JP2012032195A - Flaw detection method of turbine blade - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flaw detection method of a turbine blade capable of determining a crack generated on the internal wall surface without requiring proficiency.SOLUTION: In a representative configuration of the flaw detection method of the turbine blade, the crack on the internal wall surface is determined with respect to a turbine blade having a cooling space for passing the air for cooling through the inside. The flaw detection method includes: acquiring variation of height distribution when weight is applied to the turbine blade without the crack as reference distribution variation (step 304), acquiring variation of height distribution when the weight is applied to a turbine blade to be inspected as inspection distribution variation (step 310), and determining that the crack exists at a position where positive and negative are reversed in a difference between the reference distribution variation and the inspection distribution variation (step 316).

Description

  The present invention relates to a flaw detection method for determining a crack on an inner wall surface of a turbine blade having a cooling space through which cooling air passes.

  Thermal power plants and nuclear power plants generate electricity by rotating a turbine. The turbine is rotated at a speed of 3000 rpm at 50 Hz by passing a fluid such as high-temperature steam or combustion gas through turbine blades (turbine blades) fixed to the shaft. Several tens to 100 or more turbine blades are detachably attached to the outer periphery of the rotor (impeller). Since the turbine blades are exposed to a high-temperature fluid, a cooling space in which air and steam circulate is formed. A turbine blade having such a structure, for example, a moving blade, has a condition that it is at a high temperature in addition to the pressure received from the fluid, the bending stress of the reaction force that rotates the rotor, the strong centrifugal force, and the rotational vibration. There is a risk of cracking.

  Therefore, the turbine blade is regularly inspected. At this time, a flaw detection inspection is performed, and the turbine blade that has not yet been damaged (cracked) is continuously used. Here, in view of the accuracy of the flaw detection inspection, in order to avoid the risk of breakage during operation, a suspicious object is not used even if a crack cannot be confirmed. However, the turbine blade is an expensive member because of its complicated structure and high dimensional accuracy and high quality material. For this reason, there is a demand to appropriately evaluate the deterioration of the turbine blades and optimize the replacement time.

  For example, Patent Document 1 discloses a turbine inspection method in which an ultrasonic inspection method is applied to an attachment site between a turbine rotor and turbine blades to inspect for defects. In Patent Document 1, an installation site that is not exposed to the outside when the turbine blade is implanted in the rotor is first inspected by an ultrasonic flaw detection method. If no defect is detected, a part of the plurality of turbine blades are extracted from the rotor to expose the attachment part, and the attachment part is further detected by the defect detection limit (detectable defect detection). Inspected by non-destructive inspection method with lower minimum length.

  In Patent Document 1, as a nondestructive inspection method having a small defect detection limit, first, a well-known magnetic particle inspection method or a penetrating inspection method is applied. The replica method is applied as a method having a defect detection limit smaller than those. The replica method is a method of detecting a turbine blade defect by creating a replica in which the outer surface of a turbine blade is transferred with a resin mainly composed of liquid silicon rubber and measuring the shape of the replica. In Patent Document 1, it is said that the inspection operation of the turbine blade can be performed efficiently and accurately by these inspection methods.

JP 2003-294716 A

  The nondestructive inspection methods (magnetic particle inspection method, penetration inspection method, replica method) other than the ultrasonic flaw detection method applied in Patent Document 1 are all methods for inspecting defects on the outer surface of the turbine blade. However, cracks (defects) are likely to occur on the inner wall surface of the turbine blade. Structures such as bosses (pillars) for securing rigidity and slits for forming flow paths are formed in the cooling space, stress concentration due to shape anisotropy occurs in various places, and the wall thickness also varies. Because. It is difficult to apply a nondestructive inspection method other than the ultrasonic flaw detection method described in Patent Document 1 to such an internal wall surface crack.

