Abstract

Bellows Expansion joints are mostly linked with the piping connections of turbines, heat exchangers, process equipment’s etc. Its primary function is to absorb expansion and contraction in pipelines on which it is fixed and fulfill its functioning through peculiar springy shaped convolutions. At design stage, it is very difficult to guess fatigue life cycles due to evolved stresses in convolutions. When it is subjected to purely axial load, stress generation per convolution acting along longitudinal line is same; however the behavior is different under very small angular rotation and axial shift due to misalignments in structural mountings. To understand it, preliminary investigations on axial case is necessary and also to identify the location of various stresses in convoluted section. This work aims to determine the meridional and circumferential stresses on the convoluted shape when it is subjected to an axi-symmetric internal pressure loading. Experimentation is carried out to determine the maximum stresses and verified it with the help of numerical simulation and analytically. 10 convolution bellows is used for the experiments. It is observed that the meridional stresses are highly dominating the circumferential stresses along the same longitudinal line. Meridional membrane stresses and meridional bending stresses due to pressure are evaluated on two different locations, one on perfectly meridional line and another at the top surface of convolution along the same longitudinal line. The stresses found higher on the top surface of convolutions. Meridional membrane and bending stresses due to deflection are higher than the meridional membrane and bending stresses due to pressure. Evaluation of the maximum stresses is very helpful for the designers to develop the fatigue analysis model and exact prediction of the cycle life of the bellows.

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