Device and method for coating hard-to-reach surfaces in a gas turbine

Abstract

The invention relates to a device and a method for coating hard-to-reach surfaces of a gas turbine (20), in particular of an aircraft engine. The device (1) comprises a guide tube (2), which can be inserted through a borescope opening (22), and a repeatedly plastically deformable support element (3) for guiding a borescope head (7) positioned at one end (3') of the support element (3), wherein the guide tube (2) is designed to deform the support element (3) when the support element (3) is guided through the guide tube (2), such that the final shaping of the support element (3) when the latter is inserted into the gas turbine (20) is defined by the guide tube (2) positioned on the gas turbine (20), and wherein the support element (3) and the borescope head (7) have a working channel (15) for the passage of a slurry (30), the discharge opening (13) of which is positioned on the borescope head (7) in such a way that the slurry (30) discharged therefrom passes into the image region (8) of the borescope head (7). In the method, a slurry is discharged, for example, by a device (1) according to the invention and applied to a surface before the slurry (30) is heated such that a coating is formed.

Description

Device and method for coating hard-to-reach surfaces in a gas turbine

[0001] The invention relates to a device and a method for coating hard-to-reach components of a gas turbine, in particular an aircraft engine.

[0002] The combustion chamber of a gas turbine, as well as the guide vanes of the high-pressure turbine located directly behind the combustion chamber, are exposed to very high thermal, mechanical, corrosive, and / or erosive stresses during operation. To withstand these stresses, the combustion chamber and guide vanes are regularly coated with thermal barrier coatings (TBC) or environmental barrier coatings (EBC). However, due to these stresses, local wear of the coating or even flaking of larger areas can occur. If these remain undetected and at least permanently unrepaired, the affected parts of the gas turbine, and consequently the gas turbine as a whole, can fail.

[0003] Various methods are known in the art for the optical inspection of internal areas of a gas turbine. For example, the use of borescopes for the optical inspection of gas turbines is known. A borescope can be inserted through a lateral opening into a fully assembled gas turbine to allow for optical inspection of the turbine's interior. This allows, for instance, the combustion chamber and guide vanes of the high-pressure turbine to be examined and assessed for damage to their coatings.

[0004] If damage to the coating of the combustion chamber or a guide vane is detected, further investigation will be carried out. The investigation checks whether the damage is critical for the safe operation of the gas turbine. If damage is classified as critical, the gas turbine must be repaired appropriately, which usually means disassembling the gas turbine so that the component with the damaged coating can be replaced or removed for coating restoration.

[0005] Critical damage to the coating of a combustion chamber or guide vane of a gas turbine requires immediate and costly repairs. Damage initially classified as non-critical often worsens during continued operation of the gas turbine, so that even damage initially deemed non-critical regularly results in the later need for repairs to restore the coating.

[0006] The object of the present invention is to create a device and a method with which at least minor damage to the coating can be repaired with significantly reduced effort compared to the prior art.

[0007] This problem is solved by a device according to claim 1, and by a method according to claim 7. Advantageous further developments are the subject of the dependent claims.

[0008] Accordingly, the invention relates to a device for coating hard-to-reach surfaces of a gas turbine, comprising a guide tube that can be inserted through a borescope opening and a repeatedly plastically deformable support element for guiding a borescope head arranged at one end of the support element, wherein the guide tube is designed to deform the support element when the support element is passed through the guide tube, so that the The final shape of the support element during its insertion into the gas turbine is determined by the guide tube arranged on the gas turbine, and wherein the support element and the borescope head have a working channel for the application of a slurry, the discharge opening of which is arranged on the borescope head in such a way that the slurry discharged from it enters the image area of ​​the borescope head.

[0009] The invention further relates to a method for coating hard-to-reach surfaces of a gas turbine with a borescope-like device comprising a borescope head and a working channel for applying a slurry, the dispensing opening of which is arranged on the borescope head such that the dispensed slurry enters the field of view of the borescope head, characterized by the steps: a) Inserting the device through a borescope opening on the gas turbine; b) Aligning the field of view of the borescope head onto a region of the surface such that the slurry dispensed from the dispensing opening is applied to the surface in at least a part of the area of ​​the surface in the field of view of the borescope head; c) Dispensing a slurry from the dispensing opening and applying the slurry to the surface in at least a part of the area of ​​the surface in the field of view of the borescope head;d) Heating the slurry applied to the surface to coat the surface.

