Pipelines are by far the most economical method for transporting large amounts of CO₂ in the context of carbon capture and storage (CCS). The transport of gaseous CO₂ usually does not place any demands on the pipe material that go beyond the classic design, as long as water drop-out is prevented. However, the major challenge for line pipe steels when transporting CO₂ in the liquid or dense phase is, above all, the requirement of high toughness in the base material to prevent running ductile fracture.

When designing pipelines for the transport of compressible media in general, the required minimum toughness is usually determined by using the Battelle Two-Curve model and expressed as CVN impact energy. For modern, high-toughness line pipe steels, this concept becomes questionable when the fracture resistance curve is based on CVN impact energy, and, for incompressible media such as dense-phase CO₂, requires high toughness values to prevent running ductile fracture. One reason can be found in the CVN specimen behaviour in the regime of toughness values above 200 J, where tests typically reveal non-broken specimens with energy dissipated to a non-negligible portion in bending and plastic deformation

The framework for deriving the required minimum toughness, as contained in current regulations for CO₂ pipelines such as DNV-RP-F104, is conservatively designed, and the CVN toughness requirements are correspondingly high. At the same time, ongoing investigations are carried out to determine which alternative toughness measures can provide a reliable concept with non-oversized requirements.

In this study, CVN impact energy was evaluated for current line pipe materials from different manufacturing routes, different pipe geometries and steel grades. The results were correlated to impact energy measured in instrumented drop-weight tear tests (DWTT). DWTT-based impact energy is a promising candidate as an alternative toughness parameter at material qualification.