Optimization of the structure and properties of 12KH1MF steel pipelines by the use of regenerative heat treatment after long service life

The article presents the results of domestic and foreign studies of kinetics of metal damage depending on creep flow which served as the basis for the development of assessment scales of a pore forming degree as well as methods of resource forecasting of long-running power equipment in microdamaging. Research was carried out to study metal damage in real operating conditions at power plants by nondestructive checking with the use of the replica method of over a thousand of bends (the most stressed elements of steam lines) of MP and HP steel grades of power units with the capacity of 200 and 800 MW and a laboratory study of the structure and properties of over twenty curved and straight pipe sections cut from steam lines after a long service life. It was determined that to evaluate the efficiency of steam line bends it is necessary, in contrast to recommendations of applicable documentation, to conduct the research of bent pipe sections rather than of straight ones. The analysis of the data obtained shows that microdamaging accumulated in metal is an integral criterion of the efficiency depending on all operational factors (temperature, pressure, time), geometrical parameters (wall thickness, distortion-shaped cross-section) and metal state (structure, properties) of a particular equipment element. The research performed confirms the highest information content and reliability of the metallographic method of damage assessment of metal susceptible to creep flow in order to diagnose the state of high-temperature elements of power equipment, and to determine the possibility of their further operation or the need for conducting thermal treatment rehabilitation.