Gas Turbine Handbook : Principles and Practices

Boroscope Inspection 215
Figure 13-8. Internal boroscope view of annular combustor liner and
fuel nozzle after 1,000 hours operation.
Figure 13-18 and 13-19, and foreign object damage and cracks shown
in Figures 13-20 and 13-21, respectively. By performing periodic gas
path analysis, the changes in exhaust gas temperature, fuel flow and
rotor speed would have pointed to a diagnosis of an increase in turbine
area. The material loss visible in Figures 13-18 and 13-19 is, in
fact, an increase in turbine area. Even if the diagnosis was unclear,
it would have prompted a visual inspection of the hardware.
A flexible fiber-optic boroscope can be inserted through a first
stage turbine nozzle for a good view of the first stage turbine blades.
By rotating the turbine shaft, all of the first stage turbine blades
can be inspected, including the blade tips and rub strips as shown in
Figures 13-22, 13-23, and 13-24.
With the above inspection techniques, blade surface condition as