Role of Amine in the Mitigation of CO_2 TOP of the line Corrosion

摘要

Top-of-the-line corrosion (TLC) has the potential to lead to rapid loss of pipeline integrity. TLC also presents unique challenges in relation to its mitigation. Amine compounds are traditionally used as corrosion inhibitors in packages for mitigating CO_2 corrosion of carbon steel. They are also claimed to be effective volatile corrosion inhibitors also the mechanism involved in less clear. The principal objective of this work is to investigate and understand the TLC inhibition mechanism in the presence of diethylamine (DEA) and morpholine. In order to determine possible interactions between the tested amines and the steel surface, the surface charge was investigated by determining the potential of zero charge (PZC). The PZC was measured by means of electrochemical impedance spectroscopy (EIS) in a 1 wt.% NaCl solution at different pH values. The possible inhibitive properties of DEA and morpholine were first tested at the bottom of the line conditions by linear polarization resistance (LPR) and EIS, followed by TLC tests. The weight loss method was used to measure the corrosion rate at the top-of-the-line. After the experiments, the steel surface was characterized by scanning electronic microscopy (SEM). The results were interpreted based on the surface charge and provided key information about the possible mechanisms of adsorption amines (DEA and morpholine) on the steel surface. Results showed that the effect of the selected amines on the corrosion rate could be directly linked to the change in solution pH, both at the top and bottom of the line. Considering that the amines were almost fully protonated in the range of pH tested, their vapor pressures and consequently their concentrations in the condensed water were also very low, limiting further their effect on the corrosion at the top of the line. In addition, DEA and morpholine did not seem to have significant filming properties.