Sensitivity to hydrogenation of steel operated in the steam pipeline bend of the TPP and restored by heat treatment

Abstract

Thermal power equipment is operated under high temperature and steam pressure, maneuvering mode of operation, high cyclic, static and impact loads, and corrosion and hydrogenation effects of process environments. As a result of such operational factors, the structure and mechanical properties of steel change, damages are formed, and there is a risk of uncontrolled fracture of structures critical for the energy supply of Ukraine. The research is devoted to the restored heat treatment (RHT) of the operated (2.86∙10⁵ h) heat-resistant steel 12Kh1MF of the steam pipe stretched zone bends of the main steam pipe of the thermal power plant (TPP). The RHT mode was proposed using double normalization with tempering. As a result, carbides dissolve and solid solution homogenizes, grain and carbide sizes decrease, pores heal, pores are located in the grain body, and mechanical properties of steel such as hardness, strength, ductility, and impact toughness increase. To assess the stability properties of operated and restored steels to the hydrogenation were carried out tensile for tests in the air after their preliminary electrolytic hydrogenation. It was found that hydrogenation of the operated steel worsened its strength and plastic properties. The characteristics of the restored steel, although somewhat worsened due to the presence of hydrogen in the metal, remained higher than the values regulated by the industry document for steel in the initial state. Thus, the improvement in the structure and properties of heat-resistant steel (including after its hydrogenation), established after RHT, substantiates the prospect of its further use to extend the service life of steam pipe bends.