Zone 5 - Splash Zone 



The splash zone is where the ?,reatest attack v;ill occur unless protective 

 measures are taken. The extent of corrosion in this zone nay vary through 

 wide limits, dei-iending on the locality. Attack v/ill be frreatest v.'here 

 there is considerable wave action, and especially where breakers kick up 

 a great deal of corrosive spray. By and large, the means of protection 

 proposed for the tidal zone '.'ill also be best for the splash zone and for 

 the same reasons. The lorincipal difference will be that penetration of 

 soft coatings, such as coal tar enamels, by barnacles ■'.rill not be a pro- 

 blem. 



Practical tests, especially on offshore drilling structures , have sho^TO 

 that vinyl systems have particular merit for this service, Tlie steel 

 surfaces must be prepared carefully by sandblasting and the metal must 

 be dry when painted. The first coat should preferably be a washcoat 

 primer plus successive coats of vinyl paint so as to yield a total paint 

 film thiclmess of at least 6 mils, Tlie common pigments, such as red lead, 

 zinc chromate and iron oxide, have performed satisfactorily with the in- 

 hibitive pigments being preferred at least for the first coat over the 

 washcoat primer. 



Aluminum may be used as well as zinc as a sprayed coating above high tide 

 level. The thickness of either metal should be about 0,008 inch and the 

 metal spray should be supplemented by a coat of primer and tc'o top coats 

 of aluminum flake in a vinyl vehicle. 



Composition of Steel 



The composition of the steel used v^ill have no great effect on corrosion 

 or the facility of protection in the raud and up to half tide level. How- 

 ever, hj suitable alloying:, it is possible to effect considerable improve- 

 ment in the resistance of steel to corrosion in the upper part of the tidal 

 sone, and especially in the splash zone and above. The possible extent 

 of this improvement in corrosion resistance is indicated by results of 

 tests of steels exposed near the breakers at Kure Beach v/here the rate 

 of corrosion of a ^i nickel steel vras oal;v l/20 that of steel which con- 

 tained only 0.01,3 copper. It is not suggested that steel for this service 

 should contain as much as S)^ nickel - these data are included merely to 

 illustrate the extent of improvement that is oossible. Research is 

 currently underway with the object of developing steels of much lower alloy 

 content, e.g. 0.^/> - total made up of a combination of such elements as 

 nickel, copper and piosphorus which show promise of effecting considerable 

 improvement in corrosion resistance Y»'ith only a small increase in cost of 

 steel. Tiile this property will increase the life of the steel without 

 supplementary protection, it vfill be of particular value in increasing the 

 durability of organic coatings vfhich can be expected to shov/ improved 

 performance on the more corrosion resistant steels. 



^.i'. M. Thornton and M. L. Bilhartz, "Protection of Offshore Production 

 Equipment" - Paper presented at NACR Meeting, Galveston, March 1952. 



E - 9 



