Corrosion by Water (8) Harned, H. S.,and Hamer, W. J., J . Am. Chem. SOC.,55, 2194, (1933). (9)Hoxeng, R. B., Corrosion, 6, 308 (1950). (10) Hoxeng, R.B., and Prutton, C. F., Ibid,, 5,330 (1949). (11) McKay, R. J., and Worthington, Robert, “Corrosion Resistance of Metals and Alloys,” p. 164,New York, Reinhold Publishing Corp., 1936. (12) Schikorr, G.,Trans. Electrochem. Soc., 76,247 (1939). (13) Speller, F. N.,“Corrosion, Causes and Prevention,” 3rd ed., p. 168, New York, McGraw-Hill Book Co., 1951. (14) Tyrell, H.T.U., and Hollis, G. L., Trans. Faraday Soc., 45,411 (1949).
(15) Uhlig, H. H., ed., “Corrosion Handbook,” p. 41,New York, John Wiley & Sons, 1948. (16)Ibid., p. 129. (17)Ibid., p. 167. (18)Ibid., p. 334. (19)Uhlig, H.H., and Noss, 0. F., Jr., Covrosion, 6, 140 (1950). (20)Whitney, W. R., J. Am. Chem. Soc., 25,394 (1903). (21) Wormwell, F.,and Ison, H. C. K., Chemistry S Industry, 1951, 293. RECEIVED for review March 10, 1952.
ACCEPTED June 2, 1952.
Corrosion Control with Organic Inhibitors J. N. BRESTON Pennsylvania Grade Crude Oil Associafion, Bradford, Pa.
Inorganic inhibitors of corrosion by water are generally effective only under alkaline and oxidizing conditions. In the presence Of acid brines/ high temperatures, reducing conditions, and microbiological action they afford little or no protection. There are many large scale operations in which water is used or handled under such tions and ,,,here effective corrosion control is desirable or necessary. A solution to the problem has been found in organic compounds which, by virtue of their physical and chemical adsorption onto the corroding surface, will protect it from further corrosion. They form protecting films of molecular thickness and are effective in concentrations The paper Outlines the low as a few parts per mechanism, properties, and conditions of application of organic inhibitors, and indicates their application in acid cleaning solutions, cooling and refrigerating systems, steamgenerating systems, oil wells, and other petroleum production and handling systems.
NHIBITORS are commonly defined as substances which, when added in small amounts to the corrosive environment of a metal, will effectively decrease the corrosion rate. Where dissolved oxygen, salts, and weak acids comprise the corrosive environment inorganic inhibitors have been applied successfully to minimize corrosion of metals, particularly iron and steel. Examples of such inhibitors are soluble hydroxides, chromates, phosphates, silicates, and carbonates. However, where strong acids (dilute or concentrated), acid brines, high temperatures, and microbiological action are constituents of the corrosive environment, it has been found that polar organic compounds and colloidal organic materials are more effective corrosion inhibitors. It was observed years ago that raw feed waters containing appreciable amounts of natural organic substances were not corrosive to boilers and other equipment used in steam generation and utilization. Later observations led to theuse of potatoes, potato peelings, sugar, molasses, starch, dextrin, sugar beet, gelatin, sea weed, linseed, and various resins for the treatment of industrial waters. Some of them are still used today. French ( 9 4 ) and Fager (28) noted that waste sulfite liquors (lignin) and alkaline tannates (quebracho) have the property of combining with dissolved gases, particularly oxygen, and were effective inhibitors of corrosion and scale deposition. Hedges ( S I ) described the film-forming properties of colloids and reported their corrosion-retarding effects in acids. Ardagh ( 9 ) noted the inhibiting properties of certain organics in brine and Speller (&‘)
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August 1952
observed the protectiveeffectsof adsorbed organic matter in water. Levey (86)noted the higher inhibiting properties of crude quinaldine. De Whalley (67) reported that crude beet sugar had greater inhibiting properties than the refined sugar, Jimeno (33) observed the greater inhibiting efficiency of tannin over starch and Matthewi (40) noted the formation of protective colloidal tannin films and the formation of black iron tannates. The natural glucosides were introduced into industrial water treatment by Haering (28,29). He modified the glucosides to chrome glucosates to make them better corrosion inhibitors. The action of organic substances as inhibitors of corrosion by concentrated strong acids has been known for over 150 years. Imhoff (89) in his review of inhibitors points out the historical and technical development of pickling inhibitors. Many organic substances are effective inhibitors €or pickling acids and at least 200 of them can be found in the literature (39,63). It is difficult to classify them either chemically or physically. I n general they consist of a hydrocarbon part attached t o a polar or ionizable group, and may contain nitrogen, oxygen, sulfur, and other elements. The inhibitors may be truly soluble or colloidally dispersed. In recent years it was discovered that ethylenediamine and morpholine ( 1 9 )when injected into a steam system will materially reduce corrosion of condensate lines. Ammonia (60)and cyclohexylamine ( 2 1 ) have also been found effective and were used. Berk ( 4 ) reports comparative tests of cyclohexylamine, morpholine, and benzylamine and indicates that use of the amines gave more effective protection than reducing the carbon dioxide content of the steam down to 5 p.p.m. In order to reduce volatilization losses and increase protection against oxygen corrosion, a filming amine type of treatment was devised (58)which utilizes high molecular weight amines with straight hydrocarbon chains of 10 to 18 carbon atoms. More recently it has been discovered that polar organic compounds will effectively control corrosion in the petroleum production industry. In the past 5 years great, progress hab been made particularly in controlling corrosion in sour crude and gas-condensate wells. Analyses of the problem and suggested solutions are reported in recent articles by Copson ( I @ , Blair ( 6 ) , Bilhartz ( 5 ) , Case (16), and Shook and Sudbury (46). Except for a few simple substancee like formaldehyde and carbon disulfide, the useful inhibitors were found t o be relatively complex or high molecular weight polar compounds. One of the more novel developments in the petroleum producing industry has been the application of amine compounds to the treatment of oil field water for disposal or secondary recovery purposes ( 7 , 9,11, 80). The novel part of such treatment is that a single compound will inhibit microbiological activity as well as corrosion ( 7 , 11).
