Purging during welding of ss & ms

[son77jai]

Why do we purge the SS in one side welding .?

ANd why not we provide the purging in one side welding of MS ?

[ify09]

when SS is not given purging, then root side of the weld gets oxidised due to formation of Chromium Oxide.
So we have to displaced the air inside SS pipe so the internal environment of pipe is free of Oxygen.

Same thing dosen't happen when welding MS, as there is fraction of Cr in composition.
But for Alloys having Cr greater than 2.25 %, Purging is given for the same reason.

Hope this could help you.

[son77jai]

if your answer is correct , i want to know then y do we provide the protection of inert gas( TIG welding - shielding )on the welding side as there would also be no oxidation like that of inside as you suggest as there is no Cr present in MS.?

Dun take it wrongly i want to go to the basic of it hence clearing out all the doubt coming to my mind.

thanks for your suggestion /participation in the topic

[ify09]

Shielding provided while using bare filler wire, to protect the air to get entrapped in the weld. which will form weld defect named porosity.
Without shielding it is very difficult to maintain arc while TIG, Try to do that.

For Flux Electrode, Flux itself creates blanket which shields it from atmosphere.

I am bit in hurry.
Hope this would have answered you.