How do you prevent corrosion of pipelines underground?
(Q&A by Tim Skelly)

There is natural electricity in the ground. Electricity travels somewhat like water; both take the easiest path possible. As electricity travels in the ground it may come across a pipeline and "jump" onto it until another easier path is found. When another path is found, it "jumps off." When it jumps off, it takes with it ions from the line. Over time as ions are pulled off, the pipeline eventually wears out and breaks.

To fix this problem there must be electricity on the line all the time or there must be a man-made path so that when the electricity jumps off it corrodes something else besides the pipe. Corrosion technicians are people who mathematically calculate how to solve the problem. The most popular way is by connecting anodes (positive electrodes) to the pipeline by wire. As the electricity travels on the pipe, it will jump off with ions from the anode instead of ions from the pipe. This will corrode the anode but the pipe is saved. This may sound easy but sometimes it will take hours to figure out not just how many anodes must go on the pipeline but where. The location of these anodes are quite important. The number of anodes depends on the soil type.

In the city areas, anodes are unable to be used, so technicians use natural static electricity in the ground or else induced electricity. This allows the pipeline to remain safe and the hassle of digging up city streets is avoided. However, when a voltage reading is low, the technician must decide if he should proceed with digging or hold off on it. The source of the problem must first be found. Another pipe could be touching the problem pipeline. In this case an insulator is needed to separate them. The work of corrosion technicians results in few pipeline breaks.

"Basic Course," Appalachian Underground Corrosion Short Course, West Virginia University Copyright 1998.