INTRODUCTION 



The Naval Civil Engineering Laboratory (NCEL) investigates and 

 evaluates new coatings for the Naval Facilities Engineering Command and 

 conducts research related thereto. The evaluation of the performance of 

 such coatings under conditions similar to those encountered in actual service 

 requires considerable time, especially if the coatings have long service lives. 

 There is thus a strong need for reliable accelerated test methods. 



Many accelerated tests have been described in the literature.^ However, 

 all the tests described appear to be of limited usefulness. Some tests show 

 limited correlation for very specific applications. Others were found suitable 

 for comparing two or three coatings without much being known about their 

 general applicability. 



Accelerated tests may be useful in the prediction of performance 

 related to surface effects, such as chalking, fading, or loss of gloss. Thus, 

 accelerated weathering machines are often claimed to give useful information 

 about surface changes caused by aging. ^ No accelerated tests are known that 

 are useful in reliably assessing the long-term protection or corrosion resistance 

 of coatings. One method that showed some promise of being useful is the 

 assessment of potential performance by electrical measurements on coatings.*^ 



Several authors have suggested that electrical measurements on coatings 

 immersed in an electrolyte can be used to predict coating performance.^' ''° 

 Organic coatings with good film integrity are good insulators and have electrical 

 properties associated with good insulators, whereas coatings that have lost their 

 film integrity have lost these electrical properties. It has been found that such 

 changes in electrical properties can be detected much sooner than visual changes 

 and that they can therefore be used to predict performance. However, no 

 published papers really show good correlation of these changes in electrical 

 properties with performance for any large number of coatings, and the validity 

 of any such correlation has not really been demonstrated. Further investiga- 

 tions of some of the electrical methods, including measurements of DC resistance 

 and of various AC properties such as capacitance, resistance, and dissipation 

 factor, are needed to determine their validity as accelerated tests. 



The results of AC electrical measurements with five coating systems on 

 steel panels immersed in seawater have been reported.'"'' The systems chosen 

 for the NCEL initial study were of widely different performance in seawater. 



