[shane21]

   I am working on a water sample and trying to determine the level of corrosivity.  I have run the Langelier Index and now want to check the Ryznar Index but am not sure what the Ryznar Index is asking for when it requests [HCO3-].  I'm assuming it's asking for the alkalinity of the water expressed "mg/l as [HCO3-]" but am not sure??  I have a measurement of alkalinity expressed "mg/l as CaCO3" and think I can find a conversion formula to convert one to the other but want to make sure that's what I NEED to do first.   Any help would be great and thank you in advance.

   Also if anyone has any suggestions on another index or calculator they would recommend to examine corrosivity of water I would love that input as well.

[enahs]

This is essentially a measure of the amount of CO2 in the water. CO2 makes carbonic acid (HCO₃^-) is the the anion.

This is NOT easy to measure accurately, simply because just breathing on the sample is enough to change it. Fluctuations in the CO2 level in the atmosphere will change it. Small changes in temperature will shift the equilibrium quite a bit. Addition of other species in solution will effect it quite a bit.

It makes the water more acidic, yes, but I am not sure I would use this to determine how corrosive water is. I will also point out that corrosion happens by different mechanisms depending on what you are looking at.

[shane21]

   Well this is for a residence that is having trouble with hot water tanks rotting out in 2-3 years.  I know specifically that some water heater companies use the Ryznar Index to measure corrosivity of water when they have trouble with tanks wearing prematurely.  I believe since most corrosion indexes ask for alkalinity, - and the Ryznar calculators I have found did not specifically include the word "alkalinity" - then what they are asking for here is "alkalinity measured as HCO3-" instead of "alkalinity as CaCO3".  The link below tells me how to convert one to the other (it's very easy) but I'm just not sure this is the correct parameter I am SUPPOSED to calculate. 

   Any information is greatly appreciated.  I know someone here has to know about the Ryznar Index.

[enahs]

That all has to do with the carbonate ion, not carbonic acid. Those come from sodium and calcium carbonate (that is where the alkalinity comes from).


All you need is a pH meter to perform the test r some pH strips (can get it from pool supply shop).

[Borek]

Alkalinity is more related to buffering capacity - you check how much acid has to be added to titrate solution to the HCO₃^- equivalence point. pH measurement won't be enough, titration is the only way to go.

[enahs]

Alkalinity is more related to buffering capacity - you check how much acid has to be added to titrate solution to the HCO₃^- equivalence point. pH measurement won't be enough, titration is the only way to go.

The "Scale" he wants to use is just the pH at two different points. Yes, to really know what you have you would want to be more precise, but if he just wants to use the scale he mentions he only needs two pH points, by definition of the scale.

[shane21]

I really appreciate all the input but I think I may be asking for the information in the wrong way. 

The calculator I'm using can be found here:

http://www.lenntech.com/calculators/ryznar/index/ryznar.htm

I have all the required info except the HCO3- parameter and am not sure how to calculate it.  I think the Index is asking me for "alkalinity as HCO3-" but am not sure.  The reason I believe this is that nearly all corrosion indexes I can find ask for alkalinity in some form or fashion and find it hard to believe this one wouldn't need it as well. 

I currently have the measured "alkalinity as CaCO3" and would like to know if you guys think all I need to do is convert from CaCO3 to HCO3- OR if the index calculator is asking me for something completely different? 

The link to convert "alkalinity as CaCO3" to "alkalinity as HCO3-" is below and is very simple to calculate IF that's what I need to do.  Again I need to know WHAT the calculator is asking me for, not how to calculate it.  Once I know what it wants I'm sure finding the actual value will be pretty simple.

http://www.cdph.ca.gov/certlic/drinkingwater/Documents/Drinkingwaterlabs/AlkalinityConversions.pdf


Thanks again in advance for any answers you may have.