Development of methods for corrsion inhibitor selection and quality assurance in oil and gas technology

Abstract

Corrosion of carbon steel in the oil and gas industry is a serious problem directly associated with economic loss and safety risks. As the equipment used in the industry is faced with corrosive environment, i.e. CO2 or acidic conditions, corrosion inhibitors are applied in order to have corrosion under control. Since acid such as hydrochloric acid or acetic acid is widely used for the removal of scale in the equipment, there are corrosion inhibitors specifically against acids. Electrochemical methods have been widely used with the purposes of testing and analysing corrosion inhibitors. The objective of this master thesis was to compare efficiency of various acid corrosion inhibitors under different experimental conditions using C1020 steel. The inhibition efficiency was studied by weight loss experiments and electrical impedance spectroscopy (EIS) at different temperatures and acid concentrations. Beside EIS measurements open circuit potential (OCP) measurements and potentiodynamic polarization measurements were carried out as well. OCP was the measure for the stability of the system and with polarization measurements statements about the modus of inhibitors could be made, whether they are anodic or cathodic or mixed type of inhibitors. Furthermore, scanning electron microscopy (SEM) was used to determine whether crevice corrosion has occurred, which would impact the EIS experiments and produce incorrect data. Besides comparing the efficiency of inhibitors, an adequate method to mprove the reproducibility of electrochemical impedance spectroscopy was developed. A few experimental parameters were varied in order to improve the repeatability, such as the duration of OCP measurement, stirring during the OCP measurement or the method of adding the inhibitor, either adding it directly, diluted in hydrochloric acid or in methanol.