What can occur when black steel pipe is extended with copper pipe?

When black steel pipe is extended with copper pipe, a galvanic reaction can occur due to the different metal compositions involved. When two dissimilar metals are connected in the presence of an electrolyte (like water), galvanic corrosion can happen. In this case, the black steel pipe, which is iron-based, and the copper pipe present a scenario for corrosion to take place. The steel pipe can corrode at the junction because the copper pipe acts as a cathode, while the steel acts as an anode, leading to accelerated rusting of the steel.

Understanding galvanic action is crucial in plumbing and piping applications to prevent premature failure of materials. This is particularly important in systems involving water, where moisture can easily facilitate the galvanic reaction. Using appropriate fittings or dielectric unions can help mitigate this issue by electrically isolating the two types of metal, thereby preventing corrosion at the connection.