Can it be done? Yes.
Is it a good idea? No.
I think you are implying that the tube cross section will not allow tapping into the od.
You would have to derate the studs but by how
much is probably indeterminate and may be based
on the cross section of the tubing material
rather than the bolt. I am certain that there
would be no spec for this.
ASTM A449 covers quenched and tempered steel fasteners. It is not a good idea to weld quenched and tempered steels unless due consideration is given to the chemistry, required preheat, and the realization that the mechanical properties of the fastener material is going to be degraded. The designer must also recognize the potential for cracking is enhanced by the increased carbon equivalency of the fastener material. The cracks can be in the form of hot cracks or delayed cold cracks.
