Pumps . Generally, moving parts are difficult to protect because metals 

 in moving systems are usually galvanically active due to increased diffu- 

 sion of oxygen and removal of protective layers which would otherwise pre- 

 vent local cell corrosion currents. However, in one centrifugal pump 

 design, the impeller is coated with a neoprene coating. '^' This should 

 reduce galvanic currents as well as reduce cavitation erosion of the 

 blades. This type of coating is recommended for either a steel or titanium 

 blade. Other moving parts must also be coated wherever possible to prevent 

 production of excessive galvanic currents. The Navy has developed a neo- 

 prene coating which is listed in Table 4. The nonmoving parts of the pumps 

 that are exposed to seawater also can be protected with the same coatings. 



Housing . The housing will be moored at sea for periods up to 10 yr and 

 therefore will require high-performance anticorrosive coatings, such as 

 epoxies, for all steel parts. '^^''^^ Cathodic protection is also neces- 

 sary. ' ' Light metals, such as aluminum parts, fixed to the platform 

 must be protected with bot>> a proper coating and a cathodic protection 

 system. ^2 Corrosion potential electrodes and probes should be located on 

 critical metal structural stomponents and should be checked by periodic 



CO 



underwater inspection.-^-* 



The power modules that can be detached and towed back to a repair 

 station every 2 yr will be protected adequately by procedures well known 

 to the marine construction and ship maintenance industry .^^'-""^ These will 

 not be given in detail, but can be found elsewhere. ' 



Summary 



Two-component anticorrosion paints are recommended in lieu of one- 

 component paint, although vinyl and chlorinated rubber are .suitable single- 

 component coatings. The two-component paints highly recommended are poly- 

 amide epoxy and coal tar epoxy. The former is a universal coating, and 

 the latter is suitable for areas of high cathodic potential. Zinc-rich 

 paints are also suitable as preconstruction primers. 



In selecting anticorrosion paints, an extremely important factor is 

 the compatibility of the paints with other paints in the system, i.e.. 



22 



