USRE23740E - Corrosion inhibiting compositions - Google Patents

Description

Reissued Nov. 17, 1 953 CORROSION INHIBITING COMPOSITIONS AND METHOD John W. Ryznar, La Grange Park, and Marjorie A. Peich, Chicago, Ill., assignors to National Aluminate Corporation, Chicago, 111., a corporation of Delaware No Drawing. Original Nel 2,515,529, dated July 18, 1950, Serial No. 685,379,.Iuly- 22, 1946. Applicatlon for reissue March 18, 1953, Serial No.

13 Claims. (CI. 23-20!) Matter enclosed in heavy brackets I: 1 appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to new and improved corrosion inhibiting compositions and to a new and improved method of inhibiting'corrosion. The invention is particularly concernedwith corrosion inhibiting compositions for preventing or inhibiting underwater corrosion in systems where water is moving, as through condensers, engine jackets, spray .or cooling towers, and distribution sytems. The invention is especially valuablein inhibiting corrosion of ferrous metals, including iron and steel;

It is known that various phosphates will inhibit underwater corrosion on ferrous metals under' greatly increased by the presence of sodium chloride and-sodium sulfate. As the velocity 01 the water increases the dosage of phosphate required to inhibit corrosion normally decreases, and as the temperature of the water is increased the dosage of phosphate to inhibit corrosion also increases.

n relatively corrosive waters at'temperatures near the boiling point all corrosion cannot be stopped with phosphates alone, even when employing very high dosages of the phosphate. Our tests have indicated that with these very high dosages only partial protection can be obtained and there is looali7ed corrosion which is very undesirable. The higher temperatures also produce a greater tendency toward scale formation where the water contains substantial amounts 01' calclum.

One of the objects 01 this invention is to provide new and-improved corrosion inhibiting compositions.

A further object of the invention is to produce new and improved corrosion inhibiting compositions which are effective in preventing or retarding the corrosive effects of relatively corrosive waters on ferrous metals at relatively high temperatures. 1

Another object of the invention is to provide a new and improved method for inhibiting corrosion.

A still further object of the invention is to pro- 2 vide a newand improved method of inhibitin corrosion by a chemical treatment involving the utilization of relatively small amounts of corrosioninhibiting chemicals. Other objects will appear hereinafter.

.In accordance with the invention new and improvedcorrosion inhibiting compositions are prepared .by intimately mixing or blending a. corrosion inhibiting phosphate with a compound containinga CN group, preferably a complex inorganic cyani-de, with or without the addition of binders, algicides, bactericides and/or other water {been obtained with sodium ferrocyani Sodium nitroprusside (NB-2FB(CN)5NO.2H2O), potassium ferrocyanida'sodlum ferricyanide and/or potassiumferricyanide in conjunction with a polyphosphate. I

In order to evaluate the invention tests were made on a readily corrodible ferrous metal, namely, SAE-1020 mild steel, under various conditions of temperature and water velocity. The water used was a 1:1 mixture of Chicago tap water and distilled water, to which had been added 10.0 grains per gallon of sodium chloride. This water without treatment was very corrosive. When the water was treated with a. polyphosph'ate such'as sodium acid pyrophosphate (NazHzPzo'z) or a. molecularly dehydrated poly-phosphate such as NanP-zOzz, known as glassy septaphosphate, good protection against corrosion was obtained at 75 degrees F. with relatively small amounts of but the utilization of the phosphate in conjunction with a cyanide was efiective in inhibiting the corrosion even at temperatures above degrees F.

The invention will'be' further illustrated but is not limited by the. following examples, in which the quantities are stated in parts by weight unless 'otherwise indicated.

' Exist/nun I v A corrosive water was prepared as previously described by mixing Chicago tap water and distilled water in the ratio of 1:1 by weight and can be heated in any suitable manner to any desired temperature and maintained at that temperature. After each test the amount of corrosion can be determined by chemical analysis of the water for iron and by visual observation. Both methods were used in evaluating the results hereinafter set forth.

The following table shows the dosagein grains per gallon of NazHzPzO'r required for corrosion prevention 01 SAE-i020 mild steel under various conditions of temperature and water velocity.

