CCP 01-23-2006 - Laserfiche WebLink

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