Field inspections of United States Marine Corps (USMC) assets have identified periodic high temperatures as contributing to damage of protective coatings and sealants, resulting in corrosion of bolted and overlapping joints. Currently utilized sealants generally have maximum continuous operating temperatures of 400°F (204°C), and intermittent operating temperatures up to 600°F (316°C). The purpose of this report is to evaluate alternative sealants in temperatures that exceed these conditions, combined with their corrosion protection performance. Under the USMC Corrosion Prevention and Control (CPAC) Research, Development, Test, and Evaluation (RDT&E) program, a testing protocol was executed to evaluate silicone room temperature vulcanizing (RTV) and ceramic-based sealants in high temperature and corrosive environments. Evaluations were based on percent of corrosion on the surface, pit depth, and sealant degradation. This paper will present the findings of these novel tests and their potential applications on USMC assets.
The Verrazano-Narrows bridge is a 13,700-foot-long suspension bridge between Brooklyn and Staten Island. A major maintenance project planned for the lower level of the bridge included structural steel replacement and replacement of a 20-year-old coating system on the structural deck system and stiffening truss elements. The initial design approach was to remove the coating (SSPC-SP 10, Near-White Metal Blast Cleaning) in more corrosion prone locations and perform spot cleaning of the less corrosion prone locations. To bring the initial design estimates within the allocated funding, SSPC-SP 18, Thorough Spot and Sweep Blast Cleaning for Industrial Coating Maintenance was specified for all surfaces in lieu of the combination of full removal and spot cleaning. SSPC-SP 18 is a new procedure which saves money by only removing weak coatings and allowing well adherent, serviceable coating(s) to remain. Studies have shown that the procedure can reduce the cost of maintenance coating without any performance compromise.1,2,3,4,5,6,7 The Verrazano-Narrows project ultimately used the new procedure successfully on approximately three million square feet of coated steel. This paper describes the SSPC SP-18 procedure and it’s use on this project.
The paper discusses alternative methods of examining the performance of barrier coatings, the implications on protective methods, and recommendations for coating testing.
Corrosion rates of coated steel structures is generally assumed to be negligible while coating systems are intact. However, recent testing and detailed inspection has found that corrosion of steel during the initial stages of coating deterioration can indeed be substantial—in fact corrosion rates can exceed that of boldly exposed steel. These findings are also a function of coating type. The following paper discusses how these factors might be accounted for in coating selection and in design assumptions concerning structure life and appropriate maintenance intervals.
