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.