Pipe Material Selection and Fracture Control

Despite the very different properties of CO2, relative to natural gas, conventional pipeline materials and construction practices can be used provided certain basic precautions are observed. Clearly, the most important of these is to ensure that no free water is present in the system (see Chapter 3) since the formation of carbonic acid can lead to extremely aggressive corrosion wherever the steel internal surface is directly exposed. This requires limits on water content that are appropriate to prevent formation of free water under the most stringent operating conditions; potential upset conditions also need to be considered. In addition to very close control, during operation, of the pipeline receipt composition, it is also necessary to pay strict attention to dewatering and drying after hydrostatic testing, to ensure that water cannot remain in low points, dead legs, crevices or appurtenances. It may be necessary to delay the installation of certain types of valve, whose internal design might make complete drying difficult and which do not have corrosion-resistant trim, until after hydrostatic testing. If these precautions are adhered to, then the use of corrosion-resistant alloys or liners will not be necessary. Caution should be exercised in the use of internal coatings intended for flow optimization since they may become disbonded as a result of CO2 permeation or, for some coating formulations, solvent action. If severe, such disbondment and detachment could have significant consequences for the operability of downstream facilities.