ABSTRACT
The buried structures (tanks, bases of line transmissions, pipelines) are commonly exposed to different kind of soils and corrosivity levels. Due to this condition, it is necessary to study the corrosion on the carbon steel on these different environments. In laboratory, the NS4 solution is used to simulate synthetic soils. However, due to different kind of soils, it is necessary to develop synthetic solutions that evaluate these soils and their corrosivity. Therefore, the objective of this work was to develop synthetic solutions for laboratory use that include a large variety of kinds of soil with different physicochemical properties. The performed electrochemical tests were polarization curves, electrochemical impedance and mass loss. The solutions were obtained by altering the concentration of a standard solution of NS4 in these following conditions: in deaerated condition, in which was added sodium thiosulphate to simulate anaerobic environment of sulphate-reducing bacteria; in aerated conditions to simulate soil with the presence of H2S; adding sodium chlorate to simulate seashore areas and cement to simulate anticorrosive soils. The results demonstrated that carbon steel presents the lowest resistance to corrosion when exposed to sodium chlorate and thiosulphate solutions. Adding 5 wt. % of cement was enough to simulate anticorrosive soils, in which the passivation process occurred. To ensure the passivation process actually takes place on the metal immersed in synthetic solution with sodium thiosulfate was necessary to add 5 wt. % of cement. The stable passivation process was not reached in synthetic solutions with sodium chlorate when adding 5, 10 and 15 wt. % of cement.
Keywords:
Soil corrosivity; synthetics soil solutions; cement; sodium thiosulphate and sodium chlorate
