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Corrosion issues related to methanol as a vehicle fuel
ABSTRACTS Corrosion issues related to methanol as P vehicle fuel bv J. E. Anderson and K. Otto, Research Staff, Ford Motor Company, Dearborn, MI 48121, U.S.A. Methanol corrosion can be subdivided into (a) corrosion by bulk methanol and (b) corrosion by methanol combustion products. The first (familiar) type of corrosion occurs during contact between metals and methanol fuel. It has been observed in fuel transport and in fuel storage equipment. This corrosion represents a potential problem both globally, in fuel distribution networks, and locally, in individual vehicles. Corrosion rates of steel in methanol and in methanoLwater solutions are fairly well understood. Unresolved issuesinclude theinfluence of hydrocarbon cofuels and dissolved salts. In practical systems, this type of corrosion is minimized by material substitution. A second form of corrosion involves reactions between methanol corrosion products and metal surfaces. This (new) corrosion process has been observed within engines operating on fuel methanol at low temperatures. Combustion corrosion is caused by partial oxidation of methanol to formic acid, followed by electrochemical attack. In laboratory experiments, corrosion has been produced by interaction of gas phase methanol combustion products with metal coupons. Surface water is critically important: corrosion rates decrease markedly as the temperature is raised above the dew point[l, 21. Combustion corrosion also occurs when liquid fuel is burned on metal surfaces. Experiments confirm partial methanol oxidation to formic acid occurs within the pool liquid during these fires. Overall alcohol-to-acid conversion is small, amounting to 0.01 o/0at most. However, these acid concentrations combined with the high ionic conductivity of liquid methanol, generate large-scale corrosion in the course of a pool fire. No appreciable corrosion occurs when hydrocarbon fuels, such as gasolines, are burned under comparable conditions. 1. K. Otto, L. Bartosiewiczand R. 0. Carter, Corros. Sci. 25, 117 (1985). 2. K. Otto, J. E. Anderson, L. Bartosiewicz, R. 0. Carter and C. A. Gierczak, Corms. Sci. 26, 455 (1986).
The real and chemical Gibbs energies of silver ion transfer from water to some organic solvents by Zbigniew Koczorowski and lrwina Zagbrska, Department of Chemistry, University of Warsaw, ul. Pasteura 1, 02-093 Warsaw, Poland. The real Gibbs energy, ALa&+, and the chemical Gibbs energy, k, GQ + , of silver ion transfer from water to ybutyrolactone, isobutyl methyl ketone and ethylene glycol have been determined experimentally as well as those for methanol and, in part, for acetone, which were considered to be test solvents. The Ata*s+ measurements were carried out by the dynamical condenser method and the A:.GA~* measurements were made using transfer cells in which tetrethylammonium picrate (TEAPi) solutions were used to eliminate the diffusion potentials, mainly in dipolar solvents. The ALa&+ and ALGAL* data were used to calculate the surface potential differences between the studied solvents and water, A& The values were compared with the AQ.x values measured directly 983
by the dynamical condenser method. The salt bridge containing TEAPi was used in those measurements, too, on the organic phase side. The effect of mutual saturation of water and isobutyl methyl ketone on the A”GAa+ , A”,a&+ and A;x was studied.
Electrochemical studies of thedepassivation of alumioium in Ill-trichloroethaoe solutioos by N. Winterton, W. N. Brooks, A. C. P. Pugh, D. F. Salter and P. J. Moreland, ICI PLC, Mond Division, The Heath, Runcorn, Cheshire WA7 4QE. U.K. While the phenomena of corrosion in non-aqueous solvents have not been extensively studied, passivity and depassivation processes have received even less attention. In particular, little is known of the mode of breakdown of the passive oxide film on metals such as aluminium on exposure to industrially important chlorinated solvents, such as 11 I-trichloroethane. We report some preliminary studies of the depassivation of the air-grown oxide film on aluminium and some of its alloys in 11 I-trichloroethane solutions containing tetrabutylammonium trifluoromethanesulphonate as supporting electrolyte, using pitting induction times, thin film resistance, ac impedance, corrosion and electrode potential measurements to examine the effect of applied potential and the role of water and chloride ion. Pitting induction times r, and corrosion and electrode potentials (measured vs a Ag/AgI reference, using a Pt foil auxiliary electrode in a traditional 3-electrode set-up with a static cylindrical working electrode) displayed no perceptible dependence on supporting electrolyte concentration, though transfer resistances and capacitance data from UC impedance measurements displayed such a dependence. The qualitative dependence of T on potential, [H,O] and [Cl-] are interpreted in terms of a localized breakdown of the oxide film involving electron transfer from metal to weakly adsorbed 111-trichloroethane, this being prefered to simple dissolution of oxide by the solvent. Al”’ is formed at the metal-metal oxide interface, Cl- at the metal oxide-solvent interface releasing CHJCCl,- into solution to react further, giving as primary products 2,2,3,3_tetrachlorobutane by dimerization and 1 l-dichloroethane and vinylidene chloride by disproportionation. Field-assisted ion migration occurs followed by (an assumed) dissolution of the elements of AIOCI. The net reaction is given by: Al + Al,O,
+ 3CH,CCl,
--t 3AIOCI + 3CH,CCI,..
