Ultrasonic flaw-detection method and apparatus for blade groove in turbine rotor disc

Abstract

A method includes: an arrangement step of arranging a phased array probe including a plurality of oscillators each of which is capable of emitting ultrasonic waves on an end surface of the rotor disc, in a parallel state in which the plurality of oscillators are arranged along a circumferential direction of the rotor disc; a first transmission step of emitting ultrasonic waves from the plurality of oscillators in the parallel state, while a timing of emitting the ultrasonic waves from each of the oscillators is controlled in a first emission pattern, and receiving reflection waves of the ultrasonic waves; and a second transmission step of emitting ultrasonic waves from the plurality of oscillators in the parallel state, while the timing of emitting the ultrasonic waves from each of the oscillators is controlled in a second emission pattern different from the first emission pattern, and receiving reflection waves of the ultrasonic waves.

Claims

1. A method of performing ultrasonic flaw-detection for a blade groove portion of a turbine rotor disc for checking a blade groove portion by a phased array method, the blade groove portion being disposed on a rotor disc of a turbine for fixing a turbine blade, the method of performing ultrasonic flaw-detection comprising: a providing step of providing the rotor disc of a side entry type having the blade groove portion which is curved and deviated from an axial direction of the rotor disc; an arrangement step of arranging a phased array probe including a plurality of oscillators each of which is capable of emitting ultrasonic waves on an end surface of the rotor disc, in a parallel state in which the plurality of oscillators are arranged along a circumferential direction of the rotor disc; a first transmission step of emitting ultrasonic waves from the plurality of oscillators in the parallel state, while a timing of emitting the ultrasonic waves from each of the oscillators is controlled in a first emission pattern, and receiving reflection waves of the ultrasonic waves; and a second transmission step of emitting ultrasonic waves from the plurality of oscillators in the parallel state, while the timing of emitting the ultrasonic waves from each of the oscillators is controlled in a second emission pattern different from the first emission pattern, and receiving reflection waves of the ultrasonic waves, and further comprising: a first radial-direction moving step of moving the probe along a radial direction of the rotor disc, the radial direction being perpendicular to a circumferential direction of the rotor disc, a first detection step of performing the first transmission step and the second transmission step after the first radial-direction moving step, a circumferential-direction moving step of rotating the rotor disc with respect to the probe after the first detection step, a second radial-direction moving step of moving the probe along the radial direction of the rotor disc, and a second detection step of performing the first transmission step and the second transmission step after the second radial-direction moving step, wherein the blade groove portion of the side entry type is configured as a blade groove portion of a curved side entry type which extends in an arc shape so as to deviate from the axial direction of the rotor disc.

2. The method of performing ultrasonic flaw-detection for a blade groove portion of a turbine rotor disc according to claim 1, wherein each of the plurality of oscillators has an emitting surface capable of emitting the ultrasonic waves, and wherein the emitting surface has a concave shape extending longer in a direction that intersects with an arrangement direction of the oscillators than in the arrangement direction, and being recessed at center in a direction that intersects with the arrangement direction so that the ultrasonic waves emitted from the emitting surface converge at one focal point.

3. The method of performing ultrasonic flaw-detection for a blade groove portion of a turbine rotor disc according to claim 1, further comprising: an adjustment step of adjusting a number of the plurality of oscillators included in the phased array probe in accordance with a size or a shape of the blade groove portion.

4. The method of performing ultrasonic flaw-detection for a blade groove portion of a turbine rotor disc according to claim 1, wherein each of the plurality of oscillators is capable of receiving the reflection waves of the ultrasonic waves.

5. The method of performing ultrasonic flaw-detection for a blade groove portion of a turbine rotor disc according to claim 1, further comprising: a plurality of receiving oscillators for receiving the reflection waves of the ultrasonic waves.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a front view schematically showing an ultrasonic flaw-detection apparatus according to an embodiment of the present invention, as well as a part of a rotor disc.

(2) FIG. 2 is an explanatory diagram showing a flaw-detection method according to the above embodiment.