  On the other hand, if it is an ultrasonic flaw detection method, a flaw detection inspection of the inner wall surface can be performed. However, the incident ultrasonic waves are diffusely reflected back to the bosses and slits in the cooling space having a complicated shape as described above. Therefore, even if the echo screen of the reflected wave is observed, the reflected wave of the scratch is likely to be buried in the reflected wave due to the shape, and skill is required to identify the scratch from the echo screen. For this reason, there is a risk of overlooking the scratch or determining that there is a scratch at a portion that is not a scratch, and there is a problem that it is difficult to improve the flaw detection accuracy.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a turbine blade flaw detection method capable of determining a crack generated on an inner wall surface without requiring skill.

  In order to solve the above-described problems, a typical configuration of the turbine blade flaw detection method according to the present invention is to determine a crack in the inner wall surface of a turbine blade having a cooling space through which cooling air passes. This is a flaw detection method in which a change in height distribution when a load is applied to a turbine blade without a crack is obtained as a reference distribution change, and a change in height distribution when a load is applied to the turbine blade to be inspected. Is obtained as an inspection distribution change, and it is determined that a crack is present at a position where positive and negative are reversed in the difference between the reference distribution change and the inspection distribution change.

  When the object receives a load and undergoes elastic deformation, the outer surface of the object also deforms. Deformation of an object is related to bending rigidity, elongation rigidity, shear rigidity, etc. as physical properties, and the cross-section secondary moment and cross-section secondary pole moment can be considered depending on the shape. Stress concentration occurs due to directionality. As described above, a plurality of conditions and phenomena simultaneously act during the elastic deformation. Especially, when a crack is generated inside as in this case, the rigidity is partially reduced. Then, since additional elastic deformation is locally generated, additional deformation appears on the outer surface of the object. Then, by detecting a curved shape whose polarity is reversed in the difference between the exemplary height distribution change (reference distribution change) and the height distribution change of the inspection object (inspection distribution change), the inner wall surface is detected. It is possible to determine cracks.

  In the present invention, cracks are determined by acquiring a change in height distribution on the order of nanometers. On the other hand, the outer surface of the object has irregularities with a size that cannot be ignored from the beginning due to roughness of the surface finish, scratches, structural changes due to oxidation, attached dirt, and the like. However, as described above, the height distribution other than the deformation due to the load can be canceled by using the reference distribution change or the inspection distribution change. Further, by taking the difference between the reference distribution change and the inspection distribution change, only the shape caused by the crack can be detected.

  A digital holographic microscope may be used for measuring the height distribution on the nanometer order as described above. The digital holographic microscope has a high resolution for measuring the distance in the vertical direction, and can measure undulations of 1 μm or less (submicron). This makes it possible to accurately measure the height distribution of the outer surface of the turbine blade.

  The reference distribution change may be obtained by numerical analysis instead of applying a load to a turbine blade without a crack. Specifically, a change in the height distribution can be acquired by applying a load to the three-dimensional model using a finite element method analysis or a boundary element method analysis. Thereby, even when it is difficult to obtain a turbine blade having the same shape and no crack, the reference distribution change can be acquired.

  The reference distribution change may be obtained by changing the height distribution when a load is applied in the opposite direction to the turbine blade to be inspected, instead of applying a load to the turbine blade having no crack. When a load is applied in the opposite direction, the load is applied in the direction in which the crack is closed, and thus the same behavior as when there is no flaw is exhibited. Although the direction of the displacement is opposite, the reference distribution can be changed by taking an absolute value. As a result, it is possible to acquire a reference distribution change that is more realistic by using the turbine blade to be inspected, and to perform accurate determination.

  In the turbine blade flaw detection method described above, when acquiring the inspection distribution change, it is preferable to apply a load in a direction in which the turbine blade warps so that a crack generated on the inner wall surface spreads. At the position of the crack, the effective thickness of the wall surface decreases and the bending rigidity decreases. Therefore, the deformation of the crack position becomes large. Even if bending stress is applied in the direction in which the crack is blocked, the deformation of the crack position does not increase. For this reason, it is possible to determine the presence of a crack on the inner wall surface by elastically deforming the turbine blade in the above direction.

