Patent Application
20100050435
The disclosure relates to gas turbine blades and gas turbine blade repair methods, including the replacement of turbine blade airfoil tips.
A gas turbine blade of the type made from nickel alloys can be used to operate at high temperature in highly erosive environments. In these environments, the blade airfoil tips can crack or spall due to oxidation, damage by foreign objects in the gas stream or rubbing with the turbine casing. Due to the high cost of the blades it is often desirable to repair them so as to make them suitable for another operational cycle rather than replace them. Where the repair entails bonding of replacement parts, however, the bond, when exposed to operational load, represents a potential point of weakness due to the complexity of welding the advanced blade alloys.
There are several known tip repair methods entailing bonding. For example U.S. Pat. No. 6,908,288 discloses a repair method where a replacement tip is welded onto a straight surface (e.g., plane) made between the leading and trailing edges of an airfoil.
As an alternative DE199 63 714 and FR 2 631 268 disclose repair methods for blade airfoil tips where the radial load is partially borne by the interlocking shape of the airfoil tip interface thus reducing the stress loading and as a result the integrity requirement of the joining weld.
A method of forming and fitting a replacement airfoil tip is disclosed that can better withstand centrifugal load while maintaining repair simplicity.
A gas turbine airfoil repair method is disclosed for an airfoil which extends radially from a platform, wherein the airfoil includes a tip edge at an airfoil end radially distant from said platform, a trailing edge and a leading edge, the method comprising: a) forming a joining surface extending from said leading edge to said tip edge, wherein said joining surface forms at least one arc; b) forming a replacement tip fittable on said joining surface; and c) bonding said replacement tip to said airfoil.
A gas turbine airfoil repair method is also disclosed for an airfoil which extends radially from a platform, wherein the airfoil includes: a tip edge at an airfoil end radially distant from said platform, a trailing edge and a leading edge, the method comprising: a) forming a joining surface extending from said leading edge to said tip edge, wherein said joining surface forms an arc towards the tip edge and is angled toward the tip edge; b) forming a replacement tip fittable on said joining surface; and c) bonding said replacement tip to said airfoil.
A gas turbine airfoil repair method is also enclosed for an airfoil connected to a platform wherein the airfoil includes a tip region having a tip edge at an airfoil end distant from said platform, a trailing edge and a leading edge, the method comprising: a) forming a joining surface extending from said leading edge to said tip edge wherein said joining surface forms an arc towards the leading edge; b) forming a replacement tip fittable on said joining surface; and c) bonding said replacement tip to said airfoil.
A gas turbine airfoil is disclosed which extends radially from a platform, the airfoil comprising: a tip edge at an airfoil end configured to be radially distant from the platform and to extend around the airfoil between a trailing edge of the airfoil and a leading edge of the airfoil; a joining surface formed in the airfoil which extends from the leading edge to a portion of the tip edge located between the trailing edge and the leading edge, wherein the joining surface forms at least one arc; and a replacement tip fitted and bounded to the joining surface.
Other objectives and advantages of the present disclosure will become apparent from the following description, taken in connection with the accompanying drawings wherein by way of illustration and example, an embodiment of the disclosure is disclosed. By way of example, an embodiment of the disclosure is described more fully hereinafter with reference to the accompanying drawings, in which:
The disclosure is based on the general idea of providing a joining surface (e.g., a joining, or junction plane), onto which a replacement airfoil tip is mounted, extending from a turbine blade's leading edge to a tip edge, wherein the joining surface can include a curve.
One aspect of the disclosure provides a gas turbine airfoil repair method for an airfoil which extends radially from a platform, wherein the airfoil includes a tip having a tip edge radially distant from the platform; a trailing edge; and a leading edge.
Portions of an airfoil which are susceptible to damage include the leading edge and the blade tip, and to minimize the size of the replacement tip, an exemplary method includes:
An arc in the joining surface not only provides a solution to, for example, the problem of stress concentration, it enables optimum shaping of the replacement tip and increases the ability of the bond to withstand, during operation, centrifugal forces. It does this by, for example, effectively increasing the effective join plane area in the radial direction.
The benefit of a joining surface with arcs can be further realized in another aspect that provides an arc towards the tip edge so that the unnecessary replacement of the trailing edge, which is less susceptible to damage, can be avoided. A yet further aspect provides a joining surface that, towards the leading edge, angles towards the platform end. In this way a larger area of the leading edge, which can be susceptible to damage, can be minimized.
By combining arcs towards both the tip edge and the leading edge in another aspect provides a replacement tip with improved ability to withstand centrifugal forces.
The radii of the arcs can have a material affect on the ease of bonding where the smaller the radius the more difficult it can be to bond by weld, and so the radius can, for example, be greater than 10 mm. If the radius it too large, the benefit of increased weldability can be offset by less than optimum tip replacement size, and so an aspect provides an arc radius of, for example, less than about 20 mm (e.g., substantially between 10 and 20 mm (e.g., approximately between 10 mm+10% or greater and 20 mm±10% or greater)). Other dimensions will be apparent to those skilled in the art and can be determined empirically.
The repair method can be simplified by minimizing the size of the replacement tip, eliminating or at least minimizing any non-functional curvature in the joining surface that does not contribute positively to bond strength. An exemplary, efficient joining surface configuration is one with minimal curvature so as to minimize machining difficulties associated with curve formation, yet with enough curvature to ensure only damaged portions of the tip are replaced. It was found that by locating arcs towards the ends of the joining surface and interspersing the arcs with a straight section or sections, this could be efficiently achieved. An aspect of the disclosure therefore provides arcs that subtend an angle of, for example, substantially, or about between 70°-100° (e.g., approximately 70°±10% or greater and 10°±10% or greater) and in exemplary embodiments, preferably an angle of substantially between 80° to 90°. It was further found to be advantageous to form a straight section between the arc towards the tip edge and, depending on the configuration, the arc towards the leading edge or the leading edge itself. In another aspect at least a part of the straight section may be angled substantially between, for example, 0°-5° (e.g., between about 0°±10% or greater, and 5°±10% or greater) from the tip edge so as to avoid the need for additional joining surface curvature, and the complexities of fabricating such a curve.
In an airfoil configuration where the airfoil includes a tip plate, an aspect of the disclosure further provides a replacement tip with the tip plate wholly formed in the replacement tip.
With reference to the drawings, like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. It may be evident, however, that the disclosure may be practiced without these specific details.
Thus,
A straight section 26 in the joining surface 20, as shown in
In another embodiment, as shown in
In another embodiment of the disclosure, shown in
In an exemplary method, before damaged portions of a
Once these steps have been completed, the replacement tip can be bonded to the airfoil 10 at the joining surface 20. During this process the replacement tip 30 can be clamped to the airfoil 10 so as to ensure correct alignment of the replacement tip 30 with the airfoil 10.
Although the disclosure has been herein shown and described in what is conceived to be the most practical exemplary embodiment, it is recognized that departures can be made within the scope of the disclosure, which is not to be limited to details described herein but is to be accorded the full scope of the appended claims so as to embrace any and all equivalent devices and apparatus.
Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08163453.7 | Sep 2008 | EP | regional |
