurred. 
     [Inspecting Portion] 
     Next, details of the inspecting portion  10  will be described using  FIGS. 9 to 13 . Note that although  FIGS. 4 to 7  schematically illustrate the structure of coupling of the inspecting portion  10  to the steering wheel support portion  17  and the drive wheel support portion  16 , the inspecting portion  10  is coupled to the steering wheel support portion  17  and the drive wheel support portion  16  with securing arms  30  illustrated in  FIGS. 9 to 13 . Also, in the following description, a direction on the side of the rotor disc  5  will be referred to as one direction, and the opposite direction of the one direction will be referred to as the other direction. Moreover, an end portion on the side of the one direction will be referred to as one end portion, and an end portion on the side of the other direction will be referred to as the other end portion. 
     The inspecting portion  10  includes two ultrasonic probes  31  that transmit ultrasonic waves to the disc surface  5   a  of the rotor disc  5 , a probe-side holder  32  to which the ultrasonic probes  31  are secured, a soft gel portion (deformation portion)  33  provided between the ultrasonic probes  31  and the disc surface  5   a , a rotor disc-side holder  34  that is provided on the side of the rotor disc  5  beyond the probe-side holder  32  and holds the soft gel portion  33 , a biasing portion  35  that biases the probe-side holder  32  toward the rotor disc  5 , and an angle adjustment portion  36  that changes angles of the ultrasonic probes  31  relative to the disc surface  5   a , as illustrated in  FIG. 9 . 
     Each ultrasonic probe  31  is a device that transmits an ultrasonic wave to the rotor disc  5 . Each of the two ultrasonic probes  31  is secured to the probe-side holder  32  via an inclination adjustment mechanism  50 . Details of the inclination mechanism will be described later. The two ultrasonic probes  31  are disposed in an aligned manner. Specifically, the ultrasonic probes  31  are disposed in an aligned manner in a direction (Z direction) that intersects the radial direction when the ultrasonic inspection device  100  is mounted on the rotor disc  5 . In the following description, one of the ultrasonic probes  31  will be described as a first ultrasonic probe  31   a  while the other ultrasonic probe  31  will be referred to as a second ultrasonic probe  31   b.    
     The probe-side holder  32  is connected to a pair of securing arms  30 . The probe-side holder  32  is coupled to the drive wheel support portion  16  and the steering wheel support portion  17  via the pair of securing arms  30 . The probe-side holder  32  and the securing arms  30  are connected via the angle adjustment portion  36  and a rotation securing portion. The angle adjustment portion  36  and the rotation securing portion will be described later. 
     The probe-side holder  32  includes a first probe-side holder  32   a  with the other end portion to which the first ultrasonic probe  31   a  is secured and a second probe-side holder  32   b  with the other end to which the second ultrasonic probe  32   b  is secured. The first probe-side holder  32   a  and the second probe-side holder  32   b  have shapes obtained by symmetrically splitting a rectangular frame with reference to a central axis line of the frame. In other words, the first probe-side holder  32   a  and the second probe-side holder  32   b  constitute a frame with a substantially rectangular shape with a space SI formed at the center as illustrated in  FIG. 12  by the end portions thereof being brought into contact with each other. The space S 1  is filled with the soft gel portion  33  (see  FIG. 13 ). One end portion of the probe-side holder  32  forms a plane and abuts on the other end portion of the rotor disc-side holder  34 . The two ultrasonic probes  31  are secured to the other end portion of the probe-side holder  32 . Hereinafter, the first probe-side holder  32   a  and the second probe-side holder  32   b  will be simply referred to as a probe-side holder  32  in a case in which it is not necessary to describe them in a separated manner. 
