Efficiency of volatile corrosion inhibitors in wet gas pipelines

© 2014 by NACE International.The mechanism and mitigation of top of the line corrosion (TLC) is still an on-going research interest because of their consequences on carbon steel pipelines transporting wet gas. The use of conventional corrosion inhibitors have been very effective in protecting bottom of the pipelines but insufficiently transported to 10-2 o'clock position of the pipes leading to continuous corrosion process at the upper part of the pipe. Therefore the use of volatile corrosion inhibitor has been encouraged because of their low molecular weight and high vapour pressure which makes it easier to be transported to the upper part of the pipe to reduce corrosion process. The effect of addition of methyl di ethanol amine (MDEA) (a volatile corrosion inhibitor) and mono ethylene glycol (MEG) have been simulated in the laboratory using twoelectrode electrochemical cell configuration in CO2 and acetic acid environments. Initially, there is a progressive reduction in corrosion rate with time in CO2 environment due to the formation of protective iron carbonate film on the metal surface. However, the presence of acetic acid changes the corrosion process and results in an increase in corrosion rate due to the solubility of the complex iron acetate in acidified water. Addition of either MDEA or MEG is ineffective in acetic acid containing environment. It could be established that the presence of acetic acid breaks down the protective iron carbonate film which are difficult to be re-formed with the addition of volatile corrosion inhibitors.