Research On Naphthenic Acid Corrosion In The Static State Of High Temperature

Naphthenic acid corrosion is a kind of corrosion form which often occurs at the location of high temperature and transfer line in petroleumoil column. It is one of the hottest issues in petroleum refining industry which needs to be settled urgently. According to the experimental research and theoretic analysis on naphthenic acid corrosion in the static state of high temperature, the trends of corrosion characteristics of several typical materials(16MnR, Cr5Mo, Cr9Mo, 0Cr18Ni9(304), 00Cr17Ni14Mo2(316L)) under different conditions of TAN(Total Acid Number) and temperature were revealed. On the base of building up a database of corrosion rate of the materials mentioned above, a theoretic model is proposed to forecast corrosion rate in the static state of high temperature.Taking into account the influences from temperature, TAN, materials and states to corrosion, a test program was established. The test equipment was originally designed and manufactured. 16MnR, Cr5Mo, Cr9Mo, 0Cr18Ni9(304), 00Cr17Ni14Mo2(316L) were selected as the test materials(with 16MnR, 0Cr18Ni9 and 00Cr17Ni14Mo2 both in original steel plate and with weld). Original data were obtained in the tests which were carried out both in liquid phase and vapor phase. And the microscopic features of test specimens were analyzed by adopting the technology of FSEM and EDX.Experimental research shows that, the corrosion rate in the static state of high temperature changes exponentially with temperature. When TAN is constant, the relation between corrosion rate and temperature conforms with Arrhenius Equation. Corrosion rate grows almost linearly with TAN. However, when TAN increases to a certain level, the materials get protected by the corrosion products on the specimen surface, which leads to the reduction of corrosion rate. As the corrosion products can be dissolved in oil, Fe²⁺ is prone to diffuse into the medium solution, which makes part of carbon remain on the specimen surface and create protective films. The corrosion products fall off the specimen surface easily becaused of little adhesive force. The results of tests on corrosion rate in the static state of high temperature show that, the resistance performances increase in the way of 16MnR, Cr5Mo, Cr9Mo, 304 and 316L. The resistance performance of materials depends on the quantity of alloying elements, especially the contents of Cr and Mo, which have the effect of pushing ahead passivation.The thesis proposed a forecasting model to match the corrosion rate by using the method of gradient and the method of least squares. The model provides technical supports to the tests and enlargement of database in the future. It can also be the reliability reference of original data according to the matching degree of forecasting model and new test data.