     The rotor disc-side holder  34  is provided closer to the rotor disc  5  than the probe-side holder  32 . One end portion of the rotor disc-side holder  34  forms a curved surface corresponding to a small diameter R. Also, the other end portion of the rotor disc-side holder  34  forms a plane and abuts on the one end portion of the probe-side holder  32 . In addition, the rotor disc-side holder  34  has a rectangular frame shape and includes a space S 2  formed at the center. The length of the space S 2  in the Z direction is longer on one side than that on the other side as illustrated in  FIG. 12 . The space S 2  is formed over the entire range of the rotor disc-side holder  34  in the Z direction at the end portion on one side and is split in the X direction by the shielding plate  37 . The space S 2  communicates with the space S 1  formed at the center of the probe-side holder  32 , and S 1  and  32  form a space S that is filled with the soft gel portion  33 . 
     The rotor disc-side holder  34  includes a second magnet (sticking portion)  38  that sticks to the disc surface  5   a  and ball rollers  39  as illustrated in  FIG. 13 . The second magnet  38  is embedded in the one end portion of the rotor disc-side holder  34 . The ball rollers  35  are disposed to sandwich the second magnet  38  therebetween, with a part embedded in the one end portion of the rotor disc-side holder  34  and with another part projecting from the one end of the rotor disc-side holder  34 . The ball rollers  39  smoothen relative movement of the rotor disc-side holder  34  and the disc surface  5   a  by coming into contact with the disc surface  5   a.    
     The soft gel portion  33  is a member that keeps a predetermined shape in a state in which a pressing force does not act thereon and is deformed when the soft gel portion  33  is pressed. Also, the soft gel portion  33  is a member that suitably allows ultrasonic waves to pass therethrough. The space S is filled with the soft gel portion  33 . One end portion of the soft gel portion  33  is formed into a shape in accordance with the curved form (the small diameter R, for example) of the disc surface  5   a  to which the ultrasonic inspection device  100  is attached. The one end portion of the soft gel portion  33  is disposed to further project toward the rotor disc  5  than the one end portion of the rotor disc-side holder  34 . In this manner, the soft gel portion  33  is also pressed against the disc surface  5   a  by pressing the rotor disc-side holder  34  against the disc surface  5   a . The soft gel portion  33  is deformed to come into close contact with the disc surface  5   a  due to the pressing force. 
     The biasing portion  35  includes a plate-shaped first bracket  40  secured to the securing arm  30 , a spring  41  with the other end portion secured to the first bracket  40 , and a plate-shaped second bracket  42  secured to the probe-side holder  32  as illustrated in  FIGS. 9 and 11 . One end portion of the spring  41  abuts on the second bracket  42 . In this manner, a biasing force of the spring  41  is delivered to the probe-side holder  32  via the second bracket  42 , and the probe-side holder  32  is thus biased toward the one end side (toward the rotor disc  5 ). 
     Also, a slider portion  43  is secured to the first bracket  40 . In addition, a rail portion  44  is secured to the probe-side holder  32 . The slider portion  43  and the rail portion  44  extend in the Y direction. The slider portion  43  and the rail portion  44  are configured to be engageable. Movement of the securing arm  30  and the probe-side holder  32  in the X direction and the Z direction is restricted through the engagement between the slider portion  43  and the rail portion  44 . 
     Also, one end portion of the second bracket  42  projects beyond the one end portion of the probe-side holder  32 . The projecting part of the second bracket  42  abuts on or goes close to an end surface of the rotor disc-side holder  34  in the X direction. Therefore, the second bracket  42  restricts relative movement of the probe-side holder  32  and the rotor disc-side holder  34  in the X direction. 
     The angle adjustment portion  36  is provided between the probe-side holder  32  and the securing arm  30  as illustrated in  FIG. 10 . The angle adjustment portion  36  is adapted to be able to rotate the probe-side holder  32  about a shaft (not illustrated) extending along the central axis line C 1  (see  FIG. 6 ) relative to the securing arm  30 . Therefore, it is possible to set the inspecting portion  10  at a desired angle by moving a lever  45  provided at the angle adjustment portion  36 . Also, rotation of the angle adjustment portion  36  is restricted by fastening a rotation securing screw  46  provided at the securing arm  30  to cause a distal end of the rotation securing screw  46  formed of a rubber material and the shaft to abut on each other. It is thus possible to fix the angle of the inspecting portion  10 . 
