What is the mechanism of cavitations in pipes and drains?

Dear Dana, Cavitation is damage caused by the formation and implosion (burst inwards) of bubbles in pump systems and around propellers.
Cavitation may occur in fluid flow systems where local static pressure is below the vapor pressure.
Also Cavitation refers to the formation of air bubbles in fluid in low-pressure condition which is lower than the saturation pressure.
This is considered to be a high potential damage condition where the strength and durability of the pipes can be greatly reduced.
Hope this information clarifies the above question.

rapid changes of pressure in pipes create conditions that promote cavities which is major problem for pipe failure due to stess wear on the point of the pipe where the cavity is formed.