Test caps plug are not recommended for use with which type of pipe?

Test caps plugs are not recommended for use with copper pipe primarily due to the characteristics of copper and the nature of testing practices. Copper is a softer metal that can be deformed or damaged when subjected to excessive pressure during pressure testing. Test caps, which are often designed for PVC and other materials, may apply pressure unevenly or excessively on copper fittings, potentially leading to leaks or failure at the joints.

The other types of pipe listed, such as PVC, galvanized, and cast iron, typically tolerate the use of test caps during pressure testing without the same risk of deformation or damage associated with copper. PVC, for example, is often tested with plugs designed specifically for its rigid properties. Galvanized and cast iron also possess more structural integrity under pressure compared to copper. This makes them suitable for the use of test caps that help to ensure a proper seal during pressure tests.