Eddy current detection probe and method for inner surface cracks of gas turbine blade film inclined holes

Abstract

A probe and method for detecting cracks on the inner surface of an oblique hole in an air film of a gas turbine blade is disclosed. The detection probe comprises three coils with a centrally placed curved magnetic core, the three coils being arranged along a horizontal straight line with two detection coils on either side. The three coils are inserted into an oblique hole structure of an air film array of a gas turbine blade at the same inclination angle, a sinusoidal AC voltage signal is passed through the excitation coil to generate eddy currents in the test piece, and the magnetic lines of force are converged by the ferromagnetic properties of the centrally placed curved magnetic core to direct the magnetic field into the inner wall of the oblique hole. Due to the specific arrangement of the two detection coils, interference from the oblique hole structure can be effectively eliminated by differential detection signals. The present invention enables precise positioning of the probe relative to the array oblique hole structure, can eliminate interference signals generated by the array oblique hole structure, the centrally placed curved magnetic core can greatly improve the signal-to-noise ratio of the defect detection signal, and the multiple detection coils can effectively avoid interference from lift-off and jitter, thereby achieving high-precision detection of cracks on the inner surface of the oblique hole in the air film array of a gas turbine blade.

Description

Technical Field

[0001] The present invention relates to an eddy current nondestructive testing probe, in particular to an eddy current testing probe and method for detecting cracks on the inner surface of an inclined air film hole of a gas turbine blade. Background Art

[0002] Gas turbine blades rely on air film cooling holes to maintain their performance and lifespan. Film hole cooling technology utilizes cooling air passing through specially designed holes in the blade, forming a protective cooling air film. This air film reduces blade surface temperature and reduces heat transfer to the blade material, thereby protecting the blade from damage by high-temperature gases. However, existing manufacturing techniques can introduce damage and cracks when machining these cooling holes. These cracks can cause stress concentrations over the blade's service life, increasing the risk of damage in harsh operating environments and shortening its service life. Compared to straight holes, inclined holes are more prone to stress concentrations, leading to defects. These defects can negatively impact component performance and service life, potentially leading to blade failure or even more serious accidents. Furthermore, prolonged and complex service conditions, stress concentration, and structural aging can also cause fatigue cracks around the holes. These damages significantly reduce component service life. Therefore, production inspections of inclined hole structures and regular integrity assessments and reliability testing of in-service film hole components are essential.

[0003] Eddy current nondestructive testing technology has high sensitivity for defect detection, and its non-contact feature means that it does not need to consider coupling agents. It is the most common nondestructive testing method in the inspection of key components of major equipment. Traditional eddy current testing methods encounter many problems in the inspection process of the inclined hole structure of the gas turbine blade air film. Due to the particularity of the inclined hole structure, cracks mostly exist on the inner surface. At this time, traditional eddy current detection probes cannot detect whether there are defects due to the skin-attracting characteristics of eddy currents. In summary, considering the harmfulness of crack defects in the inclined hole structure of the gas turbine blade air film to aircraft engine components, the design and development of an eddy current detection probe for cracks on the inner surface of the inclined hole of the gas turbine blade air film is of great significance in practical engineering. Summary of the Invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide an eddy current detection probe structure and method for cracks on the inner surface of the inclined air film hole of the gas turbine blade, so as to achieve high-sensitivity detection of cracks on the inner surface of the inclined air film hole of the gas turbine blade.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] An eddy current detection probe for cracks on the inner surface of an oblique hole of a gas turbine blade film, the eddy current detection probe comprises an excitation coil 2 and a bent magnetic core 6 of the excitation coil disposed therein, a first detection coil 3 and a bent magnetic core 7 of the first detection coil disposed therein, a second detection coil 4 and a bent magnetic core 8 of the second detection coil disposed therein; during detection, the first detection coil 3 and the second detection coil 4 are located on both sides of the excitation coil 2, and the three coils are closely attached to a test piece 1. For array oblique holes with different inclination angles, the inclination angle of the bent magnetic core is changed and inserted into the oblique hole, wherein the bent magnetic core is located inside the pancake-shaped coil. Along the axis direction of the bent coil, the inner part of the inclined hole is along the axial direction of the inclined hole. By inserting the bent magnetic cores of the excitation coil and the detection coil into the inclined hole of the array air film, the magnetic field is effectively introduced into the inner wall of the inclined hole, thereby improving the signal-to-noise ratio of the detection signal, and at the same time achieving precise positioning of the relative position of the probe and the inclined hole structure; utilizing the characteristic that cracks around the hole are mostly scattered along the radius, the arrangement of the excitation coil of the probe makes the direction of the eddy current completely perpendicular to the direction of the crack around the hole, the crack defect causes the greatest disturbance to the eddy current field, and the resulting detection signal has the largest signal-to-noise ratio, thereby achieving effective detection of tiny cracks along the radial direction of the inclined hole.

