英美螺纹资料.pdf

Thread Thread 1 Definition The diameters,threads per inch(TPI)and thread pitch,etc.are necessary to completely identify a thread.In a shop,specialty gauges are required to accurately gauge or identify threads.In the field,in the absence of these gauges,thread leaf gauges can be used to identify the Threads Per Inch(TPI)and the thread pitch.On threads you have determined to be straight threads,a caliper can be used to measure the Outside Diameter of the Male(ODM)or the Inside Diameter of the Female(IDF).A caliper can also be used to take measurements of tapered thread diameters.However,these are more difficult to define because of the taper.Fortunately,there are few tapered threads to deal with and these can usually be identified from the nominal ODM and the TPI.However,identifying the thread may not fully identify what is needed in a mating fitting.The application is the primary limiting factor on the thread type used.We offer products with a wide variety of threads used with hose,pipe and hydraulics.When attempting to choose a fitting,it is always advisable to first identify the thread to which it must connect.This may entail checking with a fitting or equipment manufacturer.The fire hose thread specifications for some local municipal fire equipment and hydrants may vary according to local specifications.These can generally be most easily identified by contacting the local fire department responsible for the hydrant.The most common thread used on fire equipment is National Standard Thread(NST),also known as National Hose thread(NH).When it is not possible to identify the thread:1)Determine the number of threads per inch by measuring the distance from peak of thread to peak of thread across the largest number of whole threads.Then divide the number of threads by the measurement.(This will provide the TPI).2)Check to see if the thread is straight or tapered.a)Straight Threads Measure the Outside Diameter of the Male(ODM)or the Inside Diameter of the Female(IDF),from peak of thread to peak of thread.b)Tapered Threads Measure the Outside Diameter of the Male(ODM)at the large end and the small end,or the Inside Diameter of the Female(IDF)at the large end and the small end,from peak of thread to peak of thread.Then measure the Outside Diameter(OD)of the unthreaded pipe.Once the application and these two pieces of information have been determined,the thread can generally be determined.When in doubt,contact the manufacturer.Straight Thread Male Female Tapered Thread Male Female Threading InformationThreading Information Abbreviation System Name Compatibility Seal MethodMale BSPP with Female BSPP Washer Female BSPP with Male BSPP Washer BSPP British Standard Pipe Parallel Female BSPP with Male BSPTr Washer Male BSPTr with Female BSPTr Thread Male BSPTr with Female BSPP Washer Female BSPTr with Male BSPTr Thread BSPTr British Standard Pipe Taper Female BSPTr not compatible with Male BSPP 1Male NH(NST)with 1 Female NH(NST)Washer 1 Female NH(NST)with 1 Male NH(NST)Washer 1 Thread is used on both hose&1 hose.CHT American Standard Fire Hose Thread(1 National Hose Thread is Chemical Hose Thread,also known as Booster Hose Thread)Not compatible with other systems Male GHT with Female GHT Washer Female GHT with Male GHT Washer Thread is the same for all size hose.GHT Garden Hose Thread Not compatible with other systems Generic name for Straight Pipe Thread Washer IPS Iron Pipe Straight ThreadSee NPSH for compatibility JIC Joint Industrial CommitteeUsed with other mating JIC threads Mechanical Male NH(NST)with Female NH(NST)Washer Female NH(NST)with Male NH(NST)Washer NH or NST American Standard Fire Hose Coupling Thread(National Hose thread also known as National Standard Thread Not compatible with other systems Thread pitch and diameters of fire threads may vary according to local and municipal regulations.Male NPT with Female NPT Thread Male NPT with Female NPTF Thread Male NPT with Female NPSM Washer Male NPT with Female NPSH Washer Female NPT with Male NPT Thread Female NPT with Male NPTF Thread NPT American Standard Taper Pipe Thread(National Pipe Thread Female NPT not compatible with Male NPSM or Male NPSH Male NPTF with Female NPTF Thread Male NPTF with Female NPT Thread Male NPTF with Female NPSM Washer Male NPTF with Female NPSH Washer Female NPTF with Male NPTF Thread Female NPTF with Male NPT Thread Female NPTF with Male NPSM or Male NPSH Not CompatibleNPTF