PTFE Tape.

[Malcolm]

Does anyone know the temperature limits on PTFE tape used for sealing screwed joints? I would like to use it for sealing boiler fittings, steel to steel. pressure about 150 psi.

[paul]

Specifications:
1) Heat-proof temperature: +370°C
2) Resistant to cold temperature: -190°C
3) Resistant to high pressure: 150 - 200kg/cm²
4) Tensile strength: >= 8N/mm²
5) Extension rate: >= 25%

Depends on exact source composition I guess?

[havoc]

Depends on exact source composition I guess?

PTFE should be ptfe I suppose. There are different grades depending on density however. The lower densities are OK for water while there are high densities that are approved for gas.

[baggo]

The temperature of your steam/water at that pressure will be 181.4°C so PTFE tape should be ok. The max temperature I think is 260°C.
The thing you have to watch out for is getting loose strands of the stuff into the boiler after you've screwed in the fitting. These float around waiting to block up clacks, valves, etc. !

John

[jackrae]

I'd recommend that you only use ptfe tape when there is absolutely nothing else to use - which in plain language is "never".

Many industrial concerns ban its use because it "creeps" out of fittings and finds its way into delicate instruments.

I believe it was never intended as a sealing tape, rather it was a thread lubricant designed to prevent gauling. However over time bad working practice has become procedure with the result that most belive it is a sealing tape. I've seen male threads so thickly wrapped in the stuff that all form of the thread has disappeared.

You'd be much better using a paste or liquid type sealant specifically designed for the temperatures and pressures intended. They are also easier to use since you can wet the threads with just enough to do the job. The likes of loctite make such materials.

If you're really stuck then a small amount of oil based paint (such as humbrol) will work extremely well as both a sealant and a lubricant

Jack

[Smifffy]

A plumber mate of mine once told me to wrap 20 (yes, 20!) turns of the stuff around radiator fittings - god knows how he ever got the fittings on!

[baggo]

Rocol do a couple of liquid sealants - Oilseal and Pipeseal - which I've used with success. They come in a 300g tin with a brush in the lid but it's a bit big for our sizes! Bit like painting a loco with a yard brush! I use a small artists brush to put it on. Details are available on the Rocol website.

The Oilseal is reasonably priced (about £9 a tin ) but the Pipeseal is a liquid PTFE and pretty expensive at about £26 a tin. Mind you, a tin will probably last you a lifetime!

John

[David Thompson]

I once knew a really good plumber who taught me a few useful things. One was to use only one and a half turns of PTFE tape on a joint. Any more just makes it too tight to turn.

I think it is good practice to use if for plumbing fittings, but not anywhere else, although people do. Never use it on taper threads as they are supposed to be self-sealing.

Some people say it is bad for hydraulic (oil) systems, but this may be because it can get into delicate spool (Moog) valves rather than because it won't work.

David
I always use it at home.

[Shawki Shlemon]

I use loctite 510 thread sealant and it is great. But the question here is about ptfe tape as David says it should be used in one or so turns and that have the same effect as thread sealant and will fill the gaps as the plug or item is screwed in .Malcolm the temperature of the boiler structure is always less than the steam temperature and as mentioned above you are well within the limits .

[russell]

I've heard that it is good for gaskets for steam chests etc. Just weave it around the mating surface, both sides of the studs.

Any comments from the experts?

Russell.

[waggy]

Russell,

I've no doubt it would work as a gasket, however I think you would need some sort of retaining groove in the joint faces to stop the ring blowing out. PTFE has very little strength in the tape or string form and may need some assistance to stay put!
Saying that, I've used Loctite 574 on cylinder end covers without incident and that's a fluid that never sets!
The choice is yours, as they say.

Waggy.

[houstonceng]

David wrote : "Never use it on taper threads as they are supposed to be self-sealing."

But, before PTFE tape, you put "Boss-white and Hemp" on taper fittings because they could still leak if you didn't. The operative word here is "supposed". So now, I use PTFE tape and have no problems with leaks.

[Malcolm]

Thanks, gentlemen. It looks as though I would be OK with PTFE (I've got some gas tape, which is the same thing but thicker), but I've also got some old black Foliac (graphite), which I might use, as I know that it's OK up to 650psi, but it's terribly messy. By the way, has anyone any experience of PTFE tape twisted into a rope for packing glands (in this case a stern gland, but also for steam glands).

[waggy]

Malcolm,
There was a post on this site some time ago re PTFE for glands. I had some input as did many others. "Nuff' said" as somebody else once wrote.
PTFE tape is wonderful stuff. If you want to stop it getting into undesireable places, just wrap a thin ring around the thread to be sealed, as near to the atmosphere side as possible. Don't forget, any more than two wraps is a waste of tape!

Waggy.

[havoc]

I use ptfe tape wrapped as string in my engine as a piston "ring". Just wetted it with steam oil when wrapping it up and smoothing it in the groove. Works fine until now (years almost). Took a few tries to get the right amount. Got this from others at the club that use it as well. This is for gauge one size engines.

[wayne]

cheap ptfe tape is actualy plastic tape coated with ptfe, and this is the stuff you need to put multiple turns on, however a lot of bsp threads found on moddern fittings suposerdley comlying to bs21 fall way short.

if a bsp taper fitting has less than three threads showing after its tightend then there is something wrong.

In short, industry has probems with leaking ptfe joints this is not allways the ptfe tapes fault, if quality or pure ptfe tape are used.

[grahamo]

useful site for PTFE and other gasket materials.

No links with company except as client through work.

www.jameswalker.biz/group/categories/ptfe_jointings.html

We use it to joint between flanges instead of rubbers for some applications - food industry -as it's accepted as non toxic under normal conditions.

Beware if using it near fired areas though. PTFE has particularily nasty fumes if burnt. I have done work in the tobacco industry and PTFE is completely banned from those sites to avoid any risk of any particles of it getting in the ciggies.

[Malcolm]

Waggy, I couldn't find any reference to PTFE for glands in the index. Any further info?

[waggy]

Hello Malcolm,

Had a look through my posts, the thread was started under the heading "PTFE gland packing" on 14th June, 2004. Started by somebody you may recognise!

Regards,

Waggy.

[Malcolm]

Sorry about that Waggy! Put it down to Anno Domini. Now where did I put those rolls of PTFE tape?