This invention relates to turbine engine combustor air-cooled liner segments and, more particularly, to repair of a damaged edge portion of such segment.
One form of a turbine engine, for example an axial flow gas turbine engine to propel aircraft or marine vessels or to generate electrical power, includes a combustion section disposed generally between an axially forward compressor section and an axially aft turbine section. As is well known in the gas turbine engine art, air from the compressor section is mixed with fuel in the combustion section and ignited to provide hot expanding products of combustion for extraction of power by the turbine section. Such combustion of fuel in a rapidly flowing pressurized air atmosphere generates very strenuous high temperature environmental oxidizing and corrosive conditions along with highly erosive conditions all of which can damage components of the combustion section.
One form of a currently used combustion section is called an annular combustor. As used herein, terms such as “annular”, “radial”, “circumferential”, “axial”, etc. refer to directions about a typical axial flow gas turbine engine. One form of an annular combustor comprises an outer annular frame-like member carrying within its annular interior in which combustion is conducted at least one fuel nozzle, baffles, and a combustor liner, for example comprising a plurality of generally arcuate combustor liner segments. Such segments, typically precision cast from a high temperature alloy based on at least one of Fe, Co, and Ni interface between and protect the outer frame from conditions within the combustor as well as guide the combustion and its products. In one embodiment, each such combustor liner segment is protected on its radially inner surface with a commercially available thermal barrier coating (TBC), one example of which primarily is yttria stabilized with zirconia. In addition, cooling air is passed over the segments' radially outer surfaces that include there-across a plurality of spaced-apart generally radially outward extending protuberances or pin-like structures functioning as heat exchange surfaces or members and designed with spaces therebetween to control cooling air flow about the protuberances.
In their annular, circumferentially arcuate disposition about the combustor interior to define the combustor liner, the segments partially overlap one another axially downstream so that the cooling air traversing the radially outer surface of a segment between the protuberances is discharged over a portion of the TBC of a superimposed adjacent segment. Nevertheless, it has been observed after service operation, that the strenuous engine operating conditions can result in damage to or erosion of a downstream edge portion of certain combustor liner segments. Because such cast segments, including the radially outer spaced-apart pin-like structure, is relatively expensive to manufacture, typically by a lost wax type precision casting, it is desirable to repair rather replace such a member. However, a low cost repair method has not been available and damaged liner segments have been discarded.
Repair by bonding of a replacement edge portion by typical current bonding methods can result in flow of excessive metal flow about such protuberances. For example, current brazing methods including disposing brazing alloy at a face or surface that includes the protuberances, or bonding by typical fusion welding that melts at least a portion of parent metal as well as any weld metal, can result in excessive brazing or molten alloy flow. Such excessive flow can block, interfere with, and/or change a designed pattern and/or amount of cooling airflow on the segment radially outer surface. Provision of a segment repair method that maintains the integrity of the radially outer surface designed cooling air-flow control and, in one preferred form provides the segment with enhanced oxidation resistance at an operating temperature, can improve and enable repair rather than replacement of damaged combustor liner segments.
The present invention, in one embodiment, provides a method for repairing a damaged edge portion of an air-cooled metal combustor liner segment substantially without change in the cooling air flow control over the segment. The segment edge portion is disposed and connected between a segment radially inner surface and a segment radially outer surface spaced apart from and opposed to the segment radially inner surface. The segment radially outer surface includes a plurality of spaced-apart generally radially outwardly extending heat exchange first protuberances integral with and across the segment radially outer surface including into the damaged edge portion. The first protuberances include spaces therebetween designed to provide cooling air flow control about the protuberances.
The method comprises removing the damaged edge portion to provide a segment body having a body repair surface from which the damaged edge portion was removed. A metal replacement edge member is provided with a replacement edge member repair surface shaped to match the body repair surface, a replacement edge member radially outer surface and a plurality of spaced apart radially outwardly extending heat exchange second protuberances integral with and across the replacement edge member radially outer surface to replace the first protuberances integral with the damaged edge portion. The replacement edge member repair surface and the body repair surface are disposed in juxtaposition at a matched junction therebetween with their respective radially outer surfaces substantially coextensive. Then the replacement edge member and the segment body are bonded at the matched junction substantially without change in the cooling air flow control about the first and second protuberances.
Another form of the present invention is a repaired air-cooled combustor liner segment having a metal segment body including a segment body radially outer surface having a plurality of spaced apart radially outwardly extending heat exchange first protuberances integral with and across the segment radially outer surface. The first protuberances include spaces therebetween designed to provide cooling air flow control about the protuberances. The segment body and its radially outer surface extend to a body repair surface. Secured to the segment body at the body repair surface at a bonded joint is a metal replacement edge member including a replacement edge member radially outer surface including a plurality of spaced apart radially outwardly extending heat exchange second protuberances integral with and across the replacement edge member radially outer surface. The second protuberances include spaces therebetween designed to provide cooling air flow control about the second protuberances. The replacement edge member and its radially outer surface extend to a replacement edge member repair surface to which the body repair surface is secured at the bonded joint. The radially outer surfaces of the segment body and the replacement edge member are substantially coextensive through the bonded joint so that the cooling air flow control about the first and second protuberances is maintained substantially without interference by the bonded joint.
