Abstract: A large raw milk silo suddenly collapsed with ~500,000 litres of raw milk. The silo collapse was preceded by the growth of metal fatigue cracks in a circumferential weld at many locations around the base perimeter of the silo. The fatigue crack growth was driven by cyclic loading, most likely a combination of the accumulation of process cycles and possibly wind loading over its service life. Visual inspections showed that the weld was irregular in shape and size and insufficient in dimensions (under-filled) in some locations. Metallurgical cross-sections showed that the weld contained inherent crack-like defects, which acted as stress concentrations that served as crack initiation sites. Overall, the design was inherently difficult to manufacture and inspect. Redesign and periodic inspections are necessary for fracture-safe operations.
Author: Milo V. Kral
Keywords: Fatigue, Striations, Stainless Steel, Weld