Hydrogen diffusion in pipeline steel

Electrochemical hydrogen permeation tests were performed to measure the hydrogen permeation current through the API 5L X65 and ASTM A182 F22 pipeline steels, using the electrochemical method developed by Devanathan and Stachurski. The apparent diffusion coefficient of hydrogen was found to be within the range of 1 - 4×10-11 m2 s-1. The analysis of the permeation transients and desorption rate of hydrogen reveals two main domains that are associated with a competition between two distinct processes: hydrogen trapping and hydrogen diffusion. Partial permeation transient, namely the partial build up obtained without intermediate discharge, can better estimate the lattice diffusion of hydrogen. Lattice hydrogen diffusion coefficient for both steels were one order of magnitude higher than the apparent diffusion coefficient.