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The roles and effects of organic acid species in C02 corrosion have received relatively little attention and thus have not been included in the corrosion analysis of oil and gas systems. This is potentially detrimental as most of the predictive models used for materials selection do not incorporate considerations of the effects of such species. The scope of the study is to understand and predict the effect of organic acids, acetic acid specifically, on the C02 corrosion rate of carbon steel. The electrochemical studies consist of static test and rotating cylinder electrode (RCE) tests that focus on the effect of acetic acid species concentrations on the corrosion rate with the presence of C02 at fixed pH and different temperatures. These studies are based on linear polarisation resistance (LPR) and potentiodynamic polarisation methods of a three-electrode system. The results are compared with the performance predicted by three openly available predictive models; NORSOK, Cassandra and de Waard Milliams models. The results of static tests showed that the corrosion rate increases almost linearly with the concentration of acetic acid under non-scaling conditions and decreases to a low value after the formation of protective film. The RCE tests at pH 5.5 show similar results, with an increased corrosion rate that varies linearly with the acetic acid concentration. In addition, the presence of more than 400 ppm acetic acid at 22°C and 800 ppm at 50°C reduces the corrosion rate due to inhibition. The cathodic reaction in the presence of acetic acid is diffusion controlled but changes to mixed diffusion and charge-transfer control at high acetic acid concentration. There is no significant change in the anodic reaction mechanism with the presence of acetic acid. The overall corrosion process is mainly controlled by a charge transfer process. Based on the findings, it is concluded that acetic acid species increase the corrosion rate of carbon steel in C02 corrosion substantially from the additional cathodic reactions of acetic acid dissociation and direct reduction of acetic acid. Standard predictive models do not account for the presence of acetic acid in C02 corrosion. Thus, new equations are proposed to predict the C02 corrosion rate of carbon steel with the presence of acetic acid for stagnant/low-flow and turbulent flow conditions.

Item Type: Thesis (PhD)
Academic Subject : Academic Department - Mechanical Engineering - Materials - Corrosion engineering - Degradation of materials due to temperature, stress and environment
Subject: T Technology > TJ Mechanical engineering and machinery
Divisions: Engineering > Mechanical
Depositing User: Users 2053 not found.
Date Deposited: 30 Sep 2013 16:55
Last Modified: 25 Jan 2017 09:46
URI: http://utpedia.utp.edu.my/id/eprint/8042

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