Turbine blade inspection method
The turbine blade inspection method employs terahertz waves to accurately measure thermal barrier coating thickness in narrow sections by determining the inspection position and adjusting the measuring head's angle, addressing the inaccuracy of eddy current testing.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- MITSUBISHI HEAVY IND LTD
- Filing Date
- 2024-10-30
- Publication Date
- 2026-05-15
AI Technical Summary
Eddy current testing methods for measuring thermal barrier coating thickness on turbine blades are inaccurate in narrow, non-flat sections due to eddy currents being affected by the shape of the base material.
A turbine blade inspection method using terahertz waves to emit and detect reflected waves, determining the inspection position, adjusting the measuring head's installation angle, and calculating film thickness based on the time difference between reflected waves.
Accurately measures the film thickness of heat-shielding coatings on narrow portions of turbine blades, improving measurement accuracy by stabilizing the measuring head's posture and optimizing the incident angle.
Smart Images
Figure 2026079043000001_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a method for inspecting turbine blades.
Background Art
[0002] In a gas turbine, turbine blades provided on a rotor receive high-temperature and high-pressure combustion gas as a working fluid, thereby rotationally driving the rotor. At this time, since the turbine blades are exposed to a harsh environment of high temperature and high pressure, in order to protect the turbine blades, for example, a thermal barrier coating (TBC) may be applied to the surface of the turbine blades.
[0003] In the case of turbine blades having a thermal barrier coating applied to the surface in this way, an inspection for measuring the film thickness of the thermal barrier coating may be performed for quality control. For example, Patent Document 1 discloses a technique for measuring the film thickness of a thermal barrier coating using eddy current testing (ECT).
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] In the eddy current testing method described in Patent Document 1 above, eddy currents are generated on the surface of the turbine blade to be inspected by electromagnetic induction by energizing the coil of the probe. The thickness of the heat-shielding coating can be measured by converting the voltage change due to the eddy current, which varies depending on the distance between the coil and the base material, into a film thickness. While this type of eddy current testing method is suitable when the surface shape of the base material is relatively flat, when measuring areas with narrow shapes, such as R-shaped or C-chamfered sections (narrow areas), the eddy currents generated by the coil are affected by the shape of the base material, resulting in a decrease in measurement accuracy.
[0006] At least one embodiment of this disclosure has been made in view of the above circumstances and aims to provide a turbine blade inspection method that can accurately measure the film thickness of a heat-shielding coating applied to a narrow portion of a turbine blade. [Means for solving the problem]
[0007] A turbine blade inspection method according to at least one embodiment of this disclosure solves the above problem. A turbine blade inspection method for inspecting a heat-shielding coating applied to a narrow section of a turbine blade, An inspection position determination step for determining the inspection position in the aforementioned narrow portion, The process involves using a measuring head installed at the inspection position to emit terahertz waves into the narrow area, A reflected wave detection step in which the reflected wave of the terahertz wave is detected using the measurement head, A film thickness calculation step for calculating the film thickness of the heat-shielding coating based on the reflected wave, It is equipped with. [Effects of the Invention]
[0008] According to at least one embodiment of this disclosure, a turbine blade inspection method is provided that can accurately measure the film thickness of a heat-shielding coating applied to a narrow portion of a turbine blade. [Brief explanation of the drawing]
[0009] [Figure 1] This is a perspective view showing a turbine blade according to one embodiment. [Figure 2] This figure schematically shows how the gas turbine inspection method according to at least one embodiment of this disclosure is performed on the narrow portion of the turbine blade shown in Figure 1. [Figure 3A] This is an enlarged view of area A in Figure 1. [Figure 3B] This is an enlarged view of area B in Figure 1. [Figure 3C] This is an enlarged view of area C in Figure 1. [Figure 4] Figure 2 is a schematic diagram illustrating the principle of measuring the film thickness of a heat-shielding coating using the measuring head. [Figure 5] This is a flowchart showing a turbine blade inspection method according to one embodiment. [Figure 6] This is a schematic diagram showing how the inspection position is marked in the narrow area during step S2 of Figure 5. [Figure 7A] Figure 5 is a schematic diagram showing the auxiliary device that has been temporarily positioned in step S3. [Figure 7B] Figure 7A is a schematic diagram showing the tip of the measuring head inserted into the DD line cross-section. [Figure 8A] This is a schematic diagram showing the state in step S4 of Figure 5 where the measuring head is in the first position. [Figure 8B] This figure shows the measurement results of the first and second reflected waves detected by the measurement head in the state shown in Figure 8A. [Figure 9A] This is a schematic diagram showing the state in step S4 of Figure 5 where the measuring head is in the second position. [Figure 9B] This figure shows the measurement results of the first and second reflected waves detected by the measurement head in the state shown in Figure 9A. [Figure 10] This is a schematic diagram showing how the installation angle of the measuring head is changed in step S5 of Figure 5. [Modes for carrying out the invention]
[0010] Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the configurations described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples.
