Tim: Good question. We are not aware of threshold limits for ammonia SCC of copper and copper alloys. Unalloyed copper is more resistant than the 70-30 brasses, however, so you might try using the water at the 1.5 ppm level. All bets are off if the ammonia is allowed to concentrate under deposits, etc. Hope this helps! David Hendrix The Hendrix Group Inc.

T. Loper For the levels of ammonia used in your chillers and the temperature , the risk may not be high. In fact the risks of SCC - what you fear- may not be there at all. Yes you are right that standard corrosion coupons will not give any reasonable information to detect such fine SCC in this low ammonia concentration and at this chiller temperature. For brasses in ammonia service (prone for "season cracking" as is known in ammonia related SCC for brasses) mercurous nitrate test is the standard test to know the effect and whether your brass tubes are susceptible for SCC. If you really fear and you wish to perform a test, there is test method available to evaluate under laboratory conditions. For this you have to take out one good brass tube from the chiller and carry out a laboratory evaluation under mercurous nitrate solution - i.e, the sample tube has to be bent (regular applied stress bending) . Evaluate the result under micro-examination if IGSCC (Intergranular Stress Corrosion Cracking) is exhibited in the sample tube. Stress level and ammonia concentration will influence the rapidity of SCC in this laboratory evalution under mercurous nitrate test for suspected SCC trend. There is an ASTM standard on how to prepare and how to perform the test. Off-hand / by memory i am not able to recollect or do not remember the standard. For chiller service at this temperature and with this concentration of ammonia , given in your question, you may not worry or need not have unwanted worries on SCC of your brass tubes. Yes there is an outside chance possibility of SCC, if the tube had been procured as ERW and original purchase order had specified by mistake or by intention to be supplied in half hard conditions - where the residual stresses in half hard condition may act as nuclei for promoting SCC. This could happen under stagnant condition - more likely than in running plant conditions for this low ammonia concentration. Brass tubes procured as annealed or "bright annelaed" will not fail for this concetration of ammonia and for this chiller temperature conditions. 1.5 ppm is so low a level and at this chiller temperature even for half hard brass tube, the failure rate will be negigible. At best some tubes which are over-stressed may show trend of SCC - which is not detectable at all unless you remove the tube from service. You will have nuisance values of occasional leaky tubes - those tube which are highly stressed. These may develop minor leaks but you can safely plug those tubes and continue to operate the plant without undure worries. Exchangers are designed for additinoal capacity for such plugging of leaky tubes. Finally, i guess from published information on brass and their trend for "season cracking" SCC this level of ammonia at this temperature is not to be given importance. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai India July 17,2005 E-mail:nishi@vsnl.com >I greatly appreciate your response. If I do use a water >stream that contains some ammonia, do you know of any ways >to see an increase in risk of SCC of the copper tubes in my >chillers? Is there any way to see it coming before it >happens? I suspect standard corrosion coupons will tell me >nothing, is there some other test method that could be >employed? > >Thanks, > >Tim Loper