TIG welding is not nearly as forgiving as Mig or stick when it comes to dirty metal. For TIG welding, the metal needs to be clean; no rust, scale, paint, etc. that means hot rolled steel needs to be ground to shiny bright metal…not just polished over.
Welding hot rolled steel without grinding will make you look bad.
Don’t do it if there is a chance someone might see it. Windy conditions or drafts in the welding area and you will lose shielding coverage and get pinholes/porosity in the weld . If you have to TIG weld in windy conditions, you are going to have to spend some time making wind breaks out of cardboard, plastic, or whatever you can get.
TIG welding will just not tolerate much of a breeze much less a gust of wind. And please don’t try to TIG weld with a coat hanger or gas welding rod. They will bubble and hiss.
TIG welding rods like E70s2 have silicon and other deoxidizers designed to scavenge impurities out of the weld. GAS welding rods are pretty much copper colored coat hanger wire. Don’t use them.
If you just cannot clean hot rolled steel, using ER309 stainless looks better and stops the porosity. But it’s much more expensive and not to be used to replace engineering authority for coded or critical welds.