[0011] First, referring to FIG. 1, the turbine blade 1 which is the inspection object of the turbine blade inspection method according to at least one embodiment of the present disclosure will be described. FIG. 1 is a perspective view showing the turbine blade 1 according to one embodiment, and FIG. 2 is a diagram schematically showing a state in which the gas turbine inspection method according to at least one embodiment of the present disclosure is implemented with respect to the narrow portion 5 of the turbine blade 1 shown in FIG. 1.
[0012] The turbine blade 1 is, for example, a moving blade or a stationary blade attached so as to stand radially on a rotor (not shown) extending along the axial direction of the gas turbine. The turbine blade 1 has a blade length direction from the blade root portion 2 toward the blade tip portion 3 along the radial direction of the rotor. Further, the turbine blade 1 is configured such that the blade thickness decreases as it approaches the edge side along the blade width direction.
[0013] As shown in FIG. 2, the turbine blade 1 uses a metal material as the base material 6, and a thermal barrier coating 4 (TBC: Thermal Barrier Coating) is applied on its surface with a predetermined film thickness. The thermal barrier coating 4 is, for example, a coating obtained by applying an MCrAlY (M is Co, Ni, CoNi, etc.) alloy excellent in oxidation resistance as a bond coat and then coating a ZrO2-based ceramic with a low thermal conductivity as a top coat.
[0014] The turbine blade 1 having such a configuration has a narrow portion 5. The narrow portion 5 is any part of the turbine blade 1 that includes a non-flat characteristic shape, and is a part where the eddy current generated by the energized coil is affected by the narrow shape when the eddy current flaw detection method is applied for measuring the film thickness of the thermal barrier coating 4. Quantitatively speaking, the narrow portion 5 is a part that includes a range of, for example, 10 mm from the point of maximum curvature on the surface of the turbine blade 1.
[0015] Figure 2 shows an example of a narrow section 5, which includes two corners 6a and 6b as points of maximum curvature. The inventors of this application have verified that, if eddy current testing is used to measure the film thickness of the heat-shielding coating 4 in such a narrow section 5, the eddy currents generated by the coil are affected by the narrow shape of the base material 6, resulting in a large measurement error. This problem can be suitably solved by the turbine blade inspection method using terahertz waves (THW), as described later. In this specification, terahertz waves refer to electromagnetic waves in the frequency range of 0.1 to 10 THz (wavelength range of 3 mm to 30 μm).
[0016] Figures 3A to 3C show other configuration examples of the narrow section 5, and the turbine blade inspection method according to at least one embodiment of this disclosure is also applicable to these narrow sections 5. Figure 3A is an enlarged view of area A in Figure 1, Figure 3B is an enlarged view of area B in Figure 1, and Figure 3C is an enlarged view of area C in Figure 1.
