Internal corrosion of stabilized crude oil API-X100 steel pipelines

Carbon dioxide corrosion behavior of API-X100 steel pipeline in simulated stratified pipeline flow was investigated experimentally. An autoclave system was used to simulate the service condition. Samples were mounted on an externally controlled rotating shaft inside the autoclave. Emulsions with 1:1 and 1:9 diesel:water ratio were used at the temperature of 100^± 1 °C. In a solution with 1:9 diesel:water ratio, in the absence of carbon dioxide, the average corrosion rate of the samples was calculated to be 12 mpy after the immersion time of 24 hours. When carbon dioxide was introduced to the system at 50 psi, the corrosion rate of the samples under new conditions increased to 78 mpy after two days of exposure but decreased to an almost constant amount of 10 mpy after 16 days. Potentiodynamic polarization and Open Circuit Potential (OCP) experiments were performed at 40°C, 60°C, 80°C and 100°C while carbon dioxide was continuously purged into the systems with 1:1 and 1:9 diesel:water ratios. Corrosion rates were measured and the results were compared with the weight loss measurements obtained from the exposure experiments. Scanning Electron Microscopy (SEM) micrographs of the corroded surfaces confirm the formation of scales on the surface which become more compact as the exposure time increases. Performing Energy-dispersive X-ray spectroscopy (EDX) on the corroded surfaces revealed that in the first few days of exposure, cubic shaped deposits are present in the scale that are rich in manganese, however, as the experiment progresses the cubic deposits are disappeared and more uniform and compact scales are observed in which alloying elements are uniformly distributed.