General corrosion of X65 steel under silica sand deposits in CO2-saturated environments in the presence of corrosion inhibitor components

A series of under-deposit corrosion experiments are performed on API 5L X65 mild steel specimens in an effort to further understand the general and localized attack which occurs in under-deposit corrosion environments. A newly developed test cell is introduced exposing two steel electrodes to the bulk solution and immersing two smaller steel electrodes under a specified depth of sand. The cell arrangement allows one of each electrode located in and out of the sand to be externally coupled via a potentiostat representing the under-deposit corrosion environment in oil and gas production whereby regions of the pipeline can be partially covered by silica sand creating a galvanic effect. Whilst ZRA measurements were implemented to understand the galvanic interaction between the electrodes under the sand and in the bulk solution linear polarization measurements were employed on the two remaining uncoupled electrodes to help understand the general corrosion behavior occurring in the system. In addition to the galvanic and general corrosion rate measurements the extent of surface pitting was quantified in an effort to understand the influence that galvanic coupling has on the propagation of pits in various under deposit environments. The research presented considers the influence of sand thickness and chemical inhibitor concentration assessing the propagation of pits using a combination of surface microscopy and interferometry.