Qualification Approach Detailed for Offshore Hydrogen Pipeline Systems

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 32158, “Offshore Hydrogen Pipeline System Qualification: Design and Materials/Welds Testing in Hydrogen Environment,” by Angelo Santicchia, Elvira Aloigi, and Salvatore Terracina, Saipem, et al. The paper has not been peer reviewed. Copyright 2023 Offshore Technology Conference. Reproduced by permission. _ The qualification of a pipeline system for hydrogen transport, important in the transition to a decarbonized energy system even if strictly related to offshore pipelines, is a broad field that requires a systematic approach from basic material knowledge to complex physical models and fracture and fatigue assessments. The authors’ analysis of qualification requirements, including available test types and testing protocols, led to a matrix of potential tests, detailed in the complete paper, to be conducted in hydrogen and air environments for the steel base material, seam weld, and girth weld of offshore pipelines. Offshore Pipeline Materials Requirements vs. Hydrogen Transportation The authors’ work outlines many challenges, including the following: - Although hydrogen pipelines installed and operating onshore are common, at the time of writing, none exist in the offshore environment. - The blending percentage of hydrogen into natural gas in the future-transport scenario is still under discussion. - Small amounts of hydrogen can have a substantial effect on fatigue and fracture on high-strength materials. - The effect of hydrogen on pipe-material fatigue and fracture properties correlates directly to the specificity of the offshore environment, which will be very demanding in terms of longitudinal stress and fatigue. Another important aspect to consider is the effect of hydrogen on weldments both longitudinal and circumferential that are part of pipe-material fabrication and pipeline fabrication. A dedicated engineering team analyzed key standards and the available literature in terms of theoretical studies and experimental tests of materials in hydrogen environments. This activity indicated that, in addition to theoretical and design considerations, characterization of primary material and welding properties in hydrogen environments that will affect the failure modes of offshore pipeline design is a critical step. Testing Protocols and Equipment Slow Strain Rate Test (SSRT). Smooth cylindrical specimens were tested in inert gas (nitrogen), pure hydrogen, and a hydrogen/natural gas mixture for comparative purposes. This testing was aimed at evaluating the susceptibility of the pipeline materials (base material and weld metals) to hydrogen embrittlement when subjected to typical conditions envisaged for future hydrogen service. Tensile cylindrical specimens were tested at room temperature (24°C) in a high-pressure gaseous atmosphere. Tests were carried out in displacement control mode. In the initial part of the tensile test, in the plastic regime, after attainment of material yielding but before reaching the maximum tensile strength of the specimen, the strain distribution along the specimen was approximately uniform.