Page 252 - Root Cause Failure Analysis

240 Root Cause Failure Analysis

Table 19-1 Common Failure Modes of Centrifugal Pumps

THE CAUSES
Bent Shaft
Casing DktofW fmm Excessbe Pip Sbaln
cavyatilm

Leakage In Plplng, Vh, Vmla
Mochanlcal Def.cfs, Worn, Rusted, D&dh Beerho8

Source: Integrated Systems, Inc.

Change of Phase The formation or collapse of vapor bubbles in either the suction
piping or inside the pump is one cause of cavitation. This failure mode normally
occurs in applications, such as boiler feed, where the incoming liquid is at a tempera-
ture near its saturation point. In this situation, a slight change in suction pressure can
cause the liquid to flash into its gaseous state. In the boiler-feed example, the water
flashes into steam. The reverse process also can occur. A slight increase in suction
pressure can force the entrained vapor to change phase to a liquid.