The results showed that there was appreciable correlation between the resistance 

 and capacitance values of the coatings and the deterioration which occurred. 

 Thus, the system with the lowest performance, an oil paint system, was the 

 first to show reduced resistance values. The best performing system, a saran 

 coating, had moderately high and very steady resistance values. The other 

 three coatings were intermediate both in performance and in the stability of the 

 resistance and capacitance values. 



The results of both AC electrical measurements and DC electrical 

 measurements of an additional seven coating systems similarly exposed have 

 also been reported.^ •^ Four of these systems showed good electrical properties 

 and very little deterioration in exposure tests. For two of the systems, the AC 

 and DC resistance dropped considerably during the tests, and these systems also 

 showed some deterioration in the tests. One of the seven systems was highly 

 conductive and its electrical properties therefore could not be used as an indi- 

 cation of performance. 



It was apparent from the above results that, in order to determine the 

 validity of the method, it would be necessary to conduct experiments with a 

 larger number of coatings for which the long-term performance was known. 

 Additional experiments were therefore performed with 1 3 coating systems 

 for which the long-term performance had been or was being determined by 

 NCEL under other work units. The results of these experiments are reported 

 and discussed below. 



EXPERIMENTAL METHODS AND RESULTS 



The coatings that were employed were applied to steel panels 2-3/4 

 inches wide and 5-7/8 inches high, which were made from 1/8-inch hot rolled 

 steel plate. The panels were sandblasted and the coating systems were applied 

 at thicknesses of approximately 10 mils (250 microns). Before the panels were 

 coated, handles made of 1/4-inch stainless steel strips were attached to the panels 

 with stainless steel machine screws. The coatings were applied with a spraying 

 machine to insure even coverage. The edges were carefully touched up during 

 the painting operation. After the painted panels had dried, the upper portions 

 of the panels were covered with an epoxy coating which extended down 1-3/8 

 inches from the top, and the other three edges were dipped 1/4-inch deep into 

 the same epoxy coating to further protect the edges. The top portions of the 

 panels were then brushed with molten ceresin and the edges were dipped 1/4-inch 

 deep into molten ceresin to further insulate the edges electrically from the 

 seawater and to reduce any edge effects in the AC measurements. The area of 

 the coating of the nominal thickness was thus approximately 5.6 cm by 10.6 cm 

 on each side for a total area of 120 cm^ on the two faces of the panels. Two of 

 the panels are shown in Figure 1 . 



