Chloe Zhang
Plastic pipe threads can be sealed using thread sealants, which fill the gaps at threaded connections to prevent leaks. When working with plastic fittings, it is important to select a sealant that is compatible with plastic and will not damage the material. Some popular choices for sealing plastic pipe threads include Teflon tape, pipe dope, and PTFE paste. These sealants provide fluid-tight seals and lubricate the threads to make assembly and disassembly more efficient. It is also important to properly tighten the fittings to avoid over-torquing, which can cause smaller diameter threaded joints to split.
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What You'll Learn
Using thread seal tape
Thread seal tape, also known as Teflon tape or plumber's tape, is a popular choice for sealing threaded connections. It is easy to apply, inexpensive, and effective for many types of fittings. Due to its non-reactive nature, it is particularly useful for plastic connections.
When using thread seal tape with plastic pipes, be careful not to overtighten. The lubrication provided by the tape makes it easier to over-tighten and crack the fitting. It is important to use the correct sealant for the pipe and fluid. Thread seal tape is intended for metal pipes and fittings. When wrapped around plastic male threads, it increases the pipe diameter, prevents the pipe threads from meshing properly, and adds strain and tensile stress.
To apply thread seal tape, wrap it around the male threads of the pipe. Then, assemble the joint, tightening it securely. It is important to note that thread seal tape should not be used as a substitute for pipe glue or adhesive. Pipe glue is used to make "slip" PVC joints permanent, while thread seal tape creates a water-tight seal and lubricates the threads.
Thread seal tape can also be used in combination with pipe dope or wicking for a more secure seal. Pipe dope, or pipe thread sealant, is a paste-like substance that binds to threads to create a watertight seal. Wicking uses a string-like material to fill the gaps between threads. To use thread seal tape with pipe dope or wicking, first apply the pipe dope or wicking to the threads. Then, wrap the thread seal tape over the pipe dope or wicking before assembling the joint.
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Choosing the right sealant
When choosing a sealant for plastic pipe threads, it is important to select one that is compatible with the pipe and fluid. The sealant should be certified by the manufacturer to be harmless to the fitting material and not contaminate the fluid in the pipe.
There are various types of thread sealants available, each with its own advantages and disadvantages. Thread seal tape (also known as PTFE or Teflon tape) is a thin, non-adhesive tape that is easy to apply and undo, making it a popular choice for small-diameter pipes. However, it should not be used on plastic threads as it can increase pipe diameter and prevent proper meshing of the threads. For plastic pipes, a thread sealing compound (also known as pipe dope or pipe joint compound) is often used. This type of sealant is applied as a paste over the male threads and can provide a better seal than tape, but it can be messier and may have a limited shelf life.
Another option is an anaerobic thread sealant, which cures to form a solid, shock and vibration-resistant seal. These sealants are ideal for permanent fixtures and commercial plumbing applications but may require additional curing time. When sealing gas lines, ensure the sealant is AGA-approved, and for waterlines, look for a WaterMark approval. If the pipe will be exposed to certain chemicals, check the Safety Data Sheet to ensure the sealant is compatible.
Some people also recommend using a non-hardening sealing compound for threaded PVC fittings, as it can adapt to potential points of leakage. For larger pipes, a thread sealing compound may be easier to apply than tape. When applying tape, it is important to wrap it in a clockwise motion, just above the last male thread, to prevent unraveling during assembly.
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Applying pipe dope
When working with threaded plastic fittings, it is important to select the correct sealant for the pipe and fluid. Pipe dope, also known as pipe joint compound, is a type of thread sealant that can be used to create a fluid-tight seal in threaded pipe joints. It is important to note that pipe dope is not a glue or adhesive, but rather a lubricant that fills the gaps in the threads to prevent leaks.
To apply pipe dope, start by ensuring that you have selected a suitable product for your specific application. Pipe dope can come in different forms, including paste and tape, and it is important to read the product instructions to ensure proper use. Once you have selected the appropriate pipe dope, follow these steps:
- Clean the threads of the pipe and fitting: Before applying any sealant, it is important to ensure that the threads are free of dirt, debris, and any other contaminants that may interfere with the seal. Use a clean cloth or brush to wipe down the threads.
- Apply the pipe dope: Depending on the type of pipe dope you have chosen, the application method may vary. If you are using a paste sealant, use a brush or your finger to apply a thin, even coat of the pipe dope onto the male threads of the pipe. Be sure to follow the manufacturer's instructions for the recommended amount to apply. If you are using a tape sealant, simply wrap the tape around the male threads, pressing it firmly into the threads as you go.
- Assemble the joint: After applying the pipe dope, assemble the joint by threading the male and female fittings together. Be careful not to overtighten the connection, as this can damage the threads and increase the risk of leaks. Finger tighten the connection, and then use a wrench to gently turn the fitting no more than 1/2 to 3/4 of a turn further.
