Research Of Prosess Of Pitting Corrosion Of Stainless Steels In Simulated Deep-sea Environment

In this paper, potentiodynamic scanning, cyclic polarization measurements, electrochemical impedance spectroscopy and other techniques combined with Microscopic three-dimensional screen, Raman spectroscopy, Auger electron spectroscopy research methods were used to study Corrosion behavior of 2Cr13,0Cr18Ni9,00Cr17Ni14Mo2 in the conditions of different simulated water depth. May results of this paper were as follows:1. The corrosion rates of stainless steel 2Cr13,0Cr18Ni9 and 00Cr17Ni14Mo2 at 4℃and 15℃in natural seawater and the corrosion rusty layer samples of 2Cr13 stainless steel were studied. The result showed that the corrosion rates of stainless steel at 4℃are relatively lower, it was usually only half of the corrsion rates at 15℃。The corrosion products of 2Cr13 wereα-Fe₂O₃,γ-FeOOH,Fe₃O₄. Temperature did not significantly affect on the phase of corrosion products.2. According to different kinds of stainless steel, dissolved oxygen concentration had different effects on corrosion potentail, pitting corrosion potential and pitting corrosion protection potentials et al. The specific changes including:(1)Along with the increase of dissolved oxygen concentration, stainless steel's corrosion potentail turn to positive. This showed that the dissolved oxygen at higher concentration was conducive to the formation of passive film.(2)At 4℃, 2Cr13 stainless steel pitting corrosion potential turned to positive and (Eb - EP) decreased first and then increased with the increase of oxygen concentration. It had best resistance to pitting corrosion with dissolved oxygen concentration at 3.0mg/L. Pitting repair capacity decreased and led resistance to pitting decreased. At 15℃, due to the rapid diffusion of dissolved oxygen and high concentrations of dissolved oxygen, pitting repair capacity enhanced so that 2Cr13 stainless steel pitting corrosion resistance is better.(3) At 4℃, along with the increase of dissolved oxygen concentration, 0Cr18Ni9 stainless steel pitting corrosion shifted to positive and not sensitive to pitting corrosion. When the dissolved oxygen was 7.5 mg/L, (Eb - EP ) became larger, therefore 0Cr18Ni9 stainless steel corrosion resistant reduced at the same tempreture. (Eb - EP ) was more than 500mV and pitting corrosion potential turned to negative along with the increase of dissolved oxygen concentration at 15℃, which caused pitting corrosion sensitivity enhanced obviously and 0Cr18Ni9 stainless steel had no repair ability any more.(4) Along with the increase of dissolved oxygen concentration, 00Cr17Ni14Mo2 stainless steel pitting corrosion moved along positive. (Eb - EP ) was more than 1V at both 4℃and 15℃. Once 00Cr17Ni14Mo2 stainless steel occurred corrosive pitting, pitting corrosion would expend rapidly and pitting corrosion became to be repaired difficultly.(5) During the test soaking time, stainless steel's EIS showed as a time constant under different dissolved oxygen condition. When dissolved oxygen concentration was very low, 2Cr13,0Cr18Ni9 and 00Cr17Ni14Mo2 stainless seels's charge transfer resistance and impedances were more larger and uniform corrosion resistant performance was better. 3. Stainless steels corrosion resistance droped at circulating water pressure condition. Along with the increase of circulating water pressure, pitting corrosion potential showed negative shift, the interval of passivation potential became narrower, the amount of Carbonate accreted on the passive film increased and passive film was relatively thin under pressure conditions, stainless steel passivation become hard, passive current density increases at the same time, which caused corrosion rate increase and pits accelerated faster along vertical. The results also showed that Ni and Mo element were not the main composition of passive film.