Environmental Engineering Reference
In-Depth Information
Figure 3.58
Fatigue curves showing reduced endurance limit in the presence of
(a) corrosive environment and (b) added notches.
posed to a corrosive environment. For example, the fatigue strength at 10 million
cycles in salt water could be reduced to as little as 10% of that in moist air. The
oxygen content of the environment greatly influences corrosion fatigue. It may
be mentioned here that fatigue tests conducted in vacuum yield much higher
values of endurance limit than that encountered in normal tests in air containing
oxygen and moisture. Fatigue in their presence therefore may be considered as
a case of corrosion fatigue. Complete elimination of oxygen from a neutral solu-
tion has been found to eliminate corrosion fatigue of low-carbon steel.
Corrosion fatigue increases almost proportionately with the increase of general
aggressiveness of the corrodent. Thus an increase in temperature, a lowering of
pH, or an increase in the concentration of corrosive species leads to an aggrava-
tion of corrosion fatigue.
