P
There appear to be waters which are treated more effectively with the polyoxy chemicals and other iyaters are treated more effectively with the polyamide chemicals. I n general the polyoxy chemicals work well with low solid Jvaters and t,he polyamide chemicals work well with high solid waters. It has heen observed that ant,ifoani chemicals often function poorly with incompletely softened waters. I n many instances such antifoam chemicals are added as a finishing treatment. Both the polyoxy and polyamide antiloam clierriicals function well t o prevent foaming. HoiT-ever, in a number of instances the polyoxy chemicals have contribut,ed t o continuous spray carry-over. This is evident by t'he fact that even without blowdown a maximum boiler concentration is reached and that further steam generation merely results in the maintenance of this concentrat,ion. I n locomotives, continuous spray carry-over results in the eventual plugging of super heater units, t,lie sticking of front. end t,hrottles, and excessive cylinder viear. I n one instance a locomot,ive mas equipped with sight glasses arid intei,ior illumination of the boiler. Observers noted that a fog or aerosol formed above the surface of boiler water during t,he operation of the locomotive. Thiq fog was part~icularlysevere during the time that water was injected into the boiler.
high quality feed a a t e r is not readily available, and by allowing greater concentration variations over Tvhich steam generation may be carried out without danger of foaming.
Discuss ion When oil is the foaming agent, especially oil with a tallow additive, what effect do you get from antifoams? W. L. DENMAN: The antifoam chemicals described previously will stop boiler water foaming in t,he presence of oil and fatty acid soaps such as you get from tallow. I n fact it is the usual thing to find antifoam chemicals functioning satisfactorily in the presence of oil and fatty acid soaps. How are the antifoam agents affected by different types of organics in general use, such as algins, tannins, and lignins? W. L. DENMAN : Antifoam chemicals in some cases are very markedly affected by such organic additives, and in other cases they are not affected nearly as much. Antifoam chemicals in the prrsence of such organic mat,erials hare a greater effect in decreasing the number of nuclei from u-hich the steam bubbles form arid increasing the tendency of steam bubbles to coalesce than when such organic materials are not present'. The increased effectirenrss impart,ed to boiler water antifoam chemicals by suitable organic materials is due to synergism. Are polyamides derived from adipic and other dibasic acids and diamines highly polymeric, or are the molecular sizes limited by the ratio of the reactants? W. L. DENMAN : The polyamides obtained are regulat'ed by the ratio of the react,ants. Are there any objections to the use of silicone oils as antifoam agents? W. L. DENMAN: One objection of course is the cost. If cone oils were satisfartory boiler water antifoams, and many SI icone oils are not, they would have to be very effective to be usable a t a cost of $3 or 54 a pound. h h o , silicone oils ?onceivably might decompose in the boiler water to give rise to a certain amount of silica. However, if t,hat'did occur, the amount would be very small.
SYXERGISM I Y .4STIFO inIS
In the earliest application of castor oil, the castor oil was soniet.imes blended with organic inatel ials such as tannin or st,arch. Such combinations of arit,ifoani clieniicals with relatively inert organic materials is widely pract'iced today. I n general, the antifoam activity of antifoam chemicals is markedly aided by thc presence of a number of organic materials, among which are tannins, lignins. modified lignins. and humates. Such effects the presence of such are difficult, to predict, and in some ca additives will be much more effective than in other cases. I n summary, modern boiler water ant,ifoarn chemicals are a great improvement over the early ones and have been a great help in reducing the cod of steam generation by permitting the carrying of considerably higher dissolved solids in the boiler water, by permitting satisfactory steam generation in those cases where
After Boiler Corrosion J. J. RIAGUIRE K ' . H . & L. D. Betz, Philadelphia, Pa.
KTIL a few years ago, in any evaluation of steam and con- -;but is usually exeeded by the labor cost involved. S o t only are line replacements necessary because of corrosive failure, but densate characteristics, the primary concern was the solids content as an indication of possible carry-over of boiler water salt?. I replacements may be required because of plugging of lines with corrosion products originating in other parts of the system. Today, we are awaie that the possible corrosive characteristics of Boiler tuibining or acid washing may be requiied because of iron steam are of equal importance to its solids content. It is not oxide deposits resulting from corrosion in the condensate system. sufficient that steam be free of boiler water solids--modern steam using equipment demands steam that is also noncorrosive. CAUSES OF CORROSION Corrosion of steam and condensate return lines, and of steam using equipment, is a problem of major importance to indudrial The chief cause for corrosive steam and condensate charactwplants. Frequent replacements of lines, valves, and traps can iatics ia the presence of oxygen and carbon diovide in the steam. be cawed bv corrosive gases present in the steam. The replaceWhere corrosion is due to oxygen, it will be shown by tuberculation and pitting of ferrous metals. Carbon dioxide attack is ment cost of the corroded equipment itself may be considerable
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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Val. 46, No. 5
Boiler Water Chemistry shown by thinning and grooving of the metal, nith failure occurring most rapidly a t threaded connections. Figure 1 illustrates two sections of condensate piping. The section on the left shows characteristic carbon dioxide attack with thinning of the pipe wall and failure of the threads. The one on the right shows thinning of the wall, but pitting is also evident indicating the corrosion to have been due to a combination of oxygen and carbon dioxide.
