Hydrogen in stress corrosion cracking of X-70 pipeline steels in near-neutral pH solutions

The effect of hydrogen on the stress corrosion cracking (SCC) for X-70A and X-70B pipeline steels in near-neutral pH environments was studied by monotonic tensile tests on slow strain rate tests (SSRT) machine and cyclic tests on SSRT machine and fatigue machine. The results showed that SCC intensity increased at high cathodic protection potential. Hydrogen charged at high pressure enhanced SCC sensitivity. Cyclic tests under elastic strain condition could not take the specimens to fracture and the hydrogen content was very low. However, when the load was raised to produce plastic deformation, the specimens failed within limited time and there was brittle fracture appeared on the fracture surface. Moreover, the hydrogen content was higher than that under elastic strain condition. The SCC mechanism of X-70A and X-70B pipeline steels in near-neutral pH environments was related to hydrogen accumulation induced by plastic strain. C 2006 Springer Science + Business Media, Inc.