Some years ago, after several pipeline accidents, the oil industry invited work groups to investigate the subject of predicting the burst pressures of damaged pipelines. Several damage evaluation guidelines were produced as a result, but these remained conservative in approach and, above all, were applicable only to minor damage.
Total, however, having observed far more serious damages on offshore pipelines, wished to go further and, in 2006, initiated a specific study as part of the "Deep Offshore Development", internal R&D project.
This cross-functional work permitted in 2011 the realisation of a finite element analysis model, EMPREINTE. This application has three objectives: to model pipeline dents, calculate the pipeline ultimate burst resistance and deduce a working pressure that includes an appropriate safety factor.
To evaluate damage to pipelines, this application uses an innovative approach: from the measured damage, it recreates the shape of the object that produced the observed dent, then simulates the damage by calculation and finally predicts the rupture pressure.
The method was validated by a series of burst tests on pipes on which dent-type damage (some extending to more than 50% of the pipeline diameter) had been inflicted and metal loss deliberately induced.
The software application was used in real conditions for the first time when an explosion damaged an HP gas pipeline feeding an LNG plant. Where strict application of the damage evaluation codes dictated the conservative course of replacing the damaged section, EMPREINTE confirmed that the repair could be postponed. The plant's production was therefore quickly resumed, minimizing LNG production losses (which might have attained several millions of USD if the damaged section had been replaced immediately).