The Gas Expert's Guide to Creating a Gas Tight Seal with NPT Thread

The Gas Expert's Guide to Creating a Gas Tight Seal with NPT Thread

When dealing with natural gas, safety is always a top concern. One way in which both safety and efficiency can be optimized is by creating a proper gas tight seal at the meter set. As knowledge that every natural gas provider can benefit from knowing, consider this your complete guide to creating a gas tight seal with National Pipe Threads (NPT).

NPT thread is commonly used on the parts that make up and surround a natural gas meter set. However, there are a number of problems that can affect the NPT thread seal of 3/4”, 1 1/4”, and 2” NPT threads with Schedule 40 steel pipe, Schedule 80 steel pipe, and cast iron fittings, such as the following:

• Threads do not meet NPT gaging requirements
• Damaged or nicked threads
• Debris in the threads
• Unsuitable use of thread sealant
• Improper use of wrenches (use a smooth jaw on a hexagon or octagon)

Keep the above issues from happening in the first place by understanding that the recommended* tightening is hand tight plus 1-1 1/4 turns when using properly gaged threads and appropriate pipe dope. The total thread engagement should be between 3.5 and 6 threads. Typical sealing occurs by one turn past hand tight at the approximate values on the table to the right. A sealed assembly is easily attainable while using the smallest available wrenches (12”-18”). A complete turn beyond this sealing torque will increase torque by about 100 foot-pounds. Always verify that the seal is completed by testing the joint. Please keep in the mind the following additional tips and tricks:

• Do Not Overtighten:
  An NPT joint is formed by wedging the male thread into a female thread. Pipe threads seal by metal-to-metal interference over the tapered surface area with increasing forces as it tightens. Overtightening beyond the sealing torque continues to wedge the pipe into the body and can crack the female thread. In addition, do not back off a fitting after it has been tightened.

• PTFE Tape Should Not Be Used:
  Tape lessens the torque and leads to excessive thread engagement

• Poor Threads
  Improperly gaging threads and dirty or damaged threads can prevent joints from sealing. Excessive tightening may be attempted to stop the leak when this may only cause more damage.

• Pipe Strength Matters
  Torque increases more quickly when tightening Schedule 80 steel pipe and cast iron threaded products than Schedule 40 pipes.

• Proper Wrenching
  Wrenches should be used as close to the joint as possible without damaging the threads. Spacing the wrenches too far apart applies additional torque to the joint and can damage the pipe or body. A smooth wrench should be used whenever flats are provided to reduce the chance for damaging the body.
  

Certain scenarios may also get in the way of creating and maintaining that gas tight seal for NPT threads. Continue reading to learn what these are and the troubleshooting tactics to fix the problem:

• Orientation is not correct
  • If one full turn past hand tight does not seal, an additional turn will typically be safe to seal the joint without damage occurring
• The female thread did crack
  • Separate products and verify male thread meets standard gage requirements. May need to replace male thread if it is incorrect or damaged.
• The threads bind up or it catches before fully engaged?
  • Separate joints and inspect for debris or damaged threads. May need to clean or rethread either product.

*There is no standard torque specification that will guarantee a sealed NPT thread. This is merely a general guide with results based on A.Y. McDonald iron gas NPT threaded product. Materials may vary by supplier and product. Different thread sealers will also affect the torque results. Other manufacturers may require different torques as threads and thread quality may vary. Always test joints for proper sealing upon assembly. A.Y. McDonald recommends consulting the specific installation instructions of any product regarding thread sealing or any other instruction specific to proper installation.

You are working on a project at your home, connecting a new gas grill in an outdoor kitchen near the pool. As you consider your grill's connection to the natural gas supply line, you wonder, "Can Teflon tape be used on gas fittings?"

Teflon tape can do wonders for those small projects at your home, and you remember you have some left over from that time when you connected a new shower head in the main bathroom. But it is important to use the right tool for the job. If you are connecting gas lines and their fittings to an outdoor grill or inside stove, you should make sure to use the right Teflon tape. There is Teflon tape made to seal the threads on gas fittings and to prevent leaks in those connections. And there is a separate Teflon tape designed for water pipes that helps prevent water leaks in those connections to showers, hot water heaters, refrigerator water lines and other items.

So the answer is yes to your question, "Can Teflon tape be used on gas fittings?" But only the right type designed specifically for gas fittings. That Teflon tape can be found at hardware, home improvement and plumbing supply stores.

After ensuring you've used the correct Teflon tape for your gas fittings, it's essential to regularly inspect and maintain your gas system. Gas leaks, even minor ones, can pose a significant risk to your home and family. If you ever smell gas or suspect a leak, it's crucial to shut off the gas supply immediately and call a professional. Remember, while DIY projects can be fulfilling and cost-effective, safety should always be your top priority. Ensure you're equipped with the right knowledge and tools before embarking on any gas-related projects.

What type of Teflon tape works best for gas fittings?

The correct type of Teflon tape for gas fittings has a yellow color and is identified in the packaging as manufactured specifically for gas pipes and connecting gas lines. This type of tape is known as gas-rated Teflon tape. It is designed to accommodate all gas lines, including natural gas, propane and butane. The Teflon tape for gas lines is thicker and cuts easily with a knife or scissors. It is specifically manufactured to handle temperatures up to 550 degrees Fahrenheit, and as cold as negative 450 degrees.

What type of Teflon tape works best for water lines?

The difference between plumber's Teflon tape used on water lines and gas lines is that the tape used on water lines is thinner and a white color. While that tape will work well on water pipes to prevent water leaks, the plumber's Teflon tape for water connections will not work well on gas pipe fittings. Over time, the thinner tape will degrade on the gas line and vapors will leak from the fitting. This can create a dangerous situation in your home and could lead to an unexpected explosion or some other dangerous outcome. That's why it's important to select the proper Teflon tape for gas fittings.

How to use Teflon tape on gas fittings

There is more to the answer to the question, Can Teflon tape be used on gas fittings? You also must ensure that the proper tape is used the correct way. When applying gas-rated Teflon tape to a gas connection, make sure the tape is applied only to the fittings' threads. You should not apply the tape to the nuts and bolts used to connect gas pipes together, or the gas compression connections. You will find the gas fittings on the end of gas lines and they are not removable, unlike the gas compression connections. Before working on the gas connections, make sure to turn off the gas supply to your home. You can shut it down at the gas meter located outside your home.

How to check for gas leaks in your connections

After applying the gas-rated Teflon tape to the fitting threads, connect the two gas lines and then turn the gas back on to your home. You can now check for leaks in the gas line. An easy home recipe to check for gas leak uses dishwashing liquid and water. Mix several teaspoons of dishwashing liquid with one cup of water in a bowl. Use a cloth rag to apply the soapy solution to the gas line connection. Look for bubbles forming at that connection. If you do, you've identified a gas leak. If you are unable to tighten the connection properly to stop the leak, make sure to call a professional with experience working with gas to properly seal the connection.

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