I have a few questions here.
1. In a steel mill direct cooling water system, can alkalinity be used as a indicator for corrosion? As in, if alkalinity is low, that means corrosion rate should have been low?
2. Additionally, can the presence of iron scale in the cooling water increase the iron content in water?
3. Lastly, is the control parameter
In water quality, the alkalinity measurement has more to do with buffering capacity and the ability to neutralize acid than it does pH. I would not try to relate this to corrosion because it is not specific about the ion type, concentration, or the pH.
I do not think the presence of an iron scale can be related to the iron content in the water. There are many different types of iron scales. It would likely be very dependent on the type of iron species that are formed and their solubility. This will depend on the types of ions in the water that will vary with geography.
I would not try to use a low iron level as an indication that there is no corrosion. This condition implies that the iron produced by corrosion is soluble in water. If the iron species produced are not soluble then you would not be able to detect corrosion.
I would be careful with trying to relate water quality with corrosion as a general rule. It may work in some cases and it could work in many cases (I have not tried) however the relations are tentative at a fundamental level and would likely lead to false negatives or false positives.
The presence of iron scale reduces the corrosion rate and thus reduces the iron concentration in the water.
Hi, important parameters to monitor corrosion in water systems are temperature, O2, pH, conductivity, redox-potential. With these values and maybe coupons to look at you can try to get a clue about what happens in your system and to adjust alarm levels. To rely only on one parameter may lead to false alarms. Best regards, Andreas
For more information I propose to read two interesting documents:
1) Regularities of galvanic corrosion of the copper/stainless steel coupple in Fe(III) enironment http://mokslozurnalai.lmaleidykla.lt/chemija/2002/4/1075
2) Fundamentals of Metallic Corrosion in Fresh Water By J.R. Rossum
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