2. Protective Coatings for Steel Piling 



Protective coatings on steel piling are intended to act as a 

 barrier to separate the steel surface from its corrosive environment. 

 The development of suitable coatings for long-term protection of steel 

 in seawater has been quite slow. Coating systems which appear to be 

 worthwhile for protecting steel piling are, in general, rather new, and 

 long-range test data are not available for many of them. However, test 

 results located are presented. 



There are numerous types of coatings now in existence, many of which 

 are used in combination with other types as well as alone. References 

 to combination coating systems in this report will be made in terms of 

 the basic type of topcoat material. 



Most of the test results on coatings contained in this report were 

 obtained from tests carried out by the U. S. Naval Civil Engineering 

 Laboratory. They have apparently done most of the testing of coatings 

 suitable for steel piling. 



Some of the coating data presented resulted from testing coatings on 

 mooring buoys and panels. Although the performance of coatings on mooring 

 buoys may be similar to their performance on steel piling, this is not 

 necessarily so. It is felt, however, that the performance of coatings on 

 buoys relative to each other will be applicable for steel piling. Test 

 results for coatings on steel panels are presented since very few tests 

 have been made on steel piles. Any coating which fails on a steel panel 

 should not be expected to protect a steel pile. In addition, coatings 

 which perform well on panels should at least be considered good prospects 

 for steel pile protection. Metallic coatings especially may be adversely 

 affected by electrical currents caused by the pile passing through dif- 

 fering environments that may not exist in tests of panels. 



Types of coatings in use today may be divided into a number of cate- 

 gories, two of which are metallic and nonmetallic. Some useful test 

 information has been discovered on coatings and is presented under these 

 two classifications. Since surface preparation is an important factor 

 when coating steel for marine exposure, information thereon has been 

 included under this heading. 



The nonmetallic coatings may be further divided into organic and 

 inorganic types. 



a. Metallic Coatings . Several investigations have been m.ade to 

 determine the corrosion protection ability of metallic coatings on steel 

 piling. The metals involved were flame-sprayed zinc and flame-sprayed 

 aluminum. These metallic coatings have also been used in combination 

 with other coatings, 



(l) Flame-Sprayed Zinc . The U. S. Naval Engineering Labora- 

 tory has tested flame-sprayed zinc on steel piling (Alumbaugh, 1962 ). 



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