Recall that corrosion is an electrical release of energy in the form of electrons and d.c. current
from a metal surface when it is in contact with soil. If an insulating barrier can be applied to
block the flow of electrons along a metal surface, then the corrosion process can be stopped. It
acts as a resistor to reduce the flow of electric current from a metal surface to the earth. This
property of a material being a barrier to the flow of electrons along a metal surface or electric
current from the surface into the earth is called its "dielectric strength."
All metals have a unique voltage stored within them that is related to the amount of energy used to
create them. When two different metals such as copper and steel are connected together in the earth,
the voltage difference between them will cause an electric current to flow through the earth from
the metal with the higher voltage to the metal with a lower voltage. At the same time electrons flow
on the metal from the steel to the copper. This is called a "bimetallic or dissimilar metal
In order to prevent copper piping from corroding steel pipe or tanks, dielectric unions are inserted
between them to separate and to electrically isolate the copper pipe from the steel pipe or tank.
Dielectric unions are the perfect solution for breaking the connection between the two metals.
Underground steel propane tanks and steel piping must be electrically isolated from the buried
copper water piping to the water heater and the copper electric grounds at homes and businesses.
Unions are easily installed at the connection between a copper pipe and a steel pipe and near a
regulator or gas meter..