| The carbon dioxide corrosion of metal pipes and equipment has become an obstacle to the outstanding problems in oil and gas production. Therefore, contrary to the status that existing coating has intrinsic defects, such as poor anti-permeability, and metal surface adhesion is insufficiently strong, and CO2corrosion resistance is not good enough, this paper committed to the preparation of anti-corrosive composite coating and studied the corrosion resistance of L360MS anti-sulfuric steel under CO2conditions, these can not only provide a new method of corrosion protection of acidic oil and gas fields, but also has important theoretical and practical significance.The composite coating materials were selected by single factor experiment and were characterized by infrared spectroscopy, and the best coating formula was selected with orthogonal experiment. The results obtained that the reactive epoxy toughening diluent and modified polyamide curing agent (ZY-1062) were more suitable for the preparation of the composite coating. The optimum formula of composite coating contained that the quality ratio of phenolic resin and epoxy resin is1:8, the quality ratio of reactive epoxy toughening diluent and epoxy resin is1:2, the quality ratio of curing agent and the epoxy resin is1:3, the mass fraction of glass flake content is25%, glass flake size is150.The main performances of the composite coating were tested by coating thickness tester, adhesion tester, impact tester, thermal gravimetric analyzer etc. The results show that the solid content of composite coating is more than98%; the drying time of surface is lower than6h, the actual drying time is lower than24h; the disposable film thickness of coating up to300～400μn; the pencil hardness is not less than4H; adhesive force up to level1or more; the highest resistance impact up to40cm; coating has no cracks, peeling phenomenon after folding, and a good flexibility; coating wear amount is0.008g; no bubble and the dropping of the surface phenomenon when coatings were immersed in10%wtHCl,10%wtNaOH,10%wtNaCl after30d, coatings has excellent chemical resistance; heat resistance of coating up to288.48℃that the coating has basic stability and does not decompose. The test conditions for preparation of composite coating was preliminary optimized by single factor experiment, and finally the better conditions have been gotten that the heating voltage is0.22V, curing temperature is100℃, curing time is24h, the surface treatment of metal sample chooses280mesh sandpaper.Combined with neutral salt spray test, electrochemical test system and other analysis and testing methods, the corrosion resistance of the composite coatings was studied. The results of tests showed that the coating resistance to neutral salt fog time was longer than168h; in saturated CO2atmospheric immersion test, coating impedance values increased firstly and then decreased, the corrosion current density decreased at first and then increased, with the soaking temperature increases, and coating had the minimum corrosion rate in60℃; as the soaking time extended, coating impedance value was decreased gradually, the corrosion current was increased gradually, coating still had the preferable anti-corrosion ability of carbon dioxide in the middle of soaking time; after coatings were soaked in autoclave for72h,at100℃, the total pressure was5MPa, different CO2partial pressure, found that with the increase of CO2partial pressure, coating impedance increased at first and then decreased, the corrosion current was reduced after the first increases, coating had the minimum corrosion rate when the CO2partial pressure was1.5MPa; the usage of coating maked the specimens’ ECorr shift positive (E(blank)=-0.776V, E(coating)=-0.657V) and icorrdecreases significantly (i(blank)=1.164×10-5A/cm2, icorr(coating)=6.774×10-10A/cm2). The corrosion mechanism was discussed by SEM, XRD and other modern analysis and testing means, the anti-corrosion mechanism of composite coating is shielding effect and passivation effect. |
