US2675351A - Method for preventing corrosion and scale - Google Patents

Description

Patented Apr. 13, 1954 METHOD FOR PREVENTING CORROSIQN AND SCALE I Richard C. Ulrner, Bronxville, and John A. Ulrich, Jr., Massapequa, N. Y., assignors to E. F. Drew .& 00., Inc., New York, N. Y., a corporation of Delaware No Drawing. Application March 27, 1950, Serial No. 152,275

The present invention is directed to a composition and a method for preventing scale, deposits and corrosion in steam boilers, and corrosion in steam and condensate lines.

In the production of steam in steam boilers and the like by use of ordinary waters, there is introduced into the boiler mineral substances resulting from the dissolved salts naturally occurring in the water. Such compounds form scale, reducing the efiectiveness of the boiler and certain of such compounds cause corrosion of the metal of the boiler. Also during the formation of steam and chemical change in the dissolved compounds, carbon dioxide is formed and dissolved oxygen is released, providing substances which are corrosive. Such corrosion takes place not only in the boiler but also in the steam lines through which the steam passes and in the condensate lines. Various substances have been introduced into the water for preventing formation of scale and it has also been proposed to prevent corrosion of steam lines by the use of volatile amines which are intended to give an alkaline reaction to the steam. However, such treatment has not been entirely satisfactory in the past and it is quite desirable to improve the protective effects of compositions used for this purpose.

The present inventionis intended and adapted to overcome the difficulties and disadvantages inherent in prior methods and compositions, it being among the objects of the present invention to provide a treatment of boiler water which will be eflective in preventing corrosion and scaling oi the metal surface of the boiler and which will cifectively prevent corrosion of steam and condensate lines.

.It is also among the objects of the present invention to provide a single composition which when added to boiler water in the proper proportion will have the beneficial effect .on both the steam boilers and the steam lines.

It is further among the objects of the present invention to provide a composition which will enter into suitable reactions over a relatively long period of time to give substantially continuous and adequate protection against corrosion and scaling.

In practicing the present invention, there is provided a composition of alginic acid and a Water-soluble nitrite, preferably an alkali metal nitrite. The composition is formed by mixing solutions of the two constituents or dissolving one of the constituents in a solution .of the other. A reaction occurs whereby an addition compound is zippered which is soluble in water than the 6 Claims. (Cl. 2l0-23) individual constituents. However, the solubility thereof is sufficiently great so that it is completely soluble in boiler water in the proportions used. There may be present an excess of either of the constituents, and often the nitrite is in considerable excess.

Usually there is added thereto a substantial amount of a caustic alkali depending upon the character of the water being treated. In some cases, however, the addition of such alkali is unnecessary. In the operation of the invention a small amount of the composition is added to the boiler water and during the formation of steam in the water chemical reactions take place whereby free ammonia is eventually formed. This is produced by a gradual disintegration of the algin addition product. The product further reacts at the high temperature with substances in contact therewith, whereby a protective film, probably of a metal oxide, is formed on the surface of the metal of the boiler. Such a film prevents adherence of mineral matter to the walls of the boiler and also prevents corrosion of the surfaces.

At the same time, by reactions which are not fully understood, the nitrogen in the product is converted into ammonia. It is possible that some of the algin is broken down at the high temperature and the resulting compounds react with the nitrite radical reducing it to ammonia, .or the nitrite may react in the presence of ferrous hydroxide to produce ammonia. The algin tends to soften the water and it also prevents the formation of scale by causing the precipitated mineral matter to be deposited in a non-coherent form. The alkali metal radical present is transformed into the hydroxide.

The addition productis usually formed by adding 20 parts of a soluble nitrite such as sodium nitrite to 77 to 79 parts by Weight of water and introducing therein from 1 to 3 parts by weight of alginic acid. This provides the neutral grade of the addition compound containing an excess of the sodium nitrite. Where the water to be treated contains a moderate amount of alkalinity, it is often advisable to introduce from 15 to 25 parts by weight of free alkali, as for example, sodium hydroxide. This replaces an equal amount by weight of the water present in the neutral composition. In some instances where the alkalinity content of the water is quite low, a strongly alkaline composition is used. In such cases from 30 to ,50 parts by weight are used to replace an equal amount of the water present in 55. the composition.

