Question: I am responsible for a design of what my company calls a “lift beam”, which is a piece of equipment involved in lifting and transporting a maximum load of 34 metric tonnes. The main body of the equipment is based on an ASTM A500 square steel tube. Our procurement team is asking me to allow a supplier to substitute such a manufactured HSS with another that is fabricated from two different flat plates. The plates are each bent into a “U-shape” and then welded together. I think that accepting this substitution is possibly unwise and potentially unsafe, so your comments would be appreciated.

Answer: Square and rectangular HSS are made in North America by three different manufacturing processes: continuous forming with electric resistance welding (ERW) of the longitudinal seam and converting from round to square/rectangular shapes, the most common method, direct forming (or form-square) with ERW of the longitudinal seam, and by submerged arc welding (SAW) of two longitudinal seams joining two C-shaped plates together.

The HSS sizes produced by SAW using two C-shaped plates in the manner that you have described are made to a standard ASTM A1065 (which is similar to ASTM A500), with welding performed to AWS D1.1. These are regularly-accepted HSS and are commonly specified for very big sizes. They are mainly produced by HW Metals (member company of STI), and their website also describes all their available sizes and product grades: https://www.hwmetals.com.