Investigation of the Correlation between Hydrogen Cathodic Charging Conditions and Toughness Properties of Longitudinal Submerged Arc Welded X65 Pipeline Steels

This research work focuses on the investigation of the correlation between hydrogen cathodic charging conditions and toughness properties of a welded X65 pipeline steels. The experimental technique which was applied to determine the characteristic parameters associated with toughness was the crack tip open displacement after hydrogen cathodic charging process. The hydrogen cathodic charging process was carried out in an electrolytic cell with applied current densities of 10, 20, 30 mA/cm2 and hydrogen cathodic charging duration 48 h. Through this study, interesting results were provided concerning the diffusion depth and the diffusion coefficient of atomic hydrogen as far as toughness properties. The maximum diffusion depth value is assigned for each current density field in the region of heat-affected zone and the minimum in the area of fusion zone. In addition, the highest diffusion coefficients are attributed to heat-affected zone and the lowest to fusion zone, for all applied current densities. Finally, the fusion zone is considered to be more prone to the occurrence of embrittlement phenomena compared to base metal. The rate of toughness parameters drop is higher for current densities between 0-10 and 20-30 mA/cm2, where the cathodic current promotes the electrochemical reduction in hydrogen cations to atomic hydrogen.