#Industry News
Selection and Installation Precautions of NPT Threads
G threads, or tapered pipe threads, belong to non-sealed pipe threads, which generally rely on O-rings or gaskets to achieve ideal sealing effects.
Due to the good sealing effect, thread connection is one of the commonly used process connections in automation instruments. Threads are according NPT (National Pipe Threads) as American Standard which is the most used in the oil industry, which has a 1° 47′ tapered thread with a 60° thread angle, Chinese National standards can be found in GB/T12716.
G threads, or tapered pipe threads, belong to non-sealed pipe threads, which generally rely on O-rings or gaskets to achieve ideal sealing effects. Because the threads of the mating fittings are parallel to each other, there is no interference between the flanks, crests, and roots. Consequently, the seal must be made with a gasket, O-ring, or some metal to metal contact.
NPT threads belong to cone taper, the sealing performance is better than G threads. NPT threads are mainly used in applications with high pressure, high connection strength, and high sealing requirements, so the accuracy and the processing difficulty are also strict. For a Jiwei G thread connection product, a gasket will be provided for customer installation.
The selection of NPT threaded connections and the sealant are also carefully considered. Tapered pipe threads always need a sealant to seal system fluids and reduce the potential for galling of the threads.
Attention should be paid to the use of sealant:
1. Choose a suitable width of sealant, rather than the wider the better.
2. The appropriate number of winding circles is better than the more. The sealant with a large number of winding circles is prone to gaps between each layer, which cannot tightly fit with the thread and instead affects the sealing effect.
In addition to the need to pay attention to the winding of sealant, the fitting accuracy of NPT threads is also crucial. The storage tanks have various specifications of threaded holes. Taking Jiwei Vibrating Rod Level Switch with 1 “NPT thread as example, the outer diameter of the extended tube between the vibration probe and the process connection is 29mm.
1 “NPT female thread has a taper, with a maximum pitch diameter of 31.668mm, a minimum pitch diameter of 31.255mm and a minimum minor diameter of 29.489mm. With small fault tolerance, it is necessary to polish the weld seam after welding the extension pipe to ensure consistency of the extension pipe through the female threaded hole. Before leaving the factory, each threaded connection undergoes inspection with a pitch gauge to determine the thread pitch.
