[mr 32]

hey guys

ive been doing some pratice work, its some 20mmx20mmx2mm SHS that i made up into a frame
i welded all the joints and then put some cross supports in, nowevery so often the puddle on the frame side would pop
killing the tungsten and leaving a nice hole.
would this be pressure build up in the frame because it was sealed?

[Otto Nobedder]

I've had that happen before, when closing a weld on an unvented volume, like pipe or tube. The expanding air inside the tube will push through your puddle just as you get closure, like a soap bubble bursting. The trick is to leave a small hole at the end of the weld, let the piece begin cooling, and close the weld with a short burst that will solidify before enough heat spreads to expand the air inside.

I've also done this on purged pipe, by forgetting to open a vent for the purge gas before closing the root.

Steve

[Landyman]

A lot of the tube work we do at work is dipped in galv or a similar plating and we have to leave a small hole somewhere as it can lead to problems when it is dipped.
I have heard various reasons, from blowing crap through small holes in the weld which then leads to a crappy finish, or the tube being at risk of splitting!
We get around it by having small notches cut into the appropriate tube ends.

[ajlskater1]

Yes anytime you are closing something up you get pressure build up inside, sometimes caused by oil heating up and burning or just the argon from welding or purge. You just need to leave a little hole in a easy to reach place, let the joint cool and then quick close it up. Leaving it in a easy to reach spot is important cause you don't want to sit around really heating up the part otherwise it will pop on you.