Which schedule of PVC and CPVC pipe can be threaded?

Threaded joints are designed for use with pipes that have sufficient wall thickness to handle the stresses caused by the threads and the pressure within the pipe. Schedule 80 PVC and CPVC pipe have a thicker wall compared to Schedule 40, which allows them to withstand higher pressures and also supports the integrity of the threads when they are cut into the pipe.

Schedule 80 is commonly used in applications where higher pressure resistance is necessary. When threaded, the thicker wall provides the needed strength and durability to maintain a secure joint without risking failure. This makes Schedule 80 suitable for threaded connections in various plumbing and industrial applications.

In contrast, while Schedule 40 can also be threaded, it is not as strong as Schedule 80 and is typically used for lower pressure applications. Schedule 20 has a much thinner wall and is primarily designed for venting or drainage and is not suitable for threading due to its lower structural integrity. Schedule 100 is not commonly used in the context of threading, as piping systems typically do not utilize such a high pressure rating for threaded connections. Therefore, Schedule 80 is recognized as the appropriate choice for threading among the given options.