Abstract: A T-shaped pipe fitting element comprises a main tubular branch having first and second ends for connection to first and second pipe fitting sections of an auxiliary circuit, respectively, and a lateral branch having an axis which is at an angle to the axis of the main branch, and a free end for connecting to a third pipe fitting section of the auxiliary circuit. The first, second, and third pipe fitting sections each have different functions. One supplies the pipe fitting element with a first fluid at a high temperature, another supplies a second fluid to the pipe fitting element, at a lower temperature than the first fluid, and the third discharges a mixture of the first and second fluids. The pipe fitting sections consist of austenitic stainless steel. The T-shaped pipe fitting consists of stainless martensitic steel with improved thermal endurance properties.