National pipe thread

Threaded pipe and elbow. The pipe has a male NPT thread, while the elbow is female.

American National Standard Pipe Thread standards, often called national pipe thread standards for short, are United States national technical standards for screw threads used on threaded pipes and pipe fittings. They include both tapered and straight thread series for various purposes, including rigidity, pressure-tight sealing, or both.Template:Sfnp 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.<ref>Template:Cite book </ref>

Outside North America, some US pipe thread sizes are widely used, as well as many British Standard Pipe threads and ISO 7–1, 7–2, 228–1, and 228-2 threads.

TypesEdit

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

AbbreviationTemplate:Sfnp	Shorthand expansion	Full nameTemplate:Sfnp	CommentTemplate:Sfnp
NPT	National pipe taper	American National Standard Taper Pipe Thread	Tapered and needs thread sealant; for connections in nearly every type of service
NPS	National pipe straight	American National Standard Straight Pipe Thread	For rigidity; sealable with o-ring or gasket; sometimes male straight is mated with female tapered for low-pressure sealingTemplate:Fact
NPSC	National pipe straight–coupling	American National Standard Straight Pipe Thread for Couplings	For general couplings
NPSF	National pipe straight–fuel and oil	Dryseal USA (American) Standard Fuel Internal Straight Pipe Thread	Internal only, straight
NPSH	National pipe straight–hose	American National Standard Straight Pipe Thread for Hose Couplings	For hose couplings
NPSI	National pipe straight–intermediate	Dryseal USA (American) Standard Intermediate Internal Straight Pipe Thread	Similar to NPSF but slightly larger; internal only, straight
NPSL	National pipe straight–locknut	American National Standard Straight Pipe Thread for Loose-fitting Mechanical Joints with Locknuts	For use with locknuts
NPSM	National pipe straight–mechanical	American National Standard Straight Pipe Thread for Free-fitting Mechanical Joints	For various rigid mechanical uses
NPTF	National pipe taper–fuel and oil	Dryseal USA (American) Standard Taper Pipe Thread	For dryseal connections in nearly every type of service, especially fuel connections
NPTR	National pipe taper–railing	American National Standard Taper Pipe Thread for Railing Joints	For railings
PTF-SAE SHORT	Pipe taper, fuel, SAE, short	Dryseal SAE Short Taper Pipe Thread	Named after SAE International; similar to NPTF but one turn shorter

UsesEdit

Threaded pipes can provide an effective seal for pipes transporting liquids, gases, steam, and hydraulic fluid. These threads are now used in materials other than steel and brass, including PTFE, PVC, nylon, bronze, and cast 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 or compression fittings in which the threads merely hold the pieces together and do not provide a seal. The various types of pipe threads are designed for use both with or without thread sealants,Template:Sfnp as particular applications demand. The sealants, where used, are typically thread seal tape thread sealant or a thread seal paste pipe dope (sometimes similar in composition to plumber's putty).

Because the thread body is tapered (Template:Convert), 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 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 Template:Frac, Template:1/4, Template:Frac, Template:1/2, Template:3/4, 1, Template:Frac, Template:Frac, 2, Template:Frac, 3, Template:Frac, 4, 5, and 6 inch, as pipe and fittings by most US suppliers. Sizes smaller than Template:Frac inch are occasionally used for compressed air, while sizes larger than 6 inches are often joined by other methods.

SpecificationsEdit

NPT is defined by ANSI/ASME standard B1.20.1.<ref name="B1.20.1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The taper rate for all NPT threads is 1 inch of diameter in 16 inches of length (Template:Convert) measured by the change of diameter (of the pipe thread) over distance of thread. The half-angle (between the taper surface and the axis of the pipe) is arctan(Template:Frac) ≈ 1.7899° ≈ 1° 47′.