  The above turbine blade flaw detection method performs ultrasonic flaw detection using a reflection of ultrasonic waves to determine cracks, causes elastic deformation at a position determined to be flawed in ultrasonic flaw detection, and provides a reference for the position. Distribution changes and inspection distribution changes may be obtained.

  In the above configuration, first, an approximate position of a crack on the inner wall surface is quickly grasped by ultrasonic flaw detection. And the validity of the determination of an ultrasonic flaw can be confirmed by determining the presence or absence of the crack of the position. That is, the accuracy of ultrasonic flaw detection can be supplemented, and a quick and reliable crack determination can be performed.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the turbine blade flaw detection method which can determine the crack which arose in the internal wall surface without requiring skill.

It is a figure which shows a turbine. It is a figure which shows a turbine blade. It is a fragmentary sectional view of a turbine blade. It is a flowchart which shows the flaw detection method of the turbine blade concerning this embodiment. It is a figure which shows a mode that the height distribution of a turbine blade is measured using a digital holographic microscope. It is a figure which shows a mode that a height distribution is measured in the state to which the load was applied. It is the schematic which expanded the internal wall surface of Fig.6 (a). It is a mimetic diagram explaining standard distribution change, inspection distribution change, and these differences. It is a figure which shows the turbine blade to which the load is applied by the other method. It is a figure which shows the turbine blade to which the load is applied by the other method. It is the schematic which expanded the internal wall surface of Fig.9 (a). It is a figure which shows the FEM model of the turbine blade used in FEM analysis. The FEM model to which the load is applied is shown. It is a figure which shows the result of FEM analysis.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

(Turbine blade)
FIG. 1 is a view showing a turbine. The turbine 100 has a disk-shaped rotor 102 (blade wheel) and a turbine blade 104 (moving blade) attached to the outer periphery thereof. The turbine blade 104 is a blade that receives a flow of fluid. Several tens to 100 or more turbine blades 104 are detachably attached to the outer periphery of the rotor 102. A turbine shaft (not shown) that transmits rotational energy is inserted in the center of the rotor 102. In a power plant or the like, a generator is rotated by rotational energy obtained from the turbine 100 to generate power.

  FIG. 2 is a view showing the turbine blade 104. In order to firmly fix the turbine blade 104 to the rotor 102, the blade root 106, which is the fixing portion, has a so-called Christmas tree shape. With this shape, the centrifugal force generated when the turbine 100 rotates is dispersed. In general, the turbine blade 104 is formed by casting using a metal material.

  Since the turbine blades 104 are exposed to high-temperature steam and combustion gas, various cooling functions are provided. For example, an inner wall surface 110 indicated by a broken line is formed inside the turbine blade 104. The space surrounded by the inner wall surface 110 is formed as a cooling space through which cooling air or steam (hereinafter referred to as “cooling air”) can pass.

  FIG. 3 is a partial cross-sectional view of FIG. As shown in FIG. 3, a plurality of small circular ribs 112, vertically long ribs 114, and the like are formed on the inner wall surface 110 surrounding the cooling space to ensure rigidity. A space (wide portion 115) wider than the space is formed above the space where the ribs 112 and the like are formed. Above the wide portion 115, a plurality of flow paths 116 that lead from the wide portion 115 to the discharge hole 108 are formed. The cooling air passes through the inside of the cooling space from the blade root 106 toward the discharge hole 108.

  The inner wall surface 110 is formed using a casting core when the turbine blade 104 is cast. The channel 116 is formed by electric discharge machining or the like. Since such a cooling space is provided inside, the turbine blades 104 are configured such that stress concentration due to shape anisotropy tends to occur at various locations on the inner wall surface 110 during rotation. In particular, since the cross-sectional shape of the inner wall surface 110 in the vicinity of the wide portion 115 is abruptly changed, stress concentration may occur and a crack may occur.

