In this study, the effect of important failure modes in oil and natural gas pipeline steels has been studied by literature review and some previous investigations of authors. Two important failure modes including stress corrosion cracking and hydrogen assisted cracking were found in service pipeline steels. Hydrogen assisted cracking itself can be categorized to hydrogen induced cracking and sulphide stress cracking. The effect of different microstructural parameters on each failure mode was accurately investigated. For instance, it is found that the pH of surrounding solution has a key role in determining the nature of stress corrosion cracks. In other words, transgraular stress corrosion cracking occurs in near-neutral solution while the intergranular cracking becomes a dominant failure mode when the pH of solution reaches close to 9. Moreover, it is reported that low angle grain boundaries and coincidence site lattice boundaries may arrest short stress corrosion crack after its nucleation. Finally, some techniques for improving the resistance of pipeline steels against these failure modes were suggested.
