How can you prevent a corrosive reaction when joining a copper pipe with a steel pipe?

To prevent a corrosive reaction when joining a copper pipe with a steel pipe, utilizing a dielectric union is the most effective approach. A dielectric union is specifically designed to separate the two different metals, which helps to prevent galvanic corrosion—a type of corrosion that occurs when two different metals are in electrical contact with each other in the presence of an electrolyte, such as moisture.

By using a dielectric union, you create an insulating barrier that prevents the electrical current required for galvanic corrosion to occur, thereby protecting both the copper and steel components from degradation. This is particularly important in plumbing and piping applications where metal pipes may come into direct contact with one another.

Other options, while potentially beneficial in certain contexts, do not address the fundamental issue of preventing corrosive reactions between two dissimilar metals. For instance, extra sealant and protective tape might provide some level of moisture barrier, but they do not eliminate the electrical connection between the copper and steel, which is the root cause of galvanic corrosion. Similarly, a coupling joint simply connects the two types of pipes without any method of preventing corrosion. Hence, the use of a dielectric union is key to ensuring a long-lasting, corrosion-free joint in this scenario.