Study On Accelerated Corrosion Experiments Of Q235 Steel In DaGang Soil By Electrolyze And Galvanic Methods

The accelerated electrolytic and galvanic corrosion tests of Q235 carbon steel in Dagang sea-shore salt soil were studied in this paper. Compared with the corrosion behavior and mechanism of the process under the natural condition, the accelerate effect and pertinence of this two testing method were appraised.The results of a month natural corrosion test of Q235 in Dagang soil showed that in the soil with 10% water content, the corrosion products represent a delaminated structure where the inner layer was mainlyα-FeOOH and the outer layer consisted ofα-FeOOH, Fe₂O₃ and Fe₃O₄. When the water content got up to 20% to 34%, the delaminated structure disappeared and the products were mainlyα-FeOOH. The corrosion potential of Q235 steel in Dagang soil fell with increasing of water content, and the value kept stable when the water content was higher than 20%.Electrical resistivity of Dagang soil with different water content was measured by the DC four electrodes method. The resistivity was lower when the water content was higher. During the measurement, the calculated value of resistivity is bigger at lower potential gradient. When the potential gradient increased, the value was reduced and tends to be stable, especially for the soil with lower water content.The corrosion rate was remarkably accelerated during the electrolytic corrosion test. When the potential difference between cathode and anode was invariable, the corrosion rate got higher with the increase of water content. When the water content of soil was invariable, the corrosion rate got higher with the increase of the t potential difference between cathode and anode. Corrosion product of the test showed a very loose structure, and the mainly component was FeCl₂·2H₂O and FeCl₂·3H₂O.The galvanic corrosion behavior of Q235 steel had been studied by changing the area ratio of Cu-Fe couple buried in soil with different water content. The results showed accelerate effect of galvanic corrosion was much lower than electrolytic corrosion. When the area ratio of cathode and anode was invariable, the galvanic effect rose when the water content got higher before the value was below 15%, the galvanic effect was fell when the water content got higher after the value was above 15%. All of the results showed that the galvanic current had a peak value with the time lapsed, and the higher water content was, the earlier peak appeared. As the area ratio increased, the galvanic effect increased when the water content was invariable, but the correlation between the galvanic current and the cathode/anode area ratio did not accord to the rule of linearity. The corrosion product showed a compact pattern and the component mainly wasβ-FeOOH.Electrolytic corrosion test is a highly effective and steady method that accelerated the corrosion process, however, the pertinence of the method is poor; while the galvanic corrosion test got lower accelerate effect and much better pertinence.