ALKALIES AND POLYPHOSPHATES
Probably the earliest treatment employed for control of carbon dioxide corrosion was the feeding to the steam of a water solution of an alkali, such as sodium hydroxide. The purpose of this treatment was to neutralize carbon dioxide and to increase the pH of the condensate. Polyphosphates were used also in an attempt to inhibit corrosion by formation of an iron-phosphate film. Indifferent success was obtained with both alkalies and polyphosphates. Because of difficulties in dispersing such inorganic solids in the steam and because, similar to carry-over, inorganic solids in the steam are undesirable, alkalies and polyphosphates are employed only infrequently today. AMMONIA
Figure 1.
Corrosion of Condensate Piping
Pipe a t left shows characteristic carbon dioxide attack with wall thinning and thread failure; right view shows corrosion due to combination of oxygen and carbon dioxide with wall thinning plus pitting
Ammonia has been used for quite some time to neutralize carbon dioxide and increase the pH of condensate. Ammonium hydroxide or ammonium sulfate may be fed to a boiler feed water with resultant liberation of ammonia with the steam. This method has been employed successfully to control corrosion and iron pickup in central stations with low percentage make-up and low carbon dioxide concentrations in the steam. However, copper and zinc bearing metals can be seriously corroded where there is opportunity for ammonia to concentrate and particularly where oxygen is also present. I n industrial plants where the carbon dioxide content of the steam averages many times greater than in central stations, with consequent higher ammonia requirements, the problem of copper attack limits the application of ammonia. NEUTRALIZING AMINES
The neutralizing amines in common use are cyclohexylamine The presence of oxygen in steam and condensate can result from the oxygen content of the make-up water. The remedy for this condition is deaeration of the boiler feed water and the use of sodium sulfite. In most plants, these measures satisfactorily prevent the presence of oxygen in the steam leaving the boilers. Of course, additional sources of oxygen which cannot be controlled in this manner are air drawn into the condensate system by leaks, the breathing action of return tanks, the use of vacuum pumps, and the use of cooling water on vacuum pumps. Single pipe heating systems also introduce oxygen into the condensate. Carbon dioxide is the chief cause of return line corrosion in modern industrial plants. The source of carbon dioxide is primarily the bicarbonate and carbonate alkalinity of the boiler feed water. Under boiler conditions, decomposition of bicarbonate and carbonate takes place with liberation of carbon dioxide with the steam. External methods of treating boiler feed water to minimize the carbon dioxide content of the steam all involve reduction of feed water alkalinity. The lime-soda or lime-gypsum softening processes will reduce alkalinity to the range of 50 to 60 p.p.m., principally in carbonate form. The use of the hot lime-hot ion exchange process permits a further decrease in alkalinity of the softener effluent. Acid treatment of zeolite effluents may be employed to reduce allcalinity to the range of 10 to 20 p.p.m. Similar results are obtained with combination hydrogensodium zeolite softening. The newest development in this field is the use of chloride regenerated resins which exchange chloride for alkalinity in the softener effluent. Even with appropriate external treatment to minimize carbon dioxide in the steam, serious corrosion can still result at points of condensation and in condensirag equipment where carbon dioxide can concentrate. In addition, many plants must operate with appreciable carbon dioxide in the steam due to lack of adequate external treatment facilities. The internal treatment measures that can be employed to control carbon dioxide corrosion include the addition of alkalies and polyphosphates to the steam, ammonia, neutralizing amines, and filming amines. May 1954
(CsHIIKH2)and morpholine (C4H&0). When fed to a boiler feed water, these amines volatilize with the steam and neutralize the acidity due to carbon dioxide. The neutralizing amines, in the quantities usually required, are not corrosive to copper bearing metals. By feeding sufficient amine to adjust the condensate pH to approximately 7.0, satisfactory control of carbon dioxide corrosion is obtained. The disadvantages of the neutralizing amines lie in their relatively high cost per part of carbon dioxide neutralized and also in the lack of protection against oxygen attack. A new use for the neutralizing amines is in the prevention of acidic corrosion a t the point of initial condensation in large central station turbines. Morpholine, because of its low distribution ratio in the steam-water mixture a t this point, maintains an alkaline pH in the condensed steam and provides better control of the corrosion problem than is possible with the use of ammonia. Where the carbon dioxide content of the steam is relatively low, the neutralizing amines will usually provide the most economical control method. At higher carbon dioxide concentrations, the filming amines provide more economical treatment. In central station operations, therefore, the neutralizing amines are usually employed. In industrial plants, with higher concentration of carbon dioxide, the filming amines usually provide more economical control of this problem. FILMING AMINES
