Studies of the interaction between a quaternary amine inhibitor and pipeline steel using XPS and ToFSIMS surface analysis techniques

Coupons of X60-pipeline steel have been taken directly from electrochemical testing apparatus for characterization by surface analysis using novel sample transfer methods developed for the analysis of `wet` samples. In this way the correlation between surface concentration, solution concentration and inhibitor efficiency for a quaternary amine inhibitor has been determined. The mechanisms of surface activity of the quaternary amine inhibitor has been investigated. Firstly, surface analysis data for a liquid film of neat inhibitor has been compared with that for a steel coupon rinsed after exposure to neat inhibitor in a static immersion test. Surface analysis results have then been compared to corrosion rate measurements for a range of increasing inhibitor solution concentrations from 0--100ppm for coupons removed directly from an electrochemical test cell and transferred using a novel cryogenic method for sample transfer. Coupons were exposed to solutions of pre-inhibited, deaerated 3% NaCl solution under 1 bara CO{sub 2} at 25 C. Time of flight secondary ion mass spectrometry (ToFSIMS) and X-ray photoelectron spectroscopy (XPS) were the principal surface analysis techniques used. The results show that the quaternary amine inhibitor achieved efficiencies in excess of 90% at solution concentrations of 40ppm and above. Adsorbed inhibitor was detected both bymore » XPS and ToFSIMS at all concentrations studied. Efficiency and surface coverage of this inhibitor increase directly in proportion to solution concentration. Detailed study of surface analysis results shows that, under these cell conditions, adsorption of quaternary amine proceeds via a simple ionic interaction between the inhibitor and the coupon surface with longer chain amine components preferentially adsorbed.« less