ASME B1.20.3:1976(2018) pdf free download – DryseaI Pipe Threads
1.4.1.1 NPTF. This type applies to both external and internal threads and is suitable for pipe joints in practically every type of service. Of all Dryseal pipe threads, NPTF external and internal threads mated are generally conceded to be superior for strength and seal since they have the longest length of thread and theoretically, interference (sealing) occurs at every en- gaged thread root and crest. Use of tapered internal threads, such as NPTF or PTF-SAE SHORT in hard or brittle materials having thin sections will minimize the possibility of fracture.
1.4.1.2 PTF-SA€ Short. External threads of this type conform in all respects with NPTF threads, ex- cept that the thread length has been shortened by eliminating one thread from the small (entering) end. These threads are designed for applications where clearance is not sufficient for the full thread length of NPTF threads or for economy of material, where the full thread length, is not necessary. PTF-SAE SHORT external threads are intended for assembly with NPSI threads, but may also be assembled with NPTF in- ternal threads. They are not designed for and at ex- treme tolerance limits may not assemble with PTF- SAE SHORT internal or NPSF threads. Internal threads of this type conform in all respects with NPTF threads, except that the thread length has been shortened by eliminating one thread from the large (entry) end. These threads are designed for thin materials where thickness is not sufficient for the full thread length of NPTF threads or for economy in tap- ping where the full thread length is not necessary. PTF-SAE SHORT internal threads are primarily in- tended for assembly with NPTF external threads. They are not designed for and at the extreme tolerance limits may not assemble with PTF-SAE SHORT ex- ternal threads.
7.4.2.1 NPTF Class 1. Threads made to this class are designed to interfere (seal) at root and crest when mated, but inspection of crest and root truncation for acceptance is not required. Consequently, Class 1 threads are intended for applications where close con- trol of tooling is required for conformance of trunca- tion or where sealing is accomplished by means of a sealant applied to the threads.
7.4.2.2 NPTF Class 2. Threads made to this class are theoretically identical to those made to Class 1, howeve: inspection of root and crest truncation is re- quired. Consequently, where a sealant is not used, there is more assurance of a pressure-tight seal for Class 2 threads than for Class 1 threads.
Dryseal pipe threads are triangular with truncated roots and crests. The angle between the flanks of the thread is 60 degrees when measured on an axial plane and the line bisecting this angle is perpendicular to the axis of both the taper and straight threads making each half angle equal to 30 degrees. Thread form and limits on crest and root truncation are given in Figure 2. Although the crests and roots of the Dryseal threads are theoretically flat, they may be rounded providing their contour is within the limits shown in Figure 2. They are truncated parallel to the pitch line on both product and gage threads.