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AssigneesTechnion Research & Development, Mekoroth Water Co.
InventorsDavid Hasson, Mordechai Karmon
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Disclosed is a method for obtaining a tenacious insitu coating deposition of calcite on the inner surface of water pipes. The calcite coating method according to the present invention has an advantage that it is able to maintain a completely corrosion-free system during the coating, thus assisting the formation of a protective coating of good bonding properties. The method consists in the incorporation of a reagent selected from the group consisting of alkali metal sulfite and hydrazine, in an amount which is at least the stochimetrically required to deoxygenate the aqueous solution utilized for said coating, which is supersaturated with respect to calcium carbonate having a dissolved calcium and carbonate levels of above 100 ppm. The calcite producing ingredients are supplied to the water stream in quantities supplementing concentrations available in the natural water used, giving the required supersaturation levels by addition of suitable salts. The calcite coating can be successfully applied to large diameter mains and pipes by utilizing a large recycle ratio. The coating has in particular an improved adherence on the wall of the pipes, when the water is delivered at a flow velocity of above 1.5 m/sec.
A method for obtaining a tenacious in situ coating deposition of calcite having a thickness of above 50 microns on the inner surface of water pipes by delivering through said pipes at a flow velocity of above 1 m/sec. an aqueous solution supersaturated with respect to calcium carbonate consisting of a soluble calcium salt and soluble carbonate salt having a dissolved calcium level about 100 ppm and a dissolved carbonate level of above 100 ppm (expressed as CaCO.sub.3), being characterized by the fact that a reagent selected from the group consisting of alkali metal sulfite and hydrazine or mixtures thereof is incorporated in an amount which is at least the stoichiometrically required to deoxygenate said aqueous solution, the average degree of calcium carbonate supersaturation in the pipe being maintained at a level resulting in a turbidity equivalent to precipitated CaCO.sub.3 having a concentration not more than that of the remaining dissolved Ca.sup.++ or CO.sub.3.sup.-- ions, whichever is the smaller.
Dependencies are inferred from the claim text.