In the case of conforming sheathing, it is possible to seal the joints 

 at the top and bottom by ?/elding. However, thero is a question as to 

 whether this ser.ling is actually required. It v/o-old be expected that 

 even if these joints -ere left open the first water to seep between the 

 sheathing and the steel ivould soon form sufficient rust to occupy the 

 space and thus prevent access of any additional water or oxygen to cause 

 furth.er corrosion. The danger of corrosion here can be reduced consider- 

 ably by applying a coat of coal tar enamel to the piling or the sheathing 

 just before the latter is applied and vrithout letting the coating dry 

 before the sheathing is put into place. 



Some tubular piles have been sheathed experimentally with light gauge 

 Monel sheets held in place only by Monel bands applied in the same manner 

 as box strapping. Other Monel sheaths have been applied by the use of 

 wire bands. 



Monel is a logical choice for this sheathing because it demonstrates ex- 

 cellent resistance to corrosion under these conditions of exposure, Monel 

 sheathing has been applied to tubular sectj.ons in offshore drilling struc- 

 tures-"-. The presence of numerous cross braces in the region to which the 

 sheathing had to be applied coinplicated this operation, For this reason, 

 it viTould be desirable, if at all possible, to design braced structures 

 so that the bracing would either he below half tide level '.'here it could 

 be protected by cathodic currents, or above the splash zone where paints 

 could be applied readily, '. ■ ■ • ' 



It has been discovered that the cathodic polarization characteristics of 

 Konel as compared with steel in the tidal zone are such that the cathodic 

 protection of the associated steel is accomplished more readily with Monel 

 in the tidal zone than if the tidal zone were left as bare steel. lieasure- 

 ments of the galvanic current bet::een steel bolov; low tide and Monel in 

 the tidal zone as co:vpared .lith steel below lov: tide and steel in the 

 tidal zone have shovm less galvanic effect of the llonel than the differ- 

 ential aeration cell effect betvreen steel and steel. 



In applying Vonel sheathing in connection with cathodic protection as is 

 recommended, the sheathing should start at about half tide level and extend 

 through the splash zone where the periodic renewal of organic coatings 

 would be very difficult, if not impractical. 



Some attention is being given the use of metal protection in the form of 

 sprayed metal coatings applied to previously sandblasted surfaces. Of 

 the two metals proposed for this service, zinc seems to be preferred over 

 aluminum, 'Ihe applied thickness should be from 10 to iS mils and the 

 sprayed nietal should be su-^plemented by a plastic sealer in the form of 

 a chlorinated rubber vehicle carrying a very small amount of pigment. 

 Presumably the sprayed metal need be applied only above half tide level, 

 since cathodic protection will take care of the lower surfaces. 



If. L, LaQue, "Protection of Steel in Off-Shore Structures," DRILLING, 

 June 1950« 



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