NDT Tools for Life Assessment of High Temperature Pressure Components

Creep damage of pressure equipment involves a great variety of high temperature components ranging from superheaters, reheaters, furnaces, reactors, etc.. Consequence of failures of these components are of high economic and safety concern. Moreover, the probability of failure of high temperature components is now increasing due to frequent cyclic of power plants imposed by a deregulated market and the search for increasing temperatures in ultrasupercritical plants. In this scenario, a complete NDT campaign is necessary both during the design stage and during the in-service stage. The choice of the specific NDT tecnique for each component type is of great importance. In this work an overview of the existing NDT techniques for creep designed and operated components are presented. Together with metallographic replica, which is still considered the fundamental tool for creep damage assessment in the majority of materials, other NDT tecniques which are able to detect creep cavity or cracks are presented and compared: ultrasonic techniques (tofd and phased-arrays), acoustic emission, holographic interferometry. In the second part of this paper the ability of some NDT tools to support residual life assessments are discussed. Among the most interesting tools are oxide scale ultrasonic measurement, micro-hardness testing, small-punch testing and on-stream deformation measurement. This tools are not strictly devoted to detecting creep defects (such as microcavities or microcracks) rather they give useful information related to creep damage, such as component deformation, material degradation and maximum service temperature. Moreover, a global procedure developed by ISPESL for inspection planning and interpretation of results of NDT examination according to a risk-based approach is presented. Eventually the new features of EN 13445-5 "Creep Amendments" concerning inspection and testing on creep designed components are briefly illustrated.