Define the Fatigue failure - underwater inspection of bridge?

Fatigue failure results in the fracture of structural members as a consequence of repeated high loading.  Fatigue distress can be recognised by a series of small hairline fractures perpendicular to the line of stress in the member. Fatigue cracks are difficult to locate. Since fatigue cracks represent an extremely dangerous condition in steel marine structures, extreme care must be undertaken when inspecting structural members subjected to repetitive loading, particularly high wave loading.