Some proprietary vinyl systems are available which perform just as well. 



To date no other epoxies have shown performance equal to the systems listed. 



Surface Preparation 



Steel . The most satisfactory method of preparing the steel surface for 

 painting is abrasive blasting, ' which removes all rust, mill scale, 

 and foreign matter. Grains of abrasive hitting the surface provide a 

 beneficial surface work hardening and produce no known detrimental metal- 

 lurgical changes. The resultant surface profile of 2 to 4 mils gives a 

 "tooth" to which the coating adheres. In the present environment of strict 

 pollution control, open blasting may soon be restricted to the use of non- 

 siliceous abrasive. If open blasting is forbidden, then parts must be 

 (shot) blasted in shops during the fabrication stage. For OTEC, both 

 methods are recommended. It may be feasible to use a nonblast method of 

 surface preparation, but this should be thoroughly evaluated before it is 

 specified. 



Aluminum . Aluminum also is prepared for painting by abrasive blasting. 

 The ideal abrasive is aluminum oxide, which is very expensive. Substitute 

 abrasives may be used provided that surface cleanliness and suitable pro- 

 files are maintained. The recommended profile after blasting is 1 to 2 

 mils. Aluminum must be painted within 24 hr of blasting. The blasting 

 surface must be protected from moisture and foreign matter during this 

 period. 



Recommended Practice for OTEC Plants 



Warm or Cold Water System . The warm or cold water system can rely on both 

 types of anticorrosion coating systems, depending on the length of corro- 

 sion protection desired. Areas which are inaccessible to renewal for 

 periods greater than 5 yr will be best presevred with a combination of 

 cathodic protection and coal tar epoxy coatings. For parts which can be 

 brought in for overhauls more frequently, standard single-part anticorro- 

 sive coatings in combination with impressed current will provide adequate 

 preservation. 



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