(3) FIG. 3 is a schematic diagram showing a phased array probe of the ultrasonic flaw-detection apparatus.

(4) FIG. 4 is a schematic diagram according to yet another embodiment of the present invention, as seen in the direction of arrow B in FIG. 3.

(5) FIG. 5 is a schematic diagram of a phased array probe according to yet another embodiment of the present invention.

(6) FIG. 6 is a schematic diagram of a phased array probe according to yet another embodiment of the present invention.

(7) FIG. 7 is a view in a direction of arrow C in FIG. 6.

(8) FIG. 8 is a schematic diagram showing formation of a dead zone in a case where a ultrasonic-wave emitting part and a ultrasonic-receiving part are separated.

(9) FIGS. 9A to 9D are explanatory diagrams showing various scanning methods using a phased array probe.

(10) FIG. 10 is a perspective view of blade groove portions of a curved side entry type.

(11) FIG. 11 is an explanatory diagram showing a testing method according to a typical phased array method.

DETAILED DESCRIPTION

(12) Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.

(13) For instance, an expression of relative or absolute arrangement such as in a direction, along a direction, parallel, orthogonal, centered, concentric and coaxial shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function.

(14) For instance, an expression of an equal state such as same equal and uniform shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference that can still achieve the same function.

(15) Further, for instance, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved.

(16) On the other hand, an expression such as comprise, include, have, contain and constitute are not intended to be exclusive of other components.

(17) An embodiment of the present invention will now be described with reference to FIGS. 1 to 3.

(18) FIG. 1 illustrates a configuration of an ultrasonic flaw-detection apparatus 10 according to the present embodiment. A phased array probe 12 has a cuboid outer shape and is housed in a space formed inside a frame 14 having a quadrate shape, and in this state, fixed to the frame 14 with a fixing unit such as a bolt.

(19) The frame 14 has a rotational shaft 14a formed integrally. The frame 14 is inserted into a support frame 16 having a quadrate shape which is open at one side, and the rotational shaft 14a is fitted rotatably into a hole formed on the support frame 16. In this way, the frame 14 is supported rotatably onto the support frame 16 about the rotational shaft 14a.

(20) Two springs 18 are disposed on the bottom side of the support frame 16 facing the frame 14. The springs 18 apply spring forces that rotate the frame 14 in a direction about the rotational shaft 14a, which is a direction to bring the phased array probe 12 into close contact with the rotor-disc end surface 106a, when the phased array probe 12 is placed on the rotor-disc end surface 106a.

(21) In FIG. 1, turbine blades and blade groove portions mounted to the outer peripheral surface 106b of the rotor disc 106 are not depicted.

(22) The support frame 20 includes a support frame body 20a having a quadrate shape with one side open, and a main shaft 20b coupled to the support frame body 20a. The support frame 16 is fixed to the support frame body 20a with bolts 22.

(23) The frame 14 and the support frame 16 include four balls 24 on respective four corners on one face (the face facing the rotor-disc end surface 106a). The balls 24 are mounted rotatably to the frame 14 or to the support frame 16. The balls 24 enable the frame 14 and the support frame 16 to easily slide while being in contact with the end surface 106a of the rotor disc 106.

(24) A probe support device 26 includes a trolley 34 having four casters 36 and being capable of running in a traveling direction, a support pole 38 mounted and fixed to the trolley 34, and an arm 31 supported rotatably by the support pole 38 within a vertical plane including the traveling direction. The support pole 38 has a height adjustment part 28 which is supported slidably in the height direction with respect to the support pole 38.

(25) The arm 31 is supported rotatably within a plane via a shaft 30 with respect to the height adjustment part 28. The arm 31 has a scanning-position adjustment part 32 which supports the main shaft 20b of the support frame 20 slidably in the axial direction of the main shaft 20b within the plane.

(26) The ultrasonic flaw-detection apparatus 10 is configured such that the phased array probe 12 can be positioned in a position on the rotor-disc end surface 106a when placed so that the plane is parallel to the rotor-disc end surface 106a.

