ASME A112.14 pdf download Pipe Threads, 60 deg, General Purpose
4SPECIFICATIONS FOR GENERAL PURPOSE TAPERPIPE THREADS,NPT
4.1 Taper Pipe Threads, NPT
NPT threads made in accordance with these specifica-tions consist of an external taper and an internal taperthread, to form the normal type of joint having generalapplication on pipe and fittings. See Fig. 3.
NPT taper pipe threads are intended to be made upwrench-tight and with a sealant whenever a
pressure-tight joint is required.
Sealing is affected by out-of-roundness, which is pos-sible between the wrench-tight mated parts in final
assembly. This will vary depending on the method forproducing the thread in conjunction with the elasticityand/or ductility of the mating parts and the resultantconformance at final assembly.
4.1.1 Thread Designation. NPT taper pipe threaddesignation shall consist of the following sequence:
nominal pipe size; dash; number of threads per 254 mm-and “NPT.~If the thread is left-handed, add “-LH.”
Right-handed threads require no special designation.EXAMPLE:
‘l 4-18 NPT’ 4-18 NPT-LH
NOTE: Each letter in the symbol, NPT, has a definite significanceas follows: Np Nationall (American) standard,Pp Pipe, Tp
4.1.2 Thread Dimensions.Basic dimensions arespecified in Table 2. See para.3.1 for profile.
4.1.3 Taper of Thread.The taper of the thread is 1in 16 measured on the diameter and along the axis.
4.1.4 Engagement Between External and InternalTaper Threads.The normal length of engagementbetween external and internal taper threads when
screwed together hand-tight is shown in Columns 6 and7 of Table 2.This length is controlled by the constructionand use of the gauges. It is recognized that in special
applications, such as flanges for high-pressure work,longer thread engagement is used, in which case thepitch diameter (dimension F in Table 2) is maintainedand the pitch diameter,Eo, at the end of the pipe isproportionately smaller.
4.2.1 Manufacturing Tolerances on Product. The maximum allowable variation in the product is one turn,large or small, from gauges made to the basic dimen-
sions. See paras.7.1 and 7.2 for gauging.
4.2.2 Tolerances on Thread Elements.The permissi-ble variations in thread elements are given in Table 3.This table is a guide for establishing limits of the threadelements of taps, dies, and thread chasers.Conformance to these limits may be required on product threads, in
which case specifications shall require control and check-ing of thread elements.
On pipe fittings and valves (not steel or high-gradealloys used in critical services) for steam pressures2,1 MPa and below, it is intended that plug and ringgauge practices as established in this Standard be usedin conjunction with tooling control of thread elements,e.g., taps and dies, to provide satisfactory control offunctional size.Therefore, no tolerances on thread ele-ments have been established for this class.
For service conditions, where more exact checks arerequired, procedures have been developed by industryto supplement the standard plug and ring gauge methodof gauging.
5 SPECIFICATIONS FOR INTERNAL PARALLEL
THREADS IN PIPE cOUPLINGS, NPsc
5.1 Parallel Pipe Threads in Pipe Couplings
Threads in pipe couplings made in accordance withthese specifications are parallel threads of the same thread form as the Standard Taper Pipe Thread specifiedin para.3.1.They are used to form pressure-tight joints when assembled with a NPT external taper pipe thread,and made up wrench-tight with lubricant or sealant.
5.1.1 Thread Designation. Standard parallel pipethread designation shall consist of the following
sequence: nominal pipe size; dash; number of threadsper 25,4 mm; and “NPsC.”If the thread is left-handed,
add“-LH.” Right-handed threads require no special des-ignation.
‘ a-18 NPS’ 4-18 NPSC-LH
NOTE: Each letter in the symbol, NPSC, has a definite signifi-cance as follows: Np National (American) standard,Pp Pipe,sp Straight (parallel),cp Coupling.
5.1.2 Thread Dimensions.The thread dimensionsare specified in Table 4.The pitch diameter limits of sizecorrespond to one and one-half turns, large or small, ofthe Standard Taper Pipe Thread.The major and minordiameters vary with the pitch diameter, as the StandardPipe Thread Form is maintained within the truncatedtolerances shown in Table 1.
6 GAUGES AND GAUGE TOLERANCES FOR
STANDARD PIPE THREAD,NPT
6.1 Design of Gauges
Gauges for Standard Pipe Threads in this Standardprovide a functional check and are of the standard typeas described below.