' at about 486 F. for twenty-four hours.

positions, such as tannin or lignin. For instance, 7

from 4% to 6% of quebracho tannin has been found suitable and one may incorporate from 2% to 20% of various tannins depending on the conditions encountered. By such an addition the sludge or mineral matter deposited during the operation of the boiler has less tendency to adhere strongly to the boiler surfaces. If desired, there may be added to the composition any of the various phosphates and polyphosphates to further assist in prevention of formation of scale.

The following are specific examples of the operation of the invention.

Example 1 To a laboratory boiler containing about l gallons of water there was added 100 parts per million of a composition made up as follows:

Per cent by weight Alginic acid 1.5 Sodium nitrite 20 Water 78.5

The boiler was operated at 600 lbs. per sq. in.

After the initial operation ammonia appeared in the steam and the pH thereof became 8 to 10. The amount of ammonia in the steam was from .05 to 5.0 parts per million. During the entire period of operation a substantial amount of ammonia was present as it was liberated continuously and in relatively small quantities by the decomposition of the alginic acid addition product. The pH of the steam may be varied and controlled by the introduction into the boiler of suitable amounts of the algin-nitrite product.

In a parallel test under exactly the same conditions but omitting the .alginic acid-nitrite addition product, the pI-I of the steam was about 5.0 and there was free CO2 in the steam to the extent of to 10 parts per million. Under the latter conditions corrosion took place whereas under the former conditions the steam and condensate lines were not attacked at all.

Example 2 The following composition was used:

. Per cent by weight Alginic acid 1.5 Sodium nitrite I Sodium hydroxide 20 Tannin 5 Water 53.5

The composition was added to the laboratory boiler of Example 1, using identical conditions and operating the boiler for the same length of 4 Example 3 Another laboratory experiment was conducted in order to determine the extent of inhibition of rust or corrosion. The following composition was used:

' Per cent by weight Alginic acid 1.5 Sodium nitrite 20 Sodium hydroxide 40 Water 38.5

Corrosion testers containing specimens of metal similar to that used in boilers and steam and condensate lines were installed. Tests were made for a period of 30 days. When the inhibitor was not used very rapid corrosion took place in the steam and condensate lines, especially the latter. The corrosion, expressed in inches of penetration per year, amounted to 10.098. The pH of the steam was 5.5 and no ammonia was present.

A similar test conducted with new specimens and using the algin-nitrite inhibitor resulted in: practically no corrosion, the actual inches of penetration per year being only 0.008. Sufficient of the composition was used to maintain a pH in the range of 7.5 to 8.0. Under this condition no free ammonia was present, all of the ammonia being combined as ammonium carbonate.

Example 4 during most of the period. Under these condi -"j tions without the use of the composition the corrosion amounted to 0.049 inch per year. .'When the algin-nitrite composition was used with the above conditions existing in the boiler the corrosion amounted to 0.005 inch per year, indicating very satisfactory protection.

Example 5 The following experiment indicatesfhow scale can be inhibited or controlled in actual operating boilers through the use of the algin-nitrite composition. In a boiler operating at 250 p. s. i. (401 F.) metal test couponsv were installed throughout the boiler, that is in the boiler water. to determine the tendency toward'scale forma: tion. Accepted boiler water treating practices were followed. That is, the pH was in the range of 10.5 to 11.5, total alkalinity inthe range of 25 to 35 g. p. g. phosphate in the range of 20 to 40 p. p. m. Whenthe compositionwas not used scale formed onthe coupons especially in the high heat transfer areas. The scale consistedof cal,- cium phosphate and iron oxide and related prod ucts. When the composition wasused in suf-Q ficient amounts to give the desired pH no 's'c'a'le formed on the coupons, indicating the effectiyeness of the composition. The tests were con ducted for three months periods each.

The invention is adapted to afford substantially complete protection not only to the boiler but also to the steam lines as Well as the conde'n s'ate lines. The specific examples are intend'ed'to illus- Corrosion test coupons were installed as for example, the proportions of the constituents may be changed, other auxiliary substances may be added, and the amounts used in the boiler. Therefore, the invention is to be broadly construed and not to be limited except by the character of the claims appended hereto.

The prevention of formation of scale in the equipment is at least as important as the prevention of corrosion thereof. in the claims the term preventing corrosion is not intended to limit them, but the term is sufiiciently broad and is intended to include preventing scale formation.

