Turbine component repair and recoat
New advancements make repair worth considering
By Greg Napert
With increasing costs of engine overhauls over the years, many engine operators are continuously evaluating their options with regard to refurbishing and overhauling turbine engine components. The business of overhauling turbine components is growing, and overhaul facilities are constantly searching for more options to offer their customers, including the option of high temperature protective coatings. Additionally, the quest to improve turbine component life and performance of engines with higher thrust, operating at higher temperatures, has also created a demand for improved coatings.
Unlike other aftermarket overhaul operations in aviation, it's fairly common for turbine component refurbishment companies to seek manufacturer approvals for all of their repair processes. Due to a combination of the complexity of turbine component's geometry, access to engineering data, test facilities, and exotic superalloys; it is extremely advantageous for these companies to work closely with the original equipment manufacturer (OEM's) and to provide complementary services instead of competitive repair services.
The relationship works both ways. The OEM's can also benefit from these specialized services by providing the OEM customers with low cost options for keeping their engines running longer and take advantage of faster turnaround times.
One company that offers coating and refurbishment options for turbine components is Walbar Metals in Peabody, Massachusetts.
Walbar provides only "OEM approved repair and refurbishing processes" and offers numerous coating options for hot section components. Walbar, a division of Coltec Industries, originated in the early Ô70s, and offered metallurgical services. Since then, it has developed component repairs for operators and engine manufacturers, with a concentration on hot end components for Pratt & Whitney and GE engines, the preponderance of which are vanes, nozzles, and blades.
Jim Palatine, a plant manager for Walbar, says that the company is not limited to repairs that have already been developed. It takes pride in offering engineering service to solve problems that may exist with particular components or as a result of unusual operating conditions. For instance, if an airline wants to develop a repair scheme for a particular component, Walbar engineers will work with the airline's engineering department and in conjunction with the engine manufacturer, to find a mutually agreeable solution.
"We like to refer to these repairs as extended repairs," Palatine says, "and we offer them on a case by case basis."
Most of Walbar's repairs, however, involve "bringing the part back to the actual form, fit, and function of the original part. Any change, even in the coating applied, affects the part to a degree that it might require significant testing and a part number change" explains Palatine.
Types of coatings
Two key processes needed to complete the overhaul and repair process for turbine components are the removal or "stripping" of the old and re-application of a new coating.
Stripping involves a controlled and precise chemical etching process that takes a great deal of experience to perfect. According to Palatine, "If there is any one thing that distinguishes one company from another, it's expertise in performing the stripping process, and the ability of the company to strip components without significantly affecting the parent metal."
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