Abstract
Effectiveness of fluorescent ferric ion indicator for under film corrosion detection of coated steel panels in water ballast tank is examined. (1S)-3'-(diethylamino)-N,N-diethyl-3-oxo-3',9a'-dihydro-3H-spiro[isobenzofuran-1,9'-xanthen]-6'-amine oxide “RhoNox-1” synthesized by Hirayama et al. (2013) is chosen as Fe2+ indicator. Under film corrosion sensing semi-transparent modified epoxy films which contains RhoNox-1 are prepared. SS400 steel test panels are blasted and the prepared semi-transparent Fe2+ sensing paints are applied. Some panels are scribed after coating, and NaCl solution is dropped onto the steel surface before coating in other panels. These panels are subject to immersion tests in NaCl solution and cyclic corrosion tests by using artificial seawater. Changes in fluorescence are observed during these tests. As results, followings are found: 1) RhoNox-1 is not responsive to amine-based hardener, and "prematurely fluorescent” can be prevented; 2) RhoNox-1 is functioning as an early detection indicator for steel corrosion; 3) Steel's anode reactions in underfilm corrosion that progressed during the cyclic corrosion tests had been detected clearly by using the developed Fe2+ sensing paint. 4) It is enough to apply 1wt% RhoNox-1 containing paint as a mist coat for nondestructive monitoring of anode reaction when semi-transparent paint used in this study is applied as a top coat.