(Turbine blade flaw detection method)
FIG. 4 is a flowchart showing a method for flaw detection of the turbine blade 104 according to the present embodiment. In the following description, various data processing and calculations are performed by a calculation unit (not shown). The calculation unit can be realized by software that the CPU operates on the RAM.

  In the flaw detection method according to the present embodiment, it is possible to determine a crack on the inner wall surface 110 of the turbine blade 104 from the outer surface. In the present embodiment, the digital holographic microscope 118 (see FIG. 5) is used to measure the height distribution of the outer surface of the turbine blade 104.

  FIG. 5 is a diagram illustrating a state in which the height distribution of the turbine blade 104 is measured using a digital holographic microscope. The digital holographic microscope 118 is a microscope that can measure a three-dimensional image of a measurement target. The digital holographic microscope 118 is a three-dimensional microscope using laser holography technology, has a high resolution for measuring the distance in the vertical direction, and can measure undulations of 1 μm or less without contact. Since the turbine blade 104 is a cast product, has extremely high rigidity, and has a length of about several tens of centimeters, it is extremely difficult to measure elastic deformation without breaking by conventional measurement methods. there were. However, by using the digital holographic microscope 118, the height distribution (shape) of the outer surface of the turbine blade 104 can be accurately measured. The height distribution measured by the digital holographic microscope 118 is output as a set (profile) of heights with respect to the position. The digital holographic microscope 118 can also display the acquired profile as a 3D digital image on the monitor.

  First, in step 300, as shown in FIG. 5, the height distribution of the outer surface of the turbine blade 103 without a crack is measured by the digital holographic microscope 118. As the turbine blade 103 without a crack, for example, an unused same-type component or a same-type component confirmed to have no crack can be used.

  In step 302, the height distribution is measured with a load applied to the turbine blade 103 without a crack. FIG. 6 is a diagram illustrating how the height distribution is measured in a state where a load is applied. FIG. 6A is a conceptual diagram of a turbine blade to which a load is applied. As shown in FIG. 6A, the load is applied by supporting the root side (blade root 106 side) and the tip side of the turbine blade 103 by fixed fulcrums 120 and 122, respectively. The load is applied as a concentrated load by the head unit 124 of a load tester (not shown). FIG. 6B is a perspective view corresponding to FIG. As shown in FIG. 6B, the head portion 124 has a bifurcated tip. This is because the digital holographic microscope 118 measures the outer surface of the center of the turbine blade 103 where the concentrated load is applied (between the two tips of the head portion 124).

  Here, as shown in FIG. 6A, the load is applied from the upper side to the lower side of the turbine blade 104. This is a process in the case of inspecting the upper inner wall surface 110 indicated by a thick broken line in the drawing.

  In step 304, the calculation unit compares the height distribution before and after applying the load, and acquires the change in the height distribution when the load is applied to the turbine blade 103 without a crack as the reference distribution change. With the change in the standard distribution, even if there are irregularities on the surface of the turbine blade 103 without cracks due to the roughness of the surface finish, scratches, structural changes due to oxidation, adhering dirt, etc., this can be offset, and depending on the load Only deformations can be obtained.

  Next, in step 306, the height distribution of the outer surface of the turbine blade 104 to be inspected, which may have a crack, is measured by the digital holographic microscope 118 (see FIG. 5). In step 308, the height distribution is measured with a load applied to the turbine blade 104 to be inspected (see FIG. 6). In the present embodiment, description will be made assuming that there is a crack inside the turbine blade 104.

  In step 310, the calculation unit compares the height distribution before and after applying the load, and acquires the change in the height distribution when the load is applied to the turbine blade 104 to be inspected as the inspection distribution change. Even in the inspection distribution change, similar to the reference distribution change, the unevenness existing on the surface can be canceled and only deformation due to the load can be acquired.

