Inspection techniques for 1st stage gas turbine nozzles

[kevlar49]

What are some appropriate inspection techniques for looking for creep damage in 1st stage gas turbine nozzles? Would like a C-scan UT be difficult due to casting discontinuities?

 

[metengr]

Detailed dimensional readings to check for actual deformation between nozzles or to compare with a spare set of nozzles that have been refurbished back to OEM specifications.

I don’t believe the C-scan is going to give you the resolution you need to check for creep cavitation damage. You can possibly look at using a time of flight diffraction (TOFD) with focused beam, phased array UT. This inspection method is used to check for creep cavitation damage in high energy piping seam weld metal and base metal heat affected zones. Considering that gas turbine nozzles are austenitic materials with loads of precipitates, you might need to have a sample of the base material to evaluate.

Surface replication techniques could be used if you can get access to the nozzles. Normally, gas turbine nozzles are subjected to NDT and are refurbished by welding. If you suspect creep damage, you might need to remove a section of the nozzle and have it subjected to metallographic examination.