Pipe threads are an important component in the construction of piping systems and networks, providing a secure connection between pipes and their fittings. There are two primary types of pipe threads used in most applications across the world: British Standard Pipe (BSP) and National Pipe Thread (NPT).
BSP is primarily used in Europe, Asia, Australia, and New Zealand, and is available in two versions: Parallel (BSPP) and Tapered (BSPT). In a parallel BSP thread, the threads run straight, while in a tapered BSP thread, the threads taper towards the end, forming a seal when tightened.
The parallel thread form of BSP is also known as G-thread or BSPP, and it is commonly found in applications that use low to medium pressure liquids and gases. The thread has a constant diameter from end to end, and requires an O-ring or gasket for sealing purposes. This type of thread is easy to install, making it a preferred choice for general-purpose applications.
The tapered thread form of BSP is typically used in high-pressure applications with liquids and gases, and it's also known as R-threads or BSPT. It is similar to the parallel thread form, but the threads are slightly larger at the base than at the tip, providing better sealing characteristics. The tapered thread does not need an O-ring or washer to be installed during assembly. Instead, it relies on the thread engagement itself to create an adequate seal.
NPT threads were introduced by the United States in 1864 and have since become the standard in North America. These threads are widely used in plumbing, oil and gas, HVAC, and industrial applications. NPT threads are available in male and female forms, with both having a slightly tapered thread. The taper angle is 1.7899 degrees, and the thread pitch increases with diameter to create a leak-tight seal between the male and female threads.
NPT threads are commonly used in high-pressure applications due to their superior sealing performance. They do not require a gasket or O-ring to be installed during assembly, making them easy to install and maintain. NPT threads can handle fluids where moderate hydraulic pressures are involved, which means they are suitable for water, chemicals, gases, steam, and petroleum products.
BSP and NPT threads are two of the most widely-used pipe thread standards in the world. Both have their advantages and disadvantages, as well as unique characteristics that make them ideal for specific applications. When selecting a pipe thread type, it's important to ensure that it is compatible with the intended application, taking into consideration pressure ratings, chemical compatibility, and environmental conditions.
Knowing these differences and understanding what constitutes a good fit for your needs will benefit you in the long run, ensuring a secure connection and ultimately preventing system failure or leaks.