  FIG. 7 is an enlarged schematic view of the inner wall surface 110 of FIG. In FIG. 7, the inner wall surface 110 is indicated by a solid line. When the load P1 is applied from above by the head portion 124, the turbine blade 104 tries to bend as a whole. Specifically, a tensile stress N1 is generated on the inner wall surface 110 side, and a compressive load N2 is generated on the outer surface side. The digital holographic microscope 118 measures the height distribution of the surface of the region E1 that is intermediate between the two loads P1. At this time, when the crack 130 is generated on the upper inner wall surface 110, the crack 130 is deformed in the spreading direction.

  At the position of the crack 130, since the cross-sectional area is extremely small, the bending rigidity is locally weak, and since there is a sudden shape change, stress concentration occurs. Therefore, the deformation (refraction) of the position of the crack 130 is increased.

  FIG. 8 is a schematic diagram for explaining the reference distribution change, the inspection distribution change, and the difference between them. As indicated by a broken line in FIG. 8A, the change in the reference distribution of the turbine blade 103 without a crack causes a deformation based solely on the structure of the turbine blade 104, so that a smooth deflection curve is drawn. On the other hand, the inspection distribution change of the cracked turbine blade 104 has a sharp shape change at the position of the crack, and is shifted from the reference distribution change.

  In step 312, the calculation unit calculates the difference between the reference distribution change and the inspection distribution change. Then, as shown in FIG. 8B, the influence of the crack can be extracted as a deviation of the inspection distribution change from the reference distribution change (the vertical scale in FIG. 8B is larger than that in FIG. 8A). small). What is characteristic here is that, in general, it is expected that a crease will occur at the crack position, but one is convex and the other is concave with respect to the crack position. This is because the turbine blades 103 and 104 are cast products having high rigidity, and a minute displacement of 1 μm or less (submicron) is observed, so that the curved shape generated by the compressive load N2 is considered to be obvious. It is done.

  Therefore, in step 314, the calculation unit detects a curved shape whose polarity is reversed from the calculated difference. Thereby, in step 316, a crack can be determined on the inner wall surface 110 of the turbine blade 104. In order to prevent erroneous determination, it is preferable to provide a threshold value for the magnitude of the difference in detecting the bent shape of the crack.

  Here, even if bending stress is applied in the direction in which the crack 130 is blocked, the deformation of the position of the crack 130 does not increase. For this reason, in this embodiment, the presence of the crack 130 on the inner wall surface 110 appears more clearly as the deformation of the outer surface (region E1) by elastically deforming the turbine blade 104 in the direction in which the crack 130 spreads. . That is, it is preferable to apply the load in steps 302 and 306 in the direction in which the turbine blade 104 warps so that the crack 130 generated in the inner wall surface 110 spreads. In other words, it is preferable to measure the height distribution of the surface to which the load by the head portion 124 is applied.

  Furthermore, when a concentrated load is applied, it is desirable to apply the load so that the position of the crack 130 is most greatly deformed. Therefore, the head portion 124 has a bifurcated tip shape, and is configured to measure the height distribution between the bifurcated portions.

  In the above embodiment, as the turbine blade 103 without a crack, for example, an unused same-type component or the same-type component that has been confirmed to have no crack can be used. However, it is difficult to guarantee that the turbine blade 103 without a crack is a cast product and has no casting defect even if it is not used.

  Therefore, the reference distribution change may be obtained by numerical analysis instead of applying a load to the turbine blade 103 without a crack. Specifically, the reference distribution change (change in height distribution) can be acquired by applying a load to the three-dimensional model using the finite element method analysis or the boundary element method analysis. Thereby, even when it is difficult to obtain a turbine blade having the same shape and no crack, the reference distribution change can be acquired.

  The reference distribution change may be obtained by obtaining a change in height distribution when a load is applied in the opposite direction to the turbine blade 104 to be inspected instead of applying a load to the turbine blade 103 having no crack. Good. When a load is applied in the opposite direction, the load is applied in the direction in which the crack is closed, and thus the same behavior as when there is no flaw is exhibited. Although the direction of the displacement is opposite, the reference distribution change and the inspection distribution change can be compared by taking an absolute value. As a result, it is possible to acquire a reference distribution change that is more realistic by using the turbine blade to be inspected, and to perform accurate determination.

