Fragilização pelo hidrogênio em aço API 5L X65 em ambiente salino saturado com CO2 e CO2 com baixo teor de H2S

Abstract

The basic mechanisms of CO2 corrosion and H2S corrosion are widely known to the scientific community. However, the cracking failure mechanisms in a CO2 environment or in an environment where this species coexists with others, needs better understanding. Based on this, the aim of this work was to assess the effect of CO2 and of CO2 with low H2S content under the API 5L X65 steel, in order to better understand the cracking failure mechanisms that can occur. The main focus of this inquiry was to understand how the presence of the corrosion products (Fe3C) or surface films (FeCO3 or FeS) influence on hydrogen permeation and in cracking mechanism of the API 5L X65 steel in saline environment saturated with CO2 or with the mix of CO2 with low H2S content. Therefore, hydrogen permeation and Slow Strain Rate (SSR) tests were performed in CO2 environment, in surface conditions of wet-ground, Fe3C rich and with FeCO3 film. These tests were also performed in CO2/H2S environments to assess the contribution low H2S content in the process. The results showed that in CO2 environment the highest loss of ductility occurred for the Fe3C rich surface. Whilst, under cathodic polarization, the permeation current density increased continuously into the surface conditions wet-ground and Fe3C rich, and into the FeCO3 filmed surface declined along the time, but the embrittlement effect was higher into the wet-ground and FeCO3 surfaces. Nevertheless, in reference to all other conditions studied, permeation current density and loss of ductility were higher in CO2/H2S environments.