The area of flange joints with gasket includes many types of pressure vessels, which are mainly defined by the purpose of use and specific load conditions. These differences in definitions caused the existence of many types of pressure vessels with different shell shapes. Calculations of basic shapes are defined by standards. However, in some fields of engineering practice, these shapes are atypical. The article discusses the issue of circular sealed flange joints with a nonstandard shape of the pressure chamber shells. The aim of this article is to describe influence of shape of pressure vessel shell on bolt working load and the final tightness of the sealed joint using FEM.