GB2234530A - Heat treatment of high temperature steels - Google Patents
Heat treatment of high temperature steels Download PDFInfo
- Publication number
- GB2234530A GB2234530A GB9014419A GB9014419A GB2234530A GB 2234530 A GB2234530 A GB 2234530A GB 9014419 A GB9014419 A GB 9014419A GB 9014419 A GB9014419 A GB 9014419A GB 2234530 A GB2234530 A GB 2234530A
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- GB
- United Kingdom
- Prior art keywords
- weight
- layer
- article
- concentration
- tube
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/10—Oxidising
- C23C8/16—Oxidising using oxygen-containing compounds, e.g. water, carbon dioxide
- C23C8/18—Oxidising of ferrous surfaces
Abstract
A process for heat treatment of high temperature steels is disclosed, the process being characterized by the use of temperatures of at least 1800 DEG F and the presence of hydrogen gas and steam. Articles made by the process and having an outer layer enriched in chromium oxide are also disclosed, as well as utilization in a process for the pyrolysis of liquid or gaseous hydrocarbons to olefins.
Description
HEAT TREATMENT OF HIGH TSYPERATURE STEELS
The invention relates to the heat treatment of high temperature steels, and is particularly relevant to the heat treatment of stainless steels used in pyrolysis units and other high temperature reactors. The invention also relates to the pyrolysis of liquid and gaseous hydrocarbons, particularly to the pyrolysis of such materials to form olefins.
Steels capable of withstanding the high temperatures commonly utilized in various industrial processes, such as the pyrolysis of various hydrocarbon materials, are well known. A problem common to a number of such processes is that of the formation of "coke", a carbon-rich material which forms deposits on the surfaces defining the reaction zone and in downstream quench equipment. Coke represents a substantial deficit in operations, since it restricts flow and is a thermal insulator. Thus, as coke deposits on the reactor surfaces, higher and higher tube wall temperatures are required to sustain the reaction or process in operation.
A common practice conducted in such operations is known as "de-coking". To carry out de-coking, process operations are periodically discontinued and the deposits are removed by various techniques, e.g., by oxidation with a steam/air mixture. The required downtime results in substantial loss of operation or production, and much effort has been expended in attempts to extend the time between de-coking.
Evidence exists that nickel and iron in the steels used for reactors promote coking in certain temperature ranges. A variety of techniques have been employed to overcome the presence of the nickel and iron, with varying results . Accordingly, a technique or equipment which might extend the time before de-coking is required and/or inhibit coking so that the process operations might be carried out at greater severities would have great economic value. Also, a pyrolysis process having these characteristics would be of great importance. The invention is directed to such.
Accordingly, in one embodiment, the invention is directed to a process for heat treatment of an article of high temperature steel comprising heating at least one surface or portion of said article to a temperature of at least 18000F in the presence of hydrogen and steam for a time sufficient to produce a surface layer having a concentration of chromium greater than that of the interior of the article, the concentration of nickel of the outermost portion of said surface layer being less than three percent by weight, based on the weight of the layer, the molar ratio of hydrogen to steam being from 0.05 to 5. Unless stated otherwise, all ratios given herein are molar ratios.
In another embodiment, the invention is directed to an article of manufacture comprising an article or blank of high temperature steel, at least a portion of one side of the article or blank comprising a surface layer having a concentration of chromium greater than that of the interior of the article or blank, the concentration of nickel of the outermost portion of said surface layer being less than about three percent by weight, based on the weight of the layer. Preferably, the article comprises a tube of high temperature steel, at least a portion of the outer side of the tube comprising a surface layer having a concentration of chromium greater than that of the interior of the tube (tube wall), the concentration of nickel of the outermost portion of said surface layer being less than about three percent by weight, based on the weight of the layer.Alternately, the article may comprise a tube of high temperature steel, at least a portion of the inner side of the tube comprising a surface layer having a concentration of chromium greater than that of the interior of the tube (tube wall), the concentration of nickel of the outermost portion of said surface layer being less than about three percent by weight, based on the weight of the layer.Most preferably, the articles are formed by heating at least a portion of the inner or outer surface of the article to a temperature of at least 1800"F in the presence of hydrogen and steam for a time sufficient to produce a surface layer having a concentration of chromium greater than the interior of the article and a concentration of nickel of the outermost portion of said surface layer of the article of less than three percent by weight, based on the weight of the layer, the ratio of hydrogen to steam being from 0.05 to 5.
