I agree with rconner's statements about the black ductile iron pipe. You'd probably want to double check the contractor's intent. Sched. 80 PVC is very strong for most plumbing needs and you don't have to worry about corrosion. I would double check with the reviewer to see if PVC is what they...
I have never heard of anything done like what is being proposed. If the reviewer approves sched 80 PVC on the bends then they should be OK with sched. 80 PVC throughout the pipe run. The elbows will be where most of the turbulence and pressure will hit before making the 90 deg. bend so you...