Following pitting, chemical reaction between metal and the solvent occurs at the base of pits, with the primary products of the reaction, particularly AlC13, reacting further in autocatalytic processes leading ultimately to complete solvent degradation.
Corrosion and anodic dissolution in methanolic perchlorate solutions by R. Reich and M. Maldy, Lab. Physique des Solides, tit. 510, Universitd Paris-Sud, 91405 Orsay, France. When metals are dissolved anodically in aqueous and nonaqueous media, the weight of metal W,, dissolved is often greater than W,, calculated from Faraday’s law, assuming a normal oxidation state, n, ie n = 3 for Cd. The significant parameter which quantitatively characterizes the anodic dissolution process is the faradaic efficiency, p = n/Ne, where
984
Abstracts
Ne, the apparent valence, is calculated using the relation, Ne = A.Q/W,,F, where A = molecular weight of Gd, Q = electric charge passed, F = Faraday. The potentiodynamic curves of Cd in LiC104-MeGH solutions at -76”C[l] exhibit active, passive and transpassive ranges which correspond nearly to corrosion, pitting and electropolishing[2]. The viscosity increase (2-propanol+ MeOH) as the dielectric constant decreases (THF + MeOH) raises the transpassive potential and reduces both the passive and active current densities[l]. At -76°C the H,O influence and the solute concentration role are explained by the high viscosity increase. A constant valence value Ne = 1.415 is observed at -76°C in anhydrous MeOH and its mixtures with THF, 2propanol and H,O, which is independent of perchlorate cations (Li or alkaline earths) if the cell potential or the current density is high enough[I, 21. In anhydrous LiCIO,-MeOH solutions at every temperature a quantitative relation between the amount of Cl- liberated and the Ne value is noticed at any current density[3]. A corrected value for the apparent valence of dissolution N,,, is calculated using N,,, = (Q + Q,-t )/We, F, where Q,-t is the equivalent charge corresponding to reduction of CIO; to Cl- with 8 electron charge transfer. The very important fact is the constancy of N,,, values ( = 3) over a wide range of current density at every temperature (- 76°C to 2O”C), contrary to the exponential decrease and attaining a limiting value of Ne. Indeed, the Ne plateau corresponds to a bright surface (electropolishing conditions), contrary to the Ne falling range relative to a more or less darkening of the Cd (transpassive to active transition). In LiClO, water-MeOH solutions under potentiostatic[2] and galvanostatic[3] conditions, the significant result at - 76°C is the similar constancy of Ne over a wide rangeof H,Ocontent (0 5 y < 0.42withy = 0.42is the Hz0 mole fraction of freezing solution) and a slight variation of N corr from 3.0 to 2.8. So, at -76°C H,O does not play any spectfic role relative to MeOH in the electrolytic processes. At 20°C. an increase of Ne from 1.43 for y = 0.013 (anydrous MeOH) to Ne = 2.8 for y = 1 (pure H,O) is observed. Such a variation of Ne with H,O content results from a change in the Gd dissolution mechanism reflected by the drastic decrease of Cl- liberated. During the Gd dissolution at any current density, the pH rises (glass electrode measurements). The increase of basicity by added LiOH gives an important rise of Ne and N EOrrcontrary to acidity. The plateau of Ne us current density, irrespective of metallurgical treatment and prepolishing method, cannot be explained by the “surface disintegration model”. The same value of Ne in MeOH[2] containing 0.115 M LiCIO, + 0.115 M LiCl as in 0.23 M LiC104 contrary to Ne - 3 in 0.23 M LiCl is against the existence of a “monovalent transitory ion” Gd +, since its existence cannot depend on the nature of anion solute. These two models cannot account for the anodic potential oscillations in galvanostatic conditions. A different mechanism is proposed. 1. R. Reich and C. Francois, Meeting Electrochem. Sot., Seattle, U.S.A., Vol. 78-1 pp. 1376-1378 (1978). 2. R. Reich and M. MaMy, Ext. Abstr. 35th ISE Meeting, Vol. B%24, p. 658. Berkeley, U.S.A. (1984). 3. R. Reich, S. M. Mayanna and M. Maldy, Exr. Abstr. 36th ISE Meeting, p. 1122. Salamanca, Spain (1985).
