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CCP 01-23-2006
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CCP 01-23-2006
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5/8/2007 1:21:14 PM
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11/14/2006 4:41:45 PM
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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 />General Discussion on Maintenance Painting <br /> <br />The purpose of this coating assessment was to assess the condition of the existing <br />coatings on the structure and make appropriate recommendations for maintenance <br />painting. Many factors affect the service life of a coating system. These include the type <br />of coating originally applied, the type and quality of surface preparation, service <br />environment, number of coats and film thickness, and any subsequent maintenance <br />painting activity. <br /> <br />If a particular coating has provided satisfactory corrosion prevention and remains <br />in relatively good condition, it is cost effective to extend the life of the system through <br />overcoating and retaining as much of that original coating as possible. This strategy is <br />countered by a "full removal" approach that removes all existing lead-based coatings. <br />This strategy effectively places the tank at the beginning of a new maintenance painting <br />cycle. Little work will be required for at least 10 years, and then, it should involve only <br />minor touch-up. This strategy, while safe and effective, is also more expensive. <br /> <br />Maintenance painting options for tank structures fall into three main categories: <br />Spot repairs, spot repairs with full overcoats, and complete coating removal and <br />replacement. Each of these options is progressively more complex and requires <br />progressively more work. Correspondingly, each option also offers greater long term <br />protection to the structure, but at additional costs. Where paints containing hazardous <br />metals are present, the issues associated with removing these paints impact the decision <br />making process. Spot repairs, with or without overcoats, minimize the amount of <br />hazardous material handled, thus minimizing the cost. <br /> <br />When removal and replacement is performed, a new maintenance cycle begins. <br />As the coatings age and weather, isolated spot repairs may be required. Several spot <br />repairs may be made to the individual structure until a full overcoat is necessary. More <br />spot repairs may then be made and additional overcoats applied until extensive corrosion <br />develops, significant coating breakdown occurs, or the mechanical properties of the <br />coatings (e.g. the adhesion) degrade to the point where additional work is no longer <br />practical. At this time, complete removal may again be required, but the effective life of <br />the original coating system has been extended through the planned maintenance <br />activities. <br /> <br />There is always the option to defer maintenance painting if the service life of the <br />structure is limited or there is some other benefit for postponing the work. If <br />maintenance painting is deferred for a period of time, the level of surface preparation <br />required to properly prepare the surface increases correspondingly (i.e. total removal will <br />be required). In some cases, where the structure is corroding extensively but is still <br />structurally sound, painting is deferred because the highest level of surface preparation is <br />already needed, whether performed today or several years from now. The strategy in this <br />case is to use the money to repair coatings in other areas that are not so badly deteriorated <br />in order to stop the corrosion from propagating to the point that removal is the only <br />option. <br /> <br />Elevated Water Storage Tank <br />City of Arden Hills South Tank <br /> <br />31 <br />
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