The elements subjected to high temperatures are exposed to phenomena such as the creep, where time-dependent properties of materials should be considered. Many devices of the steam boiler work in creep conditions, what limits the time of their work. The chosen thick-walled superheater header is exposed to a high temperature and pressure and therefore it should be designed according to the European Standards. In this article, the standard requirements for a component operating in creep conditions are presented, and the FEM analysis is performed. In the FEM analysis, the proposed creep equation is used based on the results obtained from experimental tests.