The Health and Safety Executive (HSE) uses the PIPIN (PIPeline INtegrity) model to determine failure frequencies of major hazard pipelines. PIPIN calculates the failure rates for four categories of failure of pipelines (pinhole, small hole, large hole, and rupture). 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 only. The predictive model uses historical data in the form of damage data distributions and strike rates as inputs to the fracture mechanics equations. HSE asked the Health and Safety Laboratory (HSL) to rewrite PIPIN using a Monte Carlo solution approach, to update the science in the model based upon peer review recommendations, to update the damage data used in the predictive model, and to update the historical operational experience data. The effect of the revised model on the results generated from a set of 584 pipelines has been investigated and it was shown that the combined effect of all the modifications is to reduce the failure rates, on average, for all hole sizes compared to the original model.

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