Types of Threads on Gas Pipe Fittings: A Quick Guide

Disclaimer: This post may contain affiliate links, meaning we get a small commission if you make a purchase through our links, at no cost to you. For more information, please visit our Disclaimer Page.

There’s nothing worse than discovering a gas leak in your home. Suddenly, your house and your family are in danger—all because the fitting wasn’t installed correctly!

Threads are an important part of any gas pipe fitting. They create a secure, leak-free connection and ensure the safety of your home. That’s why it’s important to make the right choice regarding thread selection, sealant, and installation.

This guide will explore the most common thread types, suitable sealants used in gas pipe fittings, and provide tips on how to stay safe while changing them.

Let’s get into it!

Types of Threads

Choosing the correct thread type is the first step in ensuring a safe, leak-proof connection. It’s important to choose one that complies with industry standards and regulations.

NPT (National Pipe Taper)

In the U.S., you will generally deal with NPT (National Pipe Taper) threads. Due to their excellent sealing properties, they are the most commonly used type in standard U.S. gas pipe fittings. They come in a variety of sizes and materials according to specific parameters.

NPT threads feature a tapered design with tapered male and female threads. This allows for a tight seal when tightened. They also have a thread angle of 60 degrees, which helps enhance the sealing effect and makes them ideal for gas applications.

Teflon tape or thread sealant typically needs to be used with NPT threads to ensure proper sealing. This enhances the seal and helps prevent leaks.

Other Thread Types

While NPT is the most prevalent thread type for residential gas fittings in the U.S., there are also other options to consider. Outside of North America, BSP (British Standard Pipe) threads are the most common. They have a thread angle of 55 degrees and come in parallel or tapered forms.

Other thread types exist, including NGT (National Gas Taper); however, these threads have more specific purposes outside of residential use. For example, longer industrial pipes require different thread types to enhance safety and usability.

Plumbing and heating fittings installation and service close-up

Best Sealants for Gas Lines

Gas pipe fittings require a sealant to create a leak-proof seal. There are plenty of types available on the market based on your needs. Let’s examine a few:

Pipe Dope Compounds

Pipe dope is a popular choice for gas lines. It is a liquid sealant, which means it has a paste-like quality specially designed for metal-to-metal threads. One benefit of using pipe dope is that it has no cure time, meaning its effects work right away.

However, the downside of using pipe dope is that it can degrade over time due to heat and vibration. There are plenty of varieties of pipe dope, so it’s important to choose one formulated for gas applications to avoid this issue.

How to apply

  • Choose a sealant designed for gas applications.
  • Follow the manufacturer’s instructions to ensure proper application.
  • Clean any dirt and oil buildup from the male and female threads before applying.
  • Wearing gloves, apply the paste to the male thread. Avoid getting sealant inside the pipe.
  • Screw the threads together tightly to prevent leakage.
  • Wipe away any excess paste that squeezes out of the pipe.
  • Allow the sealant to cure according to the manufacturer’s instructions.

Anaerobic Resin Compounds

Anaerobic resin compounds are high-performance sealants typically used for commercial applications. The main benefit of using this sealant is its durability, especially under high pressure. These sealants only cure when oxygen is expelled, creating a solid, vibration-resistant seal.

When applied correctly, anaerobic resin sealant does not crack or erode over time, making it incredibly useful for high-pressure gas systems. You may need to call in a professional to apply it properly, as improper use can cause it to expand or crack.

How to apply

  • After cleaning the male and female threads, apply the anaerobic sealant to the male thread only.
  • Spread the sealant evenly around the circumference of the threads, avoiding excessive buildup.
  • Thread the male fitting into the female by hand and tighten.
  • Clear any excess sealant that squeezes out of the joint.
  • Allow it to cure following the manufacturer’s instructions.

Yellow Teflon Tape (Flex Tape)

Yellow Teflon tape is the most effective thread tape for natural gas. It is designed specifically for gas lines and is widely used in numerous industrial applications. Compared to other types, yellow Teflon tape has a higher density and is thicker, making it the preferred choice for gas applications.

