What is required to be installed where dissimilar piping materials are joined?

When different types of piping materials are joined in a plumbing or sprinkler system, it is crucial to use a dielectric fitting. This is because dissimilar metals can create a galvanic reaction when they are connected, which can lead to corrosion and deterioration of the pipe material over time. Dielectric fittings are specifically designed to prevent this type of corrosion by electrically insulating the two different materials from each other.

They typically consist of a non-metallic insulating material that separates the metals, allowing for a secure and safe connection while maintaining the integrity of both pipe materials. This prevents any unwanted electrical connections that could lead to accelerated wear or failure in the piping system.

The other options would not effectively address the specific issue of corrosion between dissimilar metals. A manual shut-off valve and a pressure relief valve serve different purposes related to flow control and pressure regulation, while expansion joints are used to absorb movement and thermal expansion in piping systems, not to mitigate corrosion. Thus, choosing a dielectric fitting for connecting dissimilar piping materials is essential for ensuring long-term reliability and safety in the system.