Visualizing the impact of mechanical strain and the environment on pipeline coatings from a three dimensional perspective

The effects of organic coating's structural characteristics such as the void structure on pipeline coating degradation under combined mechanical and environmental effects have been studied using the data-constrained modelling (DCM) technique with multi-energy X-ray computed tomography (X-ray CT), in conjunction with three dimensions (3D) finite element analysis (FEA) modelling that provides a qualitative interpretation of the DCM microstructure data in terms of the concentration of stress at heterogeneous interfaces within coatings. It has been found using the DCM technique that unstrained coating films are heterogeneous in nature, showing characteristic features similar to the D-type and I-type coating regions espoused in the historical literature. For strained coating films, the interfaces of heterogeneities were seen to provide preferential sites to form voids by mechanical straining. Moreover, the void network was also found at the interfaces of the inorganic fillers and the organic polymers. These have been corroborated by simulation carried out using the FEA modelling, with a 3D model indicating the role of fillers in the formation of a tortuous void network in a heterogeneous coating subjected to both mechanical straining and corrosive environment.