The Influence of Magnetization on Corrosion in Pipeline Steels

Abstract

Laboratory measurements have shown a strong increase on the hydrogen content in steel after electrochemical hydrogen charging with a two Tesla applied magnetic field and a serious increase in hydrogen-induced cracking and pitting. Cold work combining with the effect of applied magnetic field creates a material more crack sensitive to increased hydrogen content. A derivation based on the use of the Helmholtz Free Energy is applied to examine the thermodynamic effect of magnetization on hydrogen content. The effect of magnetization on the electronic spin configurations, magnetostriction (directional strain induced in steel from an applied magnetic field), and interstitial solute-induced strain are considered. A possible kinetic model for enhanced hydrogen ion pickup and corrosion based on surface effects associated with the Gouy-Chapman Layer and the Helmholtz Double Layer is examined. Disturbance of these layers acts to enhance hydrogen transport to the surface. The high applied and remanent magnetic fields and large cathodic protection currents returning in the pipe simultaneously may disturb these surface layers, resulting in enhancement of both cathodic and anodic reactions.