RESEARCH OF SORPTION BY HYDROGEN SOIL, ISOLATED DURING CORROSION OF GAS PIPELINE UNDER INSULATION

Abstract

Background It is known that electrochemical corrosion of carbon and low-alloyed steels in ground electrolytes occurs with hydrogen depolarization. In this case, the volume released due to the assimilation of electrons during the cathode process of molecular hydrogen is equivalent to the mass of the dissolved metal. If this process occurs under the peeling-off insulation of the cathode-protected surface of the gas pipeline laid in the soil, hydrogen diffuses into the soil located above the pipe and is sorbed by it. Later, upon reaching a certain concentration of hydrogen in the soil layer, it begins to desorb into the atmosphere over the route, which can be used to identify the presence and intensity of the corrosion process under peeling insulation by measuring the flow of hydrogen using special highly sensitive equipment. Aims and Objectives The aim of the work was to quantify the sorption of molecular hydrogen by the soil, depending on the thickness of its layer. The following tasks were solved: to determine the dependence of the concentration in the soil of hydrogen evolved during cathode depolarization of its layer thickness; to establish the effect of soil moisture on the sorption capacity of hydrogen. Methods An original method was used to study the sorption of hydrogen by the soil on a specially developed laboratory stand. This method allows us to identify the presence of a corrosion process on steel by registering the threshold values of hydrogen emission during cathode depolarization on the metal surface under the soil layer. Results Studies conducted with the help of the developed laboratory stand showed that soil samples actively adsorb hydrogen. Moreover, after a certain incubation period, the duration of which depends on the thickness of the soil layer, there comes a state of «transparency» for hydrogen: just as much hydrogen is sorbed by the soil from the side of the pipe wall as it desorbs into the atmosphere over the area chosen for measurements trails. The moisture content of the soil has a significant effect on the sorption capacity of hydrogen: its maximum amount is contained in the soil with zero humidity. When the soil is moistened, both air and sorbed hydrogen are simultaneously expelled from it.