Analysis of Hydrogen Permeation Through Pipeline Steel in Near-Neutral pH SCC Environments

Abstract

The Devanathan-cell technique has been used to determine the permeation flux of hydrogen through X-65 steel at the open-circuit potential in solutions associated with near-neutral pH stress corrosion cracking. The effects of organic material and microbial activity were also simulated by suitable additions to the solution. A model based on a constant-concentration boundary condition was found to fit the experimental data better than one based on a constant flux condition. The addition of 9,10-anthroquinone-2,6-disulphonic acid to the solution to simulate the effect of organic material lowered the hydrogen permeation flux. Sulfide additions to simulate the action of sulfate-reducing bacteria initially increased the rate of hydrogen permeation, but subsequently resulted in a decrease in permeation current. The hydrogen permeation rate measured on the original oxide-covered surface is lower and more variable than that on polished surfaces. Corrosion rate measurements were also made, from which the fraction of atomic hydrogen diffusing through the specimens was estimated. The results are discussed in terms of the mechanism of hydrogen evolution and absorption.Copyright © 2000 by ASME