Analysis of Circumferential Cracking in Hydroformed Bellows

摘要

Bellows are used in piping systems to accommodate differential displacements between various points while still maintaining pressure integrity. In hydroforming these elements, however, high tensile residual stresses can develop, which, in combination with the normal operating stresses, may lead to circumferential cracking. The stresses arising from different loading conditions are calculated for a specific bellows configuration, and the stress-intensity factors (SIF) for circumferential cracks in these stress fields are evaluated. The stress-intensity factors in the bellows are about 15% less than the values calculated for a crack in a straight pipe of similar geometry. The reduction in the SIF is believed to be due to the increased circumferential stiffness resulting from the formation of the convolutions. (ERA citation 08:034215)