Modelling hydrogen permeation in a hydrogen effusion probe for monitoring corrosion of carbon steels

Abstract

The Hydrogen Effusion Probe (HEP) is being developed for on-line corrosion monitoring of carbon steel by measuring the rate of hydrogen produced and transported through the metal which corresponds to the corrosion rate as the result of corrosion of the metal. Hydrogen accumulation inside carbon steel and stainless Steel devices shaped like cylindrical cups attached to a pipe containing 5 psig hydrogen gas at 300 ํC was modelled with MATLAB software. In this study hydrogen transfer around the bottom of the cups (edge effect) and diffusion through the cup walls (material effect) were accounted in the development of the model of hydrogen accumulation inside the cup. The hydrogen pressure inside stainless steel and carbon steel cups were predicted to design cups for specific cases. The effect of size, wall thickness, and different materials on the hydrogen accumulation inside the cups was investigated to aid future designs of HEP. The results indicated that the trend of the variation of hydrogen pressure in the cups with time was similar for the two materials, although the magnitudes were substantially different. The time to steady state (the plateau pressure) depends on the material and geometry of the cup. The attainment of plateau pressure in carbon steel cups was faster than in stainless steel cups and the plateau pressure substantially lower. A thinner wall thickness yielded a lower hydrogen pressure at steady state. The achievement of the plateau pressure inside the carbon steel cup was faster as the thickness decreases which is in contrast to stainless steel cup. and the time to reach steady state in the larger cup was shorter and the plateau pressure was higher than the smaller cup.