Under these circumstances, cathodic current is increased and the casing is sacrificed as well. Casing filler prevents this from occurring. Further, in some instances, the pipe may be shorted to the casing through a direct metal-to-metal contact and filling the casing might correct this condition on some occasions. In any case, it is difficult, if not impossible to cathodically protect pipe in casing, so that filling of the casing will protect the pipe from corrosion regardless of the circumstances.
Water or water vapor is present in most pipeline casings making possible galvanic corrosion of the carrier pipe. Also, a “water short” can occur through the water in the casing, allowing cathodic current to flow through the water and on to the pipe in the casing.