GB2487930A

GB2487930A - Inspection of engine components

Info

Publication number: GB2487930A
Application number: GB1102171.4A
Authority: GB
Inventors: James Kell; Daniel Clark
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2011-02-09
Filing date: 2011-02-09
Publication date: 2012-08-15
Also published as: GB201102171D0

Abstract

A method of inspecting a component situated within an engine, the component such as a turbine blade 10 comprising a wall having a first side and a second side, comprises inserting a fluid supply tube into the engine, placing an outlet of the fluid supply tube adjacent to the first side of the wall in a region where a hole 20 extending through the wall from the first side to the second side is nominally located, delivering a test fluid such as steam through the fluid supply tube to induce flow of the test fluid through the hole 20, deploying a sensor panel 34 on collapsible frame 28 adjacent the second side of the component wall in the path of test fluid issuing from the hole, the sensor panel being sensitive to the impingement of the test fluid, and assessing the condition of the hole in dependence on the response of the sensor panel at the location corresponding to the hole.

Description

INSPECTION OF HOLES

This invention relates to a method of inspecting a hole in a component, and to apparatus for use in such a method. The invention is particularly, although not exclusively, concerned with the in situ inspection of holes in components of gas turbine engines.

Many components of gas turbine engines, such as turbine vanes and blades, and combustor components, are exposed to very high temperatures in operation of the engine, which can be close to or exceed the melting point of the material from which the component is made. It is well known to cool such components by means of high pressure air taken from the compressor of the engine and ducted to the component.

For this purpose, turbine blades and vanes may have internal cavities to which the cooling air is supplied, and holes which extend from the cavity to the outside surface of the blade through which the cooling air can pass to rejoin the main gas flow through the engine. The cooling air not only extracts heat from the blade or vane as it passes through the cavity and the cooling holes, but also forms a film of cooler air over the surface of the blade, shielding it from the hot gas flow.

Holes are disposed in an array on the surface of the vane or blade, and the disposition of the holes in the array is carefully determined in order to provide the maximum cooling effect with minimum use of cooling air. If a hole becomes blocked, for example by debris entering the cooling air supply, the temperature of the surrounding surface of the blade or vane will increase. If enough holes become blocked, the resulting temperature increase can lead to failure of the material of the blade or vane, which can result in failure of the component itself, and possibly the entire engine. It is therefore desirable to inspect cooling holes in such components, and particularly aerofoil components such as turbine blades and vanes, to check that the cooling holes remain sufficiently clear so that they can perform their intended cooling function.

Various cooling hole inspection techniques have been proposed, for example in US 4644162, US 5111046 and US 6524395. The known techniques all require the inspected component to be removed from the engine. Strip down of a gas turbine engine to the extent required to remove turbine blades and vanes is very time consuming and expensive, and consequently extensive cooling hole inspection is not currently practical between major engine overhauls.

According to the present invention there is provided a method of inspecting a component situated within an engine, the component comprising a wall having a first side and a second side, the method comprising: (i) inserting a fluid supply tube into the engine; (ii) placing an outlet of the fluid supply tube adjacent to the first side of the wall in a region where a hole extending through the wall from the first side to the second side is nominally located; (iii) delivering a test fluid through the fluid supply tube to the outlet of the fluid supply tube to induce flow of the test fluid through the hole; (iv) deploying a sensor panel adjacent the component adjacent the second side of the wall in the path of test fluid issuing from the hole, the sensor panel being sensitive to the impingement of the test fluid; and (v) assessing the condition of the hole in dependence on the response of the sensor panel at the location corresponding to the hole.

The wall may define at least in part a cavity within the component, and the outlet of the fluid supply tube is placed in fluid communication with the component cavity.

The method may further comprise the step of making a seal between the fluid supply tube and the component such that the hole is substantially the only means for the test fluid to exit the component. The fluid supply tube may be in fluid communication with a fluid supply reservoir external to and unconnected with the engine.

A method in accordance with the present invention is particularly suitable when the hole is one of an array of holes, in which case the sensor panel may be of a sufficient size to extend into the paths of test fluid issuing from a plurality, and possibly all, of the holes of the array.

Various test fluids may be employed, in conjunction with a sensor panel, which is sensitive to the impingement of the respective test fluid. In one embodiment, the test fluid is steam.

The sensor panel may comprise a sheet impregnated with an indicator composition which changes state upon impingement by the test fluid. The indicator composition may be a universal indicator solution which undergoes a colour change when subjected to impingement by the test fluid, such as steam.

