This paper describes the satisfactical models for evaluation of the reliability of non-destructive inspections. Probability models for uncertainly in the flaw size determination and the flaw detection are constructed. The flaw sizing models are based on the asumption the teh measured and true flaw sizes are related in a simple way: two models based on logarithmic and logit transformation of the flaw sized are either through logarithmic or logit transformation. To illustrate the use of these models, they have been applied to flaw sizing data and flaw detection frequency data. Furhermore, models for Bayesian updatin of flaw size distribution were developed. In this connection, models for updating the size distribution of a single flaw as well as for handling multiple flaws are introduced.