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Mechanism
The corrosion inhibiting action of organic substances has been investigated for many years. In general there is little disagreement that these substances function essentially by treating the metal surfaces. The method by which the inhibitor functions is usually explained in terms of an electrochemical system in which the energy decrease in the corrosion process is equated t o the sum of the energies dissipated in the various parts of the system (S5,56). The first step in the mechanism has almost always been described in terms of the adsorption of the inhibitor molecule from solution onto the metal surface. However, as pointed out by Hackerman and Schmidt (26) in their excellent review on the role of adsorption in corrosion inhibitor action, there is considerable diversion of opinion as to the mechanism whereby the adsorbed molecule inhibits corrosion. Several investigators (17, 34, S9, 46,61,66) believed the corrosion inhibition was due to adsorption of the positively charged inhibitor ions at the cathodic areas of the metal. It was postulated that the presence of the adsorbed film was instrumental in reducing the cathodic reaction of hydrogen evolution through changes in the cathode potential. It was further reasoned that the corrosion inhibition could also be due t o an increase in hydrogen overvoltage, the addition of electrical resistance to passage of current, or formation of a film barrier to protect the metal surface from the acidi? medium. I n recent years a considerable amount of evidence has been introduced by various workers (2, 16, 22, S4,37, 41 ), which points to the general adsorption of the inhibitor at both anodic and cathodic areas. This has gone far in clarifying the mechanism of organic compounds in retarding corrosion. Hackerman and Sudbury (26) measured the potentials of steel in water and sulfuric acid containing amine additives. Polarization studies indicated that both anodic and cathodic areas were affected by the amine inhibitor. Anodic area inhibition was believed t o be due t o the reduced tendency of the iron ions to dissolve as a result of the migration of electrons from the metal toward the positively charged absorbed inhibitor rather than toward cathodic areas within the metal. With all the evidence available it must be conceded that organic inhibitors are effective by virtue of their attachment to the metal surface The adherence, however, may be considered to be due to purely physical forces or to the relatively stronger chemical forces. It may be argued that there is no fundamental difference between the two types of bonds, but the fact remains that in practice it is possible to distinguish between chemisorp tion and physical adsorption from a knowledge of the heat of adsorption, the ease of reversibility, the temperature coefficients, and the rate of adsorption. There are numerous data and observations in the literature which make it appear that without a doubt chemisorption is a major factor in corrosion inhibition by polar organic molecules. However, in actual systems it is more probable that the metal is never entirely covered by chemisorbed molecules. I t is reasonable to assume that the “active spots” are so covered while most of the remainder of the surface is covered by inhibitor which is held by the weaker physical forces. As pointed out bv Hackerman and Schmidt (25), theories of adsorption have never required that total coverage be obtained on solid surfaces even when the latter is essentially saturated. In the case of relatively closely packed organic molecules, lateral forces between the hydrocarbon chains can function to provide additional protection. In systems containing hydrocarbons, nonpolar molecules can in fact be oriented and incorporated in the adsorbed film, thereby providing more complete coverage. This is illustrated by the increased effectiveness of certain amine inhibitors when used in the presence of added oil. Also, condensates containing comparatively large amounts of compounded oils from reciprocating engines are practically noncorrosive. Of
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equal importance is the fact that forces operating between neighboring physically adsorbed and chemisorbed molecules should reduce the tendency of the former to redissolve. Thus, more complete coverage is provided and more easily maintained. Properties
One property which is common to practically all organic inhibitors used for the protection of metals containing or contained in aqueous media is polarity. As pointed out previously, they generally consist of a part which is hydrophobic and an ionizable part which is hydrophilic. They should be soluble or readily dispersible in a medium which can wet the metal to be protected. At the same time they should be adsorbable onto the metal under the conditions in the system and the adsorbed layer should be uniform and give adequate coverage of the surface to be protected. However, the adsorbed layer should not build up so thick as to interfere with the proper functioning of the equipment being protected. The inhibitor of course should not be corrosive in itself or react chemically with any other metal or material of construction in the system. Also, it must not react with or be neutralized by any other substance in the fluid medium. To be effective, therefore, the inhibitor must be stable chemically and physically, particularly if used in a recycle system where long time of usage is a factor. Of necessity, if the inhibitor is to be used in potable water it should be nontoxic and not have an objectionable taste. From a practical viewpoint the most important property of an organic inhibitor is that it should be effective a t low concentrations. The fact that in general they are effective in concentrations of but a few parts per million distinguishes them from the bulk of inorganic corrosion inhibitors used in aqueous systems. Other properties can be mentioned, but they are mostly circumstantial to those just outlined. Conditions of Application
