Interaction between iron oxides and iron carbonates during running-in of C-steel tubings in CO2 corrosive environment

Abstract

The present study investigates the running-in behaviour of low alloyed C-steel tubings in NaCl brine under CO2 corrosive environment. These corrosion conditions are those typically found in the oil industry. The corrosion of C-steel in CO2 environment leads to the formation of an iron carbonate scale. This scale determines the frictional behaviour at the interface between tubing and coupling. However, the tubing surface can contain iron oxides, either as a consequence of the production process or due to the presence of O2 in the environment. The role of iron oxides is addressed by investigating the running-in behaviour of tubings with and without oxide scale present, while the influence of iron carbonates is addressed by performing additional tests in distilled water under N2 environment. The results show that the interaction between iron oxides and carbonates determines the running-in behaviour of the tubings. The presence of iron oxides impairs the lubricious properties of the iron carbonate scale. This causes an increase in shear stresses at the sliding interface, as evidenced by the severe plastic deformation of the substrate. As a consequence, the presence of iron oxides during running-in leads to a transition from mild to severe wear.