Pitting Corrosion: IR-Drop Pit Stability (2D)

This 2D cross-section companion replaces the 3D version's scripted repassivation probability with the real mechanism corrosion scientists use to explain why most nucleated pits die within moments while a rare few grow into failures: Galvele's X·i pit-stability criterion. Every pit's dissolution current is solved self-consistently from Ohm's law (the ohmic drop across the pit grows with both its depth and its own current) coupled to mixed activation/mass-transport-controlled anodic Tafel kinetics — an implicit equation solved by bisection, not read off a formula. The instant a pit nucleates, that solved current at its embryonic depth is multiplied by the depth itself; only if the product clears a critical threshold does the pit escape metastability and keep growing (its growth still visibly decelerating as its own IR drop deepens), otherwise it dies immediately as a small crater. Chloride concentration does double duty here, exactly as in the real electrochemistry: it lowers the film breakdown potential and lowers the pit-cavity resistivity, which is why concentrated-chloride environments both nucleate pits more easily and let them clear the stability threshold at much lower applied potentials.