  In the above-described embodiment, an example in which a concentrated load is applied in the vicinity of the measurement position (region E1) has been described. However, the load may be applied to the turbine blade 104 using another method. 9 and 10 are diagrams illustrating the turbine blade 104 to which a load is applied by another method.

  FIG. 9 illustrates a method of fixing only the root side of the turbine blade 104 and applying a concentrated load to the tip side thereof. FIG. 9A is a conceptual diagram of this example. As shown in FIG. 9A, in this example, a jig 125 having a shape corresponding to the Christmas tree-shaped blade root 106 is used in order to more reliably fix the root side of the turbine blade 104. The load is applied as a concentrated load to the front end side of the turbine blade 104 from above by the head portion 126 of the load tester.

  FIG. 10 shows a method of fixing only the root side of the turbine blade 104 and applying a distributed load (pseudo distributed load by a plurality of concentrated loads) to the outer surface of one side. FIG. 10A is a conceptual diagram of this example. As shown in FIG. 10A, the same jig 125 as in FIG. 9A is also used in this example. The load is applied as a distributed load to the outer surface of one side of the turbine blade 104 from above by a plurality of head units 128 of the load tester.

  Both FIG. 9 and FIG. 10 show processing in the case of inspecting the upper inner wall surface 110 indicated by a thick broken line in FIG. 9 (a) and FIG. 10 (a), respectively.

  With reference to FIG. 11, the spread of a crack due to the application of a load, which is common to the load application method described with reference to FIGS. 9 and 10, will be described. FIG. 11 is an enlarged schematic view of the inner wall surface 110 of FIG. FIG. 11 corresponds to FIG. 7 and shows the inner wall surface 110 with a solid line.

  For example, in FIG. 9 (a), the root side of the turbine blade 104 is supported, and the tip P is directed downward by applying a load P2 (see FIG. 11) to the tip from above, and the turbine blade 104 is generally upward. Elastically deforms into a convex shape. At this time, as shown in FIG. 11, a load P2 (actually, the tip position of the turbine blade 104) is applied, so that almost the entire turbine blade 104 is on the convex side (upper side in the drawing) of the turbine blade 104. Tensile stress N3 occurs, and compressive stress N4 occurs on the concave side (lower side in the figure). At this time, when the crack 130 is generated on the upper inner wall surface 110, the crack 130 spreads.

  The spread of the crack 130 with reference to FIG. 11 is common to the method of applying the distributed load shown in FIG. For example, as shown in FIG. 10A, the turbine blade 104 is elastically deformed into a shape that protrudes upward as a whole by supporting the root side of the turbine blade 104 and applying a distributed load from above. At this time, as in FIG. 11, in almost the entire turbine blade 104, a tensile stress is generated on the convex side of the turbine blade 104, and a compressive stress is generated on the concave side thereof. And when the crack 130 has arisen in the upper internal wall surface 110 like FIG. 11, the crack 130 spreads.

  As described above, the presence of the crack 130 on the inner wall surface 110 can also appear as a deformation of the outer surface (region E2 in FIG. 11) by the load application method shown in FIGS. Then, the height distribution of the region E2 in FIG. 11 is measured by the digital holographic microscope 118 (see FIGS. 9B and 10B), so that the crack 130 of the inner wall surface 110 that cannot be visually recognized from the outside is obtained. Judgment is possible.

(Verification)
The processing in steps 300 to 316 is to cause the outer surface of the turbine blade to be deformed by a load load (reference distribution change and inspection distribution change), and determine the presence or absence of the crack 130 from the difference. Below, FEM (finite element method) analysis was performed in order to confirm whether the change of the height distribution could become a value large enough with respect to the vertical resolution of a digital holographic microscope.

  FIG. 12 is a diagram showing an FEM model of the turbine blade 104 used in the FEM analysis. The FEM model was a half model of the turbine blade 104. As shown in FIG. 12A, in the FEM model, the longitudinal direction from the root side to the tip side was 600 mm, and the width direction was 150 mm. Inside the FEM model, a slit having a longitudinal direction of 250 mm and a width direction of 100 mm was formed as a cooling space.

