INTRODUCTION
In sweet corrosion, corrosion scales such as iron carbonate are formed on the internal surfaces of oil and gas production and transport systems. Depending on the type of corrosion inhibition program and the age of production system before chemical treatment is implemented, the presence of corrosion scale could affect the performance of the inhibitor. Previous work completed by the authors' company investigated the interaction of iron carbonate and three inhibitor actives - quaternary amine, imidazoline, and phosphate ester. This study is a continuation and examines two more generic compounds: quaternary amine dimer and alkyl pyridine quaternary amine. Linear Polarization Resistance (LPR), Electrochemical Impedance Spectroscopy (EIS) were used to measure corrosion rates and to monitor the active-scale interaction. Scanning Electron Microscopy (SEM) was used to observe the morphology of the iron scale layer.
The second part of this paper explores aggregate formation for several generic inhibitor actives. Most actives are surfactants which form micelles above the Critical Micelle Concentrations (CMC). In theory, maximum inhibition should be observed around the CMC since additional surfactant molecules lead to the formation of micelles and do not contribute to inhibition. This concept is discussed and the relationship between surfactant concentration, adsorption and inhibition is analyzed.
The presence of quaternized amine monomer increases the precipitation rate of iron carbonate scale. The impedance value of the resulting scale is doubled compared to a non-treated iron carbonate scales.
Corrosion inhibitors have been researched for years in order to protect oil and gas production and transport systems more effectively. The composition of a commercial inhibitor usually consists of a blend of an actively adsorbing surfactant (e.g., amines, imidazolines, phosphate esters) in a solvent along with a series of supporting chemicals (i.e., emulsion breakers, salting agents, etc.) that aid in the dispersion of the active when it is applied in the field.1 The primary action of inhibition is the adsorption of the surfactant functional group onto the metal surface, hence forming a barrier that retards the electrochemical corrosion process.2 Research has been conducted continuously to understand the adsorption behaviour of various types of inhibitors and how the structure would improve the active-surface interaction.3-6Sweet corrosion is one of the most prevalent forms of attack associated to oil and gas production. The presence of carbon dioxide and water in production systems increase the extent of corrosiveness by creating an acidic environment. This leads to the formation of corrosion deposits such as iron carbide or iron carbonate scale on the internal surfaces.7 Depending on the type of corrosion inhibition program and the age of production system before chemical treatment is implemented, the presence of corrosion scale could affect the performance of the inhibitor. Some studies have been conducted on the action of corrosion inhibitors on corrosion product layers. The papers presented by Wong and Park1,8 in 2008 and 2009 explored the interactions of iron carbonate with three corrosion inhibitor generic actives - quaternary amine monomer, imidazoline, and phosphate ester. The following were concluded:
