Thanks a lot for commenting; unfortunately I was on a business trip. (1) I do not have certification of the material grade (the coil is part of the cooler, there are no specifications available); the results come from our analyses made by WDX/EDX. (2) We did some linescans on the cross-section and inside the pits there is definitely dealloying of nickel (not zinc, I made an error in the last post) in the depths about 50 micrometrs; concentration drops to 1 wt.%. (3) We have very limited knowledge about this type of material (we mostly work with stainless steels). Looking into literature I was able to fine one reference about MIC in Cu-10%Ni condenser tubes (Romero; Corrosion Vol 56 (8) 867-876), unfortunately not the paper itself, only brief description. It suggests that this happened only in highly polluted waters, which might have been our case. (4) The deposits are either green or dark brown. Unfortunately I cannot post a picture here. 96-08 water had about 90 mg/l of chlorides, and 150 mg/l of sulfides. 08-10 water has only sulfides (about 50 mg/l) and there are no chlorides (less than 1 mg/l) according to analyses. Indeed it looks like the deposits have been removed by the fresh water flow. In regions with (supposed) MIC attack there are no traces of surface nickel dealloying, it is visible only in areas of pitting corrosion. This is what drives me to two-mechanism scenario linked to different cooling water used. Couldn’t it be that there is something else in the new cooling water, which causes pitting? The surface of the pits is relatively clean seen under SEM, without any protective layer, which would indicate, that the corrosion process has not stopped with 2008 with water substitution, but rather it was started by it and still continues. The thing is that there are four other cooling coils and the operators want to have some clear answers. Being in emergency they replaced it with Cu tube, which I do not think is a good idea. To be on the safe side I would probably recommend replacement with Ti. Thanks again, I really appreciate your comments. If you would be interesting in some images, let me know, I will send them by email. Mark