One of our Cu-Ni ( 90-10 ) heat exchanger bundle in our Diesel Hydrodesulphurization plant suffers from heavy scaling. The said exchanger is the overhead trim condenser of the stripper column of Diesel Hydrodesulphurization plant. The said column is used to strip off naphtha + H2S + ammonia from the desulphruized diesel. The mentioned heat exchanger bundle which cools the top vapours (stripped product ) was found suffering from uniform corrosion in form of heavy scaling. Analysis of the scales formed on the bundle tubes comprise primarily of : Cu : 14.5 - 15.8 % Ni : 4.4 - 5.7 % Fe : 9.5-14 % Sulphides : Present in high concentrations As per ASTM Vol 13, the corrosion resistance of Cu-Ni ( grade not specified ) is as follows : * Excellent for anhydrous ammonia * Excellent for anhydrous hydrogen sulphide * Fair for moist ammonia * Fair for moist hydrogen sulphide Could someone some light on the suitability of Cu-Ni ( 90-10 ) in an environment comprising of naphtha + ammonia gas + hydrogen sulphide + moisture. If the same is unsuitable, what is the mechanism of corrosion i.e. why such thick scales are formed resulting in reducted thickness. Thanks

Sir, What is the mechanism of this corrosion ? And what would be the best material to be used in such service condtions? >As you have suggested, the copper alloys exhibit marginal >corrosion resistance in wet environments containing ammonia >and sulfur species. While 90-10 Cu-Ni is one of the more >corrosion resistant of the copper alloys, based on your >stated environment, you would seem to have ample proof of >its lack of resistance. The heavy scale buildup appears to >be base metal corrosion products. The corrosion products >have less density than the base metal, thus, their thicker >layer than the respective loss of wall thickness resulting >from corrosion. > >Hope this helps! > > >David Hendrix >The Hendrix Group Inc.