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June 25 - July 1, 2012

What coating problems are likely in storage tanks that have dissimilar metal sides and floors?


Selected Answers

From Loren Hatle of CorrLine International, LLC on July 6, 2012:
     Usually, the most common dissimilar metals issues are repairs with, i. e., new, (recycled) steel attached to the original steel. The problem with this is the contaminant load on new steel is usually very high because if the high loads of non-water-soluble sulfides  have covalent bonded salts. The quench water in recycled steel is recycled water. This recycled water exacerbates the contaminant problem and creates multiplie reactive sites on the surface of the steel. A solution would be to creat a uniform receptive surface with the removal of these contaminants. There is a solution.

From Jeremi Day of Allphaz Inspection Services on June 25, 2012:
Dissimilar metal will cause galvanic corrosion which, by definition, is "an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical or direct contact or are immersed in an electrolyte together." This process essentially turns the less noble metal into an anode. The rate of corrosion is determined by the electrolyte and the difference in nobility. The difference in nobility is determined by the difference in voltage potential. The galvanic series provides a clear understanding of electro-potential between different metals. This type of corrosion cannot be stopped using coatings. The only way is to insulate these metals from each other. In addition, due to the galvanic corrosion, other defects could potentially occur such as disbondment, cracking, flaking, checking, etc. The list goes on and on.

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Tagged categories: Metals; Quality Control; Tank interiors


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