[0007] The inner diameters of the excitation coil 2, the first detection coil 3, and the second detection coil 4 are equal to or greater than the outer diameters of the corresponding bent magnetic cores. The vertical section of the bent magnetic core is inserted into the corresponding coils and fixed. The vertical section of the bent magnetic core is consistent with the height of the corresponding coil, and the length of the bent section of the bent magnetic core is less than or equal to the length along the inclined direction of the inclined hole, so as to avoid excessive constraint of the bent magnetic core on the magnetic field, which may cause the magnetic field to be extracted from the test piece.

[0008] The probe can meet the detection requirements for inclined holes with different inclination angles and test pieces with different thicknesses by changing the number of coil turns, core length and inclination angle.

[0009] The exciting coil 2, the first detecting coil 3 and the second detecting coil 4 are pancake-shaped coils.

[0010] The detection method of the eddy current detection probe for cracks on the inner surface of the inclined hole of the air film of a gas turbine blade is a differential signal detection method. After the probe is arranged, an excitation signal is first introduced into the excitation coil 2. The excitation signal is a sinusoidal AC voltage signal. The current generated by the alternating voltage signal will generate an alternating magnetic field around the excitation coil, which is recorded as the first magnetic field. Its frequency is related to the frequency of the sinusoidal AC voltage signal. Since the excitation coil 2 contains a central excitation coil bent magnetic core 6 made of ferromagnetic material with soft magnetic properties, it can introduce more magnetic lines of force into the test piece 1, thereby increasing the magnetic induction intensity of the test piece and generating an eddy current field. The density will also be greater, greatly improving the signal-to-noise ratio of the detection; the eddy current field generated by the alternating first magnetic field on the surface of the test piece will induce another magnetic field, recorded as the second magnetic field, and the second magnetic field has a direct effect on the detection signals of the first detection coil 3 and the second detection coil 4; when there are cracks on the inner surface of the inclined hole of the gas turbine blade air film, it will affect the eddy current field generated by the first magnetic field, and then change the second magnetic field, resulting in the voltage signals detected by the first detection coil 3 and the second detection coil 4 being different in size when there is a defect or not. The voltage detection signal of the first detection coil 3 is recorded as V1, the voltage detection signal of the second detection coil 4 is recorded as V2, and V 1 and V2 are complex numbers, and the difference between the two is recorded as ΔV, that is, ΔV=|V1-V2|. In the absence of defects, the excitation coil 2 will generate an induced eddy current field around the inclined hole structure under the excitation. At this time, the voltage detection signals of the first detection coil 3 and the second detection coil 4 are exactly the same, that is, V1=V2. When there is a crack defect on the inner surface of the inclined hole of the gas turbine blade air film, the induced eddy current field will be disturbed, making V1≠V2, that is, ΔV≠0. By calculating the voltage signal difference, it can be determined whether there is a crack defect on the inner surface of the inclined hole of the gas turbine blade air film; in the actual service process of the probe, when the gas turbine blade When there are no defects on the inner surface of the inclined air film hole, the values ​​of V1 and V2 may not be completely equal due to slight differences in the structure. Therefore, a crack-free standard gas turbine blade inclined air film hole is taken for inspection, and the difference ΔV between V1 and V2 is recorded as ΔV0. The relative error Δ=(ΔV / ΔV0)×100% between the inspection results ΔV and ΔV0 of the inclined hole structure to be tested is used as the judgment standard for whether the inclined hole structure has defects. When Δ≤200%, it is judged that the structural integrity is good and there are no cracks on the inner surface of the inclined air film hole of the gas turbine blade. When Δ>200%, it is judged that the structural integrity is poor and there are cracks on the inner surface of the inclined air film hole of the gas turbine blade.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] The probe of the present invention adjusts the inclination angle of the magnetic core to adapt to the angle of the inclined hole. A specially designed curved magnetic core is used, which is arranged along the axial direction of the coil inside the probe coil and along the axial direction of the inclined hole inside the inclined hole. By using the magnetic cores of the excitation coil and the detection coil to penetrate into the inclined hole, the detection magnetic field can be effectively introduced into the inner wall of the inclined hole, thereby enhancing the quality of the detection signal and improving the signal-to-noise ratio. In addition, the design of the probe of the present invention allows for precise relative positioning, reducing the influence of probe layout errors. In particular, considering that cracks usually spread along the radial direction, the configuration of the excitation coil makes the generated eddy current perpendicular to the diffusion direction of the crack, which helps to effectively detect small cracks along the radial direction of the inclined hole. Compared with traditional detection probes, the probe of the present invention is not limited by the inclined hole structure and can detect cracks on the inner surface of the inclined hole of the gas turbine blade air film.

