Stray Current Corrosion
Definition - What does Stray Current Corrosion mean?
The stray currents responsible for this corrosion come from DC distribution lines, railway systems, substations, and alternating current, among other sources. These currents then flow through steel structures or piping systems, causing corrosion.
Stray current corrosion can be compared to the galvanic corrosion, where the current is internally generated, although different remedial measures may be taken. Also similar are the chemical and electrical reactions at the electrolyte and the metal interfaces. The anode is taken to be the metal that corrodes, where current flows to the cathode.
Corrosionpedia explains Stray Current Corrosion
The most common factors that favor stray current corrosion include:
· High electrical resistance found on running rails
· Poor installation of the running rails from the earth
· The widely spaced substations that that cause voltage drops on the rails
The corrosion may be rapid where the current produced by the galvanic cells are less than the stray current. When current leaves the metal to flow to the electrolyte medium, the part where the current leaves undergoes severe corrosion. Some metals like aluminum can be destroyed very fast.
For instance, a boat can act as a good ground for DC currents because of its low resistance compared to the current flowing all the way from the leaking boat through the water medium to the ground. Corrosion will be severe at the point where the current leaves the boat and travels to the ground.
The stray currents may be either external or internal, with the internal ones causing electric shorts in the wiring system of the boat. The external sources are mainly the shore power connections, where a leaking boat will corrode other boats on the same shore. This only happens when the other boats have better grounds compared to the one on the faulty boat.
Stray current corrosion is prevented through the use of a galvanic insulator. Modern measures include decreasing the electrical resistance, especially for the rail return circuit, and increasing of the electrical resistance between the ground and the rails. One safety regulation that can be applied is that a three-wire cable which should be used to carry the shore power from the boat. One lead grounds all the other electrical equipment, thus reducing shock from the boats.