The successful use of inhibitors requires a considerable knowledge of their action and a thorough understanding of the corrosion process in the system to be protected. A substance which may reduce the corrosion rate in one environment may in another environment be ineffective or even stimulate corrosion. For example, certain surface active compounds are effective dilute acid corrosion inhibitors in an oxygen-free environment but will accelerate corrosion where dissolved oxygen is present. Oxygen usually acts as a stimulator of corrosion and greatly diminishes the effectiveness of organic inhibitors. However, a few applications have been found where they apparently will inhibit corrosion in the presence of dissolved oxygen. One example is the use of filming amines to reduce oxygen corrosion in steam-condensate return lines (58). With organic inhibitors the percentage protection geneially increases with an increase in the concentration of the inhibitor. However, the rate of increase continually falls off and the per cent protection either reaches a limiting value or approaches 100 asymptotically. In general, the concentration of inhibitor needed for protection depends on a number of factors, among which are composition of the environment, temperature, velocity of the liquid moving past the metal, composition of the metal, strain or stresses in the metal, and bimetallic contacts. In use only a certain percentage of protection is economically practical and the maximum concentration of inhibitor t o use will usually be determined thereby. Fortunately organic inhibitors are effective at very low concentrations, and 80 to 90% protection can be afforded in most cases. When used in nonrecirculating mediums such as fluids in transmission, it becomes an economic necessity to use an inhibitor which will be effective at very low concentrations. It has been adequately demonstrated (2, 3, 33, 59,46) that
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Corrosion by Water organic inhibitors are dependent on time for effective action, one reason for which is that the rate of film build-up is a function of time. Although it would be desirable t o have an instantaneously acting inhibitor, in practice it has often been found necessary to treat for days before effective corrosion control was achieved. The element of time, however, can usually be reduced by “dosing” a system a t the start of treatment with a concentration of inhibitor in excess of the equilibrium concentration necessary for the desired protection. Where slow decomposition of the inhibitor may take place, such as in acid wash solutions or steam generators, the inhibitor action may be expected t o become less efficient with time. In general, however, organic inhibitors are quite stable under the conditions of use and are effective indefinitely if the adsorbed film is kept intact and of the proper thickness. Continuous addition of inhibitor is necessary to replenish that lost from parts of the system and t o maintain the film thickness. Although organic inhibitors are generally applied to systems in which there is only one liquid, use of them is made in such systems as oil and water. Similarly, they can also be used in systems where the corroding medium is in the gas as well as liquid phase. Ammonia is often used in solutions t o inhibit corrosion in the closed vapor space above the solution. Similarly, amines are used in steam-generating systems to inhibit vapor phase as well as liquid phase corrosion. An interesting example of corrosion inhibition in an air space is the use of dicyclohexylammonium nitrite in packaging materials for metal objects to inhibit corrosion by moisture which is present or enters the package later. I n applications where there is a plurality of fluid phases, it becomes necessary t o select an inhibitor which will protect the metal from the corrosive agents in one or all of the phases without being removed by easy resolution in any one of them. Where the corroding medium is a brine it is necessary t o select an inhibitor which will not salt out and which will not form insoluble or slightly ionizable salts with the ions in the brine. For such reasons an inhibitor which is very effective in a fresh water can be useless or even harmful in a brine. I n general, organic inhibitors can be used in acid media, providing their strength or conditions of use will not chemically decompose or neutralize the inhibitor. Treatment for corrosion inhibition in basic media is not ordinarily practiced except in the case of nonferrous metals. For iron the resistance t o corrosion increases with basicity, except in very alkaline solutions-e.g., where the pH is above 13 or 13.5-in which certain ferrous alloys are severely corroded. Corrosion of aluminum by alkaline cleansers is a common problem which experimenters are trying to combat with organic inhibitors such as vegetable gums and resins. Ordinarily such corrosion is controlled by the use of various silicate compounds. Acid corrosion of nonferrous metals can be controlled with organic inhibitors but not as effectively as that of iron. Examples of 40 to 50% corrosion protection of copper and brass by organic inhibitors have been experienced (IO). Bimetallic systems in which it is very difficult to inhibit corrosion even with inorganic inhibitors have been shown t o be protected by organic inhibitors. Under the assumption that organic inhibitors can adsorb on anodic as well as cathodic areas, it is reasonable to expect such inhibitor action t o reduce corrosion a t bimetallic couples. Considerable evidence has been presented (WO,W7, 45,48,6g) t o show that microbiological action can cause corrosion or corrosive environments. This very interesting example of a cause of corrosion has only recently been analyzed satisfactorily. Serious pipe failures in deep wells and cold water transmission lines have been traced to the reducing action of anaerobic bacteria. The use of organic compounds, particularly formaldehyde, amines, and quaternary ammonium compounds, checks the growth of bacteria and thereby controls corrosion caused by such microbiological action. August 1952
The possible synergistic action of a combination of organic compounds t o improve corrosion inhibition has not been sufficiently explored. One interesting example is the use of wetting agents t o improve the efficiency of strong acid inhibitors (14). Another is the action of oil to improve the corrosion-inhibiting
UNINHIBITED POLYETHANOL ROSIN AMINE D
2
?W 0.50 Z W
n
0.20
0.10 0.05 165
175
185
2oQ
TEMPERATURE,°F.
