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09522 Long-Term Cathodic Protection Performance Data of Two off-Shore Structures

Product Number: 51300-09522-SG
ISBN: 09522 2009 CP
Author: Takashi Tsukada, David Scantlebury and Du Min
Publication Date: 2009
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Two marine steel structures which are both largely uncoated except for the splash zone and both fully submerged are described. Both are cathodically protected with Al/Zn/In sacrificial anodes,. They are a Japanese structure installed in 1973 and based on the DNV recommendations and a Chinese structure in 1996 according to the NACE recommendations. The cathodic protection systems of these structures have been extensively monitored, anode and structure potentials versus time, depth, anode output versus time, and these values are compared with the values from the codes of practice to see how the expected and real behaviour compare and contrast. It may be seen that the design criteria originally employed provided insufficient initial current density according to the standards but that the steady state design current density was very generous leading to a substantial over design of the structures. The cathodic protection system for the older structure is shown to be at its end of life in 2006 with the anodes almost fully consumed. Even so, the structure potential is still within the recommended protection potential criterion of -800mV Ag/AgCl/sea water.

Key words: Steel, Offshore, Marine, fully submerged, aluminium sacrificial anodes, cathodic protection, operating potentials, anode output, design life
Two marine steel structures which are both largely uncoated except for the splash zone and both fully submerged are described. Both are cathodically protected with Al/Zn/In sacrificial anodes,. They are a Japanese structure installed in 1973 and based on the DNV recommendations and a Chinese structure in 1996 according to the NACE recommendations. The cathodic protection systems of these structures have been extensively monitored, anode and structure potentials versus time, depth, anode output versus time, and these values are compared with the values from the codes of practice to see how the expected and real behaviour compare and contrast. It may be seen that the design criteria originally employed provided insufficient initial current density according to the standards but that the steady state design current density was very generous leading to a substantial over design of the structures. The cathodic protection system for the older structure is shown to be at its end of life in 2006 with the anodes almost fully consumed. Even so, the structure potential is still within the recommended protection potential criterion of -800mV Ag/AgCl/sea water.

Key words: Steel, Offshore, Marine, fully submerged, aluminium sacrificial anodes, cathodic protection, operating potentials, anode output, design life
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