American Standard Taper Pipe Fuel Dryseal Thread(National Pipe Tapered Fine)Note:NPTF with NPTF threads do not require sealant for the initial use.After that,sealant is required.Male NPSH with Female NPSH Washer Female NPSH with Male NPSH Washer Female NPSH with Male NPT Washer Female NPSH with Male NPTF Washer NPSH American Standard Straight Pipe for Hose Couplings(National Pipe Straight Hose)Female NPSH with Male NPSM Washer Male NPSM with Female NPSM Male NPSM with Female NPSH Female NPSM with Male NPSM Female NPSM with Male NPT NPSM American Standard Straight Mechanical Joints(National Pipe Straight Mechanical)Female NPSM with Male NPTF Seal can be either mechanical or washer.Mating fittings must be of same type TIPT Tapered Iron Pipe ThreadGeneric name for Tapered Pipe Thread Thread Thread Dimensions Thread Dimensions Nominal Dimensions of Standard ThreadsNominal Dimensions of Standard Threads NPTNPSH NPSM Size Pipe O.D.TPITPIODM(Max)IDF(Min)TPIODM(Max)IDF(Min)1/8.405 27-270.397 0.358 1/4.504 18-180.526 0.468 3/8.675 18-180.662 0.603 1/2.840 14 140.8248 0.7395140.823 0.747 3/4 1.050 14 141.0353 0.9500141.034 0.958 1 1.315 11.5 11.5 1.2951 1.1921 11.5 1.293 1.201 1-1.660 11.5 11.5 1.6399 1.5369 11.5 1.638 1.546 1-1.900 11.5 11.5 1.8788 1.7758 11.5 1.877 1.785 2 2.375 11.5 11.5 2.3528 2.2498 11.5 2.351 2.259 2-2.875 8-82.841 2.708 3 3.500 8-83.467 3.334 4 4.500 8-84.466 4.333 5 5.563 8-85.528 5.395 6 6.625 8-86.585 6.452 8 8.625 8-10 10.750 8-12 12.750 8-ODM=Outside Diameter of Male IDF=Inside Diameter of Female TPI=Threads per Inch GHT()=1.0625 ODM,11-TPI NH(NST)BSPP(Parallel)BSPTr(Tapered)Size Pipe O.D.TPI ODM(Max)IDF(Min)TPIODM(Max)IDF(Min)TPI 1/8.405-0.383 0.33728 1/4.504-0.516 0.45019 3/8.675-0.656 0.58819 1/2.840-0.825 0.73314 3/4 1.050 8 1.375 1.2246-1.041 0.95014 11.315 8 1.375 1.2246 11 1.309 1.19311 1-1.660-1.650 1.53411 1-1.900 9 1.990 1.8577 11 1.882 1.76611 22.375-2.347 2.23111 2-2.875 7.5 3.068 2.9104 11 2.960 2.84411 33.500 6 3.623 3.5306 11 3.460 3.34411 44.500 4 5.010 4.7111 11 4.450 4.33411 4-4 5.760 5.4611-55.563 4 6.260 5.9602 11 5.450 5.35911 66.625 4 7.025 6.7252 11 6.450 6.35911 ODM=Outside Diameter of Male IDF=Inside Diameter of Female TPI=Threads per Inch GHT()=1.0625 ODM,11-TPI NOTE:Female NPT(Tapered Pipe)thread is not available on hose swivel nuts.Normal Engagement Length of NPT Thread in Inches(A)*Normal Engagement Length of NPT Thread in Inches(A)*Size 1/8 1/4 3/8 1/2 3/41 1-1-2 Length 1/4 3/8 3/8 1/2 9/16 11/16 11/16 11/16 3/4 Size 2-3 4 5 6 8 10 12 Length 15/16 1 1-1/8 1-1/4 1-5/16 1-7/16 1-5/8 1-3/4*Dimensions given do not allow for variations in tapping or threading Thread Sealing TipsThread Sealing Tips Thread Seal Type A seal is obtained by applying a sealant to the male thread before engaging.The sealant is used to prevent spiral leakage.Thread tape or paste is the preferred sealant in this type of application.Washer Seal Type A seal is obtained when the male thread is tightened down onto the washer of the female assembly.The washer should be inspected regularly and replaced as needed to prevent leakage.Mechanical Seal Type A seal is obtained through metal to metal contact or metal to seal contact,for example JIC couplings have a metal to metal seal.EZ-Boss Ground Joint couplings have a metal to seal contact(shown at left).The couplings should be retightened as needed to prevent leakage.More Thread Sealing Tips.Sealing NPT threads can be an exasperating experience if certain techniques are not followed.The following tips will help alleviate many common problems in thread sealing:1.Always use some type of sealant(tape or paste)and apply sealant to male thread only.If using a hydraulic sealant,allow sufficient curing time before system is pressurized.2.When using tape sealant,wrap the threads in a clockwise motion starting at the first thread and,as layers are applied,work towards the imperfect(vanishing)thread.If the system that the connection being made to cannot tolerate foreign matter(i.e.air systems),leave the first thread exposed and apply the tape sealant as outlined above.3.When using paste sealant,6.For sizes 2 and below,tape or paste usually performs satisfactorily.When using thread tape,four wraps(covering all necessary threads)is usually sufficient.7.For sizes 2-and above,thread paste is recommended.If thread tape is used,eight wraps(covering all necessary threads)is usually sufficient.Apply more wraps if