The effect of the cathodic current density (i) on the permeation of hydrogen through API X80 pipeline steels under cathodic protection was investigated using an electrochemical permeation technique. A proper equation was presented for determining the sub-surface concentration of hydrogen (c(0)). With the aim to enhance the predictive capabilities of the proposed equation, actual environmental parameters such as temperature were considered. The experimental results reported herein clarified the relationship between c(0) and i. It was clearly shown that the ratio of c(0) to the specimen thickness (L) was proportional to root i when i was lower than its critical value (i(H)). On the other hand, for i values above i(H), c(0) was equal to the saturation hydrogen content because of reaction equilibrium. Furthermore, i(H) was found to be dependent on temperature (i.e., i(H) increased with the test temperature). (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.