Compositions – Preservative agents – Anti-corrosion
Patent
1983-02-25
1986-05-13
Nucker, Christine M.
Compositions
Preservative agents
Anti-corrosion
106 1412, 106 1413, 106 1415, 422 12, 422 16, C09K 300, C23F 1100, C23F 1104, C04B 902
Patent
active
045885192
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the inhibiting and preventing corrosion of iron based metals which are in contact with aqueous systems, such as cooling water systems.
Iron and iron metal containing alloys such as mild steel are well known materials used in the construction of apparatus in which aqueous systems circulate, contact the iron based metal surface and may be concentrated, such as by evaporation of a portion of the water from the system. Even though such metals are readily subject to corrosion in such environments, they are used over other metals due to the strength they have.
It is known that various materials which are naturally or synthetically occurring in the aqueous systems, especially such systems formed from natural resources such as seawater, rivers, lakes and the like, attack iron based metals (the term "iron based metals" shall mean in the present disclosure and the appended claims iron metal and metal alloys containing iron therein). This is especially true where the aqueous system is a hard water i.e. contains about 300 ppm or greater of calcium and magnesium therein.
Typical apparatus in which the iron metal parts are subject to corrosion include evaporators, single and multi-pass cooling towers and associated equipment and the like. As the aqueous system passes through or over the apparatus a portion of the aqueous system evaporates causing a concentration of the materials contained in the system. These dissolved materials approach and reach a concentration at which they cause severe pitting and corrosion which eventually requires replacement of the metal parts.
Various corrosion inhibitors have been previously used. These include inorganic nitrite or phosphate salts and the like. These materials have only minor inhibiting effects and tend to decompose when used in environs such as encountered in cooling towers, evaporators and similar apparatus wherein the aqueous system is subjected to elevated temperatures.
Copolymers such as described with respect to the present invention have been found, when used alone, to have substantially no corrosion inhibiting effect.
It is desired to have a composition and a method capable of being easily worked which substantially inhibits the corrosion of iron based metals. It is desired to have a composition capable of substantially inhibiting corrosion of iron base metals of apparatus in contact with aqueous systems which tend to concentrate. It is further desired to have a composition which is capable of inhibiting corrosion when used at very lower dosages.
SUMMARY OF THE INVENTION
The present invention is directed to a method of inhibiting corrosion of iron based metals which are in contact with aqueous systems by mixing with the aqueous system a threshold quantity of an inorganic phosphate and a water soluble organic copolymer formed from acrylamido-sulfonic acid monomers and vinyl carboxylic acid monomers.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention it has been surprisingly found that the desired corrosion inhibition can be achieved by the use of a specific composition. This composition is the combination of an inorganic phosphate and certain organic copolymers as described in detail hereinbelow. It has been found that the subject combination of components results in a synergistic desired effect.
Accordingly, the present invention provides a method of inhibiting corrosion of iron base metals in contact with an aqueous system by incorporating into the aqueous system a water soluble inorganic phosphate compound e.g. orthophosphoric acid, alkali metal phosphates, such as sodium or potassium orthophosphates, sodium or potassium pyrophosphates, sodium or potassium metaphosphates sodium or potassium tripolyphosphate, sodium or potassium hexametaphosphate and the like. The phosphate compound should be water soluble. The preferred salts are the sodium salts.
The copolymeric material required to be used in combination with the inorganic phosphate described above can be represented by the gen
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Dearborn Chemical Company
McDowell, Jr. W. W.
Nucker Christine M.
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