Relation between Fluid velocity and Cavitation in a Pipeline?

In the simplest case, the cavitation number varies inversely as the square of the velocity.

The higher the fluid velocity, the lower the fluid pressure within the pipe is and the higher the chances of cavitation developing become.

Depending on how much education you want you might try to Google "differential pressure measurement" The theory you will find at a few of those sites may answer your question quite well.

just found this excellent video on cavitation

http://www.emersonprocess.com/fisher/products/severeservice/Product_Solutions/Cavitation_Demo/english/index.html