Avaliação de permeação de hidrogênio em célula multiteste e susceptibilidade ao trincamento sob tensão em presença de sulfeto de um aço de especificação API 5L X70

Abstract

The oil and gas industry faces extremely aggressive environments, which requires the use of materials with high resistance to corrosion and toughness. In the case of the Brazilian pre-salt, the problem is especially serious because of the high levels of CO2 (carbon dioxide), and especially of H2S (hydrogen sulphide), which accelerate the materials corrosion in contact with petroleum. In this environment that the API 5L X70 steel studied in this research operates. In this context, the work present the effect of different concentrations of H2S (solution of 3.5% NaCl with 10% H2S + 90% N2 and 100% H2S) and pressure (1 bar and 10 bar) in the behavior of hydrogen permeation of API 5L X70 steel, using a multitest cell. Besides, and the susceptibility to sulfide stress cracking (SSC) by the strain test at low strain rate - BTD (ASTM G129) were performed using a modified specimen. The results showed that there are strong indications of increased susceptibility to sulfide stress cracking (SSC) as the H2S concentration and pressure change, as well as the variables of permeability, solubility and hydrogen diffusivity in the material. Were also discussed the influence of the sulphide film formed during the tests on the material protection.