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When it comes to a bridge structure with a serviceable Organic Zinc / Epoxy / Urethane (OZ/E/U) coating system, there is no golden answer on the most cost-effective maintenance painting strategy. Depending on the severity and amount of corrosion and coating breakdown on the structure, planned maintenance surface preparations range from spot power tool cleaning and spot painting to a full SSPC-SP 10 media blast and full recoating operation.
Choosing the proper maintenance strategy when scoping a coatings project is difficult, and potentially costly if incorrect procedures are utilized. This is especially true for steel bridges with millions of square feet of coated surface to be repaired and coated. For the last 30 years, bridge coating maintenance has been dominated by the desire to remove lead coatings from existing structures, followed by the application of Zinc/Epoxy/Urethane or other modern coatings systems. These modern coating systems are now reaching the age where major maintenance is required, and the decision must be made regarding how much coating to retain, and what methods will be used to clean and paint. This paper presents results of field and laboratory testing of alternative approaches to maintaining an Organic Zinc/Epoxy/Urethane bridge coatings system.
Coating degradation on Army ground systems represents a significant maintenance cost and effort. The objective of this proposed work is to develop a predictive model for coating degradation and subsequent substrate corrosion on Army ground assets. Provided with a better understanding of the root causes, steps can be taken to reduce corrosion impacts on Army materiel.
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Over the past few decades surface preparation standards have been implemented to provide guidance on determining the necessary surface cleanliness for specific applications. Prior to such standards, surfaces were prepared as they saw fit at the time of application which created high variability in performance of the protective coating. Since the standards were developed, the resulting performance consistency has become increased significantly. Such standards discuss a visual inspection of the steel after an abrasive material has been used to remove scale, rust, and other discoloration soils.
Variability of operation and practices can lead to mechanical integrity issues of equipment. A similar case was observed when an external UT survey was conducted on a biocide storage tank that showed localized areas of metal loss in the tank wall. The tank was opened for inspection and extensive internal corrosion damage was observed mainly in the form of large isolated pits. Three potential corrosion mitigation options were evaluated: upgrading the tank material from coated carbon steel to 316 stainless steel, installing a non-metallic lining, or keeping using the coated carbon steel and changing the operation practices. Each mitigation option was evaluated based integrity, feasibility, and economic factors. It was found that keeping the coated carbon steel and adjusting the operation practices can ensure the integrity of the tank while lowering the required economical investment. As such, a new operation manual was issued for the biocide storage tanks that ensured that the corrosion inducing environments are avoided.