MXPA06007411A - Metal dusting resistant stable-carbide forming alloy surfaces - Google Patents

Abstract

A metal dusting resistant composition comprises an alloy capable of forming a thermally stable titanium carbide coating on its surface when exposed to a carbon supersaturated environment and, a protective coating on the alloy surface comprising an outer oxide layer and an inner carbide layer between the alloy surface and the outer layer.

Description

ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), For two-letter codes and other abbreviations. Refer to the "GuidEuropean (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, Fl, ance Notes on Codes and Abbreviatlons" appearing at the begin- FR, GB, GR, HU, ffi, IS , IT, LT, LU, MC, NL, PL, PT, RO, no ofeach regular issue of the PCT Gazette SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, Cl, CM, GA, GN, GQ, GW, ML, MR, NE, SN, TD, TG). Published: - with intemational search report STABLE CARBIDE FORMATION ALLOY SURFACES RESISTANT TO METAL SPLASHING Field of the Invention the present invention is. relates to the phenomenon of metal dusting experienced in metal appliances when exposed to elevated temperatures at environments that have high carbon activities and relatively low oxygen activities. More particularly, the present invention relates to the generation of alloys resistant to dusting of metal for the internal surfaces of high-temperature apparatuses. BACKGROUND OF THE INVENTION The hydrocarbon conversion processes in which a hydrocarbon or mixture of hydrocarbons and steam or a hydrocarbon and one or more of hydrogen, carbon dioxide and carbon dioxide are well-known processes leading to elevated temperatures and pressures in apparatuses, typically made of steels containing one or more of Ni and Co. The carburization of metallurgy of the system and sprinkling of metal are problems encountered when such steels are used. In general, the metal dusting of steels is experienced at temperatures on the scale of 300 ° C to 900 ° C in suppressed carbon environments. { carbon activity > 1) that have relatively low partial pressures of oxygen (about 10 ~ 10 to about 10"20 atmospheres) The transfer of basically fast carbon to steel leads to" metal dusting ", a release of metal particles by volume. The methodologies available in the literature to control metal dusting corrosion involve the use of surface coatings and gaseous inhibitors, especially H2S.The coatings can be degraded by interdiffusion of the coating constituents to the alloy substrate. to be appropriate for short-term protection but are generally not advisable for long term protection, especially for twenty or more years.The corrosion inhibitors using E2S have two main disadvantages: One is that H2S tends to poison most catalysts used in hydrocarbon conversion processes ^ Another is that i_2S ne It must be removed from the output process stream, which can be expensive. An object of the present invention is to provide improvements in reducing metal dusting corrosion. • Another object is to provide materials that are resistant to corrosion by dusting metal in petrochemical processes where supersaturated atmospheres of carbon and partial pressure of low oxygen are present. SUMMARY OF THE INVENTION In one aspect, the invention provides a metal dust-resistant composition, comprising: (a) an alloy capable of forming a thermodynamically stable titanium carbide coating on its surface when exposed to a supersaturated carbon environment , and, (b) a protective coating on the alloy surface comprising an outer oxide layer and an inner carbide layer between the alloy surface and the outer layer. In another aspect the invention includes a method for inhibiting metal dusting of metal surfaces exposed to supersaturated carbon environments, which comprises constructing the metal of an alloy or coating a metal surface with an alloy capable of forming a first layer of metal. thermodynamically stable carbide, and a second oxide layer on the first layer, and expose the alloy a supersaturated atmosphere of oxygen partial pressure carbon is lowered at a temperature and for a sufficient time to form an inhibition coating of metal dusting on the metal surface. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a transmission electron microscopic image (TP.M) in cross section of a Ti6A14V alloy after 66 hours at 650 ° C in a supersaturated atmosphere of carbon. ia. Figure 2 is a scanning electron microscopic image (SEM) in cross section of a 1 Cu steel. Mo after four hours at 650 ° C in a supersaturated atmosphere of carbon. Figure 3 is a cross-sectional SEM image of a metal dust-resistant alloy of the invention after _2 Jaoras at 1100 ° C in a supersaturated carbon atmosphere. Figure 4 is a cross-sectional SEM image of an incoloy 800H alloy after 160 hours at 550 ° C in a supersaturated carbon atmosphere. FIG. 5 is a cross-sectional SEM image of a KT.R-45A alloy after 160 hours at 650 ° C in a supersaturated carbon atmosphere. Figure 6 is a cross-sectional SEM image of an Inconel 600 alloy after 90 hours at 550 ° C in a supersaturated atmosphere of carbon. Detailed description of the invention. As mentioned above, in many applications of processing of Jaidrocarburo at elevated temperatures (300 ° C to 900 ° C), stainless steel is used as a structural component in reactors, heat exchange pipes and the like .. When the surface of these members, structural is exposed to a supersaturated carbon environment, is subjected to carbon-induced corrosion known as metal dusting. An object of the present invention is to inhibit said metal dusting. Accordingly, in one aspect of the invention there is provided a composition comprising: (a) a metal alloy capable of forming a thermodynamically stable carbide coating on the surface of the alloy; and (b) a protective coating on the alloy surface comprising a foreign oxide layer and an inner carbide layer between the alloy surface and the outer layer. Thus, in one embodiment of the invention, a structural member of the alloy is formed, (a), and is protected by the coating (b). In a second embodiment, a structural number of an iron alloy substrate, such as stainless steel, is formed, which is provided, on a surface to be exposed to a supersaturated carbon environment, with an alloy (a) and a protective coating (b) - An appropriate class of alloys, (a), of the invention are those that comprise at least 50% by weight of a metal selected from the group consisting of Fe, Ni, or mixtures thereof; at least 10% by weight of Ti, at least 15% by weight of Cr; and about 0.1% by weight to about 25% by weight of alloying components. Suitable alloying components include Mn, al, Si, Y, Zr, Hf, V, β, Ta, Mo, W, Re , Cu, Sn, Ga, C, 0,? and mixtures thereof. Examples of such alloys are given in Table 1 Table 1 Alloy Name% by Weight of Components JSM-FeCrNiTi Rest Fe-25_, lCr-10..2Ni ~ 10 _ 0Ti-0Y2r EM-? ICrTiAl Rest? I-20.0Cr-10. OTi-1.5A1 EM-? ICrCoTiAl Rest? I-15. OCr-15. OCo-10.0Ti-5.5A1 EM-NiCrCoTiMoKAl üesto Ni-18.0Cr-15_ 0Co-10_ 0Ti-3_ OMo- 1.5W-2.5A1 Alloys of this class can be used as structural components or as coatings on steel substrates. Another suitable class of alloys, (a), are those that comprise at least 705 by weight of Ti and from about 0.1% by weight to about 30% by weight of alloying components such as those listed above- Actually an alloy particularly preferred of this class comprises at least 70% by weight of Ti, 0.1% by weight to 30% by weight of Al and 0.0% by weight to 5% by weight of V. The alloys of the second class of preference are used as coatings on steel substrates instead of as structural members. Table 2 Name of Alloy% in Weight of Components Ti64 Rest T1-6A1-4V IMI-550 Rest Ti-4Al-2Sn-4Mo-0.5Si Ti-811 Rest Ti-8Al-lMo-lV IMI-679 Rest Ti-2All- llSn-5Zr-lMJo-0.2Si Ti-6246 Rest Ti-6Al-2Sn-4Zr-6M? Ii-6242 Rest Ti-6Al- Sn-4_Zr-2Mo Hylite 65 Rest Ti-3Al-6Sn-4Zr, 0.5Mo-0.5Si IMI-685 Rest Ti-6Al-5Zr-0.5Mo-0.25Si T1-5522S JResto Ti- 5Al-5Sn-2_Zr ~ 2Mo-0.2Si Ti-11 Rest Ti-6Al-2Sn-1.5Zr-lMo-0.1Si-0.3Bi TÍ-6242S Rest Ti-6Al-2Sn-4Zr-2Mo-0.1Si I1-55 4S Hesto Ti-5Al-5Sn-2Zr-4Mo-0YSi IMI-829 Rest Ti-5.5A1-3.5Sn-3Zr5-0.3Mol ? b-0.31 Si iMI-834 Rest Ti-5.5Al-áSn-áZr-0 ^ 3Mo-lNB- 0.35YES-0.06C Ti-1100 vTi-6Al-2.75Sn-4Zr-0.4MO-0.45Si Beta-21S Rest Ti-15Mo-3Al-2Y5? B-0.25Si JIn cases where a steel substrate is used in forming a structural component, the alloys of the invention can be applied to the surface of the substrate to be exposed to an atmosphere of carburization by techniques such as thermal spraying, plasma deposition, chemical vapor deposition, sputtering and the like. In this embodiment, the alloy deposition should generally have a thickness of from about 10 to about 200 microns, and preferably from about 50 to about 100 microns. A supersaturated carbon atmosphere suitable for forming the protective coating includes those atmospheres generated in hydrocarbon conversion processes such as atmospheres of CO, C02 and H2 generated by steam reforming of methane, or by partial oxidation of methane. Optionally, mixtures of appropriate atmospheres can be prepared such as a mixture of 50 CO: 50 H2. Therefore, the protective coatings can be formed during or before the use of the alloys under reaction conditions in which they are exposed to metal dusting environments. The invention will be further illustrated by the following examples and comparative examples in which the corrosion kinetics of various alloy specimens were investigated by exposing the specimens to an environment of 50CO-50 E2 percent by volume for 160 hours at test temperatures of 550 ° C and 650 ° C, respectively. A Cahn 1000 electrobalance was used to measure carbon collection of the specimen, carbon collection is an indication of metal dusting corrosion. A cross section of the surface of the sample was also examined using a transmission or scanning electron microscope. Example 1 and Comparative Examples 1 to 3 Following the procedure described above, samples of the following alloys were tested: Inconel 600 (7Fe: 77Ni: 16Cr (% by weight)); KHR-45A (20Fe: 45Ni: 35Cr (% by weight) and TÍ6A14V (9QTi: 6Al4 Y (% by weight)). The results of the gravimetric measurements are shown in Table 3. Table 3 No. Alloy Mass gain ' Mass gain (mg / cm2) at 550 ° C (mg / cm2) at 650 ° C Comp 1 inconel 600 120 to 130 60 to 65 Comp 2 KHR-45A 230 to 250 140 to 160 Ex. 1 TÍ6A14V 0.0 0.0 Comp, 3 1 Cr Mo Steel > 2000x > 10001 1 Gain weight measurement was not obtained because substantial amounts of carbon fell out of the sample during the test.

