National pipe thread
Encyclopedia
National Pipe Thread Tapered Thread (NPT) is a U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
standard for tapered threads used on threaded pipe
Threaded pipe
A threaded pipe is a pipe with screw-threaded ends for assembly.- Tapered threads :The threaded pipes used in some plumbing installations for the delivery of gases or fluids under pressure have a threaded section that is slightly conical . This is called a "tapered thread"...
s and fittings
Pipe fitting
Pipe fitting is the occupation of installing or repairing piping or tubing systems that convey liquid, gas, and occasionally solid materials...
. The taper rate for all NPT threads is ( inch per foot) measured by the change of diameter (of the pipe thread) over distance. The angle between the taper and the center axis of the pipe is 1° 47′ 24″ (1.7899°). Commonly-used sizes are , , , , , 1, , , and 2 inch, appearing on pipes
Pipe (material)
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases , slurries, powders, masses of small solids...
and fittings by most U.S. suppliers. Sizes smaller than are occasionally used for compressed air, while sizes larger than 2 in are uncommon, due to the use of alternative methods of joining that are used with these larger sizes. NPT is defined by ANSI
Ansi
Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....
/ASME
American Society of Mechanical Engineers
The American Society of Mechanical Engineers is a professional body, specifically an engineering society, focused on mechanical engineering....
standard B1.20.1.
Nominal Pipe Size is loosely related to the inside diameter of Schedule 40 pipe. Because of the pipe wall thickness, the actual diameter of the threads is larger than the NPS, considerably so for small NPS. Other schedules of pipe have different wall thickness but the OD (outer diameter) and thread profile remain the same, so the inside diameter of the pipe is therefore different from the nominal diameter.
Threaded pipes can provide an effective seal for pipes transporting liquids, gases, steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
, and hydraulic fluid. These threads are now used in materials other than steel and brass, including PTFE
Polytetrafluoroethylene
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....
, PVC
Polyvinyl chloride
Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...
, nylon
Nylon
Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...
, bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...
and cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
.
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 or compression fitting
Compression fitting
Compression fittings are used in plumbing and electrical conduit systems to join two tubes or thin-walled pipes together. In instances where two pipes made of dissimilar materials are to be joined , the fittings will also be made of one or more compatible materials appropriate for the connection...
s in which the threads merely hold the pieces together and do not provide the seal. However, a clearance remains between the crests and roots of the threads, resulting in a leakage around this spiral. This means that NPT fittings must be made leak free with the aid of thread seal tape
Thread seal tape
Thread seal tape, or teflon tape can be used in many ways, the most common use in America is to seal things. Thread seal tape — commonly known as "Teflon tape", "PTFE tape", "tape dope", or "plumber's tape"–is a polytetrafluoroethylene film cut to specified widths for use in sealing pipe...
or a thread sealant compound
Pipe dope
Pipe dope is slang for thread lubricants, thread sealing compounds and anaerobic chemical sealant that is used to make a pipe thread joint leak proof and pressure tight...
. (The use of tape or sealant will also help to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible.)
There is also a semi-compatible variant called National Pipe Taper Fuel (NPTF) also called Dryseal American National Standard Taper Pipe Thread, defined by ANSI B1.20.3, 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.
Sometimes NPT threads are referred to as MPT ('Male Pipe Thread'), MNPT, or NPT(M) for male
Gender of connectors and fasteners
In electrical and mechanical trades and manufacturing, each half of a pair of mating connectors or fasteners is conventionally assigned the designation male or female...
(external) threads; and FPT ('Female Pipe Thread'), FNPT, or NPT(F) for female
Gender of connectors and fasteners
In electrical and mechanical trades and manufacturing, each half of a pair of mating connectors or fasteners is conventionally assigned the designation male or female...
(internal) threads. An equivalent designation is MIP (Male iron pipe) and FIP (Female iron pipe). Also the terms NPS and NPSM are sometimes used to designate a straight, not tapered, thread. (this should not be confused with NPS meaning Nominal Pipe Size
Nominal Pipe Size
Nominal Pipe Size is a North American set of standard sizes for pipes used for high or low pressures and temperatures. Pipe size is specified with two non-dimensional numbers: a nominal pipe size for diameter based on inches, and a schedule for wall thickness...
