Life Extension of High Temperature Components

Abstract

Power producing plant operating at high temperature are designed for finite life. This is necessary because the operating conditions are sufficiently high to cause continuous growth of material damage. Failure occurs when damage reaches a critical value. Design is based on stress levels with an appropriate factor of safety. Since life is dependent on a strongly non-linear function of stress the actual life can be many times greater than the design life. In these circumstances it is then natural to explore the possibility of extending the working life. To increase the working life it is necessary to decrease the factor of safety, but it may be possible to follow this course of action provided the growth of physical damage is carefully monitored. In this paper creep damage mechanisms are reported and growth laws are proposed.