acrolein acrylonitrile ethyl acrylate ally1 chloride formic acid methyl formate aniline benzoyl chloride benzyl chloride butyraldehyde chlorobenzene chloroacetyl chloride Z-chloroethanol cyclohexanol cyclohexanone diacetone alcohol butanedione (diacetyl) dibutyl ethers l.l-dichloroethane 1.2-dichloroethane dichloromethane diethyl ether dimethyl formamide dimethyl sulphate dimethyl sulfoxide sulfur monochloride epichlorohydrin ethanol ethylenediamine ethyl formate trichloroethylsilane ethyl acetate acetic acid acetic anhydride butyl acetates furfural cresol methanol methyl-1.2dichloroethyl methyl isobutyl ketone nitrobenzol paraldehyde I-pentane pentan-2,4-dione propargyl alcohol propionaldehyde pyridine carbon disulfide ethyl alcohol thionyl chloride trichloroethane monochlorotrimethylsilane vinil acetate. All test specimen are welded. Always two specimens were compressed together, giving a crevice. The corrosion rate was investigated in the liquid, at the interphase and in the gasroom. The small corrosion rates are important for safety devices with thin foils, like manometers, control valves and float switches in the chemical industry.
Corrosion of austenitic CrNiMo stainless steel in organic media by W. Hopfner. Bundesanstalt fur Materialprufung (BAM), Writer den Eichen 87, loo0 Berlin 45, F.R.G.
Elcctrocatalysis of oxygen reduction at a polycarbazole electrode by R. N. O’Brien and K. S. V. Santhanam,’ Department of Chemistry, University of Victoria, Victoria, Canada and *Chemical Physics Group, Tata Institute of Fundamental Research, Bombay, India.
Corrosion tests of one year at 30 and 50°C were carried out with austenitic 18/8 CrNiMo stainless steel for the following media: acetone acetonitrile acetyl chloride
Polycarbazole was deposited electrolytically from DMF in an N, atmosphere in a dry box. Cyclic voltammetry of dioxygen at this synthetic metal electrode to which iron phtalocyanine had been added as a solution was performed in a 0.1 M K,SO, solution. The cathodic peak potential was shifted by about 200 mV or significant catalysis by the impregnated.
Abstracts
Corrosion and stress corrosion cracking of iron materials in methanol under practical conditions by E. Wendler-Kalsch,
University
of Erlangen-Nuernberg,
F.R.G.
The influence of water on the corrosion and stress corrosion behaviour of unalloyed and low alloy steels in pure and process methanol has been studied. With respect to corrosion potential and low cathodic polarization, the steels are characterized by a high resistance to uniform corrosion. A minimum localized corrosion attack takes place at non-metallic inclusions of the metal. When the steels are subjected to critical strain rates, cracks perpendicular and/or parallel to the tensile stress are formed depending on the water content of the methanol. In thecase of anodic polarization, both the water content of the methanol and the electrode potential have considerable influence on the corrosion behaviour of the steels. The water content turns out to be the determining factor for passivity. In pure methanol localized corrosion especially along the banded microstructure of the rolled material is observed. Film formation and pitting corrosion are the resuit of increasing the water content and the anodic polarization. Mechanical stressing or straining of the steels causes stress corrosion cracking and/or pitting corrosion depending, to a large extent, on the water content and possible impurities of the methanol and on the anodic electrode potential. Our assumption is that various mechanisms of stress corrosion cracking occur during anodic and cathodic polarization of the steels in methanol solutions. The results of our investigations are discussed with reference to damage of steels caused during practical working conditions.
