Corrosive behavior of pipeline steel 17G1C and 13G1C-U in environments NS1-NS3

Results of long-term exposure tests (20 months) of 17G1C and 13G1C-U pipeline steel samples in NS1-NS3 model environments (soil electrolyte imitations) are presented in the article. It was established that during the exposure of steel samples in the studied model environments the rate of corrosion processes depends on the component composition of the model environments, the grade of steel and pH. Regardless of the grade of steel, the highest corrosion rate was observed for the NS1 environment, while the corrosion rate for the NS3 environment was almost 21% lower. In the case of the NS2 model environment, the corrosion rate reduction for 17G1C steel was 38.68%, and for 13G1C-U steel – 28.75%, compared to the exposure of these samples in the NS1 environment. The calculated multiple coefficients of determination and linear correlation coefficients indicate a strong relationship between these indicators. The phase composition and structure of corrosion products were determined by the X-ray diffractometer Shimadzu XRD‑7000 using the method of X-ray structural analysis. On the basis of the obtained radiographs, the dominant form of iron oxide, which does not depend on the grade of steel, was determined for each environment. The research results have practical value and can be used in predicting the behavior of underground structures in soils of different corrosive activity.