| Corrosion problem exists widely in the world, and it has brought great harm to economy, environment and public security. Among many corrosion protection measures, corrosion inhibitors have the advantages of low-cost, quick effect and so on. However, the individual inhibitor can no longer meet the requirements of corrosion protection work. More and more scholars devoted to the study of the synergetic inhibition effect of the composite system and it has long been an important development direction of corrosion inhibitors.In this paper, synergistic corrosion inhibition effect was researched in high concentration KC1 solution and H2S/CO2 coexistent system. The influence of temperature, salt concentration and other factors on corrosion of different species of steel was analyzed and synergistic inhibition effect between sodium silicate and acrylamide was studied in high concentration KCl solution. While in H2S/CO2 coexistent system, the relationship between corrosion inhibition efficiency and surface activity of three kinds of cationic surfactants, namely dodecyl trimethyl ammonium bromide (DTAB), tetradecyl trimethyl ammonium bromide (TTAB) and cetyl trimethyl ammonium bromide (CTAB), was studied. The synergistic inhibition effect between pyridinium salt (PB) and three kinds of cationic surfactants was also explored. The main research results are listed as follows:1. High concentration KC1 solution(1) The corrosion rate of N80 carbon steel and 13Cr steel increases with temperature rising, but decreases with the increase of salt concentration in corrosive medium. The corrosion rate of 13Cr steel was higher than N80 carbon steel at low temperature. Although corrosion rate of N80 carbon steel was relatively high, pitting corrosion was more likely to occur for 13Cr steel.(2) Mass of Q235 carbon steel indeed increased in static weight loss test when using the synergistic combination of 0.5% sodium silicate and 0.5% acrylamide in 25% KC1 solution and it indicated that there exists good synergistic corrosion inhibition effect between two kinds of inhibitors. Firstly, sodium silicate formed a layer of deposited film which contains silicon oxide combined with iron corrosion products on metal surface. Then the acrylamide molecules which contain cationic single bond NH3+ groups can be adsorbed by electrostatic coulombic attraction at the steel surface. The protective film became more compact and carbon steel exhibited a good resistance to chloride ion corrosion.2. H2S/CO2 coexistent system(1) Surface activity of three kinds of cationic surfactants strengthens with increase of length of long hydrophobic alkyl chains. There is positive correlation between corrosion inhibition efficiency and surface activity. Better performance of surface activity, higher the corrosion inhibition efficiency. The sequence of surface activity and corrosion inhibition efficiency is as follows: CTAB>TTAB>DTAB.(2) Incorporation of PB with cationic surfactant (DTAB or TTAB or CTAB) significantly improves the inhibition performance and produces good synergistic inhibition effect, especially the synergistic inhibition effect of PB and CTAB is the most obvious. The sequence of corrosion inhibition efficiency of three kinds of synergistic combination is as follows:PB+CTAB> PB+TTAB> PB+DTAB.(3) PB was preferably adsorbed on HS- layer on carbon steel surface, but it exist defects on the adsorption film of PB. Addition of cationic surfactants plays an assistant role on corrosion inhibition. On the one hand, it can improve dispersibility, wettability and permeability of PB, on the other hand, it can be adsorbed on the active adsorption vacancy. The co-adsorption between PB and the cationic surfactant made the protective film more compact which effectively prevent carbon steel corrosion. |
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