Effect of Hydrogen Permeation and Inhibitors on Carbon Steel

Abstract

The hydrogen permeation, the effect of Na₂S as a promoter to hydrogen permeation and the effect of inhibitors was evaluated on carbon steel in 12 % HCl. In this study the electrochemical technique developed by Devanathan was employed. The experiments were performed in a special design and built two compartment-measuring cells separated by the samples made from carbon steel. The samples were first coated with palladium to one side. The electrolytes on the cathodic and anodic side of the cell were 12 % HCl and 1M NaOH, respectively. By means of a potentiostat in a three electrode arrangement where our sample was the working electrode, a calomel electrode was the reference electrode and a platinum disk served as the counting electrode was first investigated the hydrogen permeation rate in the medium of HCl 12 %. Then crystals of Na₂S were added in order to study the effect of promoters on the hydrogen permeation. To investigate the effect of inhibitors toward hydrogen permeation in HCl 12 % and HCl + Na₂S, five different organic compounds were selected: aniline, formaldehyde, benzonitril, urotropine and p-toluidine. Their concentration on the medium was 2 g/L. The obtained results clearly indicate that Na₂S strongly promotes the hydrogen permeation in carbon steel. Among the organic compounds, urotropine shows the most inhibitive effect on the Na₂S action. It is the best inhibitor also of the hydrogen permeation in HCl medium. Aniline in contrary to urotropine increases the quantity of absorbed hydrogen in the bulk metal. This organic compound seems to have a specific influence on the hydrogen evolution reaction, reducing the active site numbers were hydrogen could be reduced and partially blocking the recombination of atomic hydrogen to molecular hydrogen on the steel surface. The other organic compounds seem to have no effect on hydrogen permeation and on the Na₂S action.