ASTM A500 is the standard specification for circular, square, and rectangular tubes of cold-formed welded and seamless carbon steel structures. ASTM A500 is the most common specification for Hollow Structural Sections in North America. The correct way to specify the circular HSS section is to represent the outer diameter in decimal inches to three decimal places (i.e., 5.563 x 0.250) according to the nominal wall thickness.
Since ASTM A500 is a structural specification, circular high-speed steel produced according to this specification is suitable for structural applications and general construction purposes.
The specified yield strength of A500 Grade C (the most commonly available grade) is 46 ksi. The specified yield strength of A53 Grade B is 35 ksi. Yield strength increased by more than 30%. Therefore, the strength to weight ratio of A500 circular HSS is greater than that of A53 pipe. So, if you do the job with round HSS, you need less steel, by weight, to do the job—the lighter it is, the lower the cost.
The tolerances of A500 are tighter than those of A53, so the HSS of the A500 circle has higher quality and less variability.
Round HSS has a superior surface finish and is not as lacquered as normal A53 tubes. Since this lacquer coating needs to be removed from the A53 pipe to accommodate welding and painting, so this can save money and time.
All steel structures have their pros and cons including structural supports, building columns, highway signs, oil field services and communication towers, to name a few. But ultimately ASTM A500 is a better choice when you need a round profile.
We encourage architects, fabricators, structural engineers and contractors to read up on ASTM A500 and visit The Steel Tube Institute's website because it offers a wide variety of technical publications, load tables and design aids.