Long-term Corrosion Behavior of Q235 Steel in Some Soil Environment

The continuous positioning observation and experimental research can obtain the long-term scientific data of material corrosion in the local natural environment, which is valuable and necessary to decide the ways how the materials should be protected from the corrosion factors from the environment. According to incomplete statistics, the material corrosion data in the soil environment are mostly short-term ones, less of which covers a time span more than 10 years, and the corrosion data of 30 years can’t be found in any public reporting. The long-term corrosion data in the soil environment are more valuable and instructive for the construction and maintenance of an underground engineering. In this paper, a long-term corrosion experimental research of Q235 steel buried in a soil environment for 30 years was conducted, and the corrosion data were accumulated. The corrosion test was carried out according to the Material Soil environment Corrosion Test Method (published by the National Soil Corrosion Test Organization, China). The mass loss after burial was measured by Corrosion Weight Loss Method, the macroscopic morphology and microstructure of corrosion products at different depths were respectively analyzed by Optical Microscope and SEM, and the phase composition of corrosion products at different depths was analyzed by XRD, which was used for corrosion mechanism analysis. The electrochemical test was carried out to analyze the corrosion behavior of Q235 steel buried for 30 years, which was used to reveal the corrosion effect of corrosion products on a metal base. The results of macroscopic observation and SEM analysis showed that the surface corrosion forms of Q235 steel were uniform corrosion, crevice corrosion and pitting corrosion after 30 years of burial. In the process of soil environment corrosion, crevice corrosion and pitting corrosion accounted for a large proportion, which contributed significantly to the weight loss rate of corrosion. The structure of corrosion product layer was not complete, and there were many defects and cracks in the interior. The results of corrosion weight loss test showed that the average corrosion weight loss rate was 1.765 8 g/(dm2·a) and the average corrosion rate in depth was 0.022 6 mm/a, the maximum pitting depth was 1.59 mm, and the pitting factor was 2.66. The elemental composition of corrosion products were Fe, O and C according to the testing results of EDS. The XRD analysis showed that the main phases were FeO, Fe2O3, α-FeOOH, FeCO3, γ-FeOOH and a small amount of unconverted δ-FeOOH in the bottom layer of corrosion product. The corrosion rate of the rusted sample in the electrochemical test was significantly lower than that of the sample after rust removal, indicating that the corrosion products had a certain protective effect on the metal matrix. After 30 years of burial test and analysis, the long-term soil environment corrosion data of Q235 steel were systematically obtained. These corrosion data could provide a basic information support not only for the research on corrosion mechanism of carbon steel, but also for the material selection and design as well as the service life evaluation of engineering equipment equipped in an underground engineering. For example, the maximum pitting depth of 1.59 mm means that, a non-pressure-bearing structures made by bare Q235 steel could have a service life of more than 30 years when there is a surplus of 2 mm in design thickness. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.