Gas Turbine Handbook : Principles and Practices

Boroscope Inspection 213
Figure 13-7. View of last stage compressor blades with contamination
evident on and between blades. 5,000 horsepower gas turbine-generator
unit after 44,500 hours operation.
noticeable on the turbine blades and turbine nozzles. This is material
from the compressor blades and stators, that melts as it travels
through the combustor and is deposited as a “plasma spray” on the
turbine airfoils.
Combustor And Fuel Nozzles
If the manufacturer has not made combustor boroscope ports
available several other alternatives are possible.
• For heavy frame units the fuel nozzles can be removed and the
combustor, first stage turbine nozzles and first stage turbine
blades can be viewed. It may be necessary to fabricate a piece
of rigid tubing to guide the boroscope through the combustor to
the turbine nozzles and blades. The tubing must have an inside
diameter slightly larger than the outside diameter of the boroscope
and long enough to extend from the fuel nozzle plane to
the first stage turbine nozzle plane.
• For gas turbines with a can-annular design combustor it will be
necessary to remove at least one fuel nozzle from each combustor
to view all the turbine nozzles.