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total hardness

total hardness

(OP)
Please I would like to know the limiting values of water total hardness that use for 316L Stainless Steel Heat Exchangers?

many thanks.


RE: total hardness

The only impact that hardness has is in relation to scaling tendency.
It has nothing to do with corrosion of SS, unless you allow scale to form and then crevice corrosion under the scale does become an issue or if the pH is low(from acid that you add to suppress scale).
Typically 316L is used in water up to about 200ppm Cl. If the system is very clean and free from biofilm and scale you can push that higher, perhaps to 500ppm. but the higher you go in Cl, lower in pH, and hotter the greater the risk for corrosion.

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P.E. Metallurgy, Plymouth Tube

RE: total hardness

(OP)
So please what is the maximum values of TH to avoid scaling
Thank you

RE: total hardness

You need to look up scaling index, there are a few different versions of this. Various saturation indexes are called Langelier, Ryznar, and Stiff/Davies .
You basically use the water chemistry, all of the various ions, and the max service temp to calculate a tendency to scale. Some of the scale formers are more soluble in hotter water, and some are less.

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P.E. Metallurgy, Plymouth Tube

RE: total hardness

(OP)
Some of machine manufacturer recommend Total hardness below 100 mg/l and some between 70-600 mg/l like Evaporative Condenser and others 200 mg/l. I totally confused. please make it more clear for me. Many Thanks

RE: total hardness

Total hardness is only one of four or five critical factors, if people are telling you that you can control just on hardness then they either think that you are too stupid to do it correctly or they are too stupid to know the difference.
Use Google and read, I prefer Langelier.
One thing to watch is that some people like to use these indexes to estimate corrosivity (mostly to steel). What you want is a balance. Too far to one side and scale forms, then water is not very corrosive to plain steel, but you will get under scale attack of stainless. Too far to the other side and you will never get scale, but any plain steel in the system will be corroded.
Most systems use some water treatment. In a closed system (not open cooling tower) you can use very expensive polymer additives because they will not be lost. In open systems it is more common to use sulfuric acid to lower the pH and prevent scale formation. In open systems you also need to be very careful about biological control, so biocides are a critical part of the treatment system.

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P.E. Metallurgy, Plymouth Tube

RE: total hardness

(OP)
Dear EdStainless,
Can you please send me a manual explain this point and the relation between water quality and corrosion
Thank you

RE: total hardness

One of the most usable books is published by Nalco, the water treatment company.
If you contact a Nalco rep they may be able to provide your with one for free.
There are a number of other good references on this subject, but try starting with Nalco.

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P.E. Metallurgy, Plymouth Tube

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