Question: Are different AWS D1.1 prequalified welds required around the perimeter of a 45° miter butt joint used to connect two pieces of HSS at 90 degrees? Or, can the same weld be used around the entire perimeter? In either case, what is the prequalified weld typically used? A partial-joint-penetration groove weld?

Answer: In direct answer to your question, edge preparation (beveling) of the HSS would be required along 3 of the 4 edges of the miter joint, in order to successfully accomplish PJP welds along those 3 edges.

The capacity of such welds is limited, and the welds themselves (to matched box sections) need to be made very carefully. For such miter joints, especially if there is reasonable applied loading on the HSS members, it is recommended that the two HSS each be separately welded (usually by fillet welds) to a 45° stiffening plate. This type of “knee connection” is shown and discussed on pages 67 to 69 of CIDECT Design Guide No. 3 – “Design Guide for Rectangular Hollow Section (RHS) Joints under Predominantly Static Loading”, 2nd. edition, 2009.