Figure 1. Corrosion Rate Curves for Mild Steel Immersed in Inhibited and Uninhibited Hydrochloric Acid (72)
properties of amine compounds. N o doubt other examples will be found when the mechanism of corrosion control with organic inhibitors is better understood.
Applications One of the earliest applications of organic inhibitors has been in acid pickling of metals to remove mill scale in’ its preparation for galvanizing, tinning, enameling, plating, etc. Today it still finds its largest service in that capacity. Many organic substances are effective inhibitors for pickling acids and a t least 200 of them can be found in the literature (32, 65). Figure 1 illustrates corrosion rate curves for mild steel a t various temperatures when immersed in inhibited and uninhibited hydrochloric acid of 5, 10, and 15% concentrations. The solution rate of the metal is reduced by a factor of 50 t o 100 by the use of only 0.2% of an effective inhibitor. Analogous t o their use in pickling acids, organic inhibitors have found effective application in acid compounds used in cleaning boiler tubes, engine blocks and heads, heat exchangeis, condensers, water lines, and chemical processing equipment. They are also used in the hydrochloric acid employed t o treat oil-bearing zones of oil wells t o increase the permeability of the formation and thereby stimulate oil production. One interesting aspect of this application has been the improvement of the effectiveness of the inhibitor by incorporating a small amount of wetting agent (13). Figure 2 illustrates the weight loss of mild steel when exposed to inhibited hydrochloric acid with and without a wetting agent. Corrosion in cooling and refrigerating systems in air conditioning and humidification have been combated fairly effectively with inorganic inhibitors. However, cooling water by evaporation over towers and through spray ponds and the use of air washers subjects the water to repeated aeration. This results in a recurring contamination by oxygen, carbon dioxide, dust, and
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1.00
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I ,
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% HYDROCHLORIC ACID
Figure 2. Effectiveness of a Fatty Alcohol Sulfate in Improving the Acid Corrosion Inhibiting Action of Dibutylthiourea ( I 3)
bacteria; this condition is difficult to treat with inorganic inhibitors. Industries with such a problem have found a partial solution in film-forming and colloidal organic inhibitors. Such materials as waste sulfite liquors (lignin) and alkaline tannates (23, BQ), tannins and starch (33, do), and glucosates (28, d9j have been used and found effective. Organic inhibitors of this type have been found promising where the price is not prohibitive, especially in very hot waters (175" to 200' F.) (49). Materials such as sodium benzoate (66) have been found effective in preventing corrosion of metals in automobile radiators. Recently, instances have been found of secondary difficulties, such M excessive bacteria growth and delignification of wood parts, which have been attributed to the high pH carried with some inorganic inhibitors. Some success has been experienced in lowering the p H of such waters to the acid level and using organic inhibitors. Corrosion control in refrigerating brines is largely a matter of p H control and minimization of dissolved oxygen, since a neutral airfree brine is practically noncorrosive. Where pH and dissolved oxygen control is impractical, the glucosates have been claimed t o be effective corrosion inhibiting agents (29). One of the older applications of organic inhibitors has been in steam-generating systems. Corrosion in steam and condensate lines is a problem of major importance. Because of imperfect construction and operation of such systems and because of the prohibitive cost of' using corrosion-resistant materials for their construction, such forms of corrosion cannot be entirely prevented. In general they have been combated by treatment of the boiler feed water and improvements in design of condensers to minimize the entrainment of corrosive gases, mainly carbon dioxide and oxygen. Inhibitors which have been found to be effective are waste sulfite liquor (lignin) and alkaline tannatea (28, 24). Waste sulfite liquors are Figure 3. reported to be used extensively in locomotive
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boilers by a number of railroads (64). Glucosates ($8,$9) are also being used in boiler water treatment. Condensate return line corrosion has been a particularly difficult problem to combat. In recent years it has been discovered that oertain low molecular weight volatile amines when iniected into a steam system VTill materially reduce corrosion. They pass from the boiler with the steam and upon condensing neutralize the condensate. Upon being returned to the boiler they agsm vaporize and become available for recycling. Some compounds being used are ethylenediamine (19), morpholine (19) cyclohexylamine (81), and benzylamine ( 4 ) . One advantage of such treatment is that it may be used in conjunction with the conventional inorganic chemical treatment of the boiler feed water. Where copper and its alloys are used, such treatment must be employed with caution. The chief disadvantage of treatment with volatile amines is that they afford little or no protection againat oxygen corrosion. To correct this a very new type of treatment has been developed which utilizes high