The Health and Safety Executive (HSE) use the PIPIN (PIPeline INtegrity) model to determine failure frequencies of major hazard pipelines. PIPIN uses two approaches to determine failure rates: an approach based on operational experience data, which generates failure rates for four principle failure modes (mechanical failures, ground movement and other events, corrosion, and third party activity); and a predictive model that uses structural reliability techniques to predict the failure frequency due to third party activity (TPA) only. The science underlying the TPA model has undergone a peer review with a number of recommendations made for improvements. HSE asked the Health and Safety Laboratory (HSL) to investigate the recommendations of the peer review and ascertain which recommendations improved the scientific basis of the model. HSL considered each of the recommendations in turn and the impact on the failure rates calculated for a set of 584 pipelines. Following discussions between HSL and other experts, one of the recommendations was rejected. The effect of implementing the remaining recommendations is to increase the failure rates, on average, although some pipelines see a decrease in the failure rate calculated.
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