[0017] For example, Figure 3A shows the tip C surface on the ventral or dorsal side of the turbine blade 1. The tip C surface has two corners 6c and 6d as points of maximum curvature, and the narrowed section 5 extends 10 mm from each of these corners. Figure 3B shows the PF C surface as another example of the narrowed section 5. The PF C surface has two corners 6e and 6f as points of maximum curvature, and the narrowed section 5 extends 10 mm from each of these corners. Figure 3C shows the T / E section as yet another example of the narrowed section 5. The T / E section has an R section as a point of maximum curvature, and the narrowed section 5 extends 10 mm from the intersection point 6g with the camber line.
[0018] In the turbine blade inspection method according to at least one embodiment of the present disclosure, as shown in Figure 2, a terahertz wave THW is emitted to the narrow portion 5 using a measuring head 10, and a reflected wave RW from the narrow portion 5 is detected.
[0019] Here, Figure 4 is a schematic diagram illustrating the principle of measuring the film thickness of the heat-shielding coating 4 using the measuring head 10 shown in Figure 2. Terahertz waves THW emitted from the measuring head 10 toward the narrow section 5 are reflected by the surface of the heat-shielding coating 4 or the base material 6 in the narrow section 5, and the reflected waves RW are detected by the measuring head 10. These reflected waves RW include a first reflected wave RW1 reflected by the surface of the base material 6, and a second reflected wave RW2 from the surface of the heat-shielding coating 4.
[0020] The measuring head 10 identifies the arrival times of the first reflected wave RW1 and the second reflected wave RW2 from the detected reflected wave RW, and calculates the film thickness of the heat-shielding coating 4 based on the difference in their arrival times Δt. This conversion calculation from the arrival time difference Δt to the film thickness of the heat-shielding coating 4 may be performed by a calculation device (not shown) to which the measuring head 10 is connected.
[0021] Next, a turbine blade inspection method according to at least one embodiment of this disclosure will be described in more detail. Figure 5 is a flowchart of the turbine blade inspection method according to one embodiment.
[0022] First, the turbine blade 1 to be inspected is installed (step S1). In step S1, for example as shown in Figure 1, the turbine blade 1 is installed in a stable position by clamping the blade root 2 with the blade root 2 facing downwards.
[0023] Next, the inspection position Pk is marked on the narrow section 5 of the turbine blade 1 installed in step S1 (step S2). The inspection position Pk is a position within the narrow section 5 that is predetermined to be used for measuring the thickness of the heat-shielding coating 4. More specifically, it is the position where the auxiliary device 20 for holding the measuring head 10 is temporarily installed in the temporary positioning step (step S3) described later.
[0024] Figure 6 is a schematic diagram showing how inspection positions Pk are marked on the narrow section 5 in step S2 of Figure 5. In step S2, a template TP having a shape corresponding to the narrow section 5 to be inspected is prepared. Markers M1 to M3 corresponding to inspection positions Pk are formed in advance on this template TP, and with the template TP positioned to correspond to the narrow section 5 (Figure 6 shows an example where the long axis of the template TP is aligned with the longitudinal direction of the narrow section 5), inspection positions Pk1 to Pk3 corresponding to each marker M1 to M3 are drawn as ruled lines near the narrow section 5.
[0025] In step S2, instead of directly marking the inspection positions Pk corresponding to markers M1 to M3 on the narrow section 5, a template TP with markers M1 to M3 formed on a transparent substrate may be prepared, for example, and the template TP may be attached to the corresponding position near the narrow section 5. In this case, it becomes unnecessary to mark the inspection positions Pk around the narrow section 5 to be inspected, thus preventing contamination of the inspected object.
[0026] Next, using the inspection position Pk marked in step S2 as a reference, the auxiliary tool 20 for holding the measuring head 10 is temporarily positioned relative to the narrow section 5 (step S3). Here, Figure 7A is a schematic diagram showing the auxiliary tool 20 temporarily positioned in step S3 of Figure 5, and Figure 7B is a schematic diagram showing the tip 12 of the measuring head 10 inserted in the cross section along line DD in Figure 7A.