985
The internal corrosion protection of the petroleum white products storage vessels with the floating roof by P. Kirkov, T. Grcev, J. Arsovski, Lj. Arsov, P. Abdurauf, N. Nikolovski, D. Slavkov, T. Anovski, S. Pejovski and J. Nikolovski, Faculty of Technology and Metallurgy, University Kiril and Metodij, Centre for Radioisotopes Application in Science and Industry, 91000 Skopje, Yugoslavia
The corrosion of the storage vessels for petroleum white products is very intensive on the three-phase contact area Metal-Air-Liquid. The effect is particularly bad in storage vessels with floating roofs. The application of inhibitors for corrosion protection in the petroleum products, does not affect corrosion propagation substantively. The pretreatment of the metal surface by standard surface coverage has a limited effect. To find a solution to this problem we investigated the mechanism of corrosion propagation on the surface periodically (during charging and discharging the vessels), covered by air and petroleum products. We identified on such surface formation, microcondensation of petroleum products satured by moisture. The structure of thiscondensation is in formation, a microscopic thin layer of drops, having dimension of l-5 x IO-“ cm, sitting on the extremities of the metal crystals on the surface. Such surface structure, intensifies charge transfer between covered and uncovered by condensated metal parts, and stimulates dissolution of metals. By application of fog decompensation agents and by changing the “zeta” potential of the condensates the corrosion rate is drastically diminished. The laboratory observation of this effect has been fully verified on the storage vessels of petroleum white products.
The real and chemical Gibbs energies of silver ion transfer from water to some organic solvents by Zbigniew Koczorowski and lrwina Zagbrska, Department of Chemistry, University of Warsaw, ul. Pasteura 1, 02-093 Warsaw, Poland. The real Gibbs energy, ALa&+, and the chemical Gibbs energy, k, GQ + , of silver ion transfer from water to ybutyrolactone, isobutyl methyl ketone and ethylene glycol have been determined experimentally as well as those for methanol and, in part, for acetone, which were considered to be test solvents. The Ata*s+ measurements were carried out by the dynamical condenser method and the A:.GA~* measurements were made using transfer cells in which tetrethylammonium picrate (TEAPi) solutions were used to eliminate the diffusion potentials, mainly in dipolar solvents. The ALa&+ and ALGAL* data were used to calculate the surface potential differences between the studied solvents and water, A& The values were compared with the AQ.x values measured directly 983
by the dynamical condenser method. The salt bridge containing TEAPi was used in those measurements, too, on the organic phase side. The effect of mutual saturation of water and isobutyl methyl ketone on the A”GAa+ , A”,a&+ and A;x was studied.
Electrochemical studies of thedepassivation of alumioium in Ill-trichloroethaoe solutioos by N. Winterton, W. N. Brooks, A. C. P. Pugh, D. F. Salter and P. J. Moreland, ICI PLC, Mond Division, The Heath, Runcorn, Cheshire WA7 4QE. U.K. While the phenomena of corrosion in non-aqueous solvents have not been extensively studied, passivity and depassivation processes have received even less attention. In particular, little is known of the mode of breakdown of the passive oxide film on metals such as aluminium on exposure to industrially important chlorinated solvents, such as 11 I-trichloroethane. We report some preliminary studies of the depassivation of the air-grown oxide film on aluminium and some of its alloys in 11 I-trichloroethane solutions containing tetrabutylammonium trifluoromethanesulphonate as supporting electrolyte, using pitting induction times, thin film resistance, ac impedance, corrosion and electrode potential measurements to examine the effect of applied potential and the role of water and chloride ion. Pitting induction times r, and corrosion and electrode potentials (measured vs a Ag/AgI reference, using a Pt foil auxiliary electrode in a traditional 3-electrode set-up with a static cylindrical working electrode) displayed no perceptible dependence on supporting electrolyte concentration, though transfer resistances and capacitance data from UC impedance measurements displayed such a dependence. The qualitative dependence of T on potential, [H,O] and [Cl-] are interpreted in terms of a localized breakdown of the oxide film involving electron transfer from metal to weakly adsorbed 111-trichloroethane, this being prefered to simple dissolution of oxide by the solvent. Al”’ is formed at the metal-metal oxide interface, Cl- at the metal oxide-solvent interface releasing CHJCCl,- into solution to react further, giving as primary products 2,2,3,3_tetrachlorobutane by dimerization and 1 l-dichloroethane and vinylidene chloride by disproportionation. Field-assisted ion migration occurs followed by (an assumed) dissolution of the elements of AIOCI. The net reaction is given by: Al + Al,O,
+ 3CH,CCl,
--t 3AIOCI + 3CH,CCI,..
Following pitting, chemical reaction between metal and the solvent occurs at the base of pits, with the primary products of the reaction, particularly AlC13, reacting further in autocatalytic processes leading ultimately to complete solvent degradation.
