If you had to make a permanent seal between two metal surfaces that held gas, what would you use?  

Lets say I have a hole in a gas container that is threaded, and I need to screw something into that hole that has a nozzle at the end, how do I permanently seal the metal to metal contact?  A simple gasket will deteriorate over time.  Is there some sort of silicone or similar material you could seal it with?  Or does gas detroy everything like that?

I've used teflon tape for plumbing uses like this; I imagine it'd be inert to gas....but somebody better qualified should answer.

JB Weld. Nuff said.

Swagelok makes a thread sealant called Swak. Anerobic PTFE paste. Chemically inert thread dope..

gas = petrol = gasoline?

threaded = tapered pipe thread or straight or some other?

permanent = no SOB will ever get this apart in your lifetime or your great-grandkids lifetime or just no worries?

Duct tape or bubble gum. The universal adhesives!

Quoted: gas = petrol = gasoline? threaded = tapered pipe thread or straight or some other? permanent = no SOB will ever get this apart in your lifetime or your great-grandkids lifetime or just no worries?

1.)  Gasoline and not kerosne or diesel, well it could be kerosene or diesel.

2.)  Stright pipe thread.  Female on the tank, male on the fitting that going onto the tank.

3.)  Permanent as in no SOB will ever be able to get this off.  I know welding is the most permanent option and best sealing option, but welding on an enclosed used gas tank isn't smart in my book.  So I am not doing that.  I figure permanent will last longer then something that can be taken off later and will also seal better.

Proseal.  Found in aviation supply places.  Fuel tanks in airplanes....

DevCon

Quoted: JB Weld. Nuff said.

I found this.

jbweld.net/products/jbstik.php

It states that it is impervious to gasoline until the normal JB Weld which must be free of all petroleum products when applied.

However I have two problems with JB Weld.  It has never worked as intended or stated when I have used it.  And if I put the JB Weld into the threads when installing the fitting, I do not know how sure of a solid un-breaking seal it will make.  And once it is harded, I might be a little worried it will move or crumble a little within the threads breaking any seal it had.  

Quoted: Swagelok makes a thread sealant called Swak. Anerobic PTFE paste. Chemically inert thread dope..

From its MSDS...
Materials to avoid:
Pure oxygen, fluorine, chlorine. Oxidizers, strong reducers, free radical initiators, inert gases, oxygen scavengers, peroxides, persulfates, accelerators, strong bases, and strong acids.

PTFE by itself may be almost entirely inert, when used in some of these paste forms it has enough other substances to warrant caution.

I have nothing but success with JB Weld.  Once its on something it doesnt come off...... It hit the stuff with a damn hammer before and it not break.

Quoted: Quoted: JB Weld. Nuff said. I found this. jbweld.net/products/jbstik.php It states that it is impervious to gasoline until the normal JB Weld which must be free of all petroleum products when applied. However I have two problems with JB Weld.  It has never worked as intended or stated when I have used it.  And if I put the JB Weld into the threads when installing the fitting, I do not know how sure of a solid un-breaking seal it will make.  And once it is harded, I might be a little worried it will move or crumble a little within the threads breaking any seal it had.

Since it is pipe thread and gasoline, teflon tape and tighten the snot out of it.  Maybe an acitve Pipefitter will chime it, but Dad sez (Pipefitter) "if pipe threads leak they are not tight enough.  Teflon is to keep the threads from galling and not to make a seal."  
The above does assume deformation of the threads, and there are "dryseal" pipe threads which are designed to not use "sealant", so I am not real sure.  But since I believe Dad,  I wonder if dryseal threads were developed for people with limp wrists.

Tilt the gas tank up so your fitting spot is at the top,  fill with water just shy of the spot where you fitting goes.  Weld the fucker on.

Quoted: welding on an enclosed used gas tank isn't smart in my book.

Fill it with water.  Weld.  Drain and dry.

Quoted: Quoted: Swagelok makes a thread sealant called Swak. Anerobic PTFE paste. Chemically inert thread dope.. From its MSDS... Materials to avoid: Pure oxygen, fluorine, chlorine. Oxidizers, strong reducers, free radical initiators, inert gases, oxygen scavengers, peroxides, persulfates, accelerators, strong bases, and strong acids. PTFE by itself may be almost entirely inert, when used in some of these paste forms it has enough other substances to warrant caution.

Funnily enough we use it to seal connections for high (10k PSI) pressure nitrogen/helium/co2 lines.

