LEFM-Based Fatigue Life Assessment of Anthropogenic CO<sub>2</sub> Pipeline under Inner Pressure Fluctuation

Abstract

Natural or anthropogenic CO2pipelines have been in operation in USA, Europe and North Africa for almost three decades, which are aimed at implementing EOR(enhanced oil recovery) technology and (more importantly) developing CCS(carbon capture and storage) technology. At present, there is no specific pipe standard for CO2transportation pipelines. Instead, oil & gas pipeline system is directly introduced into the field of CO2transportation piping. Therefore, the technical details for oil & gas pipelines transporting supercritical CO2should be carefully taken into consideration due to the relevant effects of different impurities in the transported CO2and the different transportation environment for these two mediums, i.e. oil&gas mixture and CO2. For the application of anthropogenic CO2pipe transportation technique, this paper will address a FE-based method which can evaluate fatigue life of a supercritical CO2 transmission pipeline containing an inner crack. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis. And under the inner pressure fluctuation scenarios, an FRANC2D finite element procedure is generated to simulate mode-I crack extension from a given inner edge crack and to calculate the corresponding stress intension factors(SIFs) varied with different cracking depths. Afterwards, considering the effects of crack closure, the Paris equation is modified to build an integral analysis method for the fatigue life evaluation of CO2pipeline. Thus, the relation between the fatigue life and the inner pressure fluctuation range can be determined by performing the proposed fatigue crack growth analysis, which can also provide a LEFM-based pipeline selection method in terms of fatigue durability other than the conventional method coming from the structural strength theory.