[0027] The auxiliary device 20 has an opening 22 that penetrates along the thickness direction (vertical direction in Figure 7B) when installed in the narrow section 5. The opening 22 has a substantially constant diameter and is formed to be slightly larger than the tip 12 of the measuring head 10. When the tip 12 of the measuring head 10 is inserted into the opening 22, the orientation of the measuring head 10 can be rotated and adjusted with respect to the tip 12 (see Figure 10).
[0028] On the outward-facing surface (shown in Figure 7A) of the auxiliary device 20 installed in the narrow section 5, a first line L1 and a second line L2 are formed, which are perpendicular to each other. In step S3, the first line L1 is provisionally positioned to correspond to the inspection position Pk marked in step S2, and the second line L2 is provisionally positioned to correspond to the virtual centerline C of the narrow section 5 (Figure 7A illustrates the case where the device is provisionally positioned to inspection position Pk2 among several inspection positions Pk).
[0029] Next, with the tip 12 of the measuring head 10 inserted into the opening 22 of the auxiliary tool 20 that was temporarily positioned in step S3, a preliminary inspection is performed to determine the inspection position while moving the auxiliary tool 20 along the surface of the narrow section 5. During the preliminary inspection, while moving the auxiliary tool 20 in this manner, the first reflected wave RW1 from the base material 6 is monitored when a terahertz wave THW is emitted using the measuring head 10. As a result, the inspection position is determined as the range in which the peak value of the first reflected wave RW1 from the base material 6 is greater than or equal to the reference value (step S4).
[0030] Figure 8A is a schematic diagram showing the state in which the measurement head 10 is in the first position in step S4 of Figure 5, and Figure 8B is a diagram showing the measurement results of the first reflected wave RW1 and the second reflected wave RW2 detected by the measurement head 10 in the state shown in Figure 8A.
[0031] In the first position shown in Figure 8A, if the terahertz wave THW emitted from the measuring head 10 hits the inclined surface of the narrow section 5, the first reflected wave RW1 will be directed in a direction different from the incident direction of the terahertz wave THW, and the peak value of the first reflected wave RW1 detected by the measuring head 10 will be less than the reference value. In this case, as shown in Figure 8B, the reflected wave RW detected by the measuring head 10 does not contain a balanced amount of the first reflected wave RW1 and the second reflected wave RW2 necessary for calculating the thickness of the heat-shielding coating 4 (because the first reflected wave RW1 is in a range that cannot be measured, making it impossible to accurately determine the time difference Δt), and the accuracy of measuring the thickness of the heat-shielding coating 4 decreases.
[0032] On the other hand, Figure 9A is a schematic diagram showing the state in which the measurement head 10 is in the second position in step S4 of Figure 5, and Figure 9B is a diagram showing the measurement results of the first reflected wave RW1 and the second reflected wave RW2 detected by the measurement head 10 in the state shown in Figure 9A.
[0033] In the second position shown in Figure 9A, when the terahertz wave THW emitted from the measuring head 10 strikes the flat surface of the narrow section 5, the first reflected wave RW1 is directed back towards the measuring head 10, and the peak value of the first reflected wave RW1 detected by the measuring head 10 is greater than or equal to the reference value. In this case, as shown in Figure 9B, the reflected wave RW detected by the measuring head 10 contains a balanced amount of the first reflected wave RW1 and the second reflected wave RW2 necessary for calculating the thickness of the heat-shielding coating 4, enabling accurate measurement of the thickness of the heat-shielding coating 4.
[0034] In the turbine blade 1, the heat-shielding coating 4 applied to the base material 6 may have its surface polished or otherwise treated, resulting in the surface of the base material 6 and the surface of the heat-shielding coating 4 not being perfectly parallel to each other, and the thickness of the heat-shielding coating 4 may vary depending on the inspection location. In step S4, by determining the inspection location to be within a range where the peak value of the first reflected wave RW1 from the base material 6 is relatively large, the accuracy of the film thickness inspection can be suitably improved.
