New Aspects on Modeling Ductile Fracture Arrest Performance of Large-Diameter Pipes in Dense-Phase Carbon Dioxide

Abstract When designing pipelines for the transport of compressible media, the required minimum toughness is usually determined by using the Battelle Two-Curve model and expressed as Charpy V-notch (CVN) impact energy. For modern, high-toughness line pipe steels, in particular in the context of carbon dioxide (CO2) as liquid or dense phase, this concept becomes questionable since the CVN impact test loses significance for high-strength steels exhibiting high CVN toughness levels. However, due to the small number of full-scale test results in CO2 available to date that additionally encompass only a narrow envelope of geometries and material properties, it is difficult to derive both validated toughness concept improvements as well as requirements for pipeline design. This paper examines a numerical modeling approach to ascertain the fracture arrest behavior of pipe transporting dense-phase CO2. The model was tuned to published data on full-scale CO2 burst tests. Multiple pipe diameters and wall thickness/diameter ratios were evaluated. The new model was developed with the intent of better characterizing modern line pipe steels as well as the unique operating aspects of dense-phase CO2. The results follow the predictions of a DNV RP F104 assessment and show the expected conservatism of the given recommendations.