Hydrogen-embrittlement resistance of X100 steels for long-distance high-pressure pipelines

Publisher Summary The cracking behavior of traditional pipeline steels with yield strength of ∼450 MPa is well known from both field experience and laboratory studies. Mechanisms that are proposed to describe the environmentally assisted cracking (EAC) behavior of such steels include: carbonate-bicarbonate stress corrosion cracking; near-neutral pH stress corrosion cracking; and hydrogen embrittlement caused by the application of cathodic protection (CP). EAC is observed during slow strain rate tensile (SSRT) tests of which stress–strain curves differ significantly from stress–strain curves in air. The difference is more pronounced at the strain rates of 10-6 and 10-5 s-1 and cathodic potential of –2.0 V vs. SCE. At this potential, the fracture surface is characterized by extensive brittle areas of crack growth. In addition, several secondary cracks perpendicular to the tensile load are observed on the fracture surface at –2.0 V vs. SCE. The effect of smaller cathodic polarization on susceptibility of X 100 steels to EAC is less obvious. However, both secondary cracks and brittle crack propagation areas are also observed on fracture surfaces at less negative potentials.