Acknowledgments
The authors gratefully acknowledge the help given this work b y C. B. Belt, Jr., Department of Geology, St. Louis University, who arranged for use of the X-ray equipment and counseled us in the use of the machine and interpretation of the data. Literature Cited
Buckland, B. O., Ind. Eng. Chem., 46, 2163 (1954). Buckland, B. O., ASME Paper 58-GTP-17, 1968. Buckland, B. O., Gardiner, C. >I Sanders, ., D. G., ASME Paper A-52-161, 1952. Cunningham, G. \V., Brasunas, A . de S., Corrosion, 12, 35 (1956). DeCrescente. 31.A.. Bornstein. N . S..ibid.. 24. 129 11968). Elshout, A . J., J l i l f . ’ V e r . Grosskesselbklr., 49, lk2 (li69). ’ Foster, A4.l)., J . Eng. Power, 81,235 (1959). Foster, W. lt., Leipold, 11. H., Shevlin, F. S., Corrosion, 12, 23 114.?A) \ _ - ,-,.
Ginsheig, A. S., %. Anorg. Allg. Chcm., 61, 122 (1909). Greeneit, It‘. J., Corrosion, 18, 57t (1962a). Greenert, W.J., ibzd., 18,9 l t (1962b). Illarionov, V. V., Ozerov, It. P., Kil’disheva, E. V., Zh. Seorg. Khirn., 2, 883 (1957).
Kohlmuller, R., Perraud, J., Bull. SOC.Chim. Fr., 642 (1964). Lewis, A., Paper No. 2, Sec. VI/D, Fourth World Petroleum Congress, Rome, 1965. Lucas, G., Weedle, X, Preece, A., Iron Steel (London), 28, 264 (1955). Matveevicheva, V. A., Eehkova, Z. I., Zaitsev, B. E., Lyubarskii, Russ. J . Phys. Chem., 43, 143 (1969). May, W. R., Zetlmeisl, ?VI.J., Bsharah, L., Annand, R. R., Ind. Eng. Chem., Prod. Res. Develop., 11, 438 (1972). May, W. R., Zetlmeisl, M. J., Bsharah, L., Annand, It.It., zbid., 12, 145 (1973). Nakao, K., Herai, H., Omair, T., Combustion, 39, 23 (1968). Xiles, W. D., Sanders, H. R., J . Eng. Power,84, 178 (1962). Niles, W. D., Siegmund, C. W., “The Mechanism of Corrosion by Fuel Impurities,” p 332, H. It. Johnson and D. J. Littler, Ed., Butterworths, London, 1963. Pollard, A. J., NItL Report 6038, U. S. Xaval Research Laboratory, Feb 14, 1964. Sachs, K., Metallurgia, 77, 123 (1968). Slobodin, B. U., Fotiev, A. A,, J . A p p l . Chem. L7SSR, 38, 799 (1965). Speranskaya, E. I , Znorg. Xater. ( U S S R ) ,7, 1611 (1971). Wollast, It., Tazairt, A,, Szlrcates Ind., 34, 37 (1969). RECEIVED for review November 3, 1972 ACCLPTLUFebruary 5, 1973
High-Temperature Corrosion in Gas Turbines and Steam Boilers by Fuel Impurities. 111. Evaluation of Magnesium as a Corrosion Inhibitor Walter R. May,* Michael J. Zetlmeisl, and lewis Bsharah Corporate Research Laboratories, Petrolite Corp., St. Louis, M o . 63119
Robert R. Annand Tretolite Division, Petrolite Corp., St. Louis, Mo. 6311.9
The corrosion rates for Udimet 500 in a variety of sodium sulfate-magnesium sulfate-vanadium pentoxide slag compositions were measured electrochemically at temperatures varying from 800 to 950”.The weight ratios of the elemenis, sodium to vanadium and magnesium to vanadium, were defined for acceptable corrosion rates. The effects of sodium level and temperature are discussed. A simple rationale for the effectiveness of magnesium as a corrosion inhibitor i s presented.