[0013] To accurately detect cracks in inclined holes, the present invention incorporates a probe design that includes an excitation coil and two detection coils, each with an inner diameter equal to or slightly larger than the outer diameter of a central curved magnetic core within the probe. During probe assembly, the vertical portion of the central curved magnetic core is inserted into the excitation and detection coils and secured securely. The curved portion of the curved magnetic core is precisely inserted into the inclined hole to be inspected, enabling accurate positioning of the inner wall of the inclined hole. When designing the probe, attention must also be paid to the length of the central curved magnetic core. The vertical section of the magnetic core should match the height of the pancake coil within the probe, while the length of the curved section should be consistent with or slightly shorter than the depth of the inclined hole along the inclined direction. This is done to prevent the magnetic core from overly confining the magnetic field, preventing excessive concentration of the magnetic field within the inclined hole, which would affect the effective distribution of the magnetic field and the accuracy of crack detection. This design not only allows the probe to adapt to the specific structure of the inclined hole but also ensures a reasonable distribution of the magnetic field during crack detection, improving the signal-to-noise ratio of detection and achieving efficient and high-precision detection of small cracks.

[0014] The probe's excitation coil and detection coils on both sides are placed in close proximity to the specimen during testing. Using different excitation and detection coils effectively eliminates the effects of uneven probe lift. Furthermore, close proximity to the specimen increases the intensity of the induced eddy current field, significantly enhancing the probe's ability to detect defects. Taking advantage of the fact that circumferential cracks often scatter along a radius, the probe's excitation coils are arranged so that the direction of the generated eddy currents is completely perpendicular to the direction of the circumferential crack. This maximizes the crack's disturbance of the eddy current field and the resulting detection signal's signal-to-noise ratio.

[0015] Traditional eddy current detection probes are subject to the influence of eddy current detection skin depth and are unable to effectively detect cracks on the inner surface of the inclined air film holes of gas turbine blades. To address this problem, the present invention proposes a new probe configuration to solve such problems, which can achieve effective detection of cracks on the inner surface of the inclined air film holes of gas turbine blades. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The figure is a schematic diagram of an eddy current detection probe for cracks on the inner surface of an inclined air film hole of a gas turbine blade according to the present invention.

[0017] Figure 2 This is a schematic diagram of the structure of the excitation coil and the bent magnetic core embedded therein of the present invention.

