Balancing Hydrogen Networks Safely: A Method for Calculating Linepack Potential Without Causing Integrity Risk Due to Hydrogen-Enhanced Fatigue

The hydrogen economy is about to shift towards a large-scale decarbonization solution, a transition in which green hydrogen will take the stage. An increasing share of green hydrogen means that supply and demand will be more widely spread, in terms of distance as well as timing. Transport system operators see a temporary role for themselves in solving this issue of imbalance. Gasunie will have developed a ‘hydrogen backbone’ by 2030, approximately 1200 km in length, of which 80% will consist of re-used natural gas pipelines with 36–48 inch diameters. Hydrogen pipeline networks can efficiently accommodate temporal imbalances via their linepack. However, there is a downside to using linepack this way. Highly volatile production volumes of green hydrogen, caused by volatile wind and solar profiles, will result in frequent significant pressure fluctuations in the pipelines. This is worrying because pipeline crack-like defects in contact with hydrogen gas grow about ten times faster compared to natural gas under the same pressure fluctuations. This effect is known as hydrogen-enhanced fatigue defect growth. Increasing the frequency and amplitude of pressure fluctuations for balancing using linepack will lead to even higher defect growth rates, compared to a more constant pressure regime. Enhanced fatigue can be prevented by controlling the pressure fluctuations, but this limits the maximum available linepack. This difficult choice between commercial interests and pipeline integrity justifies performing a quantitative analysis of market-driven pressure fluctuations in hydrogen networks and their effect on defect growth and lifetimes of these hydrogen networks. This paper describes an integrated simulation model that can calculate dynamic network behaviour for hydrogen transport networks and give an indication of the corresponding defect growth risks that come with this network behaviour. By using this integrated simulation model, safe margins can be calculated for providing sufficient linepack without risking increased hydrogen-enhanced fatigue defect growth, which can undermine the integrity of a pipeline and reduce the lifetime of this asset. Insights from this model are applied by Gasunie to maximize security of supply and minimize integrity risks. This is essential in the start-up phase of the hydrogen economy due to the absence of sufficient flexibility in production and storage.