The newest principle in the prevention of return line corrosion is based on the deposition of a film of long chain polar amines on the metal surfaces. The filming amines do not neutralize carbon dioxide. Instead, they function by forming on the metal surfaces a nonwettable film that acts as a barrier between the metal and the condensate, protecting against both oxygen and carbon dioxide attack. When the filming amines are adsorbed on a metal surface, water will not wet that surface. The film formed by these amines is of substantially monomolecular thickness and does not increase in thickness with continued treatment.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
995
Figure 2 shows two steel specimens 011 the left and two brass specimens on the right aft'er 30 days exposure in a plant condensate system treated with filming amines. The water repellency of the specimens is shown by the spherical form assumed by the drops of r a t e r .
centration variw in each individual case. However, t'he percentage reduction in corrosion is an accurat,evalue since the test specimens were exposed at the same point in the system and under the same operating condit,ions, both hefore and after the application of the filming amine. A small industrial plant producing 300,000 pounds of steam daily showed a yearly reduction of $8000 maintenance costs upon application of filming amiues. =Z plant generating 5,000,000 pounds of steam daily showed an amiual mluction in return line maintenance of approsi1n:ttely $40,000. CONCLU SI os
LIaintenance data from many plants have confirmed t'he reduction in corrosion rates shon-n in Table I. Additional case historie3 are in the literature showing practical evidence that the use of various treatment' measures to control carbon dioxide rorrosionwhether these meaaures are external or internal--can result it\ considerable savings in maintenance costs. Usually thc coyt of treatment is only a fraction of the savings secured. Prevention of corrosion of steam and condensate lines is :in integral part of a complete feed water conditioning program. The steam produced from the boilers must not only be low in solids content, but it should ~ 1 . tie ~ 0noncorrosive.
The filming amines possessing value in the cont,rol 01 return line corrosion are those with straight carbon chains containing 10 to 18 carbon atoms. Oct,adecylainine (C~SH~;?JI,) is the amine employed in plant practice and is usually processed anti emulsified so that dispersion and feeding from water solution is possible. The point of appliuation may be a t the Eeed water pump or to the steam line a t a poirit where the amine will be rye11 mixed witlh the steam. Piotrtction of saturated st'eain lines, as mell as condensate lines, is ohtained. Toxicit,y investigations have shown no ill eff'ect from octadecylamine a t many times treatment concentrations. Tests have sliown no undesirable dermal effects. The filming amines 1i:ivc. heen approved for limited use in live steam cooking of food. Table I illustrates condensed data secured in typical plants by exposure of test specimens before and after the use of filming amines. As can tie notred, the carbon dioxide content of the st'eam ranges from 4 to 160 p.p.m. The corrosion rate ehonn by tlie test specimens is not directly proport'ional to the carbon dioxide content of the steiini in each plant. Flow rate past. tlie test specimen installation, temperatmure,and oxygen con-
4 5
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18 23 25 28
45 49 57 62 75 80 100 103 112 156 160
996
228 400
600 250 336 600 400
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.Discuss What are the differences between the effectiveness of filming versus neutralizing amines? J. J. MAGUIRE: Both will do a good job. The problem of carbon dioxide corrosion can be solved adequately by eithrr material and the treatment for a particular plant should t w selected on the basis of costs and ease of handling. To date, what is the maximum steam pressure at which filming amine (octadecylamine) has been effective in preventing after boiler corrosion? Are there temperature limitations for such treatment? J. J. MAGUIRE: The filming amine treatment has h e m applied successfully a t 650 pounds per square inch. I do not want. to imply that it has failed above 650 pounds per square inch We have not applied it a t higher pressures. A plant that operates a t higher pressures is generally provided with adequatr external feed water treatment facilit,ies so that it has a minimum carbon dioxide problem. As to tempemture limitations 011 octadecylamine, we have not observed any. What specific amines are now used for this treatment? J. J. MAGUIRE : Research worlcers have reported optimum and t,his malaboratory results with octadecylamine (C18Ha71iH2) terial is the only filming amine in commercial m e , SO far a8 I know. How would filming amines behave at the dew point in turbines? J. J. MAGUIRE: V'hen a filming amine is present in steam, the nonwettable film will be deposited wherever condensate is deposited. W e have fed filming amines directly to the steam entering a turbine in vhich corrosion had begun to be a seriow problem and quite satisfactory results were observed. It war also rioted that the amine did not huild up in the turhine to Corm serious deposits. Would either filming or neutralizing amine be considered practical to protect a steam main approximately 2000 feet long and carrying 175 pounds per square inch saturated steam against corrosion resulting from normal condensation from steam with a carbon dioxide content of 10 to 15 p.p.m.? J. J. MAGUIRE: l-es. Except that the temperature in the, steam main is somewhat higher, the problem ia no different from that in oondeiisat,e piping which is protected by surli treatmeril.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 46, No. 5
Boiler Water Chemistry In fact, some plants that have no return condensate now use amines to protect saturated steam lines. What can be done to prevent condensate corrosion where government regulations prevent the use of amine treatments in effective amounts when the steam is used for live-steam cooking of food products?
