Section VIII. CONCLUSIONS 



The corrosion rate of steel piling in seawater varies considerably 

 depending on water conditions and the zone of exposure on a given pile. 

 According to information from various reports, the loss of steel thick- 

 ness in seawater may vary from no loss to as much as 373 mils per year. 

 The higher rate occurred where sand abrasion was present in steel sheet 

 pile groins. The corrosion rate of bare steel submerged in normal sea- 

 water is generally considered to be 5 mils per year. 



Since corrosion rates of steel piling may vary widely in seawater, 

 the estimation of corrosion rates should be guided by test data from 

 structures having as nearly as possible the same exposure conditions as 

 the proposed structure. This survey indicates that more pile corrosion 

 test data are needed for estimating corrosion rates, especially in colder 

 waters . 



Considerable progress is being made in the development of coatings 

 capable of protecting steel piling in seawater. Partially completed 

 tests indicate that such coatings as saran, phenolic mastic, coal-tar 

 epoxy, epoxy, flame-sprayed aluminum coatings, and flame-sprayed zinc 

 coatings topcoated with saran, vinyl, epoxy or furan, may effectively 

 protect steel piling in seawater for 15 or more years provided severe 

 conditions such as sand abrasion are not involved. Where sand abrasion 

 exists, incomplete tests indicate that phenolic mastic and coal-tar epoxy 

 coating systems, and possibly others, may approach 10 years of effective 

 protection for steel in seawater. Coating systems consisting of flame- 

 sprayed zinc topcoated with saran or vinyl appear to be two of the most 

 effective coatings for steel tested to date. 



Surface preparation of steel is very important when coatings are to 

 be applied for seawater exposure. Blasting the surface with abrasive 

 material and pickling are the generally accepted methods of surface 

 preparation. Commercial blasting is considered adequate for many coat- 

 ings. When better blasted surfaces are required, near white or white 

 blasting of the steel is specified. 



Cathodic protection systems, properly designed, and maintained are 

 very effective in preventing the corrosion of steel immersed in seawater. 

 Cathodic protection is often used in combination with protective coatings, 

 the coatings protect the unsubmerged portion of the steel and reduce the 

 area of submerged steel requiring cathodic protection. 



Properly designed concrete jackets are reported to be very effective 

 in protecting steel from corrosion by seawater, however, there is appar- 

 ently very little data available for accurate evaluation. 



There appears to be a great need for data to develop the initial 

 cost, and cost per year of protection, for various corrosion protection 

 methods. Such information is needed to determine the most economical 

 protection system for a given structure. 



48 