(27) A face of the phased array probe 12 that emits ultrasonic waves is fixed to the frame 14 so as to be substantially flush with the frame 14 and the support frame 16. A cable 40 is connected to the phased array probe 12. Control signals are inputted into the phased array probe 12 and detection signals are outputted from the phased array probe 12, via the cable 40.

(28) A detection target of the ultrasonic flaw-detection apparatus 10 is the blade groove portion 108 of a curved side entry type depicted in FIG. 10, for instance. The ultrasonic flaw-detection apparatus 10 is moved to the rotor disc 106, and the phased array probe 12 is disposed on the rotor-disc end surface 106a. In this case, with the shaft 30 being disposed orthogonal to the rotor-disc end surface 106a, the arm 31 can be rotated within a plane parallel to the rotor-disc end surface 106a, and the scanning-position adjustment part 32 can move the phased array probe 12 in the radial direction of the rotor disc 106.

(29) A radial-direction moving step is performed, in which the rotor disc 106 is supported rotatably with a rotor-disc support device 39, and the phased array probe 12 is moved along the radial direction of the rotor disc 106.

(30) During this time, the phased array probe 12 emits ultrasonic waves toward the blade groove portion 108 while being disposed on the rotor-disc end surface 106a, and receives reflection waves reflected by the blade groove portion 108. Waveforms of the reflection waves are analyzed to check presence and size of defects such as cracks.

(31) Next, a turbine rotor is rotated manually or by a driving motor, and the radial-direction moving step is performed again. Performing the radial-direction moving step repeatedly makes it possible to radiate ultrasonic waves to all the blade groove portions 108 mounted to the entire periphery of the rotor-disc outer peripheral surface 106b, thereby checking all the blade groove portions 108.

(32) FIG. 2 is a diagram showing an emission range of ultrasonic waves emitted by the ultrasonic flaw-detection apparatus 10. FIG. 3 is an enlarged view of the phased array probe 12.

(33) As depicted in FIG. 3, the phased array probe 12 includes a plurality of oscillators 42. The oscillators 42 have a rod shape with a quadrate cross section, and arranged in the circumferential direction (direction of arrow b) of the rotor disc 106. The cable 40 transmits electric pulses to the oscillators 42 to excite the oscillators 42. When the ultrasonic waves emitted by the oscillators 42 are reflected by the blade groove portion 108, and the reflection waves are received by the oscillators 42, the cable 40 transmits the received reflection waves to a processing part (not depicted).

(34) As depicted in FIG. 2, the phased array probe 12 emits ultrasonic waves to the blade groove portion 108 at a skew angle A. As depicted in FIG. 2, the skew angle A is defined as an angle formed by the radiation direction of ultrasonic waves or the front-rear direction of the phased array probe 100 with the radial direction a of the rotor disc 106.

(35) FIGS. 9A to 9D schematically describe various scanning methods using the phased array method. The phased array probe 12 includes a plurality of oscillators 42 arranged in parallel, and the timing to apply a pulse voltage to each oscillator 42 is controlled, whereby the exciting time is controlled for each oscillator 42, and the timing to emit ultrasonic waves (emitting pattern) can be controlled. Accordingly, it is possible to flexibly change the radiation direction of a composite wave front s (an envelope surface of each ultrasonic wave u) formed by combination of wave fronts of ultrasonic waves u emitted from the respective oscillators 42, and the focal range where the composite front s has a line focus f1 or a focal point f2.

(36) The excitation timing between the oscillators 42 is controlled so that scanning can be performed as depicted in FIGS. 9B and 9C, for instance. The emitting pattern depicted in FIG. 9B is employed in the first transmission step, and the emitting pattern depicted in FIG. 9C is employed in the second transmission step, for instance.

