In-situ studies of rust layer formed on OCTG N80 steels alloyed with rare earth elements

In this study, the effect of rare earth (RE) alloying on the rust formed on N80 steels was investigated with in-situ micro-Raman spectroscopy and optical microscopy. Under potentiostatic tests at potentials representing accelerated conditions, there was formation of goethite phase on N80RE, while this protective and stable rust layer was not found on N80. The presence of goethite might explain the smaller corrosion rate of N80RE than N80 at later stages of corrosion, although the initial corrosion rate of N80RE was greater, which was probably due to RE modified inclusions.