Reaction Paths of Thiosulfate during Corrosion of Carbon Steel in Acidified Brines

Abstract

Corrosion tests with gaseous H 2 S require special facilities with safety features, because H 2 S is a toxic and flammable gas. The possibility of replacing H 2 S with thiosulfate (S 2 O 3 2− ), a non-toxic anion, for studying stress corrosion cracking of stainless and carbon steels in H 2 S solutions was first proposed by Tsujikawa in 1993. H 2 S production was detected in presence of carbon steel corroding in acidified thiosulfate-containing solutions. In this paper, the kinetics of H 2 S evolution are used to estimate the range of partial pressure of H 2 S that can be simulated with thiosulfate solutions. It was determined that acid brines containing 10 −4 M and 10 −3 M S 2 O 3 2− could be used for replacing continuous bubbling of dilute H 2 S/N 2 mixtures in tests of degradation of carbon steels, with H 2 S partial pressures ranging between 0.03 and 0.56 kPa. The kinetics of H 2 S production were compared with the amount of sulfur in side reactions, like formation of iron sulfide films and elemental sulfur.

Estudo e proposição de soluções sintéticas de solos para avaliação da corrosividade do aço X65

“…Como citado anteriormente o processo de corrosão do aço imerso na solução NS4 padrão (solução 1) é controlado pelo processo de transferência de carga, por apresentar um semicírculo na região de baixa frequência. Enquanto, as soluções com a presença de cimento, em baixas frequências, exibiram a forma de linha reta como comportamento, indicando uma sobreposição dos semicírculos, relativos ao processo de transferência de carga e ao processo de difusão, que ocorre através da camada passiva [29], isso devido as soluções apresentarem condições termodinamicamente estáveis para a criação do filme de óxido [16].…”

“…Segundo Xin e Li [29], esse comportamento aponta a sobreposição dos processos difusivos e de transferência de carga.…”

A Novel Emulsion Flow Loop for Investigating the Corrosion of X65 Steel in Emulsions with H2S/CO2

“…) being a metastable anion, reduces to form H 2 S gas at the metal surface (Eq 1 and 2), which is spontaneous at open circuit potential of steel (Ref 5,20).…”

“…The exact disproportion reaction of thiosulfate is still not fully understood, but it is believed that the reduction of the thiosulfate anion produces elemental sulfur, which reacts with protons to form H 2 S as shown in Eq 1 and 2 (Ref 4,5,20,21).…”

A mechanistic study on sulfur-induced passivity degradation on Alloy 800 in simulated alkaline crevice chemistries at temperatures ranging from 21 °C to 300 °C

“…Typically, both thiosulphate and chloride species exist in the crevices between heat-exchanger tubes and support plates under start-up transient conditions at temperatures in the range of 21-300 • C following prolonged shutdown. It is well known that the detrimental effect of S x depends on solution pH [25,26], temperature [22] and other factors such as chloride-to-thiosulphate concentration ratio [20,27]. For example, in neutral and acidic solutions and the chloride-to-thiosulphate concentration ratios are high, S x may have combined effects with chloride ions on film degradation in terms of decreasing pitting potential [13,16,28], stabilizing metastable pits [22,23] and increasing oxygen vacancies in the passive layer [19]; however, S x has no noticeable effect on film degradation in neutral solution if the chloride-to-thiosulphate concentration ratios are low [20], and S x has no noticeable effect in alkaline solution at room temperature [6].…”