An evaluation of the structural integrity of HSLA steels exposed in simulated flue-gases under dynamic conditions for anthropogenic CO2 transport.

Abstract

Carbon capture and storage (CCTS) is a transitional technology offering a nearterm method of mitigating climate change. Pipelines are considered to be the most suitable systems for CCTS; however, structural integrity of pipeline has to be guaranteed in order for this technology to become a practical technical solution. The investigation detailed here is based on a systematic experimental approach to investigate the structural integrity of API X100, X60 and X70 steels exposed in simulated flue-gas under dynamic conditions. A core of the structured experiments through some methods such as aging test, tensile properties, fracture toughness, residual stress and engineering critical assessment was accomplished in parent material and exposed samples on flue-gas. The temperature range of evaluation for tensile test covers -70C to 21C while fracture toughness was over the range -196C to 21C. Tensile properties of virgin material show that steels meet standard specification while aging samples do not show significant scatter compared with parent steels. Ovalisation of the fracture surface and splitting phenomenon was observed which is related with steel anisotropy. Fracture toughness obtained from experiment was compared with that calculate by two existing correlations. However both correlations did not predict the level of fracture toughness expected indicating the methods used in this work has limited applicability under the test conditions used here. Residual stress (RS) induced in API X100 steel by cold rolling method was characterised using two complementary techniques known as Neutron Diffraction (ND) and Incremental Hole Drilling (IHD). The RS distribution shows good agreement for both techniques used but reproducibility of them depends on their own inaccuracies. An Engineering Criticality Assessment (ECA) was performed based in Failure Assessment Diagram (FAD) approach using all the experimental data obtained by a leak-before-break method under three operational pressures. The results showed the effect on the integrity of material under the presence of a flaw length assessed. Overall, the thesis presents a combined engineering critical assessment which involved the examination of materials used to transport flue-gas and established a methodology to determine fracture toughness alongside with the FAD to assess the integrity of pipelines.