I n the previous papers in t’hisseries (May, el al., 1972, 1973), tlie high-temperature corrosion problems encountered in gas turbines aiid steam boilers caused by sodium and vanadium iii tlie fuel were delineated. Crude oil usually contains 1-500 ppm of vanadium in the form of a porpliyriii complex (Dicksoii aiid Petrakis, 1970; Sacks, 1954) de1)eiidiiig 011 the source. Because of its origin as a colicelitrate from the refining process, residual oil contains several times more vanadium than the crude from wliich it \\-as derived. The conibustioii of these vanadium-coiitaiiiing fuels lirocluces very corrosive T r z 0 5 deposits which can destroy :I turbine p u t in a matter of days. Although the vaiiadium ~ 1 1 he 1 i~enioved,tlie cost’ of tlie l’rocess caiicels the economic :idvarit:ige of using iuirefinetl fuels. T’aiiadic corrosion is, therefore, usua!ly controlled with chemical additives and optimization of operating conditions.
Sodium is almost always present in lowquality fuels, eitlier directly in the crude oil or indirectly though contamiiiation from various sources. The technology for removing sodium is well developed (Waterman and hloechel, 1957 ; Stenzel, 1957; Petrolite Corp., 1968; Greenlee arid Lucas, 1972). These are limiting processes, however, and a trace of sodium must always be dealt with. For example, in maritime use the sodium level can be increased because of the introduction of sodium chloride through the air intake and coiitamiiiatiou of the fuel by sea water. During combustion, the sodium reacts with the sulfur in the fuel to form the sulfate which is deposited in turbine parts. This reaction has been shomi to be thermodynamically favored and results in the only sodium compound that will deposit under these conditioiis (DeCrescente aiid Bornstein, 1968). The mechanism of corrosion by vanadium and sodium Ind. Eng. Chem. Prod. Res. Deveiop., Vol. 12, No. 2, 1973
145
Table I. Corrosion Rate for Udimet 500 in Various NasSOa-MgSOa-Vz05 Compositions from 800 to 950" VZ06
34.056 20.714 14,884 11.614 9,523 5.010 2,572 1,730 1.303 0,951 29.918 19.106 14,035 11.09 9.168 4.911 2.546 1.719 1.297 1.042 4.094 2.307 1.606 1.23 0.999 0.514 0.261 0,175 0,425 0,236 0.163 0.125 0.101 0.0427 0.0236 0.0163 0.01 0.0101 0.50 1.00 5.00 10 25 33.3 50 75 90 100 0
64.408 78.352 84.445 87.862 90.050 94,763 97.311 98.191 98.637 99.005 56,581 72.271 79,631 83.90 86,694 92.875 96.306 97,507 98.118 98,488 77.429 87.279 91.144 93.21 94.495 97,170 98.565 99.038 80.39 89.13 92.48 94.25 95.35 80.700 89.319 92.617 94.36 95.435 99.50 99.00 95.00 90 75 66.7 50 25 10 0 90 80 70 60
1.535 0.934 0.671 0.524 0.429 0.226 0.116 0.0781 0.0588 0.0430 13.502 8.623 8.334 5.01 4.137 2.214 1.148 0.775 0.585 0.470 18,477 10.413 7.250 5.56 4,506 2.317 1,175 0.787 19.18 10,63 7.36 5.62 4.55 19.257 10.657 7.367 5.63 4.555 0.00
MgIV
W t ratio Na/V
10 20 30 40 50 100 200 300 400 500 1 2 3 4 5 10 20 30 40 50 1 2 3 4 5 10 20 30 1 2 3 4 5 1 2 3 4
5
0.00 0.00 0 0 0 0 0 0 0
10 2.45 20 0.95 30 0.56 40 0.36 90 0 10 0 80 20 0 0 75 0 25 0 66.7 33.3 0 0 50 50 0 0 14.3 0 85.7 0 0 0 100 Slag washability: good, washed in less than 1 hr;
0 0 0
10 10 10 10 10 10 10 10 10 10 1 1 1 1 1 1 1
-.
