Revising models of maintenance and inspection

Formal methods of updating delay-time models of industrial inspection practice associated with maintenance are proposed. Delay-time models are derived from subjective estimates and consequently are not guaranteed to model the status quo, i.e., the observed failure characteristics and downtime, say of a system under an existing inspection practice. The existence and uniqueness of solutions when updating the prior distribution of delay-time using a linear transform of delay-time are discussed. The scope for updating the prior model through modifying the perceived degree of perfectness of inspection is also addressed. Criteria for selecting an updating procedure in the case where options are not unique are proposed, and the decision conseqences of the change in the optimum inspection interval commented on. A case study is used to highlight the problem and to demonstrate the methods suggested.