As Europe is gradually moving towards a hydrogen based society it has been acknowledged that adding certain amount of hydrogen, as a clean energy carrier, to the existing natural gas pipeline will help reduce the CO2 emissions which contribute to the greenhouse effect. On the other hand, hydrogen has been demonstrated to be able to change the behaviour of the pipeline steel such as lower toughnessand faster crack growth due to hydrogen embrittlement. Therefore, it is necessary that the risks associated with the failure of the pipeline carrying mixtures of natural gas and hydrogen be assessed.

The study reported in this paper is part of European NATURALHY project, whose aim is to investigate the possibility of using the existing natural gas transmission pipelines to convey naturalgas/hydrogen mixtures. According to the EGIG database, the most common cause of failure for the existing natural gas pipelines is third party damage, which mainly refers to a gouge, a dent/gouge combination of known geometry. Among third party damage failures, 90% are the result of immediate failure i.e. leakage or rupture of the pipeline and only 10% of them are the result of delayed failure. While its not expected that hydrogen will impact the immediate failure it could increase the vulnerability of the pipe to delayed failure through the initiation or activation of crack like defects.

This paper will present a methodology to predict the probability of increased failures and describe a software tool that has been developed to perform the calculations.