2-Dimensional Simulations of Pit Propagation and Multi-Pit Interactions

Abstract

This work presents a reaction-transport model for pit propagation coupled with a phase field method to model the moving boundary at the corroding surface. This enables numerical simulations of the simultaneous propagation of multiple pits in close proximity to each other to study the interactions between pits under galvanostatic conditions, with limited applied currents. Results show the formation of lacy covers over pits in stainless steel, which is due to undercutting of the surrounding surface, and reveal the development of other complex morphologies arising from the interaction between neighboring pits; e.g., the growth of “pits within pits” and the evolution of “champion pits.” Such observations are due to the shrinkage of the total active surface to sustain the limited current as pits grow larger. The proposed model can be a valuable tool for studying the evolution of pit morphology in more realistic scenarios when multiple pit initiation sites are present.

Understanding the Effect of Applied Current and Potential on Pitting in 316L Stainless Steels

“…The top surface of the pit dissolved when the surface concentration beneath it reached a critically aggressive concentration, which has been supported by the modelling works from Laycock et al 40 and Nguyen et al 19 The presence of a lacy cover and its morphology depended on the applied current and potential. Under potentiostatic conditions, the perforation cannot continue, creating discrete perforations when the pit solution can be readily diluted through the perforated openings (i.e., when i diss < i mass,crit , where i diss is the dissolution current density and i mass,crit the current density associated with the mass transfer of a critical metal cation concentration) (Fig.…”

“…8,[11][12][13] Pit morphology and its geometric characteristics have been studied extensively. 11,12,[14][15][16][17][18][19] The pit morphologies can be influenced by various factors such as solution composition, 12,14,15,[20][21][22] temperature, 12,[23][24][25] applied potentials and currents. [26][27][28][29][30][31][32][33][34][35] Two typical pit morphologies: crystallographic attack or etched surface, and polished surface, were identified at different potentials.…”

Hollow wire corrosion of stainless steel ropes in a marine mooring system and its relation to microstructure

“…For the wire diameter of 640 μm, this means that in total material corresponding to a wire length of 750 μm has got dissolved during the experiment, which is in the order of the diameter. Since the pit growth direction even in homogenous SS is governed by complex processes, as was summarized and demonstrated recently, [ 9 ] we may conclude that potentiodynamic experiments are not necessarily suitable for replicating HWC distinguishable from pitting since the amount of dissolved metal is insufficient.…”