INFLUENCE OF THE LONG-TERM OPERATION OF 12KH1MF STEEL OF THE BENDS OF MAIN STEAM PIPELINES OF THERMAL POWER PLANTS ON ITS MECHANICAL PROPERTIES

We investigate 12Kh1MF steel of two bends of the main steam pipelines of thermal power plants. It is shown that they are damaged by the mechanism of intergranular fracture due to creep. In one of these bends, despite the agreement of the metal in all zones of the bend to the requirements imposed on the chemical composition, hardness, and characteristics of tensile strength, we detect through axial cracks in its zone of tension. At the same time, despite the fact that the strength of the metal is lower than the specified value in almost all zones of the other bend, only a shallow (up to 8 mm) axial crack was recorded in the zone of tension. However, the impact toughness of the metal in the zone of tension of both bends is lower than the specified value (almost three times lower for the first bend and two times lower for the second bend). The extremely low brittle-fracture resistance for this class of steels was regarded as a sign that the metal of both bends attained the critical engineering state.