molecular weight amines with straight carbon chains of 10 to 18 carbon atoms. They function not by neutralizing the acidic constituents in the system but by forming a nonwettable film of moleculai thickness on the metal surface. The film acts as a barrier betneen the metal and the corrosive constituents in the condensate. Thus it is claimed that protection is afforded against oxygen as well as carbon dioxide corrosion. Commercial steam plant tests (39) have shown that up to 99% reduction in corrosion may he effected by filming amine treatment. One of the newer and most rapidly expanding applications of organic compounds for corrosion control is in the petroleum production industry. For years the producer of oil has been plagued with the destruction by corrosion of well casing and tubing, roda, pumps, strainers, well head equipment, flow lines, and other lease equipment such as tanks and separators. The cost of repairs and replacement is increased by losses from shutdown and damage to producing formations. The problem has been most noticeable in fields producing brine and hydrogen sulfide along with the oil but is not confined to such fields. Some so-called sweet-oil areas experience severe corrosion and a large percentage of gas and gas-condensate n ~ l l undergo s corrosive attarlr.
Corrosion Rate in Gas-Condensate Well before and during Treatment with Organic Inhibitor (6)
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Corrosion by Waterorganic inhibitors in combating oil field corrosion haa been widely demonstrated. Figure 3 illustrates the effectivenem of a semipolar, heterocyclic ring compound in combating corrosion in a deep gaa-oondensate well. Although &he data were d o u l a t e d from weight loss meaaurernenta of test coupons in the well head, they are believed to be related proportionately t o the degree of protection obtained at lower levels in the well. Water-soluble as well aa oil-aoluble organic compounds have been proved to be applicable according to a report on a corrosion survey of Kansas oil wells (16). In general, oil-soluble and water-dispersible compounds are more popular a t the present time and more widely applied. The use of organic inhibitors in the oilB I P 3 4 8 0 7 I) CQNC. OF INHlelTOR IN P.RM. producing industry has spread from oil and gas-condensate wells to sour gaa difrtribution Figure 4. Reduction in Corrosivity of a Fresh Flood Water When Treated systems, crude transmission and storage syswith Various Concentrations of an Organic Inhibitor ( 7 7 ) tems, and gaaoline plants. One of the more novel applications has been in the treatment of oil field water for disposal and secondary recovery purposes (7, 11, 30). Since the average pore diameters Tlw type of corrosion differs in several aspects from that genof some oil-producing sandstones are but a few microns, it ie erally observed in other industries. Attack takes place under imperative that the water be as free as possible of solid reducing or anaerobic conditions, usually two or three phases are material which could plug the sandstone and prevent the entry in contact with the metal, and the products of corrosion do not of flood water. Such possible plugging materials are the inform thick or highly adherent films. It baa been fairly well essoluble products of pipe corrosion and bacteria multiplicatablished that the attack originates from acidic constituents such tion. Both water-soluble and water-diepersibie amine comas hydrogen sulfide, carbon dioxide, and low molecular weight orpounds have been proved to be effective corrosion inhibitors ganie acids in the oil, brine, or gas. I t is abetted by high temfor flood water when used in concentrations as low aa 1 t o peratures, turbulence, and, t o some extent, by erosion and me10 p.p.m. Figure 4 illustrates the reduction in corrosivity of chanical abrasion. The complexity of the problem can be apa fresh flood water when treated with various concentrations of preciated by mentioning some of the variables involved, such aa the composition of the brine, the oil-water ratio, wetting power of rosin amine acetate. Some such inhibitors are applicable to brines as well as fresh the oil, pH, temperature and pressure, the flow velocity, and the waters, and although they are most effective in closed systems, formation of coatings such as paraffin or carbonates. I n the past they often give satisfactory protection in the presence of a few 5 years great progress has been made particularly in the applicaparts per million of dissolved oxygen. I t has been found that tion of organic corrosion inhibitors to sour crude and gas-condenwhen organic inhibitors are w e d it is not necessary to eliminate sate wells. Useful surveys of the problem aa well as suggested corrosion entirely since the residual corrosion is generally quite solutions are t o be found in recent articles (6,6,16,18,46). uniform. Pitting is eliminated even a t low inhibitor concentraThe earliest efforts a t combating such corrosion involved the tions, thus doing away with the most common cause of pipe failuse of inorganic alkaline reagents and the results were poor and ure. For petroleum recovery by water injection a slightly coreconomically unsound. Chromate8 were tried and found applirosive water with strict exclusion of oxygen is favored. Such wacable only where reducing conditions were not severe. The earliters are used with the thought that as long aa the water is in est use of organic inhibitors appeared in the application of soa atate such that