(37) Accordingly, it is possible to change the radiation direction of ultrasonic waves emitted from the oscillators 42 not only to the direction defined by the skew angle A but also to the circumferential direction b of the rotor disc 106. Thus, it is possible to expand the scanning range t of ultrasonic waves to a wide range in a fan shape. The emitting pattern is not limited to the first emitting pattern and the second emitting pattern. For instance, a plurality of emitting patterns may be employed to scan the radiation direction of ultrasonic waves electrically and continuously, which makes it possible to analyze the scanning range t in detail.

(38) According to the present embodiment, the plurality of oscillators 42 are arranged along the circumferential direction b of the rotor-disc end surface 106a, and ultrasonic waves are emitted in the first emitting pattern and the second emitting pattern, whereby it is possible to easily change the radiation direction of ultrasonic waves in the circumferential direction b of the rotor-disc end surface 106a without changing the direction of the phased array probe 12.

(39) Changing the radiation direction of ultrasonic waves in the circumferential direction b of the rotor-disc end surface 106a makes it possible to detect defects such as cracks in the second emitting pattern, even if the defects cannot be detected in the first emitting pattern, and vice versa.

(40) Accordingly, even if the blade groove portion 108 is of a curved side entry type in which defects are formed in more various and complicated directions than in a side entry type, it is possible to detect defects in a wide range and at high accuracy.

(41) Furthermore, the first transmission step and the second transmission step are performed before and after the radial-direction moving step, and thereby it is possible to detect defects easily at high accuracy over a wide range without changing the direction of the phased array probe 12.

(42) Furthermore, since the oscillators 42 have both functions of emitting and receiving ultrasonic waves, it is possible to detect defects easily at high accuracy with a simple configuration.

(43) The ultrasonic flaw-detection apparatus 10 includes the rotor-disc support deice 39, and thereby it is possible to move the phased array probe 12 easily along the radial direction of the rotor disc 106. Thus, it is possible to detect defects accurately and easily over a wide range for one blade groove portion 108.

(44) Furthermore, it is possible to easily place the phased array probe 12 on a position on the rotor-disc end surface 106a by rotating the rotor disc 106, moving the trolley 34, extending and contracting the support pole 38, extending and contracting the arm 31, and rotating the arm 31. Thus, it is possible to detect defects accurately and easily over a wide range for more than one blade groove portion 108.

(45) Furthermore, since it is possible to bring the phased array probe 12 into close contact with the rotor-disc end surface 106a with elastic forces of the springs 18, it is possible to improve the accuracy in detecting defects even further.

(46) FIG. 4 is a schematic diagram of an oscillator 42 according to yet another embodiment of the present invention, as seen in the direction of arrow B in FIG. 3. In some embodiments, each of the oscillators 42 has an ultrasonic-wave emitting surface 44 having a concave shape extending longer in a direction that intersects with an arrangement direction of the oscillators 42 than in the arrangement direction, and being recessed at center from the blade groove portion 108 in a direction that intersects with the arrangement direction so that ultrasonic waves emitted from the ultrasonic-wave emitting surface 44 converge at one focal point.

(47) With this configuration, the composite wave front s of the ultrasonic waves u emitted from the ultrasonic-wave emitting surfaces 44 of the respective oscillators 42 converges at one focal point, which makes it possible to increase the accuracy in detecting defects in the vicinity of the focal point.

(48) In some embodiments, in the phased array probe 12, each of the oscillators 42 is disposed in a state in which the longitudinal direction of the oscillator 42 is inclined from the rotor-disc end surface 106a so that the incident angle of ultrasonic waves is oblique with respect to the rotor-disc end surface 106a.

(49) FIG. 5 is a schematic view of a phased array probe 12 according to another embodiment of the present invention applied to a small turbine rotor. In the present embodiment, the rotor disc 106 and the blade groove portion 108 are reduced in size, and thus the phased array probe 12 is also reduced in size, so that the number of the oscillators 42 is about half of that in the above embodiment. For instance, if the number of oscillators 42 in the present embodiment is 32, the number of the oscillators 42 is 16 in the present embodiment.

