US3011862A

US3011862A - Sodium carbonate as inhibitor against corrosion by ammonia-ammonium nitrate solutions

Info

Publication number: US3011862A
Application number: US860642A
Authority: US
Inventors: Franklin M Watkins
Original assignee: Sinclair Refining Co
Current assignee: Sinclair Refining Co
Priority date: 1959-12-21
Filing date: 1959-12-21
Publication date: 1961-12-05
Anticipated expiration: 1978-12-05

Description

United States Patent 3,011,862 SODIUM CARBONATE AS INHIBITOR AGAINST CORROSION BY AMMONIA-AMMONIUM NI- TRATE SOLUTIONS Franklin M. Watkins, Flossmoor, 111., assignor to Sinclair Ilsiefining Company, New York, N.Y., a corporation of ame No Drawing. Filed Dec. 21, 1959, Ser. No. 860,642 3 Claims. (Cl. 212.5)

This invention relates to a process for preventing corrosion to ferrous metal containers and more particularly to a process for inhibiting corrosion to ferrous metal surfaces when contacted with aqueous ammonia-ammonium nitrate solutions. Today, large volumes of aqueous ammonia-ammonium nitrate solutions are used in agriculture, and these solutions are generally corrosive to mild steel surfaces such as the type which are utilized in the handling and storage of fertilizer solutions and the like. Thus, the industry has necessarily been required to utilize the more costly aluminum and stainless steel.

Methods of controlling this corrosion have been devised, but each method heretofore utilized, has certain shortcomings. U.S. Patent 2,366,796 shows that the surface of light steel may be passivated by treating with an electrical potential of 1.22 to 2 volts. This major wealo ness of this technique is that the passive film must be reestablished at frequent intervals since control of corrosion is provided for only about days and if the solution stands for extensive periods of time, the interior surfaces of the tank begin to corrode. Thus, each tank or car must be equipped with an electrical system capable of re-establishing passivity at frequent intervals. This is impractical as most tank and pipe systems are utilized only intermittently as carriers or storage housings for fertilizer solutions and thus could not be economically equipped with the necessary equipment.

An object of this invention is to provide a simple, inexpensive method of treating ferrous metal containers to prevent corrosion to containers which normally occurs during the handling and storage of aqueous ammoniaamrnonium nitrate solutions. This invention further pro vides a method for treating these metallic surfaces so that there will not be substantial surface corrosion. Normally, inhibiting corrosion of a metallic surface due to one component such as sulfuric acid, etc. would not be satisfactory in preventing corrosion to the same metallic surface by another material such as an ammonia solution. Thus, there is no assurance that a surface which has been treated to prevent corrosion under given conditions will successfully resist corrosion when these conditions are changed such as by the addition of another corrosive element.

This invention provides a method of protecting ferrous metal surfaces against corrosion caused by aqueous ammonia-ammonium nitrate solutions which include exposing the ferrous metal surface to an aqueous solution of sodium carbonate for a period long enough to prevent corrosion to the surface upon subsequent contact with an aqueous ammonia-ammonium nitrate solution. The preferred embodiment of this invention includes a process for inhibiting corrosion of metallic surfaces utilized in fertilizer handling systems wherein a minor amount of sodium carbonate, e.g. soda-ash or sal soda is added to water to form a solution. The metallic surface is usually con- "ice tacted with this solution for a period at least about 10 hours. There is generally little advantage to be gained by contacting the metallic surface with the sodium carbonate solution for more than 3 to 5 days. The sodium carbonate treatment may be utilized alone to provide corrosion inhibition or further protection may be afforded by including a corrosion inhibitor in the ammonia solution which inhibitor is effective should the inactivation provided by the sodium carbonate become inadequate. The corrosion inhibitor should be compatible, i.e. not destroy the inactive state of the metal, and may be for instance a minor corrosion inhibiting amount of soluble trivalent arsenic. The arsenic can be added in various forms, such as AS203 in a sodium hydroxide solution or complexed with ethylene glycol, in an amount to provide say about 0.1 gram of As O per 100 ml. of the ammonia solution.

The amount of sodium carbonate in the aqueous treating solution may vary depending upon the peculiar characteristics of the metallic surfaces to be protected and the existing external conditions affecting corrosion. The amount of sodium carbonate is suflicient to inhibit corrosion and is generally at least about .1 percent by Weight of the aqueous treating solution, with a preferred amount being from about .5 to 5, 10 or more weight percent. The maximum amount of sodium carbonate employed is a matter of economics. The metallic containers normally treated with this solution have ferrous surfaces and may be of the type known as mild steel surface containers.