Corrosion and anodic dissolution in methanolic perchlorate solutions by R. Reich and M. Maldy, Lab. Physique des Solides, tit. 510, Universitd Paris-Sud, 91405 Orsay, France. When metals are dissolved anodically in aqueous and nonaqueous media, the weight of metal W,, dissolved is often greater than W,, calculated from Faraday’s law, assuming a normal oxidation state, n, ie n = 3 for Cd. The significant parameter which quantitatively characterizes the anodic dissolution process is the faradaic efficiency, p = n/Ne, where
984
Abstracts
Ne, the apparent valence, is calculated using the relation, Ne = A.Q/W,,F, where A = molecular weight of Gd, Q = electric charge passed, F = Faraday. The potentiodynamic curves of Cd in LiC104-MeGH solutions at -76”C[l] exhibit active, passive and transpassive ranges which correspond nearly to corrosion, pitting and electropolishing[2]. The viscosity increase (2-propanol+ MeOH) as the dielectric constant decreases (THF + MeOH) raises the transpassive potential and reduces both the passive and active current densities[l]. At -76°C the H,O influence and the solute concentration role are explained by the high viscosity increase. A constant valence value Ne = 1.415 is observed at -76°C in anhydrous MeOH and its mixtures with THF, 2propanol and H,O, which is independent of perchlorate cations (Li or alkaline earths) if the cell potential or the current density is high enough[I, 21. In anhydrous LiCIO,-MeOH solutions at every temperature a quantitative relation between the amount of Cl- liberated and the Ne value is noticed at any current density[3]. A corrected value for the apparent valence of dissolution N,,, is calculated using N,,, = (Q + Q,-t )/We, F, where Q,-t is the equivalent charge corresponding to reduction of CIO; to Cl- with 8 electron charge transfer. The very important fact is the constancy of N,,, values ( = 3) over a wide range of current density at every temperature (- 76°C to 2O”C), contrary to the exponential decrease and attaining a limiting value of Ne. Indeed, the Ne plateau corresponds to a bright surface (electropolishing conditions), contrary to the Ne falling range relative to a more or less darkening of the Cd (transpassive to active transition). In LiClO, water-MeOH solutions under potentiostatic[2] and galvanostatic[3] conditions, the significant result at - 76°C is the similar constancy of Ne over a wide rangeof H,Ocontent (0 5 y < 0.42withy = 0.42is the Hz0 mole fraction of freezing solution) and a slight variation of N corr from 3.0 to 2.8. So, at -76°C H,O does not play any spectfic role relative to MeOH in the electrolytic processes. At 20°C. an increase of Ne from 1.43 for y = 0.013 (anydrous MeOH) to Ne = 2.8 for y = 1 (pure H,O) is observed. Such a variation of Ne with H,O content results from a change in the Gd dissolution mechanism reflected by the drastic decrease of Cl- liberated. During the Gd dissolution at any current density, the pH rises (glass electrode measurements). The increase of basicity by added LiOH gives an important rise of Ne and N EOrrcontrary to acidity. The plateau of Ne us current density, irrespective of metallurgical treatment and prepolishing method, cannot be explained by the “surface disintegration model”. The same value of Ne in MeOH[2] containing 0.115 M LiCIO, + 0.115 M LiCl as in 0.23 M LiC104 contrary to Ne - 3 in 0.23 M LiCl is against the existence of a “monovalent transitory ion” Gd +, since its existence cannot depend on the nature of anion solute. These two models cannot account for the anodic potential oscillations in galvanostatic conditions. A different mechanism is proposed. 1. R. Reich and C. Francois, Meeting Electrochem. Sot., Seattle, U.S.A., Vol. 78-1 pp. 1376-1378 (1978). 2. R. Reich and M. MaMy, Ext. Abstr. 35th ISE Meeting, Vol. B%24, p. 658. Berkeley, U.S.A. (1984). 3. R. Reich, S. M. Mayanna and M. Maldy, Exr. Abstr. 36th ISE Meeting, p. 1122. Salamanca, Spain (1985).
