THE FOURTH REPORT from the Intergovernmental Panel on Climate Change states that “Warming of the climate system is unequivocal…”. It further states that there is a “very high confidence that the global average net effect of human activities since 1750 has been one of warming.” One of the proposed technologies that may play a role in the transition to a low-carbon economy is carbon dioxide capture and storage (CCS). The widespread adoption of CCS will require the transportation of the CO2 from where it is captured to where it is to be stored. Pipelines can be expected to play a significant role in the required transportation infrastructure.
The transportation of CO2 by long-distance transmission pipeline is an established technology; there are examples of CO2 pipelines in USA, Europe, and Africa. The design and operation of a CO2 pipeline is more complicated than a typical hydrocarbon pipeline, because of the highly non-linear thermodynamic properties of CO2 and because it is normally transported in a pipeline as a dense-phase fluid. There are number of issues to be considered. Furthermore, CO2 captured from fossil-fuel power stations may contain different proportions and/or types of impurities from those found in the sources of natural or anthropogenic CO2 transported in existing CO2 pipelines.
Fracture propagation control is one such issue that requires careful consideration in the design of a CO2 pipeline. CO2 pipelines may be more susceptible to long running ductile fractures than hydrocarbon gas pipelines. The need to prevent such propagating fractures imposes either a minimum required toughness (in terms of the Charpy V-notch impact energy) or a requirement for mechanical crack arrestors. Indeed, fracture propagation control has implications for the diameter, wall thickness, and grade of the pipeline, in addition to the Charpy V-notch impact energy of the linepipe steel, because in some situations the requirement for fracture propagation control will dictate the design of a CO2 pipeline.
The issues surrounding fracture propagation control in a CO2 pipeline are illustrated through the means of two simple design examples: a 24-in (609.6-mm) diameter pipeline with a design pressure of 100bar (1450psi), and a 18-in (457.2-mm) diameter pipeline with a design pressure of 180bar (2610psi). It is been shown that fracture propagation control in a CO2 pipeline can be addressed relatively simply. Some care is required because the trends observed in CO2 pipelines are not the same as those in natural gas pipelines, and the required toughness to arrest a ductile fracture may be very sensitive to small changes in the design parameters. Nevertheless, provided that fracture control is considered early in the design, any constraints on the design can be identified and, in principle, resolved without too much difficulty. It is important not to forget that transportation is an implicit, and essential, part of CCS.
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