This invention is particularly effective in protecting mild steel against corrosion by aqueous ammonia solutions such as solutions containing a predominant amount of NH.,NO and a minor amount of NH Generally, the solutions contain about 1 to preferably about 40 to 80% ammonium nitrate and about 5 to 35%, preferably about 10 to 35%, ammonia with substantially the balance being water, for instance about 10 to 65% It is preferred that the metallic container be treated for a period of from about 2 to 3 days.

Various tests were conducted under static conditions using mild steel coupons which were cleaned by surface finishing with a grit surface silica carbide abrasive cloth and then contacted for about 3 seconds at a temperature of F. with an aqueous solution having 15% hydrogen chloride. These mild steel coupons were selectively immersed in a solution having 66.8% NH NO 16.6% NH; and 16.6% H 0 and the corrosion rate determined.

EXAMPLE I A mild steel coupon was tested according to the above procedure and found to be corrosive, the rate of corrosion of the coupon was measured as 6255 MDD. MDD is milligrams loss per square decimeter of surface area per day.

EXAMPLE II A mild steel coupon was surface finished and treated with hydrogen chloride according to the procedure above and then immersed in a 1 percent by weight solution of sodium hydroxide for one day and then immersed in the 66.8% Nl-I NO 16.6% NH;, and 16.6% water solution. The rate of corrosion was 1700 MDD.

Table I illustrates the results obtained by testing a series of mild steel coupons which were activated by either sand blasting or surface finishing, with or without hydrogen chloride treatment, before immersion in a 1% solution of sodium hydroxide.

Table I [Corrosion record of test coupons in a solution of 66.8% NH NO;+16.6% NH +16.6% H20] Coupon 1st Test Retest No. Finish Activation Rate, Deactivation Rate,

MDD MDD 2 Sand blasted 5, 380 1% NaOIEL. Inactive.

d 5,035 One day. Do. 5, 715 doc Do.

5,400 5,355. Inactive.

do 190 do 0.

Surface fin- 5,810 1% NaOH 1,690.

6,255 onedayufl 1,700.

do Inactive.

1 Previous contact with a solution of 66.8% NH NO 16.6% NHQ and 16.6% H2O.

Representative samples of the coupons which were tested and found subject to corrosion according to Table I were then immersed in a 1 percent by Weight aqueous solution of sodium carbonate for 64 hours and immersed again in the solution of 66.8% NH NO 16.6% NH and 16.6% water. The results of these tests demonstrated that the coupons which were initially corrosive became inactive upon sodium carbonate contact and that no appreciable corrosion to their surfaces occurred. The results of the tests are given in Table II.

4 Table II [64 hours in 1% NBQOOS] Coupon No.

Inactive.

A comparison of Tables I and II demonstrates the ability of sodium carbonate solutions to deactivate ferrous metal surfaces consistently while other solutions such as sodium hydroxide are unable to deactivate consistently similar metal surfaces.

I claim:

1. A procem for inhibiting corrosion to ferrous metal surfaces caused by aqueous ammonia-ammonium nitrate solutions which consists essentially of contacting the ferrous metal surface with an aqueous solution of sodium carbonate to inhibit corrosion of said ferrous surface caused by aqueous ammonia-ammonium nitrate solutions, and contacting the ferrous metal surface with an aqueous ammonia-ammonium nitrate solution.

2. The process of claim 1 wherein the sodium carbonate solution contains about 0.5 to 5 percent sodium carbonate.

3. The process of claim 2 wherein the contact of the ferrous surface with sodium carbonate solution is for at least about 10 hours and the aqueous ammonia-ammonium nitrate solution contains about 40 to 80% ammonium nitrate and about 10 to 35% ammonia.

References Cited in the file of this patent UNITED STATES PATENTS 1,841,825 Kriegsheim Jan. 19, 1932 2,755,166 Marsh July 17, 1956 FOREIGN PATENTS 691,578 Great Britain May 13, 1953 OTHER REFERENCES NACE Technical Committee Reports, Corrosion, vol. 11, No. 4, April 1955, pp. 65-67.

Claims

1. A PROCESS FOR INHIBITING CORROSION TO FERROUS METAL SURFACES CAUSED BY AQUEOUS AMMONIA-AMMONIUM NITRATE SOLUTIONS WHICH CONSISTS ESSENTIALLY OF CONTACTING THE FERROUS METAL SURFACE WITH AN AQUEOUS SOLUTION OF SODIUM CARBONATE TO INHIBIT CORROSION OF SAID FERROUS SURFACE CAUSED BY AQUEOUS AMMONIA-AMMONIUM NITRATE SOLUTIONS, AND CONTACTING THE FERROUS METAL SURFACE WITH AN AQUEOUS AMMONIA-AMMONIUM NITRATE SOLUTION.