(50) Accordingly, the phased array probe 12 can be reduced in size by adjusting the number of the oscillators 42 in accordance with the size and shape of the rotor disc 106 and the blade groove portion 108. Thus, even if a turbine rotor has small gaps between rotor discs and between blade groove portions, it is possible to check the turbine rotor easily at high accuracy.

(51) Next, yet another embodiment of the present invention will be described with reference to FIGS. 6 and 8. As depicted in FIGS. 6 and 7, in the present embodiment, a ultrasonic-wave emitting part 46 and a ultrasonic-wave receiving part 48 are separately provided, each comprising the oscillator 42. The ultrasonic-wave emitting part 46 and the ultrasonic-wave receiving part 48 are disposed on different positions inside the phased array probe 12. The emitting surface of the ultrasonic-wave emitting part 46 and the receiving surface of the ultrasonic-wave receiving part 48 are inclined in such directions that the surfaces face each other.

(52) The ultrasonic-wave emitting part 46 emits ultrasonic waves u to the blade groove portion 108, and the ultrasonic-wave receiving part 48 receives reflection waves e reflected from the blade groove portion 108, to analyze waveforms of the like of the reflection waves e and detect presence and size of defects. The configuration is otherwise the same as that of the above embodiment.

(53) As depicted in FIG. 8, if the ultrasonic-wave emitting part 46 and the ultrasonic-wave receiving part 48 are constituted by the same oscillator, incident waves and reflection waves interfere with each other and a dead zone n is formed to face the surface of the rotor-disc end surface 106a.

(54) In the present embodiment, since the ultrasonic-wave emitting part 46 and the ultrasonic-wave receiving part 48 are separately provided, it is possible to suppress interference between ultrasonic waves emitted by the oscillator 42 (incident waves) and reflection waves, in the vicinity of the rotor-disc end surface 106a. As a result, it is possible to reduce the dead zone n that develops on the surface of the rotor-disc end surface 106a, and thereby it is possible to detect defects easily at high accuracy even in a region closer to the surface of the rotor-disc end surface 106a.

(55) In some embodiments, the ultrasonic-wave emitting part 46 and the ultrasonic-wave receiving part 48 are arranged in the width direction of the phased array probe 12, and the plurality of oscillators of the ultrasonic-wave emitting part 46 and the ultrasonic-wave receiving part 48 are also arranged in the width direction of the phased array probe 12. The emitting surfaces of the plurality of oscillators of the ultrasonic-wave emitting parts 46 and the receiving surfaces of the oscillators of the ultrasonic-wave receiving part 48 are inclined from the end surface of the rotor disc, specifically, inclined so that normals of the emitting surfaces and normals of the oscillators intersect with each other at the side of the rotor disc.

(56) Embodiments of the present invention were described in detail above, but the present invention is not limited thereto, and various amendments and modifications may be implemented.

INDUSTRIAL APPLICABILITY

(57) According to at least one embodiment of the present invention, it is possible to easily and accurately detect defects such as cracks in a blade groove portion for fixing a turbine blade disposed on a rotor disc of a turbine.

DESCRIPTION OF REFERENCE NUMERALS

(58) 10 Ultrasonic flaw-detection apparatus 12, 100 Phased array probe 14 Frame 14a Rotational shaft 16 Support frame 18 Spring 20 Support frame 20a Support frame body 20b Main shaft 22 Bolt 24 Ball 26 Probe support device 28 Height adjustment part 30 Shaft 31 Arm 32 Scanning-position adjustment part 34 Trolley 36 Caster 38 Support pole 40 Cable 42, 110 Oscillator 44 Ultrasonic-wave emitting surface 46 Ultrasonic-wave emitting part 48 Ultrasonic-wave receiving part 102 Turbine blade 104 Blade root portion 106 Rotor disc 106a End surface 106b Outer peripheral surface 108 Blade groove portion A Skew angle c Crack e Reflection wave n Dead zone s Composite wave front t Scanning range u Ultrasonic wave