Table Temperature Degrees F. Water Velocity FtJScc.

Indicates amount used was not suillcient to prevent all corrosion.

It will be observed that at 75 degrees F. good corrosion protection could be obtained with relatively small amounts of the phosphate. At 150 degrees F. quite high dosages were required but corrosion was inhibited by using the dosages shown. At 180 degrees F. and 210 degrees F. all corrosion could notbe stopped even when very high dosages of the sodium acid pyrophosphate were employed except in one instance when the water velocity and dosage (15.0) were high. The use of such high dosages at these hightemperatures is not only expensive but also causes other undesirable operating conditions such as sludge formation. Similar results were obtained with other-phosphates, such as glassy septaphosphate. The use of cyanide compounds alone, such as sodium or potassium ferro or ferricyanides, or sodium cyanide, did not substantially inhibit corrosion.

At a flow rate of 1.9 feet per second and 180 degrees F., using the same test conditions described under A, no corrosion was obtained when the water was treated with 1.0 grain per gallon of NanP'zOn glassy septaphosphate and 0.1 grain per gallon of potassium ferrocyanide.

EXAMPLE II The testing equipment described in Example IA was employed with a water temperature 01' 210 degrees F. and a velocity of 1.9 feet per second.

N0 corrosion was obtained when a blend of 4.0

Tests made in the manner described under I Example IA showed that 3.0 grains per gallon of NanPvOu glassy septaphosphate and 0.2 grain per gallon of sodium cyanide (NaCN) gave very good 4. corrosion protection at a temperature of degrees F. and 1.9 feetper second velocity.

EXAMPLE IV This example illustrates the preparation of a corrosion inhibiting composition suitable for the practice or the invention. This composition was prepared by pulverizing and blending together The resultant pulverized composition can be added directly to the water to be treated.

EXAMPLE V A ball briquette was prepared by briquetting the composition consisting of the following ingradients:

Ingredient: I Parts by weight Sodium ferrocyanide 7 Glassy septaphosphate 50 Anhydrous .etrasodium pyrophosphate 27- Ligno-sulflte binder (Bindarene) 8 Water 8 This composition can be used in a ball feeder for the treatment or water.

From the foregoing and many other tests it is apparent that the dosage of the cyanide need not be very high to exert a, very marked effect in corrosion protection. The optimum amount of the cyanide is usually within the range of 0.05 to 0.5 of the phosphate, and very good results have been obtained when the amount of cyanide is around 0.33 of the amount of phosphate by weight. In terms of grains per gallon of water treated the ratio of phosphate is preferably within the range of 0.1 grain per gallon to 5 grains per gallon, and the ratio of cyanide is preferably within the range of 0.05 grain per gallon to 0.5 grain per gallon. Very excellent results have been obtained when only 0.1 grain per gallon of potassium ferrocyanide was added along with the phosphate.

The invention is not limited to the use oi a y particular type of corrosion inhibiting phosphate. If the temperature of the water treated is low and the calcium content is low orthophosphates can be used, as, for example, trisodium phosphate,

monosodium dihydrogen phosphate and disodium phosphate is preferred, including, for example,

one or more oi. the following phosphates: sodium acid pyrophosphate, tetrasodium pyrophosphate, sodium tripolyphosphate (NasPaOw), sodium tetraphosphate (NBAPGOIS), calcium acid pyrophosphate, sodium trithiotetraphosphate (NasPrOwSz) any of the water soluble polyphosphate glasses or so-called molecularly dehydrated phosphates in which the ratio or Na-lO to P205 may be variable, including sodium hexametaphosphate and the glassy septaphosphate, as well as complexes containing calcium-sodium, magnesium-sodium and aluminum-sodium complexes.

All of the common inorganic cyanide compounds which were tried were found-to be effective for the purpose of the invention, thus indicating that at least a partial reason for the improved results may be attributed to the cyanide (9N) radical. Stearyl nitrile, although substantially water insoluble, was also found to be effective.

Throughout the specification and claims it will be understood that the expressionat a temperature near the boiling point" as applied to the water being treated is intended to include temperatures of at least about 180 degrees F.

