Stress corrosion cracking (SCC) in near neutral pH conditions have been investigated by using notched specimens of some pipeline steels, whose strength grades cover American Petroleum Institute (API) specification 5L B to X80. These steels were manufactured by
quenching and tempering (QT), thermomechanical-controlled processing (TMCP), or controlled rolling (CR). The SCC resistance of these pipeline steels were rated as follows:- X65QT was most resistant to SCC. X65TMCP and X80TMCP were also resistant, although they were more
susceptible to SCC than X65QT. On the other hand, 5L B and X65CR were susceptible to SCC. 5L B was most susceptible among them. The microstructures of TMCP and QT steels were bainitic ferrite and / or bainite, while those of CR and 5L B steels were ferrite-pearlite. It
can be proven that uniform microstructures, such as bainitic ferrite or bainite, are more resistant to SCC than mixed microstructures of ferrite and pearlite. Effects of test conditions on SCC, hydrogen permeation, polarization and others have also been investigated. The results of this study are consistent with a hydrogen embrittlement mechanism for SCC, although sufficient information were not obtained to prove this
relationship.
Keywords: near neutral pH SCC, pipeline, carbon steels, microstructures, bainitic ferrite, bainite, ferrite-pearlite, thermomechanical-controlled processing (TMCP), controlled rolling (CR), quenching and tempering (QT)