In another embodiment, the invention is directed to a process comprising a) pyrolyzing a liquid or gaseous hydrocarbon material in a high temperature steel pyrolysis reactor; b) discontinuing pyrolyzing said material, and de-coking the surface or surfaces which define the reaction zone of said reactor; c) discontinuing the de-coking of said surface or surfaces; and d) heating at least a portion of the surface of the wall or walls of high temperature steel which define the reaction zone of said reactor to a temperature of at least 18000 F, in the presence of hydrogen and steam, for a time sufficient to produce or provide a surface layer on at least a portion of said wall or walls having a chromium concentration greater than that of the interior of said wall or walls and a concentration of nickel in at least the outermost portion of said surface layer of less than three percent by weight, based on the weight of the layer, the ratio of hydrogen to steam being from 0.05 to 5.0.
The term "hydrogen", as used herein, includes the use of pure hydrogen as well as streams containing large amounts of other gaseous materials, provided that they do not interfere with the nickel concentration reduction phenomena described herein. For example, the hydrogen may be supplied from streams commonly found in chemical operations or in refineries. The hydrogen ( and steam ) will be supplied in an amount sufficient to reduce the nickel to the level mentioned. However, significant amounts of components that inhibit or prevent the reduction of nickel concentration must be avoided.While applicants have no desire to be bound by any theory of invention, it is believed that the hydrogen and steam selectively oxidize the surface of the steel to provide a build up of chromium oxide, and there is also support for the migration of nickel and iron to the interior of the metal structure.
Accordingly, the heat treatment is carried out in the absence of materials which might maintain the presence of nickel in undesired concentrations at the surface in contact with the gases. In this regard, as described in the aforementioned application, the presence of significant amounts of methane as a component of various streams has been found to maintain the nickel concentration, and is deleterious to the treatment process of the invention. Thus, in the present invention, significant quantities of methane or hydrocarbons which form methane under the conditions of the heat treatment described herein are to be avoided.
In a similar manner, the steam need not be pure, provided that compositions that prevent the increase of chromium or the reduction of nickel concentration are avoided. Those skilled in the art may readily determine the suitability of a given stream for the process of the invention simply by testing it at appropriate temperatures.
The heat treatment is carried out, as indicated, at a temperature of at least 1800 F, preferably l9OO F or 19250to about 2200"F. Pressures are not critical, ranging from one atmosphere to one hundred atmospheres or more. Similarly, volumes and velocities of the gases employed are not critical, as will be understood by those skilled in the art, and will be adjusted depending on the need to maintain the appropriate temperature and gas composition. As indicated, the hydrogen to steam ratio will be maintained from 0.05 to 5, preferably 0.05 to 2.
The heat treatment is carried out for a time sufficient to achieve the desired reduction of nickel concentration. This may be determined by experimentation, i.e., by treatment of the surface for a time and then analysis of the surface. In general, the treatment will be carried out for a period of from 2 hours to 24 hours, preferably from 4 hours to 6 hours.
The types of steels employed are those commonly used for high temperature purposes, i.e., 1500"F to 2200"F. Preferred steels are those commonly described as austenitic, but other steels may be employed.Suitable steels include cast or wrought heat resistant stainless steels such as HK-40 and Incoloy 800, and will generally include those steels having minimum nickel concentrations of about 8 percent and chromium concentrations of at least 15 percent, all percentages based on the total weight of the steel.
It has been determined that the heat treatment of the invention produces a chromium oxide layer strongly depleted in nickel and iron, relative to their content in the steel, i.e., enriched in chromium, on the surface of the steel, the oxide layer being from 1 to 5 microns or so in depth. This effect occurs whether or not the steel is virgin metal or carburized metal. The layer will comprise an outer or "sub-layer" which is highly enriched in chromium, the chromium present substantially or substantially completely as chromium oxide (Cr203), and the chromium concentration decreasing in a gradient toward the interior of the steel, the sub-layer, which will be of at least 0.1 to 0.2 microns in thickness, having a nickel concentration of less than three percent by weight, as noted.Articles produced according to the invention have been determined to maintain low nickel concentrations on subsequent exposure to various atmospheres including steam/hydrogen sulfide/methane. However, articles made according to the invention and subsequently heat treated at lower temperatures with hydrogen and steam increase nickel and iron concentrations near their surfaces.
The particular manner of pyrolysis and the method of de-coking form no part of the invention, and may suitably be carried out by those skilled in the art. For example, those procedures, materials, and conditions described in U.S. patent 3,433,731 and
U.S. patent 4,279,734 may be used.
Illustrative Embodiments
The following experiments were performed.
I.
A coupon of HK-40, a high temperature stainless steel, was heated at about 17500F in the presence of hydrogen and steam for a period of about two hours, the molar ratio of hydrogen to steam being 50 to one. A surface layer somewhat enriched in chromium oxide, but having only a slightly reduced content of Ni and iron, of about 0.1 to 0.2 microns was produced.
