Is using Teflon a no-no on cast fittings?

Tom R.

Has always been a good choice for water and steam since the red & white spool by Dupont - but it's a first cousin to oil and gasoline. BTW, for obviously resistant threaded connections (and old rusty flange bolts), melt a candle into the joint while the heat's on. Come back tomorrow, and it'll be a pleasure to take apart. "You get old, you get smart"

Ken C.

I was on a service call recently to replace a thermal expansion tank. Whoever installed the old tank tightened the heck out of it, as they rounded off the nut below the threads. Before I installed the new tank, I used Teflon tape and pipe dope and then screwed it into the air scoop.

After I filled and purged the boiler, I noticed water dripping down the tank. I thought it was just from the hy-vent, but when I looked closer, I saw that the air scoop had a hairline crack where the tank screwed in.

My boss told me not to use Teflon tape when screwing anything into cast iron, because it’s too easy to over-tighten something and crack a fitting. I used both tape and dope because I didn’t want a leak, and I wasn’t worried about cracking the air scoop because it’s a pretty heavy casting that seemed to have a lot of meat around the threads where the expansion tank screws in. Who knows, maybe it was close to cracking from the original installation, and I just pushed it over the edge.

But, from now on, I’m going to use just pipe dope, but I’m sure there are others who use both tape and dope on hot water systems. By the way, has anyone ever cracked an air scoop?

And what about steam systems? Just pipe dope on these, since Teflon would make it too easy for fittings to move with the expansion and contraction of the piping?

-Ken

EJW

Teflon

That happened to me once and iv'e never used tape on the expansion tank again unless its a spiro. I'm probably over doing it here,but I won't tape supply or returns going into the boiler either. EJW

Brad White_27

Teflon is first and foremost

a lubricant.

You think you are doing God's Work and then, oops...

I cracked a dear now departed radiator years ago. That last quarter turn and I heard a *tink*. It still hurts to think about it....

I stick to brush-on pipe dope (the Blue Stuff) but am leaning to lamp-wick discussed in recent threads. Always something new to someone on The Wall...

Phil_6

teflon

I never use it on threads going into a cast iron boiler, radiator or anything expensive or that I only have one of ;-)

Phil_6

teflon

I never use it on threads going into a cast iron boiler, radiator or anything expensive. Wick and dope. Fittings I'll use it on unless it's like a big $30 steam tee or something.

gerry gill

i haven't had a problem

with the teflon..but then again, i'm not very big either..

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EBEBRATT-Ed

In Mass. it can't be used on oil. Some people say it getts inside fittings. Tape and dope is my choice (the blue dope) on things that cant leak. Other than that just be cautious about tightening torque-teflon will allow the joint to be made up with less effort so you must use caution. JMHO.

ed

jim f_3

> I was on a service call recently to replace a

> thermal expansion tank. Whoever installed the

> old tank tightened the heck out of it, as they

> rounded off the nut below the threads. Before I

> installed the new tank, I used Teflon tape and

> pipe dope and then screwed it into the air

> scoop.

>

> After I filled and purged the boiler, I

> noticed water dripping down the tank. I thought

> it was just from the hy-vent, but when I looked

> closer, I saw that the air scoop had a hairline

> crack where the tank screwed in.

>

> My boss told

> me not to use Teflon tape when screwing anything

> into cast iron, because it’s too easy to

> over-tighten something and crack a fitting. I

> used both tape and dope because I didn’t want a

> leak, and I wasn’t worried about cracking the air

> scoop because it’s a pretty heavy casting that

> seemed to have a lot of meat around the threads

> where the expansion tank screws in. Who knows,

> maybe it was close to cracking from the original

> installation, and I just pushed it over the

> edge.

>

> But, from now on, I’m going to use just

> pipe dope, but I’m sure there are others who use

> both tape and dope on hot water systems. By the

> way, has anyone ever cracked an air scoop?

>

> And

> what about steam systems? Just pipe dope on

> these, since Teflon would make it too easy for

> fittings to move with the expansion and

> contraction of the piping?