[0018] Figure 3 This is a schematic diagram of the structure of the first detection coil and the second detection coil and their respective centrally placed curved magnetic cores of the present invention.

[0019] Figure 4 Schematic diagram of the inclined hole structure (including cracks) to be tested.

[0020] Figure 5 This is a schematic diagram of the relative position of the probe of the present invention and the inclined hole structure to be measured (including cracks) during service. Specific implementation methods

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, the present invention is an eddy current detection probe for cracks on the inner surface of the inclined hole of the air film of a gas turbine blade. The probe includes an excitation unit composed of an excitation coil 2 and a bent magnetic core 6 of the excitation coil disposed therein, a first detection coil 3 and a bent magnetic core 7 disposed therein, and a second detection coil 4 and a bent magnetic core 8 disposed therein to constitute a detection unit.

[0023] like Figure 2 and Figure 3 As shown, the inner diameters of the excitation coil 2 and the first and second detection coils 3 and 4 on either side of the probe are equal to or slightly larger than the outer diameters of the corresponding curved magnetic cores. The vertical section of the curved magnetic core is inserted into the corresponding coils and secured; the curved portion of the curved magnetic core is inserted into the inclined hole of the test piece to achieve precise positioning. It is worth mentioning that the length of the curved magnetic core should not be too long. The vertical section of the curved magnetic core should be consistent with the coil height of the pancake coil, and the curved section of the curved magnetic core should be consistent with or slightly shorter than the inclined length of the inclined hole. This prevents the curved magnetic core from excessively constraining the magnetic field, which could lead to the magnetic field being extracted from the test piece.

[0024] like Figure 4 As shown in the figure, the characteristic of the crack in the oblique hole structure in the air film hole is that it mostly appears in the connection direction of the hole center. The coil arrangement of the probe of the present invention generates an induced eddy current field that can be guaranteed to be perpendicular to the crack direction at all times. At this time, the crack defect has the greatest disturbance on the eddy current field, and the detection signal is the most obvious.

[0025] like Figure 5The figure shows the relative position of the probe of the present invention and the inclined hole structure to be tested (including cracks) during service. The excitation coil 2 and the first detection coil 3 and the second detection coil 4 on both sides are close to the test piece 1 during detection. The different coils for excitation and detection can effectively eliminate the influence of uneven probe lifting. At the same time, close contact with the test piece 1 can make the induced eddy current field stronger, greatly improving the ability of the probe to detect defects; the central curved magnetic core of the excitation-detection unit is respectively inserted into the inclined hole, which can achieve precise positioning and reduce the generation of detection errors.

[0026] The working principle of the present invention is as follows: The present invention is to achieve high-sensitivity detection of cracks on the inner surface of the inclined air film hole of the gas turbine blade. The specific implementation steps are as follows:

[0027] Step 1: Adjust the angle of the central curved core and insert the vertical section into the probe excitation-detection unit. The bending angle of the curved section should be consistent with the inclination angle of the inclined hole. Insert the curved section into the inclined hole to achieve positioning. Press the upper part of the probe tightly to minimize the impact of lift-off.

[0028] Step 2: Arrange the excitation-detection unit according to step 1, and pass an alternating excitation current into the excitation coil 2. The alternating excitation current will generate a primary magnetic field in the space. Under the action of the central curved magnetic core, the alternating primary magnetic field will introduce the magnetic field into the inclined hole structure. The inner wall of the inclined hole structure will excite an induced eddy current field, which will generate a secondary magnetic field. The secondary magnetic field will in turn act on the first detection coil 3 and the second detection coil 4 to generate voltage signals, namely V1 and V2. At this time, the magnitude of the induced signal is ΔV = V1-V2.

