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Development of predictive models of flow induced and localized corrosion

dc.contributor.advisorPostlethwaite, Johnen_US
dc.contributor.advisorEvitts, Richard W.en_US
dc.contributor.committeeMemberSumner, Robert J.en_US
dc.contributor.committeeMemberPhoenix, Aaronen_US
dc.contributor.committeeMemberNemati, Mehdien_US
dc.contributor.committeeMemberBergstrom, Donald J.en_US
dc.creatorHeppner, Kevin Len_US
dc.date.accessioned2006-09-18T20:50:28Zen_US
dc.date.accessioned2013-01-04T04:59:06Z
dc.date.available2006-09-20T08:00:00Zen_US
dc.date.available2013-01-04T04:59:06Z
dc.date.created2006-05en_US
dc.date.issued2006-05-05en_US
dc.date.submittedMay 2006en_US
dc.description.abstractCorrosion is a serious industrial concern. According to a cost of corrosion study released in 2002, the direct cost of corrosion is approximately $276 billion dollars in the United States – approximately 3.1% of their Gross Domestic Product. Key influences on the severity of corrosion include: metal and electrolyte composition, temperature, turbulent flow, and location of attack. In this work, mechanistic models of localized and flow influenced corrosion were constructed and these influences on corrosion were simulated.A rigourous description of mass transport is paramount for accurate corrosion modelling. A new moderately dilute mass transport model was developed. A customized hybrid differencing scheme was used to discretize the model. The scheme calculated an appropriate upwind parameter based upon the Peclet number. Charge density effects were modelled using an algebraic charge density correction. Activity coefficients were calculated using Pitzer’s equations. This transport model was computationally efficient and yielded accurate simulation results relative to experimental data. Use of the hybrid differencing scheme with the mass transport equation resulted in simulation results which were up to 87% more accurate (relative to experimental data) than other conventional differencing schemes. In addition, when the charge density correction was used during the solution of the electromigration-diffusion equation, rather than solving the charge density term separately, a sixfold increase in the simulation time to real time was seen (for equal time steps in both simulation strategies). Furthermore, the charge density correction is algebraic, and thus, can be applied at larger time steps that would cause the solution of the charge density term to not converge.The validated mass transport model was then applied to simulate crevice corrosion initiation of passive alloys. The cathodic reactions assumed to occur were crevice-external oxygen reduction and crevice-internal hydrogen ion reduction. Dissolution of each metal in the alloy occurred at anodic sites. The predicted transient and spatial pH profile for type 304 stainless steel was in good agreement with the independent experimental data of others. Furthermore, the pH predictions of the new model for 304 stainless steel more closely matched experimental results than previous models.The mass transport model was also applied to model flow influenced CO2 corrosion. The CO2 corrosion model accounted for iron dissolution, H+, H2CO3, and water reduction, and FeCO3 film formation. The model accurately predicted experimental transient corrosion rate data.Finally, a comprehensive model of crevice corrosion under the influence of flow was developed. The mass transport model was modified to account for convection. Electrode potential and current density in solution was calculated using a rigourous electrode-coupling algorithm. It was predicted that as the crevice gap to depth ratio increased, the extent of fluid penetration also increased, thereby causing crevice washout. However, for crevices with small crevice gaps, external flow increased the cathodic limiting current while fluid penetration did not occur, thereby increasing the propensity for crevice corrosion.en_US
dc.identifier.urihttp://hdl.handle.net/10388/etd-09182006-205028en_US
dc.language.isoen_USen_US
dc.subjectcrevice corrosionen_US
dc.subjectflow influenced corrosionen_US
dc.subjectmass transport modellingen_US
dc.subjectelectromigration and diffusionen_US
dc.titleDevelopment of predictive models of flow induced and localized corrosionen_US
dc.type.genreThesisen_US
dc.type.materialtexten_US
thesis.degree.departmentChemical Engineeringen_US
thesis.degree.disciplineChemical Engineeringen_US
thesis.degree.grantorUniversity of Saskatchewanen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophy (Ph.D.)en_US

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