BOO0
950'
0.533 0.941 1.76 2.98 1.09 1.38 1.45 0,571 0.835 1.78 1.11 3.23 2.12 1.34 0.768 1,lO 2.37 1.83 0.341 0.675 0.578 0.117 0.247 0.167 0.184 0.149 0,0760 0.0257 0.102 0.0361 14.0 24.7 26.1 25.8 29.6 29.6 2.48 3.12 4.87 5.22 4.62 3.67 9.70 3,67 3.67 1.54 0.314 0.536 0.154 0.400 0,092 1 0.0985 0.138 0.0833 1 0.0219 0.0820 0.0165 1 0.0258 0.0185 0.048 0.1 3.48 3.20 1.74 0.785 0.1 1.58 1.58 1.45 0.1 2.57 1.80 0.379 1.35 0.1 0,230 0,258 0.1 0,387 0.371 1.03 0.491 0.392 0.1 0.123 0.1 0.151 0,0943 0.043 0.1 0.035 0.033 0.01 0.714 0,349 0.261 0.324 0.01 0.531 0.189 0.0710 0.0432 0.01 0,0674 0.01 0.0319 0.0172 0.0680 0.00950 0.01 0,00640 0.00665 5.31 3.22 0.001 1.81 0.001 0.152 0,0136 0,0136 0.111 0,0418 0,0275 0.001 0.001 0.0536 0.0276 0,0161 0.0289 0.0289 0.0144 0.001 0.0169 0.0169 0.0190 0,277 0.196 0.162 2.09 1.05 0.755 3.70 1.99 1.71 2.30 1.39 1.01 0.552 4.28 2.51 1.76 1 .OB 5.43 3.62 2.59 1.56 4.43 4.43 1.95 1.39 2.18 0.957 0.567 0.794 0.542 1.66 0.361 0.101 0.194 0 0.0607 0.0382 0.932 6.95 0 0.835 0.557 0.727 0.388 0 0.483 0,340 0 44.8 89.8 25.8 22.7 22.7 4.06 20.0 25.0 34.3 1.81 40.1 28.6 30.9 23.8 28.9 40.7 1.35 50.8 47.3 0.90 66.2 36.4 38.1 95.7 73.5 89.8 0.45 81.8 123 0,075 94.8 107 65.8 32.2 79.3 191 59.3 fair, washed after several hours of soaking; poor, did not wash.
has received much attention. Nascent oxygen species has been proposed as the coriosive active agent in Vz06 melts (Paiitoiiy and Vasu, 1968a,b,c,). Various mechanisms have been presented to explain corrosive attack by sodium sulfate a t metal surfaces (Simoiis, et al., 1955, Se) bolt aiid Beltran, 146 Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 2, 1973
0.408 0.581 0,283 0,723 0.274 0.684 0.211 0.0291 0,0154 0.0154 17.8 11.8 2.30 2.55 2.98 0.214 0.056 0.039 0,0137 0.0185 0,290 0.163 0,0358 0.0673 0.023 0.349 0.0898 0.054 0.162 0.129 0.0351 0.0290 0.00324 0.998 0.0136 0.0350 0,0130 0.00722 0.0127 0.0116 0.157
Corrosion rate.. ma/cm2 hr 850' 900'
Slag washa
Poor Poor Poor Poor Poor Good Good Good Good Good Poor Poor Poor Poor Poor Fair Fair Fair Good Good Poor Poor Fair Fair Poor Poor Good Good Good Good Good Good Good Good Good Good Good Good Good Good Fair Good Fair Poor Poor Good Good Good Good Good Good Fair Poor Poor Poor Poor Poor
1967; 13ornsteiii and DeCrescente, 1969, 1970, 1971; Bornstein, e! a1 , 19i1, 1972; Seybolt, 1970). The classical method of irihibitiiig the corrosi\ e characteristics of VA3, aiid Sa2SO4 melts has been to form high-melting >amdates of the former and minimize the level of the latter. Xagnesium has been the
most successful substance for this type of protection. The optimum levels of magnesium addition are not precisely known. J u s t as the mechanism of corrosion is only partially understood, so too is t h a t of its inhibition. I n the first paper of this series (May, et al., 1972), a n electrochemical measurement of corrosion rate in fused-salt systems was presented. The second paper of the series (May, et al., 1973) presented a phase diagram for the h'azS04MgS04-VzOs system. The purpose of the present work is to apply the electrochemical rate measurement in conjunction with the phase diagram information to determine the optimum levels of magnesium as a n inhibitor. A simple rationale for the effectiveness of magnesium as a corrosion inhibitor is presented.
P
Experimental Section
Materials. T h e melts were prepared from reagent grade chemicals obtained from Fisher Scientific Co. Samples of 40-g size were prepared b y weighing appropriate quantities of t h e constituents a n d thoroughly mixing t o ensure a homogeneous sample. Electrochemical Measurements. T h e electrochemical cell a n d corrosion rate measuring apparatus, source of materials, a n d sample preparation were described earlier ( X a y , et al., 1972). Care was taken with each melt to ensure that it was heated above the melting or sintering point so that compound formation had occurred and intimate contact was made with the electrodes before the measurements were made. The slags with high magnesium content did not melt to the point of flowing. As was pointed out earlier (May, et al., 1972), the rates measured by this method are accurate within a factor of 2. Although care must be taken in comparing values with this level of reliability, the data are sufficiently accurate for observing trends. Slag Evaluation. A t t h e end of a r u n t h e slags were washed with water a n d a n arbitrary rating was given t o t h e ease with which t h e slags were removed from t h e crucibles. X-Ray Analysis. T h e same equipment used t o identify compounds in the ternary phase diagram (May, et ai., 19i3) was used to identify compounds on the corroded coupon surface. The X-ray analysis of the corroded coupon surface was carried out by smoothing the surface as much as possible without removing all of the corroded material. A sample holder was constructed to fix the coupon in the X-ray beam in the same position as the powder sample. The Udimet 500 and 700 coupons were prepared b y slicing l/s-in. pieces from a bar and grinding to the desired shape and surface area. Results and Discussion
The corrosion rates (in mg/cm2 hr) for Udimet 500 in a variety of slag compositions measured a t temperatures ranging from 800 to 950" are presented in Table I. The data in Table I span several orders of magnitude in corrosion rate. In order to place these numbers on a more realistic basis, the following situation is considered. d turbine bucket or nozzle is about l / g in. or 120 mils thick. The minimum expected time for replacement of turbine parts subjected to corrosion from crude and residual oils is 3 years. This corresponds to 40 MPY or 0.10 mg/cm2 hr for Udimet 500. Since this technique is accurate within a factor of 2, we have chosen 0.050 mg/cm2 hr as the acceptable corrosion rate. Crude and residual oils used in gas turbines are analyzed for levels of metals present rather than the metal compounds.
I
'?
?I
X
----2
/
I I
800'
I
850'
I
Corrosion Rate
/
4
I
900° 950° Temperature
1
1000"
Figure 1 . The effect of the M g / V ratio on corrosion rate a t a 0.01 N a / V ratio
Sodium is usually maintained in the 0.1-10 ppm range and vanadium can range to 500 ppm, but turbine users rarely use fuels with more than 50 ppm. Alagnesium-containing corrosion inhibitors are normally added at a 3/1 ratio of magnesium to vanadium. I n the slag formed from combustion of these fuels, proportionately less vanadium appears in the deposit than the other metals so that the ratios of sodium and magnesium to vanadium in the slag are greater than in the original fuel. Thus, a fuel containing 0.8 ppm of sodium and 10 ppm of vanadium and being treated with 30 ppm of magnesium will yield a slag with metal ratios of Na/V = 0.1 and Mg/V = 4. I n order to apply our data to fuels encountered in field use, we have evaluated slags in terms of metal ratios. The data at 800" indicate that acceptable corrosion rates can be obtained a t metal weight ratios in the slag of Xa/V = 0.1 and Mg/V = 3. A t 900-950°, the operating range now being sought for gas turbines operated on residual and crude oils, the weight ratios must be maintained a t Na/V = 0.01 and Rfg/V = 4 for acceptable corrosion rates, as illustrated in Figure 1. The situation in which the sodium level exceeds the vanadium level is discussed later. Magnesium appears to inhibit vanadium corrosion by diluting the liquid phase and interfering with (a) dissolution of the protection metal oxide layer on the alloy surface and (b) the transport of 02-to the metal surface. The RSgS0,V205 phase diagram predicted formation of X ~ Z V S Oand , free LLIgS04 a t > i O mol % JlgSO,. At less XgSO,, a melt, plus possibly solid 1\Ig2V207,was predicted. Our corrosion rate data reflected this boundary. At 60 mol yo AfgS04, the corrosion rate was similar to 100 mol yoVz05whereas a t i o mol yo RIgS04, the rate was reduced by a factor of 100. A Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 2, 1973
147
I
IO-^
Ixlo-'
IXIO-'
Ixlo-2 Na/V R a t i o
1x10-'
lXl00
1x10'
Figure 2. The effect of the Na/V ratio on corrosion rate at a 4/1 M g / V ratio
Table II. Magnesium Required to Inhibit Corrosion Satisfactorily at 0.5 Ppm of Sodium and Various Vanadium levels Ppm in fuel
Na/V
0.001 0.01 0.1 1 10
Mg/V
3
4 30 50 500
Na
V
Mg
0.5 0.5 0.5 0.5
500 50 5 0.5 0.05
1500 200 150 25 25
0.5
trend is seen from 70 to 95 mol 70 MgS04: the corrosion rate is reduced as the MgSO, content is increased. Apparently, the MgS04 must be present a t >90 mol % for acceptable corrosion rates. There was no apparent correlation with the Sa2S04.6V205 compound line determined by the phase diagram. I t was found in general that the lower the melting point of a composition on the phase diagram, the higher the corrosion rate of a slag with that composition. In the Ka~SO,-MgSO, system, the corrosion rates are less than in V20j by a factor of 10. However, sodium corrosion appears to be much more difficult to control and sodium sulfate must be maintained a t about 0.5 mol 70for effective control. The sensitivity of corrosion rate to sodium level a t several temperatures is illustrated in Figure 2. The NanS0,14gS04 phase diagram has a eutect,ic a t about 690" and a second compound melting a t about 840' which cont'ribute liquid to the melt. This liquid apparently serves as the solvent for the protective metal oxide layer and 0 2 - ions. T o interrupt corrosion, it must be diluted to the point of dryness. Out data indicate that a fuel containing the maximum of 5 ppm of sodium and 2 ppm of vanadium as permitted in ASTM No. 3 G T fuel by ASTX tentative specification D 2883-7OT would be very corrosive. Lee and coworkers (1972) found this to be the case using a burner test rig. Satisfactory 148 Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 2, 1973
inhibition can be maintained a t greatly increased Mg/V ratios when the sodium level is equal to or greater than the vanadium level. The data iri Table I1 (taken from Table I) indicate bhat the X g / N a ratio must be maintained a t above 50 to effectively inhibit corrosion when Xa 2 V. The sodium level of 0.5 ppm was arbitrarily chosen for this illustration and represents a level that can easily be achieved by desalting. Fortunately for the gas turbine or steam boiler operator, situations in which the sodium level esceeds the vanadium level by a factor of 10 are rare for desalted fuels, and when they occur, the metal levels are low and small amounts of slag are produced. These data further emphasize the fact that magnesium inhibits sodium corrosion only by dilution. Compounds on the surface of corroded specimens were identified to find if the samples were undergoing normal corrosion reactions. Udiniet 500 and 700 coupons of approximately the same size were placed in a n equimolar Xa2S04-1\IgS04V 2 0 j slag a t 1000" for sufficient time to corrode the sample. The corroded coupons were then cleaned and polished to as smooth a surface as possible. h n X-ray diffraction pattern was run OIL each coupon. These data are presented in Table 111 with published patterns for nickel and several nickel compounds. The data indicated that the oxides and vanadates of nickel were present. Two points must be kept in mind when comparing these X-ray patterns. First, the alloys are predominantly nickel and contain significant amounts of chromium and cobalt and small amounts of aluminum, molybdenum, and titanium. Thus, some small peaks may be due to oxides and vanadates of the elements present in smaller quantities. Second, small deviations in d spacings from published patterns can be attributed to imperfect alignment of the sample in the beam. The data presented here support the following mechanism for inhibition of vanadium and sodium corrosion with magnesium. llagnesium forms a vanadate which removes the extremely corrosive V205 from the scene. Then, l\lgSod serves as a diluent which prevent,s dissolution of the protective oxide layer 011 the metal surface arid interrupt's transport
