Galvanic Localized Corrosion of Mild Steel under Iron Sulfide Corrosion Product Layers
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| Language: | English |
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Ohio University / OhioLINK
2018
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=ohiou151551709542735 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-ohiou151551709542735 |
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NDLTD |
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English |
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Chemical Engineering Localized corrosion galvanic iron sulfide H2S mild steel |
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Chemical Engineering Localized corrosion galvanic iron sulfide H2S mild steel Navabzadeh Esmaeely, Saba Galvanic Localized Corrosion of Mild Steel under Iron Sulfide Corrosion Product Layers |
| author |
Navabzadeh Esmaeely, Saba |
| author_facet |
Navabzadeh Esmaeely, Saba |
| author_sort |
Navabzadeh Esmaeely, Saba |
| title |
Galvanic Localized Corrosion of Mild Steel under Iron Sulfide Corrosion Product Layers |
| title_short |
Galvanic Localized Corrosion of Mild Steel under Iron Sulfide Corrosion Product Layers |
| title_full |
Galvanic Localized Corrosion of Mild Steel under Iron Sulfide Corrosion Product Layers |
| title_fullStr |
Galvanic Localized Corrosion of Mild Steel under Iron Sulfide Corrosion Product Layers |
| title_full_unstemmed |
Galvanic Localized Corrosion of Mild Steel under Iron Sulfide Corrosion Product Layers |
| title_sort |
galvanic localized corrosion of mild steel under iron sulfide corrosion product layers |
| publisher |
Ohio University / OhioLINK |
| publishDate |
2018 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou151551709542735 |
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AT navabzadehesmaeelysaba galvaniclocalizedcorrosionofmildsteelunderironsulfidecorrosionproductlayers |
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1719453303014686720 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-ohiou1515517095427352021-08-03T07:05:20Z Galvanic Localized Corrosion of Mild Steel under Iron Sulfide Corrosion Product Layers Navabzadeh Esmaeely, Saba Chemical Engineering Localized corrosion galvanic iron sulfide H2S mild steel Iron sulfide corrosion product layers commonly form on mild steel surfaces corroding in aqueous H2S environments. These layers present a barrier which may retard the corrosion rate. However, their semiconductive nature leads to an acceleration of corrosion via galvanic coupling, by increasing the cathodic surface area. The electrocatalytic properties of different iron sulfides, which are important in this process, were heretofore unknown. The research herein reports cathodic reaction rates on the surfaces of geological specimens of both pyrite and pyrrhotite along with mild steel in HCl, CO2 and H2S aqueous solutions at different pH values. The results show that in solutions where H+ reduction dominates pyrite has similar electroactivity to X65 steel, while pyrrhotite exhibits approximately one order of magnitude smaller current densities. An extra wave observed in the cathodic sweeps on pyrrhotite was due to conversion of pyrrhotite to troilite. In aqueous CO2 solutions similar results were obtained, while in H2S aqueous environments both pyrite and pyrrhotite showed similar electroactivity that was slightly less than that of X65 steel.Zero resistance ammeter (ZRA) measurements were utilized in order to measure the galvanic current between an X65 mild steel surface and a pyrite or pyrrhotite surface; cathode to anode surface area ratios of circa 20 and 7 were employed in separate sets of experiments. The results were compared with the proposed model which takes into account the reduction rates, changes in surface characteristics of the iron sulfides and their surface area. Due to the electrical conductivity and the observed galvanic current between pyrrhotite and a mild steel, it was hypothesized that its presence in the corrosion product layer on a steel surface could lead to localized corrosion. Mild steel specimens (API 5L X65) were pretreated to form a pyrrhotite layer on the surface by high temperature sulfidation in oil. The pretreated specimens were then exposed to a range of aqueous CO2 and H2S corrosion environments at 30 and 60¿C. X-ray diffraction data showed that the pyrrhotite layer changed during these exposures; in an aqueous CO2 solution it underwent dissolution, in a mixed CO2/H2S solution it partially transformed to troilite with some mackinawite formation. Initiation of localized corrosion was observed in both cases. It was concluded that this was due to a galvanic coupling between the pyrrhotite layer and the steel surface. The intensity of the observed localized corrosion varied with solution conductivity (NaCl concentration), a more conductive solution resulted in higher localized corrosion rates consistent with the galvanic nature of the attack.One of the aims of the present research project was to establish physicochemical scenarios where localized corrosion should be expected in H2S containing environments. It is hypothesized that any disruption leading to a discontinuity of a corrosion product layer results in initiation of localized corrosion, where a galvanic coupling between the underlying steel and the conductive iron sulfide layer would lead to propagation of localized corrosion via a galvanic effect at an enhanced rate. This hypothesis was investigated based on five case studies from the research conducted by J. Ning, S. Navabzadeh Esmaeely, W. Zhang, and S. Gao. In all cases, localized corrosion was observed confirming the proposed mechanism (case 1: a partially dissolved pyrrhotite layer; case 2: a disrupted pyrrhotite layer due to pyrite formation; case 3: a disrupted pyrrhotite layer due to interference by sand; case 4: a disrupted mackinawite layer due to pyrite interference; case 5: a poorly formed mackinawite layer). 2018-07-05 English text Ohio University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=ohiou151551709542735 http://rave.ohiolink.edu/etdc/view?acc_num=ohiou151551709542735 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |