After 1 year of immersion in aerated seawater at 25°C, 1 of the 1 3 

 systems showed essentially no rusting or blistering and were given ratings of 

 10 in both categories. System 1 17 received a rusting rating of 9 and a blistering 

 rating of 2F. All three panels of the latter system showed some small rusty 

 tubercules. Systems 1 12 and 1 19 showed small blisters and were given a rating 

 of 8M. After 2 years of immersion, the blistering ratings of Systems 1 12 and 

 1 19 changed to 6D and Systems 1 14 and 1 18 received blistering ratings of 8F. 

 All other ratings remained the same. 



The same coating systems used for the electrical measurements had 

 some years earlier been placed on 6 x 12-inch, and in some cases 12 x 14-inch, 

 panels and had been subjected to marine atmospheric environments at Port 

 Hueneme, Calif., Kaneohe, H. I., and Kwajalein, M. 1.''^ One-half of the panels 

 so exposed had been scribed and the others were unscribed. The performance 

 of the 13 systems under atmospheric exposure at Kwajalein is shown in Table 3. 



Other coated steel panels 4 inches wide and 10 feet long had been 

 exposed in the harbor at Port Hueneme.^^ These panels were so placed that 

 they were exposed in an atmospheric zone, in an intertidal zone, and in an 

 immersed zone. The performance of 11 of the 13 systems in the immersed 

 zone is shown in Table 4. 



DISCUSSION 



The majority of organic protective coatings are nonconductive. When 

 such an organic coating on a steel panel is immersed in seawater, the coating 

 provides a comparatively high electrical resistance. This resistance (R) is 

 related directly to the specific resistance (p) and to the coating thickness (t), 

 and it is inversely related to the area of the coating (A): 



^ " A 



At the same time, the coating is also a dielectric between two conductors, 

 one of which is the steel plate and the other the salt water. This system is thus 

 a capacitor whose capacitance (C) is proportional to the dielectric constant of 

 the coating (e) and to the area of the coating (A) and inversely proportional to 

 the coating thickness (t), as follows; 



C = 



eA 

 t 



30 



