Advanced Weld Repair of Gas Turbine Hot Section Components

Abstract

In the 21st century, generation of electrical power will play a critical role due to constantly rising global population and increasing energy demand. While energy resources such as oil, coal and natural gas are being rapidly exhausted, environmental concerns of global warming due to CO2 emissions are simultaneously imposing limits on consumption of these limited resources. Natural gas is one of the most efficient industrial fuels and therefore, over the last two decades, its use with stationary gas turbines has increased dramatically. New nickel based superalloys and advanced coating systems have been introduced to further advance the efficiency of such natural gas power generation equipment. While such new technologies increase the cost of newly manufactured parts, refurbishment of service exposed parts has become of increasing importance in the gas turbine business. For this reason, for example, modern joining methods have been developed to repair single crystal parts at significantly lower prices compared to manufacture of new parts. Repair of turbine hot gas path components is a proven service offered to customers by Siemens Power Generation (Siemens PG). Highly advanced brazing and welding processes are routinely applied to repair gas turbine parts. Particular concerns in the repair of such turbine parts made of cobalt and nickel based superalloys include high susceptibility to hot cracking during welding and post weld heat treating. Special technological subtleties must be applied for successful repair including use of ductile filler materials, welding methods with low heat input, hot box welding and complicated pre- and post-weld heat treatments to avoid weld cracking. This paper deals with some repair welding technologies currently used at Siemens PG.