Study on Corrosion Inhibitor Efficiency for Carbon Steel in CO2 Corrosion

CO2 corrosion is the main threat in oil and gas industry. In order to reduce the corrosion
of carbon steel pipelines in CO2 environment, inhibitors are added to control corrosion
rate to an acceptable level. However, the successful of the corrosion inhibitor injection
depends not only on the good inhibitor formulation used but also operational parameters
such as temperature, pH and flow conditions. The objective of the project is to investigate
the main operational parameters that influence the efficiency of the corrosion inhibitor for
carbon steel in CO2 environment. Temperature and pH are varied from 250C to 800C and
pH 5 and 6, respectively. The corrosion inhibitor used is AMTECH and dosage is set at
500 ppm. The test medium is 3% NaCl solution saturated with carbon dioxide gas at 1
bar. From the experiment, it is found that the efficiency of inhibitor increased when
temperature increases from room temperature 250C to 800C. The highest efficiency of
inhibitor is at temperature 800C with the value of 97.4% at pH 5. However, at pH 6, the
inhibitor efficiency decreased when the temperature is increased. The efficiency of
inhibitor for pH 6 at 800C is 46.2%. This is possibly due to the effect of the corrosion
product film formation that protects the metal surface at pH higher than 5. Therefore, the
inhibitor efficiency will decrease for higher pH 6. The recommendations are to do further
testing to simulate the turbulence flow condition and to investigate the formation of
corrosion product film at higher pH that affects the efficiency of the inhibitor.