Computer Program for Approximating the Reliability Characteristics of Acyclic Directed Graphs

Reliability graphs having only one source node and one sink node, containing no feedback loops, and whose every event is directed are commonplace in the chemical process industry. The use of highly sophisticated techniques for evaluating the reliability characteristics of these graphs is not necessary in this situation; such graphs facilitate the use of simple techniques which are computationally very efficient. The computer program presented in this paper applies to this type of graph and evaluates upper and lower bounds to three system-reliability characteristics: availability, mean time-to-fail, and mean time-to-repair. Data required are simply a mean time-to-fail and a mean time-to-repair for each event together with structural information relating each event to the graph. The program is written in FORTRAN IV; a listing and instructions for its use are available from the author and in a Supplement.