NPT - American National Standard Taper Pipe Threads Size Chart

NPT pipes are used in a wide variety of applications ranging from electrical conduits to high-pressure piping that carry natural gas and chemically reactive and aggressive liquids.

Some applications that use NPT are as follows:

• Pneumatic systems
• Hydraulic systems
• Plumbing and fittings
• Fire protection systems
• Chemical industry
• Processing industry
• Agricultural industry
• Irrigation systems
• Control systems
• Air-conditioning systems

NPT threaded plastic fittings can be readily found as they are standard. However, there are distinct and specific installation and sealing recommendations for installations involving plastic Vs metals. Also, both thread types have installation methods that are different based on gauging the threads for conformance before true installation is complete.

Although these standards are manufactured in order to maintain the uniformity in fittings, tapered pipe threads can become unreliable over time. Due to the continued usage and repair, the threads can become damaged and susceptible to leakage. As a result of this, the area on the pipe where the crest and the root of the thread meet can form a spiral leak path. When this happens, no amount of tightening can make the joint leak proof.

To face this situation, a leak proofing sealant is used. Most of the time, Teflon based sealant is recommended and used on all plastic pipe threads. Most commonly, Teflon tape is wrapped in about two to three turns around the male thread before the final assembly.

Sometimes, liquid Teflon based sealants are also used in order to ensure a pressure tight seal. However, it is always important to ensure that sealants are applied with maximum care so as to prevent from introducing the sealant materials into the flow path of the system.