What’s the difference between a TS and an HSS?
For most of us, this may seem like a silly question. A hollow structural section, or HSS, is the same thing as tube steel, or TS, right? Actually, I’ve been asked this very question, so I feel a short explanation may be necessary. Steel tubing, or tube steel, is what we used to use in the U.S. to describe a closed steel section — whether of rectangular, square or round shape. These sections are commonly made in the U.S. in accordance with the ASTM A500 specification. In Canada, the typical specification is CSA G40. You can even see the history of the term in the name of the organization created to promote steel tubing: the Steel Tube Institute.
Now, a pipe is something completely different (because it’s produced to a different specification), but that is a subject for another day.
In Canada, Europe and Asia, the typical nomenclature for these closed steel sections or tubes has always been some variation of hollow structural section. In some places, there exist the variations of SHS (square hollow section), RHS (rectangular hollow section) and CHS (circular hollow section).
In the early 1990s, the American Institute of Steel Construction (AISC) decided to transition from TS to HSS in order to align with the rest of the world. Starting with the second edition of AISC’s LRFD Steel Construction Manual (the silver two-volume set), the designation of hollow structural section was established as the correct way to call out steel tubes. This also coincided with the publication of the black HSS Connections Manual, published jointly by AISC and the Steel Tube Institute.
A corollary question is “Why can’t I get certain TS sizes anymore?” The answer is simple: the particular size you’re looking for is not made anymore. This question usually arises when an engineer is referring to an older edition of the AISC Steel Construction Manual. The HSS industry has definitely evolved over time and some sizes have come and gone, so not all the sizes listed in, say, the green ASD ninth edition are still produced. If you’re having trouble locating a size, I encourage you to pay a visit to the steel availability page of the AISC website to see who may produce that size, if anyone. A word of caution: just because a size is listed on the database or in the manual doesn’t mean it’s readily available. Some sizes require a minimum order to be produced. To be absolutely sure a size you’re considering is readily available, contact an HSS producer before you release those drawings for bid. I do happen to know of a friendly tube mill that may be able to offer some help. Please feel free to contact me at firstname.lastname@example.org.