the products of corrosion are kept in soludium cresylate, sodium phenolate, and similar alkali salts of weak tion, it is preferable t o submit t o slow internal corrosion organic bases. Results with these were poor and expensive. It rather than risk the precipitation of plugging material from a became apparent from these earlier experiences that a practical inhibitor must be effective at concentrations far below that rescaleforming water. quired for removal of the acidic corrodants and should be capable The novel part of such a treatment i s the fact that a single compound inhibits bacterial growth as well as corrosion. Plugging of acting in the presence of both oil and brine. Formaldehyde (4%')and carbon disulfide were found to be effective in systems of flood and disposal wells as a result of microbiological growths has turned out to be more serious than that by inorganic precipicontaining hydrogen sulfide and have found considerable commercial use. tates. A fortuitous discovery (7, 11) showed that many of the Except for these simple organic substances, the development of organic compounds applicable to corrosion control had considerinhibitors has led t o the use of relatively complex or high molecable bactericidal potencies even a t such low concentrations as 1 ular weight compounds. Most of them are characterized by a to 10 p.p.m. Figure 5 illustrates how 10 p,p.m. of rosin amine polar structure containing a large hydrocarbon radical and a acetate controlled the bacteria count of the flood water on a lease group containing elements such as oxygen, nitrogen, and sulfur. in the Bradford oil field. Examples of such substances are naphthenic acids, tannic acids, The control of bacteria in oil field waters may not be entirely crude coal tar bases, bone oil, Turkey Red oil, sulfonated fatty incidental to corrosion control. Two of the more oommonly acacids, aliphatic amines, cyclo aliphatic amines, quaternary amcepted causes of corrosion in the oil fields are acidic conditions monium salts, esters of polycarboxylic acids (high molecular caused by carbon dioxide and hydrogen sulfide. Both of these weight), ester alcohols, ether alcohols, heterocyclic ring comare products of bacterial action and multiplication. Although pounds, and pyrrolidine derivatives. The results obtained with bacteria are not indigenous t o oil-producing formations, sulfateeach of these compounds vary widely with the field, conditions, reducing bacteria have been found to abound in oil field waters in and method of application. However, the general utility of such surface equipment as well as down in water injection wells. It is
August 1952
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believed that the effectiveness of corrosion control by organic inhibitors may be due in part to bacteria control. Another source of serious corrosion in the petroleum industry is in products pipelines ( 1 , 44). Besides being destructive to the pipelines, such corrosion develops secondary problems such as the products of corrosion being abrasive in close clearance equipment. 10,000
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ROSIN AMINE D ACETATE
5000 -
TREATED FLOOD WATER I
Conclusions There is no doubt that organic inhibitors constitute a useful and important means for combating corrosion by water. 81though they are used t o great economic advantage in many industrial fields, much more widespread use of them could be made. Their application on a wider scale has possibly been delayed by a lack of Understanding of them and the mechanism by which they protect against corrosion. Compared to the enormous cost of corrosion destruction, relatively insignificant sum8 have been expended for the scientific study of corrosion. However, it is gratifying to see a number of national industries sponsoring the expansion of such research.
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Figure 5.
JUNE
JULY
AUG.
SEPT
OCT
NOV.
Bacteria Control in an Oil Field Flood Water with an Organic Inhibitor (8)
Water and dissolved oxygen are the main causes of such corrosion. Small amounts of water may wet only a limited portion of the pipe area, which then becomes a region of accelerated iron solution. Traces of oxygen carried by the oil accelerate such action. Inhibiting such corrosion has been accomplished with inorganic and organic inhibitors with about equal effectiveness. Organic inhibitors such as mercaptobenzothiazole, amine salts of naphthenic acids, and the alkali metal salts of esters of sulfosucchic acid have been found effective. It has been found ideal to use a compound which is soluble in oil, slightly soluble in water, and which \vi11 cause the metal t o be preferentially wet by oil. Inorganic inhibitors of corrosion for potable waters are available but their use is limited. Considerably more experimental work is needed in this field, particularly for hot water corrosion inhibition. The great damage that may be caused by a relatively small amount of corrosive hot water in the intricate piping system of a large building would warrant treatment a t a cost that would be prohibitive for a large municipal supply. Treatment with organics has not been attempted. The corrosion-inhibiting properties of the quaternary ammonium compounds have been noted where they have been used as germicides in swimming pool waters and in hospital and restaurant sterilizers. Toxicity and taste specifications may make it difficult to find an organic compound for corrosion inhibition in potable waters.
