Assumed Current Density for Anode Calculation Cooling Water HeatExchgs
Assumed Current Density for Anode Calculation Cooling Water HeatExchgs
(OP)
Friends,
I am putting together some calculations for Zn and Mg anode sizing for heat exchangers in cooling water service. We tend to operate at about 120 F, with flow speeds of 2-7 fps. Some exchangers may eventually use sea, rather than fresh water for cooling.
My question is this: What current density should I be assuming for each of the two (sea and fresh water scenarios)? I was assuming 11 mA/ft^2 and 4 mA/ft^2 assuming conditions would be similar to this paper (http:/ /www.stopr ust.com/pd f/5/(2001) -corrosion -protectio n-program- for-high-t emp-subsea -pipeline- mike-surke in-and-ste ve-leblanc -shannon-r ichards-jo hn-p.-lafo ntaine.pdf).
I want to be conservative, yet practical, ie not have a calculation that spits out that you need 30 anodes when the exchanger can only fit 9 or 10. Does anyone know of any NACE papers or their own formulas or experience that could help me out?
Thanks,
Paul
Berkeley, CA
I am putting together some calculations for Zn and Mg anode sizing for heat exchangers in cooling water service. We tend to operate at about 120 F, with flow speeds of 2-7 fps. Some exchangers may eventually use sea, rather than fresh water for cooling.
My question is this: What current density should I be assuming for each of the two (sea and fresh water scenarios)? I was assuming 11 mA/ft^2 and 4 mA/ft^2 assuming conditions would be similar to this paper (http:/
I want to be conservative, yet practical, ie not have a calculation that spits out that you need 30 anodes when the exchanger can only fit 9 or 10. Does anyone know of any NACE papers or their own formulas or experience that could help me out?
Thanks,
Paul
Berkeley, CA





RE: Assumed Current Density for Anode Calculation Cooling Water HeatExchgs
Regarding current densities, your numbers sound about right for bare steel. You need to know the water resistivity, presence of coating/lining will of course change things by orders of magnitude.
For the fresh water option you may want to consider a small impressed current system. Make it adjustable enough and it should cope with seawater service in future too without changing anodes etc.
Good luck.
RE: Assumed Current Density for Anode Calculation Cooling Water HeatExchgs
http://www.corrosion-doctors.org/Alphabet/A.htm
RE: Assumed Current Density for Anode Calculation Cooling Water HeatExchgs
the values are higher than yours.
http://www.wbdg.org/ccb/DOD/UFC/ufc_3_570_02n.pdf
S
Corrosion Prevention & Corrosion Control