ASME B1.20.3:1976(R2018) pdf download

ASME B1.20.3:1976(R2018) pdf download.Dryseal Pipe Threads
1.1.2 Even without truncation gages, the standard practice of using two separate thread gages for Dryseal pipe threads, each with a difference in truncation, length of engagement and point of engagement, pro- vides a more detailed check of angle, lead and taper deviations than is required for non-dryseal taper pipe threads. 1.1.3 One method of checking crest truncation is by using 6 step plain gages. It should be recognized that this method may give misleading results in that the crest truncation of the product threads is always less (flat narrower) than that indicated by the position of the gages, the degree of inconsistency depending on the angle, lead and taper deviations present in the product thread. 1.1.4 Another method employs both crest and root truncation check gages. The root check gage is m’ade with a thread form having an included angle of 50 degrees and with a smaller gage crest flat than the root flat to be checked. The major diameter of this gage is controlled in relation to 6 gaging steps in a similar manner to the plain 6 step crest check gage. Like the crest check gage, the results may be some- what misleading except that in the case of the root check gage, the root truncation of the product thread is always more (flat wider) than is indicated by the position of the gages. 1.1.5 Unless lead, angle and taper of product threads are very well controlled, use of 6 step crest and root check gages will result in product threads with nar- rower crest flats and wider root flats than envisioned by the dryseal tolerances. Use of such a gaging system could result in rejection of threads which would ac- tually conform to the dryseal tolerances specified. The only completely reliable referee method for deter- mining whether crest and root truncation has been held within tolerance is direct measurement of the ex- ternal thread flats and measurement of these flats on a cast or section of the internal thread. 1.1.6 This standard covers two classes of NPTF Dry- seal pipe threads; Class 1 and Class 2. The classes differ only in inspection requirements, with Class 1 threads exactly those standardized in ANSI B2.2-1968 (in- spection of root and crest truncation not specified). Class 2 threads are identical to Class 1 threads except that inspection of root and crest truncation is re- quired. For Class 2 threads, direct measurement of crest and root truncation is the referee method. These classes do not apply to other than NPTF Dryseal pipe threads. 1.1.7 All dimensions in this standard including all tables are in inches unless otherwise noted.
1.4 Applications
1.4.1 Type 1.4.1.7 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.