     [Inclination Adjustment. Mechanism] 
     Next, the inclination adjustment mechanism  50  will be described using  FIGS. 14 to 17 . The inspecting portion  10  according to the present embodiment can cause the first probe-side holder  32   a  and the first, ultrasonic probe  31   a  to be inclined at a desired angle on the opposite side of the second probe-side holder  32   b  and the second ultrasonic probe  31   b  using the inclination adjustment mechanism (a first inclination means and a second inclination means)  50  as illustrated in  FIG. 14 . Also, it is possible to cause the second probe-side holder  32   b  and the second ultrasonic probe  31   b  to be inclined at a desired angle on the opposite side of the first probe-side holder  32   a  and the first ultrasonic probe  31   a  using the inclination adjustment mechanism  50 . 
     The inclination adjustment mechanism  50  that causes the first probe-side holder  32   a  and the first ultrasonic probe  31   a  to be inclined and the inclination adjustment mechanism  50  that causes the second probe-side holder  32   b  and the second ultrasonic probe  31   b  to be inclined are symmetrically configured. Therefore, the inclination adjustment mechanism that causes the first probe-side holder  32   a  and the first ultrasonic probe  31   a  to be inclined will be described below, and description of the inclination adjustment mechanism  50  that causes the second probe-side holder  32   b  and the second ultrasonic probe  31   b  will be omitted. 
     The inclination adjustment mechanism  50  includes two outer screws  51  that penetrate through the first probe-side holder  32   a  and the rotor disc-side holder  34  and two inner screws  52  as illustrated in  FIGS. 15A and 15B . The length of the inner screws  52  is longer than the length of the outer screws  51 . Distal ends of the screws are provided with spherical portions  51   a  and  52   a . The two outer screws  51  are disposed to sandwich the first ultrasonic probe  31   a . Also, the two inner screws  52  are provided further inward than the outer screw  51  and are disposed to sandwich the first ultrasonic probe  31   a.    
     Two outer screw holes  53  through which the outer screws  52  are inserted and two inner screw holes  54  through which the inner screws  52  are inserted are formed in the first probe-side holder  32   a . Both the outer screw holes  53  and the inner screw holes  54  formed in the probe-side holder  32  penetrate through the probe-side holder  32 . In the outer screw holes  53 , female screws into which the outer screws  51  can be screwed are formed in inner circumferential surfaces. The inner screw holes  54  are formed to have a sufficiently larger diameter than the diameter of shaft portions of the inner screws  52 . In other words, the inner screws  52  are not screwed into the inner screw holes  54 . 
     Two outer screw holes  56  into which the outer screws  51  are inserted and two inner screw holes  57  into which the inner screws  52  are inserted are formed in the rotor disc-side holder  34 . Each of the inner screw holes  57  and the outer screw holes  56  formed in the rotor disc-side holder  34  has a recessed portion shape with a bottom. Spherical spaces  56   a  and  57   a  into which the spherical portions  51   a  and  52   a  are inserted are formed at the bottom portions of the outer screw holes  56  and the inner screw holes  57 . Also, inner circumferential surfaces of the outer screw holes  56  and the inner screw holes  57  are inclined to be separated from the second probe-side holder  32   b  and the second ultrasonic probe  31   b  such that the inner screws  52  and the outer screws  51  can be inclined. 
     Also, nuts  58  are screwed onto the inner screws  52  on the other side beyond the first probe-side holder  32   a . The positions where the nuts are screwed differ depending on applications. In a case in which the nuts  58  are screwed to come into contact with the first probe-side holder  32   a  as illustrated in  FIG. 15B  and the outer screws  51  and the inner screws  52  are caused to rotate at the same time as illustrated by the arrows in  FIG. 15B , for example, the first probe-side holder  32   a  and the first ultrasonic probe  31   a  are separated from the rotor disc-side holder  34  with a parallel state maintained as illustrated in  FIG. 15C . 
