T. Milleti You have faced problems with changes in metallurgy and materials, faced problems with exchagner design change and also with crude process stream through out . I guess that it would be difficult to give a simple and straight answer to your questions, unless some other user plant had experienced similar problems with similar material usage, mechanical and process design changes and in similar crude throughout increases. A detailed analysis is needed to know which is the main contributing factor for such a rapid deteriroation. Unless each case history failure is analyzed in detail with analysis on the mode and type of failure for each change of material and also a study with reference to a particular exchanger mechanical and process design changes. A study is also needed to what extent crude throughput increase contributed to the rapid failures, i guess that a simple answer to your question may be difficult from a discussion forum like this. Trust that you will appreciate this. C.V.Srinivasan Nishi Engineers Pvt Ltd India Sept 13, 2005 E-mail: nishi@vsnl.com >Hi , > >Historically, our Crude/ BPA Exchanger' bundles downstream >of the desalter have suffered from excessive corrosion on >the tubes OD (arabian light crude in the shell side) >predominantely on the top half of the bundle in the area >between the floating head tubesheet and the 2nd baffle. > >The very first carbon steel bundle, installed in 1984, >lasted for about 4 years. The bundle was upgraded to 5Cr >which lasted only 18 months (worse damage than the CS). and >13Cr lasted only 13 months. Then it was decided to use >Hastelloy C-276, unexpectedly, it failed after 3 months of >operation. In between all these materials upgrade, other >design changes, such as the use of Helical baffle design, >aimed at minimizing tube OD fouling was done. Currently CS >bundle with J-baffle design is in service, installed in May >2004 , have tube leak in July 2005. > >It looks like that the higher crude throughput is a factor , >as it seems the carbon steel tube bundle gave only 14 months >life at 390+ crude rate vs about 2 years min cycle at 360 >tbd & 6 year at the early start up between 1984-1990 @320 >-340 tbd crude . The effiecency of the desalter is also a >factor, we are currently working to improve the performance >of the desalter.. We continousely injecting caustic upstream >the exchangers. > >your input in this issue in order to overcome the >fouling/corrosion problems and increase the life of the >bundles along with specific comments on the failure of the >Hastelloy material will be highly appreciated. > >Thanks > >T. Milleti

Hi Actually your problem with 5, 12, 13 CR was due to presences of aqueous NaCl at any temp. even room temperature the Cr will corrode and the h2s in your system will attack the carbon steel after the de passaviation by Nacl and the bundles is starting to leak. In crude unit equipment e.g. the preheats, fin fans and piping system all CR material are not recommended. What I you can do is to use coated carbon steel. The coating type is very important like SAFKEN Coating. Moreover, the fouling problem if a refinery world wide problem but you needs to try to do some monitoring to the factor key which is the caustic. If caustic injection increased dramatically you will notice the pressure drop is increasing . Erosion here is an issue but it likely you would see it very clearly at the overhead line. You should make some calculation to face this management of change at the overhead line better than the preheat (if it is not shutdown item). Use the Hastelloy at the top portion of the overhead line. More details if you wish will provide to you. Mark Corrosion Engineer USA