>

> -Ken



i use tephlon tape and megalock pipe dope on every joint steel,copper adapters, brass, gas, steam.
big no no to use tephlon tape on oil fittings.
never had a problem in 16 years

Mitch_6

Teflon past on the thread then tape \"always\"

only exception is gas and oil lines that tape is prohibited.
use to use wicking at my grandfathers shop. But have been using Teflon paste and tape for 20 years no problem.
The only other exception is Runtle radiators the only thing that seals them is rectorseal #5.

Mich S.

Leo

On Parts

On parts that will be replaced at some point I only use teflon tape to make removal easier. You stated that the nut on the old tank was rounded off, to me that's what ruined it. I have never had to use a wrench to tighten an expansion tank to the point of no leaks, they are hand tightened.

Leo

[Deleted User]

Been doing it for a third of a century...

common sense goes a LONG ways. And yes, I have cracked fittings before (flanges), but I suspect they had been dropped and previoulsy fractured prior to my working on them, because they were no where near tight when they gave up the ghost.

Some people think that if a little tightness does a little good, then a LOT of tightness will do a LOT of good, and then as Brad says *tink*.... AW SHUX.

I'm certain cast fittings can be cracked without teflon. It's just a matter of who's on the end of the wrench, and how much torque they can apply...

ME

J.C.A._3

I use Teflon,

After snapping a 6" steel pipe wrench because someone Didn't know about pipe dope at the time of install, I'll use it on all diaphram tanks. HAND tight only and don't go crazy!

It seems that the steel from the diaphram tank and the cast of the air scoop had some sort of "harmonic convergence" ....and had become 1. I still keep the broken 6" wrench for a teaching tool, and because it's the only thing that fits well enough between a scoop and the tank. MHO. Chris

John Ruhnke

Teflon and steam............

I use teflon on all of my steam joints. I wouldn't use anything else. I once had a client, Fred that owned a dry cleaners. He was a Chemical Engineer. I was about to use pipe dope without teflon tape. He got mad!! He said I hate it when plumbers don't use teflon tape on steam because you can't ever take the joint apart. You see Fred was constantly makeing repairs on his high pressure steam system. He taught me that the only way to get a joint apart on steam is if it has teflon tape on it.

JR

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Anthony Menafro

Teflon

You can't use teflon on oil because it is broken down by the oil and will leak or worse, suck in air causing problems.

Anthony Menafro

EBEBRATT-Ed

"never seize" works good on steam even high pressure-you can get it apart years later.

ed

hr

Teflon is becoming

a must have these days due to the poor quality of threaded fittings and nipples being sold.

Even pipe threaded on the job with brand new die segments you will see tearing and questionable threads.

Has something to do with the steel quality. Too much carbon, or impurities? Somethings changed.

I thought it was only me for a while.:) But I hear this complaint here and at the supply counters all the time now.

I would also concur on the operator error!

Rounded off shoulders on the expansion tank would indicate the previous installer was trying to deal with a cracked fitting. Either without knowing it, or not wanting to replace the cracked purger

The second option would be my guess

hot rod

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ScottMP

\" Tight is tight \"

I will Never forget when I was a young stupid apprentice and I asked the plumber on the job: " How tight should this be ? ". He answered me " Tight is tight ".

I mumbled something under my breath about what the hell does that mean.

Years later .... I know exactly what it means. It means its a touch, a feel for tight a fitting should be. As Chris said, I use teflon and pipe dope on all near boiler piping and never have a problem over tighting Because ... Tight is tight.

HR, we've had a Hell of a problem with bad threads and threading pipe and No Its not our teeth.

Scott

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Ken C.

If somebody previously cracked the air scoop, wouldn't tightening it further just force the crack further apart?

Wayco Wayne_2

It's been a long time

since I've cracked a cast iron fitting. Maybe it's because I have developed a good touch, or maybe I've grown weaker with age. I also use the locktite 55 wicking on fittings 1 inch and above. I always use teflon on water pipes below that. You only have to tighten it enough to seal it. You don't have to use every ounce of your strength. WW

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