[0029] Step 3: In the absence of defects, the excitation coil 2 generates an induced eddy current field around the oblique hole structure under the action of excitation. At this time, the voltage detection signals of the first detection coil 3 and the second detection coil 4 are exactly the same, that is, V1 = V2, ΔV = 0. When a crack defect occurs on the inner surface of the oblique hole of the gas turbine blade film, the induced eddy current field is disturbed, making V1 ≠ V2, that is, ΔV ≠ 0. By calculating the voltage signal difference, it can be determined whether there is a crack defect on the inner surface of the oblique hole of the gas turbine blade film. When there is no defect, ΔV = 0; when there is a defect, ΔV ≠ 0. At the same time, based on the positive and negative values ​​of the voltage signals V1 and V2 generated by the first detection coil 3 and the second detection coil 4, the approximate location of the crack can be determined.

[0030] Step 4: During the actual service of the probe, when there are no defects in the inclined hole, the values ​​of V1 and V2 may not be completely equal due to slight differences in the inclined hole structure. Therefore, a standard inclined hole structure without cracks is taken for testing, and the difference ΔV between V1 and V2 is recorded as ΔV0. The relative error Δ between the test results ΔV and ΔV0 of the inclined hole structure to be tested (Δ=ΔV / ΔV0)×100% is used as the judgment standard for whether the inclined hole structure has defects. When Δ≤200%, it is judged that the structural integrity is good and there are no cracks on the inner surface of the gas turbine blade air film inclined hole. When Δ>200%, it is judged that the structural integrity is poor and there are cracks on the inner surface of the gas turbine blade air film inclined hole.

[0031] The present invention inserts three coils with a central curved magnetic core into the inclined hole structure of the gas turbine blade air film array with the same inclination angle, passes a sinusoidal AC voltage signal into the excitation coil, generates eddy currents in the test piece, gathers magnetic lines of force through the ferromagnetic properties of the central curved magnetic core, and introduces the magnetic field into the inner wall of the inclined hole, thereby improving the probe's detection capability for fine cracks; arranging the central curved magnetic core in the detection coil can increase the detection signal and improve the defect detection capability; due to the specific arrangement of the two detection coils, the interference of the inclined hole structure can be effectively eliminated through differential detection signals; compared with traditional probes for gas turbine blade air film hole crack detection, the present invention realizes precise positioning of the probe for the array inclined hole structure, and the special probe configuration can eliminate the interference signal generated by the array inclined hole structure, the central curved magnetic core can greatly improve the defect detection signal-to-noise ratio, and multiple detection coils can also effectively avoid the interference of lift-off and jitter, thereby realizing high-precision detection of cracks on the inner surface of the gas turbine blade air film array inclined hole.

Claims

1. An eddy current detection probe for cracks on the inner surface of the inclined air film hole of a gas turbine blade, characterized by: The eddy current detection probe comprises an excitation coil (2) and a bent magnetic core (6) of the excitation coil disposed therein, a first detection coil (3) and a bent magnetic core (7) disposed therein, and a second detection coil (4) and a bent magnetic core (8) disposed therein; during detection, the first detection coil (3) and the second detection coil (4) are located on both sides of the excitation coil (2), and the three coils are closely attached to the test piece (1); for array inclined holes with different inclined angles, the inclined angle of the bent magnetic core is changed and inserted into the inclined hole, wherein the portion of the bent magnetic core inside the pancake coil is along the curved direction. The direction of the coil axis is along the axial direction of the inclined hole in the internal part of the inclined hole. By inserting the bent magnetic cores of the excitation coil and the detection coil into the inclined hole of the array air film, the magnetic field is effectively introduced into the inner wall of the inclined hole, thereby improving the signal-to-noise ratio of the detection signal and realizing the precise positioning of the relative position of the probe and the inclined hole structure. Taking advantage of the fact that most cracks around the hole are scattered along the radius, the arrangement of the excitation coil of the probe makes the direction of the eddy current completely perpendicular to the direction of the crack around the hole. The crack defect has the greatest disturbance to the eddy current field, and the signal-to-noise ratio of the detection signal is the largest, thereby realizing effective detection of tiny cracks along the radial direction of the inclined hole.

