Role of inclusions in the pitting initiation of pipeline steel and the effect of electron irradiation in SEM

The role of inclusions in the initiation of corrosion pits for a high strength pipeline steel in NaCl solution was investigated. The inclusions with typical compositions of Al-Mg-Ca-S-O were found typically spherical and responsible for the initiation of circular corrosion pits. The possible formation mechanism of the spherical inclusions and their role in the initiation of pitting corrosion are discussed. The electron irradiation in scanning electron microscopy, including the morphology observation and energy-dispersive X-ray spectroscopy test, was found to have significant influence on the pitting susceptibility around the inclusions.