relationship between the DC resistance changes and the performance of 

 coatings. Anderton and Brown''' more recently had suggested a performance 

 qualification based on such a relationship, which would require that three 

 coated panels maintain resistances above 10'' ohms during 1 year of seawater 

 immersion. 



In Table 6 the various coating systems for which performance data in 

 Port Hueneme Harbor are available are rearranged in the order of performance 

 of the coatings. As pointed out earlier, all of the systems performed well and 

 the relative protection ranking may not be too meaningful. 



The changes in electrical properties do not correlate with these high 

 estimated protection rankings. Four of the five systems which seem to be 

 best in their performance show low AC and DC resistances after 1 year of 

 exposure on small panels immersed in seawater at 25°C. 



The above results would appear to cast some doubts on the validity 

 of a qualification requirement for coatings proposed for the Royal Canadian 

 Navy, which requires the maintenance of a minimum DC electrical resistance. 

 The results do not disprove the usefulness of such a test because the coatings 

 that passed the test, by maintaining a resistance above 10' ohms for each of 

 three panels, did perform well. But if this test is useful in passing only coatings 

 that perform well, it has the drawback that it would also reject many coatings 

 of superior performance. 



A number of claims have been made that the AC electrical properties 

 of coatings, or the changes in these properties, are related to the performance 

 of the coatings under atmospheric exposure. Changes in capacitance have been 

 used as indication of performance,^ and it has been claimed that capacitance 

 changes^" or the values of dissipation factors at various frequencies^- ' could 

 be used to predict performance. 



In Table 7 the coating systems are arranged according to the performance 

 of unscribed panels in a marine atmosphere at Kwajalein. The first two systems 

 had not yet failed and their performance is estimated; all other systems had been 

 exposed sufficiently long to produce coating failure. When the coatings are thus 

 arranged, the electrical changes, including strong initial changes in and low final 

 values of the resistances, are somewhat randomly distributed. Coatings of higher 

 protection rankings as well as lower protection rankings show the strong initial 

 changes associated with water uptake and low final resistances. 



In Table 8 the coatings are arranged according to the performance of 

 scribed panels in marine atmospheric exposure at Kwajalein. Again, there is 

 limited correlation between changes in electrical properties and the protection 

 rankings of the coatings. 



Visual inspection of Tables 7 and 8 thus showed no definite relationships 

 between the protection rankings of the coating systems and major changes in 

 electrical resistance. However, a mathematical comparison of the electrical 

 properties with the protection rankings showed better correlations (see Table 9). 



