The design of pressurized equipment involves consideration of a wide range of complex load combinations. Cyclic loading involving fatigue of structures is one of the most complex engineering issues. The purpose of this project is to provide the design engineer with a methodology for addressing the complexity of biaxial fatigue problems at elevated temperature where the loading is both mechanical and thermal and the phase relationship between them varies from in-phase to out-of-phase. The project also demonstrates the ability to perform biaxial thermo-mechanical fatigue (TMF) testing.Typical fatigue data was performed at a constant temperature (isothermal) and under uniaxial conditions. However, typical reactors, pressure vessels, piping or other structural components may be subjected to complex thermal and mechanical transient loading conditions with a wide variety of phase relationships. The objective of this project is to provide the design engineer with a tool for addressing these issues.