PTC 2024: In-Situ Measurement of Fracture Toughness for Safe Conversion of Existing Pipelines to Hydrogen Service

Hydrogen blending into natural gas pipelines has been proposed as a possible solution for delivering low-carbon energy to the urban market while leveraging the existing infrastructure. One of the concerns is that hydrogen may lower the fracture toughness of pipeline steels. Recent research has demonstrated that risk but also provided insight into how variable service conditions and variable characteristics of vintage steel can lead to a range of low to high risks depending on the assets. Measuring the fracture toughness of hydrogen embrittled steels can be complicated and usually requires destructive cutouts and laboratory tests. This paper presents a potential solution where pipe toughness is measured in-situ through a surface test using a new method, planing-induced microfracture. It involves using a specialized blade, featuring a central opening, to plane the surface of a material. As the blade moves across the surface, the material at the central opening is not machined but rather deformed in tension until fracture. Characteristics of residual ligaments on the cut surface of the substrate and the opposite face of the separated chip are correlated with the material’s fracture toughness. Results from a proof-of-concept lab test that implements this method and the development of a field prototype will be presented in this paper. This method will facilitate pipeline integrity assessment and support the introduction of hydrogen blends into existing pipelines.