The sensor panel may comprise a sheet of absorbent material such as a woven or non-woven textile material, or paper. The sensor panel may also include a backing material, such as a fine gauze or mesh to support the sheet in a desired configuration to match the profile of a surface of the component in which the hole, or the array of holes, is provided.

In an alternative method, the sensor panel may comprise an array of electromechanical transducers, each of which can generate an electrical signal on impingement of the test fluid. The disposition of the transducers in the transducer array may correspond to the disposition of holes in the hole array.

The sensor panel may be supported by a frame. The frame may be of variable geometry so that it can assume a collapsed condition and a deployed condition. Thus, the frame, with the sensor panel, can be delivered to a position adjacent a component inside a gas turbine engine or other machine in the collapsed condition, and then transformed into the deployed condition when in the desired position. The frame may have locating means for cooperation with the component to locate the deployed sensor panel in a desired position with respect to the component.

While a method in accordance with the present invention may be employed to inspect one or more holes in a component when in situ within a machine, or after removal from the machine, a method in accordance with the present invention is particularly suitable for the in situ inspection of a hole, or array of holes, in a component while in situ in a gas turbine engine, for example air bearings, valve seals, pressure seals, perforated noise reduction features, fuel injector nozzles and cross-flow heat exchangers. The method is also suitable for inspecting cooling holes in components, for example combustor liners. More specifically, a method in accordance with the present invention is suitable for inspecting cooling holes in an aerofoil component of the gas turbine engine, for example turbine rotor blades and turbine stator vanes (i.e. nozzle guide vanes). The method is also suitable for inspecting holes in components which are present for purposes other than cooling, for example for supplying air for air bearings.

The present invention also provides a device for conducting a method as defined above, the device comprising a sensor panel which is sensitive to the impingement of the test fluid. The device may comprise a frame of variable geometry which carries the sensor panel.

The present invention also provides for a fluid supply tube to conduct a method as defined above wherein the fluid supply tube comprises at least part of a borescope. The fluid supply tube may define the central core of the borescope. Alternatively the fluid supply tube may be coupled to the outer surface of the borescope. The fluid supply tube may comprise a heat insulation jacket.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a partial sectional view of a gas turbine engine; Figure 2 shows a turbine blade of the engine of Figure 1; Figure 3 represents the blade of Figure 2 in conjunction with a device for inspecting cooling holes of the blade; Figure 4 is a view of the device in the direction of the arrow A in Figure 3; Figures 5 and 6 show the device of Figure 4 in different configurations; and Figure 7 and 8 show different views of a fluid supply tube in accordance with the present invention.

Figure 1 shows part of a compressor 2, a combustor 4 and a high pressure (HP) turbine stage 6 of a gas turbine engine. The HP turbine stage comprises a nozzle guide vane 8 and a turbine blade 10. In operation of the engine, as is well known, air is compressed by the compressor 2 and supplied to the combustor 4, where it is mixed with fuel and ignited. The combustion products then flow through the HP turbine 6, and other turbine stages, to generate power.

The compressor 2, the turbine 6 and the combustor 4 are situated within an engine casing 12. A partition 14 defines an annular chamber 16 around the combustor. The blade 10 is shown in Figure 2, and comprises an aerofoil section 18 having one or more internal cavities 26 (shown in Figure 1) which, when the engine is operational, are supplied with cooling air from the compressor 2. The air circulates within the aerofoil section 18 and is eventually discharged into the main gas flow through the engine via an array of cooling holes 20.

In the same manner, the vane 8 also has one or more internal cavities 26 and cooling holes corresponding to the cooling holes 20.

In operation, cooling air issuing from the holes 20 forms a film of relatively cool air over the surface of the aerofoil section 18, shielding it from the hot gases issuing from the combustor 4. Complete or partial blockage of any of the holes 20 reduces the volume of issuing air forming the film, and so can result in overheating of the material of the blade 10 (or vane 8). Misshapen holes, for example due to erosion, damage or process variation, may also effect the flow rate of air passing through the holes, and hence result in under or over cooling of the material of the blade 10 (or vane 8). However, it will be appreciated that it is difficult, or impossible, to inspect the condition of the holes using conventional means while the vane 8 and blade 10 are situated within the engine.

