inside the steel pipe on wliich tine zinc anode had been cast and were 

 silver-soldered to the pipe (Figure 8). Thus, the control heads were 

 bypassed in the circuitry and served merely as securing brackets. The 

 connections were wrapped with electrical tape, and the buoy was returned 

 to the water, 



The nnagnesium anode on each of the four concrete sinker blocks 

 was similarly replaced with a zinc anode. The magnesium anode and the 

 two ends of the remote ground cables that were severed at the control head 

 were brought to the surface by a diver. The two ends were silver-soldered 

 into the pipe on which the zinc anode had been cast. This unit was then 

 lowered to the sinker block and secured in place. 



Performance. Immediately after installation of the zinc anodes on 

 the buoy and sinker blocks, the buoy potential was -865 mv, while halfway 

 down the riser-chain the potential was -830 mv and that on the ground ring 

 was -780 mv. The potential on each of the four A-links, which were near the 

 ground ring, to which the remote ground cables were connected was also 

 -780 mv. This immediate increase in potential over that previously imparted 

 by the magnesium anodes indicates that the control heads used on the original 

 system had not permitted the greater driving force produced by the magnesium 

 anodes (potentials of -1 ,450 mv were measured on the steel pipes supporting 

 the magnesium anodes) to reach the buoy and ground tackle. 



Three months after the zinc anodes were installed in the cathodic 

 protection system, a potential profile was made of the mooring complex. 

 The values received are listed in Table 2, and they indicate that the buoy 

 was receiving full protection, the riser-chain moderate protection, but the 

 round legs insufficient protection. The potential of the control buoy at this 

 time was -710 mv, while that of its ground ring was -715 mv and that of the 

 ground legs averaged -660 mv. 



Four months later, the complete mooring was picked up to determine 

 its condition, and tests were made to determine the reasons for the inadequate 

 protection of the ground legs. Before pickup, the buoy had a potential of 

 -830 mv. The underwater portion of the buoy was covered with heavy 

 fouling. There was no fouling on the zinc anodes, but they were covered with 

 a loose, yellow film that was easily removed by high-pressure hosing. The 

 underlying metal was bright and crystalline in appearance, giving no indication 

 of passivation. The square of bare steel on the underwater portion of the buoy 

 was free of corrosion. The coating on the entire riser-chain was in good condi- 

 tion, and no corrosion was in evidence. The ground ring and the adjacent links 

 on the ground legs were also free of corrosion. In contrast, the square of bare 

 steel on the control buoy was pitting, and almost all of the coating had been 

 lost from the riser-chain, which was corroding badly. 



11 