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(1) Am. Petroleum Inst. Proc., 24 (IV), 39-135 (1943). (2) Ardagh, G. E., Roome, R. M. B., and Owens, H. H., IND.ENG. CHEW,25,1116 (1933). (3) Armbruster, H. H., and Austin, J. B., J . Am. Chem. Soc., 61, 1117 (1939). (4) Berk, A. A,, Industry and Power (November 1947). (5) Bilhartr, H. L., Cormsion, 7, 256-64 (1951). (6) Blair, Jr., C. M., Ibid., 7, 189-95 (1951). (7) Breston, J. N., Oil Gas J . , 48, h-0. 16, 96-100, 123-7 (1949). (8) Ibid., 49, NO. 16, 159-66 (1950). (9) Breston, J. N., Producers Monthly. 10, No. 7, 19-22 (1946). (10) Breston, J. N., unpublished data, Pa. Grade Crude Oil Assoc. Lab., Bradford, Pa. (11) Breston, J. N., and Barton, K., Producers Monthly, 12, No. 1, 13-17 (1947). (12) Bried, E. A., and Winn, H. M., Corrosion, 7, 180-5 (1951). (13) Cardwell, P. H., and Eilers, L. H., IND.ENG.CHmr., 40, 1951-6 (1948). (14) Cardwell, P. H., and Eilers, L. H., Oil Gas J.,46, No. 8, 124 (1947). (15) Case, L. C., “Control of Sour Crude Corrosion in Kansas Production Operations,” paper presented at annual X.A.C.E. Meeting, New York, March 13-16, 1951. (16) Centnerawer, M., and Heller, W. J., J. Chim. Phys., 34, 217 (1937). (17) Chappell, E. L., Roetheli, B. E., and McCarthy, B. Y.,IND. ENG.CREM.,20,582 (1928). (18) Copson, H. R., Corrosion, 7, 123-7 (1951). (19) Cox, H. L., U. S. Patent 1,903,287 (1933). (20) Doig, K., and Wachter, A., Corrosion, 7, 212-24 (1951). (21) Dreyfue, M. E., Heating and Ventilating, 39,31-3 (June 1942). (22) Erbacher, O., 2. physik. Chem., A182, 243, 256 (1938); 2. Elektrochem., 44,594 (1938); 50,9 (1944). (23) Fager, E. P., and Reynolds, -4.H., IND.ENG.CHEM.,21, 357 (1929). (24) French, D. K., Ibid., 15,1239-43 (1923). (25) Hackerman, N., and Srhmidt, H. R., Corrosion, 5, 237-43 (1949). (26) Hackerman, N., and Sudbury, J. D., J . Electrochem. SOC.,97, 109 (1950). (27) Hadley, R. F., “The Corrosion Handbook,” H. H. Uhlig, ed., pp. 466-81, liew York, John Tiley & Sons, 1948. (28) Haering. D. W., IND. ENG.CHEM.,30, 1356-61 (1938). (29) Haering, D. W., “Organic Methods of Scale and Corrosion Control,” 5th ed., Chicago, D. W. Haering and Co., Inc., 1943. (30) Heck, E. T., Barton, J. X., and Howell, W. E., Producers Monthly, 13, No. 7, 27-34 (1949). (31) Hedges, E. S., “Protective Films on Metals,” pp. 33, 200, New York, D. Van Nostrand Co., 1933. (32) Imhoff, W. G., W i r e and W i r e Products, 21, Part I, Section A , 447-50, 478-82 (June 1946); Section B, 520-3, 542-6 (July 1946). (33) Jimeno, E. J., Grilfoll, I., and Morral, F. R., Trans. Electrochem. Soc., 69,105 (1936). (34) Lawrence, R. W,, and Wdton, J. H., J . Phys. Chem., 46, 609 (1942). (35) Leighou, R. B., and Warner, J. C., “Chemistry of Engineering Materials,” 4th ed., pp. 424-5, Xew York, McGraw-Hill Book Co., Inc., 1942. (36) Levey, H. A., Chem. Inds., 37. 124-6 (1935). (37) Machu, W., Trans. Electrochem. Soc., 72,333 (1937). (38) Maguire, J. J., Power & Works Engr., 54 (June 1950). ENG.CHEM.. (39) . . -Vann, C. A.. Lauer. B. E.. and Hulton. C. T.. IND. 28, 159, 1048 (1936); hlann, C. A.,’Trans. Electrochem. Soc., 69,115 (1936). (40) Matthews, F. J., “Boiler Feedwater Treatments,” p. 113, New York, Chemical Publishing Co., 1936.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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-Corrosion Mayne, J. E. O., J. Sor. Chem. I n d . (London),65,196 (1946). Menard, P. L., and Dunn, T. H., Petroleum Develop. and Technol., 165,26(1946). Olsen, E., and Szybalski, W Corrosion, 6,N o . 12,405-14(1950). Parker, I. M., Oil Gas. J.,45,No. 28,255-9 (1946). Rhodes, F. H.,and Kuhn, W. E., IND.ENG.CHEM.,21, 1066 (1929). Shock. D. A,. and Sudburv. - . J. D.. Petroleum Enar.. - . 23. N o . 8. 86B’(1951): Speller, F. N., “Corrosion, Causes and Prevention,” 2nd ed., pp. 186.360.New York. McGraw-Hill Book Co.. Inc.. 1935. laid., ’3rd ed., pp. 212-13, New York, McGraw-Hill Book Co., Inc., 1951.
