| 3. Exceptional
Operating Conditions |
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Over Speeding/ Over Boosting/ Excessive Temperature
Typical damage is high temperature at bearing journals, on sever
examples, the oil burns and "cokes" the shaft. Often the back
face of the turbine wheel is slightly concave, usually accompanied by an
"orange peel" effect on the back face of the compressor wheel -
very clear signs of over speeding and over boosting.
Concave Back Face
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Over Speeding
Over speeding can also cause the loss of a portion of the
blades. The damage may look similar to FOD, but is often accompanied
by cracking at the exducer (outlet) blade root and...
|
...in extreme cases, the wheel can burst due to over
speeding. Minute stress cracks appear as the wheel is "stretched"
beyond its design limits and these gradually increase during over speeding
cycles followed by a final rapid failure
|
4.
Foreign Object Damage |
|
 
Hard Foreign Object- Compressor
This damage was caused by a foreign object entering the
compressor. The object may bounce around in the compressor inlet
causing the type of damage seen to the left and right.
 Salt
or sand causes severe erosion and corrosion, eventually leading to blade
failures.
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|
Soft Foreign Object
Soft foreign objects such as workshop cloths or even paper wipes can
cause the damage shown above. Typically, the blades bend backwards
and in extreme cases sections of the blade may break away due to metal
fatigue.
|
Hard Foreign Object - Turbine
A hard foreign object entering the turbine will damage the inducer
(inlet) blades as shown. Even small objects such as rust scale (from the
manifold) can cause considerable damage to such high speed components.
|
