The preferred material specification for round HSS is ASTM A500 Grade C (Fy = 46 ksi, Fu = 62 ksi). Note that A1085 Grade A (Fy = 50 ksi, Fu = 65 ksi) may also be specified for round HSS members for tighter wall thickness and ...is hoped to supersede A500 relatively soon.
If you are practicing in the United States and we are talking about a building application, ASTM A500 Grade C is the most common material for hollow, round steel members. Every once in a while I get a request from a contractor to substitute ASTM A53 Grade B and will gladly evaluate it on a case-by-case basis. ASTM A1085 Grade A is another option but it may not be readily available in your area; check with a local fabricator.
To minimize availability issues, I specify ASTM A500 shapes in the same nominal wall thicknesses that are available in ASTM A53 Grade B. This practice has worked well for me over the years.
Depending on the application, one of the main issues with using A53 rather than A500 or A1085 (other than strength) is that A53 has a black lacquer coating that makes fabrication and galvanizing more difficult. Here is an article discussing the differences,
As Hokie93 stated, stick to specifying shapes in the same sizes as standard pipe as these are the most readily produced and stocked shapes available. Atlas Tube is a pretty good reference for finding typical sizes and availability,
If the steel sizing is more nominal than needed for strength, then just give the contractor the option. It's probably a wash for cost unless you have miles of it or are specifying an unusual size.
I think in years past, the A53 spec was more common and less expensive than A500, but, all things being equal, the A500 should be cheaper to produce since it doesn't have to be pressure rated.
The A500 also has tighter controls on its strength min and max so it is better for seismic design, i.e. Ry = 1.6 (!) for A53 pipe and 1.4 for A500 tube compared to 1.1 for A992 material.
The A1085 tube people are trying to get the A1085 tube Ry to be more favorable yet, but I don't know if they have succeeded. I imagine they are hoping for R = 1.1 or 1.2.
The A500 also has tighter controls on its strength min and max so it is better for seismic design, i.e. Ry = 1.6 (!) for A53 pipe and 1.4 for A500 tube compared to 1.1 for A992 material.
The A1085 tube people are trying to get the A1085 tube Ry to be more favorable yet, but I don't know if they have succeeded. I imagine they are hoping for R = 1.1 or 1.2.
