An appreciable amount of corrosion was found to exist on the lead sheaths of underground power cables where these cables were located in concrete tunnels. The corrosion occurred at several locations in a metropolitan city where the lead sheathed cables were installed in continuous, precast concrete ducts and in ducts of other non-metallic materials encased in concrete and placed in concrete tunnels under waterways. Tests indicated that the corrosion on the lead sheathed cables was caused by calcium hydroxide from incompletely cured concrete.
Typical chemical analyses are shown of water from the continuous ducts. The sheath voltages and water conditions under which these cables operated are given and the methods employed to reduce the concentrations of calcium hydroxide in the continuous ducts are described. The pH values and concentrations of calcium hydroxide are shown for the water in the conduits in two tunnels prior to, and after corrective measures were taken.
The methods now used by this company to cure concrete in tunnels before lead sheathed power cables are installed are described. A brief description is given of the prelubrication of continuous tunnel ducts before pulling in large cables. Corrosion is reduced by the application of pulling grease to the cables at the time of installation.
