Leading the Energy Transition: A Novel Approach to Existing Gas Pipelines Retrofitting for Hydrogen Transport

Abstract Considering future developments and plans of decarbonization, the H2 pipeline transport technology will play a key role, and it could also be implemented as a component of an integrated system with CO2 pipelines (i.e. blue hydrogen). A key aspect of H2 technology development is the possibility to use existing natural gas transport infrastructure to be retrofitted for H2 transport. It is recognized that the transport of natural gas mixtures containing a 10% of hydrogen content could be in general feasible in existing onshore natural gas pipeline systems with minor modifications. Higher hydrogen contents, however, appear to have a large impact on the system components, requiring significant modifications instead. The more important bottleneck is related to the utilization of carbon steel grades normally used for natural gas transmission pipelines. Most of literature sources report a higher susceptibility of high steel grades to hydrogen embrittlement, i.e. the loss of toughness in steel which results from adsorption of hydrogen. Corresponding to the loss of net material toughness is a reduction in fatigue life, causing crack growth and propagation. There is a need to complement existing standards on hydrogen piping, pipeline and their components part of the hydrogen value chain to fulfill the energy transition design scenarios and the need to reuse existing gas transport infrastructure to support the economics of the transition. This translates to the definition of a clear methodology to carry out the assessment of existing natural gas pipeline systems (both onshore and offshore), in such a way to identify the tolerance to hydrogen of the different system components. All the engineering disciplines need to be involved, including piping & materials, machinery, instrumentation, as well as loss prevention & safety. Since the potential transport service conversion is normally carried out in steps, starting from a low H2 content in the blend with natural gas up to possibly 100% H2, the number of affected components will increase during this evolution; some of them could be ready to tolerate 100% H2 from the beginning, others will need some modifications, while some will need a complete replacement. This paper presents a description of Saipem methodology, that has been applied to a number of conversion studies relevant to transport systems mainly located in Europe.