Liquid purification or separation – Flow – fluid pressure or material level – responsive – Proportionate feed means
Patent
1986-11-24
1990-07-24
Cintins, Ivars
Liquid purification or separation
Flow, fluid pressure or material level, responsive
Proportionate feed means
210134, 210143, 210434, 210662, C02F 500
Patent
active
049433717
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and apparatus for reducing pitting in copper water pipes.
The term "pitting" is intended to describe local corrosion in patches on the inside of the pipe or the like. Hemispherical pits occur in the patches. In the most extreme cases, a hole is corroded right through the copper water pipe wall and leakage results.
The causes of pitting have not been entirely explained. Factors of significance in relation to the occurrence of pitting are; the acidity of the water (pH value): its bicarbonate content, its temperature, and its degree of hardness. If the pH value and the bicarbonate content are too low, building up of a protective depositi of copper hydroxycarbonate inside a pipe is made impossible. In order to prevent pitting it is therefore being proposed that the bicarbonate content of the water should be raised by treating it with lime and carbon dioxide, see VVS and Energi 12, 1983, "Gropfratning av typ III i kallvattenledningar av koppar" (Type III pitting in cold water pipes), by E. K. Lindman and M. Linder, p. 64-66. For hard water it has also been proposed to increase the pH value of the water to over 7.5 (preferably 8.0-8.5) - see VVS, 3, 1972, "Korrosionshardigheten hos vattenledningar av koppar" (Corrosion resistance in copper water pipes), by E. Mattsson, p. 47-53. Such raising of the pH value takes place, for example, by alkalinization of the water at a waterworks, using sodium hydroxide, calcium hydroxide (milk of lime) or sodium carbonate (soda).
In areas with hard water, it is usual to use softening filters for softening the water. The term "hard water" here used to refer to water having a calcium content exceeding about 70 mg/1. Hard water forms lime deposits in pipes, valves and sanitary ware, as well as causing difficulties in the use of soap detergents. In extreme cases, the lime deposits on the inside of the pipes grow to such an extent that they block the pipes. On the other hand, softened water, particularly completely softened water, also results in disadvantages since copper dissolves in the water. In extreme cases, this can give rise to forms of copper intoxication, particularly diarrhoea in babies. Such a release of copper is encouraged in acidic water.
Softened water, with a high content of free carbonic acid (which attacks marble), is also considered to contribute to pitting in copper pipes.
The technical background of the invention is the following. To avoid lime deposits in pipework and apparatus, when the water has too great a degree of hardness, usually greater than 8.degree. dH, it is necessary to use a softening filter. The calcium ions, causing the previously mentioned deposits, are exchanged for sodium ions in this filter. This means that the water leaving the filter does not contain any calcium ions at all. Since there are no calcium ions, no protective layer of lime in pipework and apparatus can be formed.
Since water often contains substances which attack the metal --usually copper--from which pipework and apparatus are made, corrosion damage occurs (in the form of pitting) when the water is completely softened to a hardness of 0.degree. dH. This will in time lead to leakage in pipework and/or apparatus.
There is here a technical problem. On the one hand, if water, with a large degree of hardness is not softened, there will be deposits of lime which will block up pipes and apparatus. On the other hand, if softening is performed in a softening filter and water is obtained without calcium ions, the aforementioned corrosion damage will occur. It is thus desirable to produce water which has a sufficient degree of hardness (i.e. a calcium content which is suffiently large to form a protective calcareous layer on the interior of the pipework), yet which is not large enough to cause growing deposits to block up pipework and/or apparatus. It has hitherto not been possible, to solve this problem in a satisfactory way.
The Applicant is not the first to discover that a mixture of softened and hard water can give protection against the undesired dep
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Comsumers' Research Magazine, 10/83, p. 2, "Softened Water".
Goran Fallman
Tsviatko Ganev
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