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ISRN Materials Science
Volume 2012 (2012), Article ID 945235, 14 pages
http://dx.doi.org/10.5402/2012/945235
Research Article

Numerical Study of Hydrogen Trapping: Application to an API 5L X60 Steel

1Materials Division, Hydrogen in Metals Group, Instituto de Tecnología Jorge Sabato, Av. General Paz 1499, B1650KNA, San Martín, Prov. de Buenos Aires, C1033AAJ Buenos Aires, Argentina
2CNEA/CAC, UAM, Avenida General Paz 1499, CP1650 San Martín, Argentina

Received 4 May 2012; Accepted 12 June 2012

Academic Editors: J. Foct, K. Kusabiraki, and M. Nazmy

Copyright © 2012 Patricia Castaño-Rivera et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

A numerical finite difference method is developed here to solve the diffusion equation for hydrogen in presence of trapping sites. A feature of our software is that an optimization of diffusion and trapping parameters is achieved via a non linear least squares fit. On the other hand, we have demonstrated that usual electrochemical hydrogen permeation tests are enough to assess hydrogen free energies of trapping in the range of −35 kJ/mol to −70 kJ/mol. These conclusions are obtained by assuming the presence of saturable traps in local equilibrium with hydrogen and are validated by means of simulated permeation and degassing transients. In addition, we check our model performing electrochemical hydrogen permeation tests at 30°C, 50°C, and 70°C, on an API 5L X60 as received steel state to study its trapping and diffusion properties considering only one type of trapping site. The binding energies () and the trap densities () are determined by fitting the theoretical model to the experimental permeation data. The steel presents a high density of weak traps,  KJ/mol, namely,  mol cm−3. Strong trapping sites which alter the shape of the permeation transient are also detected; their values ranged from 57 to 72 KJ/mol.