NPT 和NPTF螺纹

NPT 和NPTF螺纹有什么区别，我今天看了螺纹手册也没有看出多大的区别，用NPT 的螺纹规可以检验NPTF螺纹吗？

NPT Vs. NPTF Taper Pipe Threads

The two most common taper pipe threads used in the United States are NPT and NPTF. Applications range from electrical conduits and hand railings to high-pressure pipe lines that carry gas or caustic fluids. NPT threads are for mechanical or low-pressure air or fluid applications and require the use of sealing compounds like Teflon tape, to provide the seal. When the application is more critical, and the sealing compound may fail due to high heat or pressure, NPTF Dryseal threads are used. This mechanical seal is produced by the mating and slight crushing of the threads when a wrench is applied to tighten the fittings.


Visually, both threads appear to be identical. Both have a ¾” taper over one foot of length. Both have the same pitch diameter at the top of the hole of internal threads or end of the pipe on external threads, and both have the same thread lengths or depths. However, there is a subtle difference in the thread form that differentiates the two. The major and minor diameters of both threads differ slightly. With NPT threads, after a wrench is applied, slight spaces at the major and minor diameters may exist that would allow the assembly to leak and therefore a sealing compound is used to fill any gaps. On the other hand, NPTF threads are designed to ensure that sufficient crushing of the entire thread form will take place to produce a mechanical seal.



How does the difference in thread forms effect the tooling used to produce NPT and NPTF threads? Taps are available for both NPT and NPTF threads having the appropriate form to produce each type of thread. Since NPT threaded parts require sealing compounds, it is acceptable to use an NPTF tap for NPT applications. However, NPT taps cannot be used for NPTF applications, as it will likely produce a thread that will leak. The same is true of external threads. In most cases the tap drill is the same for both forms.



The most significant difference in the two threads is the inspection required. Since sealing compounds will be used for NPT threads, only a single plug with a step, known as an L1 plug (internal thread) or a single thin L1 ring (external) are required to check size. However, since the taper and the position of major and minor diameters are so critical to the sealing of NPTF threads, the additional threads in the assembly known as L2 and L3, and the major and minor diameters are inspected with either special plug or ring gages.
此部份為之前看過的資料 其中有說明兩種螺紋在使用上的差異
不過能否可以檢驗
我並不清楚
我猜應該是可以的?
因為兩者尺寸相去極小

上面不是说要用专用的螺纹赛规或环规吗？！对于NPT检验可以松一点，对于NPTF要用专用塞规！两者主要的差别是大径尺寸

美国标准管螺纹 NPT

检验的时候要买专用的NPTF螺纹规吗？

当然要买专用量规了

使用工况有什么区别?

美制干密封管螺纹（NPTF）要保证在不使用密封填料的情况下能实现密封。所以，它的单项螺纹参数精度（牙高、螺距和牙侧角）要比美制一般用途管螺纹的高。另外，它的牙顶与牙底处的配合为过盈配合；而美制一般用途管螺纹的牙顶与牙底处的配合为过渡配合。美制干密封管螺纹主要用于对密封有严格要求的特殊场合，例如毒气弹、汽车、飞机、航天器等。

螺纹代号Thread Code

            一、英制螺纹（螺纹牙型角55度）Thread of British standard ( Thread pitch shape angle 55°)
            BSW－－－－英国标准惠氏螺纹（粗牙）British Standard Whitworth Thread ( Coarse )
            BSF－－－－英国标准惠氏螺纹（细牙）British Standard Whitworth Thread ( Fine )
            G－－－－直管螺纹（外螺纹分A、B两面级、丝锥分G、G－D）Straight pipe thread ( Outside )
                      thread in AB: taps in G、G－D )
            R－－－－锥管外螺纹（旧代号ZG;KG）Outside paper pipe thread ( Old thread code  ZG,KG )
            RC－－－－锥管内螺纹（旧代号ZG;KG）Inside taper pipe thread ( Old thread code ZG,KG )

            二、美制螺纹（螺纹牙型角60度）Thread of American standard ( Thread pitch shape angle 60°
            UNC－－－－统一制粗牙螺纹（代替NC）Unified coarse pitch thread ( Instead of NC )
            UNF－－－－统一制细牙螺纹（代替NF）Unified fine pitch thread ( Instead of NF )
            UNEF－－－－统一制超细牙螺纹Unified superfine pitch thread
            UN－－－－－统一制不变螺距螺纹Unified thread
            UNS－－－－统一制特殊螺纹Unified Special thread
            NPT－－－－一般用途锥管螺纹（旧代号Z;K）Taper pipe thread for general purpose ( Old
                          thread code Z,K )
            NPSC－－－－管接头直管内螺纹Internal straight pipe thread for connection
            NPSM－－－－设备上自由配合，机械连接用直管螺纹Straight pipe thread for general purpose
            NPTF－－－－干密封锥管螺纹Dryseal taper pipe thread
            NPSF－－－－干密封燃油直管螺纹Dryseal straight pipe internal thread
            NGT－－－－气瓶用锥螺纹Special thread for gas cylinder

            三、米制螺纹Metric thread
            ZM－－－－－米制锥管螺纹 Metric taper pipe thread
           
四、其它螺纹Other threads
            SM－－－－缝纫机螺纹Thread for sewing machine
            PZ－－－－气瓶用锥螺纹Special thread for gas cylinder
            5V1－20V1－气门芯螺纹5V1－20V1－Tyre valve thread

            螺纹代号说明示例：Explanation of thread code. e. g.
            1/4－20UNC
            1/4－公称直径1/4" nominal dia. 1/4"
            20－每寸20牙twenty teeth per inch
            UNC－美标统一制粗牙螺纹unified coarse pitch thread ( American standard

NPT检验规一个，NPTF三个，其中一个和NPT一样的