Dope & tape?

bignozzle

I was wondering can I use dope over Teflon tape? I’ve used both for years, has anyone tried it?

Ironman

That’s the only way I’ve done it for the last 25 years.

The cheap Asian fittings that are being provided have much looser tolerances than American ones. The exception being on gas lines. Tape can get into the line and under the seat of a gas valve causing it not to shut off completely.

Intplm.

Years ago it was either tape or dope. Didn't need both just one or the other.

Since the era of poor quality imports, as what @Ironman makes some mention of above.

Both tape and dope is now used as a habit for what many are doing now. Too many leak issues have made this issue a thing.

There are some types of tape that can be used on gas threads. Some code jurisdictions will only allow for dope, and no tape at all.

ChrisJ

bignozzle said:

I was wondering can I use dope over Teflon tape? I’ve used both for years, has anyone tried it?

You're asking if you can, but then say you have for years.

I'm confused?

On good threads I use either dope or tape, usually dope.
On questionable threads I use tape and then dope over it.

JenniferP

I have ran into the same thing starting about 10 years ago.. Tape, dope, and good to go.

Anybody have a favorite tape or favorite dope?

EBEBRATT-Ed

Another Dope question. You will get 30 different posts from 30 different replies. It really doesn't matter as long as the dope you use is good for what the pipe is conveying. Most dope can handle most any fluid or gas but read the can and make sure the dope is good for steam or gas or water or whatever your using it for.

ChrisJ

JenniferP said:

I have ran into the same thing starting about 10 years ago.. Tape, dope, and good to go.

Anybody have a favorite tape or favorite dope?

Favorite tape, Blue Monster.

Favorite dope @KC_Jones

KC_Jones

ChrisJ said:

JenniferP said:

I have ran into the same thing starting about 10 years ago.. Tape, dope, and good to go.

Anybody have a favorite tape or favorite dope?

Favorite tape, Blue Monster.

Favorite dope @KC_Jones

Awww shucks, nice of you to think of me.

GroundUp

I've tried it many different ways with many different kinds of tape and dope. As of current, my go-to for gas is just dope- something relatively thick like Rectorseal #5, Gasoila, or TruBlu. Pretty much anything else gets 3-6 wraps (depending on size and thread quality) of silver MegaTape or Blue Monster if it's really bad and then a thin layer of the aforementioned dopes on the first 4-5 threads. Sometimes small threads with known quality I skip the dope, like an expansion tank nipple or tridicator gauge. I worked with some guys for awhile who would always put a fat layer of dope on first, and then 3 wraps of Blue Monster. I didn't stick around long enough to see how many leaks they had to fix (if any), but I tried that method on a small job and about 40% of them leaked because the tape would catch the fitting and spin up the threads rather than stay in them. Everyone has "their way" and none of them are wrong if they work.

Mad Dog_2

Blue Monster Tape 1/2" good for all.

Dope Megaloc for traps, nuts & ferrules, most joints.

Rectorseal #5 (yellow) on Natural Gas and fuel oil joints.

Lamp wick (thin) with dope on Domestic water, steam, Hydronics AND dope.

Pipe Dope choice is like Who is your favorite guitarist 🎸?  It's a pride thing, a differentiation thing. They ALL get the job done.  

Mad Dog 🐕 

SuperTech

I use Blue Monster white Teflon paste on gas lines, three wraps of Blue Monster tape and Teflon paste for water lines and leak lock on oil line fittings.

Teemok

The term sealant on many products runs contrary to what I was taught. I was taught dope and tape is solely to reduce friction so that the fittings threads will make up properly. Peaks to valleys, metal to metal is the seal with minimal deformation and good physical binding. Applications of dope or tape was for lubrication, intended to reduce the forces that cause a false tight. Friction makes heat, heat expands the threads and they lock up early while tightening, then they cool and leak. Also to prevent Galling: https://en.wikipedia.org/wiki/Galling
Stainless steel galls easily. With poor quality machining and dissimilar galling prone materials I guess filling voids and gaps is more of a thing now. Maybe tape mixed with dope is a thread gap sealant to some degree. Overdoing it within limits it is good insurance. You don't need insurance till you do. The rest of the time, it's just a bet against yourself that you really want to lose. That said, I can't stand to see a big pile of tape and dope bunched up and wasted at each joint.

jacobsond

how about a good liquid thread sealant and forget about the dope.

Larry Weingarten

Hi, Just to muddy the conversation, I should throw in that the "rules" change when using plastic fittings, or plastic to metal. For example, tape on a male threaded plastic fitting, going with metal female threads, seems to shrink the male threads down and eventually leak. Heat speeds this up. When I use a metal male fitting with a plastic female, I like to put a hose clamp around the female fitting before tightening things together. Lots to pay attention to in making durable connections.

Yours, Larry

bignozzle

I’ve been using both for years, just not at the same time. Sorry that I wasn’t clear. I agree on the fittings, it seems like the Chinese micrometers are a little off:) Thanks for all the feedback.

