TABLE 3 -DESIGN CRITERIA FOR CATHODIC PROTECTION SYSTEMS 



Production 

 Area 



Environmental Factors* 



Water 



Resistivity 



(ohm-cm) 



Water 

 Temperature 



(° c) 



Turbulence 



Factor 



(Wave 



Action) 



Lateral 

 Water 

 Flow 



Typical 



Design 



Current 



Density 



(mA/ft2) 



Gulf of Mexico 

 U.S. West Coast 

 Cook Inlet 

 North Sea 

 Persian Gulf 

 Indonesia 



20 

 24 

 50 

 26 

 15 

 19 



22 

 15 

 2 

 12 

 30 

 24 



Moderate 



Moderate 



Low 



High 



Moderate 



Moderate 



Moderate 



Low 



High 



Moderate 



Low 



Moderate 



5-6 

 7-8 

 35-40 

 8-15 

 7-10 

 5-6 



^Typical values and ratings based on average conditions, remote from 

 river discharge. 



A 4000-ft steel cold water pipe will be difficult and costly to protect 

 and maintain. The pipe is not a replaceable item and will require cathodic 

 protection during its service life. Anode weight will probably preclude a 

 sacrificial anode system and require the use of impressed current. However, 

 problems such as repair depth and high internal resistance drops in long 

 anode leads will require special design to minimize maintenance require- 

 ments and guarantee adequate protection. ' The number, type, current 

 capacity, and location of exterior anodes on either modules or the cold 

 water pipe will depend greatly on the physical configurations of each 

 component. Shape will strongly influence current and potential distribu- 

 tion from the anodes.-*^ 



In the OTEC application, the proposed aluminum heat exchangers will 

 be anodic to both steel and bronze components in the pump housing and 

 impeller. Additionally, copper ions from the freely corroding bronze will 

 deposit on less noble heat-exchanger surfaces and cause accelerated attack 

 of the aluminum by the heavy-metal ion displacement effect. It is impera- 

 tive that these thin-walled heat-exchanger tubes not be subjected to any 

 galvanic attack. The galvanic relationships would be reversed if titanium 

 heat exchangers were used; steel components would be anodic and would 



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