Abstract
Bivariate log-normal distribution analyses were conducted on the specific output class of steam turbine components such as rotors, moving blades, nozzles, casings. The damage phenomena were erosion, creep deformation, fatigue cracking, wear, fouling, scoring and so on excluding the repeated events after repairs. Using the statistical parameters such as mean and variance, the events were plotted against operation time and start up cycles. The order of event occurrence was determined by the time-cycle based statistical data manipulation. The prescribed risk values for individual events could be easily transformed to the equi-risk ellipse contours of chi-square distribution of parameter Q as the quadratic function of operation and start-up cycles derived from the bivariate log-normal distribution on the cycle-time diagram. The expected values of total maintenance costs for repairing the individual damage were obtained by the sum of ellipse contours of respective damage modes in the subject components. This diagram could be a useful measure of expecting maintenance period to minimize the total cost by controlling operation patterns both considering start-up cycles and operation hours.