II.
In the manner of the invention, a coupon of HK-40 was heated at about 19500F in the presence of hydrogen and steam for a period of about two hours, the molar ratio of hydrogen to steam being 1 to 4. A surface layer enriched in chromium oxide of about 1 to 2 microns was produced, the layer being substantially depleted in Ni and iron (less than three percent by weight nickel in the upper 0.1 to 0.2 microns of the layer, based on the weight of the layer).
In order to describe the pyrolysis aspect of the invention, the following illustrative embodiment is given. All values are exemplary or illustrative.
Accordingly, naphtha is pyrolyzed under suitable conditions until it is determined by measurement of pressure drop or outer tube wall temperature that excess coke is present on the tube surfaces of a conventional pyrolysis reactor. Alternatively, de-coking may be carried out as a regularly scheduled procedure in plant operation. Whatever the case, the reaction is discontinued, and the reactor is then de-coked according to standard procedure, e.g., utilization of steam/air to burn the coke off. De-coking is then stopped, and the heat treatment of the invention is begun.
Preferably, the pyrolysis reactor is swept with a diluent gas, such as nitrogen or steam, and hydrogen is introduced. Steam is mixed with the hydrogen so that the tubes of the reactor are treated with a mixture of steam and hydrogen having a ratio of 1.1 parts steam to 1 part hydrogen (molar basis). By way of illustration, assuming a steam flow of 10,000 pounds of steam per hour, about 1000 pounds of hydrogen will be used. The temperature is maintained at about 1950"F, and the treatment is carried out for about 4 hours. At this point the flow of the steam-hydrogen mixture is stopped, and the pyrolysis reaction is resumed.
Various changes and modifications may be made without departing from the spirit and scope of the invention, as will be apparent to those skilled in the art.
Claims (9)
1. An article of manufacture comprising an article of high temperature steel, at least a portion of the article comprising a surface layer having a chromium concentration greater than that of the interior of the article, the chromium present at least substantially as chromium oxide, and having a concentration of nickel in the outermost portion of said surface layer of less than about three percent by weight, based on the weight of the layer.
2. An article of manufacture comprising a tube of high temperature steel, at least a portion of the outer side of the tube comprising a surface layer having a chromium concentration greater than that of the interior of the tube, the chromium present at least substantially as chromium oxide, and having a concentration of nickel in the outermost portion of said surface layer of less than about three percent by weight, based on the weight of the layer.
3. An article of manufacture comprising a tube of high temperature steel, at least a portion of the inner side of the tube comprising a surface layer having a chromium concentration-greater than that-of the interior of said tube, the chromium being present at least substantially as chromium oxide, and having a concentration of nickel in the outermost portion of said surface layer of less than about three percent by weight, based on the weight of the layer.
4. A process for heat treatment of an article of high temperature steel comprising
heating at least a portion of said article to a temperature of at least 1800"F in the presence of hydrogen and steam for a time sufficient to produce a surface layer on said article having a concentration of chromium greater than that of the interior of the article, the concentration of nickel of the outermost portion of said surface layer being less than about three percent by weight, based on the weight of the layer, the ratio of hydrogen to steam being from about 0.05 to about 5.0.
5. An article of manufacture comprising an article of high temperature steel, at least a portion of the surface of the article comprising a surface layer having a chromium concentration greater than that of the interior of said article, the chromium being present at least substantially as chromium oxide, and having a nickel concentration of less than about three percent by weight, based on the weight of the layer, the layer being formed by heating an article of high temperature steel to a temperature of at least 1800 F in the presence of hydrogen and steam for a time sufficient to reduce the concentration of nickel of a surface layer of said article to less than three percent by weight, based on the weight of the layer, the ratio of hydrogen to steam being from 0.05 to 5.0.
6. An article of manufacture comprising a tube of high temperature steel, at least a portion of the outer side of the tube comprising a surface layer having a chromium concentration greater than that of the interior of the tube, and having a concentration of nickel of the outermost portion of said layer of less than about three percent by weight, based on the weight of the layer, the layer being formed by heating a tube of high temperature steel to a temperature of at least 1800"F in the presence of hydrogen and steam for a time sufficient to reduce the concentration of nickel of a surface layer of said tube to less than three percent by weight, based on the weight of the 'ayer, the ratio of hydrogen to steam being from 0.05 to 5.0.
7. An article of manufacture comprising a tube of high temperature steel, at least a portion of the inner side of the tube comprising a surface layer having a chromium concentration greater than that of the interior of the tube, and having a concentration of nickel of the outermost portion of said layer of less than about three percent by weight, based on the weight of the layer, the layer being formed by heating a tube of high temperature steel to a temperature of at least 1800"F in the presence of hydrogen and steam for a time sufficient to reduce the concentration of nickel of a surface layer of said tube to less than three percent by weight, based on the weight of the layer, the ratio of hydrogen to steam being from 0.05 to 5.0.
