Substantiation of the critical structural and mechanical state of low-alloy heat-resistant steel from steam pipelines of thermal power plant

Abstract

The paper discusses metallographic studies and the results of mechanical testing of 15Kh1M1F (DIN 15CrMoV5-10) steel in the initial state and after its long-term operation in the steam pipeline of TPP. The revealed adverse impact of shutdowns of TPP units on the structural and mechanical state of steel is associated with the occurrence of cyclic thermal stresses in the pipe walls. Structural changes in metal across the pipe wall are uneven and consistent with regularities of mechanical properties changes. Intergranular fragments detected on the background typical transgranular relief of specimen’s fracture surfaces are considered fractographic signs of steel’s degradation. The part of intergranular fracture in the unit area of the fracture surfaces is proposed as the quantitative indicator of the changes in the structural and mechanical state of 15Kh1M1F steel due to its degradation. The critical state of steel is substantiated based on the regularities of operational changes in its mechanical properties and the revealed fractographic features.