Patent Application
20140157597
The subject matter disclosed herein relates to coated components, such as those found in turbine systems, and relates more particularly to methods of locally inspecting a coated component.
In turbine systems, such as a gas turbine engine, a combustor converts the chemical energy of a fuel or an air-fuel mixture into thermal energy. The thermal energy is conveyed by a fluid, often compressed air from a compressor, to a turbine where the thermal energy is converted to mechanical energy. As part of the conversion process, hot gas is flowed over and through portions of the turbine as a hot gas path. High temperatures along the hot gas path can heat turbine components, causing degradation of components. A coating is typically applied to various turbine components that are subjected to the hot gas to protect the turbine components, while also improving the efficiency of the gas turbine engine by allowing an increase in operating temperature.
Despite the coating, damage may occur to the turbine component. Such damage may include cracking, for example. Various damage detection methods have been employed to determine whether repair to the turbine component is necessary. Typically, all or a large portion of the coating must be removed to inspect the turbine component for damage. The removal process may include subjecting the coating to exposure to acid, for example. Subsequent to the inspection and/or repair, all or a large portion of the turbine component must be recoated. Requiring a large area of the turbine component to be stripped of coating and subsequently recoated undesirably results in substantial monetary and time costs.
According to one aspect of the invention, a method of locally inspecting and repairing a coated component is provided. The method includes determining an area of interest on the coated component, wherein the area of interest has little to no visible damage. The method also includes removing a coating proximate the area of interest to expose a base material of the coated component. The method further includes inspecting the area of interest for damage to the base material.
According to another aspect of the invention, a method of locally inspecting and repairing a coated component is provided. The method includes identifying an area of interest on the coated component which is susceptible to damage, the area of interest identified based on at least one known design or operational factor. The method also includes removing a coating proximate the area of interest to expose a base material of the coated component. The method further includes inspecting the area of interest for damage to the base material. The method yet further includes repairing the base material proximate the area of interest if damage is observed during inspection of the base material. The method also includes recoating the coated component proximate the area of interest.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
Referring to
In operation, air flows into the compressor 12 and is compressed into a high pressure gas. The high pressure gas is supplied to the combustion arrangement 14 and mixed with fuel, for example natural gas, fuel oil, process gas and/or synthetic gas (syngas), in the combustion section 18. The fuel/air or combustible mixture ignites to form a high pressure, high temperature combustion gas stream. In any event, the combustion arrangement 14 channels the combustion gas stream to the turbine section 24 which converts thermal energy to mechanical, rotational energy.
Turbine components are located throughout the gas turbine engine 10 and subjected to the hot gas, where hot gas flow across the components may cause creep, oxidation, wear and thermal fatigue of turbine components. Examples of applicable turbine components include bucket assemblies (also known as blades or blade assemblies), nozzle assemblies (also known as vanes or vane assemblies), shroud assemblies, transition pieces, retaining rings, and compressor exhaust components. The listed components are merely illustrative and are not intended to be an exhaustive list of exemplary components subjected to hot gas.
Referring now to
The base material 42 of the coated component 40 is coated with at least one coating 44 for protection of the base material 42 during normal operation of the coated component 40. The precise number and types of layers of the at least one coating 44 that is applied over the base material 42 may vary. In one embodiment, only a bond coating 46 is applied over a surface 48 of the base material 42 (
In an alternate embodiment, a thermal barrier coating 50 is applied in addition to the bond coating 46 (
Although the at least one coating 44 protects the base material 42 to a certain extent, a damaged area 54 may form during normal operation. In the illustrated embodiment, the damaged area 54 comprises a crack extending through at least a portion of the base material 42. As shown, the damaged area 54 may be contained within the base material 42, such that little to no visible damage is observed during a visual inspection of the coated component 40, based on the otherwise normal appearance of the at least one coating 44. Although illustrated as a crack propagated entirely through the base material 42, the embodiments described herein are also particularly beneficial for cracks that extend through merely a portion of the base material 42.
Referring to the flow diagram of
Once the area of interest 56 has been determined, the at least one coating 44 is removed proximate the area of interest to expose a base material of the at least one coating 104 of the base material 42. The at least one coating 44 may be removed in a number of manners, with an exemplary embodiment employing a water jet stripping process that involves imposing a stream of supersonic water at pressures between about 1,000 psi to about 100,000 psi (about 6.9 MPa to about 689 MPa) to quickly and precisely remove the at least one coating 44 from the base material 42. In one embodiment, the water pressure is about 30,000 psi to 60,000 psi (about 207 MPa to about 414 MPa). The water jet stripping process typically includes a pump, as well as hydraulic and control systems. The at least one coating 44 is essentially eroded from the base material 42 by high pressure water droplets, while brittle coatings may be fractured and spalled. Removal of the at least one coating 44 proximate the area of interest 56 by water jet stripping allows for precise removal of the at least one coating 44, such that specific desired geometries of the at least one coating 44 may be removed while the at least one coating 44 proximate the removed coating is preserved. For example, a relatively square or rectangular geometry may be removed, as illustrated in
The area of interest is inspected for damage to the base material 106 once the at least one coating has been removed. In the event that damage is observed during the inspection, the base material is repaired proximate the area of interest 108. Additionally, inspection may reveal damage significant enough to require scrapping of the coated component 112. Subsequent to the inspection and possibly repair of the base material, the coated component is recoated proximate the area of interest 110.
It is to be appreciated that although the above-described method of inspecting and possibly repairing a coated component has been illustrated and described as a single coated component, such as a bucket of a turbine system, a plurality of buckets may be inspected during an inspection process. Specifically, the plurality of buckets inspected and potentially repaired may comprise a representative sample of an entire set of buckets of the turbine system, such that information regarding the entire set of buckets may be obtained from inspection of the representative sample. Alternatively, the entire set of buckets may be periodically inspected based on data indicating damage as a function of operation. The method described in detail above pertains to a single coated component merely for clarity of explanation and to avoid duplicative description.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
