An anode is the positively charged electrode of an electrolytic cell that attracts electrons or negative charge. In an electrolytic cell, it is the anode that gets attacked because it is the place where the current leaves the metal to enter the electrolyte.
Anodes corrode over time and when this electrochemical cell is created on metal pipes due to conditions favorable to corrosion such as moist earth, pits or tubercules are formed.
Corroded pipes can cause failure of the pipe but thanks to trenchless technology it is now possible to use remote video inspection to detect corrosion and use trenchless rehabilitation methods, such as mechanical spot repair, cured-in-place pipe (CIPP) and sliplining.
Trenchlesspedia Explains Anode
For a metal pipe buried in moist soil, small potentials are set up between the pipe surface and surrounding areas. This is similar to what happens in a battery. From the negatively charged areas, current flows into the electrolyte, which in the case of a buried pipe is the soil. The current flows to the positively charged area or the cathode and then travels back through the pipe, creating a circuit.
As this process takes place, the negatively charged area of the metal begins to dissolve creating what we observe as pits. Nothing happens at the positively charged area or the cathode, however; for a circuit to be created, a cathode is equally important. In some instances where pipes have to be buried in a medium that would assist corrosion, sacrificial anodes are used to create cathodic protection. The metal alloy used for the purpose has a more active voltage than the metal of the pipe it is protecting causing the sacrificial anode to corrode first.