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(49)Ibid., pp. 396,409. ( 5 0 ) Speller, F,N., Proc. Natl. Dist. Heating Assoc., 24,203 (1933). (51) Saeller. F. N.. and Chsppell, E. L., Chem. & Met. Eng., 34, 421 -(1927). (52) Uhlig, H. H., “The Corrosion Handbook,” pp. 480-1, New York, John Wiley & Sons, 1948. (53)Ibid., pp. 909-13. (54) U. S. Bur. Mines, Bull. 433, 68,71 (1941). (55) Vernon, W. H. J., J. SOC.Chem. Znd. (London),66,138 (1947). (56) Warner, J. C., Trans. Electrochem. SOC.,83,328 (1943). (67) Whalley, H. C. S. de, J. Soc. Chem. I n d . (London), 56, 569-70 (1937). ’
RECEIVED for review February 21, 1952.
ACCEPTED June 20, 1952.
Inhibito rs for Eliminati ng Gorrosion 0
in Steam and Condensate Lines R.
c.
ULMER AND J. W. WOOD
Power Chemicals Division, E. F. Drew 8, Co., h e . , New York, N. Y.
steam condensate, the followONTROL of corrosion Control of corrosion in steam condensate i s of vital iming are cited: W h i t m a n , in steam condensate portance to the power industry. In general, two types of Russel, and Altieri (11)noted systems is of vital imtreatments have been advocated to control corrosion: the corrosiveness of carbon portance to the power indusdioxide in solution and the introduction of alkaline substances to neutralize the acidity try. Not only does such corincreased aggressiveness of rosion damage the equipment and introduction of film-forming materials to coat the metal. systems containing both carwhich is attacked, but the Corrosion test data were obtained in 600-pound-perbon dioxide and oxygen. corrosion products are resquare-inch boiler condensate with representative maSkaperdas and Uhlig ( 16) and turned to the steam-generterials of both types. In general the type that neutralizes Uhlig (10)discuss most asa t i n g e q u i p m e n t . There pects of the subject, includacidity was found to give the best results. Raising the pH they promote formation of ing the anodic and cathodic deposits, e.g., magnetic iron to around 8.0 decreased the corrosion to an inappreciable reactions, the effect of pH oxide, and the development amount in the case of iron. Use of film-forming materials and oxygen content, and the of electrolytic corrosion cells. also decreased the corrosion rate but not to such a low effect of temperature. The Straub (17, 18) and Corey value as in the case of the neutralizing type. With both extensive studies of Collins (8),among others, citenumerand Henderson ( 7 ) present a types i t was found that the rate of corrosion increased at ous examples of boiler tube wealth of information confailure which can be traced to higher concentrations of dissolved oxygen. This also was cerning the quantitative redeposits f o r m e d i n t h i s true in the case of the controls. In the case of copper and lationships among pH, carbon fashion. brass both types gave good results. In selecting a treatdioxide and oxygen content, Considerable work hasbeen ment for a given case, the metals in the system and the flow rate, and rate of cordone on the general subject dissolved oxygen content of the steam should be considered. rosion. Of particular imporof steam and condensate cortance are their findings conrosion. Numerous corrective cerning- the effect of volume means have been proposed. flow rate, as distinguished from velocity and carbondioxide conThere is, however, no clear-cut understanding in industry regardtent, on the corrosion rate. They suggest (6) that corrosion rate of ing the applicability of such methods. I n fact, there is some steel is a function of the rate of delivery of carbon dioxide t o the concern about some of the modern recommendations as they zone of corrosion, according to the equation: may involve the use of ammonia or ammonia-base materials and in some cases a material is added to the steam that will actually R = 5.7W0.” cause a “deposit” in the system. With the need for supplying where R = corrosion rate, milligrams per square decimeter per answers to some of these questions an investigative program was day, and W = rate of delivery of carbon dioxide to specimen in started some years ago, the results of which are presented in this pounds per hour X 100,000 = carbon dioxide concentration in paper. parts per million x flow rate in pounds per hour X 0.1. The principal source of oxygen and carbon dioxide in condenBackground of Study sate has been shown to be the boiler feed water. The gases are expelled from solution in the boiler and pass into the steam lines, The generally accepted explanation for corrosion of piping and redissolving when the steam is condensed. Collins ( 4 ) and Mcrtuxiliary equipment in condensate return systems is acid attack Kinney, McGovern, Young, and Collins (13) have shown that on the metal by the carbonic acid which is formed when carbon when steam consumption of pressure equipment is high, very dioxide dissolves in the condensate. Dissolved oxygen, when great concentrations of noncondensable gases may accumulate in present, aggravates such corrosion appreciably, owing t o depolarthe vapor space; this leads to solution of excessive quantities in ization of cathodic areas on the metal surface. the condensate. Deaeration, alone or followed by chemical treatOf the many investigators who have contributed t o presment of the feedwater, is of great importance in reducing corent-day understanding of the mechanism of corrosion by
C
August 1952
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