National pipe threadFrom Wikipedia, the free encyclopedia

Threaded pipe andelbow. The pipe has amaleNPT thread, while the elbow's isfemale.National Pipe Thread Taper(NPT) is aU.S.standard fortapered threadsused onthreaded pipesandfittings. In contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal. In America,William Sellersset the standard for nuts, bolts, and screws which became the National Pipe Tapered Thread (NPT) in 1864.[1]Contents[hide] 1Usage 2Specifications 2.1Thread form 2.2NPTF 3Informal Subsets 3.1MPT 3.2FPT 4Table of standard sizes 5See also 6References 7Further reading 8External linksUsage[edit]Threaded pipes can provide an effective seal for pipes transportingliquids,gases,steam, andhydraulicfluid. These threads are now used in materials other than steel and brass, includingPTFE,[2]PVC,nylon,bronze, andcast iron.The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings orcompression fittingsin which the threads merely hold the pieces together and do not provide the seal. As the thread body is tapered (0.75in/ft or 62.5mm/m) a larger diameter keeps compressing into a smaller diameter and finally forms a seal (no clearance remains between the crests and roots of the threads because of the taper). This means that NPT fittings should be burr-free and lubricated using a lubricating material like lubricating paste ortape. The use of tape also helps to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible.Commonly used sizes are18,14,38,12,34, 1,114,112, and 2inch, appearing onpipesand fittings by most U.S. suppliers. Sizes smaller than18inch are occasionally used for compressed air, while sizes larger than 2inches are uncommon, due to the use of alternative methods of joining that are used with these larger sizes.Specifications[edit]NPT is defined byANSI/ASMEstandard B1.20.1.[3]Pipe threads are different from machine-screw and bolt threads. Those are designated NC (national coarse) and NF (national fine.) The biggest difference is the taper on pipe threads.The taper rate for all NPT threads is 1 in 16 (34inch per foot or 62.5 millimeters per meter) measured by the change of diameter (of the pipe thread) over distance. The angle between the taper and the center axis of the pipe istan1(132) = 1.7899 = 14724.Nominal Pipe Size (NPS) is loosely related to the inside diameter ofSchedule 40pipe. Because of the pipe wall thickness, the actual diameter of the threads is larger than the NPS, considerably so for small NPS. Pipe of other schedules with a certain NPS has different wall thickness, but the same outside diameter and thread profile as Schedule 40, so the inside diameter of the pipe is therefore different from the NPS.Thread form[edit]NPTE and NPS threads have a 60 included angle and have aSellers thread form(flattened peaks and valleys).NPTF[edit]A semi-compatible variant calledNational Pipe Taper Fuel(NPTF), also calledDryseal American National Standard Taper Pipe Thread, defined by ASME B1.20.3, is designed to provide a more leak-free seal without the use of teflon tape or other sealant compound. NPTF threads are the same basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leakage path.Informal Subsets[edit]MPT[edit]MPT can mean Male Pipe Thread or Mechanical Pipe Thread (a non-tapered variety) and is a subset of NPT for male connections.FPT[edit]FPT means Female Pipe Thread and is a subset of NPT for female connections.

Table of standard sizes[edit]NPT American Standard Pipe Thread Taper[4]

Pipe size (inches)TPIThreads per InchPitch(inches or mm)Approximatelength of thread(inches or mm)Approximate number ofthreads turnsto be cutApproximatetotal thread makeup,hand andwrench(inches or mm)NominaloutsidepipediameterOD(inches or mm)Tap drill(inches or mm)

116270.03703704in or 0.9407mm0.313in or 7.950mm

18270.03703704in or 0.9407mm38in or 9.525mm1014in or 6.350mm0.405in or 10.287mmR0.339in or 8.6106mm

14180.0555in or 1.4097mm58in or 15.875mm1138in or 9.525mm0.540in or 13.716mm716in or 11.113mm

38180.05555555in or 1.4111mm58in or 15.875mm1138in or 9.525mm0.675in or 17.145mm3764in or 14.684mm

12140.07142857in or 1.8143mm34in or 19.0500mm10716in or 11.1125mm0.840in or 21.3360mm2332in or 18.2563mm

34140.07142857in or 1.8143mm34in or 19.0500mm1012in or 12.7000mm1.050in or 26.6700mm5964in or 23.4156mm

111-1/20.08695652in or 2.2087mm78in or 22.2250mm10916in or 14.2875mm1.315in or 33.4010mm1532in or 29.3688mm

11411-1/20.08695652in or 2.2087mm1in or 25.4000mm11916in or 14.2875mm1.660in or 42.1640mm112in or 38.1000mm

11211-1/20.08695652in or 2.2087mm1in or 25.4000mm11916in or 14.2875mm1.900in or 48.2600mm14764in or 44.0531mm

211-1/20.08695652in or 2.2087mm1in or 25.4000mm1158in or 15.8750mm2.375in or 60.3250mm2732in or 56.3563mm

21280.125in or 3.1750mm112in or 38.1000mm1278in or 22.2250mm2.875in or 73.0250mm258in or 66.6750mm

380.125in or 3.1750mm112in or 38.1000mm121in or 25.4000mm3.500in or 88.9000mm314in or 82.5500mm

31280.125in or 3.1750mm158in or 15.8750mm131116in or 26.9875mm4.000in or 101.6000mm334in or 95.2500mm

480.125in or 3.1750mm158in or 41.2750mm131116in or 26.9875mm4.500in or 114.3000mm414in or 107.9500mm

41280.125in or 3.1750mm5.000in or 127.0000mm434in or 120.6500mm

580.125in or 3.1750mm134in or 44.4500mm141316in or 30.1625mm5.563in or 141.3002mm5932in or 134.1438mm

680.125in or 3.1750mm134in or 44.4500mm141316in or 30.1625mm6.625in or 168.2750mm61132in or 161.1313mm

880.125in or 3.1750mm178in or 47.6250mm151516in or 33.3375mm8.625in or 219.0750mm

1080.125in or 3.1750mm2in or 50.8000mm16112in or 38.1000mm10.750in or 273.0500mm

1280.125in or 3.1750mm218in or 53.9750mm17158in or 41.2750mm12.750in or 323.8500mm

1480.125in or 3.1750mm14.000in or 355.6000mm

1680.125in or 3.1750mm16.000in or 406.4000mm

1880.125in or 3.1750mm18.000in (457.2000mm)

2080.125in or 3.1750mm20.000in (508.0000mm)

2480.125in or 3.1750mm24.000in (609.6000mm)