Active dissolution and natural passivation of carbon steel in carbon dioxide-loaded alkanolamine solutions

Abstract

Corrosion rates of carbon steel specimens were measured in carbon dioxidc(CO2)-loadcd alkanolamiue(aniine) solutions bv weight-loss tests and bv the polarization resistance method. In dilute amine solutions, lower than II) M, corrosion rates were controlled by the formation of protective FeCO3 scale as in hol. CO2 -II.O environments. Tested amines inhibited CO2 induced corrosion in the concentration range between II2 and 2M. In concentrated amine solutions, higher than 3M, primary and tertian amines showed markedly different effects on carbon steel corrosion. The corrosion rates o I carbon sleel rose with the increase in primary amine concentration, whereas the corrosion rales of carbon sleel staved low in tertian amine solutions even al 6M, dueto the formation of protective FeCO3 scale. Terliarv amines absorb CO2 as HCO3 in the presence of water. On the contrary, priman amines absorb CO. bv two wavs. One is as HCO, like tertiary amines, and the other is direct absorption of CO2 without water, producing amine-carbamate. The chemical substances produced dueto the absorption of CO2 by amines are considered to play important roles not only on corrosion rales but also on the morphology and protecljveness of corrosion products.