Atmospheric Corrosion Tests of Selected Steel/Coating Materials in Okinawa

Atmospheric corrosion in marine environments is primarily due to airborne chlorides (transported from the ocean by wind and wave action), time of wetness, high relative humidity, and temperature.  A performance evaluation and comparison of three commercially available coatings on steel substrates and two noncoated 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, 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.  Although this was a relatively short-term test (~ 250 days), the results indicated relative abilities of high performance coating systems to protect steel and the limitations of low chromium stainless steel alloys in  coastal  environments.