this coating, these blades are very susceptible to
by a rough or crusty appearance at the leading edge,
sulfidation.
on the concave side of the airfoil section, or on the
platform at the root of the air-foil. The rotor should be
Turbine Blade Sulfidation
replaced if there is evidence of splitting,
delamination, separating, flaking, or loss of material
in any area of the blade. Figure 10-11 shows an
Sulfidation is high-temperature corrosion.
example of unacceptable sulfidation of turbine blades.
Sulfidation starts with the excessive levels of sodium
and sulfur in the air and fuel mixture entering the
engine. This type of environment attacks turbine
Turbine Blades
blades and stator vanes.
Sulfidation first appears
as a rough or crusty surface on the leading edge and
concave surface of the airfoil. It progresses to scaling,
splitting (delamination), and eventual metal loss. The
You may inspect turbine blades on axial-flow
sulfidation process accelerates with an increase in
engines, and clean them in the same manner as
sulfur intake and an increase in engine operating
compressor blades. However, because of the extreme
temperature.
heat under which the turbine blades operate, they
All blades should be inspected for sulfidation.
are more easily damaged. Inspect the turbine blades
This form of corrosion is permissible if evidenced only
for stress rupture cracks and deformation of the
leading edge. See figures 10-12 and 10-13.
Stress rupture cracks usually appear as fine
hairline cracks. These cracks are found on or across
the leading or trailing edge at a right angle to the
edge length. Visible-cracks may range-in length from
one-sixteenth inch upward.
Deformation, due to overtemperature, appears as
waviness along the leading edge. The leading edge
must be straight and of uniform
Figure 10-12.-Stress rupture cracks.
Figure 10-13.-Turbine blade waviness.
10-15
