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

Abstract

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.

Modelling and testing of optimum soil moisture levels in the corrosion of underground pipelines

“…However, this study does not consider factors that accentuate such effects such as passivation and corrosion product deposition. These effects and their time-dependent influence on corrosion were discussed in a previous paper [12]. The 3D simulation involving a hypothetical saturation distribution shows that the level of corrosion becomes a maximum corresponding to the optimum point, while also highlighting the development of macro cells due to differential aeration.…”

“…To ascertain the active area, the corroded electrode surfaces were digitally imaged after each polarisation test. Subsequently, the images were thresholded using Otsu's algorithm [19] and the active area, normalised to the total electrode area, were determined [12]. The relationship between the active area and the degree of saturation was established in this manner.…”

“…While the electrical conductivity of soil is important in macro cell corrosion usually observed in the field, it has no direct impact in uniform corrosion [5], which is usually assessed in laboratory experiments. However, in uniform corrosion, the active area which is the actual area on the electrode with electrolyte contact and undergoes corrosion, is an influential factor that depends on soil moisture [8,9,12]. Variations of soil properties such as electrical conductivity, oxygen diffusivity and active area with soil saturation can be experimentally established.…”

Corrosion resistance of hot-dip galvanized steel in simulated soil solution: A factorial design and pit chemistry study

“…Using Equations 4-8 one can estimate oxygen accessibility at the electrode surface within the soil [14].…”

“…Using a numerical model, it was shown that differential aeration can lead to severe corrosion of a buried pipeline [14].…”