INFLUENCE OF VARIOUS FACTORS ON GROUND CORROSION OF STEEL

Abstract

Soil corrosion of underground steel pipelines is the main reason for their depressurization - the occurrence of emergency situations. The loss of tightness of such pipelines brings not only large economic losses, but also leads to social and environmental problems. Forecasting the corrosion activity of soil, based on physicochemical characteristics, is a priority task in the operation of steel pipelines.

It is known that the most common components of soil are chlorides, and due to the non-uniform moisture of the soil, unevenly aerated vapors are formed on steel. The corrosion scheme of unevenly aerated steel in the soil is similar to the operation of a corrosive galvanic cell, since in the presence of moisture, the soil serves as a corrosive electrolyte. In the cathode sections, the main depolarizing reaction is the reduction of oxygen, and in the anodic sections, to which oxygen access is difficult, metal destruction occurs.

The effect of uneven aeration of the model soil (sand) on the rate and nature of corrosion of grade  steel 3 is studied. The rate and potential of corrosion of steel samples and changes in the pH of their near-surface soils are estimated depending on the distance from the soil interface and the humidity of the surrounding soil.

The leading role of soil humidity in the formation of uneven aeration pairs is shown. The formation of anodic and cathodic sections, changes in their pH and potential are established. Wetter soil (near the anode) becomes acidic, less wet soil (near the cathode) becomes alkaline. In the anodic sections, the potential stabilizes faster, and in the cathodic sections - more slowly. It is found that in the anodic sections there is intense uniform corrosion with weak traces of localization, and in the cathodic sections - predominantly pitting corrosion. The corrosion rate in the anodic sections is maximum near the soil interface and decreases with distance from it.

Based on the current strength of the unevenly aerated pair, it is possible to determine the intensity of steel corrosion at different distances from the soil interface, and identify the most corrosion-hazardous areas.