Home>ASME standards>ASME B1.20.1-2013 pdf download

ASME B1.20.1-2013 pdf download

ASME B1.20.1-2013 pdf download.Pipe Threads, General Purpose (Inch).
1 INTRODUCTION 1.1 Scope This Standard covers dimensions and gaging of pipe threads of the following series: NPT NPSC NPTR NPSM NPSL 1.2 Related Standard Hose coupling joints are ordinarily made with straight internal and external loose-fitting threads. There are sev- eral standards of hose threads having various diameters and pitches, one of which is based on the American National Standard Pipe Thread. By the use of this thread series, NPSH, it is possible to join small hose couplings in sizes 1 ⁄ 2 to 4, inclusive, to ends ofstandard pipe having American National Standard external pipe threads, using a gasket to seal the joint. For dimensions, toler- ances, and gaging, see ASME B1.20.7. 1.3 Thread Designations 1.3.1 The types of pipe threads included in this Standard are designated by specifying in sequence the nominal pipe size, number of threads per inch, and the thread series symbol as follows: 1 ⁄ 8 –27 NPT 1 ⁄ 8 –27 NPSC 1 ⁄ 2 –14 NPTR 1 ⁄ 8 –27 NPSM 1 ⁄ 8 –27 NPSL Decimal equivalent notation may be substituted for fractional pipe sizes. For example 0.125–27 NPT For left-hand threads, add “LH” to the designation. For example 1 ⁄ 8 –27 NPT–LH Designations without “LH” will signify right-hand threads. 1.3.2 Each ofthese letters in the symbols has signif- icance as follows: N p National (American) Standard 1 P p Pipe T p Taper S p Straight C p Coupling R p Railing Fittings M p Mechanical L p Locknut 1.4 Sealing (NPT and NPSC Only) 1.4.1 Mating Threads. Mating threads should always contact on the thread flanks. The design toler- ances are such that mating crests and roots may clear, contact, or interfere (see Fig. 1). This joint may not neces- sarily seal, unless a sealant is used. 1.4.2 Sealant. Where pressure-tight, leak-free joints are required, it is intended that threads conforming to this Standard be made up wrench-tight with a sealant. To prevent galling during installation, the sealant may have lubricating properties. 1.4.3 TighteningTorque. Due to application-specific variables such as materials, wall thickness, operating pressures, etc., no guidance is given in this Standard regarding joint-tightening torque. However, joints should be tightened beyond the hand-tight engagement position. Advancing the joint past hand-tight creates interference between external and internal thread flanks, produces a seal (with the use of a sealant), and helps prevent loosening of the joint. Overtightening may be detrimental to the sealing function of the joint. 1.4.4 Other Considerations. Out-of-roundness of mating parts can negatively affect their ability to seal when made up wrench tight. The product’s elasticity and ductility will also affect sealing. 1.4.5 Pressure-Tight Threads Without Sealant. Pipe threads designed for pressure-tight joints that may be used without sealing compounds (Dryseal Threads) are covered in ASME B1.20.3. 1.5 Appendices Useful and supplementary information that is not a part of this Standard is presented in a nonmandatory appendix. Specifically, the nonmandatory appendices cover the turns of engagement method of gaging, sug- gested prethreading hole diameters, and an explanatory gaging matrix.
For a symmetrical straight screw thread with a 30-deg flank angle, Hp cot ␣ /2n p 0.86602540P. For a symmet- rical taper screw thread with a 30-deg flank angle and diametral taper of 0.750 in./ft, H p (cot ␣ − tan 2 ␤ tan ␣ )/2n p 0.86574320P. For an 8-pitch thread, which is the coarsest standard taper pipe thread pitch, the corres- ponding values ofHare 0.1082179 and 0.1082532, respec- tively. The difference of 0.000035 in. being insignificant, the value of H p 0.86602540P is used for all straight and tapered threads in this Standard. 2.4 Thread Truncation The maximum height of the truncated thread, h (see Fig. 2), is based on factors entering into the manufacture of cutting tools and the making of tight joints. h p 0.800P The crest and root of pipe threads are truncated a minimum of 0.033P. The maximum depth of truncation for the crest and root of these pipe threads will be found in Table 1. The crests and roots of the external and inter- nal threads may be truncated either parallel to the pitch line or parallel to the axis. The illustration in Table 1, giving a sectional view of this Standard thread form, represents the truncated thread form by a straight line and sharp corners. However, a radius form is acceptable, as long as the crests and roots lie within the limits shown in Table 1. Some of the truncations in this illustration are shown with dotted lines as radii. 3 SPECIFICATION FOR TAPER PIPE THREADS, NPT 3.1 General NPT joints made in accordance with these specifica- tions consist of an external taper and internal taper thread (see Figs. 1 through 3). NPT taper pipe threads are intended to be made up wrench-tight and with a sealant when a pressure-tight joint is required. 3.1.1 Notation. The standard notation applicable to the American National Standard Taper Pipe Thread, NPT, is shown in Fig. 3. 3.1.2 Symbols. The following symbols are specific to this Standard: D p outside diameter of pipe E 0 p basic pitch diameter at small end of external thread (or end of pipe) E 1 p basic pitch diameter at plane of hand-tight engagement length (L 1 ), external thread, and large end of internal thread E 2 p basic pitch diameter at plane of effective thread length (L 2 ), external thread E 3 p basic pitch diameter at plane ofwrench-tight engagement E 5 p basic pitch diameter pipe at L 5 , plane ofcom- plete thread length

Related PowerPoint Templates

Template Categories
Popular Tags