Decision guidelines for transformer tank stress analysis using finite element method

The transformer tank is designed to withstand pressure and vacuum loads as required by the standards and customer requirements. The analysis of the design requires finite element analysis since closed form solutions are not available for the transformer tank type structures. The transformer tank failure is usually due to excessive permanent deformation but sometimes the tank also develops cracks under pressure loads. Materially nonlinear analysis is required because rarely, if ever does transformer tank not sustain permanent deformations which are caused by material nonlinearity. But the analysts often resort to linear analysis as the nonlinear analyses are very time consuming. Generally Localized high stresses due to stress concentrations are often ignored since the steel used for tank is ductile and localized plasticity is usually alleviated by the plastic deformation of the plates. This analysis procedure poses problems as the stress concentration can sometimes cause local cracking of the tank. In this work, this phenomenon is investigated and guidelines to deal with the same are formulated. Also a case study is presented implementing the same.