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Intro to Black Iron Pipe Fittings

hose school | Posted: 8/4/2021

Black iron pipe is strong, and despite its name, it is actually made of a low-grade “mild steel” compound, not iron. This steel allows the pipe, and its fittings, to have more strength than its copper, aluminum, or PVC counterparts. It is commonly used to transport gas as the extra strength in this metal pipe could be what keeps potentially deadly gas from leaking throughout a home!

What’s an NPT Thread?

While black iron is a low-pressure pipe, the temperature rating is where this metal really shines. The black iron pipe can withstand temperatures of over 538°C and black iron pipe fittings are NPT threaded. Well, NPT stands for National Pipe Tapered, and NPT fittings seal by a wedging action, which makes for an easy installation.

Three Main Types of Black Iron Pipe Fittings

Here at, we carry three types of black iron pipe fittings; malleable iron, forged steel, and seamless fittings.

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Malleable iron fittings are made for light industrial and plumbing use up to 300psi. These common fittings are more ductile, which means that they are able to be deformed without losing toughness or becoming brittle. This makes them great for industrial use.

Forged fittings are made of carbon steel, stainless steel, or nickel alloy. The forging process involves heating a piece of carbon steel and molding it into the desired shape, which creates a stronger fitting than casting. Forging actually changes the structure of the steel, specifically the steel grain. Altering the grain flow in fact makes it tighter, which creates a metal that has greater impact and shear strength.

Lastly, we have Seamless fittings. These fittings are made directly from a section of seamless pipe material by applying heat and pressure. Their design allows them to withstand greater pressures and they won’t crack under an extreme load. Since there are no welded parts, these fittings are perfect for use in the oil and gas, chemical, plumbing, and fabrication industries!

Ways to Seal Black Iron Pipe

NPT black iron pipe seal through a wedging action, but they also need a sealant to create a leak-proof seal. Luckily, sealing tape and pipe sealant are inexpensive and easy to apply! But, be careful you need to be sure you’re selecting a sealant that’s compatible with whatever material you’re moving through the pipe.

Black Pipe Fittings
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Sealing tape, commonly referred to as “Teflon Tape” or “PTFE” tape, is a simple way to seal joints without making a mess. PTFE can only withstand temperatures up to 260°C, but that’s more than enough to handle anything nature can throw at it. But best of all, it only takes a few seconds to apply.

Your other option is a pipe sealant, also known as “joint compound” or “pipe dope.” This is a liquid sealant that oozes between threads to maintain a tight seal. Pipe sealant lubricates while it fills in all the microscopic imperfections in a thread. However, the downside to pipe sealant is that it can be quite messy compared to sealing tape.

What are Pipe Nipples?

Pipe nipples are often used in plumping and other hydraulic applications as adaptors. A pipe nipple is a length of straight pipe with male threads on both ends, as opposed to most fittings or pipes, which have one end with male, or external threads and the other with female, internal threads. Although you may be familiar with the standard barrel nipple, did you know that there are actually several different types of pipe nipples? A shortlist includes close, hex, hose, and welding nipples. There are, of course, more types out there, but these are the most commonly found.

Different Types of Pipe Nipples

Pipe Nipples
Black Malleable Barrel Pipe Nipple. Part Number: blaxhnip150cl

Barrel Nipple

The most basic type, a barrel nipple, is a short length of pipe with male pipe threads at both ends. These threads are for connecting other fittings. For instance, the connection between the pipes in your wall and the shut-off valve under your sink is most likely a barrel-style pipe nipple! These nipples can range anywhere from 1-1/2” to 60” long, not including the threads.

Close Nipple

If you have a nipple but there is no bare or unthreaded pipe between the two connecting ends, you know you’ve got a closed nipple. With closed nipples, the connected fittings come very close to touching one another and barely any of the nipples can be seen between them. Some construction sites require this kind of tight placement, but sometimes, close nipples can be difficult to work with. This is because unscrewing them requires a tight hold on part of the threaded area, which will damage the threads. That’s why some industries, such as oil and gas, where these nipples are being used for intense applications, don’t allow the use of closed nipples. However, for job sites where closed nipples are used often, an internal pipe wrench is a great investment.

Hexagonal Nipple

If you can spare a bit of room between the threaded ends on your nipple, you may choose to use a hexagonal nipple. Hex nipples have a hexagonal section in the middle, which works just like a nut. This means that you can grip it with a wrench and torque, tighten, or loosen it much more easily than a normal, rounded pipe.

Threaded Nipple 

The rounded cap that’s used to plug the end of a pipe or pipeline section is called a bull plug. This threaded nipple has a rounded, closed-end to seal off a pipe. These plugs are usually found on unfinished pipelines to keep dust and moisture, but they can also be used as an isolation device in piping systems.

Hose Nipple

The next nipple is a bit different and that’s because it’s made specifically for hydraulic applications. A hose nipple, which is a specialty nipple designed for hoses that require connection to a pipe. These are commonly found in low-pressure hydraulic systems since the hose barb connection doesn’t fare well in high-pressure applications. The barb on this fitting may be the same size as the pipe connection, or it might be smaller, depending on its usage.

Welding Nipple

Finally, there’s the welding nipple. This variant has a threaded connection on one end, and a beveled pipe on the other. The key to this nipple is in its name – the cut end is designed to be welded to piping, a fitting, or a tank. This allows for easy connection of pipes or other fittings once the unthreaded end has been welded to the surface of your choice. These are typically found in heavy-duty applications, like hydraulic presses, mining equipment, and steel mills.

What About Pipe Schedules?

One key point to keep in mind when choosing the correct pipe nipple is the pipe schedule. Pipe schedules relate to the thickness of the pipe wall and the most common schedules are 40 and 80. As the number increases, so does the wall thickness. For instance, a 1” schedule 40 pipe nipple will have a wall thickness of 0.133”, while a 1” schedule 80 pipe nipple will have a wall thickness of 0.179”. However, while the schedule number can be the same for pipe nipples with different outside diameters, the actual wall thickness will vary.

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Pipe Schedules and Weights

So, the best way to see the relationship between nipple size, schedules, and wall thickness is to refer to a conversion chart! Another thing to keep in mind is that the nominal pipe size, or NPS, represents the approximate inside diameter of the pipe nipple. That’s because if the schedule number on size is changed, it affects the inside diameter, but not the outside diameter. For instance, a 2” nominal pipe nipple will always have an outside diameter of 2.375”, however, depending on the strength of the pipe nipple, the wall thickness could be either 0.154” or 0.218”.

That just about covers everything about pipe nipples, but if you have any questions feel free to contact us here, and make sure to subscribe to our email list so you can keep up to date with the latest offers, flyers, new products, and giveaways here at

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