The best part about yellow Teflon tape is that it’s easy to install and provides an effective seal. It is suitable for both metal and plastic threads and is resistant to most chemicals and solvents, making it perfect for use as a sealant.

How to apply

  • Remove any dirt or grease from the threads before you begin.
  • Ensure that the threads are running in a clockwise direction, and hold the tape roll in the same orientation.
  • Start wrapping the tape around the male threads, beginning at the second thread from the end of the fitting.
  • Follow the direction of the threads (clockwise) around the pipe 3-4 times, overlapping each layer by about half of the tape’s width.
  • When finished, cut the tape cleanly. Press the tape gently into the threads to ensure good adhesion.

PTFE Tape

While not a sealant on its own, PTFE tape is still an effective tool for assembling gas pipe fittings. You can use it with NPT threads to ensure a stable, leak-free attachment. It’s typically used alongside a gas-related sealant to fill any gaps in the thread connection.

Safety Tips

Installing gas pipe fittings is a fairly straightforward process. Here are a few tips you can follow to ensure a safe and stable connection:

Use the Correct Thread Type and Size

In the U.S., NPT threads are the standard type used for gas pipe fittings. However, they aren’t compatible with other thread types, such as BSP. This is why it’s important to choose the correct thread type to avoid improper connections.

Additionally, NPT threads come in various sizes and materials. You’ll need to determine the nominal pipe size (NPS) required for your application before you begin to avoid leaks due to incorrect installation.

Apply Thread Sealant or Tape Properly

Always follow the manufacturer’s instructions depending on the type of sealant you’re using. For example, each type of sealant will have different curing allowances and times.

Remember to clean the threads thoroughly before applying any sealant or tape. Any buildup of dirt, grease, or debris can be potentially hazardous and prevent a leak-free connection.

You should also wear gloves when applying sealants, such as pipe dope or anaerobic resin, as these materials can potentially be harmful when in contact with skin. Ensure you work in a well-ventilated area or have a fan on while applying.

Plumber putting a paste sealant.

Tighten Fittings to the Correct Torque

Once you have applied the seal, securely tighten the fittings to the correct torque to ensure a secure connection. Use a torque wrench, tightening until the proper torque is achieved. This step is important, as over- or under-tightening can damage the threads or compromise the seal, potentially becoming a health and safety hazard.

Inspect for Leaks After Installation

You should always check for leaks after installing gas pipe fittings. There are a few methods to do so after allowing time for the sealant to set:

  • Visual inspection: First, look closely at the joints for any signs of moisture or dripping. Even if you don’t find any wet spots, you should continue with the following.
  • Soap bubble test: This method uses a soapy water solution to check for leaks in the pipe. Simply mix dish soap and water, then apply it to the threaded joint with a brush or spray bottle. If any bubbles form, this indicates a leak.
  • Gas leak detector: A leak detector can come in different forms, from color-changing fluid to an electronic device. Use the detector around joints to detect a potential gas leak.

If in Doubt, Consult a Professional

While it’s fairly easy to DIY your gas fittings, you should always call a professional when in doubt. This is advisable if you’re unsure which thread type to use or which sealant would work best for your needs. A professional can help ease your concerns and ensure a safe connection that aligns with industry standards.

Conclusion

It’s important to use the correct thread type and sealant for gas pipe fittings to ensure a safe and leak-free connection. Using the wrong type can be potentially dangerous and increases the risk of a gas leak in your home.

NPT threads are the most common type and create a secure connection when used with an appropriate sealant, such as yellow Teflon tape or liquid paste. Proper installation and sealing are crucial to ensuring your safety.

While DIY applications are suitable for minor fixes and installations, you should seek professional help for more complex scenarios. Not only will this provide peace of mind, but it will also help prevent any problems from occurring in the future.

Marco
Marco
Meet Marco, a lifelong tinkerer and DIY enthusiast, developed a passion for plumbing after fixing a leaky faucet in his own home. Years later, he turned that passion into a thriving business, Amarco Plumbing, where he shares his knowledge and expertise with the community.