Patent Description:
Gas turbine engines are known and include a compressor compressing air and delivering it into a combustion section. The air is mixed with fuel and ignited and products of that combustion pass downstream over turbine rotors, driving them to rotate.

Casings typically surround and enclose the turbine section and the compressor section. The casing will typically have a case wall and a bolt hole strap or flange extending radially away from the wall. A plurality of bolt holes are formed within the flange.

It is known that the flange may develop cracks and, in particular, extending from the bolt holes. If the crack extends radially from the bolt hole and away from the wall, weld repair techniques may be utilized. Further, a wedge method has also been utilized.

However, the crack may also extend toward the case wall and this is less susceptible to weld repair.

It is known to remove the entire flange and replace it.

<CIT> relates to methods for repairing gas turbine engine components. <CIT> relates to fastener shields in a fluid flow path. <CIT> relates to a method of repairing a flange of a casing.

In accordance with the present invention, a method of repairing a casing for a gas turbine engine according to claim <NUM> is provided. Various preferred features are defined in the dependent claims.

The embodiment and preferred features of the preceding paragraph, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

The fan section <NUM> drives air along a bypass flow path B in a bypass duct defined within a fan case <NUM>, while the compressor section <NUM> drives air along a core flow path C for compression and communication into the combustor section <NUM> then expansion through the turbine section <NUM>.

A turbine exhaust case <NUM> also provides a mount for the engine.

In one disclosed embodiment, the engine <NUM> bypass ratio is greater than about ten (<NUM>), the fan diameter is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>). The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>.

The fan section <NUM> of the engine <NUM> is designed for a particular flight conditiontypically cruise at about <NUM> Mach and about <NUM>,<NUM> (<NUM>,<NUM> feet). The flight condition of <NUM> Mach and <NUM>,<NUM> (<NUM>,<NUM> ft), with the engine at its best fuel consumption - also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')" - is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about <NUM>/second (<NUM> ft / second).

<FIG> shows a casing <NUM> which may be utilized to enclose any number of parts of the gas turbine engine <NUM> of <FIG>. The casing <NUM> is generally cylindrical and extends for <NUM> degrees about a center axis A (see also <FIG>). As shown, a case wall <NUM> extends between radially outwardly extending flanges <NUM>.

While the casing <NUM> is shown as cylindrical, it may also be conical, or any other shape. Generally, the casing extends axially about some central reference axis.

<FIG> shows a detail of the flange <NUM> and, namely, a plurality of bolt holes <NUM>. As can be appreciated, the flange <NUM> extends radially from the wall <NUM> and the bolt holes <NUM> are formed in the flange <NUM>. A crack <NUM> extends radially outwardly from the bolt hole <NUM>. Such a crack <NUM> may be repaired by welding techniques.

Further, while the flange <NUM> is shown extending radially outwardly, radially inwardly extending flanges are also known. Further, it should not be implied that the flanges extend at a right angle relative to the case wall <NUM>, but rather, simply that it does extend with at least a component in a radially extending direction.

As shown in <FIG>, a crack <NUM> is propagated from a bolt hole <NUM> toward the surface of the flange <NUM> which is connected to the wall <NUM>. As mentioned above, it is somewhat unsatisfactory to repair such a crack with existing welding techniques. As can be seen in <FIG>, the flange <NUM> has an outer portion <NUM> generally circumferentially aligned with the bolt hole <NUM>, and scalloped portions <NUM> which are intermediate adjacent bolt holes <NUM>.

<FIG> shows a first step in repairing the casing <NUM>. When the crack <NUM> is identified, the following repair process is initiated. A section <NUM> of the wall <NUM> and a section <NUM> of the flange is removed. This would be the section associated with the hole <NUM> with the crack <NUM>. While a single bolt hole portion has been removed, a worker of ordinary skill in the art would recognize that more than one bolt hole could be removed. Notably, a plurality of other bolt holes <NUM> and their respective flange portions do remain. As can be seen, the removed portion may be intermediate to portions of two scallops <NUM> in the remainder of the flange <NUM>. Of course, the scallops are optional, and the teachings of this application would extend to casings not having such scallops.

