Detrimental Effects of Acetic Acid on Corrosion of Carbon Steel Pipelines Transporting Wet Gas

Abstract

The integrity of pipelines transporting wet gas has been a concern to oil and gas industry in recent times. Top of the line corrosion (TLC) in particular is important because of the inability to protect the upper wall of pipelines (i.e. in the vapour space) with conventional corrosion inhibitors. Organic acids, such as acetic, are volatile components in oil and gas reservoirs and play significant roles in determining the corrosion process that occurs at the 10-2 o'clock position of the pipelines. TLC of a typical carbon steel pipeline containing 1% NaCl (containing acetic acid) saturated with CO2 gas at 60°C for a period of 100hrs was investigated by applying electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and linear polarisation resistance to mild steel samples exposed to these conditions. Both CO2 and acetic acid are transported in the gas phase and condensed with water thereby contributed to corrosion processes at the top of the line. Preliminary results demonstrated a progressive reduction in corrosion rate with time in the CO2 environment indicated by an increase in the polarisation resistance. However, with the introduction of acetic acid the corrosion rates increased significantly. The results of this study will form the basis of an understanding of the corrosion experienced at the top of the line and determining the amount of corrosion inhibitors to be injected using V-Jet™ pig in similar field environment to prevent carbon steel pipeline failure, and subsequent oil spillage.