acrolein acrylonitrile ethyl acrylate ally1 chloride formic acid methyl formate aniline benzoyl chloride benzyl chloride butyraldehyde chlorobenzene chloroacetyl chloride Z-chloroethanol cyclohexanol cyclohexanone diacetone alcohol butanedione (diacetyl) dibutyl ethers l.l-dichloroethane 1.2-dichloroethane dichloromethane diethyl ether dimethyl formamide dimethyl sulphate dimethyl sulfoxide sulfur monochloride epichlorohydrin ethanol ethylenediamine ethyl formate trichloroethylsilane ethyl acetate acetic acid acetic anhydride butyl acetates furfural cresol methanol methyl-1.2dichloroethyl methyl isobutyl ketone nitrobenzol paraldehyde I-pentane pentan-2,4-dione propargyl alcohol propionaldehyde pyridine carbon disulfide ethyl alcohol thionyl chloride trichloroethane monochlorotrimethylsilane vinil acetate. All test specimen are welded. Always two specimens were compressed together, giving a crevice. The corrosion rate was investigated in the liquid, at the interphase and in the gasroom. The small corrosion rates are important for safety devices with thin foils, like manometers, control valves and float switches in the chemical industry.
Corrosion of austenitic CrNiMo stainless steel in organic media by W. Hopfner. Bundesanstalt fur Materialprufung (BAM), Writer den Eichen 87, loo0 Berlin 45, F.R.G.
Elcctrocatalysis of oxygen reduction at a polycarbazole electrode by R. N. O’Brien and K. S. V. Santhanam,’ Department of Chemistry, University of Victoria, Victoria, Canada and *Chemical Physics Group, Tata Institute of Fundamental Research, Bombay, India.
Corrosion tests of one year at 30 and 50°C were carried out with austenitic 18/8 CrNiMo stainless steel for the following media: acetone acetonitrile acetyl chloride
Polycarbazole was deposited electrolytically from DMF in an N, atmosphere in a dry box. Cyclic voltammetry of dioxygen at this synthetic metal electrode to which iron phtalocyanine had been added as a solution was performed in a 0.1 M K,SO, solution. The cathodic peak potential was shifted by about 200 mV or significant catalysis by the impregnated.
Abstracts
Corrosion and stress corrosion cracking of iron materials in methanol under practical conditions by E. Wendler-Kalsch,
University
of Erlangen-Nuernberg,
F.R.G.
The influence of water on the corrosion and stress corrosion behaviour of unalloyed and low alloy steels in pure and process methanol has been studied. With respect to corrosion potential and low cathodic polarization, the steels are characterized by a high resistance to uniform corrosion. A minimum localized corrosion attack takes place at non-metallic inclusions of the metal. When the steels are subjected to critical strain rates, cracks perpendicular and/or parallel to the tensile stress are formed depending on the water content of the methanol. In thecase of anodic polarization, both the water content of the methanol and the electrode potential have considerable influence on the corrosion behaviour of the steels. The water content turns out to be the determining factor for passivity. In pure methanol localized corrosion especially along the banded microstructure of the rolled material is observed. Film formation and pitting corrosion are the resuit of increasing the water content and the anodic polarization. Mechanical stressing or straining of the steels causes stress corrosion cracking and/or pitting corrosion depending, to a large extent, on the water content and possible impurities of the methanol and on the anodic electrode potential. Our assumption is that various mechanisms of stress corrosion cracking occur during anodic and cathodic polarization of the steels in methanol solutions. The results of our investigations are discussed with reference to damage of steels caused during practical working conditions.
985
The internal corrosion protection of the petroleum white products storage vessels with the floating roof by P. Kirkov, T. Grcev, J. Arsovski, Lj. Arsov, P. Abdurauf, N. Nikolovski, D. Slavkov, T. Anovski, S. Pejovski and J. Nikolovski, Faculty of Technology and Metallurgy, University Kiril and Metodij, Centre for Radioisotopes Application in Science and Industry, 91000 Skopje, Yugoslavia
The corrosion of the storage vessels for petroleum white products is very intensive on the three-phase contact area Metal-Air-Liquid. The effect is particularly bad in storage vessels with floating roofs. The application of inhibitors for corrosion protection in the petroleum products, does not affect corrosion propagation substantively. The pretreatment of the metal surface by standard surface coverage has a limited effect. To find a solution to this problem we investigated the mechanism of corrosion propagation on the surface periodically (during charging and discharging the vessels), covered by air and petroleum products. We identified on such surface formation, microcondensation of petroleum products satured by moisture. The structure of thiscondensation is in formation, a microscopic thin layer of drops, having dimension of l-5 x IO-“ cm, sitting on the extremities of the metal crystals on the surface. Such surface structure, intensifies charge transfer between covered and uncovered by condensated metal parts, and stimulates dissolution of metals. By application of fog decompensation agents and by changing the “zeta” potential of the condensates the corrosion rate is drastically diminished. The laboratory observation of this effect has been fully verified on the storage vessels of petroleum white products.