TIG, SS & backpurging

No backing tape either? I am guessing you have access to the inside. I have heard (not personally tried) of using tin foil and masking tape. Best I remember he had about a 2" dome over the weld area and masked off the sides and ends. If you are using alot of amperage you might want to make a larger dome of sorts so as not to destroy the foil. Of course, he had one end with a purge hose and I am guessing about 2 or 3 cfh for purge.

Is there room to weld it from both sides?

JTMcC.

nope, no backing tape. think aluminum foil with no purge would do anything at all?

re: welding it from both sides -- i could climb into the tank, sure, but wouldn't i be chasing my own tail?

not sure how thick the tanks are ... i'd wager around 3mm, min, going by their size.

-tony

Sorry but I don't have any idea what you mean.

JTMcC.

my apologies for the confusion.. if i weld from the inside, wouldn't i need to purge the outside, then?

maybe i dont understand what you meant in being able to weld from both sides.

-tony

think he's featuring welding it from the inside, then prep and finish from the outside?

You would be purging....This is the original message........

No backing tape either? I am guessing you have access to the inside. I have heard (not personally tried) of using tin foil and masking tape. Best I remember he had about a 2" dome over the weld area and masked off the sides and ends. If you are using alot of amperage you might want to make a larger dome of sorts so as not to destroy the foil.

You don't remember reading this section of my reply?

Hi Tony,

Although it is advisable to have a separate small tank (10 cuft) with a flow regulator for this situation, and many others, there are alternatives. While these alternatives are not as good as back- gassing, they can allow the job to get done in a pinch.

Copper sheeting, anywhere near 1/16" thick can easily be shaped to mate very closely with the inside of the tank. The idea is to make a patch big enough to cover the HAZ, and to affix in place with tape. The important part is to virtually eliminate air getting in there. You can tape the periphery of the sheet. Having a larger patch will allow the tape to survive longer. Copper is great because it can be shaped to conform to just about anything, and it is relatively soft in thin sheets.

The foil stuff doesn't work well because it's too thin. You can use aluminum sheet as well, as long as you can easily shape the stuff to reduce air infiltration. You don't have a back- gassing rig, but you may have a $200K milling that will make an excellent jig.

If you really are far from civilization, and you need to get to basics, you can tape a metal can, or a glass jug to the back of the tank. You put a candle in there as you tape in place. The candle consumes the oxygen, and leaves a rather nasty, but relatively inert atmosphere.

Yet another far-fetched idea that has been know to work, but that is also not without hazards, is to use the exhaust from a vehicle. This can be dangerous, be advised. It is best to use a vehicle with fuel injection, and that has a properly operating oxygen sensor. It is also prudent to wait until such a vehicle is warmed up, so that there aren't too many unburned hydrocarbons kicking around. It is further advisable that the vehicle exhaust not be piped into a closed room, or building, since this could kill the occupants. The great part about the vehicle is that there is a lot of relatively inert gas coming out. The rub is that you need to get some good hose that won't melt on the tail pipe. Some hoses are purpose built.

If this is a plant, you could also use steam. It can preheat the part too! It's also dangerous to handle as well.

There you have a few suggestions, we'll leave the more exotic ones for more challenging situations. ;-) BTW, standard disclaimers apply, use at your own risk.

Guy