Effect of electrochemical hydrogen-charging conditions on nanomechanical properties of X80 pipeline steel

Abstract

In this work, nanoindentation tests, combined with hydrogen (H)-permeation testing, were used to study the effect of electrochemical H-charging conditions on H-permeating parameters and nanomechanical properties of X80 pipeline steel. The steady-state H-permeating current density, H-permeating flux, and the H subsurface concentration obtained in 0.5 M H2SO4 solution are apparently greater than the parameters obtained in near-neutral pH NS4 and 0.1 M NaOH solutions. The nanomechanical properties of X80 steel are heavily dependent on the electrochemical H-charging conditions (i.e., solution, time, and cathodic current density). The changes in nanohardness of the steel subjected to electrochemical H-charging depend on the charging solution used. In 0.5 M H2SO4 solution, as the electrochemical H-charging time increases, the nanohardness of the steel continues to decrease. However, in NS4 and 0.1 M NaOH solutions, the steel nanohardness increases with time. This phenomenon is attributed to the formation of corrosion product films on the steel surface. The softening and hardening transition phenomenon occurs on the steel subjected to electrochemical H-charging. Although measurement errors may cause variations in the nanohardness results, the evolution of nanohardness upon electrochemical H-charging exhibits a discernible tendency. H atoms could affect the elastic modulus of steel. When electrochemical H-charging promotes a uniform distribution of H atoms within the steel, achieved through either extended charging time or application of a cathodic current density, the elastic modulus of the steel tends to increase.