  FIG.12 (b) is AA sectional drawing of Fig.12 (a). As shown in FIG. 12B, the thickness of the FEM model was 20 mm. In addition, as shown in FIG.12 (b), the location where a cooling space does not exist is a solid structure.

  FIG.12 (c) is BB sectional drawing of Fig.12 (a). As shown in FIG. 12 (c), the cooling space was formed in the center in the thickness direction of the FEM model so as to have a length of 4 mm. A wide space having a length of 5.0 mm and a width of 5.0 mm in the figure was formed at the front end side of the cooling space.

  In this FEM analysis, both an FEM model with a crack and an FEM model without a crack were prepared and analyzed. FIG. 12D shows a crack in the FEM model having a crack. The crack was formed in the center of the upper surface in the wide space at the front end side of the cooling space. The crack depth (longitudinal direction in the figure) was 1.0 mm. FIG.12 (e) is CC sectional drawing of FIG.12 (d). As shown in FIG. 12 (e), the crack length was set to 5.0 mm. In addition, the crack is located in the approximate center of the width direction (100 mm) of the slit of Fig.12 (a).

  With reference to FIG. 13, the load application conditions in the FEM analysis will be described. FIG. 13 shows an FEM model to which a load is applied. FIG. 13A corresponds to the application of the load described with reference to FIG. 6 and shows an example in which the concentrated load is applied in the vicinity of the crack while supporting the base side and the tip side of the FEM model. FIG. 13B corresponds to the application of the load described with reference to FIG. 9 and shows an example in which only the base side of the FEM model is fixed and the concentrated load is applied to the tip side thereof. FIG. 13C shows an example in which only the base side of the FEM model is fixed and the distributed load is applied to the outer surface of one side corresponding to the application of the load described with reference to FIG. These loads were applied to both the FEM model with and without the crack.

  FIG. 14 is a diagram showing the results of FEM analysis. The table of FIG. 14A shows the load application conditions, the displacement (the amount of movement of each point caused by the load application) and the stress calculation results in each FEM model. As shown in FIG. 14A, the maximum axial stress generated in the crack portion differs between the FEM model with a crack and the FEM model without a crack. In particular, under the load application condition of concentrated load (crack position), the maximum axial stress (stress in the direction of opening the crack) generated in the crack is large in the FEM model with and without the crack. Differences appear.

  In the present FEM analysis, the applied load is set so that the maximum axial stress generated in the crack is such that the crack does not progress (around 100 MPa). Moreover, the difference between the FEM model with a crack and the FEM model without a crack was not seen in the maximum displacement and the beam bending stress.

  FIG. 14B is a graph showing the difference between the reference distribution change of the FEM model without a crack and the inspection distribution change of the FEM model with a crack when a load under each condition is applied. Note that the solid line graph shows the difference of the change almost immediately above the crack, and the broken line shows the difference of the change in the side portion (the position where there is no crack in the wide space of the cooling space). It has been confirmed that local uneven deformation does not occur in the FEM model without a crack when a load is applied.

  As shown in the solid line graph of FIG. 14B, a curve of a curved shape in which positive and negative are reversed is drawn under each load application condition. This gradient appears particularly conspicuously under the load application condition of concentrated load (crack position), which is a curved shape (wrinkle-like shape) with convex deformation and concave deformation on the outer surface of the crack position. ) Occurs. This curve-shaped gradient slightly appears in the graph on the side of the crack indicated by a broken line under each load application condition.

  Here, in the FEM analysis described above, it was possible to obtain a remarkable curved shape between the FEM model with a crack and the FEM model without a crack. The change in the height distribution was sufficiently large with respect to the vertical resolution of the digital holographic microscope.

