The initiation of crevice corrosion in stainless steels

Effects of applied potential on stable pitting of 304 stainless steel

“…The relationship between pitting current density and applied potential indicates that an ohmic potential drop occurs between the pit internal surface and the bulk solution. Because the bulk solution has a relatively high concentration of sodium chloride, and the metal chlorides precipitate inside the pit, the vast majority of ohmic drop is across the salt film and precipitates [27,28], and of course across the metal cover over the pit mouth [9,20]. It is difficult to say that stable pit growth is controlled by ohmic potential drop, because ohmic potential drop cannot lead to the concentration of metal cations and chloride anions, and hydrolytic acidification also cannot occur because of ohmic potential drop control.…”

“…As is well known, a chloride-induced pit must be either enriched in chloride, or of a lower pH, or both relative to the bulk solution, in order to sustain continuous propagation of pit [18][19][20][21]23,26]. This mechanism is also suitable for crevice corrosion [27,28]. Because the anodic reaction occurs inside the pit and the supporting cathodic reaction occurs on the passive metal surrounding the pits, the electroneutrality of the pit anolyte necessitates a local accumulation of chloride anions acting as the counter-ion, as a natural consequence of metal cations dissolving within the anolyte [11,19,21,23,29,30].…”

“…Local acidification also occurs from hydrolysis of the dissolving metal cations with the anolyte inside the pit. The diffusion of corrosion products controlled propagation can lead to an accumulation of metal cations and chloride, and significant local acidification [18][19][20][27][28][29][30]. Therefore, it is reasonable to believe the accuracy of diffusion controlled theories regarding pit propagation.…”

Critical pitting and repassivation temperatures for duplex stainless steel in chloride solutions

“…This result is in accordance with the previous study reported by Abd EI Meguid. He found that the temperature difference between CPT and T r varied between 20 and 25 • C for 254SMO using the potentiodynamic cyclic anodic polarization technique [18]. It was also found that the critical crevice temperature (CCT) was commonly 30 • C lower than the CPT [19]. That means the T r is probably close to the CCT, which is assumed to be attributed to the similar h for both the stable pits and the crevice (h, 0.1-1 mm).…”

A corrosion study of nickel–copper and nickel–copper–palladium welding filler metals

“…The crevice corrosion test results were in agreement with cyclic polarization test results in which the breakdown potentials of Ni-Cu alloys were lower than that of base metal, and the repassivation potentials were higher. Some researchers [32][33][34] proposed that crevice initiation could be related to the metastable pitting stage of an alloy. Pd addition increases the corrosion resistance of Ni-Cu alloys so that 308L/304L, with lower repassivation potential than Ni-Cu and Ni-Cu-Pd, is more susceptible to crevice attack.…”