protection unless it leads to coating erosion. Some discoloration, such 

 as yellowing or rust streaking, was evident on all systems. Systems 38 

 and 39 (nearest the ground) had the most discoloration; systems 16 and 

 23 (positioned in a more protected area) had the least. Rusting, ASTM 

 Type I (pinpoint), was found on 13 of the 32 systems. Showing the most 

 rusting were systems 38 and 39; while systems 11, 14, 17, 20, 21, 34, 

 35, 36, 37, 40, and 41 were slightly better. Systems 17, 20, and 21 

 exhibited peeling, and systems 11, 14, 17, and 20 exhibited cracking. 

 Wrinkling shows on systems 34 through 41. No blistering was observed on 

 any of the coating systems. 



LABORATORY SALT-SPRAY EXPOSURE OF COATING SYSTEMS 



Laboratory salt-spray testing (Method 6061 of Ref 2) is often used 

 as a relatively quick procedure for screening coatings for ability to 

 protect steel from corrosion. In such testing, coated panels are exposed 

 in an enclosed chamber in an atmosphere of 5% or 20% salt spray at a 

 temperature of approximately 95°F. 



The results of salt-spray exposure of systems 42 through 53 were 

 reported in Reference 1. Systems that provided above-average protection 

 in Phase 1, plus 25 additional coating systems, are discussed in this 

 section of this document. This group of coatings, then, form the basis 

 for selection of those coatings that could be used for field exposure on 

 vortex towers at PMTC. 



First Series 



Panel Preparation . Prerusted 6xl2-inch steel panels were cleaned 

 manually — first by wire-brushing and then by scrubbing in water with a 

 medium-hard bristle brush. The panels were then dipped in methyl ethyl 

 ketone (MEK) to remove water and allowed to dry. No desiccator large 

 enough to hold these panels was available, so they were placed overnight 

 in a slightly warm dry oven to prevent corrosion before use. One-half 

 of the cooled panels received a special surface treatment before coating 

 (see Table 2). This surface treatment consisted of brushing with the 

 same metal conditioner and rust converter used with systems 43, 45, and 

 47 in the initial study (Ref 1). All coatings were primed, using a 

 1-inch-wide brush. One-half of each set of treated and untreated panels 

 were machine-scribed to bare metal with an "X." This first series used 

 MIL-P-24441 (Formula 150) epoxy-polyamide primer and MIL-P-24441 (Formula 

 152) epoxy-polyamide topcoat as the coating system standard. Systems 

 10, 12, 13, 15, 16, 18, 19, 21, 34, 35, 36, 38, 40, and 41 (Ref 1) were 

 tested. The coated panels were placed in a 5% salt-spray cabinet and 

 rated periodically by the same rating system used in Reference 3. 



Results . The panels were left in the salt spray for 154 days 

 (Table 3) . At the end of this period all the scribed panels had discol- 

 ored from rusting and tuberculation in scribed areas. All systems 



