Additive manufacturing is gaining increasing interest as an alternative manufacturing process to produce conventional or engineered materials for pipelines. In this context, during 2021 Saipem launched an R&D initiative to explore the possibility to deploy Wire Arc Additive Manufacturing Process (WAAM) to produce typical components of a subsea pipeline system. The main objective is to demonstrate that WAAM is suitable to produce pieces having similar properties than the ones manufactured via traditional methods and that they could be used for typical offshore components. As a first trial, Saipem decided to start with the production and testing of a subsea flange and the scope was assigned to Vallourec S.A. Scope of the present paper is to share the main challenges faced during the activity and the main outcomes of it. The selected grade was an ASTM A694 F65 equivalent grade that is considered a representative case for several offshore scenarios and the produced flange was a WELDING NECK 11" API 6A (10.000 psi) which represented in terms of WAAM technology the largest part ever printed by Vallourec. Manufacturing, inspection, and testing has been carried out following the requirements of DNVGL-ST-B203 for AMC 3 category. After the printing of a pre-build piece to verify the main properties and to confirm that the parameters were suitable for the production, the full-scale component was then printed as well and destructive testing has been done in critical areas of the piece after NDT inspection.

COVID-19 pandemic is accelerating the transition to decarbonized energy systems. In this context, major Operators and Contractors are bound to promote innovation and technological development. The paper describes how this is being applied to the design of offshore pipelines that are now required to transport not only Hydrocarbons but also anthropogenic CO2 and low-carbon Hydrogen. In order to evaluate all the new technical challenges presented in designing CO2 and H2 pipelines, a state of art has been carried out and is here presented focusing on all the new technical aspects associated to the main disciplines involved in the pipeline network design. Different technical aspects (such as performances evaluation of Equation of State in CCS, Design Standards application to both CO2 and hydrogen pipelines, energy capacity of hydrogen pipelines and others) have been also analytically or numerically addressed simulating credible pipeline operating scenarios. To achieve that, an intensive engineering effort is being dedicated to the development of knowledge, engineering tools, methods and procedures that will be the basis for the execution of future projects concerning H2 and CO2 transportation and storage. A particular focus has been dedicated to offshore pipeline design both for new installation and repurposing of existing ones. In parallel, the cooperation started between Operators, Contractors, Manufacturers, Institutions and Universities, as described in the present paper, acts as a "booster" for the consolidation of knowledge and for the advancing of technology to put in place to overcome those new challenges. Recommendations are made in relation to the gaps found in experimental evidence present in literature and gaps in Standards coverage for the proper pipeline design in those new scenarios.

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.