Dirty oil damages the turbocharger by causing heavy scoring of critical bearing surfaces.
To avoid damage, oil and filters should be of a quality recomended by the engine manufacturer. These should be changed when a new turbocharger is fitted and at regular intervals according to the vehicle/engine manufacturers specification.
Dirty oil damage could result from:
Blocked, damaged or poor quality oil filter
Dirt introduced during servicing
Engine wear or manufacturing debris
Malfunctioning oil filter by-pass valve
Degraded lubrication oil.