The synergetic effect of natural polymer inhibitors and microstructure on the corrosion process of carbon steel under high temperature and CO2 pressure for the oil and gas industry

Carbon and low alloy steels are the most commonly used construction materials for pipelines in the oil and gas industry. They are, however, very susceptible to corrosion in environments containing CO2. When carbon dioxide dissolves in the presence of a water phase, carbonic acid forms, which is corrosive to carbon steel. Due to these processes, a corrosion layer is formed on the steel surface. The protectiveness of this surface layer depends on the nature of the environment (temperature, CO2 partial pressure, pH) and of the nature of the base alloy (composition, heat treatment). The use of corrosion inhibitors is one of the most cost-effective and practical methods for controlling CO2 corrosion in the oil and gas industry. The inhibitor will form a protective layer on the metal surface shielding from the aggressive environment. However, the efficiency of an inhibitor is largely dependent on its adsorption on the metal surface, which in turn it depends not only on certain physicochemical properties of the inhibitor molecule and environmental factors such as pH, temperature, etc. Inorganic inhibitors such as chromates, dichromate, phosphates, etc. have been found to exhibit excellent anti-corrosion properties. However, their toxicity to both environment and human health led the Environment European Commission (EEC), through the Directive 76/464/EEC, to limit their usage. Their limitation has brought many researchers to look forward to the use of alternative and more eco-friendly corrosion inhibitors. Plants extract products have been highly considered as eco-friendly corrosion inhibitors. They are abundant and environmentally sustainable and have appreciable solubility. Water-soluble polysaccharides proved to be promising candidates as environmentally friendly corrosion inhibitors of the metal infrastructures. In addition, these substances being biodegradables, non-toxic organic compounds provide more environmental benefits than the common toxic inorganic inhibitors, with great benefits for the environment.