Corrosion in fresh water (Topic 11014)

The corrosivity of fresh waters depends on the hardness and pH of the water, chloride and heavy metal concentration in addition to flow rate temperature and O2 -concentration.

A combination of sour water, with a pH value below 6 and small quantities of chlorides and heavy metal salts may promote pitting on aluminium. The water hardness depends on the calcium carbonate concentration. The number of pits and the pit depth on aluminium have been found to increase with increasing carbonate concentration. The combined effect of chloride and carbonate can be seen below. The most serious corrosion, i.e. the deepest pits will occur in the area with much carbonate (hard water) and a chloride content above about 10 ppm. The water quality varies a lot from area to area. Some typical water analyses are given, indicating the wide range that may occur. In general, water from surface sources is softer than water from under ground sources.

Copper in the water can have a serious influence on the corrosion properties of aluminium in fresh water. Normally the amount of copper in fresh water is very low, but even copper levels as low as 0,02 ppm have been seen to initiate pitting on aluminium in hard waters.

The influence of the combination of chloride and calcium carbonate content in fresh water, on pitting corrosion of aluminium.[43]