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CATHODIC PROTECTION FIGURE 3
Results of the three-dimensional modeling of the (a) ship repair dock and (b) bay dock. FIGURE 4
Results of the three-dimensional modeling of a section of the two parallel sheet piling sections in the cofferdam area.
The Sheet Piling Dock sheet pilings are usually exposed
to three different media: 1) the bottom of the sheet piling is immersed in the under- water soil, 2) the middle part is exposed to water on one side and soil on the other side, and 3) the top part is exposed to the air. This exposure to different media can cause potential gradients that can pro- mote corrosion processes on the structure. The Madero Maritime Terminal has a steel sheet piling divided into three zones: 1) the bay dock, 2) the dry dock, and 3) the ship repair dock. Altogether, the piling comprises an area of 30,085 m2 which means that 60,170 m2
, of metallic
structure have to be protected against corrosion. Nevertheless, only 8% (4,606
NACE International, Vol. 51, No. 3
Sheet Piling Protection To stop the generalized corrosion of the sheet piling, an impressed current CP
) of the sheet piling surface is protected by CP systems. Figure 2 shows the three areas where the sheet piling is located. Physicochemical analysis of the water
m2
showed a high concentration of chlorine (16,000 ppm). This has caused a general metal thickness loss of >25% due to corro- sion on the unprotected face of the sheet piling, which is in contact with soil. In ad- dition, 300 corrosion pits were discovered, some of which have penetrated through the steel sheets. Crevice corrosion was also present in almost every joint between the steel sheets forming the sheet piling.
(ICCP) system using distributed semi- deep anodes was proposed. Current de- mand measurements were performed showing that ~0.48 A/linear meter of sheet piling was needed, meaning a total of 614 A. In addition, a three-dimensional model of the sheet piling and its surround- ing media was constructed using the boundary elements method. The opti- mum distribution of the anodes was de- termined using the simulations. Figure 3 shows, in a color scale, the potential dis- tribution calculated with the numerical modeling. The sheet piling is supported with
anchors and steel beams buried behind it. The area known as the cofferdam is a corridor with two parallel sheet piling sections attached to each other by steel beams (Figure 4). By modeling this struc- ture, it was possible to propose the instal- lation of anodes between the sheet piling sections to protect both structures and the anchor beams.
The Dolphin
The dolphin is a steel-reinforced con- crete structure supported by 50 steel piles. The piles are 18-m long, with 8 m im- mersed in water and the remainder bur- ied under the river base soil. The two different views in Figure 5 show the dis- tribution of the dolphin's piles. The steel piles are exposed to corro- sion risks. The total metallic surface of the piles is 1,866 m2
; 829 m2 are exposed to March 2012 MATERIALS PERFORMANCE 33