[0010] First, some terms used in connection with the invention will be explained.

[0011] A "slurry" is a suspension in water in which, upon sufficient heating, the water evaporates, leaving behind the initially finely dispersed solid particles. These remaining solid particles can then directly form a coating. It is possible that the coating formed from the solid particles can be further solidified, particularly through further and / or sustained heating, for example, by sintering. It is also possible that, after the water evaporates, a chemical reaction is initiated on the solid particles in a coating by other environmental changes, such as the introduction of process gas, which can also solidify the coating. Instead of water, a water- and / or polymer-based gel can also be used for the slurry; the essential requirement is simply that the gel evaporates upon sufficient heating.

[0012] The "boroscope head" is the part of a boroscope that ultimately determines its imaging area. In a purely optical boroscope, this corresponds, for example, to the boroscope lens or the entry surface of a fiber optic cable, which defines the final imaging cone; in a video boroscope, this is the imaging area of ​​the dedicated image acquisition sensors. It is irrelevant whether the boroscope optics are used for 2D image acquisition in the visible spectrum, imaging in the non-visible spectrum (e.g., infrared), and / or the acquisition of 3D data, e.g., via triangulation. The boroscope head can be mounted on a rigid or flexible shaft. However, it is also possible to mount the boroscope head without its own structural shaft on another element, such as the support element.

[0013] A "boroscope-like device" is a device that is fundamentally comparable to, or at least can be used in conjunction with, a boroscope. The device comprises a boroscope head with an image area, and the image captured in the image area of ​​the boroscope head can be displayed remotely from the boroscope head. The transmission of the image from the boroscope head to the display can be configured in any way, for example, by optical fibers or by electrical transmission of a recorded video image. The boroscope head can be guided on a rigid or flexible shaft, in which case the device is directly similar to a known boroscope. However, the boroscope head can also be arranged on a repeatedly plastically deformable support element and thus resemble the device according to the invention, or, if a working channel and a discharge opening are provided, be essentially the same.

[0014] The invention recognizes that by selectively introducing a slurry into a gas turbine and subsequently heating the slurry, a coating can be produced, at least in areas of minor damage, which can at least delay further damage propagation without having to disassemble the gas turbine – as is necessary in the prior art. Accordingly, extensive repair measures for the coating can be postponed.

[0015] The device according to the invention is particularly well suited for the targeted introduction of a slurry into a gas turbine. For this purpose, the slurry is introduced into the gas turbine in such a way that, after exiting the designated discharge opening, it enters the field of view of the borescope head directly. By appropriately aligning the device or the borescope head, the slurry can be applied in a targeted manner, ensuring the proper application of the The application of the slurry to a desired surface can be monitored directly via the device.

[0016] The slurry to be applied is conveyed to the dispensing opening via a working channel provided in the support element. The invention recognizes that, due to fluid dynamics, the intermittent conveyance of a slurry through the working channel in boroscopes known from the prior art with a flexible – i.e., particularly flexible – shaft causes the position and orientation of the dispensing opening to change unpredictably, thus making targeted dispensing of a slurry with a flexible boroscope impossible.

[0017] To nevertheless enable the targeted application of a slurry, the device according to the invention has a repeatedly plastically deformable support element for guiding a borescope head arranged at one end of the support element. The final shape of the borescope head during insertion into a gas turbine is determined by a guide tube arranged on the gas turbine. The guide tube also defines the point at which the support element actually projects freely into the gas turbine. By a suitable design and arrangement of the guide tube, and optionally by suitable pre-deformation of the support element (e.g., bending or torsional deformation), a predetermined path of the support element can be achieved inside the gas turbine, thereby allowing the borescope head with its attached dispensing opening to be precisely positioned.As also indicated by the designation as a support element, the shape of the support element achieved after deformation is essentially maintained even with the borescope head attached to it, meaning that the support element is self-supporting in this respect.

