Tack welding A108 gr.1045 rod

[specialinspectormike]

Hi All,
I am inspecting a project where the jurisdiction has instructed the contractor to tack weld threaded A108 gr.1045 rod to fastening nuts for the purpose of fouling the thread. The rod material isn't pre qualified per AWS D1.1. I suspect that there is a reason for this. Can anyone tell me the downside of tack welding to this material without pre or post heat. By the way these rods are being used as hangers for heavy utilities.
Thanks for your time,

 

[Duwe6]

IF the tack-weld is outboard of the nut, and is predominately [or wholly] on the threaded rod, no problem exists; it just 'boogers' the threads and keeps the nut from loosening.
On the other hand, if that weld is in an area that is carrying a load, the contractor has now degraded, and thus ruined, a load-bearing member. Contractor now has to calculate the new, lower, strength of the assembly, and get this value approved by the design engineer.

 

[MotorCity]

My first question is why is the jurisdiction giving directions to the contractor?

To answer your question, the concern with tack welding is that it can create local stress raisers due to the localized heating and cooling effect. The heating and cooling causes expansion and contraction over a very small area and the weld heat can change the material properties of the steel. That said, tack welding a nut to an anchor rod is done quite frequently and I am not aware of any failure that has been attributed to such a practice.

 

[Duwe6]

Quibble:
"The heating and cooling causes expansion and contraction over a very small area and the weld heat can change HAS changed the material properties of the steel."

 

[specialinspectormike]

Thanks for your responses. I am aware that this is a common practice but that being said... It doesn't necessarily make it a sound practice. In other settings such as OSHPD or DSA I have seen entire systems rejected and replaced for the same reasons. I should have mentioned that a qualified WPS is not on file for this application and my concern was for the carbon content of this material and the lack of preheat potentially causing a crack.
Thanks

 

[Tmoose]

Some millwrights refer to welding nuts and bolts to prevent loosening as "killing" them.

I agree.