Energy transition

Qualification Approach Detailed for Offshore Hydrogen Pipeline Systems

The authors’ work states that the qualification approach for offshore hydrogen pipeline systems should include material properties testing under various conditions.

Rising-load fracture toughness testing machine.
Fig. 1—Rising-load fracture toughness testing machine.
OTC 32158.

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.

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