Role of Amines in the Mitigation of CO2 Top of the Line Corrosion

• Published in: Corrosion (Houston, Tex.) Tex.), 2016-10, Vol.72 (10), p.1300-1300
• Main Authors: Belarbi, Z, Farelas, F, Singer, M, Nesic, S
• Format: Article
• Language: English
• Subjects: Adsorption; Amines; Analytical methods; Aqueous solutions; Atmospheric corrosion; Carbon dioxide; Carbon steel; Carbon steels; Condensation; Corrosion; Corrosion effects; Corrosion inhibitors; Corrosion mechanisms; Corrosion potential; Corrosion rate; Electrochemical impedance spectroscopy; Electrochemistry; Electrodes; Experiments; Gas pipelines; Gases; Immersion tests (corrosion); Inhibition; Linear polarization; Microscopy; Mitigation; Morpholine; Natural gas; pH effects; Pipelines; Properties; Sodium chloride; Spectroscopy; Steel; Steels; Submarine pipelines; Submerging; Surface charge; Surface chemistry; Transport; Vapor phases; Vapor pressure; Water; Weight loss measurement
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/2121

The principal objective of this work is to investigate and understand the top of the line corrosion (TLC) inhibition mechanism in the presence of amines: diethylamine and morpholine. TLC can be defined as corrosion of carbon steel under water condensation conditions in the presence of acid gases such as CO2, which can be a problem in wet natural gas transportation lines. In order to define the 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 diethylamine and morpholine were first tested under full immersion in the water phase-a condition corresponding to the so-called "bottom of the line" situation in gas pipelines, using linear polarization resistance and EIS. This was followed by tests in the gas phase under water condensing conditions, corresponding to TLC, when the weight loss method was used to measure the corrosion rate. After the experiments, the steel surface was characterized by scanning electronic microscopy. The inhibition was affected by the surface charge that provided key information about the mechanism of adsorption of amines (diethylamine and morpholine) on the steel surface. In addition, the effect of inhibition of corrosion rate was directly linked to the change in solution pH. Considering that the amines were almost fully protonated in the range of pH tested here, their vapor pressures and consequently their concentration in the condensed water was very low. Given that there was no chloride in the condensed water, this further limited the inhibitive effect. In addition, when adsorbed at the surface, diethylamine and morpholine did not seem to demonstrate any significant filming properties because of the weak interaction of the nonpolar groups in the amine molecules.