Acoplamento de modelos da mecânica do dano e da fratura para avaliação da integridade de estruturas sob efeito do hidrogênio gerado em sistemas de proteção catódica.

Abstract

This work presents a numerical simulation of the hydrogen assisted cracking process in the API 5CT P110 steel, under the effect of hydrogen produced in cathodic protection systems. This steel is used in risers for oil and gas production. The simulations were performed using a mathematical model based on a synthesis of fracture mechanics and continuum damage mechanics proposed for Bolotin & Shipkov (2001). The model was enhanced through the incorporation of a new equation of hydrogen damage and the substitution of trapping terms on the hydrogen transport equation by the equivalent terms of model of Turnbull et al. (1989). To obtain parameters for the model, were realized mechanical and electrochemical tests on samples extracted from pipe wall of API 5CT P110 steel. Hydrogen permeation tests on metallic membranes under different cathodic potentials were performed on a Devanathan-Stachurski electrochemical cell. The diffusivity was calculated from two consecutive hydrogen permeation transients plotted for each sample, and the hydrogen trapping was characterized by superposition of these normalized transients. The susceptibility to hydrogen embrittlement of steel was evaluated in round tensile samples, with and without hydrogen, submitted to uniaxial tensile test until failure. The experimental results show that the hydrogen trapping in the API 5CT P110 steel is predominantly reversible, which is strongly associated with its high susceptibility to hydrogen embrittlement. The simulation results show that the time of onset and crack propagation are highly dependent on the hydrogen concentration and trapping, and that the hydrogen embrittlement resistance is enhanced by the presence of irreversible traps. These results are consistent with the experimental results and observations of the phenomenon, reported in the scientific literature.