We claim:

1. A method of preventing corrosion of steam boilers and steam and condensate lines which comprises adding to boiler water a composition made by mixing in aqueous solution about 20 parts by Weight of an alkali metal nitrite and 1-3 parts of alginic acid heating said water to form steam under high p .essure to cause a chemical reaction to take place with the formation of free ammonia in sufficient amounts to render the steam alkaline and simultaneously forming a film on the metal of the boiler to provide protection against scale formation and corrosion.

2. A method of preventing corrosion of steam boilers and steam and condensate lines which comprises adding to boiler water a composition made by mixing in aqueous solution about 20 parts by Weight of an alkali metal nitrite, 1-3 parts of alginic acid, and free caustic alkali, heating said Water to form steam under high pressure to cause a chemical reaction to take place with the formation of free ammonia in sufficient amounts to render the steam alkaline and simultaneously forming a film on the metal of the boiler to provide protection against scale formation and corrosion.

3. A method of preventing corrosion of steam boilers and steam and condensate lines which comprises adding to boiler water a composition made by mixing in aqueous solution about 20 parts by weight of an alkali metal nitrite, 1-3 parts of alginic acid, and about 20 parts of free caustic alkali, heating said water to form steam under high pressure to cause a chemical reaction to take place with the formation of free ammonia in sufiicient amounts to render the steam alkaline and simultaneously forming a film on the metal of the boiler to provide protection against scale formation and corrosion.

4. A method of preventing corrosion of steam boilers and steam and condensate lines which comprises adding to boiler water a composition made by mixing in aqueous solution about 20 parts by weight of an alkali metal nitrite, 1-3 parts of alginic acid, and an amount of tannin less than the nitrite, heating said water to form steam under high pressure to cause a chemical reaction to take place with the formation of free ammonia in sumeient amounts to render the steam alkaline and simultaneously forming a film on the metal of the boiler to provide protection against scale formation and corrosion.

5. A method of preventing corrosion of steam boilers and steam and condensate lines which comprises adding to boiler water a composition made by mixing in aqueous solution about 20 parts by Weight of an alkali metal nitrite, 1-3 parts of alginic acid, an amount of tannin less than the nitrite, and free caustic alkali, heating said water to form steam under high pressure to cause a chemical reaction to take place with the formation of free ammonia in sufficient amounts to render the steam alkaline and simultaneously forming a film on the metal of the boiler to provide protection against scale formation and corrosion.

6. A method of preventing corrosion of steam boilers and steam and condensate lines which comprises adding to boiler water a composition made by mixing in aqueous solution about 20 by weight of sodium nitrite and 1-3 parts of alginic acid, heating said water to form steam under high pressure to cause a chemical reaction to take place with the formation of free ammonia in sufiicient amounts to render the steam alkaline and simultaneously forming a film on the metal of the boiler to provide protection against scale formation and corrosion.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,395,730 Reiohinstein Nov. 11, 1921 1,903,041 Hall et al Mar. 218, 1933 2,053,024 Dreyfus Sept. 1, 1936 2.102.825 Woodhouse et a1. Dec. 21, 1937 2,264,389 Lamprey Dec. 2, 1941 2,297,670 Schroeder et a1. Sept. 29, 1942 2,411,676 Burghart Nov. 26, 1946 OTHER REFERENCES Ind. Eng. Chem, vol. 37, pp. 749-51, 1945.

Smith, J. Soc. Chem. Ind., p. 519, September 29, 1835.

Metallic Corrosion Passivity and Protection, by Evans, p. 543, 5'76 and 577, 1948.

Claims (1)

1. A METHOD OF PREVENTING CORROSION OF STEAM BOILERS AND STEAM AND CONDENSATE LINES WHICH COMPRISES ADDING TO BOILER WATER A COMPOSITION MADE BY MIXING IN AQUEOUS SOLUTION ABOUT 20 PARTS BY WEIGHT OF AN ALKALI METAL NITRITE AND 1-3 PARTS OF ALGINIC ACID, HEATING SAID WATER TO FORM STEAM UNDER HIGH PRESSURE TO CAUSE A CHEMICAL REACTION TO TAKE PLACE WITH THE FORMATION OF FREE AMMONIA IN SUFFICIENT AMOUNTS TO RENDER THE STEAM ALKALINE AND SIMULTANEOUSLY FORMING A FILM ON THE METAL OF THE BOILER TO PROVIDE PROTECTION AGAINST SCALE FORMATION AND CORROSION.