Pipes for plumbing and other systems that convey liquid or gas throughout your home usually include many straight or angled components, linked by various connections, or joints. These joints generally connect using screw threads called National pipe taper (NPT) threads. For all NPT joints, the American Society of Testing and Materials (ASTM) recommends the use of a joint sealant, which can take the form of Teflon tape, also called polytetrafluoroethylene (PTFE) tape, or a liquid pipe thread compound.
Yellow Teflon Tape
Yellow Teflon tape is one of several varieties designed and approved for use in different systems and scenarios. The yellow colour indicates that the tape is double density and appropriate for use with gas piping. The more common white Teflon tape is single density and is recommended for general use in pipes 3/8 inch or smaller. Red tape is triple density and is appropriate for use with pipes 2 inches or smaller, as in water distribution lines. Green, oil-free tape is less common and is typically used in oxygen lines.
Pipe Thread Compound
Pipe thread compound also comes in many varieties, and you can usually find an appropriate compound to use instead of tape in any pipe-fitting application. While you may not find pipe compound specifically labelled as an alternative to yellow Teflon tape, you can match a product to the size and nature of the pipes you'll be joining. In fact, many people prefer pipe thread compound to yellow Teflon tape for gas lines, although both are effective.
In addition to categorising pipes based on their diameter and what they carry (whether water, natural gas, fuel oil or oxygen, for example), many experts divide joints into two broad categories: permanent and semipermanent. As their name implies, permanent joints are designed to last as long as a home remains standing. They are usually found in essential home systems, installed as part of the original construction and difficult to reach or replace after the fact. Most gas lines are considered semipermanent joints, as are the main water pipes leading into and out of a home.
Semipermanent joints are usually more accessible and less critical than permanent joints, because they are used in situations where joints may need to be replaced at some point when occupants undertake repairs or renovations. Examples of semipermanent joints include shower heads and bath fixtures.
Choosing a Sealant
While it is important to choose a sealant approved for a given task, whether you opt for Teflon tape or pipe thread compound is primarily a matter of preference. Some users lean toward tape for semipermanent joints, because it doesn't harden the way thread compound can, making replacement easier down the road. However, despite the fact that many gas line joints are permanent, yellow Teflon tape is a fine choice and is specifically approved for use in many gas systems.
Applying yellow Teflon tape or pipe thread compound is a simple process, and any product you purchase should have step-by-step instructions for use. With Teflon tape, the key is to wind tape around the threads at least three times and work in the direction of the threads, which ensures the tape won't shred or slide off when you connect the pipes. With pipe thread compound, you want to coat the threads thoroughly and evenly, but leave a thread or two dry at the end of the pipe to avoid getting the compound inside the pipeline itself.
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