Offshore Hydrogen Pipeline System Qualification: Design and Materials/Welds Testing in Hydrogen Environment

Abstract

The qualification of a pipeline system for hydrogen transport, even if strictly related to offshore pipelines, is a broad field that requires a systematic approach from basic material knowledge to complex physical models, fracture, and fatigue assessments. The combination of embrittlement with the severe loads of an offshore pipeline calls for a comprehensive awareness of material performance under such conditions. To achieve that, the first step has been the classification of failure modes by type of installation condition and selection of the tests required to characterize materials against them. A second step was to strengthen the state-of-the-art knowledge on data and tests availability for such failure modes. A third step was to set up and conduct a dedicated testing campaign focusing on girth welds and develop a pipeline system qualification procedure. The technological and standardizations gaps, identified in the design, construction and installation process chain are described, along with the actions taken by an offshore EPCI contractor to overcome and fix them. The analysis of qualification requirements, including available test types and testing protocols, led to a matrix of potential tests to be done in hydrogen and air environment for the steel base material, seam weld and girth weld of offshore pipelines. The final design of the test campaign included the minimum number of key tests necessary to assess the effect of atomic hydrogen inside the steel matrix and the related changes in mechanical properties, including the evaluation of tensile behavior and ductility, impact properties, fracture toughness (through KIH and rising load tests) and the critical soaking time in H2 environment. The tests were performed in different concentrations of hydrogen (i.e., different blending scenarios) at a given pressure which was considered potentially representative of the future main operating conditions in offshore hydrogen transportation systems. The main findings of the R&D work presented in the paper confirm that the qualification approach should include material properties testing under various conditions to support and provide a strong and sound scientific basis for the standardization process of the offshore EPCI pipeline system. The new tests and test conditions concur to complete the knowledge on the materials suitability for transporting hydrogen and hydrogen blends in offshore pipelines.