  As a simple implementation method of the above embodiment, the following method is also possible. That is, it has been confirmed that local uneven deformation does not occur in the FEM model without a crack when a load is applied. Therefore, it is possible to acquire only the inspection distribution change without using the reference distribution change and determine the presence or absence of a crack based on the presence or absence of local uneven deformation.

  In this case, it is possible to cancel the unevenness present on the surface and obtain only the deformation due to the load. However, since there is no change in the reference distribution which is a master curve, the overall deformation cannot be canceled, and the curved shape cannot be detected with positive and negative reversals. Therefore, the change in the inspection distribution may be differentiated to obtain the rate of change, and the crack may be determined based on the presence of a rapid change (spine wave) in the rate of change.

  As described above, according to the method for flaw detection of the turbine blade 104 according to the present embodiment, a crack generated on the inner wall surface can be determined without requiring skill.

  In order to search for scratches by the above method, it is essential to measure the surface shape of the entire surface of the turbine blade 104. Therefore, it is preferable to scan the entire turbine blade 104 by moving the tip of the digital holographic microscope 118. However, depending on the shape of the inner wall surface 110, it is sufficient to measure only the location where cracks are likely to occur.

  In particular, when a concentrated load is applied, it is efficient to apply the load after grasping a portion where a crack may exist to some extent. Therefore, before performing each process shown in FIG. 4, ultrasonic flaw detection is performed in advance to determine cracks using reflection of ultrasonic waves, and elastic deformation is caused at a position determined to have flaws in ultrasonic flaw detection. The reference distribution change and the inspection distribution change at the position may be acquired.

  In the above configuration, the approximate position of the crack on the inner wall surface can be quickly grasped by ultrasonic flaw detection. And the validity of the determination of an ultrasonic flaw can be confirmed by determining the presence or absence of the crack of the position. That is, the accuracy of ultrasonic flaw detection can be supplemented, and a quick and reliable crack determination can be performed.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  INDUSTRIAL APPLICABILITY The present invention can be used for a flaw detection method for determining a crack on an inner wall surface of a turbine blade having a cooling space through which cooling air passes.

P1 ... Load, P2 ... Load, N1 ... Tensile load, N2 ... Compression load, N3 ... Tensile load, N4 ... Compression load, E1 ... Area, E2 ... Area, 100 ... Turbine, 102 ... Rotor, 103 ... None) Turbine blade, 104 ... (inspected) turbine blade, 106 ... Blade root, 108 ... Discharge hole, 110 ... Internal wall surface, 112, 114 ... Rib, 115 ... Wide part, 116 ... Channel, 118 ... Digital holo Graphic microscope, 120, 122 ... fixed fulcrum, 124, 126, 128 ... head, 125 ... jig, 130 ... crack

Claims (5)

It is a flaw detection method for determining a crack on the inner wall surface of a turbine blade having a cooling space through which cooling air passes.
The change in height distribution when a load is applied to a turbine blade without cracks is acquired as the reference distribution change,
The change in height distribution when a load is applied to the turbine blade to be inspected is acquired as the inspection distribution change,
A method for detecting flaws in a turbine blade, wherein a crack is determined to exist at a position where positive and negative are reversed in a difference between the reference distribution change and the inspection distribution change.   The turbine blade flaw detection method according to claim 1, wherein the reference distribution change is obtained by numerical analysis instead of applying a load to a turbine blade without a crack.   The reference distribution change is characterized in that instead of applying a load to a turbine blade without a crack, a change in height distribution is obtained when a load is applied in the opposite direction to the turbine blade to be inspected. The turbine blade flaw detection method according to claim 1.   4. The load according to claim 1, wherein when acquiring the inspection distribution change, a load is applied in a direction in which a turbine blade warps so that a crack generated in the inner wall surface spreads. 5. Turbine blade testing method. Perform ultrasonic flaw detection using ultrasonic reflection to determine cracks,
5. The elastic deformation is caused at a position determined to have a crack in the ultrasonic flaw detection, and the reference distribution change and the inspection distribution change at the position are acquired. 6. The method for detecting flaws in a turbine blade according to claim 1.

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