610 BELL SYSTEM TECHNLCAL JOURNAL 



It will be seen that of the two variables, soil character and alloy 

 composition, the former is decidedly the more important in its effect 

 upon rate of corrosion. From an inspection of the data it would 

 appear that there is no definite trend of corrodibility which may be 

 correlated with composition. From a statistical analysis of the data 

 obtained in this test it was concluded that variations in alloy compo- 

 sition within the scope of the test had no significant effect upon the 

 corrosion behavior of the materials. In other words, the variations 

 observed may be ascribed to chance and there is no indication of a 

 significant difference in the rates of corrosion of lead and lead-antimony 

 alloys when buried directly in the earth. 



Corrosion of Cables in Conduit 



The conduit mainly employed in the underground cable plant of 

 the Bell System is a good grade of vitrified clay with glazed surfaces. 

 Creosoted wood is widely used, particularly for single subsidiary cables. 

 Wood has been employed extensively for main cables on the Pacific 

 Coast where it offered an economical advantage. Steel or iron pipes 

 find a limited application for certain special cases such as dips and 

 relatively sharp bends. Heavy paper or fibre generally embedded in 

 concrete has been used in a few instances. Concrete conduit has been 

 employed by the utilities for power cables and in the telephone field to 

 some extent abroad -^ but the danger of corrosion has militated against 

 its adoption by the Bell System. It is possible that the greater heat 

 dissipation of power cables as compared with telephone cables renders 

 concrete conduit less hazardous for power cable use. 



The environment to which underground cables in conduit are ex- 

 posed is complex and varied. It is impossible to exclude moisture and 

 soil air or vapors from the conduit. Surface waters may enter the 

 cable compartments by way of the manholes and soil waters may seep 

 through at duct joints or at small fissures which sometimes develop. 

 The soil atmosphere tends toward higher concentrations of carbon 

 dioxide and lower oxygen than the outside air; it is often high in 

 humidity resulting in the condensation of drops of moisture on the 

 sheathing. Acetic acid vapors arising from wood conduit or other 

 sources may contaminate the duct air. Muddy soil waters may 

 deposit a layer of silt on the sheathing. These waters contain varying 

 amounts of salts, acids or alkalies. Free lime leached from concrete 

 structures or caustic alkali produced, as indicated in the following 

 paragraph, by the electrolysis of sodium chloride are the principal 

 alkaline constituents. Even leakage from sewers is sometimes a con- 

 taminating influence which induces corrosion. 



