Pipes are only as good as their connection. If two pipes come together without a snug fit, then you have a problem on your hands.
A big part of making sure pipes fit together perfectly is their threading. To make things easier, industry professionals got together a long time ago to standardise pipe threading. Much like Henry Ford and the assembly line, these pioneers started out to make life easier for every industry that requires pipefitting.
The result is two specific standards for the threading on the ends of pipes. NPT threads and BSP threads have become the standard on all pipes around the globe. Your location in the world will dictate which one is the standard. But, no matter where you go, you can be sure you're going to deal with either NPT or BSP.
So, what are they? Which one works best? Are they even compatible?
Well, we're going to cover all of that and more. Consider today's article your go-to guide for understanding BSP and NPT threads.
What Are NPT Threads?
NPT stands for National Pipe Thread Tapered. This is the standard for threading and fitting pipes in the U.S. The American National Standard Pipe Thread is the one that originally established the standard.
The standard NPT threads are available in several different types of pipes. It has become the national standard in the U.S. for both straight and tapered threaded pipe.
These pipes can be useful for a wide variety of applications. The most common uses are pressure-tight sealing and rigidity.
NPT threads break down further into two different types. Industry workers can choose from either NPT threads or NPS threads. NPT is the threading for tapered pipes. NPS is the threading configuration for straight pipes.
What Are BSP Threads?
BSP stands for British Standard Pipe. It's the standard for pipe threads in the U.K. and various other countries throughout the world. This threading format was established by ISO measure 228.
BSP uses the Whitworth standard thread. It is also one of many threading parameters adopted internationally. All of the technical standards adopted internationally aim to standardise and improve the sealing of pipes and pipe fittings.
The BSP threads are more far-reaching than the NPT threads. BSP threading has become the standard almost worldwide.
Just like NPT threads, BSP threads can also be divided into two different types. International workers can use BSPT for the tapered pipe. They also have the option of BSPP, which stands for British Standard Parallel Pipe.
That would be the equivalent of the "straight pipe" in the U.S.
Why Standardise Pipe Threads?
At the turn of the century (the early 1900s), the world was experiencing the Industrial Revolution. Major cities like New York and London were experiencing building and growth at a pace that had never been seen before. Many of the iconic buildings we see today owe to that era.
With so many manufacturers, builders, and users needing pipe for a variety of different uses, something had to be done. Without pipes being compatible, the world wouldn't have been able to evolve the way it did during this time.
William Sellers of the U.S. was the first to standardise pipe fitting and pipe threading in the United States. He did this by establishing the U.S. standard for tapered pipe threads in 1864. Sellers' influence began to reach even further when he went on to become president of the Franklin Institute.
During his time in this position, Sellers applied the standardisation of threading to screws, nuts, bolts, and other fasteners as well as pipes. Before that time, these tools had no standardised threading. This made it hard for them to use in common applications like building and construction.
The reason his design took off is an interesting one. Sellers' design for the standardised threads used something known as the "peak and valley" method. This method created a 60° angle of torque on the screws.
This new angle and "peak and valley" configuration were easier for manufacturers to mass-produce.
In 1841, over two decades before Sellers, Joseph Whitworth began to standardise pipefitting and threading in Britain. His thread design was quickly adopted. Its primary use was for the construction of the railroads throughout the country.
Eventually, Whitworth's thread design would become the standard for all of Britain and the United Kingdom at large. It would become known as the British Standard Whitworth.
The British Standard Whitworth was actually used throughout the U.S. and Canada for some time. This was done up until the 1860s. (Probably around the time that Sellers' came along with his standardisation).
But, although it was widely accepted as "the standard" it still competed with a variety of thread designs. Progress was being made, but a universally compatible thread design was still a challenge at this point. Over time, Sellers' thread became the standard in North America.
The reason that the U.S. and Canada moved away from the Whitworth thread is that Sellers' thread began to be used in work on government contracts. It also became the standard screw for the U.S. Railroad boom. And, for those that don't know, railroad companies at this time were very influential.
State and federal governments responded to railroad makers throughout the country. So, if they liked Sellers' thread, it was going to be the one. No questions asked.
Once Sellers' thread was adopted by the U.S. government and major railroads, many other businesses and manufacturers soon followed suit.
And that's how we've arrived at the threading standardisation we know today.
Uses for Threads
The two formats, tapered threads, and straight threads, have different uses. Tapered threads, of both the U.S. and British standards, are used in cases where pipes need to be fastened tightly. The tapered thread allows for the creation of an airtight seal between the two pipes.
These are a great option in any application that requires fluid running through the connected pipes. When pressure and torque are applied, the threads "pull together" to create a leakproof or airtight seal. This is because the torque and pressure will actually compress and seal the pipe.
Straight threads have their place, too. But, they are usually used just as a connector between two pipes.
Tapered pipes can be used in a variety of industries. They can hold hydraulic fluid, gas, and they can even be used as a conduit for steam. As a result, they become an integral part of the operations for power plants, manufacturing facilities, gas companies, oil companies, and companies dealing with chemicals.
Many pressure systems found in ships use BSP threading. NPT threads are found more in the oil and gas industry. But, these threads aren't used only for metal piping.
Both BSP and NPT have been adopted for a wide range of materials. You can see both types of threading on cast iron, copper, PVC, bronze, PTFE, and nylon.
Are BSP and NPT Threads Compatible?
While the BSP and NPT systems make for great thread standardisation on their own, it's not possible to cross the thread designs. If you are looking to connect a BSP pipe to an NPT pipe, it won't work.
The reason they don't fit together is that their individual thread designs are different. The NPT design has a 60° angle and the "flattened peak and valley" design pioneered by Sellers. While the BSP design has a 55° angle and "rounded peak and valley" design.
The two thread forms are also incompatible because of the thread pitch. Pipes of different diameters have different thread pitches. The thread pitch is a measurement of TPI or the Threads per Inch.
For example, in a 5" diameter pipe, an NPT thread design would have 8 threads per inch. A BSP pipe of the same diameter would have 11 threads per inch. The difference in the number of threads per inch would prevent the two pipes from locking together.
Connecting It All
Now you know all there is to know about NPT threads and BSP threads. These two thread configurations changed the landscape of history as we know it. We wouldn't be where we are today if it wasn't for the help of William Sellers and Joseph Whitworth.
When used for the proper applications, these thread designs can help manufacturers and other businesses accomplish their goals and keep the world running.
If you have any more questions about NPT or BSP threads and pipefitting, contact us today. We are more than happy to help. And our friendly and knowledgeable staff will help you find the pipe product that's perfect for your project.