Erosion-corrosion is a complex mechanism of material degradation resulting from interactions between electrochemical and mechanical processes. The consequences of erosion-corrosion are severe with economic penalties resulting from premature failure of components, increased downtime and increased maintenance costs. This paper assesses the efficiency of two commercial corrosion inhibitors in reducing material damage occumng as a consequence of erosion - corrosion processes. An assessment of the damage is made using gravimetric techniques, electrochemical measurements and visual observation. This paper identifies the role that inhibitors can play in reducing damage, in addition to that caused by corrosion processes alone. The performance of inhibitors in these extremely aggressive erosion-corrosion conditions is discussed in relation to their ability to maintain carbon steel degradation at an acceptable level.
Erosion-corrosion of carbon steel pipelines is an important consideration for every oil and gas production company. When sand is present in the production line and carbon dioxide is present as the gas phase, the damage to the interior of pipe walls can be substantial. In recent years, due to the use of CO2 injection for enhanced oil recovery and active exploitation of deep natural gas reservoirs, the entire sweet gas pipeline can be exposed to erosion-corrosion conditions ~.
There has been considerable effort devoted to studies on CO2 corrosion over a number of decades such that the current understanding of CO2 corrosion is well advanced. These studies have included aspects of the dissociation of CO2 2, CO2 corrosion mechanisms 1, 3-5, formation of protective films 6-8 and the influence of fluid velocity on CO2 corrosion TM. Most recently Nesic et al. 12-15 presented their mechanistic model for CO2 corrosion of mild steel where they developed the numerical model for film formation and verified carbonate film mechanisms.
Erosion-corrosion is tribo-corrosion material loss mechanism, which presents different challenges to material selectors and designers than pure corrosion situations. The material loss experienced in erosion-corrosion conditions includes chemical dissolution (which can be increased by mass transfer at the surface), mechanical erosion caused by fluid flow and/or impingement of particles on the pipe wall and electrochemical corrosion enhanced erosion and vice versa TM. There has been a lot of emphasis in erosion-corrosion in determining the contributions to mass loss from these different components 19-2~ in order to understand what processes are controlling the mass loss in different situations. Because of the strong interactions between mechanical erosion and electrochemical corrosion the production of surface films (e.g. corrosion products) are very important in erosion-corrosion. Depending on the flow conditions, Shadley et al. 22 determined the corrosion regimes to be 1) FeCO3 scale formation and low metal loss rates at low velocity 2) sand abrasion and removal of the scale and high metal loss rates at high velocities and 3) partial removal of scale and localized pitting at intermediate velocities. Of course the regimes and the transition velocities will be dependent on the environment as well as the material.
Although chemical inhibitors have been shown in field experience to allow production to take place at higher rates 23 there is little fundamental understanding of how inhibitors can, or do, affect the erosion-corrosion process. In recent work 24 the expression for calculating the erosion rate h, produced by McLaury et al. 25 and Jordan 26 have been adapted to include an empirical const
