Performance of Coating Systems 



The performance of the 13 coating systems under atmospheric 

 exposure at Kwajalein is indicated in Table 3. Each coating system was given 

 a protection ranking for performance on unscribed panels and for performance 

 on scribed panels. This protection ranking is approximately 1 times the 

 number of years of exposure required to produce failure of the coating system. 

 To provide comparative ratings among several coatings that failed at the same 

 time, the protection rankings were weighted on the basis of other performance 

 factors. For coating systems that had not yet failed at the time of the last 

 rating, an approximate protection ranking was assigned, which was obtained 

 by adding to 10 times the years of exposure additional points depending 

 on the condition of the coating at the last rating. These additional points 

 were about 10 for a protection rating of 8, 20 for a protection rating of 9, 

 and 40 for a protection rating of 10, but were varied somewhat depending 

 on other performance factors. Because of the lesser accuracy of these protection 

 rankings they are indicated by ~ in Table 3. 



Failure of a system was considered to have occurred when the overall 

 protection rating^"^ decreased to a value of 7. This rating was essentially the 

 same as the ASTM rusting rating, and failure was thus generally the point where 

 30% of the area had rusted. The degrees of blistering and of undercutting at 

 the time of failure are also shown in Table 3, A "greater than" sign (>) indicates 

 failure after the time specified; a "less than" sign (<) indicates failure before 

 the time specified. 



The performance of 1 1 of the systems immersed in Port Hueneme 

 Harbor is shown in Table 4. The systems had been exposed for varying periods 

 of time before the last rating inspection, as shown by the times during which 

 the systems had not failed. Only one of the systems. System 123, had actually 

 failed. Prbtection rankings are shown for each system, and these are again 

 approximately 1 times the number of years required for failure. For the 

 systems that had not failed, the protection rankings are based on the degree of 

 protection and blistering at the last rating, and also on the comparative deteri- 

 oration of the systems after 5 years of exposure. For systems still in perfect 

 condition after 6.5 years of exposure, up to 85 points were added. These quality 

 ratings are thus very approximate, because an extrapolation of the service life 

 to some 12 or 15 years is not valid. 



All systems performed well while immersed in seawater at 25°C on the 

 small panels used for the electrical measurements. Only one system. System 

 1 17, allowed appreciable rusting, even after 2 years. Three systems had a few 

 blisters after 2 years, and only two systems dense blisters. These Laboratory 

 immersion results are shown in Tables 5 through 8. 



35 



