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Plant assets for hydrocarbon and power generation systems are prone to numerous damage mechanisms that arise from operating and/or upset conditions, environmental factors, material defects as well as other neighborhood factors 1-2. Corrosion is one of the key degradations that pose a substantial economic burden, and may result in severe safety and environmental hazards 3. While considering the percentage for global economy in terms of corrosion, the total cost of corrosion globally amounts to ∼2.5 trillion US dollars per year. Among the corrosion mitigation measures, organic protective coatings are the most widely used, and their costs add up to two-thirds of all anti-corrosion overheads 4.
Surface coatings are a cost-effective method for protecting metals surface and is well known for versatility, ease of maintenance, and various compositions specific to service involved. In this case study, a detailed investigation was conducted to discover the reason behind the failure of the external coating system (aliphatic polyurethane) on a riveted fire water tank for a turnkey project located in the Arabian Gulf region. Visual inspections of longitudinal seams alongside the failed coatings revealed rust stains which came from the seepage of the service. The under fill / primer layer’s dry film thickness showed significant and consistent variation from the topcoat’s thickness. Pull off adhesion tests advocated an adhesion failure between epoxy primer and aliphatic polyurethane. Cathodic disbondment test confirmed the paint manufacturer`s report and created confidence on the product chemistry. The corrosion mechanism leading to the in service failure of the applied coating is explained.
Coatings are a composite blend of raw ingredients that are mixed, applied to a prepared substrate, and dried and cured correctly to perform to their maximum capability. Failures and defects can appear themselves at numerous times in the life of a coating. Prior to application, they can take the shape of settlement and skinning, during application as runs and sags, shortly after application as solvent popping and orange peel, and during service as blistering and rust spotting. Therefore, it is not unexpected that those coatings can suffer from premature failure and/or exhibit defects that may or may not result in failure. Coatings nowadays are the most efficient method to shield metals and thus has been widely engaged among various protective techniques 1, 2.
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Every year millions of dollars are spent litigating the responsibility issues associated with the repair or replacement of coated products that have prematurely lost their decorative or protective value due to improper coating specification or application. Many of these failures could have been avoided if the proper finishing materials and methods were specified, followed, certified and documented.
This paper presents an in-sight to the standard “ISO 12944 – Corrosion Protection of Steel Structures by Protective Paint Systems”, from the angle of prevention of premature coating-failure, but also how the standard can be used to help analyze premature coating-failures (if and when a coating-project was done as per ISO 12944).