Remaining life assessment (RLA) of gas based units — case studies

Abstract

Gas based power plants, particularly the hot gas path components, are subjected to very harsh and rigorous environments. Many time dependent degradation mechanisms such as creep, fatigue, erosion, corrosion, electro mechanical fretting and embrittlement act in combination. The plants are, therefore, designed for a finite life. In order to avoid premature failures, margins of safety are provided and a number of critical components are recommended for replacement at fixed intervals. However, in view of the in-built safety factors, variation in operating conditions, use of lower bound material properties etc. can result in the components recommended for replacement to have a large percentage of their life still remaining. On the other hand, premature failures can occur due to operational and other factors not envisaged in the original design. Methodologies and techniques have been developed to assess the remaining life of gas based power units. Case studies related to the work carried out on land based and marine gas turbines are covered in this paper.