[Bob-Moutch]

Hello,

For the last 3 days, I've been trying to understand Leroy index (=TAC/TH). It allows to confirm or not the corrosion tendency of a water. With concentrations expressed in meq/l, the water is considered non-corrosive if the index is between 0.7 and 1.3.

I found an article written by Pierre Leroy with this self-explanatory graph that I want to use (the graph is an attachment with the name corrosion.PNG). But I can track down the function.

Can someone help me ?

The graph links the Saturatio (=([Ca²⁺]×[CO₃^2-])/Ks') to the Larson Index (=([Cl^-]+[SO₄^2-])/[HO₃^-]).

Moreover Leroy index defines different sectors :
- orange : pipe are covered in scale
- green : scales (carbonate calcium) protect the pipe from corrosion
- yellow : there are not enough scales to protect the pipe form the corrosion
- pink : there are no scale and the pipe corrodes

I really want to use the graph for my presentation but i can't track down the function linking Saturatio to Larson Index. I think my hypothesis are wrong.

Here are my hypothesis :
- [Ca²⁺]>>[Mg²⁺]  TH=[Ca²⁺]
- TH - TAC = [Cl^-]+[SO₄^2-]
- TAC/2 > TA  [HO₃^-]=TAC-2×TA and [CO₃^2-]=2×TA

Thank you for your help