INTRODUCTION
Atmospheric corrosion in marine environments is primarily due to airborne chlorides, time of wetness, high relative humidity, and temperature. A performance evaluation and comparison of three commercially available coatings on steel substrates and two non-coated steel materials was conducted at military sites near the ocean in the severely corrosive coastal environment in Okinawa Japan. Twelve test panels (sized 10 cm. X 15 cm. X 3.125 mm.) were exposed for each of the following systems: (1) hot dip galvanized coatings on low carbon steel, (2) zinc rich primer system on low carbon steel, (3) phenolic system on low carbon steel, (4) uncoated AISI 410 series stainless steel, and (5) uncoated low-carbon steel. Scribes lines were introduced into the coatings to test for undercutting, and each system was exposed on test racks at two locations, ~150 m. and ~600 m. from the ocean, respectively. Three panels were removed from each system, at 60-70 days intervals and evaluated with respect to corrosion rates and coating performance, until all 120 panels had been evaluated. The results of this short test (~ 8 months) indicated relative abilities of coating systems to protect steel and the limitations of low chromium stainless steel alloys in coastal environments.
Facilities and equipment operated by the U.S. Army are exposed to a wide variety of environmental conditions, including soils, waters or atmospheres of varying corrosivity. The various types of resulting corrosion can create a costly maintenance and repair (M&R) burden while adversely affect Army operations. The characteristics of soils, waters, and atmospheres at Army installations can be expected to vary greatly, and that this variation has important implications for corrosion mitigation strategies. No two installations have identical environmental conditions, and corrosion-promoting conditions can even be expected to vary within the boundaries of a given installation. For example, many island and peninsular locations have atmospheric conditions that are severely corrosive on the windward sides but relatively mild on the leeward sides. Due to such close proximity to the ocean, structural materials and appurtenances at military installations in Okinawa, Japan are potentially susceptible to severe atmospheric corrosion damage. Such degradation can affect buildings and mission-critical equipment, increase direct maintenance and operational costs, and impact personnel safety. The primary factors contributing to atmospheric corrosion in marine environments include: airborne salt (specifically chloride) transported from the ocean by wind and wave action, time of wetness, high relative humidity, and temperature. Frequent rainfall can have a beneficial effect on boldly exposed (e.g. skyward-facing) surfaces if the chlorides are washed off. Although many advances have been made in conducting corrosion tests on bare metal and coated specimens in the laboratory, the “gold standard” for establishing performance in atmospheric environments continues to be outdoor exposures at representative locations. This approach was also used for evaluating performance of selected systems at an Army installation in Okinawa. Short term testing <1 year, was employed in hopes of obtaining atmospheric corrosivity data that would give some indication of the suitability of materials in this coastal environment.
