A. Neidel, S. Riesenbeck, S. Wallich
July 6, 2020
Impingement cooling plates welded to the inner shrouds of first-stage turbine vanes were found cracked after refurbishment, before installation in a heavy-duty gas turbine engine. The metallurgical root cause of the failure was determined to be embrittlement and surface melting from thermal over-exposure. This was not brought about by engine service, but was a result of the complex repair process, part of which are several heat treatment operations. The latter are tailor-made for the base alloy of the turbine vanes. For the lower-grade impingement cooling plates, however, the peak temperature from these furnace runs was too high. They should have been removed from the vanes prior to the high-temperature heat treatment operations, but were left attached to the vanes for cost reasons.