Figure 1 is a cross section TEM image of the T16A14V alloy after 66 hours at 650 ° C in an atmosphere of 50CO-50H2. Figure 2 is a cross-sectional SEM image of the steel 1 Cr ^ steel Mo after 4 hours at 650 ° C in an atmosphere of 50CO-50H2. Fe3C metastable and carbon deposit is clearly present. Example 2 and Comparative Example 4 Two alloys containing titanium were prepared by arc fusion. The alloy of Example 2 contained 55Fe: 25Cr: 10Ni: 10Ti (% by weight). The alloy of Comparative Example 4 contained 60Fe: 25Cr ^ 10Ni 5Ti. { % in weigh). The arc-cast alloys were laminated to thin sheets of 1,588 mm (1/16 inch) thickness. The leaves were annealed at 1100 ° C overnight under an inert argon atmosphere and cooled in an oven at room temperature. Rectangular samples of 12.7 mm x 6.35 mm (0.5 inches x 0.25 inches) were cut from the leaves. The sample faces were polished to 600 grit finish and cleaned in acetone. They were exposed to a gaseous environment of 10CH4-90HX percent by volume at 1100 ° C for 24 hours. In Figure 3 a cross-sectional SEM image of the alloy surface of Example 2 is shown after exposure. In addition to a stable TiG surface layer, both TiC and (Cr, ie) 7Cr carbides were precipitated within the alloy. The stable TiC surface layer was identified as the reason for metal dusting resistance. An SEM image in cross section of the Comparative alloy surface 2 after exposure showed a discontinuous TiC surface layer which would not be very effective in providing metal dusting resistance. Comparative Examples 5 and 6 Commercial alloys containing titanium (Incoloy 800H and Incoloy 803) were also tested for metal dusting by exposing the specimens to a gaseous environment of 50CO-50H2 percent by volume at 550 ° C for up to 160 hours. After exposure to metal dusting, the sample surface was covered with carbon, which always accompanies the corrosion of metal dusting. The corrosion susceptibility by dusting of metal was investigated by optical microscopy and SEM examination of cross section of the corrosion surface. The average diameter and number of corrosion wells observed on the surface are used as a measure of corrosion by dusting metal. These results are summarized in Table 4. Table 4 No. Alloys Composition Number of Wells Diameter (um) Wells by 25 mm2 Comp. 4 Incoloy 800H BalFe: 3 Ni ^ 0Cr: 400 135 0_5Al: 0_4Yes: 0.8Mn Comp. 5 Incoloy 803 BalFe: 35? I: 25C: 100 10 0.5Ti: 1.5Al 1.2Si The Incoloy alloy suffered extensive metal dusting attack as shown in table 4. The electron microscopic image shown in Figure 4 indicates the morphology of sting, characteristic of dusting of metal, in the corroded region. Carbon deposition, which invariably accompanies such an attack, is also seen in Figure 4. The depth of this particular pit defined as a metal recession of the alloy surface is measured at approximately 20 um.

