DAMAGE AND FUZZY RISK ASSESSMENT IN STEAM PLANTS

Abstract

The various methods of damage assessment in steam plants are reviewed. An example of estimating the remaining life of steam pipe welds containing cracks is discussed. Modelling techniques provide a quantitative evaluation of the risk of failure. However, damage assessment is not an exact science. Thus the fuzzy set method of risk assessment is introduced. Most material data for creep are obtained from accelerated tests, and the extrapolation of shorter time data to longer times at different stresses and temperatures is used in the prediction of remaining life. Inexact knowledge of load and temperature variations in the operation of actual steam plant further complicates overall risk assessment. Estimation of the overall risk of failure in the plant using the fuzzy set method requires identification of critical areas in different components at which damage may have accumulated, together with nondestructive testing, microstructural evaluation and other methods to define the extent of the damage. The importance of the particular component to the operation of the whole system must be assessed before a judgement can be made to provide a prediction of the plant’s remaining life.