2. The eddy current detection probe for cracks on the inner surface of the inclined air film hole of a gas turbine blade according to claim 1, characterized in that: The inner diameters of the excitation coil (2), the first detection coil (3) and the second detection coil (4) are equal to or greater than the outer diameters of the corresponding curved magnetic cores, and the vertical sections of the curved magnetic cores are inserted into the corresponding coils and fixed; the vertical sections of the curved magnetic cores are aligned with the height of the corresponding coils, and the length of the curved sections of the curved magnetic cores is less than or equal to the length in the inclined direction of the inclined hole, so as to avoid excessive constraint of the magnetic field by the curved magnetic core, which may lead to the magnetic field being led out of the test piece.

3. The eddy current detection probe for cracks on the inner surface of the inclined air film hole of a gas turbine blade according to claim 1, characterized in that: The probe can meet the detection requirements for inclined holes with different inclination angles and test pieces with different thicknesses by changing the number of coil turns, core length and inclination angle.

4. The eddy current detection probe for cracks on the inner surface of the inclined air film hole of a gas turbine blade according to claim 1, characterized in that: The excitation coil (2), the first detection coil (3) and the second detection coil (4) are pancake-shaped coils.

5. A method for detecting cracks on the inner surface of an oblique air film hole of a gas turbine blade using an eddy current detection probe according to any one of claims 1 to 4, characterized in that: The detection method is a differential signal detection method. After the probe is arranged, an excitation signal is first introduced into the excitation coil (2). The excitation signal is a sinusoidal AC voltage signal. The current generated by the alternating voltage signal generates an alternating magnetic field around the excitation coil, which is recorded as the first magnetic field. The frequency of the first magnetic field is related to the frequency of the sinusoidal AC voltage signal. Since the excitation coil (2) contains a central excitation coil bent magnetic core (6) made of ferromagnetic material and has soft magnetic properties, it can guide more magnetic lines of force into the test piece (1), thereby increasing the magnetic induction intensity of the test piece and generating a larger eddy current field density, thereby greatly improving the signal-to-noise ratio of the detection. The eddy current field generated by the field on the surface of the test piece will induce another magnetic field, which is recorded as the second magnetic field. The second magnetic field has a direct effect on the detection signals of the first detection coil (3) and the second detection coil (4); when there is a crack on the inner surface of the inclined hole of the gas turbine blade, it will affect the eddy current field generated by the first magnetic field, thereby changing the second magnetic field, resulting in the voltage signals detected by the first detection coil (3) and the second detection coil (4) being different in size when there is a defect or not. The voltage detection signal of the first detection coil (3) is recorded as V1, and the voltage detection signal of the second detection coil (4) is recorded as V2. V1 and V2 are plural numbers. The difference is recorded as ΔV, that is, ΔV=|V1-V2|. In the absence of defects, the excitation coil (2) will generate an induced eddy current field around the inclined hole structure under the excitation action. At this time, the voltage detection signals of the first detection coil (3) and the second detection coil (4) are exactly the same, that is, V1=V2. When there is a crack defect on the inner surface of the inclined hole of the gas turbine blade air film, the induced eddy current field will be disturbed, making V1≠V2, that is, ΔV≠0. By calculating the voltage signal difference, it can be determined whether there is a crack defect on the inner surface of the inclined hole of the gas turbine blade air film; in the actual service process of the probe, when the inclined hole of the gas turbine blade air film is When there are no defects on the inner surface of the hole, the values ​​of V1 and V2 may not be completely equal due to slight differences in the structure. Therefore, a crack-free standard gas turbine blade air film inclined hole is taken for inspection, and the difference ΔV between V1 and V2 is recorded as ΔV0. The relative error Δ=(ΔV / ΔV0)×100% between the inspection results ΔV and ΔV0 of the inclined hole structure to be tested is used as the judgment standard for whether the inclined hole structure has defects. When Δ≤200%, it is judged that the structural integrity is good and there are no cracks on the inner surface of the gas turbine blade air film inclined hole. When Δ>200%, it is judged that the structural integrity is poor and there are cracks on the inner surface of the gas turbine blade air film inclined hole.

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