Rupture Proof CO2 Pipelines by Design – Not by Chance

Abstract CO2 pipelines are being proposed for CCS of anthropogenic CO2. CO2 can be transported by pipelines in gaseous or liquid (dense-phase) states. In the dense-phase state, the traditional fracture control design procedure frequently requires such a high toughness for axial ductile fracture arrest in the pipe body that crack arrestors are needed. Even if material could be procured to meet the regulatory arrest criterion, such design conditions might result in an undesirable double-ended full-bore for hazard analysis. The full-bore opening from a pipe rupture can involve significant safety risk to the population along the right-of-way, as was experienced in the Denbury CO2 pipeline failure. An alternative design of a dense-phase CO2 pipeline that can prevent large openings/ruptures from happening was explored in this paper. With this design criterion, a new CO2 pipeline can become “Rupture-Proof”, and evaluations to date have shown that the hazard zone could be reduced by a factor of ∼100. The “Rupture-Proof” design for a CO2 line involves two modifications to the traditional pipeline design. The first design modification is to ensure that there is a “Quick Crack Arrest” of any potential axial flaw. With the appropriate thickness and material toughness specification, the crack would only propagate a few inches, ergo the “Quick Crack Arrest.” The material aspects for the quick axial crack arrest require understanding of the material developments over the decades, and as shown there are four different types of line pipe behavior when conducting ductile fracture control analyses. An assessment of more recent CO2 full-scale burst tests in the UK is presented to show a more precise way of determining the arrest toughness for axial ductile fracture control. Using the best of the current material types, the methodology for a “quick crack arrest design” procedure was found viable with sample calculations. The second modification is to eliminate the circumferential pipe break at a girth weld, like what occurred at Denbury. From work done in the nuclear piping industry for repair of circumferential flaws in girth welds, a modest change to the weld cross-sectional geometry can make it so that even with large unintentional girth weld defects or undermatched weld metal, the girth weld would not fracture, and the rest of the pipe body could take the longitudinal strain.