CORRELATION BETWEEN CRITICAL HYDROGEN CONCENTRATION AND HYDROGEN DAMAGE OF PIPELINE STEEL

The critical hydrogen concentration for the low sulfide pipeline steel was determined in the electrochemical permeation tests. To correlate this value with the state of metal degradation, the internal friction measurements within the grain boundary relaxation, as well as tensile and permeation tests were conducted for the specimens hydrogen treated to the concentration below and above the critical one and then degass ed. Hydrogen treatment below the critical content was found to modify the internal friction spectrum, the mechanical properties and hydrogen permeation parameters, revealing substantial rearrangement of disloca tions and decohesion of grain boundaries. In overcritical condition, t he formation of micro crevices at the grain and phase boundaries accom panied by the recovery of IF peak parameters and by the decrease in th e steel plasticity has been observed. Copyright (C) 1997 International Association for Hydrogen Energy.