Corrosion Mechanisms
23
2.6 Other Factors Affecting Corrosion
Temperature can have a significant influence on the corrosion process. This
is not unexpected because it is an electrochemical reaction and reaction rates
do increase with increasing temperature. There are additional influences on
corrosion other than the corrodent itself.
The relative velocities between the component and the media can have a
direct effect on the corrosion rate. In some instances, increasing the velocity of the corrodent over the sufface of the metal will increase the corrosion
rate. When concentration polarization occurs, the increased velocity of the
media will disperse the concentrating species. However, with passive materials, increasing the velocity can actually result in lower corrosion rates. This
occurs because the increased velocity shifts the cathodic polarization curve
such that it no longer intersects the anodic polarization curve in the active
corrosion region, as shown in Figure 2.14.
Increasing
temperature
Increasing chloride
Increasing
chromium
Increasing
molybdenum
Log i
L og i
V
V
Log i
Log i
V
V
FigurE 2.13
Effects of environment and alloy content on anodic polarization behavior.