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• • • • • • • • is to culture the mound materials in, say, postgate media to see if sulfate-reducing bacteria (SRB) are present. You can try other cultures to see if other types of bacteria are also present, but do not forget that each method has its pros and cons. What is the average water velocity, especially where the leaks have happened? Are the leaks normally seen at the 6 o'clock position or elsewhere? What do you know about the history of the pipes that have leaked? For example, do you know how they were hydrostatic tested? You mention that chlorine is being added to the water before it enters the pipeline network. How much is being injected, and how much remains in water? Can it be at a level that can kill a majority of planktonic (foating) bacteria? Do not forget that sessile bacteria are no different from foating bacteria. They just differ from each other in their states. If the foating bacteria can stick on the surface, they become "motionless" or sessile. If you have no foating bacteria, sessile bacteria are unlikely. Analysis for only carbon can be misleading—this carbon may be coming from the steel itself, and as far as I know this will not help. Instead, you can try to fnd some well-known corrosion products, such as sulfdes. When you remove the mounds, do you see the bright metal beneath with pits? You can alternately put some drops of hydrochloric acid (HCl) solution to see if a "rotten egg" scent will emit. That is a rapid check for SRB. Why do you not use rapid check kits available on the market? They are easy to use, but of course you must be aware of their limits. Get a microbiologist to collect the samples for you and culture them. Better yet, consult with a corrosion NACE International, Vol. 52, No. 5 A engineer with hands-on experience Check the chlorine dosage. I have in MIC. The added chlorine may seen pronounced iron oxide tuhave killed the present bacteria so bercles over deep pits formed in that the problem is not microbial CS piping handling fresh or at all; however, too much chlorine brackish water because the maximum may have been added, which may recommended chlorine dosage was have caused a type of underdeposit exceeded. corrosion. May 2013 MATERIALS PERFORMANCE 63