STP558

    Corrosion Tests in the Gulf Floor

    Published: Jan 1974


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    Abstract

    Because of the importance of good corrosion control to the safe operation of offshore pipelines, a test program was started in 1966 to study the behavior of pipeline materials in and near the ocean bottom in waters of pipeline depth (50 to 500 ft). This program has included the study of the corrosion of pipeline steels in and near the ocean bottom, the cathodic protection required to control this corrosion, and the performance of coating, paint, and anode systems in and near bottom sediments of the Gulf of Mexico.

    Results to date have shown that the corrosion of separate, buried steel panels and the cathodic protection current densities required to control this corrosion are less than in the ocean immediately above the mudline. The corrosion rate of unprotected steel panels exposed to seawater above the mud is as high as 11 mpy (mils per year) depending on the time and location of exposure. Unprotected panels below the mudline, however, corrode at rates of 1 to 3 mpy. Pitting corrosion of these panels is also more intense in the water above the mud than buried in the mud. The current density required to reduce the corrosion rate of these panels to less than 1 mpy is in excess of 3.2 mA/ft2 above the mudline; below the mudline a current density of 0.6 to 2.5 mA/ft2 is required to reduce the cor- rosion rate to the same level. The current density required to control corrosion decreases with increasing depth of burial below the mudline. The corrosion rates of electrically connected pipe lengths partially buried in the mud are inde- pendent of position relative to the mudline. A large amount of calcareous deposit was formed on zinc metal when it was made electrically negative for 10.5 months in seawater.

    Keywords:

    corrosion, cathodic protection, offshore, ocean bottom, marine pipelines, current density, materials behavior


    Author Information:

    Di Gregorio, JS
    Chemist and supervisor, Shell Development Company, Pipeline Research and Development Laboratory, Houston, Tex.

    Fraser, JP
    Chemist and supervisor, Shell Development Company, Pipeline Research and Development Laboratory, Houston, Tex.


    Paper ID: STP32164S

    Committee/Subcommittee: G01.09

    DOI: 10.1520/STP32164S


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