ASME B1.20.1 pdf download Pipe Threads, General Purpose (Inch)
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 corresponding 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.
3.1.3 HandlingConsiderations. The potential effects on thread form and gaging must be considered when choosing coatings and other processes. Some processes, such as barrel coating, can be damaging to the thread form, especially the crests of external threads. See para.
3.2.3 on gaging nicked threads.
3.1.4 Form of Thread. The form of the thread is specified in para. 2.1.
3.1.5 Taper of Thread. The basic taper of the thread is 1 in 16 or 0.75 in./ft measured diametrically relative to the axis.
3.1.6 Pitch Diameters of Thread. The basic pitch diameters of the tapered thread are determined by the following formulas based on the outside diameter of the pipe and the pitch of the thread: