Safety and inspection planning of older installations

A basic assumption often made in risk/reliability based inspection planning is that a Bayesian approach can be used. This implies that probabilities of failure can be updated in a consistent way when new information (from inspections and repairs) becomes available. The Bayesian approach and a no-crack detection assumption implies that the inspection time intervals usually become longer and longer. For aging platform several small cracks are often observed - implying an increased risk for crack initiation (and coalescence of small cracks) and increased crack growth. This should imply shorter inspection time intervals for ageing structures. Different approaches for updating inspection plans for older installations are proposed. The most promising method consists in increasing the rate of crack initiations at the end of the expected lifetime - corresponding to a bath-tube hazard rate effect. The approach is illustrated for welded steel details in platforms. Systems effects are considered including use of dependence between inspection and failure events in different components for inspection planning.