The purpose of thread sealant tape (a.k.a. “Teflon tape”) or pipe dope is threefold:
- First, the lubricant qualities allow male threaded pipe to be turned deeper into female threaded fittings to prevent leaks;
- Second, it acts as a filler to smooth out micro abrasions or surface irregularities on threads;
- Third, it keeps the male and female threads from rusting together (a.k.a. seizing);
PIPE THREAD TYPES
AN thread is a type of fitting used to connect flexible hoses and rigid metal tubing that carry fluid (it stems from a joint standard by the U.S. Army and U.S. Navy, hence “AN”).
AN thread provides a positive seal that should seal correctly with specified torque torque range with no leaks. The AN should not require a thread sealant.
National Pipe Thread (NPT) taper is a U.S. standard for tapered threads used on threaded pipes and fittings.
In contrast to straight threads that are found on a bolt, a tapered thread will pull pipes and fittings tight together, providing effective seal for pipes transporting liquids, gases, steam and other fluids.
Although SAE and ASTM (organizations that set U.S. industry standards) set very precise thread class specifications, many threaded products carried by large box retailers have varying degrees of deviations from set specifications (i.e. micro surface imperfections like chatter or spalling), thus requiring a use of thread sealants.
USE SETTINGS
In a residential home environment, we are primarily transporting non-caustic substances like water, natural gas, Liquified Petroleum Gas (LPG), fuel oil (and maybe compressed air and oxygen).
Although there is no hard and fast rule, we can broadly categorize residential threaded joints as either permanent or semi-permanent joints to identify appropriate applications for thread sealants:
| Joint Type | Description | Product Suggestion |
|---|---|---|
| Permanent Joints | Any joints which would normally be installed during the rough-in or stack-out phase of the plumbing and which could be reasonably expected to last the lifetime of the structure. These would include galvanized iron water lines, threaded connections on main & zone valves on the water distribution system and gas lines. | Pipe Dope |
| Semi-permanent Joints | Any joints which we typically make during the final trim out phase such as fixture angle stops, shower arms, shower heads, tub spout to the stub outs or any joint which we could reasonably expect may be changed periodically for general maintenance or aesthetics purposes during the life of the structure. | Sealant Tape |
PTFE THREAD SEALANT TAPES
When a thread seal tape was first introduced, it only came in a single density type (“white Teflon tape(1)“) that was commonly found in large home improvement stores. Later they began making a double density version, which was twice as thick in the same color (unfortunately with the same “white” color).
(1)Teflon tape is used ubiquitously when referring to a thread sealant tape. However, the word “Teflon” is a trademark name owned by Dupont Chemical Corp. Although Dupont no longer manufacturers Teflon tapes, it still enforces its trademark rights. That is why you see other manufacturers like Oatey refers to it as PTFE (PolyTetraFluoroEthylene) thread sealant tapes.
One very important thing to remember is that PTFE thread sealant tapes and pipe joint compounds are only to be used on NPT male threads. Neither should be used on SAE mechanical threads or as a gasket sealer (i.e. sink basket gasket).
PTFE THREAD SEALANT TAPE COLORS
Since many state and local codes adopted the use of double density tapes when making connections for natural gas, the use of same color for two different thickness presented a challenge when time came to inspect a job. Thus, a “yellow TEFLON tape” was later introduced for such application.
Since then, ASTM has broadened the specifications for PTFE tape colors:
| Tape Color | Description | Example/th> |
|---|---|---|
| White | single or double density, should only be used on NPT threads up to 3/8 inch in diameter | LASCO White 1/2-Inch Double Density PTFE Thread Seal Tape |
| Yellow | double density, often labeled as “gas tape” | Oatey Yellow 1/2-Inch Gas PTFE Thread Seal Tape |
| Pink | triple density, required on all joints 1/2″ or larger | LASCO Pink 1/2-Inch High Density PTFE Thread Seal Tape |
| Green | Oil Free PTFE tape, required for use on all lines carrying oxygen (i.e. – medical oxygen or welding oxygen lines) | Gasoila, 1/2-Inch Green PTFE High Density Thread Tape, 3.7 mil Thick |
PIPE DOPE / LIQUID THREAD SEALANT
Pipe dope, technically known as pipe joint compound is both a thread lubricant and thread sealing compound. Unlike a thread sealant tape, pipe dope is designed to make a pipe thread joint leak proof and pressure tight by brushing on a pasty substance to a male thread (never to a female thread because some of it will push into the pipe.
