The main issue in pH 3 or ...

The main issue in pH 3 or less environment of steel is going to be general anodic loss of metal in a rapid manner, leading to pinholes in the pipe or vessel.  This is true even when certain anodic inhibitors are present over a long period of time of exposure.  If a smaller portion of the metal is exposed, then expect the anode reaction to focus on this small area, resulting in faster loss of metal thickness in the area.  The presence of sulfides may have a slight inhibitory effect when the FeS as ions in water is too concentrated to support a solution.  Iron sulfide is considerably more soluble than you may have been led to believe, however.  Certain bacteria have specialized intransporting iron from metal surfaces utilizing sulfides.