May 29 - June 1, 2012
In preparing for coating, what is the best way to treat a steel surface that has been attacked by microbiologically influenced corrosion (MIC)?
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Harry Peters of CHLOR RID International, Inc. on
June 1, 2012:
A leading source of MIC is the presence of residual sulfates remaining on surfaces prior to coating. Under coatings and in low dissolved oxygen environments, the sulfates can be reduced by the bacteria from sulfates to sulfides in the presence of hydrogen and aided by the presence of a metal surface. In this condition the mere presence of bacterial deposits can promote aggressive pitting corrosion. Test for and remove residual sulfates. Our experience is that sulfates adsorbed to the metal surface are difficult to remove, and dry abrasive blasting is in no way sufficient to accomplish this task.
Timothy Coleman of Poxycor on
May 29, 2012:
Depending upon weather, the surface profile, and the type of coating being applied, I would first dry abrasive blast with a good, clean, hard abrasive. I would then UHP the surface to clean any contaminants left by the abrasive and or/ the MIC, thoroughly dry the surface, and check the PH of the surface as well as for chlorides.
Jeremi Day of Allphaz Inspection Services on
May 30, 2012:
Deployment of Dynamic Bio-static Coatings
Otto Drozd of J. Mori Painting, Inc on
May 29, 2012:
Microbiologically-influenced corrosion is brought about by the presence of microorganisms in biofilms on the surface of the corroding material. A biofilm is an assemblage of surface-associated microbial cells that is enclosed in an extracellular polymeric substance, a matrix of microbial cells that is not removed by gentle rinsing. They are not only very tenacious but also highly resistant to disinfectants such as chlorine. Depending on the amount of MIC present on the surface ( 33% or less), the problem can be treated by high pressure water jetting (SSPC-SP12/ NACE No 5). Above 33 % the surface should be prepared by Commercial Blasting (SSPC-SP6/ Nace No 3). Unfortunately, there are no standards present today that regulate the treating of MIC-affected surfaces.
Loren Hatle of CorrLine International, LLC on
May 29, 2012:
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Because of the covalent bonds created between the non-water- soluble metabolic by-products produced by microbial activity and the possible availability of water-soluble contaminants, i.e., chlorides, the success of a coating life will be compromised without removing the MIC by-products. There is a solution.
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