In accordance with the present invention, the condition of the holes 20 is assessed as follows. A fluid supply tube 22a,b is inserted through a port 24 provided in the wall of the engine casing 12. The fluid supply tube 22a,b is fed through the port 24 towards a component 8,10 for inspection, in this embodiment a turbine stator vane 8. The fluid supply tube 22a,b is fed through any available route through the engine. In the example shown, two possible routes are presented by lines 22a and 22b through ports 24a and 24b respectively. In the first case, the fluid supply tube 22a is fed through an inner casing, then through port in the combustor 4, across to an opposite wall of the combustor 4, through another port and then routed around the outside of the combustor 4 to a radially inner port on the stator 8. In the second case the fluid supply tube is passed through a more direct route through a port 24b in the engine casing 12, through an inner casing and into a port in the radially outer end of the stator 8. The exact route is dependent on the configuration of the engine and location of the component, and the described routes are presented merely as examples. In the example the fluid supply tube 22 may be routed to the component 8 by the 22a route, the 22b route, or both.

The outlet 27 of the fluid supply tube 22a,b is thus placed in fluid communication with the component cavities 26. That is to say, fluid passing from the fluid supply tube 22a,b will be delivered to the cavity 26 of the component. Thus, in use a test fluid (for example steam) is delivered from a fluid supply reservoir external to and unconnected with the engine via the fluid supply tube 22a,b, and exhausted from an outlet 27 of the fluid supply tube into the cavities in the vane 8 (or blade 10), and issues from the holes 20.

The fluid supply tube 22a,b may be simply inserted in the component 8,10. Alternatively a seal may be made between the fluid supply tube 22a,b and the component 8,10 such that the holes 20 are substantially the only means for the test fluid to exit the component 8,10, thus preventing it from leaking between the fluid supply tube 22a,b and the port in the component 8,10 through which it has been inserted or engaged with.

An inspection device 28 (Figures 3 to 6) is introduced into the engine by any suitable route and deployed to detect the steam issuing from the holes 20 of the vane 8 or blade 10. It will be appreciated from Figures 5 and 6 that the device 28 can be transformed from a collapsed condition shown in Figure 6 to a deployed configuration shown in Figure 5. In the collapsed condition shown in Figure 6, the device has a small profile and so can be inserted into the engine through a relatively small opening, or along a relatively convoluted passage. Routing and final positioning of the device 28 can be assisted visually by means of, for example, a borescope.

Figures 3 and 4 show the device 28 in the deployed configuration. As shown in Figure 4, the device 28 comprises a frame 30 having a pair of parallel members 32 which support a sensor panel 34. The sensor panel 34 comprises a backing member which may comprise a fine gauze or other mesh which supports a paper sheet of sensor material which is impregnated with a universal indicator solution. Spring loaded tension members 36 extend between the members 32 to bias the frame 30 and the sensor panel 34 into a desired configuration.

As shown in Figure 3, the deployed sensor panel 34 is positioned close to the blade 10.

Although not shown, the members 32 of the frame 30 may have locating features which engage the blade 10 to locate the sensor panel 34 precisely with respect to the surface of the blade 10, and at a desired distance from it.

The spacing, or stand-off, of the sensor screen 34 from the surface of the blade 10 is such as to allow the steam serving as a test fluid, (although another test fluid may be employed) to issue freely from the holes 20 and to impinge on the surface of the sensor panel 34. Each hole 20 that is open will thus produce a jet of steam which, when impinging on the sensor panel 34, will change the state of the indicator solution and so provide a visual indication that the hole 20 in question is open. No steam will issue from a blocked hole 20, and consequently the state of the indicator solution at the respective position on the sensor panel 34 will not change. Any partially blocked or misshaped hole will produce a relatively weak flow of steam, and, in some circumstances, this may show up on the indicator panel as a distorted, mis-positioned, or undersized area on the sensor panel 34 as a result of the change of state of the indicator solution. There is thus at least a qualitative indication of reduced flow through the partially blocked hole.

The sensor panel 34 is exposed to the steam issuing from the holes 20 for a relatively short period, for example approximately 1 second. This is long enough to cause the change of state of the indicator solution at positions directly opposite open holes 20, while avoiding any additional change of state, at regions not directly opposite the holes 20, as a result of diffusion or turbulent interactions in the issuing steam.

Where the test fluid is steam, it is supplied to the cavity 26, for example, at a pressure not greater than 0.2 Mpa, for example 0.l5Mpa, above atmosphere, and at a temperature of approximately 120°C. It will be appreciated that, if steam is used as the test fluid, it will be supplied at an elevated temperature, for example up to 200°C, whereas other fluids, such as air with or without any additives to enhance sensing reliability, may be supplied at lower temperatures, for example down to ambient temperature.

