In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Victaulic vs Threaded Steel Pipe & Fittings
The code books don't state that there is only one particular joining system approved. There may be certain type systems that are approved for a given fluid or pressure rating and maybe that's what the engineer is hung up on.
Vic is so much faster than threaded that it's not even funny. Large bore threaded pipe is so difficult to handle when you start dealing with full lengths that your labor will be double what it is for Vic.
If it's a hot water system and the job is good sized, now might be the perfect time to invest in a ProPress setup and price them a copper install. Viega is currently bringing in and getting approvals for their large bore fittings that are copper instead of brass. Going to be a fair amount less expensive.
As an example, 2 of my guys hung 320' of 2 1/2" steel using Vic fittings in less than 7 hours. That included strut and hangers 22' off the floor.