A critical review of mathematical models used to determine the density of hydrogen trapping sites in steels and alloys

•Mathematical models were analyzed to determine the trapping sites of hydrogen.•The use of these models has been proven unsatisfactory.•To prove such failures, we performed electrochemical permeation tests on 5L X65.•Some concepts and models were revised to correct errors found in some publications.

Different mathematical models based on electrochemical permeation tests have been proposed to determine the density of hydrogen trapping sites (NT) in metals. However, recent mathematical models that have been used to determine NT contain mathematical errors or have been based on the work of researchers whose works contain no mention of equations or mathematical terms related to hydrogen trapping, which calls into doubt the validity of the models' applicability. In this work, based on permeation test results for X65 steel, we show that the use of incorrect mathematical models leads to values of NT that differ by four orders of magnitude.