The Study Of Marine Corrosion And Detection Of Vessel Steel

Marine environmental is a rigorous corrosion environmental, materials in the process of using is confronted with badly ocean corrosion circumstance all the time. The proportion of accident's economic loss caused by seawater corrosion is quite high.At present, the method which appraise the anti-corrode performance of vessel steel is loss weight in natural seawater. The measurement's merit is experiment condition's reality, operation simple and result credibility. While there are many shortages in the measurement. For example, the periods of experiment are very long, usually, the shortest experiment periods are one year; the circumstance factors are out of control; consequential the recurrence is bad; the risk caused by losing sample in the process of experiment is high. All shortages above, are mostly issues which restrict the use of new material, new craftwork.This paper mostly research the anti-corrode performance of three representative vessel steel: A, B, C in different experiment circumstances. Through electrochemistry experiment, we probe into the influence of different experiment circumstances with the corrosion of material, find material corrosion disciplinarian in different experiment circumstances, the function relation between corrosion rate and time in different experiment circumstances from mathematical view and simulation formula which simulate material corrosion in this region. The conclusions of this paper are as follows:1) Through monitoring corrosion potential in natural seawater, we find that the stabilization potential of B is most positive, the second is C, and A is most negative. While the result gained by natural seawater is different from the conclusion gained by indoor static seawater.2) Linear polarization test and AC impedance test have been separately carried out on samples immersing entirely in natural seawater, and it give us the change of instantaneous corrosion rate(i_corr) vs. immersing time and polarization resistance(R_P) vs. immersing time, it dedicates that the changes are the result caused by the accumulation of surface rust layer and seawater temperature's change together.3) Four kinds of impedance models are adopted to fit EIS plot which represent four different stages. At the early stage, the equivalent circuit only includes double electricity layer capacitance (C_dl) and charge transfer resistance(R_t). Following the time's fluid, rust layer capacitance (C_f) and rust layer resistance (R_f) appear in equivalent circuit. And then, as time's more prolonging, there are capacitance and resistance caused by microorganism. And the corrosion behaviour of rust-layer/metal system is characterized by the changing trend of Cdl and Rct on time.4) The corrosion production has been analysed by laser Raman technology and it gives us that the structure and component of corrosion production, while the outer corrosion production is mostlyγ-FeOOH and smackα-Fe₂O₃ and inner corrosion production is mostlyα-Fe₂O₃, Fe₃O₄ and littleγ-FeOOH.5) The order of stabilization potential tested by indoor aerated seawater condition is consistent with that in natural seawater circumstance. And that the instantaneous corrosion rate(i_corr) and polarization resistance(R_P) vs. immersing time are as same as that in natural seawater. The result gained by indoor aerated seawater experiment can recure the result of natural seawater experiment.6) There are more difference between two indoor experiment and natural seawater experiment. The reason of above issue may be the difference influence of microorganism. The microorganism influence made by natural seawater is strong, and the other is less.7) Through integral fit, we find the mathematics formulas between corrosion rate and immersing time in three corrode circumstance separately and then contrast them with the mathematics formulas gained by weight loss experiment in three different corrode circumstance. After that, only indoor aerated condition, we find out the result gained by integral fit is inosculating with that gained by weight loss. It shows the method that forecasting corrosion rate gained by integral fit the data of electrochemical test can substitute the method of weight loss's. 8) The research of this paper show that the integral fit corrosion rate gained by indoor aerated condition can forecast material's corrosion rate and thereby substitute weight loss experiment. But only the frequency of monitoring is more coarctation, can we assure the veracity of forecasting result.