Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Carbonate Alkalinity

Last updated: July 3, 2018

What Does Carbonate Alkalinity Mean?

Carbonate alkalinity is a measure of the carbonate and bicarbonate anions in a solution. Carbonate and bicarbonate anions contribute to alkalinity due to their basic nature, hence their ability to neutralize acid. It is usually expressed as parts per million (ppm), milligrams per liter (mg/L) or in degree KH (dKH).

Carbonate alkalinity can determine water hardness. Higher carbonate alkalinity usually translates to harder water, which causes scale formation in water distribution systems or boilers, leading to corrosion.

Carbonate alkalinity is also known as carbonate hardness or temporary hardness.


Corrosionpedia Explains Carbonate Alkalinity

Carbonate alkalinity calculates the amount of negatively charged carbonate and bicarbonate atoms in a solution. Mathematically, the carbonate anion concentration is counted twice due to its ability to neutralize two protons, while bicarbonate is counted once as it can neutralize one proton. They are often found together in their most common applications. Alkalinity is usually measured in milligrams per liter of calcium carbonate, which is a calcium ion bound to a carbonate ion.

Carbonate alkalinity is especially important in environmental contexts. When a water's pH is above 8.3, its alkalinity tends to come from carbonate ions, and below that threshold the alkalinity usually comes from bicarbonate ions. Measuring alkalinity is important in determining water's ability to neutralize acidic pollution from rainfall or wastewater.

Carbonate ions are also quite useful for purifying water. Carbonate and bicarbonate ions can bind to toxic metals in water and precipitate them out of the water as solids, acting as a natural cleaning system and giving the water somewhat of a resistance to certain types of pollution.

Carbonate alkalinity is also measured to monitor the pH of swimming pools. Alkalinity is closely linked to pH, so when water testing kits measure pH, they are also indirectly measuring alkalinity. Since alkalinity, hardness and pH influence corrosion in water distribution systems, they interact to determine whether the water will produce scale or corrosion or will be stable.



Carbonate Hardness

Temporary Hardness

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