Cyclic crack Resistance of the Steels of Bends of Steam Pipelines After Long-Term Operation

Abstract

The operational degradation of 12Kh1MF and 15Kh1M1F steels decreases their resistance to the nucleation and subcritical growth of a fatigue crack, especially near the external surface of tension zone of the bends of steam pipelines. Durability in the stage of nucleation of an initial macrocrack is the most sensitive to the structural-mechanical damaging of degraded steels. We show that MnS-type sulfide inclusions decrease the serviceability of such steels due to the formation of wedge-like microhollows near them. We have developed a method for the accelerated degradation of the steels of steam pipelines under laboratory conditions at a temperature of 540 to 630°C and under cyclic loading with a high load ratio (R = 0.6), which models the maneuver conditions of operation of steam pipelines.