The aim of this study is to investigate the fracture surfaces and crack propagation in an API X70 pipeline steel in
acidic environment. To this purpose, as-received and electrochemically hydrogen-charged tensile specimens are
subjected to tensile testing. Moreover, EBSD measurements were carried out on the cross section (RD-ND plane)
in as-received and hydrogen-charged specimens. The results showed that hydrogen charging and strain rate of
tensile testing were considered as two effective parameters in determining the type of fracture. Moreover, the
fracture of the uncharged specimens was quite ductile and the strain rate had little effect on the fracture type. A
direct correlation was found between type of fracture and the strain rate in hydrogen-charged specimens. With
increasing strain rate, the fracture in hydrogen-charged specimens did not have enough time to initiate from
inclusions and precipitates and connect to the main fracture surface. <001>‖ND oriented grains have the highest
hydrogen atoms due to the largest interatomic space and the distortion energy accumulated at grain boundaries
due to the lack of sufficient activated slip system. The variation of KAM distribution to higher values of hydrogencharged
specimen could be effectively associated to the formation of dislocation walls and dislocation tangles
especially in the vicinity of bcc grain boundaries. The higher volume fraction of the grains with high Taylor
factor data formed in the hydrogen-charged specimen were highly susceptible to plastic instability, enhancing
the crack propagation.