Pipe corrosion. (Photo: kittisak/Adobe Stock)
A typical failure mode of steel or cast iron water pipes is a result of corrosion. A common cause of corrosion-related failure is electric current traveling through the pipe and discharging. Figure 1 is a diagram showing how electric current traveling along a steel pipe causes localized corrosion. How does electric current find its way into a water pipe?
Figure 1. It is not unusual for a variety of electrical equipment to be connected to steel piping, assuming it is at ground potential — i.e., zero volts — often called earth. Induced current from nearby electrical equipment — including electric transit systems, cathodic protection systems and welding equipment — is one of the sources of current flowing through steel piping, and is often called stray current. When conductive soil conditions are encountered by the pipe, the current can leave the pipe and flow to a lower potential. This is called the point of discharge where the corrosion occurs.
Figure 2. (Photo: C. Roberts) Want to continue reading?
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