[0018] According to the invention, the support element is repeatedly plastically deformable, whereby this deformability must be such that actual deformation is possible or actually occurs when the support element is passed through the guide tube. "Repeatedly plastically deformable" refers to the property that the support element exhibits no or only minimal signs of fatigue during deformation and essentially retains the shape achieved by deformation, in particular that any elastic component of the deformation is less than the plastic deformation component of the support element. Preferably, the support element is deformable for several cycles, e.g., at least 20 cycles, and more preferably at least 50 cycles, within the range of deformations expected when using the device according to the invention, without any noticeable signs of fatigue occurring.

[0019] Several types of pipes are known in the prior art that are fundamentally suitable as support elements for the device according to the invention. It is particularly advantageous and therefore preferred if the support element is a composite material pipe. The support element can comprise a core made of wound metal strip, the metal strip preferably being aluminum and / or longitudinally wound. To maintain the dimensional stability of the support element after deformation, a plastic sheathing, preferably polyethylene, is preferably provided around the core. A protective coating, preferably a protective film, can be provided on the side of the core opposite the sheathing, so that in this case the core is completely surrounded by the sheathing and protective coating. This ensures a smooth surface on both the outer and inner sides of the support element.Furthermore, the risk of damage to a gas turbine component in the event of (unintentional) contact with the support element is reduced. Suitable pipes are used. At the priority date, they were available, for example, under the trade name "Dekabon" or under the brand name "Synflex" of Eaton Corporation, USA, and are described in more detail, for example, in patent US 4,216,802.

[0020] The guide tube of the device can be designed for direct attachment to the gas turbine in a fixed and thus reproducible position, for example, by attaching the guide tube to the borescope openings themselves or to surrounding attachment points on the gas turbine. However, it is also possible to provide a guide tube mounting that, while also allowing attachment to the gas turbine in a fixed position, permits the position of the guide tube relative to the mounting to be changed in a planned and preferably controllable manner. It is then possible, after attaching the guide tube mounting to the gas turbine, to guide the support element successively along different paths inside the gas turbine by appropriately changing the position of the guide tube. Boroscope openings can be openings specifically designed for this purpose, but—for example—in an aircraft engine - also spark plug, fuel nozzle or maintenance openings.

[0021] The device preferably includes a pre-deformation unit for pre-deforming the support element before it passes through the guide tube. Even if the support element is deformed by the guide tube during insertion into an aircraft engine, the final shape of the support element, and thus the path along which a borescope is guided through the aircraft engine, can be influenced by the shape of the support element before it passes through the guide tube. This applies particularly to deformations such as torsional pre-deformation, but also to bending pre-deformation. It is preferred that if the pre-deformation unit is controllable. By appropriately controlling the pre-deformation unit, different paths for the support element inside the aircraft engine can be achieved.

[0022] It is preferred if the device includes a drive unit for the support element. The drive unit can be designed to propel the support element. It is preferred if the drive unit is also designed to rotate the support element.

[0023] Alternatively or additionally to the aforementioned possibilities for influencing the final path of the support element inside the gas turbine, the guide tube can be adaptively adjustable, i.e., its shape is fundamentally changeable. This adaptive adjustment can be achieved mechanically, thermomechanically, and / or electromechanically.

[0024] To further increase the adjustability of the boroscope head, it is preferred if the boroscope head can be adjusted relative to the support element via at least one Bowden cable. In particular, an angle between the boroscope head and the support element, or their respective axes, can be changed by a Bowden cable. If at least two Bowden cables are provided and suitably arranged on the boroscope head, the boroscope head can be pivoted relative to the support element in any direction.

[0025] A nozzle is preferably provided at the dispensing opening. This nozzle allows for increased precision in the application of the slurry. The nozzle can be adapted to the properties of the slurry as well as the dispensing parameters, such as pressure.

[0026] The device can include a pump for dispensing the slurry. The pump can convey the slurry directly through the working channel. Alternatively, instead of being configured as a liquid pump, the pump can also be designed to generate compressed air. The compressed air can then be used to convey the slurry through the working channel of the device.

