Erosion Corrosion and Cavitation
Erosion Corrosion , also known as flow-enhanced corrosion or impingement
attack, takes place in flowing systems where turbulence occurs, typically in pipe
bends (elbows), tube constrictions, and other structures that alter flow direction
or velocity. The mechanism for this type of corrosion is the continual flow of water,
which removes any protective film or metal oxide from the metal surface. The exposed
surface quickly corrodes and the resulting oxide is in turn eroded away. Erosion
corrosion usually leads to rapid failure.
Erosion corrosion can occur both in the presence and in the absence of suspended
matter in the flow stream. In the presence of suspended matter, the effect is very
similar to sandblasting, and even strong films can be removed at relatively low
Cavitation is similar to erosion corrosion in that they both occur in piping
systems and also that protective films are removed from the metal surface during
fluid flow. Low pressure, which could be caused by changes in velocity due to discontinuity
in the flow path, causes gas or vapor bubbles to form in the fluid stream. When
these bubbles hit the metal surface, they rapidly collapse or implode, producing
a shock wave sufficiently strong to remove protective films.
Controlling Erosion Corrosion and Cavitation
Some prevention methods for erosion corrosion and cavitation include improving the
flow lines within the pipe, by deburring (smoothing out irregularities), allowing
bends to have larger angles, and changing pipe diameters gradually rather than abrupt
changes. Other methods include slowing the flow rate (reducing turbulence), reducing
the amount of dissolved oxygen, changing the pH, and changing the pipe material
to a different metal or alloy.
Example: The pipe shown below is leaking due to erosion corrosion. A) Indicate the
most probable locations for leaks. B) This is one example of a way to redesign the
pipe to eliminate or minimize erosion corrosion.
The following images show examples of pipes designed to minimize erosion corrosion: