The classification method and the technical condition evaluation of the critical elements’ material of power boilers in creep service made from the 12Cr–1Mo–V

Metallographic examinations were carried out on ferritic 12Cr–1Mo–V steel with tempered martensite structure after 68,000–150,000 h service in creep conditions. Structural evolution related to the form of martensite, carbide precipitation and internal damage due long-term action of thermally activated processes was discussed. A generalised scheme of structural evolution and progress of the internal damage was developed in correlation with the life exhaustion ratio. Principles of a classification for ferritic 12Cr–1Mo–V steel after long-term-service were proposed together with a method for evaluation of the state of the material for the industrial practice.