Some people use pipe dope on top of thread sealant tape but many manufacturers say there is no added benefit to that setup.
Pipe dope itself can be classified into 2 distinct categories:
| Pipe-Dope Type | Description | Example |
|---|---|---|
| Oil Based | Usually comes in a dark gray paste designed to work on all metal based pipes and fittings | Oatey Pro Dope |
| Non-Oil Based | Usually comes in a white paste that works with all metal and PVC-based pipes (make sure to read the product label to verify that a given product can be applied to PVC/cPVC threads such as P-traps, tailpieces, waste & overflow, etc.) | Rectorseal Pipe Thread Sealant |
While there are number of pipe dope product on the market, the one that seems to be most widely accepted by plumbers, pipe fitters, HVAC techs and electricians is products from RectorSeal.
If the thread you are working on will be exposed to extreme temperatures, a better suited product might be a liquid thread sealant called Permatex Thread Sealant with PTFE
TIPS TO REMEMBER
- The main purpose of a thread seal tape / liquid thread sealant is to seal out micro abrasions or surface irregularities on threads. If you have a major gash or nick on a thread, you will need to replace the pipe section or re-thread it, rather than applying a thicker seal tape layer;
- Applying more than 3 layers of sealant tape is not recommended;
- When starting out, make sure the seal tape is not covering the pipe opening. Any exposed seal tape may break loose over a period of time and cause a blockage problem; in the future;
- Pipe connections generally turn clock-wise but there are instances when that is not true (i.e. gas pipe union joint). Always test out and make a note of the pipe rotation before applying the tape and remember that the tape application must “go with the flow”;
- You cannot connect dis-similar pipes together (i.e. copper-to-steel) and hope that a thread sealant tape will prevent from interacting with each other, possibly causing corrosion problems. In this situation, you must use a dielectric union (something like this)
- If you need a gasket sealer, you may want to checkout can use hyolomar based products like Valco Cincinnati Hylomar Compound
or Permatex Oil Resistance RTV Silicone Gasket
.
Final Thoughts
So what do I use in my plumbing projects?
I tend to apply both the sealant tape and pipe dope if there is plenty of space around the pipe I am working on or if I am working with black steel pipes (generally used for natural gas) because their threads tend to be rougher.
If the working space is tight (let’s say a 1/2″ water pipe straddling a floor joist), I tend to go just with pipe dope. I only use sealant tapes for drink water supply lines (i.e. kitchen sink).
Well, I hope you found my post on pipe thread sealants to be useful and signup for my free newsletter. The sign up form is found on the upper right screen and I promise it will be spam free.
Thanks again for reading my post and good luck with your DIY project!
Great Article, thanks for the data.
For the average DYI’er tho, that top picture is a bit misleading, as:
1. It’s usually easier to apply the tape under tension with the roll reversed from what is shown, and
2. That pipe in the picture would have to be left handed thread if the tape was applied as shown – which is not common and only used in some gas fittings – which would also mean that it should probably be yellow tape.
Obviously a stock photo of some kind, but again, a bit misleading. Cheers!
@faz
thanks for the feedback (and yes, it was a stock photo)
kevin
The photo above the article is showing the incorrect direction for wrapping Teflon tape (assuming that the pipe has RH threads).
I think the photo shows the correct direction, so the exposed tail of the tape doesn’t get mashed up, it goes with the direction of the female threads sliding over it.
Hi Andy-
Thanks for your feedback. Yes, the earlier comments were made to the stock photo that had incorrect wrapping direction. Since then, that picture has been replaced with my own (what you see now).
Thanks
Kevin
DuPont name is now Axalta. You may want to update that information before some cooperate freak show tries to shut down your site. Great info, thank you.
@JR-
Thanks for the heads up!
