Informative indices of the biocorrosion activity for the determination of the character of the aggression ground

Underground corrosion is referred to the most difficult types of corrosion in connection with that it is multifactorial and differs in progressive dynamics of the participation of each parameter in the process of destruction of the metal. With the aim of the evaluation of the informativeness of the index of the biocorrosion activity caused by the influence of various factors to determine the character of the soil aggressiveness in the district of pipeline laying there was studied the complex of microbiological and physical-chemical indices). There was determined the amount of sulfur cycle bacteria (autotrophic thiobacteria and sulphate-reducing bacteria), the total concentration of sulfur and iron in the soil samples adjacent to the surface of the underground pipelines in the territory of the Khanty-Mansi Autonomous District of Yugra, and the ratio of these indices with a specific electrical resistance of the soil. There was established the predominance ofsamples with weak aggressiveness of the soil (55.17% of cases), with the criterion ofbiocorrosion soil activity of 2,44 ± 0,19. The results show significant differences in the thiobacteria content and mobile iron in the studied soil-ground samples. There was revealed a direct correlation of the average force of concentrations of identified bacteria and iron content in the soil. There was shown the necessity of the implementation of dynamic control and the development of methods of protection of metal structures to prevent biocorrosion in the design and in the process of the operation of the pipeline.

Effect of Underground Corrosion on the Buckling of Al Alloy 6061-T4 Columns under Increasing Load

This research deals with the extent to which corrosion affects the behavior of buckling for 6061-T4 aluminum alloy under increasing compressive dynamic loads. Two types of columns, long, and intermediate were used.1% of the length column is the allowable lateral deflection. This is called the critical buckling of the columns. For the purpose of calculating the critical deflection, a digital dial gauge was used and set at a distance of 0.7 of column length from the fixed end condition for the column. The experimental analysis revealed that the corrosion time negatively affects the mechanical properties of materials such as the corroded specimens of 60 days (The least time to observe the corrosion of aluminum in the soil) which have approximately 2.7 % reduction in ultimate strength compared with the non-corroded specimen. Increasing the corrosion time reduces the critical load such as the maximum reduction will be 4.24% in critical buckling load for 60 days’ corrosion time. The results obtained were experimentally compared with the theoretical formulas of the Perry-Robertson and Euler-Johnson formula with the results of the ANSYS. It was found that the Perry-Robertson formula has a good agreement with the experimental results with a safety factor of 1.2, while the Euler-Johnson formula agreed with the experimental results taking a safety factor of 1.5. The ANSYS results showed a good agreement between the measured and calculated values by taking 1.1 factor of safety.

Coupled Electro-Chemical-Soil Model to Evaluate the Influence of Soil Aeration on Underground Metal Pipe Corrosion

A mechanistic understanding of the process of underground corrosion is important for modeling pipeline deterioration. In this study, a time-dependent multiscale numerical model incorporating electrochemistry and soil hydrology is developed. The model realistically simulates soil moisture and aeration conditions and their influence on anodic/cathodic activity without prior definition. In this manner, both micro- and macrocell corrosion and their evolution with time are simulated along with the effects of differential aeration. The model was validated with low-alloy cast iron corrosion data from the United States National Bureau of Standards corrosion exposure study. The effect of soil aeration in controlling soil corrosiveness was simulated with suitable boundary conditions. It was demonstrated that macrocells arising due to differential aeration can lead to elevated levels of corrosion in pipelines, especially in fairly aerated soils.

Underground Corrosion Model of Steel Pipelines Using In Situ Parameters of Soil

A simple yet practical model to estimate the time dependence of metal loss (ML) in underground pipelines has been developed considering the in situ soil parameters. These parameters are soil resistivity, pH, moisture content, chloride content, and salinity. The time dependence of the ML was modeled as Pmax = ktn, where t is the time exposure, k is ML constant, and n is the corrosion growth pattern. The results of ML and in situ parameters were analyzed using statistical methods such as data screening, linear correlation analysis, principal component analysis, and multiple linear regressions. The best model revealed that k is principally influenced by ressistivity, and n appears to be correlated with chloride content. Model optimization was carried out by introducing several observation criteria, namely, water access, soil color, and soil texture. The addition of these factors has improved the initial accuracy of model to an R2 score of 0.960. As a conclusion, the developed model can provide immediate assessment of corrosion growth experienced by underground structures.