Waterhouse Corporation - Corrosion Control

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Waterhouse Corporation
Water Softening
Deltona, FL 32738
United States
ph: 407-509-9658
fax: 386-789-6697
reruckstuhl@engineeredwater.us

Corrosion Control

Calcium Saturation and Corrosion Control

Alkalinity (carbonates CO3 and bicarbonates HCO3) and the free carbon dioxide CO2 in water influence corrosion and scale formation. Scaling typically refers to hardness scale and its degree of scale potential (normally calcium hardness). Sulfate and chloride ions also can increase the corrosion potential of water. Above 250 ppm silica can act as a corrosion inhibitor.

Historically, the Langelier Calcium Carbonate Saturation Index, and the Ryznar Index have been used to approximate calcium saturation in water systems. In recent years computer models predict water chemistry and take into account all of the ions present in a water sample to allow corrosion control utilizing existing water ions.

Scale modification polymers, chelants, phosphate and phosphonate threshold inhibitors are commonly used to prevent scale formation in water systems. These molecules interfere with crystal formation kinetics or the crystal lattice structure which allows them to be in solution and provide corrosion resistance.

Cathodic Protection

The first practical use of cathodic protection is generally credited to Sir Humphrey Davy in the 1820s. Davy’s advice was sought by the Royal Navy in investigating the corrosion of copper sheeting used for cladding the hulls of naval vessels.

Davy found that he could preserve copper in sea water by the attachment of small quantities of iron or zinc; the copper became, as Davy put it, “cathodically protected”.

Cathodic protection may be achieved in either of two ways. By the use of an impressed current from an electrical source, or by the use of sacrificial anodes (galvanic action).

Sacrificial anodes are used today to control corrosion on the steel tubesheets of heat exchangers that have brass or copper tubes.

What is "Balanced Water"

Years ago the “marble test” was used as a measure of a water balance. A sample of water shaken with finely ground marble then filtered was analyzed for hardness and alkalinity before and after.

If the water had a high scale forming potential, the hardness and alkalinity would drop; if the water was aggressive (corrosive) water, the values would increase.

If there was little change, the water was "balanced", neither corrosive nor scale forming.

Langelier developed an index based on solubility products and dissociation constants which ingeniously related alkalinity, pH, and calcium hardness to determine the pH at which saturation should occur at various temperatures.

Waterhouse Corporation
Water Softening
Deltona, FL 32738
United States
ph: 407-509-9658
fax: 386-789-6697
reruckstuhl@engineeredwater.us