CARRASCO, J. A. P.; http://lattes.cnpq.br/9085140310628380; CARRASCO, Jorge Antonio Palma.
Resumo:
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.