Welding Tips and Tricks

OK I have welded some scrap after the fact to make sure I hadn't lost today. This one tube was welded to my project about a year ago and welded fine, at each end. Now today I tried to weld on the gussets that were required and got a surprise. The gusset welded OK to the uprights. But when I tried to lightup on the upper tube it blowed a hole in it ! So I went to the other side to let that one cool. This upper tube started to sink in on the other side and away as it got hot enough to wet out. So I stopped. Now this is going to be a real pain to remake this upper tube that wont weld now for some reason. I am on a new bottle of gas....but it welds fine on scraps. What gives? pic is what I have....have used 2 or 3 hundred lds. of pressure from bottle before today.

JJF

What material is the tube made from?

What are all of your settings?

Without knowing any parameters like this, it's difficult to start to provide an accurate assessment.

"have used 2 or 3 hundred lds." Presumably that means pounds of gas (i.e. have used 2 or 3 hundred lbs)

Trev

Do you have an "escape hole" for pressure in the tube?

If this is the last or only weld on a closed tube, the air inside will expand rapidly and blow your weld out.

Steve S

Was there any kind of vent hole for the tube to "breathe" with the expansion/contraction of the air inside?

Almost sounds like it sealed up after the 1st blow out, cooled, creating enough of a vacuum to suck it in upon your 2nd attempt. Know it's a stretch, but seen stranger things happen.

EDIT: Ahhh, Steve beat me to it....

That is exactly what I was thinking. I've welded a lot of roll bars and had to drill vent holes in them to prevent this exact thing.

It is 4130 x .035" tube...ER70-S2 filler .045"....55 amps w/pedal. I feel like a dumba$$ now for sure. No vent holes. I guess when the first attempt got hot enough to wet it blew through. Got it sealed up after it cooled. I guess a vacuum is what sucked the other side before it could wet out....sounds good to me as a reason why its acting goofy. Will vent and go for a outer patch repair this evening. Thanks guys. Forgot this tube was closed up tight both ends totally.

jumpinjackflash,

One solution is to drill a vent hole with a tap-drill sized for 1/8" NPT pipe and thread it. When welding is done, you can use this hole to attach a fitting to alternately pressure/vent with inert gas, argon or N2, several times to displace atmosphere and moisture, then thread a 1/8" MNPT pipe plug in it to seal it up. One plus, is while the pipe is pressurized during the purging, you can hit every joint with soapy water to confirm your welds are tight.

Steve S