[0035] Next, the installation angle of the measuring head 10 is determined at the inspection position determined in step S4 (step S5). In step S5, with the position of the auxiliary device 20 relative to the narrow section 5 fixed at the inspection position determined in step S4, a preliminary inspection is performed while changing the angle of the measuring head 10 to find an installation angle of the measuring head 10 suitable for the inspection.
[0036] Here, Figure 10 is a schematic diagram showing how the installation angle of the measuring head 10 is changed in step S5 of Figure 5. As mentioned above, the opening 22 provided in the auxiliary device 20 is formed to be slightly larger than the tip 12 of the measuring head 10, so that, as shown in Figure 10, the measuring head 10 can rotate with the tip 12 as the reference point while the tip 12 is inserted into the opening 22. In step S5, while changing the installation angle of the measuring head 10 in this way, the reflected wave RW generated by the terahertz wave THW emitted from the measuring head 10 is detected, and the installation angle in which the peak value of the first reflected wave RW1 included in the reflected wave RW is maximized is identified.
[0037] As mentioned above, the heat-shielding coating 4 applied to the turbine blade 1 may have its surface polished or otherwise treated, resulting in the surface of the base material 6 and the surface of the heat-shielding coating 4 not being perfectly parallel to each other, and the thickness of the heat-shielding coating 4 may vary depending on the inspection position. Therefore, by changing the installation angle of the measurement head 10 and identifying the angle at which the peak value of the first reflected wave RW1 is maximized, the angle at which the thickness of the heat-shielding coating 4 is minimized at that inspection position can be identified.
[0038] Next, at the inspection position determined in step S4, terahertz waves are irradiated using the measurement head 10, which is set at the installation angle determined in step S5 (step S6), and the reflected wave RW is detected (step S7). Based on the reflected wave RW detected in step S7, the thickness of the heat-shielding coating 4 in the narrow section 5 is calculated (step S8). Specifically, the thickness of the heat-shielding coating 4 is calculated based on the time difference Δt between the first reflected wave RW1 and the second reflected wave RW2 contained in the reflected wave RW detected in step S7.
[0039] As described above, according to the above embodiment, a terahertz wave THW is emitted from the narrow portion 5 of the turbine blade 1 using the measuring head 10, and its reflected wave RW is detected. Based on the reflected wave RW of the terahertz wave THW detected in this way, the thickness of the heat-shielding coating 4 applied to the narrow portion 5 of the turbine blade 1 can be measured with high accuracy.
[0040] Furthermore, it is possible to replace the components in the above-described embodiments with well-known components as appropriate, without departing from the spirit of this disclosure, and the above-described embodiments may also be combined as appropriate.
[0041] The contents described in each of the above embodiments can be understood, for example, as follows:
[0042] (1) A turbine blade inspection method according to one embodiment is: A turbine blade inspection method for inspecting a heat-shielding coating applied to a narrow section of a turbine blade, An inspection position determination step for determining the inspection position in the aforementioned narrow portion, The process involves using a measuring head installed at the inspection position to emit terahertz waves into the narrow area, A reflected wave detection step in which the reflected wave of the terahertz wave is detected using the measurement head, A film thickness calculation step for calculating the film thickness of the heat-shielding coating based on the reflected wave, It is equipped with.
[0043] According to the embodiment described in (1) above, a measuring head is used to emit terahertz waves into the narrow portion of the turbine blade, and the reflected waves are detected. Based on the reflected terahertz waves detected in this way, the thickness of the heat-shielding coating applied to the narrow portion of the turbine blade can be measured with high accuracy.
[0044] (2) In other embodiments, in the embodiment of (1) above, The reflected wave includes a first reflected wave from the base material surface of the turbine blade and a second reflected wave from the surface of the heat-shielding coating. In the aforementioned film thickness measurement step, the film thickness is calculated based on the difference in arrival times of the first reflected wave and the second reflected wave at the measuring head.
