We have several components in our product line that involve an issue similar to what you've described. Our Engineers have approved the tack-welding of nuts for those applications where the tack-weld is only intended to hold the nut in place and keep it from spinning when a bolt is inserted and torqued, and the strength of the mechanical connection is in the bolt-nut configuration and does not rely on the tack-weld in any way. I'm pretty sure this is a common practice...
Good Day SafetyThird,
MERRY CHRISTMAS AND A SAFE, PROSPEROUS, AND PEACEFUL NEW YEAR TO YOU AND ALL HERE.
AND, WELDCOME TO THE ORIGINAL AWS WELDING FORUM!! THE GREATEST WELDING FORUM IN THE WORLD, BAR NONE.
So, the main objective, especially in your application, appears to be to prove that the base material is not damaged by the welding. The normal prohibition is because the strength of the nut is compromised by welding so a structural connection is not safe and sound for the designed strength of joint required.
As with many other issues, it is not that the codes PROHIBIT as much as it is that they 'RESTRICT' the welding of nuts. And, it is for the integrity of the nut. Integrity of the base material can be proven with a PQR if this is something done often enough to warrant the added expense.
I personally have seen engineers sign off on this application using both soft, grade 2 or A307, nuts as well as structural nuts. They are not hard enough for a tack weld to meld the properties of the two and effect the base material. And, as we all know, the engineer may delete from, add to, or modify in any way they deem necessary the applicable code.
Lawrence gave you the specific Official Interpretation applicable to your situation. There may be another one but I will have to look.
He Is In Control, Have a Great Day, Brent