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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br /> <br />Photograph 27 - Localized Areas of Corrosion on Tank Roof and Roof Handrail <br /> <br />The results of the total system dry-film thickness measurements from various <br />locations on the exterior of the tank are summarized in the following table. <br /> <br />Area DFT Range (mils) DFT Average (mils) <br />Pedestal (at Base) 10.8 to 20.4 15.4 <br />Baseplate 10.7 to 14.9 13.3 <br />Pedestal (at Top Platform) 11.1 to 14.7 12.4 <br />Roof 14.8 to 23.0 18.6 <br /> <br />A SOX microscope was used to examine the substrate in random areas to <br />determine if poor surface profiles, mill scale, intercoat contamination, voids, underlying <br />rust, mill scale, and/or pinholes existed. The substrate appeared to be blasted and free <br />from any of the fore mentioned conditions. <br /> <br />The adhesion on the exterior pedestal and roof was found to be good (4-5A). <br /> <br />Ultrasonic thickness readings were performed on the vessel and are summarized <br />below. The following represents the best estimate of the average steel thickness without <br />taking destructive samples: <br /> <br />Elevated Water Storage Tank <br />City of Arden Hills South Tank <br /> <br />25 <br />