information relative to the stage, location on the blade
(estimate the percent of chord and span), and the
condition of the surrounding airfoil. You do not have to
record the appearance of the defect (sharpness and
contour). Compressor stall is one of the worst things
that can happen to an engine. tip clang damage is
difficult to spot and gives the appearance of minor
damage. The V-shaped notch on the top of a blade
caused by tip clang is only an indicator; it in itself is not
the damage. The damage is at the blade root and
normally cannot be seen.
If a blade has been
overstressed, it must be replaced.
Platform Distortion.— Compressor blade platform
fretting or shingling (fig. 2-14) can be observed on some
after stage blades. These distortions are the overlapping
of one blade platform mating edge with the adjacent
platform edge. When shingling is found, the platforms
will be distorted and bowed (fig. 2-15). When the
platforms are shingled, only the locking lug blades will
exhibit this defect. Monitor this condition to see if a
platform crack develops. Also look for missing pieces
around the locking lugs. You must report and record any
cracks in the platform. Be sure you have included the
following information:
The stage
The number of blades
Figure 2-14.—Platform fretting or shingling.
Figure 2-15.—Platform bowing.
The spacing of the blade numbers separating the
shingled blade platforms
The platform gap observation (estimate gap as
percent of circumferential span of the platform)
The condition of the shingled edge (bent, fretted,
or stepped as per table 2-1)
Midspan
Shroud
Wear.—
Some stage 1
compressor blades show wear at the mating surfaces of
the midspan damper shrouds. (See figs. 2-16 and 2-17.)
Wearing of the tungsten-carbide wear coat causes the
mating face contour to change from a straight line to a
stepped line.
This occurs at the after edge of the
clockwise blade midspan (trailing edge) and the forward
edge of the counterclockwise blade midspan shroud
(leading edge). In the step area, some metal maybe
turned or protruding from the midspan shroud mating
line (mushrooming). This protrusion is indicative of
wear-through. A missing pad on one face would initiate
an accelerated failure of the mating surfaces.
BLADE DEPOSITS.— Compressor blades and
stator vanes exhibit varying degrees of cleanliness.
Variables such as air-inlet configuration, ambient
atmospheric conditions, and air contaminants
(chemicals, salt, dirt, water, and so forth) all tend to
affect the surface condition of the compressor rotor and
stator blades.
A l u m i n u m D e p o s i t s . — Two areas in the
compressor assembly are coated with aluminum, the
2-13
