51312-01470-Interaction between Two Pre-Existing Micro Pits on Pitting Propagation

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Product Number: 51312-01470-SG

ISBN: 01470 2012 CP

Author: Zhenjin Zhu

Publication Date: 2012

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Although numerous models have been developed for predicting localized pitting corrosion less research was reported on pit-to-pit interaction. An active pit can affect the propagation and passivation of nearby pitting events because only those stronger pits can survive and develop through a competitive interaction between initiated pits. To elucidate the intrinsic mechanisms this paper investigated the interaction between two pre-existed micro-pits under a sweet (CO2) environment using a Finite Element Analysis. Specifically this study designed the computational domain with a thin boundary layer of an electrolyte solution as well as two hemispherical pits which have different initial diameters and inter-pit distances. Transient corrosion behaviour of each individual pit was predicted by solving the Nernst-Planck equation. Velocity distribution of electrolyte flow was governed by the Navier-Stokes equations. Distribution of electric potential in the solution was computed by solving the Poisson equation. The anodic potentials at the metal boundaries of two interacting pits were governed by the Nernst equation whereas the cathodic potentials at the scale side were determined in terms of the balance between the sum of all anodic currents and all cathodic currents. Distribution of the ionic concentration was solved using Fick’s Second Law. Consequently growth or passivation of each individual pit was understood. Furthermore the effects of the initial pit sizes inter-pit distance and local shear stress on pit interaction were examined. Efforts were made to improve a fundamental understanding of propagation of a newly initiated pit once encountered with another pre-existed pit.