Claims (15)

1. CLAIMS 1. A metal dust-resistant composition comprising: (a) a titanium alloy comprising at least 70% by weight of Ti and from about 0.1% by weight to about 30% by weight of alloying components selected from the group consisting of Mn, Al, Si, Y, Zr, Hf, V, Nb, Ta, Mo,, Re, Cu, Sn, Ga, C, O, N, and mixtures thereof capable of forming a thermally stable carbide coating on its surface when exposed to a supersaturated carbon environment; and, (b) a protective coating on the alloy surface comprising an outer oxide layer and an inner carbide layer between the alloy surface and the outer layer. 2. - The composition according to claim 1, wherein the titanium alloy is deposited on a metal substrate. 3. The composition according to claim 2, wherein the substrate is a steel. 4. The composition according to claim 1, wherein the titanium alloy comprises at least 70% by weight of Ti, 0.1% by weight to 30% by weight of Al and 0.0% by weight to 5% by weight V. The composition according to claim 4, wherein the titanium alloy comprises 90% by weight of Ti, 6% by weight of Al and 4% by weight of V. 6.- A method for inhibit metal dusting of metal apparatuses having surfaces exposed to supersaturated carbon environments, comprising: building the metal apparatus of a titanium alloy or coating the surfaces of the metal apparatus with a titanium alloy comprising at least 70 % by weight of Ti, and from about 0.1% by weight to about 30% by weight of alloy components selected from the group consisting of Mn, Al, Si, Zr, Hf, V, Nb, Ta, Mo, W, Re, Cu, Sn, Ga, C, O, N, and mixtures thereof capable of forming a first layer of thermodynamically stable carbide and a second layer of oxide on the first layer; and exposing the alloy or coating to a supersaturated atmosphere of carbon, partial pressure of oxygen low at a temperature and for a time sufficient to form, a coating of inhibition of dusting of metal on the metal surface. 7. The method according to claim 6, wherein the temperature is on the scale of about 300 ° C to about 1100 ° C and the time is on the scale of about 1 about 200 hours. 8. - The method according to claim 7 wherein the metal apparatus is a steel and is coated with a titanium alloy comprising at least 70% by weight of Ti, 0.1% by weight to 30% by weight of Al and 0.0% by weight to 5% by weight of V 9. A metal dust-resistant composition comprising: (a) a titanium alloy comprising at least 50% by weight of a metal selected from the group consisting of Fe, Ni, Co, and mixtures thereof; at least 50% by weight of Ti, at least 15% by weight of Cr; and about 0.1% by weight to about 25% by weight of alloy components selected from the group consisting of Mn, Al, Si, Y, Zr, Hf, V, Nb, Ta, Mo, Re, Cu, Sn, Ga , C, O, N and mixtures thereof capable of forming a thermally stable coating on its surface when exposed to a supersaturated carbon environment; and (Lb) a protective coating on the alloy surface comprising an outer oxide layer and an inner carbide layer between the alloy surface and the outer layer. 10. The composition according to claim 9, wherein the titanium alloy is deposited on a metal substrate. 11. - The composition according to claim 10, wherein the substrate is a steel. 12. A method for inhibiting metal dusting of metal apparatus having surfaces exposed to supersaturated carbon environments, comprising: constructing the metal apparatus of a titanium alloy and coating the surfaces of the metal apparatus with an alloy of titanium comprising at least 50% by weight of a metal selected from the group consisting of Fe, Ni, Co, and mixtures thereof; at least 105 by weight of Ti, at least 15% by weight of Cr; and about 0.1% by weight to about 25% by weight of alloy components selected from the group consisting of Mn, Al, Si, Y, Zr, Hf, V, Nb, Ta, Mo, W, Re, Cu, Sn, Ga, C, O, N and mixtures thereof capable of forming a first thermodynamically stable carbide layer and a second oxide layer on the first layer; and exposing the alloy or coating to a supersaturated atmosphere of carbon, low partial pressure of oxygen at a temperature and for a time sufficient to form a coating for inhibition of dusting of metal on the metal surface. 13. - The method according to claim 12, wherein the temperature is in the range of about 300 ° C to about 1100 ° C and the time is on the scale of about 1 about 200 hours. 14. The method according to claim 13 wherein the metal apparatus is a titanium alloy comprising at least 10% by weight of Ti, at least 15% by weight of Cr and about 0.1% by weight at about 25% by weight of alloying components. 15. The method according to claim 13, wherein the metal apparatus is a steel and is coated with a titanium alloy comprising at least 10% by weight of Ti, at least 15% by weight of Cr and around from 0.1% by weight to about 25% by weight of alloying components.