<FIG> shows a subsequent step. Namely, a replacement part <NUM> is obtained and includes a hole <NUM>. As can be seen, there may be scallop portions <NUM> on the replacement part <NUM>. In one embodiment, the replacement part <NUM> may be fabricated from a pre-machined section or block of a material similar or identical to the material of the flange <NUM>. In one aspect, the pre-machined section also includes a pre-machined bolt hole <NUM>. In one aspect, the removed section <NUM> is sized to include the bolt and the crack as described above, while also being sized to match the pre-machined section. That is, the pre-machined section may be of a standard size. In this aspect, the pre-machined section may not require additional fabrication. In another aspect, the pre-machined section is machined onsite to match the dimensions of the removed section <NUM>, removed from the flange <NUM>.

As shown in <FIG>, the replacement part <NUM> has now been inserted into the prior opening <NUM> and <NUM>. The replacement portion <NUM> is welded at <NUM> to the wall <NUM>, and welded at <NUM> to circumferentially adjacent portions of the flange <NUM>. Now, a relatively simple method of repairing a bolt hole flange having a crack has been developed that does not require complete replacement of the bolt hole flange.

<FIG> shows a distinct type defect which may be repaired by the method graphically illustrated by <FIG>. The defect illustrated in <FIG> relates to a bolt hole <NUM> which may have been damaged or mis-drilled such that the bolt hole <NUM> is outside of acceptable limits, and thus requires replacement of a flange portion such as described with regard to <FIG>. As an example, the bolt hole <NUM> may have been drilled to be too large.

Types of welding processes suitable for securing the replacement portion <NUM> to the flange <NUM> include Gas Tungsten Arc, electron beam (EB), and laser or directed energy welding process in addition to others known to those of ordinary skill in the art.

The cracks <NUM> could also extend radially outwardly from a radially inwardly extending flange.

The replacement part <NUM> may not initially have a hole <NUM> when secured into the repair location. Rather, the replacement part may have an undersized bolt hole, or no bolt hole at all, until after the steps of <FIG>. The hole can then be drilled.

While the term "bolt holes" has been utilized in this application, it should be understood that other securement members may be utilized, and may extend through the holes <NUM>. Such a hole would still meet the definition of "bolt holes" as utilized in this application.

Claim 1:
A method of repairing a casing (<NUM>) for a gas turbine engine, wherein the casing has a wall (<NUM>) extending generally axially, and between radially outwardly extending flanges (<NUM>), said radially outwardly extending flanges (<NUM>) extending radially from said wall (<NUM>), and at least one radially extending flange being formed with a plurality of bolt holes (<NUM>), the method including the steps of:
removing a portion of said flange (<NUM>) including at least one of the plurality of bolt holes (<NUM>) and removing a portion of said wall (<NUM>), a remaining portion of said flange (<NUM>) including at least one non-removed bolt hole (<NUM>);
obtaining a replacement portion (<NUM>) to replace the removed portion, said replacement portion (<NUM>) including replacement portions of said flange (<NUM>) and said wall (<NUM>); and
welding said replacement portion (<NUM>) in an opening left in said flange (<NUM>) by said removed portion; wherein the welding step is provided by welding the replacement portion (<NUM>) into circumferential edges of the flange (<NUM>) defining the removed portion, and
wherein the welding step includes welding the replacement portion (<NUM>) into a remaining portion of said wall (<NUM>),
characterized in that
the removed portions of said flange (<NUM>) and said wall (<NUM>) are associated with a defect, the removed portion of the wall (<NUM>) and the replacement portion of the wall (<NUM>) including a wall portion extending axially away from the flange (<NUM>).