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The difference between NPT thread and NPTF thread

Luna 2023-07-07 16:47:53
1.NPT and NPTF threads are two of the most commonly used taper pipe threads in the United States for applications ranging from electrical piping and handrails to high-pressure lines transporting gas or corrosive liquids. NPT is used for mechanical or low-pressure gases and liquids that require the use of sealants to ensure sealing. When the sealing requirements are strict, the sealant may fail due to high temperature and pressure, then NPTF dry sealing thread can be used. When the fitting is tightened with a wrench, this mechanical seal produces a sealing effect with a threaded fit and slight deformation.

2. The two threads are identical in visual inspection. Both have a 3/4 taper in a foot length. The tip of the hole in the internal thread or the end of the pipe in the external thread have the same middle diameter and have the same thread length and depth. Nevertheless, there are slight differences in the shape of the thread. There is a slight difference between the large and small diameters of the two threads. For NPT threads, tightening with a wrench may allow air leakage after assembly on both large and small diameters, so sealants are used to fill all gaps. The NPTF thread, on the other hand, is designed to ensure that sufficient deformation is generated across the dentition to produce this mechanical seal.

3. How do different tooth types affect the tools used to produce NPT and NPTF threads?
NPT and NPTF thread profiles are produced using taps for each thread. Because NPT threaded parts require sealants, it is acceptable to tap NPT threads with NPTF taps. But NPT tap can not be used for NPTF thread, because it produces thread leakage.

4. The biggest difference is the inspection requirements of these two kinds of threads.
Because NPT threads need to use sealant, just use a plug gauge, called L1 gauge (internal thread) or L1 ring gauge (external thread) to check the size. However, because of the taper and large diameter, small diameter is important for sealing NPTF threads,Therefore, other thread gauges L2 and L3 are required, and special plug or ring gauges are used to check large and small diameters.

5 US dry seal pipe thread (NPTF) to ensure that the seal can be achieved without the use of sealing filler. Therefore, its single thread parameter accuracy (tooth height, pitch and tooth side Angle) is higher than that of the United States general purpose pipe thread. In addition, the fit between the top of the tooth and the bottom of the tooth is an interference fit, while the NPT is a general purpose pipe thread, and the fit between the top and the bottom of the tooth is a transitional fit. For NPT inspection can be loosened a little, for NPTF to use a special plug gauge! The main difference between the two is the large diameter