Just my "2 cents" then I'll shut up, ERW, DOM, are fabrication process, and have nothing to do with the alloy of the tubing.
When buying, and/or selecting tubing, you select the material by ASTM # , and then decide the fabrication technique Ie, seamless, ERW, DOM, and the finish condition such as Hot Rolled, Heat Treat, as Rolled, or Normalized.
So; ASTM#*****+ Fabrication technique+ finish condition, and your ready to place your order.
Rouse