CARVALHO, J. P. D.; http://lattes.cnpq.br/2033392540252868; CARVALHO, João Paulo Dantas de.
Resumo:
Since its discovery in 1864 by Cailletet, hydrogen embrittlement of metals, was subjected to
numerous investigations, first being studied with the injection of gaseous hydrogen in metals and
alloys. Devanathan and Stachurski (1962) developed the electrochemical technique of hydrogen
permeation in metals and alloys, making it the study more practical this methodology is based on
a dual symmetrically arranged electrochemical cell where the metal to be studied is inserted
between them. One known as load cell will generate H2 to be permeated through the specimen
and the other, known as the detection cell, it will be oxidized and its flow quantified. All detection
is performed potentiostaticly, but the generation can be performed by galvanostatic (galvanostaticpotentiostatic
method), potentiostaticly (double- potentiostatic method), or by hydrogen
permeation on acid environment method known as a PCAA. The regulations ASTM 148-97
(2003) and ISO 17081 (2004) standardize the electrochemical hydrogen permeation experiments.
How different methods are based on different workarounds for solution of the second Fick's law,
such rules do not take this into account by adopting the calculation of the hydrogen diffusivity
only by the dual voltage method, even for those who study the phenomenon, say passing for the
most part, using the galvanostatic-potentiostatic methodology. Authors such as McBreen et al
(1966) and Boes & Züchner (1972) describe the hydrogen permeation phenomenon in
mathematical form of metal from the solution of the second Fick law, these works attest to the
difference between the double-potentiostatic methods and galvanostatic-potentiostatic, but has
never proposed a model that describes the behavior of the PCAA method. Thus, the study aims to
elucidate the use of mathematical models to determine the hydrogen diffusion coefficient in
metals through the different electrochemical techniques permeation using the API 5L steels X70
and X65, in addition sought a mathematical model for the case where the hydrogen generation is
performed by the PCAA method. This work testifies that the use of the equations proposed by the
standard at first underestimate the value of diffusivity. The equation proposed for the PCAA
method, presented a perfect fit experimental permeation data. The proposed correlations for
calculating the diffusivity was found to be consistent to estimate this parameter not only to the
case PCAA, but also for all cases.