The standard for Nominal Pipe Size (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 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 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 formEdit

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 the 0.125 pitch of Sellers. <ref name="B1.20.1"/>

National pipe taper fuel (NPTF)Edit

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 PTFE 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 sizesEdit

American Society of Mechanical Engineers National Pipe Thread Taper (NPT)<ref>Engineering toolbox</ref>
Nominal pipe size	Thread density	Thread pitch P		Length L₁	Turns	Diameter E₁	Length L₂	Turns	Diameter E₂		Overall length L₄<ref name="piping-designer" />	Actual outside diameter D		Tap drill
Nominal pipe size	Thread density	Thread pitch P		Hand-tight engagement<ref name="piping-designer">{{#invoke:citation/CS1\|citation			CitationClass=web }}</ref>	Effective thread<ref name="piping-designer" />			Overall length L₄<ref name="piping-designer" />	Actual outside diameter D		Tap drill
inch	inch⁻¹	inch	mm	inch		inch	inch		inch	inch	inch	mm	inch	mm
Template:Frac	27	Template:Convert	0.1600	4.32	0.28118	0.2611	7.05	0.2875	0.3896	Template:Convert
Template:Frac	27	Template:Convert	0.1615	4.36	0.37360	0.2639	7.13	0.38000	0.3924	Template:Convert	Template:Convert
Template:Frac	18	Template:Convert	0.2278	4.10	0.49163	0.4018	7.23	0.50250	0.5946	Template:Convert	Template:Convert
Template:Frac	18	Template:Convert	0.2400	4.32	0.62701	0.4078	7.34	0.63750	0.6006	Template:Convert	Template:Convert
Template:Frac	14	Template:Convert	0.3200	4.48	0.77843	0.5337	7.47	0.79178	0.7815	Template:Convert	Template:Convert
Template:Frac	14	Template:Convert	0.3390	4.75	0.98887	0.5457	7.64	1.00178	0.7935	Template:Convert	Template:Convert
1	Template:Frac	Template:Convert	0.4000	4.60	1.23863	0.6828	7.85	1.25631	0.9845	Template:Convert	Template:Convert
Template:Frac	Template:Frac	Template:Convert	0.4200	4.83	1.58338	0.7068	8.13	1.60131	1.0085	Template:Convert	Template:Convert
Template:Frac	Template:Frac	Template:Convert	0.4200	4.83	1.82234	0.7235	8.32	1.84131	1.0252	Template:Convert	Template:Convert
2	Template:Frac	Template:Convert	0.4360	5.01	2.29627	0.7565	8.70	2.31630	1.0582	Template:Convert	Template:Convert
Template:Frac	8	Template:Convert	0.6820	5.46	2.76216	1.1375	9.10	2.79063	1.5712	Template:Convert	Template:Convert
3	8	Template:Convert	0.7660	6.13	3.38850	1.2000	9.60	3.41563	1.6337	Template:Convert	Template:Convert
Template:Frac	8	Template:Convert	0.8210	6.57	3.88881	1.2500	10.00	3.91563	1.6837	Template:Convert	Template:Convert
4	8	Template:Convert	0.8440	6.75	4.38713	1.3000	10.40	4.41563	1.7337	Template:Convert	Template:Convert
Template:Frac	8	Template:Convert								Template:Convert	Template:Convert
5	8	Template:Convert	0.9370	7.50	5.44929	1.4063	11.25	5.47863	1.8400	Template:Convert	Template:Convert
6	8	Template:Convert	0.9580	7.66	6.50597	1.5125	12.10	6.54063	1.9462	Template:Convert	Template:Convert
8	8	Template:Convert	1.0630	8.50	8.50003	1.7125	13.70	8.54063	2.1462	Template:Convert
10	8	Template:Convert	1.2100	9.68	10.62094	1.9250	15.40	10.66563	2.3587	Template:Convert
12	8	Template:Convert	1.3600	10.88	12.61781	2.1250	17.00	12.66563	2.5587	Template:Convert
14	8	Template:Convert	1.5620	12.50	13.87263	2.2500	18.00	13.91563	2.6837	Template:Convert
16	8	Template:Convert	1.8120	14.50	15.87575	2.4500	19.60	15.91563	2.8837	Template:Convert
18	8	Template:Convert	2.0000	16.00	17.87500	2.6500	21.20	17.91563	3.0837	Template:Convert
20	8	Template:Convert	2.1250	17.00	19.87031	2.8500	22.80	19.91563	3.2837	Template:Convert
24	8	Template:Convert	2.3750	19.00	23.86094	3.2500	26.00	23.91563	3.6837	Template:Convert

File:NPT Dimensions.svg

Hand-tight and effective thread engagement lengths

HistoryEdit

Template:See also In 1864, William Sellers, then president of Franklin Institute, presented a standard for nuts, bolts, and screws. Out of this effort came the first United States Standard threads, including pipe threads.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

ReferencesEdit

Template:Reflist

BibliographyEdit

Template:MachinerysHandbook25e

External linksEdit

ru:Трубная резьба