Power Turbine Remaining Life Assessment
The design life of an industrial power turbine has traditionally been 100,000 hours or 5,000 starts, based on a specific set of assumed operating conditions. Actual operating conditions vary from site to site, and are often less severe than the initial assumptions used by the manufacturer. This is why Dresser-Rand has developed a Remaining Life Assessment program. The objective of this program is to assist operators in extending the life of expensive components, determining inspection intervals, developing component replacement schedules, and establishing a spare parts stocking program. A comprehensive remaining life assessment must take into account unit operating history, a thorough non destructive examination of the components being considered for reuse, thermal and structural analyses using current analytical techniques, and material evaluations. There is some amount of variability in the input and output for each of these steps. Defects smaller than a given size are not always detected, material test results have a statistical distribution, and each operating cycle is unique. Traditionally the expected life has been based on a predetermined set of assumptions, such as stress analyses using typical dimensions, minus three sigma fatigue and creep properties, etc. The Dresser-Rand approach accounts for these inherent variations and establishes the statistical probability of successfully extending power turbine life without failure or unplanned maintenance as a function of time.