     On the other hand, in a case in which the nuts  58  are screwed on the proximal end side of the inner screws  52  as illustrated in  FIG. 15D , only the inner side of the first probe-side holder  32   a  and the first ultrasonic probe  31   a  moves to the other side due to the pressing force (see the arrow A 3 ) of the soft gel. In this manner, the first probe-side holder  32   a  and the first ultrasonic probe  31   a  are inclined on the opposite side of the second probe-side holder  32   b  and the second ultrasonic probe  31   b.  The first probe-side holder  32   a  and the first ultrasonic probe  31   a  are stopped at the position where the nuts  58  and the first probe-side holder  32   a  come into contact with each other, and it is thus possible to set an inclination angle θ 1  of the first probe-side holder  32   a  and the first ultrasonic probe  31   a  to be a desired angle by adjusting the position where the nuts  58  are screwed. The inclination angle θ 1  is an angle formed by the one end surface of the first probe-side holder  32   a  and the other end surface of the rotor disc-side holder  34 . 
     Also, in a case in which a nut (not illustrated) is further provided between the first probe-side holder  32   a  and the rotor disc-side holder  34  and the nut is caused to come into contact with the one end surface of the first probe-side holder  32   a , it is possible to support the first probe-side holder  32   a  and the first ultrasonic probe  31   a  with the nut and thereby to secure the first probe-side holder  32   a  and the first ultrasonic probe  31   a  at the desired inclination angle θ 1  regardless of the pressurizing force of the soft gel. 
     [Modification of Inclination Adjustment Mechanism  50 ] 
     Note that the inclination adjustment mechanism  50  may be configured as illustrated in  FIGS. 16A to 16C . 
     The configuration of the modification is different from the configuration illustrated in  FIGS. 15A  to I 5 D in that a hinge  61  and a tension spring  62  are provided instead of the outer screws  51 . Since the configuration of the inner screws  52  is substantially the same as the configuration illustrated in  FIGS. 15A to 15D , description will be omitted. The hinge  61  is secured to the outside of the rotor disc-side holder  34  in the Z direction. Also, the hinge  61  is secured to the outside of the first probe-side holder  32   a  in the Z direction via the tension spring  62 . The tension spring  62  biases the first probe-side holder  32   a  in the direction of the rotor disc-side holder  34 . 
     With such a configuration, only the inner side of the first probe-side holder  32   a  and the first ultrasonic probe  31   a  also moves to the other side due to the pressing force (see the arrow A 3 ) of the soft gel in a case in which the nuts  53  are screwed onto the proximal end side of the inner screws  52  as illustrated in  FIG. 16C . In this manner, the first probe-side holder  32   a  and the first ultrasonic probe  31   a  are inclined on the opposite side of the second probe-side holder  32   b  and the second ultrasonic probe  31   b . Since the first probe-side holder  32   a  and the first ultrasonic probe  31   a  are stopped at the position where the nuts  58  and the first probe-side holder  32   a  come into contact with each other, it is possible to set the inclination angle θ 1  of the first probe-side holder  32   a  and the first ultrasonic probe  31   a  to be a desired angle through adjustment of the position where the nuts  53  are screwed. 
     [Inspection Method] 
     Next, a method for inspecting the rotor disc  5  of the steam turbine  1  using the ultrasonic inspection device  10 G according to the present embodiment will be described in detail using the flowchart in  FIG. 18 . 
     First, as illustrated in Step S 1 , the ultrasonic probe  31  is secured to the probe-side holder  32  (see  FIGS. 9 and 11 ). 
