Catastrophic Failure of Flex Hose Bellows Due to Lateral Offset and Internal Pressure

Abstract

This paper describes the analytical and empirical analyses conducted in the catastrophic failure of a flexible hose utilized in a petro-chemical environment. Specifically, the issues associated with the instability of the metal u-shaped bellows, from which the hose derives its overall flexibility and name, are reviewed and discussed in detail. In an effort to provide a comprehensive examination of the flexible hose’s use in the petro-chemical industry, a discussion of the applied mechanics associated with column buckling of the bellows (also known as “squirm”) is presented. In addition, the fabrication details that also proved detrimental to the structural adequacy of the subject flexible hose are highlighted. Results from an elastic-plastic finite element analysis of the u-shaped bellows are described and compared against previously published theoretical works on the instability of shells of revolution and most specifically, toroids. The applied loads in the finite element analyses include both internal pressure and transverse displacements (i.e., lateral offset). Furthermore, the guidance provided by the rules of the Expansion Joint Manufacturers Association Standards (EJMA) with regard to squirm are also reviewed and discussed. Finally, the results of the theoretical, empirical, and analytical investigations into the squirm phenomenon are utilized to identify some very practical solutions and recommendations to avoid the possibility of catastrophic failure of u-shaped bellows from column type instability.