Cooling Water Systems FAQ

Got a question not answered by the FAQ? Contact our technical staff. Perhaps we'll add your question to the list and you will help out other users of our site.

1. How do I prevent Legionella from developing in my system?
2. What are acceptable corrosion rates?
3. How do I clean a system on line that has been fouled with calcium carbonate (lime)?
4. How do I prevent stress corrosion cracking?
5. How can I prevent scaling in once through cooling systems?

1. How do I prevent Legionella from developing in my system?
   
   First, legionella is an anaerobic microbe – hence keeping the sump clean of sediment and debris is important. Additionally, properly controlling microbiological activity is essential. For a detailed discussion of legionella please see our technical tip.
   
2. What are acceptable corrosion rates?
   
   General corrosion rates on mild steel should be under 3.0 mils/year while corrosion rates for copper should be under 0.2 mils/year. Having stated that, pitting corrosion can cause failure much more quickly than general corrosion and all coupons should be measure for pit depth, with the corresponding corrosion rate calculated. If you experience excess general or pitting corrosion please contact our technical support staff for a consultation.
   
3. How do I clean a system on line that has been fouled with calcium carbonate (lime)?
   
   In order to dissolve calcium carbonate you must operate the system at a negative LSI. Use the calculator on our site to determine what pH must be maintained to achieve a negative LSI. Once sufficient acid has been added, you will notice an increase in conductivity as the calcium carbonate scale dissolves. This is normal – when the conductivity stops increasing this is an indication that most of the calcium carbonate has been removed. Note that the carbonate released into the water during this process will increase the pH, so continuous pH control will be necessary. Finally, products which remove calcium carbonate scale and give a visual indication of completion are available. Please email our technical support staff for more information.
   
4. How do I prevent stress corrosion cracking?
   
   For stress corrosion cracking to occur, three conditions need to be present – stressed metallurgy, high chloride levels and high temperatures. The simplest way to prevent the possibility for stress corrosion cracking is to reduce the chloride levels, either through blowdown or different makeup water source. However, since each system is different, we suggest you contact our technical support staff for further assistance.
   
5. How can I prevent scaling in once through cooling systems?
   
   The answer to this question depends on whether the system is potable, and what are the constituents of the scale. If the system is potable and the primary constituent of the scale is calcium carbonate, 2 to 4 ppm of hexametaphosphate should help control the situation. If the system is potable and iron is the primary foulant you should feed low levels of pyrophosphate. Finally, if the system is not potable HEDP will work to control both calcium carbonate and iron scaling. Depending on the system 1 to 4 ppm should be sufficient. Note that to test for the levels of the chemicals you will need to properly digest the sample and test for phosphate.