full pen tig roots with no purge gas

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So here's a question that none of my companies weld engineers have been able to answer but has been bugging me for a while:When doing full penetration root welds that do not require interior root shielding, such as a36-70s or aluminum, how is it that the weld can retain acceptable levels of contamination, yet if you do any other weld without surface shielding, you blow in porosity?
Reply:Originally Posted by pat8703So here's a question that none of my companies weld engineers have been able to answer but has been bugging me for a while:When doing full penetration root welds that do not require interior root shielding, such as a36-70s or aluminum, how is it that the weld can retain acceptable levels of contamination, yet if you do any other weld without surface shielding, you blow in porosity?
Reply:So you're saying the surface layer of the interior of the pipe is not 100% molten, and with the deodorizers in the rod, is enough to keep contamination low?
Reply:It is molten, it does oxidize, what i am saying is a portion of the gas follows ahead of the arc, and it shields the pool, and the deoxidizers do help with a portion of it, like i said do a slow weld, vs a fast root weld, the difference is unmistakably visible. FYI the iron oxide floats to the surface, the AL3O2 (Al oxide) is heavier therefore you have a higher chance of trapping AL302 on aluminum welds, it all has to do with cooling rate as well as material. I have never read anything written about this subject and i am shooting completely from my hip so there is a possiblity i am full of ****.I forgot how to change this.
Reply:Sounds good to me, it seems like the silica forms over the root on the inside of the pipe I wonder if this helps??
Reply:The welding engineers should know the answer to this honestly, i might ask someone that might know but it wont be until at least Thursday.I forgot how to change this.