     Next, as illustrated in Step S 2 , the angle θ of the steering wheel  13  is adjusted in accordance with the rotation radius of the steering wheel  13 . At this time, an original angle θ (the angle θ of the steering wheel  13  when the inspection of the rotor disc  5  is started using the ultrasonic inspection device  100 ) of the steering wheel  13  is adjusted such that the ultrasonic inspection device  100  moves and rotates in accordance with the rotation radius r. Specifically, the angle θ is set to satisfy Equation (1) below. 
       θ=L/r   (1)
 
     where L denotes an arc length (the separation distance between the steering wheel  13  and the drive wheel  12 ), and r denotes a rotation radius (the distance from the center of the rotor disc  5  to the steering wheel  13 ). 
     Next, as illustrated in Step S 3 , the ultrasonic inspection device  100  is mounted on the curved surface of the disc surface  5   a  of the rotor disc  5 . Specifically, the ultrasonic probe  31  is held on the disc surface  5   a  by causing each first magnet  11  to stick to the curved surface of the disc surface  5   a  as illustrated in  FIG. 7  (holding process). At this time, it is possible to suitably cause the first magnets  11  to stick to the disc surface  5   a  by setting the projecting length of each stroke control device  18  to be the length in accordance with the curved surface as described above. The steering wheel  13 , the drive wheel  12 , and the inspecting portion  10  (specifically, the probe-side holder  32 ) are mounted on the disc surface  5   a  by causing each first magnet  11  to stick to the disc surface  5   a . Also, the hook portion provided at the distal end of each stroke sensor  14  is hooked on the shoulder portion  5   b  of the rotor disc  5 . At this time, a value of the distance between the ultrasonic inspection device  100  and the shoulder portion  5   b  may be stored as an initial value in the storage portion  21 . 
     Note that the surface on which the ultrasonic inspection device  100  is mounted is not limited to the curved surface of the disc surface  5   a . The ultrasonic inspection device  100  may be mounted on a flat surface of the disc surface  5   a.    
     Next, as illustrated in Step S 4 , the inspecting portion  10  is manually rotated in the roll direction (see the arrow A 2  in  FIG. 6 ) to adjust an incident angle of the ultrasonic wave transmitted from the ultrasonic probe  31  of the inspecting portion  10 . At this time, the shape echo of the blade groove portion  6  is checked with the inspecting portion  10  rotated in the roll direction, and the orientation of the inspecting portion  10  is adjusted such that the incident angle of the ultrasonic wave transmitted from the ultrasonic probe  31  becomes an appropriate angle. Then, the inspecting portion  10  is secured such that the orientation of the inspecting portion  10  becomes an appropriate orientation. 
     Next, as illustrated in Step S 5 , the ultrasonic inspection device  100  is caused to travel on the disc surface  5   a  of the rotor disc  5  (moving process). At this time, the ultrasonic inspection device  100  travels on the disc surface  5   a  in the circumferential direction as described above. At this time, the ultrasonic inspection device  100  detects the self-position using the self-position detecting portion  23  (position detecting process), adjusts the moving direction using the steering wheel control portion  22  (adjustment process), and moving in the circumferential direction with the predetermined radial position maintained (control process). Also, the ultrasonic inspection device  100  transmits an ultrasonic wave from the ultrasonic probe  31  to the rotor disc  5  while traveling (ultrasonic wave transmission process). The ultrasonic inspection device  100  may travel by causing the drive wheel  12  to rotate using a motor or the like. In other words, the ultrasonic inspection device  100  may travel by itself. Also, the ultrasonic inspection device  100  may perform the inspection by manually pressing the probe-side holder  32  and the like in the rotation direction. In other words, the ultrasonic inspection device  100  may be caused to perform semi-automatic scanning. 
     Next, as illustrated in Step S 6 , inspection data is recorded (recording process). The inspection data may be recorded for the entire region of the rotor disc  5  in the circumferential direction or may be recorded for a part of the rotor disc  5 . Specifically, the ultrasonic inspection device  100  detects the self-position in the circumferential direction using the self-position detecting portion  23  and records the inspection data at predetermined pitches while moving in the circumferential direction with the predetermined radial position maintained using the steering wheel control portion  22 . 
