Preparation And Properties Of Organic Sulfur Corrosion Resistant Coating

The sulfur corrosion which makes negative impacts in the oil and gas industry includes hydrogen sulfide corrosion, sulfur ions corrosion, elemental sulfur corrosion and so on. The existence of sulfur ions in the water environment result in serious corrosion on the pipeline. Therefore it has important practical significance to study a kind of organic coating to prevent corroding from sulfur for the equipments which are used in the water environment including sulfur.The novolac epoxy which has been characterized by the infrared spectroscopy and thermogravimetric analysis is synthetized with orthogonal method. The results show that the epoxy value increases with the elevation of molar mass ratio of hydroxyl group and epichlorohydrin, which is contrary to the rule of reaction temperature. When the dosage of sodium hydroxide and reaction time increase, the epoxy value rises firstly and then decreases. The epoxy value is0.4221when the ratio of hydroxyl group and epichlorohydrin is1:5.5、 reaction temperature is65℃、the dosage of catalyst is25%and reaction time is4.5h.The heat resistance of resin is138℃, the absorption peaks of phenolic hydroxyl group and epoxy group are3319.37cm-1and914.29cm-1.The optimum dosage of fillers、promoters and curing agent are obtained by single factor experiment. The properties of the coating are tested with the adhesion tester、hardness tester, impact tester and abrasion tester. The consequences reveal that the adhesive force is first grade,the hardness is0.986,the impact resistance is45cm and the abrasion loss is0.006g when the coating contains35%by weight of novolac epoxy resin, talcpower5%wt,1.5%wt titanium dioxide, zinc powder4.5%wt, zinc phosphate4.5%wt,carbon black1.5%wt, barium sulfate12%wt, poly-amic35%wt, and silane coupling agent1%wt. There is no blistering and shedding on the surface of the coating when it has been soaked30d in10%wtHCl, NaOH or NaCl.The corrosion resistance of the coating and its mechanism had been studied with neutral salt spray test,electrochemical workstation and X-Ray Diffraction.The results show that the surface of coating is intact when the coating tested168h in salt spray; with the ascension of the sulfurion content, the impedance value of the coating declines firstly then raises; when the temperature increases, the impedance of coating presentes downtrend, but the impedance of sample with coating which has been soaked in80℃for3d is still far greater than the uncoated specimen; the coating resistance value declines firstly then rises with extension of the soaking time. There are pinholes on the surface of coating when it has been immersed72h in the solution whose sulfurion content is1%.in120℃,4MPa.The useage of coating makes the specimens’Ecorr shift positive (E(biank)=-0.8073V,E(coating)=-0.3004V) and icorr decrease significantly(i(blank)=3.523×10-5A/cm2,icorr(coating)=2.502×10-9A/cm2).The mechanism of coating is shielding effect and cathodic protection.