Kickstand55

I use both often, but not on gas. I don't want the fittings to move after installation.
Best to begin wrapping back a thread or two from the end. That way no tape enters the pipe.
Use caution when using pipe dope on plastic. Read the label, it may not be compatible.
Other than that, Happy Plumbing!

Teemok

Back in the late 90's the CA C-4 boilers and steam fitting contractors test had a question on it asking what is used to make up the threads of black iron pipe. They offered three nonsense answers. The correct answer was linseed oil. Lubrication. It also had some questions about the rate of feed and appropriateness of different coal feed methods for certain types of boilers. Questions from way back in the day.

HomerJSmith

My take. The best sealant is, drum roll please. But first a word from our sponsor. Nah, just kidding.
I had a Lochinvar indirect with a leaking copper to stainless heat exchanger connections. I un-soldered it three times using different sealants, all but the last leaked. The third time I used a cyanoacrylate sealer, Locktite. It worked. I had a gas fitting that would not seal to black iron nipple, I tried it all to no avail. The manufacturer rep said to use Locktite, worked like a charm. Did I say I love Locktite? I love Locktite. When all else fails that maybe the go to product.

Intplm.

Pipe dope / tape. Thread compound.

I was taught a very long time ago that it was simply used to fill the imperfections in metal threads or plastic threads. The microscopic imperfections. That it is used to prevent leaks.
In resent years I have seen some labels saying that it is a thread lubricant. A lubricant?!

pedmec

Tape and pipe dope. most of the time. only dope on pvc fittings. Tape allows you to over-tighten (slides thru the threads too easy but puts pressure on the pvc fitting) and split. Rectorseal #5 immediate pressure grey. #5 yellow ruined too many tools back in the day when i forgot to tighten the cover lol and didn't seal as well.

Long Beach Ed

Generally we use Teflon dope, unless some old nasty thread requires tape. But we ONLY use domestic iron castings. Never had a problem with them.

EBEBRATT-Ed

You have to love how these tape/dope discussions go on for days. Like i said in my first post 30 poster, 30 answers. We are up to about 20 now.

MikeL_2

Larry Weingarten said:

Hi, Just to muddy the conversation, I should throw in that the "rules" change when using plastic fittings, or plastic to metal. For example, tape on a male threaded plastic fitting, going with metal female threads, seems to shrink the male threads down and eventually leak. Heat speeds this up. When I use a metal male fitting with a plastic female, I like to put a hose clamp around the female fitting before tightening things together. Lots to pay attention to in making durable connections. Yours, Larry

 I agree, Larry. And I've repaired scores of split plastic female adapters in my career. I try to avoid using them, but when I do, I use a hose clamp. 
  The only thing plastic female adapters are good for is business.

Teemok

Tight threaded seals are made every day with zero application of any dopes or tapes: NPTF.
The slight differences between NPTF and NPT are why we use dope and tape. I had to correct my understanding after deciding to risk being wrong and reading about it. Yes, friction reduction is a critical task of dope and tape but there is some sealing going on.
Some pipe fitters tend to be very attached to their dope - tape choices. Like those choices are what makes us good. Handed down as gospel or developed through trials or what they heard or think. Science is the closest to truth we get, the rest is just stories we tell.
Proof is in the pudding right?. Just because you can make joints that don't leak doesn't mean you accurately know why or how it works. The obvious truth is you don't need to know the science to not leak. Some like to know why and others are happy to just do it if it works. If I want know, I'll have to investigate it. It's got to be a bit more complicated than just, the screws fit together and some crap fills the gaps..... well, that's not really off the mark.
With our US common NPT threads the interference fit forces are biased to the thread flank (side wall of the thread tooth) NPT peaks and valleys are designed to have less interference. The flanks friction are what gives the tightening feel as surface area that's involved in interference increases. Keep tightening and deformation starts. Normal tightening leaves a spiral path for leaks at the peaks and valleys. As you spin threads in, there's more and more potential for friction and heat (un-lubricated) leading to false tightening and galling and (well lubricated) thread deformation. The spiral gap will get smaller with more deformation till there's peaks and valleys interference fitment (damaged threads). If you don't over tighten, then some little bit of dope and or tape stops up the spiral path of leakage sufficiently.
Over tighteners deform threads needlessly. Too little sealant and a false tightening is likely. Too much sealant and you're wasting product and making a mess.
With NPTF fittings the metal to metal interference joints don't leak. They don't need sealant or lube. Even at the molecular level. The interference fit is designed to deform the treads to make closure . Because of that, reuse is not advised and means a sealant would be needed if you did reuse them. Our common NPT is a compromise, so that threaded joints can be more reusable. That requires some crap to plug up the designed for remaining small spiral gap. How much gap is left is a combination factors of arm strength, wrench, feel, materials property and amount of friction. This is why with the same amount and type of products one guy leaks and the other doesn't. It's also why some destroy threads and others don't. Some make messes and waste. Balance and knowledge of materials is key.
https://www.industrialspec.com/about-us/blog/detail/npt-nptf-tapered-threads-and-leakproof-seals