The frame 30 may be constructed from interconnected links, including the parallel elements 32, which may be hollow, and provided with an internal cable. Joints 38 between links are formed as cammed structures, so that, depending on the tension t (Figure 6) applied to the cables, the device 28 transforms between the collapsed and deployed configurations shown in Figures 6 and 7. In the collapsed configuration, the device 28 may, for example, be sufficiently slender to fit through a borescope inspection port (typically having a diameter of 2 to 8 mm).

In an alternative embodiment, the sensor screen 34 may comprise other means for responding to impingement of the test fluid. For example, the sensor screen could comprise an electro-mechanical system, such as a MEMS-type (microelectro-mechanical system) sensor. Such sensors could operate using fibrous defiectors or piezo-electric devices coupled to, or serving as, transducers, which convert deflection, under the influence of the impinging test fluid, to electrical signals.

Regardless of the type of sensor panel 34, the sensor panel response can be analysed to establish the existence, and location, or any blocked, or possibly partially blocked, or misshapen, holes 20. That is to say the sensor panel 34 response can be analysed to assess the condition of holes 20 at the location corresponding to the holes.

It is desirable for the sensor panel 34 to be positioned as close as possible to the surface of the component in which the holes 20 are provided, without causing stagnation of the flow through the holes 20. This is particularly important where the holes 20 in the array are disposed close to one another, in order to enable adequate resolution of the sensor panel response. It is desirable for the sensor panel 34 to be positioned closer to the surface than the separation distance between adjacent holes 20, so that the flow issuing from each hole 20 impinges on the sensor panel 34 before mixing with flow from any other hole. If necessary, the sensor panel 34 can be permeable by the test fluid to avoid stagnation of the flow, or the sensor panel can be inclined so that the jets issuing from the holes 20 impinge obliquely on the sensor panel 34, again to avoid stagnation of the flow. In such circumstances, and also if the jets issuing from the holes 20 are themselves inclined to the surface of the component 8, 10, the shape of the area which responds to the test fluid may be elliptical rather than circular, as is the case when the jets from the holes 20 impinge perpendicularly on the sensor panel 34.

In order to avoid poor sensor response as a result of jets from the holes 20 impinging in an oblique manner on the sensor panel 34, the sensor panel 34 may comprise a plurality of tubes extending normal to the plane of the sensor panel, so that oblique flows are redirected in the normal direction. The tubes may be disposed in an array corresponding to the array of holes in the component 8, 10 so that each hole 20 has a corresponding tube on the sensor panel 34.

In such an embodiment, the vibration of each tube as a result of test fluid impingement from the respective hole 20 stimulates the respective MEMS sensor.

An advantage of an electro-mechanical sensor system is that the sensor panel 34 would not be a "one-shot" device, but could remain within the engine and displaced from one vane 8 or blade 10 to another as each reading is taken. The response of the sensor panel 34 to each vane 8 or blade 10 could be transmitted to a suitable processor outside the engine for analysis of the data. The response could be in the form of a still or video image calibrated to illustrate absolute or relative exit velocities from each hole. For example, different colours could be used to indicate different flow rates in a still or moving image. By contrast, a sensor panel 34 utilising an absorbent material impregnated with an indicator solution would normally need to be retrieved from the engine after each vane or blade has been tested for either visual analysis of the resulting response, or for analysis by a suitable image capture system. As an alternative, if the image generated by the change of state of the indicator solution is carried through the thickness of the absorbent material so as to be visible from the rear -11 -of the sensor panel 34, a "close in" camera system could be used to image the sensor panel response without withdrawing the sensor panel 34 itself. If required, illumination may be supplied, for example via a fibre optic device, to improve the image captured by the camera.

Figure 7 and 8 illustrate an embodiment of a fluid supply tube 22a,b. The fluid supply tube 22a,b comprises at least part of a borescope 40. In this context "borescope" is taken to mean an inspection instrument that can be inserted into a structure to examine the inside of the structure. In this embodiment the fluid supply tube 22a,b defines the central core of the borescope 40, with the sheath around the outside of the fluid supply tube defining an annular gap 47 which is utilised for the delivery of inspection tools 48, the details of which are not relevant to the present invention. In the example shown, one quadrant of the gap 47 is shown as being a bundle of fibre optic cables for the delivery of light for illumination.

The outlet end 27 of the fluid supply tube 22a,b, and hence the end of the borescope, has a manoeuvrable portion 44. This section may be remotely controlled such that the tip 44 can bend up, down, left and right to allow a user to steer the fluid supply tube (and the associated borescope) around obstacles, such as pipework 46 as shown in Figure 7, in the engine as it is inserted and directed towards the component 8,10 for inspection. Articulation cables 50 are provided at 12, 3, 6 and 9 o'clock positions of the borescope. The cables 50 are fixed to the manoeuvrable portion 44, and free to slide along channels in the 12, 3, 6 and 9 o'clock positions along the length of the borescope.

