Corrosion Activity of Carbon Steel B450C and Low Chromium Ferritic Stainless Steel 430 in Chloride-Containing Cement Extract Solution

The carbon steel B450C and low chromium SS 430 ferritic samples were exposed for 30 days to chloride-containing (5 g L−1 NaCL) cement extract solution. The initial pH ≈ 13.88 decreased to pH ≈ 9.6, associated mainly with the consumption of OH− ions and the formation of γ-FeOOH, α-FeOOH, Fe3O4 and Cr(OH)3, as suggested by XRD and XPS analysis, in the presence of CaCO3 and NaCl crystals. The deep corrosion damages on B450C were observed around particles of Cu and S as local cathodes, while the first pitting events on the SS 430 surface appeared after 30 days of exposure. The change in the activity of each type of steel was provided by the potentiodynamic polarization curves (PDP). Two equivalent electrical circuits (EC) were proposed for quantitative analysis of EIS (Nyquist and Bode diagrams). The calculated polarization resistance (Rp), as an indicator of the stability of passive films, indicated that SS 430 presented relatively constant values, being two-three orders of magnitude higher than those of the carbon steel B450C. The calculated thickness (d) of the SS 430 passive layers was ≈0.5 nm and, in contrast, that of the B450C passive layers tends to disappear after 30 days.

Monitoring of technological environments at petrochemical plants as a means of ensuring their safe operation

The cooling recycled water of petrochemical enterprises is characterized by high corrosion activity, unstable composition and, due to the evaporation of water in cooling towers, a constant increase in the concentration of dissolved salts, suspended particles and organic pollutants. Some of the salts formed by divalent metal ions fall out in the form of deposits, and the water is satu-rated with chlorine, sulfate, phosphate, and carbonations and becomes corrosive. At the same time, the corrosion activity of reservoir water varies widely depending on the saturation of cer-tain ions and other ingredients. It is established that monitoring the composition of recycled water and determining the corrosion rate of equipment and pipelines, carried out within 1-2 months, allow us to build a regression model of the dependence of the corrosion rate on the technical parameters of water, with which we can accurately calculate the values of the corrosion rate on the evaporation coefficient. Monitoring of technological environments and optimization of their composition through mathematical modeling will significantly improve the safety of equipment and pipelines operation at oil refining enterprises. Keywords: corrosion inhibitor; scale inhibitor; biocide; water circulation system; evaporation coefficient; monitoring; cooling water; regression model.

Research of atmospheric corrosion activity on oil pumping stations with tank farms

В настоящее время в отечественных национальных и международных стандартах отсутствуют данные по коррозионной активности атмосферы регионов, в которых расположены нефтеперекачивающие станции с резервуарными парками, эксплуатируемые российским оператором магистральных нефте- и нефтепродуктопроводов. В нормативных документах ПАО «Транснефть», регламентирующих требования к антикоррозионным покрытиям для наружной поверхности резервуаров, определены три категории коррозионной активности атмосферы по ISO 12944-2:2017. Данная классификация учитывает климатические условия регионов, но не учитывает скорость коррозии стали. В этой связи с целью определения скорости коррозии стальных конструкций в различных климатических районах, где расположены объекты организаций системы «Транснефть», была проведена серия испытаний. На 28 НПС в восьми климатических районах были установлены стенды с образцами из стали 09Г2С. Скорость коррозии металла образцов определяли гравиметрическим методом после выдержки в течение шести месяцев, одного года, двух, трех, четырех и пяти лет. Установлено, что скорость коррозии металлических образцов составила от 55 до 236 г/(м∙год), что соответствует категории коррозионной активности атмосферы С2 и С3 по ISO 12944-2:2017 и ГОСТ 34667.2-2020. Наибольшая скорость коррозии - от 177 до 236 г/(м∙год) - наблюдалась в районах расположения НПС в непосредственной близости от моря (до 1,5 км от береговой линии). Currently, there is no data included in the state and international standards on the corrosion activity of the atmosphere in the regions in which oil pumping stations with tank farms are situated, which are operated by Russian main oil and oil products pipeline operators. In the regulatory documents of Transneft PJSC, which specify the requirement for anticorrosion coatings for the outer surfaces of tanks, three categories of atmospheric corrosion activity are defined as per ISO 12944-2:2017. This classification takes into account the climatic conditions of the regions, but not the steel corrosion rate. In this regard, in order to determine the corrosion rate of steel structure in various climatic regions, where Transneft facilities are situated, a series of tests was performed. The test bench with 09G2S steel samples was installed on 28 oil pumping stations in eight climatic regions. The corrosion rate of the metal samples was determined by the gravimetric method after tempering within the period of six months, one year, two, three, four and five years. It has been established that the corrosion rate of the metal samples amounted from 55 to 236 g/(m·per year), which corresponds to the atmospheric corrosion activity category C2 and C3 as per ISO 12944-2:2017 and GOST 34667.2-2020. The highest corrosion rate, from 177 to 236 g/(m·per year) - was observed in the OPS location regions with close proximity to sea (1,5 km to shore line).