- Check for leaks: Once the joint is assembled, check for any signs of leaks by performing a pressure test or inspecting the joint for any visible signs of moisture or dripping. If a leak is detected, disassemble the joint, inspect for damage, and reapply the pipe dope, ensuring that the threads are fully coated and that the connection is not overtightened.
It is important to note that pipe dope is not always necessary for plastic pipe threads. Some plastic pipes may seal adequately without the use of sealants due to the ductility of the material. Additionally, some sources advise against the use of pipe dope on plastic fittings, as it may increase the risk of overtightening. Therefore, it is crucial to consult manufacturer recommendations and industry best practices specific to your application before applying pipe dope.
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Using PTFE tape
PTFE tape, also known as Teflon tape, is a common material for pipe thread sealants because it is chemically unreactive, slippery, and stable at extreme temperatures. It is made of polytetrafluoroethylene (PTFE) and will be labelled as "thread seal" or "thread-sealing" tape. It is important to note that plumber's tape, or "strapping", is not the same as PTFE tape and is used to support pipes.
PTFE tape is typically used on metal pipes and fittings, as it can add lubrication and make it easier to tighten the fittings too much, which can crack the fitting. It is not recommended for use on PVC, copper, or PEX pipe threading, as these fittings often have a gasket or O-ring to create a seal. It is also important to avoid using PTFE tape on fluid power (hydraulic) systems and under brass's compression nut flare threads or any other compression fitting type.
When applying PTFE tape, it is important to wrap it around the pipe in the same clockwise direction as how the pipe will turn into the fitting. This will prevent it from unraveling. Start by cleaning the male threads at the end of the pipe with a clean rag. Place the end of the PTFE tape on the second thread from the end of the pipe and hold it in place with your finger or thumb. Ensure that the tape lies flat and extends perpendicularly to the length of the pipe.
PTFE tape is sufficient on its own, but some people choose to use it in combination with pipe dope (a thread sealant paste) for added security. However, it is important to note that using both can overload the threads and affect the seal. Additionally, PTFE tape should not be used with other thread sealants as it is not a sealant itself but rather a lubricant that makes assembly and disassembly easier.
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Avoiding leaks
Plastic piping with threaded fittings is usually reliable and leak-free. However, leaks can occur due to improper assembly of threaded joints and the use of incorrect thread sealants. To avoid leaks, it is important to follow these steps:
First, ensure that the pipe manufacturer follows the American National Standard B2.1 for quality assurance. This standard specifies the amount of "taper", where each successive male thread is slightly larger in diameter than the previous one, while female threads get successively smaller. Over-tightening can cause the female part to stretch and split, so finger-tighten first, then add no more than 1/2 to 3/4 of a turn.
Second, select the correct sealant for the pipe and fluid. The sealant should be certified by the manufacturer as harmless to the fitting material and the fluid in the pipe. It should also add a little slipperiness to lubricate the joint, allowing for smooth tightening and uniform meshing of the mating pipe threads. Fluoramics Formula-8 and Lox-8 Thread Sealant are safe to use with plastic pipes and fittings, including nylon.
Third, properly apply the thread sealant. Follow the instructions for your chosen sealant, ensuring that it is compatible with plastic. Some popular options include Teflon tape (also known as plumber's tape or thread seal tape), pipe dope (a paste-like substance), and wicking (using a string-like material to fill gaps between threads). When using Teflon tape, apply it from the tip first and wrap it with the thread right-handed. Pipe dope should be applied thinly and evenly to the male threads using a brush or applicator before assembling the joint. Wicking can be used in combination with pipe dope for extra protection against leaks, especially on older fittings.
Finally, avoid using thread seal tape or PTFE tape, which are intended for metal pipes and fittings. When wrapped around plastic male threads, they increase the pipe diameter, preventing proper meshing of the threads and adding strain and tensile stress. Instead, opt for sealants specifically designed for plastic fittings, such as those mentioned above.
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Frequently asked questions
Finger tighten, and then add no more than 1/2 to 3/4 turn.
Pipe dope, or pipe thread sealant, is a paste-like substance that binds to threads to create a watertight seal. Pipe dope is compatible with any pipe material, even plastic, and it hardens quickly. PTFE tape is also a good option.
Clean the threads thoroughly. Apply a thin, even coat of pipe dope to the male threads using a brush or applicator. Spread the sealant evenly around the entire circumference of the threads. Assemble the joint, tightening it securely.
Pipe dope provides a more durable seal than PTFE tape, making it suitable for high-pressure applications. PTFE tape is easy to apply, inexpensive, and effective for many types of fittings.
In addition to using a sealant, it is important to use the correct thread sealant and to properly assemble the threaded joints.