[0027] In the inventive method, which is preferably carried out using the inventive device, a device with a borescope head and working channel is inserted into the gas turbine such that the area of ​​the surface to be coated lies within the field of view of the borescope head. The slurry is then applied to the area in question through the dispensing opening. Upon heating, the water in the slurry evaporates, leaving a coating of solid particles on the surface. The coating can be further hardened by additional process steps, e.g., by sintering.

[0028] To prevent the borescope head from moving unintentionally due to the slurry flowing through the working channel for dispensing, it may be provided that the slurry is dispensed at low pressure, e.g., a maximum of 4 bar (4xl 0). 5Pa ) , preferably at most 2 bar ( 2xl 0 5 Pa ), is carried out. Alternatively, the slurry can be applied with the aid of compressed air, whereby the slurry is conveyed through the working channel by the compressed air.

[0029] To prevent the working channel from becoming clogged by evaporation of water during the heating of the applied slurry, it is preferred if the device is removed before the applied slurry is heated. or the working channel is completely emptied. In the latter case, the device can remain in the gas turbine during heating, so that the heating process and any subsequent process steps can be monitored directly.

[0030] The heating of the slurry applied to the surface, required during the process, can be achieved by a suitable heating device, which, for example, is temporarily installed in the gas turbine. However, it is also possible for the slurry to be heated by starting up the gas turbine in which the slurry was applied. It is only necessary to ensure that the heating during startup or operation of the gas turbine is sufficient and occurs quickly enough to create the desired surface coating, while simultaneously ensuring that the airflow generated during startup or operation does not blow away any applied, but potentially not yet fully solidified, slurry.

[0031] The slurry can be, in particular, a ceramic or MCrAlY slurry. These materials are suitable for coating, among other things, combustion chambers and guide vanes in a gas turbine.

[0032] The invention will now be described by way of example with reference to an advantageous embodiment and the accompanying drawings. These show: Figure 1: a schematic representation of an exemplary embodiment of a device according to the invention; Figures 2a-c: schematic representations of the implementation of a method according to the invention with the device from Figure 1; and

[0033] Figure 3: Schematic representation of damage to a coating repaired using the inventive method. Figure 1 schematically shows a device 1 according to the invention in an exemplary state of use for the inspection and repair of the combustion chamber 21 of a gas turbine 20 (in this case, an aircraft engine). For the sake of clarity, only the combustion chamber 21 of the gas turbine 20 is shown. However, the device according to the invention can be used, in particular, with the combustion chamber 21 installed in a gas turbine 20 and especially also in an aircraft engine mounted on an aircraft.

[0034] The device comprises a guide tube 2, which is attached to the aircraft engine 20 via a guide tube mounting 4 and projects into the combustion chamber 21 through a borescope opening 22. The guide tube mounting 4 can also be adjusted manually or automatically in the attached state on the aircraft engine 20 such that the position of the guide tube 2 relative to the borescope opening 22 can be deliberately changed.

[0035] A repeatedly plastically deformable support element 3 is inserted into the guide tube 2. The support element 3 is a composite material tube comprising a core of longitudinally wound aluminum strip, an outer sheath of polyethylene, and a protective film as a coating on the inside. The support element 3 is self-supporting and also supports the borescope head 7 located at the end 3' of the support element 3 that is inserted into the combustion chamber 21, so that after the support element 3 passes through the guide tube 2, during which deformation occurs, the borescope head 7 follows the path 90 inside the combustion chamber 21.

[0036] To ensure that the support element 3 actually follows the depicted path 90, which in this example is in A pre-deformation unit 5 is provided for the support element 3 to run along a plane 11, with which the support element 3 is pre-deformed before passing through the guide tube 2, particularly with regard to torsion, in order to prevent any torsional deformations that may occur due to the design of the support element 3 during deformation in the guide tube 2.

[0037] The pre-deformation unit 5 integrally incorporates a drive unit 6, with which the propulsion, i.e. the final passage of the support element 3 through the guide tube 2, is achieved.

[0038] The boroscope head 7 includes an image acquisition unit, which defines the image area 8 of the boroscope head 7. The images acquired by the boroscope head 7 are transmitted to a display 9 via a data line routed through the carrier element 3. Alternatively or additionally, the acquired images can also be transmitted to other devices for further processing.

