US2357275A - Corrosion inhibition coating composition - Google Patents

Description

Patented Aug. 29, 1944 CORROSION INHIBITION COATING COMPOSITION Aaron Wachter, San Francisco, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware N Drawing. Application July 22, 1941, Serial No. 403,533

Claims. (01. 44-72 The present invention relates to corrosion prevention coatings and more specifically to coatings for preventing corrosion of metal surfaces by the water often associated in small amounts with water-immisible liquids.

In the storage and handling of various waterimmiscible liquid materials, particularly hydrocarbons it is often necessary both to transport and/or to store such materials in metal containers, as in steel drums or tanks and thelike. Since these materials often contain varying amounts of water in solution or in suspension, which may separate clue to temperature changes for example, internal corrosion of the container by the water almost always occurs to a greater or lesser degree. This problem is particularly serious when gasoline is under consideration. In spite of all reasonable and practicable precautions during the manufacture of gasoline, when the same is stored in drums or tanks for a period, especially as is so often practiced in handling aviation gasoline, an appreciable amount of water separates and will be found as a film or in minute droplets on the container Walls or even in small pools in the bottom of thecontainer. This of course brings about ideal conditions for corrosion and consequent damage to the container as Well as the even more serious contamination of the gasoline or similar product stored within the container.

It is to be clearly understood that the corrosion inhibiting coating described below is intended for use only in those cases in which relatively small quantities of water come in contact with the surfaces to be protected, as distinguished from primarily aqueous systems, such as water tanks, etc.

. As a result of the above described corrosion, it has become necessary for manufacturers .and shippers of such products to apply various internal coatings to the walls of such containers or to add corrosion inhibitors of one type or another to the product being stored.

It is an object of the present invention to provide an improved internal coating for containers which are to be used as described above.. It is a further object of this invention to provide an internal coating which will both prevent corrosion and remove to a large extent any corrosion products already present in material which may be transferred to containers protected with the hereinafter described improved coating. Another object is to provide an internal container coating which will prevent contact between the container walls and the material stored therein, thus preventing corrosion of the container by materials which may be dissolved in the stored material, such as organic acids and sulfur compounds. Further objects are to supply a coating which is inexpensive, easily applied and removed, and

which does not contaminate in any way materials stored in containers protected by the same.

Broadly, the present improved coating oompr ises a hydrocarbon insoluble, water-soluble mucilaginous material, a plasticizer if necessary, and sodium nitrate. By mucilaginous material is meant those materials which either alone or in the presence of a suitable plasticizer provide a continuous, pliable film when applied in solution and the solvent removed therefrom. Most of the proteins and carbohydrates of animal and vegetable origin and products derived therefrom fall within the limits of this definition. For example, pure grades of the following types of compounds and mixtures of the same will be found suitable: proteins, albuminoids, glues, gelatins, phosphoproteins, caseins, sugars, starches, dextrins, gums and cellulose derivatives. More specifically, the following compounds are among those suitable as the mucilaginousbase material in the presently disclosed coating: corn starch (partially hydrolyzed) molasses, gum arabic, agar-agar, dextrin, pectin, barley sugar, caramel, xylan, wheat gluten and gum tragacanth.

As a specific example and in a preferred embodiment of the invention, the following composition has been found especially satisfactory:

Per cent by weight, approximately.

Dextrin 60 Glycerin 30 Inhibitor 10 identical tests were severely corroded and their contents so thoroughly contaminated as to be practically 'valueless without recovery treatment.

The coating is preferably applied'by spraying a quantity of the 40% solution into the container and drawing ofi any excess before drying, although other methods such as brush application in large storage tanks may be utilized if desired. In any .case, application conditions should be adjusted to provide at least approximatelyt milligrams of dehydrated coating per square inch of surface to be protected. A usually satisfactory coating is attained if from 1 to 2 fluid ounces of the 40% solution are sprayed into a 55 gallon drum, in a manner to cover all internal surfaces, the drum then being subjected to a temperature of about 250. F. for approximately 5 minutes.

This process may be easily included in the commonly employed drum cleaning treatment wherein dirty drums are washed with a hot alkaline solution, rinsed, steamed, dried and heated prior to painting the exterior surfaces. After the drums have been dried, the above described'coat- 1 ing may be applied and the drums passed on to the heating stage in the usual manner. The washing steps will remove all traces of a previous protective coating if such has been applied.

Although glycerin is the preferred plasticizer for use in the present coating, glycol and other hydrocarbon insoluble polyhydric alcohols, glycerinpolymers, amines, hydroxy amines, hydroxy 'ethers, and similar materials which have known plasticizing properties will also usually be found satisfactory.

The amounts of the various components of the coating may be varied within certain limits without deleterious effects. The formula given above, i. e. base, plasticizer and inhibitor in the approximate proportions of 60:30:10 has been found to be generally satisfactory for normal conditions of service and in fact includes an appreciable safety factor in the quantity of inhibitor incorporated. Sodium nitrite, for example, is known to be an efficient inhibitor at concentrations as low as .02%'; however, in view of the relatively small quantities actually used in employing the preferred formula (1.5 grams in a-55 gallon drum) and in order to obivate completely any danger of localized corrosion due to the possibility of a relatively large pool of water occurring in the container, it is considered preferable to employ a reasonable excess of inhibitor. The relative proportions of base and plasticizer used will of necessity vary with the specific materials utilized.

In the case where dextrin is used as a base and glycerin as a plasticizer, from approximately 40% to 85% dextrin, the balance being glycerin and inhibitor (from .02 to has been found satisfactory.

As has been mentioned above, the inhibitor coating is applied in solution, water being the preferred solvent. A solution containing 40% by portions noted:

Per cent by weight,

approximately Arrowroot starch Glycerin 85 Sodium nitr 10 In this formula, the quantity of starch may be varied from approximately .5% by weight to approximately 10% by weight. Notless .than approximately 60% by weight of glycerin should be used, however, or an unsatisfactory coating will result. This composition is preferably applied in an approximately solution in water.

Another coating which has been found suitable is formulated as follows:

Per cent by weight,

approximately Liquid glue (animal) 80 Glycerin g 10 Sodium nitri 10 amounts of water against corrosion comprising I from 40% to 85% by weight of dextrin, at least .02% by weight sodium nitrite and the balance a water-soluble polyhydric alcohol.

2. A water-soluble corrosion inhibiting coating composition suitable for protecting metal surfaces in contact with hydrocarbons containing small amounts of water against corrosion comprising approximately by weightof dextrin, approx,- imately 30% by weight of a water-soluble polyhydric alcohol and the balance sodium nitrite, said coating having a pH of at least 6 in water solution.

3. A water-soluble corrosion inhibiting coating composition suitable for protecting metal surfaces in contact with hydrocarbons containing small amounts of water against corrosion comprising about 5-80% by weight of a water-soluble hydrocarbon-insoluble mucilaginous base, about 1085% by weight of a water-soluble polyhydric alcohol, and about .02 to 10% by weight of sodium nitrite.

4. A water-soluble corrosion inhibiting coating composition suitable for protecting metal surfaces in contact with hydrocarbons containing small amounts of water against corrosion comprising about 51-80% by weight of a water-soluble hydrocarbon-insoluble mucilaginous base, about 10-85% by weight of a water-soluble polyhydric alcohol, and at least .02% by weight of sodium nitrite. .7

5. A water-soluble corrosion inhibiting coating composition suitable for protecting metal surfaces in contact with hydrocarbons containing small amounts of water against corrosion comprising from 40% to by weight of dextrin, at least .02% by weight of sodium nitrite and the balance glycerin.

AARON WACHTER.