Investigation of Fracture Toughness Behavior for Carbon Steel Line Pipes Under Hydrogen and CO2 Environment

Abstract Within the global effort to reach carbon emission targets, low carbon hydrogen production and CO2 capture, and sequestration are two crucial focus areas for energy transition. Pipelines are expected to play a critical role in the energy transition as transportation systems of hydrogen and CO2. For hydrogen pipelines, sufficient fracture toughness is one of the key design requirements in ASME B31.12. Further, blue hydrogen production requires capturing CO2 after steam methane reforming and transporting to an underground sequestration site. However, the impact of residual H2 within dense phase/supercritical CO2 has not been broadly studied In this investigation, API 5L sour grade (PSL2 + annex H) and non-sour grade (PSL2) carbon steel line pipes (X65 amdX70) were tested to evaluate the fracture toughness values under (1) 100% H2 at 2400 and 3600 psi and, (2) a mixture of 99% CO2 and 1% H2 at a total pressure of 2400 psi. All measured fracture toughness results were above the ASME B31.12 required fracture toughness value (55 MPa-m1/2). Critically, initiation toughness values were observed to be near-identical between experimental conditions, indicating a strong effect of hydrogen even at low concentrations. The present study underscores the need for detailed experimentation to study the effect of residual-low hydrogen concentrations on the mechanical properties of common transmission pipeline materials.