[0039] Furthermore, the borescope head 7 is pivotable relative to the support element 3. For this purpose, the borescope head 7 is pivotably connected to the end 3' of the support element 3. A Bowden cable 10 is guided through the support element 3, so that the pivot position of the borescope head 7 relative to the support element 3 can be adjusted manually or automatically at the control element 11.

[0040] From borescope head 7 onwards, a nozzle 12 is provided, which functions as a dispensing opening 13. A slurry can be conveyed via the nozzle 12 or the dispensing opening 13 by means of the pump 16 through the working channel 15 extending through the support element 3, so that the slurry is dispensed in the direction indicated by the dashed line 14. Due to the orientation of the nozzle 12 or the dispensing opening 13 ensures that the slurry is dispensed in the image area 8 of the boroscope head 7, i.e., that the slurry is dispensed directly into the image area 8 of the boroscope head 7 or the device 1.

[0041] The use of the device 1 and thus the method according to the invention will now be explained with reference to Figures 1 and 2.

[0042] After the device 1 has been inserted into the gas turbine 20, the borescope head 7 is moved and aligned through the combustion chamber 21 via the pre-deformation unit 5, the drive unit 6 and the control element 11 for pivoting the borescope head 7 relative to the carrier element 3, so that the coating 23 of the combustion chamber 21 can be inspected.

[0043] An image captured by the device 1 is shown by way of example in Figure 2a, in which damage 24 to the coating 23 is present in the depicted image area 8. The damage 24 found is still considered so non-critical that extensive repair of the coating in this area and the disassembly of the gas turbine 20 required for this purpose are not yet indicated.

[0044] If damage 24 is detected, the borescope head 7 is aligned with respect to the damage 24 in such a way that the pump 16 is used under a pressure of 1.5 bar (l.5xl 0 5 The slurry 30 dispensed through the nozzle 12 or the dispensing opening 13 not only reaches the image area 8 of the borescope head 7, but also reaches the area of ​​the coating 23 with the damage 24, whereby due to the surface tension of the slurry, a curved surface is initially formed (Figure 2b).

[0045] Subsequently, the remaining slurry is removed from the working channel 15 using pump 16, before the applied slurry 30 is heated to such an extent that the water it contains evaporates. The remaining solid – in this case MCrAlY – then forms a coating 30' which completely covers and compensates for the original damage 24 (Figure 2c).

[0046] The process is thus essentially complete. However, it is of course possible to further treat the solid remaining from the applied slurry, e.g. to sinter it, in order to further harden the coating 30'.

[0047] Figure 3 schematically shows examples of damage 24 to a coating 23 repaired with the device 1 from Figure 1 in a sectional view.

[0048] The coating 23 in the illustrated embodiment has a multi-layered structure. On a substrate 25, which is part of the coated structure, namely, for example, the wall of a combustion chamber 21 of a gas turbine 20, an adhesive layer 26 is first applied, which improves the bond between the substrate 25 and the actual protective layer 28.

[0049] Figure 3 shows three different types of damage 24 as examples. The damage shown on the left extends essentially only through the protective layer 28. In the case of the damage 24 shown in the middle, the degree of damage is greater, since the damage 24 has already penetrated through the protective layer 28 into the adhesive layer 26. extends. In the case of the damage 24 shown on the right, the substrate 25 has also already been affected.

[0050] All damages 24 shown in Figure 3 have already been repaired using the inventive method as explained in connection with Figure 2, with the aid of the device 1 according to Figure 1, which is why reference is made to the preceding explanations.

[0051] The damage 24 shown in the center and on the right, which extends beyond the protective layer 28, was repaired using a two-stage process. First, a slurry 30' adapted to the technical properties of the adhesive layer 26 and / or the substrate 25 was applied and heated sufficiently to solidify. Then, a further slurry 30, whose technical properties are based on those of the protective layer 28, was applied and cured. For the damage 24 shown on the left, only the latter slurry 30 was used for repair.

