This study evaluates the pitting susceptibility and cathodic activity for endogenous, nonmetallic inclusions in the high-strength API-X52 and 60 in near-neutral, chloride and bicarbonate solutions. The inclusions are characterized in relation to the steel making method, particularly to the compositional variation across the thickness of a pipeline steel slab. Using conventional potentiodynamic scans, the pitting potentials (along with the transpassivation's) are first systematically linked to the constituents of a matrix of test solutions. The local kinetics of corrosion are studied by Scanning Vibrating Electrode Technique (SVET). The local physical phenomena, including the different modes of localized attacks are studied by suitable microscopic and spectroscopic techniques. For comparison, the electrochemical findings are corroborated by testing synthesized Al2O3 and MnS inclusions, mechanically alloyed to pure iron.