Evaluation of mechanical behavior of new type bellows with two-directional convolutions

Bellows are widely used as the element of expansion joint in various piping systems. Piping systems for industrial plants often suffer excessive deformations or displacements caused by heat expansion, vibration, nonuniform subsidence of ground, etc. Bellows have the function to absorb regular or irregular expansion and contraction in such piping systems. Conventional bellows, however, have difficulties such as the instability of deformations under cyclic loadings, and the inability to absorb torsional deformations. In order to solve these problems, a new type of bellows, so-called "double convolution bellows", were proposed. This new type of bellows has convolutions in two directions: the first convolutions in the longitudinal direction are the same as the conventional bellows; and the second convolutions are added in the lateral direction. This paper presents a study on the mechanical behaviors of the newtype bellows and conventional bellows to examine the deformation behaviors under repeated axial loading, internal pressurizing and torsional loadings, and the results show an improvement in thickness distribution, instability and torsional flexibility.