[0045] According to the embodiment of (2) above, the thickness of the heat-shielding coating in a narrow area can be accurately measured based on the difference in arrival time at the measurement head of the first reflected wave and the second reflected wave contained in the reflected wave detected when terahertz waves are emitted to the turbine blade.
[0046] (3) In other embodiments, in the embodiment of (2) above, In the inspection position determination step, the inspection position is determined as a range in which the peak value of the first reflected wave detected by the measuring head is equal to or greater than a reference value when the measuring head is moved along the surface of the narrow portion and the terahertz wave is emitted using the measuring head.
[0047] According to the embodiment of (3) above, the inspection position where the measuring head for detecting the emission and reflected waves of terahertz waves is installed is identified as the range in which the peak value of the first reflected wave from the base material is equal to or greater than a reference value when terahertz waves are emitted while the measuring head is moved along the surface of the narrow section. The heat-shielding coating applied to the turbine blade may have its surface polished or otherwise treated, so the surface of the base material and the surface of the heat-shielding coating are not necessarily parallel to each other, and the thickness of the heat-shielding coating may vary depending on the position. In this embodiment, by determining the inspection position as the range in which the peak value of the first reflected wave from the base material is relatively large, the reflected wave from the narrow section in response to the terahertz waves emitted from the measuring head can be suitably detected, and the accuracy of measuring the thickness of the heat-shielding coating can be suitably improved.
[0048] (4) In other embodiments, in the embodiment of (3) above, In the inspection position determination step, an auxiliary tool is placed on the surface of the narrow portion, and with the tip of the measuring head inserted into the opening of the auxiliary tool, the measuring head is moved along the surface of the narrow portion.
[0049] According to the embodiment described in (4) above, the measuring head is moved when determining the inspection position while its tip is inserted into an opening in an auxiliary device installed on the surface of the narrow area. This makes it possible to determine the inspection position while stabilizing the posture of the measuring head relative to the narrow area to be inspected.
[0050] (5) In other embodiments, in any one embodiment of (2) to (4) above, In the inspection position determination step, the installation angle of the measuring head at the inspection position is determined such that the peak value of the first reflected wave detected by the measuring head is maximized when the incident angle of the terahertz wave on the surface of the narrow portion is changed.
[0051] According to the embodiment of (5) above, the installation angle of the measuring head at the inspection position is determined such that the peak value of the first reflected wave from the base material is maximized when the incident angle of the terahertz wave is changed. As mentioned above, the heat-shielding coating applied to the turbine blade may have surfaces that are not parallel to each other due to polishing or other treatments performed on its surface. In this embodiment, by determining the installation angle of the measuring head such that the peak value of the first reflected wave from the base material is maximized, it is possible to identify the orientation of the measuring head that allows for the appropriate detection of reflected waves necessary for measuring the thickness of the heat-shielding coating in a confined space.
[0052] (6) In other embodiments, in the embodiment of (5) above, In the inspection position determination step, an auxiliary device is placed on the surface of the narrow portion, and the tip of the measuring head is inserted into the opening of the auxiliary device. The incident angle is then changed by changing the installation angle of the measuring head.
[0053] According to the embodiment of (6) above, by inserting the tip of the measuring head into the opening of an auxiliary device installed on the surface of the narrow part and changing the installation angle of the measuring head, the installation position of the measuring head relative to the narrow part can be stably maintained while suitably searching for the incident angle of the terahertz wave that maximizes the peak value of the first reflected wave from the base material.
[0054] (7) In other embodiments, in any one embodiment of (1) to (6) above, In the inspection position determination step, when an auxiliary tool having an opening into which the tip of the measuring head can be inserted is placed on the surface of the narrow portion, a provisional position is performed such that a first line formed on the surface of the auxiliary tool corresponds to a marker pre-formed on the narrow portion, and a second line formed on the surface of the auxiliary tool and perpendicular to the first line corresponds to the virtual center line of the narrow portion.
