Vikas: Admiralty brass tubes in cooling water can pit when exposed to several corrodents in the water, the most likely being amines, ammonia, or decomposed organic matter. We have also seen Admiralty zinc tube dezincify. Hope this helps! David Hendrix The Hendrix Group Inc.

Vikas Admirlaty Tubes in Cooling water 1. Failure of Admiralty tubes - Is it occurring at the bottom areas or is the failure close to the top entry of cooling water? 2. If failure of Admiralty is at the top - then it is a question of impingement and a combination of stagnant liquid for a long time. 3. If the failure is at the bottom zone areas, then it could be due to stagnant water during shut-down of the plant. 4. De-zincification is one common mode of failures for Admiralty tubes in cooling water service. Other modes are Pitting, SCC . Contaminants in lube oil will also create conditons for promotion of SCC (stress corrosion cracking). 5. Pitting and perforation could be due to stagnant condition prevailing in the exchanger. One way is to flush the system and drain to make sure to prevent stagnant water for a long time. If the draining system does not work well then stagnant condition will prevail. Check if the gradient given for exchanger inlet and outlet is OK. at the support areas. Unknowingly support conditions could contribute to failrues - if suports do not have proper gradients for liquid to drain when exchanger is shut down. Please check on this also. 6. If the top section of the tubes are affected then check if an impingement plate had been provided at the top entry of cooling water. 7. If Adimratly tubes had been supplied in quarter hard or half hard condition, or as ERW then pitting will initiate at the HAZ of ERW tubes or in quarter hard tubes at the higher hardness areas. For quater hard or semi hard tubes, a combination of pitting, SCC and perforation will occur. 8. One way is to avoid : choose only annealed tubes and with a little higher percentafe of Sn in Admiratly tubes. Better still think of Cu-Ni tubes if problems crop up. 9. Do a mercurous nitrate test to ascertain if the tube had failed by SCC and a micro-strcuture analysis on the failed tubes. 10. After ascertaining the mode of failure, the type of crack morphology, micro-hardness and microstriucture analysis, then think of material change, design imporvements, process improvements includign inhibitor injection close to this exchanger for avoiding future failures. Do not think of only inhibitor addition as the solution for this problem. Othwerwise it will cloud your analysis and compound solving the problem. A proper diagnosis and analysis is needed for this. Trust this helps you to solve your problem C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai 20 India Nov 8 E-mail: nishi@vsnl. com / nishi@hathway.com Nov 8,2004 >What about Corrosion Inhibitors ? Don't they help in >avoiding dezincification / pitting ?