Most pipeline cathodic protection applica-tions involve either galvanic anode or impressed current systems installed in earth for protection of external surfaces. Of the galvanic anode installations, most use magnesium as the anode material. Rectifiers are the most common source of direct current power for impressed current systems. For pipelines installed in the ocean bed (as for long harbor crossings and lines to offshore drilling operations), considerable use has been made of galvanic anode bracelets. These are essentially a ring of specially cast anodes encircling the pipe and attached directly to it. This permits having the anodes already attached to the pipe as it is laid. By doing so, the pipeline will be cathodically protected as soon as it becomes submerged. Used in conjunction with a good coating, sufficient anode material may be provided for long useful life. Zinc has been used most frequently for this type of installation.
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