Table Ill. X-Ray Data for Corroded Coupons Compared with Nickel and Several Nickel Compounds
(d lines,
8)
Udimet 700 Time in slog, hr
Udimet 500 Time in slag, hr
0
0.5
1.5
0
0.25
1 .o
2.0
Nickel
NiO
NizOI
Ni(VO&
2.0651 1.7891
3.2406 3.0153 2.4926 2.0451 1.7730 1.4638
3.2120 2.4793 2.0386 1.4617
2.069 1.797
3.195 2.7361 2.4859
3.229 2.736 2.5196 2.4926 2.4792 2.2413 2.0606 1.4616 1.3992
3.2406 3.1184 2.9760 2.9051 2.8376 2.5197 2.4926 2.4024 2.0832 2.0606 2.0386 1.4617
2.034 1.7633
2.409 2.08 1.47
2.402 2.0832 1.4763
3.49 2.52 2.48 2.06
of the 02- ions. Koiie of tlie cornpouiitls foriiietl between sodium sulfate aiiti niagiiesiuiii sulfate reduced corrosion rates for sodium niid the iiiliibitioii occurs solely by the dilutioii effect’. Conclusions
Our data indicate t h a t iiiagiiesiiim can control sodiuin aiid vaiiadiuiii corrosion to 900-950’ wlieii weight ratios of hIg/V = 4 aiid S a T = 0.01 are maintained in the ash. Effective control of corrosioii call be niaiiitaiiied with higher ratios of S a , K at lower tem1)eratures or with greatly incre:rsed ratios of 1 1 g N . A reasoiiable mecliaiiisiii for iiiagiiesiuiii iiiliibitioii based 011 tlie ternary l\;a?SO4-1\IgPO4-V2O5 phase diagram has been preseiited i i i n-hicli mngiiesiuin iiiliibits ~ a i i a d i u r nthrough both com1)ouiid forination and. dilution. I t inhibits sodiuin solely bj- dilution. Udimet 500 coupoiis corroded in YarSO,1lgSO4-Tr2Oj slags yielded predoiiiinaiitly nickel oxide. This is iii agreenieiit nitli our inechaiiism aiid tlie electrochemical obsermt,ions. literature Cited
Bornstein, N. S.,DeCrescente, R l . A . , Trans. AIIZPE, 245, 1947 (1969). Bornstein, X. S., DeCrescente, 11. A., Corrosion, 26, 209 (1970). Bornstein, S . S.,DeCrescente, 11.A., Met. Trans., 2, 287.5 (1971). Bornstein, K.S., DeCrescente, RI. A., Roth, H. A., Annual Report, Contract N 00014-70-c-0234, XR-036-089/1-12-70(471 ),
conducted for the Office of Kava1 Researrh. of . .~..~~ ,~Tlenartmmt .r..._..._.___. the Navy, Washington, D. C., 3iarch 1971. Bornstein, S . S.,DeCrescente, AI. A., lioth, H. A . , Annual Report, Contract S 00014-70-c-0234, NR-036-089 /1-12-70(471 ), conducted for the Office of Saval Research, Department of the Navv. Washinnton. D. C.. June 1972. DeCrescente, 11. A,, Bornstein, S . S.,Corrosion, 24, 127 (1968). Dickson, F. E., Petrakis, L., J . Phys. Chem., 74, 2850 (1970). Greenlee, R. W., Lucas, R. X., “Electrical Purification of Gas Turbine Fuels,” ASTN 75th Meeting and Exposition, Los Angeles, Calif., June 25-30, 1972. Lee, S.Y,, Young, W.E., Hussey, C. E., J . Eng. Power, 94, 149 11972). JIay, it’. li.,Zetlmeisl, 31. J., Bsharah, L., Ind. Eng. Chem ., Prod. Kes. Develop., 12, 140 (1973). May, IT.li., Zetlmeisl, AI. J., Bsharah, L., Annand, R . 12., ibid., 11, 438 (1972). Pantony, D . 4.,Vasu, K. I., J . Inorg. Sucl. Chem., 30, 423 11968a). Pantony,’D. A., Vasu, I(.I., i b i d . , 30, 433 (196813). Pantony, D. A., Vasu, K. I., ibicl., 30, 755 ( 1 9 6 8).~ Petrolite Corp., Laboratories Staff, “Impurities in Petroleum,” Petreco Division, Petrolite Corp., Houston, Tex., 1968. Sacks, \T.j J . Eng. Power, 7 6 , 375 (1954). Seybolt, A. U., “High-Temperature Metailic Corrosion of Sulfur and Its Compounds,” Z. A. Foroulis, Ed., p 159, The Electrochemical Society, Kew York, N . Y., 1970. Seybolt, A. U., Beltran, A., “Hot Corrosion Problems Associated with Gas Turbines,” ASTRI STP 421, p 21, American Society for Testing and Materials, Philadelphia, Pa., 1967. Simons, E. L., Browning, G. V., Liebhafsky, H. A., Corrosion, 11, 505 (1955). Stenzel, R. W., W o r l d Petrol., Annual Refinery Review Issue, 28, 78 (1957). Waterman, L. C., Moechel, J. R., Kcjining Eng., 29, 546 (1957). RECEIVED November 3, 1972 ACCEPTED February 5, 1973
Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 2, 1973
149