     Next, as illustrated in Step S 7 , inspection 3D data is generated. Specifically, the inspection 3D data is generated by merging the inspection data on a plurality of sections recorded in Step S 6  with 3D-CAD data. The 3D-CAD data may be stored in the storage portion  21 . 
     Next, as illustrated in Step S 3 , the inspection 3D data is analyzed. Specifically, scratching echo identification is performed by overlapping and comparing the inspection 3D data generated in Step S 7  with the 3D-CAD data. In other words, the shape echo and noise are identified. In this manner, whether or not any damage has occurred in the rotor disc  5  is inspected (determination process). Note that the 3D-CAD data as a comparison target is data on the rotor disc  5  before being damaged and may be 3D-CAD data at the time of design, for example. 
     Note that the scratching echo identification may be performed on the basis of operator&#39;s decision. Also, the control device  15  may be provided with an identification portion to identify a scratching echo, and the scratching echo may be identified by the identification portion. Alternatively, AI that has performed learning on the basis of accumulated inspection 3D data may perform the identification. 
     According to the present embodiment, the following effects and advantages are achieved. 
     In the present embodiment, the ultrasonic inspection device  100  is movably held relative to the disc surface  5   a  of the rotor disc  5 , and the ultrasonic inspection device  100  moves using the drive wheel  12 . In this manner, the ultrasonic inspection device  100  travels on the disc surface  5   a  of the rotor disc  5 . Also, in the present embodiment, the control device  15  controls the steering portion such that the radial position of the ultrasonic probe  31  (X direction) becomes the predetermined position. It is thus possible to set the radial position of the ultrasonic probe  31  to be the predetermined position when the ultrasonic probe  31  moves in the direction (Z direction) that intersects the radial direction of the rotor disc  5 . In other words, it is possible to cause the ultrasonic probe  31  to move in the circumferential direction with the predetermined radial position maintained. 
     In this manner, according to the present embodiment, the ultrasonic inspection device  100  can travel in the circumferential direction on the disc surface  5   a  of the rotor disc  5 . It is thus possible to reduce the size corresponding to non-provision of a carriage and the like as compared with a configuration in which the radial position of the ultrasonic probe  31  is fixed, by providing the carriage and the like secured to a rotor shaft  4 , for example. Therefore, even in a case of the rotor disc  5  at a short distance from an adjacent rotor disc  5  like a large-sized rotor disc  5 , for example, it is possible to curb an interference with the adjacent rotor disc  5  and to easily mount the ultrasonic inspection device  100  on the disc surface  5   a  of the rotor disc  5 . 
     In the present embodiment, the ultrasonic inspection device  100  includes a motor that drives the drive wheel  12 . There is thus no need to obtain power from the outside, and the ultrasonic inspection device  100  can thus travel by itself on the disc surface  5   a  of the rotor disc  5 . Therefore, it is possible to simplify the structure as compared with a structure in which the ultrasonic inspection device  100  obtains power from the outside. 
     Also, since the ultrasonic inspection device  100  travels by itself, there is no need for an operator to manually move the ultrasonic inspection device  100 , and it is also possible to apply the ultrasonic inspection device  100  to inspection of a large-sized rotor disc  5  that it is difficult for the operator or the like to reach with his/her hands. 
     In the present embodiment, the ultrasonic probe  31  is held relative to the disc surface  5   a  such that the ultrasonic probe  31  does not come into contact with the disc surface  5   a , using the first magnets  11 . It is thus possible to reduce a traveling resistance when the ultrasonic inspection device  100  moves. 
     In the present embodiment, the encoder that detects the distance of movement is included. It is thus possible to grasp the position of the ultrasonic inspection device  100  in the circumferential direction. Therefore, it is possible to associate the inspection result of the ultrasonic probe  31  with the position in the circumferential direction. Accordingly, it is possible to specify the position of a damage that has occurred in the rotor disc  5 . 