A combustor liner provides protection for a gas turbine engine combustor case or structural support during ignition of fuel in pressurized air during engine operation. Forms of annular type combustors, including an air cooled combustor liner or inner case, and associated fuel nozzles, baffles, etc., are shown in U.S. Pat. No. 5,289,687—Kress et al; and U.S. Pat. No. 5,355,668—Weil et al. In forms of such annular combustor liners, the combustor liners comprise a plurality of combustor liner segments in an annular assembly of at least partially overlapping annular rings. Cooling air flowing over the radially outer surface of the segments passes between the assembled rings and is discharged into the combustor interior. Nevertheless, corrosive and/or erosive type damage to an edge portion of certain combustor liner segments has been observed after engine service operation. The present invention provides a repair of such damage and a repaired combustor liner segment.
The perspective, fragmentary partially sectional view of
After engine service operation of combustor liner segment 18 shown diagrammatically in the fragmentary perspective view of
According to a form of the present invention, damaged portion 32 of edge portion 26, including first pins 22, is removed, for example by machining or grinding, to provide segment body 34 as shown in the perspective, fragmentary exploded view of
In this embodiment, member 38 is of a second metal alloy different from the original or first alloy from which segment 18 was made at least to the extent that it has an oxidation resistance property at an operating temperature greater than that of the original alloy. In one example, member 38 was made of a high temperature Co base alloy of a type commercially available as Mar-M-509 alloy, typical of certain other commercial high temperature alloys based on Co and having an oxidation resistance property at the operating temperature greater than the above identified Rene' 77 and Rene' 80 Ni base alloys. Typical oxidation rate test data under Mach 0.05 conditions for less than about 500 hours comparing Ni base and Co base alloys included an oxidation rate (mils/hour) at 1900° F. for Rene' 80 alloy of about 0.05 compared with Mar-M-509 alloy only of about 0.03; and at 2000° F. for Rene' 80 alloy of about 0.1 compared with Mar-M-509 alloy only of about 0.06.
Member 38 is of a second shape matched with the first shape of removed damaged portion 32 and includes a replacement edge member repair surface 40 shaped to match body repair surface 36. As used herein in respect to the relative shapes of cooperating repair surfaces 38 and 40, terms such as “matched” or “matches” means shaped to enable provision of a very narrow generally uniform gap, and preferably contact, between such surfaces when in juxtaposition.
In practice of a form of the present invention, body repair surface 36 and replacement edge member repair surface 40 are disposed in close juxtaposition, preferably substantially in contact, at a matched junction 42 therebetween so that segment body radially outer surface 30 and replacement edge member radially outer surface 39 substantially are coextensive. Then replacement edge member 38 and segment body 34 are joined by bonding replacement edge member surface 40 to body replacement surface 36 at junction 42 across a bonded joint that does not change and that maintains control of cooling air flow 24 about the pins or protuberances 22. As used herein, terms relating to no change in cooling air flow control or maintaining cooling air flow control is intended to mean no change, other than minor, that materially affects a designed cooling air flow about pins 22.
One preferred embodiment of such bonding was by welding using a low energy welding method that focuses energy at junction 42 to result in a very narrow total heat affected zone adjacent the weld. As is well known in the metallurgical art, a heat affected zone, sometime referred to as HAZ, adjacent a weld is the extent into a substrate at the weld in which local changes occur to the morphology or in the microstructure of the material as a result of exposure to certain levels of heat. For example, precipitation, grain growth and/or change in grain size and hardness can occur.
As shown in the enlarged, fragmentary sectional view of
In another embodiment of such bonding shown in the enlarged fragmentary sectional view of
Practice of forms of the method of the present invention provides a repaired air-cooled combustor liner segment having a segment body 34 of a first alloy having a first oxidation resistance property and a replacement edge member or portion 38 of a second alloy having a second oxidation resistance property greater than the first oxidation property. In forms of a repaired air-cooled combustor liner segment, segment body 34 is bonded with replacement edge 38 at junction 42 therebetween across a bonded joint so that their respective radially outer surfaces 30 and 39 substantially are coextensive and control of cooling air flow is maintained across such surfaces and about pins 22.
The present invention has been described in connection with specific embodiments, structures, materials and methods. However, it will be understood that they are intended to be typical and representative of rather than in any way limiting on the scope of the present invention. Those skilled in the various arts involved, for example relating to turbine engines and their repair, to materials, and to material joining methods and apparatus, will understand that the invention is capable of variations and modifications without departing from the scope of the appended claims.