N.P.T. nipples or National Pipe Threaded nipples or fittings are standard threaded nipples used within the United States. N.P.T. nipples consist of a tapered threading which has “imperfect threads” at the end of the threading. The “imperfect threads” create your seal when connecting a male to a female N.P.T part. The seal is created by torquing the NPT threads. When the National Pipe Thread fittings are torqued, the threads flanks compress against each other creating a successful seal.
Creating a successful seal while routing pipe is very important regardless of the material being transferred. Without a seal, the risk of leaking liquid or vapors of potentially harmful material is severely increased. To reduce the risk of leakage NPT fittings, if properly installed can create a flawless piping system. The metal to the metal connection of a male to female NPT fitting or nipple will deform after the required torque, which completes your seal.
It is important to note that disassembling and then reassembling the same threaded fittings is not recommended. This is because after you set an NPT fitting connection, you have formed the threads to that specific connection. Trying to reconnect those already formed NPT fittings or nipples with another NPT fitting or pipe will create leaks. This is because your seal will not be properly formed.
Also, while connecting the NPT piping system, refrain from over tightening the connection. If you over tighten your National Pipe Threaded nipple, you will split the female connection which will also result in leakage. When a male N.P.T fitting is connected to a split female N.P.T nipple, your seal will not properly set after your final torque.