Compensated Hardness

Last updated: August 15, 2017

What Does Compensated Hardness Mean?

This is a quantitative measurement of the condition of water in relation to its actual hardness and iron content. The value is arrived at by adding the hardness of the water to a multiple of iron and manganese; no single formula has yet been widely accepted since many companies have their own. It is used to determine the capacity of a water softener to be used to prevent scaling and corrosion in metal pipes.


Corrosionpedia Explains Compensated Hardness

Hard water is known to contain calcium and magnesium compounds, which form salts that alter the acidity and softness of the water. Corrosive water is described by:

  • Low pH factor (a pH greater than 9 will protect ferrous metals)
  • High hardness properties
  • Low alkalinity quantity
  • Presence of hydrogen ions
  • Presence of oxygen and oxidizing agents

Since pure water has an attraction for metals, there are particles of minerals suspended or dissolved in the water. The materials exist as ions in the water, hence are able to create an electrochemical circuit that leads to galvanic erosion. The measurement of these particles is in parts per million (ppm) or grains per gallon (gpg). A hardness of above 10 grains will reduce the lifespan of a piping system through corrosion.

The calculation of the compensated hardness is noted to have relatively more focus on iron since it is prone to causing more problems and interfering with the correcting process of the softeners. By determining the compensated hardness, one is able to estimate the required amount of softener to use in order to suppress the conditions that make the water corrosive.

This value can also be used in the selection of the treatment to be used when correcting the properties of the water in use. Softeners are used to replace the active ions with inert ions such as sodium.


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