Hey Kevin! Been a pipe fitter propane tech,(no license of course) I think your info is right on during any gas or propane ppropane install I have done 2 today! There is always a problem thread!!The nearest store is 50 miles and doesn’t stock much.anyway I always carry several rolls of yellow!! And #5 pipedope! If you can’t fix the joint with that combo it’s time for a beer!! Start fresh with new parts tommorow!! Frustrations a DIY most common mistake! Good info thanks.
I am surprised you did not mention the Third type of pipe sealer, which is the oldest, and also the BEST, especially for iron pipe. I have had Teflon leak, and I especially have had pipe dope leak. I won’t use the dope any more unless there is a compelling reason. Question: What do you think they used before there was Teflon? Pipe Stick is the best if it absolutely has to seal the first time, again especially for iron but works very well with brass and copper. And unlike Teflon, you cannot apply too much. Plus for joints out in the weather, spreading it around exposed threads provides a perfect rust preventative. You can throw a pipe stick in your toolbox and it will remain usable for decades. Just peal the hardened skin off. And it doesn’t blow out the threads like dope will.. Doesn’t shred either. And if you do have to take a joint apart, you don’t have to pick the Teflon out of the threads, especially female.
Hi Milo
Thank you for your comment about the pipe stick. Can you recommend a brand or two that you use on a regular basis? The only pipe stick I used were epoxy putty (which I avoid due to it permanent nature).
Thanks
Kevin
Concerning your updated photo, what Faz also mentioned about the original photo concerning which side of the tape to use is also true when the diameter of the roll is larger than the diameter of what you are wrapping. For that condition, (most common) it is easier to have what was toward the inside of the roll be on the outside of the fitting in order to control the tension as you are wrapping, i.e flipped around from what you show.
@ Mikey-
that is also a good suggestion. thank you!
Kevin
Since Oatey’s Yellow Gas Line Thread Seal Tape With PTFE has a temperature range of up to 500 degrees Fahrenheit, would it be suitable to seal the joints (where male segments go into female ones) of the exhaust vents of dryers, water heaters, and the central heating system of my house?
If not, what is an appropriate tape? It must be able to withstand high temperatures.
@ Hi David-
To seal exhaust vent duct work, use foil tape (I use 3M foil tape or Nashua foil tape, depending on which one is on sale).
For water heaters (assuming water pipes), just use a regular white tape;
For central heating duct work, use water-based mastic sealant like this one. I would use the yellow tape for natural gas applications only.
I have noticed propane fittings with a yellow/white sealant that is hardened. No one talks about this sealant. Example is the orfice fitting in a gas grill. What is it?
@ Gary-
I am not aware of any special sealant used in propane fittings, other than a yellow ptfe and pipe dope
I recently helped my sister move into her duplex where the existing gas connection for the dryer was not in code. I replaced the gas line coming off of the existing valve where the gas shutoff was located. I used a flexible conversion gas dryer kit with appropriate connectors. I also used yellow teflon tape at all the connections and soaped to make sure there were no leaks when done. Within 2 days the gas smell in her duplex was so intense, she called DTE gas to investigate. They came in and said that the yellow teflon “gas” tape should NEVER be used and this was the source of the leak!!! Why would places ever sell this to the public if it’s not supposed to be used to seal connectors?
@ Hi Kelly-
Sorry to hear about that. I think the use of tape is dependent on where you live and even, which gas company you deal with.
For example, when I worked with my gas company, they told me to not use any tapes when joining “black (supply) pipes” but that I could use the tapes when connecting the last leg of the supply pipe (post shutoff valve) to the appliance.
Kevin
I am connecting an “H” burner to a stubbed & capped, ready to use natural gas supply line to the fireplace in my living room. The gas line and fire place are new construction and neither have ever been used. The “H” burner is also new and is appropriate for use with natural gas.
Question:
Is it OK to use yellow gas tape instead of pipe joint compound to connect the final connections inside the fireplace on this installation ?
Many thanks for any guidance here.
@ Hi Tim-
I believe Oatey tape is rated up to 500 degrees but I am uncertain if it was meant to be used in direct flame.
You should contact your local plumbing inspector to determine the correct method of sealing your H burner
Thanks
Kevin
Can I use yellow tape on water pipe?
@ Kirk-
I would not. Yellow tape is thicker that is suitable for more coarse threads. use the white tape on water pipe threadding
Can I use white tape for a gas dryer connection?