A square tube failed where a gusset plate weld had been placed. The tube fracture surface is shown below in Photograph A.
Photograph A Overall view of failed square tube fracture surface.
The fracture surface displays an area of “old” (rusted) fracture at the 6 o’clock location. The area of old fracture is characterized by a concentration of red/brown rust indicating longer standing fracture.
The tube fracture increased in size from the “old/rusted” origin area by cyclic fatigue and/or overload stress. The appearance of intermittent zones of fatigue and/or overload are observed on the vertical legs of the tube fracture shown in Photograph A.
The fracture surface grew or extended around the tube until final fracture occurred in the between 11 o’clock and 1 o’clock.
A gusset weld, which contained what were believed to be weld cracks, had been placed on the mating tube at the 6 o’clock location. The fracture initiated, at the time of initial welding, at the 6 o’clock location. Cyclic fatigue permitted the initial manufacturing defect to propagate circumferentially until final failure occurred.