AC-IMPEDANCE INVESTIGATIONS ON THE PERFORMANCE OF INHIBITORS AND SURFACTANTS IN CO2 CORROSION OF STEEL UNDER NATURAL-GAS PRODUCTION CONDITIONS

Inhibition mechanisms of CO2 corrosion of low alloy carbon steel (38 M n 6) were studied under production conditions of sweet natural gas (1 M NaCl + 0.1 M CaCl2; 1 and 5 bar CO2; 80 degrees C) in the presence o f surface active compounds (inhibitors, surfactants) with AC impedance spectrometry. Based on a pore model an equivalent circuit was develop ed which explains the action mechanisms of the substances tested. Fatt y amines and imidazolines inhibit the interface reaction at the bottom of pores in the corrosion product scale due to adsorption. Non-ionic surfactants can impair the effectivity of N-containing inhibitors. 1-O ctyne-3-ol acts through formation of polymer films and reduces the por osity of the scale. All substances under investigation influence the m orphology of the scale and the kinetic of its formation.