In the tests which have been made to evaluate the invention neither the phosphates alone nor the cyanides alone were eflective in providing adequate corrosion protection at temperatures near the boiling point of water, whereas the combination of both was surprisingly efiecti e. This improvement in the efiectiveness could not have been predicted from the existing knowledge of the chemistry and the behavior of these chemicals. The invention, therefore, provides new and useful water treating compositions which are effective in preventing corrosion over a wide range of temperature, and in waters that are normally very corrosive when not treated. The invention has important advantages in providing a method of protection against corrosion by the addition of relatively small amounts of substances which do not cause other undesirable operating conditions. The use of such relatively small amounts has the added advantage of reducing the cost of corrosion protection. Thus, it has been demonstrated in Example IB that adequate corrosion protection at 180 degrees F. can be obtained with as little as 1.0 grainper gallon of glassy septaphosphate in conjunction with 0.1.

grain per gallon 01' potassium ferricyanide, whereas, as shown by Table L Withoutthe addition of the cyanide, at the same water velocity the polyphosphate used did not give adequate corrosion protection when 6 grains per gallon were employed at 180 degrees F.

In corrosion tests of the type previously d"- scribed, it is conventional to use a 24-hour test period.

Having thus described the invention, what we claim is new and desire to secure by Letters Patent oi the United States is:

1. A corrosion inhibiting composition comprising essentially a water soluble polyphosphate and a water soluble inorganic complex cyanide, the ratio of said cyanide to said phosphate being within the range of 0.05 to 0.5 by weight of said phosphate, and said composition being capable of dissolving in water to give a dissolved phosphate concentration within the range ot 0.1 grain per gallon to 5 grains per gallon of water and a dissolved cyanide concentration within the range of 0.05 grain per gallon to 0.5 grain per gallon of.water.

2. A corrosion inhibiting composition comprising essentially a water soluble glassy polyphosphate and a water soluble inorganic complex cyanide, the ratio of said cyanide to said phosphate being within the range of 0.05 to 0.5 by weight of said phosphate, and said composition being capable of dissolving in water to give a dissolved phosphate concentration within the range oi 0.1 grain per gallon to 5 grains per gallon of water and a dissolved cyanide concentration within the range of 0.05 grain per gallon to 0.5 grain per gallon of water.

3. A corrosion inhibiting composition compris ing essentially a water. soluble molecularly dehydrated phosphate and an alkali metal ferroeyanide, the ratio of said cyanide to said phosphate being within the range of 0.05 to 0.5 by weight of said phosphate, and said composition being capable oi. dissolving in water to give a dissolved phosphate concentration within the range of 0.1 grain per gallonto 5' grains per gallon of water and a dissolved cyanide concentration within the range of 0.05 grain per gallon to 0.5 grain per gallon of water.

4. A corrosion inhibiting-composition comprising essentially approximately 7% of sodium ferrocyanide, approximately 50% of glassy septaphosphate, and approximately 27-28% of anhydrous tetrasodium pyrophosphate.

5. A method of inhibiting corrosion in water which is in contact with ferrous metals at temperatures above about degrees F. which comprises essentially incorporating with the water so that both are present at the same time (1) a polyphosphate and 2) a water soluble inorganic complex cyanide, the quantity of said polyphosphate in said water being within the range of 0.1 grain per gallon to 5 grains per gallon of said water, and the quantity of said inorganic cyanide in said water being within the range of 0.05 to 0.5 by weight of said polyphosphate. f 1

6. A method of inhibiting corrosion in water which is in contact with ferrous metals at temperatures aboveabout 180 degrees F. which oomprises incorporating with the water so that both are present at the same time (1) a polyphosphate,

and (2) a water soluble potassium ferrocyanide, the quantity of said polyphosphate in said water being within the range of 0.1 grain per gallon to 5 grains per gallon of said water, and the quantity of said ferrocyanide in said water being within the range of 0.05 to 0.5 by weight of said polyphosphate.

