PREDICTING THE KINETICS OF HYDROGEN GENERATION AT THE TIPS OF CORROSION FATIGUE CRACKS

A model has been developed to predict the rate of generation of hydrogen atoms at the tips of fatigue cracks for steel cathodically protected in marine environments. The model incorporates crack-tip chemistry, scraping electrode measurements, and crack-tip deformation. The current density for generation of hydrogen atoms by reduction of water at the crack tip has been calculated for a range of electrochemical and mechanical variables. To ensure that crack growth rates are double prime steady-state double prime values, test times have to be long enough to establish steady conditions of hydrogen charging. Crack growth data from fracture mechanics specimens may not be directly relevant to cracking in tubular sections because of hydrogen concentration gradients in the latter.