"seem" /= "seam". I think you wanted to use the latter.
It's also worth noting that, when doing "hard" fabrication, DOM should not have a seam - and should be available in common "mill shapes" for tubing. The "seam" found in most tubing indicates that the tubing is either HREW - Hot Rolled Electrically Welded - or CREW - Cold Rolled Electrically Welded. The latter is slightly stronger, because of the work hardening taking place during forming. Also, CREW can be used when aesthetics are important, because most hot-rolled steel shapes develop scale while cooling (while cold-rolled does not.)
If the seam cannot be seen on the outside of the tubing, just clean a short section of the inside (about an inch or so) - which should show up the welded seam neatly.
DOM (Drawn Over Mandrel) is hot-formed tubing. They take a bloom or a billet of steel (both are mill shapes, no matter what marketing wants you to believe "billet" means,) heat it until it becomes readily plastic, and then force it through a die with the desired outer shape (and a mandrel with the desired inner shape.) Then, it is allowed to cool. Typically, there is a second heating process that causes the steel to "form closed" where there would be voids due to the mandrel supports.
Now you know why DOM costs more - it's more energy-intensive to manufacture, and there is a certain amount of wear that takes place on the mandrel and the die.
5-90
