The Health and Safety Executive (HSE) uses a computer code PIPIN (PIPeline INtegrity) to determine the failure frequencies of major accident hazard (MAH) pipelines for land use planning (LUP) purposes. PIPIN calculates the failure rates of pipelines for various modes of failure, including that of third party activity (TPA). The model for TPA requires the fracture toughness of the pipeline steel as an input. This is known to be adversely affected by the presence of hydrogen and must therefore be modified for the PIPIN approach to be applicable to hydrogen pipelines.
A stepwise approach for accounting for the effect of hydrogen on the fracture toughness of pipeline steels for use within PIPIN has been proposed. This is based on the use of the Kiefner correlation between Charpy impact energy and fracture toughness, which is currently used in PIPIN. The estimated fracture toughness is then reduced by a specified factor to account for the effect of hydrogen. Checks against a published data set on the fracture toughness of relevant steels in 100 bar hydrogen showed that the mean predicted toughness using the developed method was 1.29 times the actual measured toughness.
The proposed approach applies to estimations of failure frequencies for LUP purposes, where the condition of the pipe is unknown. The level of conservatism is therefore considered acceptable. The approach is not applicable to fitness-for-service determination for pipes containing known or postulated damage.
This report and the work it describes were funded by the Health and Safety Executive. Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.
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