[0055] According to the embodiment of (7) above, an auxiliary tool having mutually orthogonal first and second lines formed thereon allows for the simple and accurate temporary positioning of a measuring head used for measuring the thickness of a heat-shielding coating in a narrow portion of a turbine blade.
[0056] (8) In other embodiments, in any one embodiment of (1) to (7) above, The aforementioned narrow portion includes a range of 10 mm from the point of maximum curvature on the surface of the turbine blade.
[0057] When eddy current testing is used on the turbine blade surface, the measurement accuracy decreases in the 10 mm range from the point of maximum curvature because the eddy current used for measurement is affected by the shape of the base material in the narrow area. In the embodiment described in (8) above, the thickness of the heat-shielding coating can be measured with good accuracy in the narrow area where the measurement accuracy decreases with eddy current testing. [Explanation of Symbols]
[0058] 1 Turbine blade 2 Wing root 3 Wing tip 4. Heat-shielding coating 5 Narrow area 6 Base material 10 measuring heads 12 Tip 20 assistive devices 22 Opening C Virtual Centerline L1 Line 1 L2 2nd Line M1~M3 Marker Pk inspection location THW Terahertz waves RW reflected wave RW1 1st reflected wave RW2 2nd reflected wave TP Template
Claims
1. A turbine blade inspection method for inspecting a heat-shielding coating applied to a narrow section of a turbine blade, An inspection position determination step for determining the inspection position in the aforementioned narrow portion, The process involves using a measuring head installed at the inspection position to emit terahertz waves into the narrow area, A reflected wave detection step in which the reflected wave of the terahertz wave is detected using the measurement head, A film thickness calculation step for calculating the film thickness of the heat-shielding coating based on the reflected wave, A turbine blade inspection method comprising the following features.
2. The reflected wave includes a first reflected wave from the base material surface of the turbine blade and a second reflected wave from the surface of the heat-shielding coating. The turbine blade inspection method according to claim 1, wherein the film thickness measurement step calculates the film thickness based on the difference in arrival times of the first reflected wave and the second reflected wave at the measuring head.
3. The turbine blade inspection method according to claim 2, wherein in the inspection position determination step, the inspection position is determined as a range in which the peak value of the first reflected wave detected by the measuring head is equal to or greater than a reference value when the measuring head is moved along the surface of the narrow portion and the terahertz wave is emitted using the measuring head.
4. The turbine blade inspection method according to claim 3, wherein in the inspection position determination step, an auxiliary device is installed on the surface of the narrow portion, and the tip of the measuring head is inserted into the opening of the auxiliary device, and the measuring head is moved along the surface of the narrow portion.
5. The turbine blade inspection method according to claim 2, wherein in the inspection position determination step, the installation angle of the measuring head at the inspection position is determined such that the peak value of the first reflected wave detected by the measuring head is maximized when the incident angle of the terahertz wave to the surface of the narrow portion is changed.
6. The turbine blade inspection method according to claim 5, wherein in the inspection position determination step, an auxiliary device is installed on the surface of the narrow portion, and the incident angle is changed by changing the installation angle of the measuring head while the tip of the measuring head is inserted into the opening of the auxiliary device.
7. The turbine blade inspection method according to claim 1 or 2, wherein in the inspection position determination step, when an auxiliary tool having an opening into which the tip of the measuring head can be inserted is placed on the surface of the narrow portion, a provisional position is performed such that a first line formed on the surface of the auxiliary tool corresponds to a marker previously formed on the narrow portion, and a second line formed on the surface of the auxiliary tool and perpendicular to the first line corresponds to a virtual center line of the narrow portion.
8. The turbine blade inspection method according to claim 1 or 2, wherein the narrow portion includes a range of 10 mm from the point of maximum curvature on the surface of the turbine blade.