)
Pipe thread sizes
| Nominal pipe size (in) | Pipe outer diameter | Threads per inch | Thread pitch |
|---|---|---|---|
| 0.3125 in (7.94 mm) | 27 | 0.03704 in (0.940816 mm) | |
| 0.405 in (10.29 mm) | 27 | 0.03704 in (0.940816 mm) | |
| 0.54 in (13.72 mm) | 18 | 0.05556 in (1.41122 mm) | |
| 0.675 in (17.15 mm) | 18 | 0.05556 in (1.41122 mm) | |
| 0.84 in (21.34 mm) | 14 | 0.07143 in (1.81432 mm) | |
| 1.05 in (26.67 mm) | 14 | 0.07143 in (1.81432 mm) | |
| 1 | 1.315 in (33.4 mm) | 0.08696 in (2.20878 mm) | |
| 1.66 in (42.16 mm) | 0.08696 in (2.20878 mm) | ||
| 1.9 in (48.26 mm) | 0.08696 in (2.20878 mm) | ||
| 2 | 2.375 in (60.33 mm) | 0.08696 in (2.20878 mm) | |
| 2.875 in (73.03 mm) | 8 | 0.125 in (3.175 mm) | |
| 3 | 3.5 in (88.9 mm) | 8 | 0.125 in (3.175 mm) |
| 4 | 4.5 in (114.3 mm) | 8 | 0.125 in (3.175 mm) |
| 5 | 5.563 in (141.3 mm) | 8 | 0.125 in (3.175 mm) |
| 6 | 6.625 in (168.28 mm) | 8 | 0.125 in (3.175 mm) |
| 10 | 10.75 in (273.05 mm) | 8 | 0.125 in (3.175 mm) |
| 12 | 12.75 in (323.85 mm) | 8 | 0.125 in (3.175 mm) |
| 14 | 14 in (355.6 mm) | 8 | 0.125 in (3.175 mm) |
| 16 | 16 in (406.4 mm) | 8 | 0.125 in (3.175 mm) |
| 18 | 18 in (457.2 mm) | 8 | 0.125 in (3.175 mm) |
| 20 | 20 in (508 mm) | 8 | 0.125 in (3.175 mm) |
| 24 | 24 in (609.6 mm) | 8 | 0.125 in (3.175 mm) |
Thread form
NPT and NPS threads have a 60° included angle and have a Sellers thread form (flattened peaks and valleys).Terminology
Sometimes these terms may be used:- MIP: stands for Male Iron Pipe, or Male International Pipe, or MPT Male Pipe Thread. It is a term for pipe fittings.
- FIP: stands for Female Iron Pipe, or Female International Pipe, or FPT. It is a term for pipe fittings that MIP fittings fit into.
The difference between FIP, MIP and Compression fittings is in the tapering of the thread. FIP has taper of 1:16 (6.25% slope), compression has taper of 13:96(13.5% slope).
A female iron connection has a tapered thread, which thins out to the end of the pipe. As the fitting is tightened, the ever-decreasing thread depth means that the connection becomes watertight. To properly seal the fitting, paste thread sealant or PTFE (polytetrafluoroethylene) tape wrapped around the thread is required.
MIP fittings are usually found in thicker copper pipe, iron pipe, steel pipe, gas pipe, gas stove, gas oven, gas heater, and gas water heater connections.
See also
- AN threadAN threadThe AN thread is a particular type of fitting used to connect flexible hoses and rigid metal tubing that carry fluid. It is a US military-derived specification that dates back to World War II and stems from a joint standard agreed upon by the Army and Navy, hence AN.AN sizes range from -2 to -32...
- British standard pipe threadBritish standard pipe threadThe British Standard Pipe thread is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external with an internal thread.-Types:...
- PanzergewindePanzergewindeThe Stahlpanzerrohrgewinde standard for screw threads, more often called by the shorter name Panzergewinde , is a technical standard created in Germany and subsequently used in various countries, such as the German-speaking zone and neighboring European countries...
- Thread angleThread angleThe thread angle of a screw is the angle between the threads. This is a defining factor for the shape of a screw thread. Standard values include:...
- Threaded pipeThreaded pipeA threaded pipe is a pipe with screw-threaded ends for assembly.- Tapered threads :The threaded pipes used in some plumbing installations for the delivery of gases or fluids under pressure have a threaded section that is slightly conical . This is called a "tapered thread"...