When connecting copper to steel pipes, you should use Dielectric Unions. These fittings prevent electrolytic reactions that naturally occur when water come in to contact with two types of metal. The result of this reaction is a galvanic corrosion that over time will corrode the pipes. Look for a powdery, crumbling white powder that builds up on the connection of the pipes. Dielectric Unions have a non-conductive washer between the two side of the fitting which prevents the metals from reacting. Canarsee offers a a selection of Dielectric Unions that will protect your connection for a long time.