7. A method of inhibiting corrosion in water at temperatures above about 180 degrees P. which comprises incorporating with the water so that both are present at the same time (1) a polyphosphate and (2) a water soluble potassium ferrocyanide, the quantity of polyphosphate being within the range of 1' to 5 grains per gallon. and the quantity of potassium ferrocyanide bein within the range of 0.1 to 0.5 grains per'gallon, the ratio of said ferrocyanide to said polyphosphate being within the range of 0.05 to 0.5 by

weight of the polyphosphate.

glassy septaphosphate, and a cyanide from the group consisting of sodium ferrooyanide, sodium nitroprusside, potassium ferrocyanide, sodium ferricyanide, potassium ferricyanide, sodium cyanide and stearyl nitrile, the ratio of said cyanide to said polyphosphate being within the range of 0.05 to 0.5 by weight of said polyphosphate and said composition being capable of dissolving in water to give a dissolved polyphosphate concen tration within the range of 0.1 grain per gallon to 5 grains per gallon of water and a dissolved cyanide concentration within the range of 0.05 grain per gallon to 0.05 grain per gallon of water.

9. A corrosion inhibiting composition comprising essentially a water soluble polyphosphate and sodium cyanide, the ratio of said cyanide to said polyphosphate being within the range of 0.05 to 0.5 by weight of said polyphosphate and said composition being capable of dissolving in water to give a. dissolved polyphosphate concentration within the range of 0.1 grain per gallon to 5 grains per gallon of water and a dissolved cyanide con- 7 centration within the range of 0.05 grain per gallon to 0.5 grain per gallon of water.

10. A corrosion inhibiting composition comprising essentially a water soluble polyphosphate and stearyl nitrile, the ratio of said nitrile to said polyphosphate being within the range 01' 0.05 to 0.5 by weight of said polyphosphate and said composition being capable of dissolving in water to give a dissolved polyphosphate concentration within the range of 0.1 grain per gallon to grains per gallon of water and a dissolved nitrile concentratlonwithin the range of 0.05 grain per gallon to 0.5 grain per gallon of water.

11. A method of inhibiting corrosion in water which is in contact with ferrous metals at temperatures above about 180 degreesF. which comprises essentially incorporating with the water so that both are present at the same time (1) a poly-.

phosphate from the group consisting of sodium .acid pyrophosphate, tetrasodium pyrophosphate,

sodium tripolyphosphate, sodium tetraphosphate, calcium acid pyrophosphate, sodium trithiotetraphosphate, sodium hexametaphosphate and glassy septaphosphate and (2) a cyanide from the group consisting of sodium ferrocyanide, sodium nitroprusside, potassium ferrocyanide, sodium ierricyanide, potassium ferricyanide, sodium cyanide and stearyl nitrile, the quantity of said polyphosphate in said water being within the range of 0.1 grain per gallon to 5 grains per gallon of said water and the quantity of said cyanide in said water being within the range or 0.05 to 0.5 by weight of said polyphosphate.

12. A method of inhibiting corrosion in water which is in contact with ferrous metals at temperatures above about 180 degrees F. which com- -nide, the quantity 0! said polyphosphate in said water being within the range 01' 0.1 grain per gallon to igrains per gallon of said water and the quantity or sodium cyanide in said water being within the range 01' 0.05 to 0.5 by weight of said polyphosphate.

13. A method of inhibiting corrosion 'in water which is in contact with ferrous metals at temperatures above about degrees F. which comprises essentially incorporating with the water so that both are present at the same time (1) a water soluble polyphosphate and (2) stcaryl nitrile; the quantity of said polyphosphate in said water being within the range or 0.1 grain per gallon to 5 grains per gallon oi said water and the quantity of stearyl nitrile in said water being within the range of 0.05 to 0.5 by weight of said polyphosphate.

NATIONAL ALUMINATE CORPORATION, By P. W. EVANS,

Vice-Pres.

References Cited in the flle of this patent or the original patent UNITED STATES PATENTS Number Name Date 1,926,265 Darsey Sept. 12, 1933 1,942,923 Irion Jan. 9, 1934 2,120,212 Curtin June 7, 1938 2,332,209 Enquist Oct. 19, 1943 2,337,856 Rice et a1 Dec. 28, 19,43