1,2, and 3 are proprietary, although you should be able to get the design points for your plant from either the contractor or UOP. Have you contacted UOP?
V2O5 readily forms a protective coating over Fe. You may find something on the specific chemistry in the old Bureau of Mines papers, either Joe Field or Don McCrea would be an author. I suspect either inadequate passivation or low V2O5 concentration for corrosion, unless the solution also...