I have a question regarding the corrosion issue in fractionator on CDU. However, during the turnaround we have noticed very severe corrosion on the first three trays of column. The third tray has mostly corroded. These trays are made out of Monel. The top pumparound goes from the third to the first tray. The corrosion coupon that are placed on the suction of pump-around pump have shown different corrosion rates during last year - from low to severe corrosion rate. The top temperature is lowered to about 120 oC to maximize middle distillate yield. Did anybody face with similar problem?
I know that ammonia, amines, nitric acid are corrosive to monel. I am suspicious about the presence of tramp (or even neutralizing) amines on the first three trays. However, in open literature on internet I have found also different opinions the resistance of monel on hydrochloric acid.
Did anybody face similar problem? Could it be the issue due to change in the crude blend? Any help would be helpful. Thank you in advance.