Exam Question

(a) Common Forms of Seal Failure:
Friction between the sealing rings and the liner generates heat. Excessive heat causes the rubber sealing rings (e.g., Nitrile rubber) to harden and lose their elasticity, ultimately leading to leakage.
The chrome-plated liner serves as a rubbing surface for the lip seal. Frictional wear can create grooves or scoring on the liner surface, reducing its smoothness and preventing effective sealing. This uneven surface allows oil to bypass the seal.
If the internal oil pressure within the stern tube exceeds the external seawater pressure, oil can be forced past the seal. This pressure imbalance can arise due to variations in ship's draught and the resultant hydrostatic head of seawater.