Page 76 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

54 INTRODUCTION AND FORMS OF CORROSION

Figure 1.17 Cavitation erosion damage of a cylinder liner of a diesel engine. (Reproduced
by permission, John Wiley and Sons (8).)

because of the water turbulence, bubbles of air or gas of a size larger than the thickness
of the layer can interrupt, break the border layer, and cause a continuous rupture
of the protective film. A film of semiconductor oxide on the surface such as Cu O,
2
surrounding the damaged areas, produces a big cathode for reduction of dissolved
oxygen on the surface and causes pitting.

1.7.20 Impacting Bubbles
When bubbles collapse that are in contact with or very close to a solid surface, they
collapse asymmetrically. When a spherical bubble impacts a plane solid surface, the
bubble becomes elongated with a tail and collapses. The jet from the bubbles can
cause cavitation erosion on a solid wall (64). The implosion of a vapor bubble cre-
ates a microjet of liquid or microscopic “torpedo” of water that is ejected from the
collapsing bubbles at velocities ranging from 100 m to 500 m/s. When the torpedo