     In the present embodiment, the soft gel portion  33  that is deformed by being pressed against the rotor disc  5  is provided between the ultrasonic probe  31  and the rotor disc  5 . In this manner, the soft gel portion  33  is deformed in accordance with the surface of the rotor disc  5  by pressing the soft gel portion  33  against the rotor disc  5 , and it is thus possible to remove an air layer on the surface of the rotor disc  5 . It is possible to remove the air layer between the ultrasonic probe  31  and the rotor disc  5  and thereby to suitably deliver the ultrasonic wave from the ultrasonic probe  31  to the rotor disc  5 . Therefore, it is also possible to suitably perform inspection on the rotor disc  5  with the curved disc surface  5   a  like a large-sized rotor disc  5 , for example, by causing the soft gel portion  33  to be deformed. 
     Moreover, in the present embodiment, the soft gel portion  33  changes in accordance with the curved form of the disc surface  5   a , and it is thus possible to remove the air layer regardless of the curved form. Therefore, if curved surfaces of flange portions with similar shapes in a vertical sectional view are present in the disc surface in a case in which flaw detection is performed on a plurality of disc blade groove in the same turbine rotor, for example, the curved form (large diameter R) of the disc surface  5   a  that is an inspection target changes depending on the diameter dimension at the position on the disc where the probe is placed. The soft gel portion  33  is deformed in accordance with the change in curved form of the disc surface  5   a  in such a case as well. Therefore, it is possible to suitably perform the inspection while causing the same ultrasonic inspection device  100  to move without changing the probe and the holder for the flange portions with the same shape even if the disc diameters are different. 
     Also, in the present embodiment, the probe-side holder  32  is biased toward the rotor disc  5  by the biasing portion  35 . It is thus possible to press the soft gel portion  33  against the rotor disc  5  via the probe-side holder  32 . Therefore, it is possible to more suitably press the soft gel portion  33  against the rotor disc  5 . Accordingly, it is possible to more suitably cause the soft gel portion  33  to be deformed in accordance with the disc surface  5   a  of the rotor disc  5  and to remove the air layer. 
     In the present embodiment, the angle adjustment portion  36  that changes the angle of the ultrasonic probe  31  relative to the disc surface  5   a  of the rotor disc  5  is included. It is thus possible to appropriately transmit the ultrasonic wave to the target location (inspection target location) through adjustment of the angle of the ultrasonic probe  31 . 
     In the present embodiment, the inclination adjustment mechanism  50  that causes the first ultrasonic probe  31   a  to be inclined on the opposite side of the second ultrasonic probe  31   b  and the inclination adjustment mechanism  50  that causes the second ultrasonic probe  31   b  to be inclined on the opposite side of the first ultrasonic probe  31   a  are included. In this manner, it is possible to cause the ultrasonic wave transmitted from the first ultrasonic probe  31   a  and the ultrasonic wave transmitted from the second ultrasonic probe  3 ib to be focused inside the rotor disc  5  by transmitting the ultrasonic waves from the first ultrasonic probe  31   a  and the second ultrasonic probe  31   b  in a state in which the first ultrasonic probe  31   a  and the second ultrasonic probe  31   b  are inclined. Also, it is possible to adjust a depth L (the distance from the disc surface  5   a  of the rotor disc  5 ; see  FIG. 13 ) of the focusing position of the ultrasonic waves through adjustment of the inclination angle θ 1 . Therefore, even for a turbine in which the disc surface  5   a  is curved like a large-sized rotor disc  5 , for example, it is possible to cause the ultrasonic waves to be focused at a desired position through the adjustment of the inclination angle θ 1  of the first ultrasonic probe  31   a  and the second ultrasonic probe  31   b  in accordance with the shape of the curved portion. Accordingly, there is no need to prepare an element or the like with a refraction angle calculated in accordance with the shape (curvature) of the curved portion, and it is thus possible to simply perform the inspection. 
     The inclination adjustment mechanism  50  can set the inclination angle θ 1  to a desired angle. Also, it is possible to place the focusing position of the ultrasonic waves on the first ultrasonic probe  31   a  or on the second ultrasonic probe  3 ib by setting the inclination angle of the first ultrasonic probe  31   a  and the inclination angle of the second ultrasonic probe  31   b  to be different angles. In other words, in a case in which the inclination angle of the first ultrasonic probe  31   a  is set to be larger than the inclination angle of the second ultrasonic probe  31   b , a focusing position P′ of the ultrasonic waves is located on the second ultrasonic probe  31   b  as illustrated in  FIG. 17 . On the contrary, in a case in which the inclination angle of the second ultrasonic probe  31   b  is set to be larger than the inclination angle of the first ultrasonic probe  31   a , the focusing position of the ultrasonic waves is placed on the first ultrasonic probe  31   a . It is thus possible to cause the ultrasonic waves to converge in a wider range. In particular, it is possible to cause the ultrasonic waves to converge in the direction in which the blade groove portion  6  extends without using a wedge or the like for the skewed-type blade groove portion  6  as illustrated in  FIG. 3  and thereby to simply perform the inspection. 
     Note that the present disclosure is not limited to each of the aforementioned embodiments and can be appropriately deformed without departing from the gist. 
     For example, the ultrasonic inspection device  100  may further include an inertial measurement device, a laser range finder, a sonar, and the like. It is possible to improve control accuracy of the ultrasonic inspection device  100  by providing such instruments. 
     Also, surfaces of the first magnets  11  may be covered with a low-friction material such as a gel, and the low-friction material may be brought into contact with the disc surface  5   a . It is possible to reduce the traveling resistance by such a method as well. 
     Also, although the example in which the ultrasonic inspection device  100  is secured to the curved surface of the disc surface  5   a  of the rotor disc  5  has been described in the aforementioned embodiment, the present disclosure is not limited thereto. The ultrasonic inspection device  100  may be secured to a flat surface of the disc surface  5   a  of the rotor disc  5 . 
     REFERENCE SIGNS LIST 
     
         
           1  Steam turbine 
           2  Turbine rotor 
           3  Rotor blade 
           4  Rotor shaft 
           5  Rotor disc 
           5   a  Disc surface 
           6  Blade groove portion 
           10  Inspecting portion 
           11  First magnet (holding portion) 
           12  Drive wheel (moving portion) 
           13  Steering wheel (adjustment portion) 
           14  Stroke sensor (position detecting portion) 
           15  Control device (control portion) 
           16  Drive wheel support portion 
           16   a  Facing surface 
           17  Steering wheel support portion 
           17   a  Facing surface 
           13  Stroke control device 
           21  Storage portion 
           22  Steering wheel control portion 
           23  Self-position detecting portion (moving distance detecting portion) 
           24  Damage grasping portion 
           30  Securing arm 
           31  Ultrasonic probe 
           31   a  First ultrasonic probe 
           31   b  Second ultrasonic probe 
           32  Probe-side holder 
           32   a  First probe-side holder 
           32   b  Second probe-side holder 
           33  Soft gel portion 
           34  Rotor disc-side holder 
           35  Biasing portion 
           36  Angle adjustment portion 
           37  Shielding plate 
           38  Second magnet 
           39  Bali roller 
           40  First bracket 
           41  Spring 
           42  Second bracket 
           43  Slider portion 
           44  Rail portion 
           45  Lever 
           46  Rotation securing screw- 
           50  Inclination adjustment mechanism (first inclination means, second inclination means) 
           51  Outer screw 
           51   a  Spherical portion 
           52   a  Spherical portion 
           52  Inner screw 
           53  Outer screw hole 
           54  Inner screw hole 
           56  Outer screw hole 
           56   a  Spherical space 
           57   a  Spherical space 
           57  Inner screw hole 
           58  Nut 
           61  Hinge 
           62  Tension spring 
           100  Ultrasonic inspection device