I am curious as to why some of the most common grades of pipe and tube do not have pre-qualified status in any group listing in D1.1. i.e. ASTM A512 MT1010, ASTM A513 MT1020, ASTM A519 Gr 1018 and ASTM A120. Since prequalified mateials appear to be based on "weldability", I am at a loss here as to why these in particular were excluded. I must be overlooking some metallurgical factor. Thank you.