We use only mechanical seals on the 10k PSI hydrogen stuff though.

welding has always worked for me......

Quoted: Proseal.  Found in aviation supply places.  Fuel tanks in airplanes....

Bingo! Go to your local airport FBO (fixed base operator) ask the parts guy for a 6oz semkit of PR1422B1/2. Mix it well, apply it to the threads, screw the parts together and add a bead around the outside surface. It won't leak.

I would heat both metals to their melting point, add a filler metal, then check for leaks.  Kind of like welding.



Edit read the clarifications - teflon tape should work fine.

Devcon titanium putty.

http://www.grainger.com/Grainger/searchresults.jsp?search_type=keyword&QueryString=titanium&catindx1=Putty%2C&catindx2=Titanium&xi=xi

Clean threads, mix putty, apply.  After cured, will never come apart.

Seal All. Gasoline will not penetrate it, like it would JB Weld or Devcon.


AB

Quoted: JB Weld. Nuff said.

I agree, if it can't be fixed with jb weld or great stuff it isn't woth fixing!

you could purg the tank and then weld it.


There are several sealer putty compounds used for gas tanks availible at most automotive stores.

I keep reading your post over and over trying to figure it out. I'm probably thinking too much. Anyway, I used to sell petro equip to farmers back in the day.
What kind of tank , 5 gal.,aboveground, etc ? Will the nozzle have any pressure,if your are using gravity ?
Pipe dope can work as will teflon tape.Could use a gasket made of viton,or a crush washer along with a nut and flat washer on the pipe.
Without any more info thats the best I can do.

Teflon tape will work, and so will any epoxy if it's mixed correctly so it can cure.  I wouldn't use any epoxy filled with steel or aluminum if you want this joint ot truly last many years since the both those metals are not corrosion resistant.

Proseal is not fuel proof, it's fuel resistant.  It's commonly used for sloshing aircraft fuel tanks.  It also deteriorates when soaked with fuel and it's common enough to find tanks where the Proseal is coming loose.

Silicon compunds are not remotely fuel resistant and are about the worst choice for that application.

Polyester resin is fuel resistant and makes a poor component in a fuel system.

I have some experience with this, Teflon tape is good for many things, but it will NOT work with gasoline. It will certainly leak if used on threads in fuel.

JB weld is also a great product, we use it at the shop for many purposes, but not for sealing threads, especially where gasoline is the substance in question. It would be good for bonding the two parts though.

The key is using something that won't be affected by gasoline and can seal without tiny air pockets because they will leak.

In the absence of welding equipment, or experience, -more on that below- you would need two different products to make it permanent, well nothing is really permanent, but you get the idea.

To seal the threads on the Fuel Fitting, use Permatex High Performance Thread Sealant. Gas will not eat away the sealant. Part number 25117(small) or 56521(large)

To make it a permanent fitting -in a 'weld-like' way- we use Permatex Epoxy Cups, they are not used to stop fuel leaks, that's why you need the thread sealant, but they bond dissimilar metals better than anything I've tried. Similar to JB weld, but thinner and easier to spread. Very strong. Part number 21425(small) or 21426(large) We get them in a 10 pack tin, I would use one or two large cups, mix it up and spread it on the pipe and housing, work quick, you don't have a lot of time before it sets.


Welding a fuel tank is not as difficult as you may think.

Here's how we do it; Drain fuel, wait a few minutes to vent fumes, fill with some water, swoosh it around, drain, fill again, swoosh, drain once more. Fill the tank with water one last time, just below the neck -or fitting- and leave it. Set up your equipment and weld while it's full with water. This is the only safe method when working with fuel tanks.
Drying is done with low heat, compressed air, or evaporation over time(or any combo thereof).

Good Luck with your project.

MarineTex. I've used it to bed rifles and make a seal that will hold.
Titanium Devcon works just as well.

Another vote for Proseal.

Pipe dope rated for fuel. Works on Coast Guard fuel tanks should for yours.

There are at least three different types of teflon tape, the regular white kind, a very thick pink tape that is used for chemical applications, and a yellow  tape that is used for gas.

Use the yellow teflon tape.......I also have extensive experience in this, threading pipes that have considerably more pressure than you are talking about.

BTW, the regular teflon tape will work fine just as an FYI....if it didn't every person with a Holly Carb would have their gas lines leaking like hell.

Another vote for welding. Pump that tank full of exaust or water and weld it.