Hence pulling on one of the cable 50 will pull the manoeuvrable portion 44 towards its respective 12, 3, 6 and 9 o'clock position.

The fluid supply tube may further comprise a heat insulation jacket 52. In the example shown this sits between the wall of the fluid supply tube and the annular gap 47. The heat insulation jacket 52 will maintain test fluid passed along the fluid delivery tube 22a,b at a preferred temperature, and also reduce any heat transfer between the fluid and the annular gap 47.

Alternatively the fluid supply tube 22a,b is coupled to the outer surface of the borescope 40.

A fluorescent gas, such as fluorescein, may be introduced into the test fluid, and illuminated by a light source on the end of the borescope, which can then be detected by an appropriately configured sensor panel.

Claims

CLAIMSA method of inspecting a component situated within an engine, the component comprising a wall having a first side and a second side, the method comprising: (iv) inserting a fluid supply tube into the engine; (v) placing an outlet of the fluid supply tube adjacent to the first side of the wall in a region where a hole extending through the wall from the first side to the second side is nominally located; (vi) delivering a test fluid through the fluid supply tube to the outlet of the fluid supply tube to induce flow of the test fluid through the hole; (iv) deploying a sensor panel adjacent the component adjacent the second side of the wall in the path of test fluid issuing from the hole, the sensor panel being sensitive to the impingement of the test fluid; and (v) assessing the condition of the hole in dependence on the response of the sensor panel at the location corresponding to the hole.
2 A method as claimed in claim 1, wherein the wall defines at least in part a cavity within the component, and the outlet of the fluid supply tube is placed in fluid communication with the component cavity.
3 A method as claimed in claim 2, further comprising the step of making a seal between the fluid supply tube and the component such that the hole is substantially the only means for the test fluid to exit the component.

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4 A method as claimed in claim 1, claim 2 or claim 3 wherein the fluid supply tube is in fluid communication with a fluid supply reservoir.
A method as claimed in any one of the preceding claims, in which the hole is one hole of an array of holes, the sensor panel being of a size to extend into the path of test fluid issuing from a plurality of the holes of the array.
6 A method as claimed in any one of the preceding claims, in which the test fluid is steam.
7 A method as claimed in any one of claims 1 to 6, in which the sensor panel comprises a sheet impregnated with an indicator composition which changes state upon impingement by the test fluid.
8 A method as claimed in claim 7, in which the sheet comprises a woven or non- 9 A method as claimed in claim 7 or 8, in which the sheet comprises paper.A method as claimed in any one of claims I to 6, in which the sensor panel comprises an array of electro-mechanical transducers, whereby impingement of the test fluid on a transducer of the array generates an electrical signal.11 A method as claimed in claim 10, in which the disposition of the transducers in the transducer array corresponds to the disposition of holes in the hole array.12 A method as claimed in any one of the preceding claims, in which the sensor panel is supported by a frame.13 A method as claimed in claim 12, in which the frame is of variable geometry and is transformable between a collapsed condition and a deployed condition.14 A method as claimed in claim 12 or 13, in which the frame has locating means for cooperation with the component to locate the sensor panel with respect to the component.A method as claimed in any one of the preceding claims for inspecting a hole, or an array of holes, of a component within a gas turbine engine.16 A method as claimed in claim 15, in which the component is an aerofoil component.17 A device operable to conduct a method in accordance with any one of claims 1 to 16, the device comprising a sensor panel sensitive to the impingement of the test fluid.18 A device as claimed in claim 17, in which the sensor panel is supported by a frame of variable geometry.19 A fluid supply tube to conduct a method in accordance with any one of claims 1 to 16 wherein the fluid supply tube comprises at least part of a borescope.A fluid supply tube as claimed in claim 19 wherein the fluid supply tube defines the central core of the borescope.21 A fluid supply tube as claimed in claim 19 wherein the fluid supply tube is coupled to the outer surface of the borescope.22 A fluid supply tube as claimed in any one of claims 19 to 21 further comprising a heat insulation jacket.23 A method substantially as herein described and with reference to the accompanying figures.24 A device operable to conduct a method of inspecting a hole in a component substantially as herein described and with reference to the accompanying figures.A fluid supply tube operable to conduct a method of inspecting a hole in a component substantially as herein described and with reference to the accompanying figures.