Langelier Index

[BRIS]

The Langelier Index is a saturation index which measures the potential to dissolve or deposit calcium carbonate. In the past it has been used, incorrectly as a corrosion index to assess corrosivity. AWWA have recommended that this practice be abandoned

My question is to what extent is the Langelier index still being used as method of control and monitoring of water quality. i.e are there any mandatory requirements in the US to measure the Langelier Index.

 

[bimr]

The Langelier Index is a quick and dirty method to evaluate if water has a tendency to scale. The LI does not incorporate piping material nor corrosion control additives so the ability to make definitive recommendations regarding corrosion using jist the LI is somewhat limited.

Don't think anyone requires the LI us used. The LI is just one tool in the toolbox.

Regarding the comment "AWWA have recommended that this practice be abandoned", AWWA still has LI on the website:

http://www.awwa.org/Resources/RTWCorrosivityCalc.cfm?navItemNumber=1576

 

[BRIS]

bimr - thanks your views are exactly the same as mine: The LI, on its own will not predict corrosion/scaling but it is still a useful tool to be used for comparisons. Also the Marble Test.

I am out in the sticks of Africa and I am being given the story that the LI and physical Marble Tests have virtually been abandoned. I am sure that is not the case and that the LI and Marble Test (together with other SI indices) are still common practice in the western world.

I am not sure what other practical means there are to assess corrosivity ?

 

[bimr]

The most practical and probably the most accurate test is probably to do an actual coupon test.

http://www.alspi.com/water.pdf

Another method is to survey existing users especially the professionals like the well drillers.

 

[CivEnvEng98]

CCPP (Calcium Carbonate Precipitation Potential) measures the amount of supersaturation (mg/L) of CaCO3. You'll need a specific Caldwell-Lawrence diagram (depending on TDS and temperature) or a desktop software to figure it out the saturation concentration of CaCO3 for your specific water conditions.

Basically its:

CCPP = ([Ca observed] - [Ca saturation])

Generally you want a -5.0 mg/L CaCO3 or better.

Then there is another index out there called the Rynzar Stability Index (RSI).

RSI - 2pHs - pH

pH is the measured water pH
pHs is the pH at saturation in calcite or calcium carbonate

RSI < 6 = scale forming
RSI 6 to 7 = little scale or corrosion
RSI > 7 = corrosion significant

 

[orenda1168]

The Langlier Index is still widely used in the recreational water industry as an indicator of scaling/corrosion tendency of pool and spa waters.

Orenda

 

[BRIS]

http://www.corrosion-doctors.org/Cooling-Water-Towers/corrosivity.htm

The above link gives a good description of various indices.

 

[KiwiMace]

The Langlier Saturation Index was recently presented in a water treatment report. The French Creek water cycle software seems to provide it as a simulation output.

The other comps were: Calcium Phosphate, and Magnesium Silicate saturation.