[0052] The coating 23 shown in Figure 3 can be a thermal barrier coating (TBC), in which a substrate 25, usually based on nickel or cobalt, is provided, for example, with an adhesive layer 26 made of an MCrAlY material and a protective layer 28 made of 7% yttrium-stabilized zirconia (7YSZ). The slurries 30, 30' are to be selected accordingly.

[0053] Is the coating 23 shown in Figure 3 an environmental barrier coating (“environmental barrier coating”, EBC) for a substrate 25 e.g. made of silicon carbide or fiber-reinforced silicon carbide (SiC-SiC (CMC) ) The adhesive layer 26 can be made of silicon, while the actual protective layer 28 can be made of yttrium silicate or yttrium-ytterbium silicate (mono- or di-silicate) or comprise any combination of these materials. Here too, the slurries 30, 30' are to be selected.

Claims

Patent claims 1. Device (1) for coating hard-to-reach surfaces of a gas turbine (20) comprising a guide tube (2) insertable through a borescope opening (22) and a repeatedly plastically deformable support element (3) for guiding a borescope head (7) arranged at one end (3') of the support element (3), wherein the guide tube (2) is designed to deform the support element (3) when the support element (3) is passed through the guide tube (2), such that the final shape of the support element (3) when inserted into the gas turbine (20) is determined by the guide tube (2) arranged on the gas turbine (20), and wherein the support element (3) and the borescope head (7) has a working channel (15) for carrying out a slurry (30), the dispensing opening (13) of which is arranged on the boroscope head (7) in such a way that the slurry (30) dispensed from it enters the image area (8) of the boroscope head (7).

2. Device according to claim 1, characterized in that the borescope head (7) can be aligned relative to the support element (3) preferably via at least one Bowden cable (10).

3. Device according to one of the preceding claims, characterized in that a nozzle (12) is provided at the dispensing opening (13).

4. Device according to one of the preceding claims, characterized in that the device (1) includes a pump (16) for the direct conveyance of slurry (30) through the working channel (15) or a compressed air pump for generating compressed air for the conveyance of the slurry (30) through the working channel (15) includes.

5. Device according to one of the preceding claims, characterized in that the support element (3) is a composite material tube, preferably comprising a core of wound metal strip, preferably aluminium strip and / or longitudinally wound, with a sheathing made of plastic, preferably polyethylene, and / or a protective covering, preferably a protective film, on the inside.

6. Device according to one of the preceding claims, characterized in that a pre-deformation unit (5) is provided for pre-deformation, in particular torsional and / or bending pre-deformation, of the support element (3) before the support element (3) is passed through the guide tube (2), wherein the pre-deformation unit (5) is preferably controllable.

7. Method for coating hard-to-reach surfaces of a gas turbine (20) with a borescope-like device (1) comprising a borescope head (7) and a working channel (15) for applying a slurry (30), the dispensing opening (13) of which is arranged on the borescope head (7) such that the slurry (30) dispensed from it enters the image area (8) of the borescope head (7), characterized by the steps: a) Inserting the device (1) through a borescope opening (22) on the gas turbine (20); b) Aligning the image area (8) of the borescope head (7) with a region of the surface such that the slurry (30) dispensed from the dispensing opening (13) a) dispensing a slurry (30) from the dispensing opening (13) and applying the slurry (30) to the surface in at least a part of the area of ​​the surface in the image area (8); d) heating the slurry (30) applied to the surface to coat the surface.

8. Method according to one of the preceding claims, characterized in that the application of the slurry (30) is carried out with low pressure or with the aid of compressed air.

9. Method according to one of the preceding claims, characterized in that the application of the slurry (30) is carried out at a pressure of at most 4 bar (4x0 5 Pa), further preferably of at most 2 bar (2xL0 5 Pa) is carried out.

10. Method according to one of the preceding claims, characterized in that the device (1) is removed before heating the applied slurry (30) or the working channel (15) is completely emptied.

11. Method according to one of the preceding claims, characterized in that The slurry (30) applied to the surface is heated by starting up the gas turbine.

12. Method according to one of the preceding claims, characterized in that the slurry (40) is a ceramic or MCrAlY slurry.

13. Method according to one of the preceding claims, characterized in that the method is carried out with a device (1) according to one of claims 1 to 6.

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