J. J. MAGUIRE: Practically all government operated heating plants are now permitted to protect return lines against corrosion with any one of the amine treatments. Usually, permission to apply such treatment must be obtained in advance from central (Washington) or a divisional headquarters. The permissible concentrations are adequate for preventing corrosion.
Joint Research Committee on Boiler Feed Water Studies EVERETT P. PARTRIDGE Hall Laboratories, Pittsburgh, Pa.
The committee, cooperatively sponsored by six technical societies, encourages investigation and research on the problems connected with the use of water in steam power plants.
T
HE Joint Research Committee on Boiler Feed Water Studies is made up of a group of individuals particularly concerned with the problems resulting from the use of water in steam power plants. Because these problems can be grouped in three categories, there are three subcommittees whose special provinces are, respectively, corrosion, deposits, and steam contamination. To an unusual extent, the committee cuts across technical society lines. A a official sponsors it has six technical organiaations--American Boiler Manufacturers’ Association and affiliated industries, American Railway Engineering Association, American Society for Testing hfaterials, American Society of Mechariiral Engineers, American Water Works Association, and Edison Electric Institute. Each of these organizations names two representatives to the executive committee, which also comprises the current officers and the past chairman and secretary. A committee on technical papers is headed by the first vice chairman, currently R. C. Adams of the U. s. Saval Engineering Experiment Station. Plans for the procurement of research funds are supervised by the second vice chairman, P. B. Place of Combustion Engineering-Superheater, Inc. The executive committee has recently set up a finance committee to sell to industry the value of the research projects outlined by the technical subcommittees. The committee determines areas in its special field where basic facts are least adequate and elicits cooperative efforts to provide these missing facts. One past achievement of which the committee is particularly proud is the research project relating to the embrittlement of boiler steel conducted in cooperation with the Bureau of Mines.
The project started with the limited objective of measuring solubility equilibria so that it could be determined when a concentrating boiler water would deposit sodium sulfate in the capillary spaces of a riveted seam in a boiler. This project proved unusually fruitful, as a result of the energy and imagination of the investigators, W. C. Schroeder and A. A. Berk, and from it came not only a great deal of fundamental information, but also two developments of great practical value. These are the embrittlement detector, a mechanical device for determining whether or not the water in a specific operating boiler is capable of producing embrittlement, and the evidence that sodium nitrate is a particularly effective inhibitor of the intergranular attack which causes failure of the steel. Currently, the campaign is just starting to procure funds for a study of the interaction of water and steel a t high temperatures and pressures, for an investigation of the formation of iron oxide on turbine valves, and for other projects not yet specifically recommended by the technical subcommittees. I n addition to its function of sponsoring research, the Joint Research Committee on Boiler Feed Water Studies attempts to disseminate technical information. It has cooperated during the past year with the Water Conference of the Engineers’ Society of Western Pennsylvania, the American Society of Mechanical Engineers, the American Power Conference, and the AMERICAN CHEXICAL SOCIETY. Reprints of a recent symposium on steam contamination have been made available in composite form through the headquarters of the American Society of Mechanical Engineers. An extensive bibliography on steam contamination is now being published and will be available a t cost through the same source.
End of Symposium Reprints of this symposium may be purchased for 75 cents each (special price on bulk orders) from the Reprint Department, AMERICAN CHEMIC4L SOCIETY, 1155 Sixteenth St., N.W., Washington 6, D. C. May 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
997
