Patent Application
20100068050
The subject matter disclosed herein relates to gas turbine engines and, more particularly, to the attachment of vanes within a casing of a compressor of a gas turbine engine.
Stator vanes located in the back-end stages of a compressor are typically configured as singlets (one airfoil per attachment), and have a square base that includes an attachment hook on the forward and aft sides of the base. The hooks are commonly constructed with a straight geometry such that when they are slid into the radial compressor casing grooves, the resulting reaction load distribution is concentrated at discrete (determinable) point locations or contact zones. This is due in part to the fact that the base of a vane is planar while the casing grooves are curved to some extent. During operation at load, the stators are subject to an unsteady aerodynamic vibratory environment that causes vibration motion to be transmitted to the constraint points in the base hooks. In addition, the responsive mode of vibration can result in a concentration of vibratory stress near these same attachment points. These hook attachment points experience fretting related damage, including fretting wear and fretting fatigue, which significantly shortens the design life of the vane.
Vanes and case hooks experience fretting wear damage as indicated by stator rock-check measurements and pictures of case hook material degradation upon top-halving a unit. If the stator hook damage becomes excessive before repair, the stator airfoils can clash into the rotating stages in front of the stators, resulting in catastrophic damage to the flowpath components.
During an outage with the gas turbine not operating, displacement measurements may be performed on the stator attachment bases while pushing the airfoil in a specified direction. These measurements, referred to as a “rock check”, indicate the level of hook deterioration associated with the fretting wear and fretting fatigue experienced during operation. If the measured values exceed a specified threshold, then the stators are removed from the compressor. After the required inspection of the compressor discharge casing (CDC) grooves and of the stator attachment hooks, and depending upon the extent of the damage, the casing section can be machined out. After machining, a custom patch ring may then be retrofitted with a custom fit to provide a restored assembly groove for the stators. New stators may then be installed in the patch ring. However, while this solution may provide extended operation capability, it does not address the root cause of the problem. Another stopgap measure is to attach adjacent vanes together in packs through welding or bolting, which again does not address the root cause of the problem.
According to one aspect of the invention, the base hooks of a vane includes an approximate two times thicker radial geometry of the hooks, with a dimensioning and tolerancing scheme that results in a line-line to loose fit on the forward outer diameter (OD) hook surface and the same on the aft inner diameter (ID) hook surface. Tolerances are thus allowed to stack up on the opposite, non-critical, surfaces of the hooks (i.e., the forward ID hook surface and the aft OD hook surface). The base of the vane is curved to match the curvature of the casing that the base resides in.
According to another aspect of the invention, a material interface is provided between the vane base and the casing groove. The material interface includes a metal alloy liner that interfaces between the base of the vane and the associated casing in which the vane is disposed. Also, a wear coating is provided on the vane attachment hooks. The liner protects the casing groove from wear damage, while the combination of the hook coating and the liner provide a wear coupling between the base of the vane and the casing. The wear coupling provides a barrier between the vane bases and the casing to decrease the wear rate.
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 objects, 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
Referring to
Although not clearly seen in
The hooks 110, 112 of the vanes 106 of this aspect of the invention are thicker and longer than the prior art designs. The dimensioning and tolerancing scheme for the vane hooks or rails 110, 112 are tighter, allowing for better fit-ups and reduced manufacturing variation. Assembly clearances are increased over that of the prior art for ease of assembly. Because durability of the vanes 106 and the case 102 has been increased, customer down time is reduced.
According to another aspect of the invention, a material interface is provided between the base of the vane 106 and the groove 128 of the casing 102. Referring to
In further accord with an aspect of the invention, a hard-face wear coating may be provided on the surface of the vane attachment hooks 110, 112. The hook coating may comprise a metal alloy, for example, a cobalt-based alloy that may comprise that sold under the trademark Stellite®. The coating may be approximately 5 mils thick and may comprise a thermal spray coating applied by the high velocity oxygen fuel (EVOF) process.
The hook coating and the liner 140 together provide an improved wear couple for the base of the vane 106 and the casing groove 128. The cobalt-based wear couple provides a barrier between the base of each vane 106 and the casing 102 to decrease the wear rate when compared to the bare 403cb stainless steel vane and 2.25CrlMo steel alloy case materials used in the prior art. Also, the improved wear couple provides a wear liner interface to protect the casing material, and provide a load surface for the critical hook surfaces of the vanes. The wear couple liner and the hard-face coating on the hooks 110, 112 provides a long term durable interface in a dynamic environment. Suitable alternative wear coatings include tungsten carbide, chromium carbide, T800, T400, T400C (all cobalt-based materials) or other cobalt-based materials.
Embodiments of the present invention have been described and illustrated herein for use with stator vanes that are located within a compressor of a gas turbine engine. However, various aspects of the present invention contemplate other types of vanes for use therewith. Also, embodiments of the invention can be retrofitted in the field onto older vanes.
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.
