| In recent years,with the development of acid gas field in post production period, the concentration of water and H2S increased,the process of natural gas gathering and transportation made the internal corrosion of the pipeline getting worse and the potential safety hazard existed. Therefore, the demand for natural gas pipeline protection was more important. The protective coating was the commonly used method to decrease the corrosion, and the inorganic ceramic material was finally chosen to improve the anti-corrosion performance of X80steel,which was of practical significance.Silica, aluminum oxide and titanium oxide were used as inorganic aggregate of the coating material.Magnesium oxide was the paint curing agent, and aluminum dihydrogen phosphate was the binder. Then the proportion of each component of the coating was optimized by the method of orthogonal experiment. The conventional properties of the coating such as adhesive force, hardness, impact strength were evaluated.Electrochemical experiments studied the corrosion resistance of ceramic coating. Friction and wear experiments was used to evaluate the wear resistance of the coating. Immersion test at atmospheric pressure and high temperature and pressure was used to evaluate the performance of the coating to resist corrosion medium. The results were as follows:(1)When the mass fraction of titanium oxide, sillicon dioxide, aluminium oxide, magnesium oxide and Aluminum dihydrogen phosphate respectively valued19.3%,6.4%,10.3%,10%and54%, the coating was best prepared at the curing temperature of200degree centigrade after2hours. The thickness of the coating was26microns. The level.of adhesion ranked first. The microhardness valued637.5HV. The impact resistance was20cm and the wearing amount was0.0003g. When the temperature was30degree centigrade, the sample was soaked in the simulated sulfur formation water after3days, which concentration of sulfur was1.75mg/L. It was turned out that the coating had good corrosion resistance, since the corrosion potential was-0.5316V, and the corrosion current density was1.004x10-11A/cm2.(2)In a simulated luojiazai sulfur formation water environment,study on the corrosion resistance of the different environment temperature,solution concentration,soaking time fact-ors of coating specimens by electrochemical impedance spectroscopy experiments testing and analysis,the results showed that the coated sample resistance to neutral salt spray test was over72h. The corrosion protection performance of coating samples showed a trend of weakening the roughly, with the increase of these factors. At30℃sulfur concentration of1.75mg/L medium environment. The coating had good corrosion resistance,since the corrosi-on potential to-0.4651V,the corrosion current density of2.899×10-8A/cm2. Coating corrosion process was diffusion controlled by the media. Then the corrosive medium had reached the substrate interface.The protection of coating decreased. Analog Luojiazhai sulfur formation water ambient conditions under60℃as the actual oil field corrosive environments, the polarization resistance coating of which decayed exponentially with the extension of soaking time,met the function relation:Rp=2131.29+28714.24e-t/30.66+711.421et/3.49-1015.15et/5.09,icorr and experimental time showed a linear relationship:icorr=2.41923x10-7+1.71647x10-8t.At autoclave experiments the impedance values of coating sample was more than blank sample, explained that the coated specimens remained trial.Combined with on-site environmental conditions, physical properties of the coating were texted through neutral salt spray test specimens at different derusting grade,coating thickness,air purge pressure,substrated temperature. The coating process conditions were determined by orthogonal test method.Then the substrate temperature conditions was20oC. Sand-blasting grade was Sa2.5,air purge pressure was0.5MPa, when the coating had thickness of26μm. |
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