Comparative Review of Risk-Informed Inservice Inspection Methodologies

In the 1970’s and early 80’s there was a reevaluation of the role of inservice inspection programs. Inservice inspection programs as originally developed under the ASME Section XI Code requirements were based on the best information available at the time and helped establish the safety of the subject components. However, it was determined that the examination requirements were not efficient because examinations were being focused on many welds, components, and systems that are not as important as originally thought when the ASME Section III Classes 1, 2, and 3 categories were developed. It was determined that the appropriate locations were not being inspected and that the most effective types of examinations were not being performed. It was felt that a more optimal inspection approach was needed. This eventually led to the development of the risk-informed inservice inspection (RI-ISI) methodology. RI-ISI provides a structured and systematic framework for allocating inspection resources in a cost-effective manner while improving plant safety. It helps focus inspections where failure mechanisms are likely to be and where enhanced inspections are warranted. This paper examines the foundations for the current RI-ISI initiatives and how the RI-ISI methodology may be used in the future for current and next generation plants.