American National Standard Pipe Thread standards, often called national pipe thread standards for short, are United States national

technical standard A technical standard is an established norm or requirement for a repeatable technical task which is applied to a common and repeated use of rules, conditions, guidelines or characteristics for products or related processes and production methods, ...

s for

screw thread A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a ...

s used on

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 liquids under pressure have a tapered thread that is slightly conical (in c ...

s and pipe fittings. They include both tapered and straight thread series for various purposes, including rigidity,

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

-tight sealing, or both. The types are named with a full name and an abbreviation, such as NPT, NPS, NPTF, or NPSC. MIP is an abbreviation for male iron pipe, and FIP is an abbreviation for female iron pipe. Outside North America, some US pipe thread sizes are widely used, as well as many

British Standard Pipe British Standard Pipe (BSP) is a set of technical standards for screw threads that has been adopted internationally for interconnecting and sealing pipes and fittings by mating an external (male) thread with an internal (female) thread. It has b ...

threads and

ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Iso ...

7-1, 7-2, 228-1, and 228-2 threads.

Types

The various types are each named with a abbreviation and a full name, as follows:

Uses

Threaded pipes can provide an effective seal for pipes transporting

liquids A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, an ...

gases Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...

, and

hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counter ...

fluid. These threads are now used in materials other than steel and brass, including

PTFE Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemour ...

, PVC,

nylon Nylon is a generic designation for a family of synthetic polymers composed of polyamides ( repeating units linked by amide links).The polyamides may be aliphatic or semi-aromatic. Nylon is a silk-like thermoplastic, generally made from petro ...

bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids such ...

, and

cast iron Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...

. 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 A compression fitting is a fitting 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 (most commonly PVC and copper), the ...

s in which the threads merely hold the pieces together and do not provide the seal. The various types of pipe threads are designed for use both with or without thread sealants, a
particular applications demand
The sealants, where used, are typically

thread seal tape Thread seal tape (also known as PTFE tape, Teflon tape, or plumber's tape) is a polytetrafluoroethylene (PTFE) film tape commonly used in plumbing for sealing pipe threads. The tape is sold cut to specific widths and wound on a spool, making it ...

thread sealant or a thread seal paste

pipe dope Pipe dope is any thread lubricant, thread sealing compound, or anaerobic chemical sealant that is used to make a pipe thread joint leak proof and pressure tight. It is also referred to as "thread compound" or "pipe thread sealant." Although com ...

(sometimes similar in composition to

plumber's putty Putty is a material with high plasticity, similar in texture to clay or dough, typically used in domestic construction and repair as a sealant or filler. Although some types of putty (typically those using linseed oil) slowly polymerise and bec ...

). Because the thread body is tapered (), 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

lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...

like lubricating paste or thread seal tape. The use of tape also helps to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible. Commonly used sizes are , , , , , 1, , , 2, , 3, 4, 5, and 6 inch, as

pipe Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circula ...

and fittings by most US suppliers. Sizes smaller than inch are occasionally used for compressed air, while sizes larger than 6 inches are often joined by other methods.

Specifications

NPT is defined by

ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

ASME The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing ...

standard B1.20.1. The taper rate for all NPT threads is 1 inch of diameter in 16 inches of length () measured by the change of diameter (of the pipe thread) over distance of thread. The angle between the taper and the center axis of the pipe is tan⁻¹() ≈ 1.7833° ≈ 1° 47′. The standard for

Nominal Pipe Size Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. "Nominal" refers to pipe in non-specific terms and identifies the diameter of the hole with a non-dimensional number (for ...

(often abbreviated NPS, which should not be confused with the abbreviation NPS for the straight thread form standard) is loosely related to the inside diameter of

Schedule 40 Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures. "Nominal" refers to pipe in non-specific terms and identifies the diameter of the hole with a non-dimensional number (for ...

series of sizes. Because of the pipe wall thickness of Schedule pipe, the actual diameter of the NPT threads is larger than the Nominal Pipe Size outside diameter, and considerably so for small sizes. Pipe of a given size in a different Schedule than Schedule 40 provides a different wall thickness, while maintaining the same outside diameter and thread profile as Schedule 40. Thus the inside diameter of a given size of Schedule pipe differs from the Nominal Pipe Size, while outside diameters for a given nominal Schedule size are the same between Schedules.

Thread form

National Pipe Thread series have the same 60° included angle as Sellers thread. On the other hand, for sealing capability, tapered (pressure-tight) threads have crest and root shapes that differ from Sellers. For example, the NPT has a crest width of 0.038 to 0.062 pitch, which is sharper than 0.125 pitch of Sellers.

National pipe taper fuel (NPTF)

National Pipe Taper Fuel (NPTF, also called Dryseal 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

tape (often referred to by the popular brand name "Teflon") or another sealant compound. NPTF threads have the same basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leakage path.

Standard sizes

History

In 1864,

William Sellers William Sellers (September 19, 1824 – January 24, 1905) was a mechanical engineer, manufacturer, businessman, noted abolitionist, and inventor who filed more than 90 patents, most notably the design for the United States standard screw thread ...

, then president of

Franklin Institute The Franklin Institute is a science museum and the center of science education and research in Philadelphia, Pennsylvania. It is named after the American scientist and statesman Benjamin Franklin. It houses the Benjamin Franklin National Memori ...

, presented a standard for nuts, bolts, and screws. Out of this effort came the first

United States Standard thread United States Standard thread (USS thread), also known as Sellers Standard thread, Franklin Institute thread and American Standard thread, is a standard for inch based threaded fasteners and washers. The USS standard is no longer supported. It, t ...

s, including pipe threads.

References

Bibliography

External links

NPT Pipe Thread Dimensions

ASME B1.20.-1983 Pipe Threads, General Purpose, Inch
* https://web.archive.org/web/20111001055253/http://publicaa.ansi.org/sites/apdl/Documents/Standards%20Action/2011%20PDFs/SAV4220.pdf
pipeandhose.com
* http://www.engineeringtoolbox.com/npt-national-pipe-taper-threads-d_750.html {{DEFAULTSORT:National Pipe Thread Thread standards Piping Plumbing Standards of the United States ru:Трубная резьба