The problem of thermal fatigue in pipe connections under the influence of streams mixing is one of the most discussed problems on international conferences. Numerous failures occur in industry as a result of this damage mechanism. It is caused by frequent stress changes developed by an effect of non-stationary thermal fields. The degree of damage is greatly dependent on characteristic of material geometrical design of a pipe connection in operational conditions. The report is dealing with influence of temperature differences of mixing media streams upon pipe material damage cumulation. It is focused on a perpendicular T-junction made of ferritic steel, which is protected inside with an anticorrosive weld deposit from austenitic steel. Six cases of temperature differences will be considered for particular operational conditions with a step of 50 °C, and the damage cumulation process will be observed. Thanks to it, it will be possible to judge better the meaning of streams temperature differences. and Obsahuje seznam literatury