Failure of a conveyor trunnion shaft on a centrifuge

Abstract The purpose of this case study is to determine the cause of failure of a conveyor trunnion shaft from a solid bowl centrifuge. The trunnion shaft fractured at the weld joint, which joins a flange to the end of the shaft. Fracture occurred through the walls of the shaft. It was determined that the failure was caused by defects related to the welding procedures. These defects included cracks in the weld joint, unfused welds, slags, and porosity. The causes of these defects were due to poor welding techniques prior to and during the welding procedure. The weld joint was an area of high stress concentration, in addition the flange was inaccurately machined, which may have caused high bending stresses during operation and contributed to the failure. It is recommended that certain welding techniques be used prior to and during welding to reduce incomplete fusion and to prevent the formation of slags and porosity. It is also recommended that the trunnion shaft be redesigned to reduce stress concentration at the weld joint between the shaft and the flange and to properly machine the flange to reduce high bending stresses.