Electrochemical hydrogen charging and permeation techniques were used to characterize hydrogen distribution, trapping, and diffusion in X60 and X60 sour service (X60SS) pipeline steels. The results obtained
contribute to better understanding of hydrogen-induced cracking (HIC). SEM observations illustrated that
all HIC cracks were formed at the center of cross section in the X60 steel after 3-h hydrogen charging and
length of cracks increased with charging time. No HIC cracks were recorded at the cross section of X60SS
steel after the same charging for different durations. Hydrogen permeation tests showed that the density of
reversible hydrogen traps was lower at the center of cross section in the X60SS steel compared to the X60
one, and this is considered as one of the main reasons for high resistance of X60SS steel to HIC. EBSD
orientation imaging results proved that the accumulation of <111>||ND-oriented grains at the center of the
cross section in the X60SS steel was high. This is also considered as another reason for higher resistance of
this steel to HIC. Finally, the center segregation zone with higher hardness value in the X60 steel was more
pronounced than in the X60SS steel which made the X60 steel susceptible to HIC cracking.