necessary.8.For stubborn to seal threads,apply a normal coating of thread paste followed by a normal layer of thread tape.9.For extremely stubborn to seal threads,apply a normal apply to threads with a brush,using the brush to work the sealant into the threads.Apply enough sealant to fill in all the threads all the way around.4.When connecting one stainless steel part to another stainless steel part that will require future disassembly,use a thread sealant that is designed for stainless steel.This stainless steel thread sealant is also useful when connecting aluminum to aluminum that needs to be disconnected in the future.These two materials gall easily,and if the correct sealant is not used,it can be next to impossible to disassemble.5.When connecting parts made of dissimilar metals(i.e.steel&aluminum),standard tape or paste sealant usually performs satisfactorily.coating of thread paste followed by a single layer of gauze bandage followed by a normal layer of thread tape.Caution!When this procedure is done,the connection becomes permanent.Extreme measures will be necessary to disconnect these components.All other measures to seal the threads should be explored prior to the use of this technique.10.Over-tightening threads can be just as detrimental as insufficient tightening.For sizes 2 and below,hand tighten the components and,with a wrench,tighten 3 full turns.for sizes 2-and above,hand tighten the components and,with a wrench,tighten 2 full turns.2 Pipe Thread Standards Two common pipe thread standards exist:National Pipe Thread(NPT)-a tapered thread National Standard Free-Fitting Straight Mechanical Pipe Thread(NPSM)-a straight thread Less common standards also exist:Garden Hose Thread(GHT)Fire Hose Coupling(NST)British Standard Taper Pipe Thread(BSPT)Female NPT threads can be designated as FPT and male NPT threads can be designated as MPT.I have also seen female NPT threads designated as FNPT and male as MNPT.Straight Versus Tapered Threads Threaded pipe can be connected to join things together,which does not necessarily produce a leakproof seal,or they can be joined and sealed.Straight threads only provide a mechanical junction.They dont really seal.Tapered threads both join and seal.The deeper you drive them,the tighter the seal.Pipe Thread Tape Whenever you want a good seal when screwing together pipes and fittings,use pipe thread tape.This is usually made of PTFE,the most famous brand of which is Teflon.In addition to sealing,pipe thread tape also lubricates the joint,which:makes it easier to tighten it makes it easier to disassemble the joint in the future reduces/eliminates thread galling Thread galling is when threads weld themselves together.This is more common with pipes and fasteners made from alloys that protect themselves from corrosion by developing their own oxide surface film,like aluminum and stainless steel.Standard Pipe Sizes Pipe sizes do not refer to any physical dimension of modern pipe.If you measure a piece of 1/4 NPT pipe,you will have a hard time finding anything there that measures 1/4.Historical note:The sizes derive from the days when pipes were made of iron,pipe walls were rather thick,and the internal diameter(ID)was standardized.At that time,if you specified a 1/2 pipe,it had an internal diameter of 1/2,and an outer diameter that depended on the thickness of the wall.Nowadays,the standards measure the threaded part of the pipe,the outer diameter(OD).This lets thin-wall and thick-wall pipe use the same fittings.But we kept the same names,so when you say 1/2 pipe,you get a pipe whose outer diameter is the same as that of an old-fashioned iron pipe whose inner diameter was 1/2.In order to get the right size,you should measure the outer diameter(OD)of the pipe,and look it up in a table to find out what it is officially called.Its also a good idea to measure the threads per inch(TPI).The combination of OD and TPI provide positive identification of standard pipe sizes.Pipe Thread Size Threads per Inch OD Fraction(approximate)OD Decimal(actual)Normal depth for tight joint 1/16 27 5/16 0.3125 0.2611 1/8 27 13/32 0.405 0.2639 1/4 18 35/64 0.540 0.4018 3/8 18 43/64 0.675 0.4078 1/2 14 27/32 0.840 0.5337 3/4 14 1-3/64 1.050 0.5457 1 11-1/2 1-5/16 1.315 0.6828 1-1/4 11-1/2 1-21/32 1.660 0.7068 1-1/2 11-1/2 1-29/32 1.900 0.7235 2 11-1/2 2-3/8 2.375 0.7565 2-1/2 8 2-7/8 2.875 1.1375 3 8 3-1/2 3.5 1.2000 3-1/2 8 4 4.0 1.2500 4 8 4-1/2 4.5 1.3000 3,