Residual Life Assessment/RLA

Residual life of a material (especially an engineering material) is the time period during which it shall retain the fitness for service characteristics. Assessing the condition and remaining life of industrial plants that operate at high temperature and high pressure becomes more critical as the plant ages. Extensive and expensive inspection programs, besides the routine operations, have to be undertaken in order to monitor the extent of in service deteriorations. Conducting RLA is important to maintain the efficient operation of a process plant unit and avoid failure of critical equipments, which lead to costly downtime problem. Such equipments include pressure vessels, piping, storage tanks, valves, pumps, compressors, boilers, turbines etc. The actual life of a component may be more than the design life if the properties assumed were lower or the factor of safety was higher or if the plant was operated conservatively or the oxidation effects were over estimated, hence a residual life assessment may be quite appropriate. The importance of conducting RLA studies also arises from the regulations that are in place for a number of industrial equipments, like boilers, turbines etc. Also, conducting RLA studies properly can safeguard human lives loading conditions.

Two methods are available for Residual Life Assessment Plant components, one using data analysis based on operational history and the other based on periodic examination of critical components. The latter method is widely adopted in the industry as it is more reliable. Standard techniques utilized for RLA studies include: Visual inspection and Non destructive testing techniques such as Dimensional measurement, Ultrasonic thickness gauging, Penetrant testing, Magnetic particle inspection using wet fluorescent method and Eddy current test. Correlation of the NDT test results with the operational parameters is used to estimate the Residual Life of any equipment.