A novel framework for assessing the fracture toughness through the wall thickness of hydrogen pipelines

• A novel model for assessing the fracture toughness in hydrogen pipelines. • The model accounts for hydrogen concentration gradients and surface barriers. • The hydrogen-affected fracture toughness across the pipe wall is determined. • Embedded defects may possess higher fracture toughness compared to inner surface defects. • The model may reduce conservative approaches for assessing embedded defects. This article presents a novel model for assessing the fracture toughness in hydrogen pipelines. By combining experimental fracture toughness data with recognized hydrogen uptake and diffusion models, the local hydrogen-affected fracture toughness across the wall thickness of a hydrogen pipeline can be determined. The model specifically accounts for hydrogen concentration gradients across the pipe wall thickness and the existence of surface barriers. Presented results demonstrate that embedded defects may possess higher fracture toughness values compared to inner surface flaws for the same operating pressure, reducing their criticality compared to that of inner surface defects. The model has thus the potential to reduce conservative selection of hydrogen-affected fracture toughness, yielding less restrictive flaw-acceptance criteria in pipeline integrity assessments. The approach can efficiently be applied in combination with various integrity assessment methods as a readily accessible and easy to use engineering tool for fracture analysis of hydrogen pipelines and pressure vessels.