8. A process comprising a) pyrolyzing a liquid or gaseous hydrocarbon material in a high temperature steel pyrolysis reactor; b) discontinuing pyrolyzing said material, and de-coking the surface or surfaces which define the reaction zone of said reactor; c) discontinuing the de-coking of said surface or surfaces; d) heating at least a portion of the surface of the wall or walls of high temperature steel which define the reaction zone of said reactor to a temperature of at least 18000F in the presence of hydrogen and steam for a time sufficient to produce a surface layer on said wall or walls having a chromium concentration greater than that of the interior of said wall or walls and a concentration of nickel of at least the outermost portion of said surface layer of less than three percent by weight, based on the weight of the layer, the ratio of hydrogen to steam being from 0.05 to 5.0.
9.
The process of claim 8 wherein pyrolysis of the liquid or gaseous hydrocarbon is resumed after the heating of step d).
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US37437589A | 1989-06-30 | 1989-06-30 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9014419D0 GB9014419D0 (en) | 1990-08-22 |
| GB2234530A true GB2234530A (en) | 1991-02-06 |
Family
ID=23476540
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9014419A Withdrawn GB2234530A (en) | 1989-06-30 | 1990-06-28 | Heat treatment of high temperature steels |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2234530A (en) |
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0510950A1 (en) * | 1991-04-26 | 1992-10-28 | Ngk Insulators, Ltd. | Treatment of sintered alloys |
| EP0576067A1 (en) * | 1992-06-25 | 1993-12-29 | General Motors Corporation | Hydrogen-water vapour pre-treatment of Fe-Cr-Al alloys |
| US5406014A (en) * | 1993-01-04 | 1995-04-11 | Chevron Research And Technology Company | Dehydrogenation processes, equipment and catalyst loads therefor |
| US5405525A (en) * | 1993-01-04 | 1995-04-11 | Chevron Research And Technology Company | Treating and desulfiding sulfided steels in low-sulfur reforming processes |
| EP0647726A1 (en) * | 1993-10-06 | 1995-04-12 | Messer Griesheim Gmbh | Method for treatment of pieces |
| US5413700A (en) * | 1993-01-04 | 1995-05-09 | Chevron Research And Technology Company | Treating oxidized steels in low-sulfur reforming processes |
| DE19523637A1 (en) * | 1994-12-27 | 1996-07-04 | Mtu Friedrichshafen Gmbh | Corrosion protective layer for substrate against high temp. carburising atmos. |
| US5575902A (en) | 1994-01-04 | 1996-11-19 | Chevron Chemical Company | Cracking processes |
| US5674376A (en) | 1991-03-08 | 1997-10-07 | Chevron Chemical Company | Low sufur reforming process |
| US5866743A (en) | 1993-01-04 | 1999-02-02 | Chevron Chemical Company | Hydrodealkylation processes |
| US6093260A (en) * | 1996-04-30 | 2000-07-25 | Surface Engineered Products Corp. | Surface alloyed high temperature alloys |
| US6258256B1 (en) | 1994-01-04 | 2001-07-10 | Chevron Phillips Chemical Company Lp | Cracking processes |
| US6274113B1 (en) | 1994-01-04 | 2001-08-14 | Chevron Phillips Chemical Company Lp | Increasing production in hydrocarbon conversion processes |
| US6419986B1 (en) | 1997-01-10 | 2002-07-16 | Chevron Phillips Chemical Company Ip | Method for removing reactive metal from a reactor system |
| US6503347B1 (en) | 1996-04-30 | 2003-01-07 | Surface Engineered Products Corporation | Surface alloyed high temperature alloys |
| USRE38532E1 (en) | 1993-01-04 | 2004-06-08 | Chevron Phillips Chemical Company Lp | Hydrodealkylation processes |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1075045A (en) * | 1964-04-02 | 1967-07-12 | Owens Illinois Inc | Oxidation of chromium-contaning alloys |
| GB1205250A (en) * | 1966-10-21 | 1970-09-16 | Toyo Kogyo Kabushiki Kaisha | Heat resistant alloy steel |
| GB2001677A (en) * | 1977-07-27 | 1979-02-07 | Hultquist G | Oxidising iron-chromium alloys in vacuum |
| US4266987A (en) * | 1977-04-25 | 1981-05-12 | Kennecott Copper Corporation | Process for providing acid-resistant oxide layers on alloys |
| GB2092621A (en) * | 1981-02-06 | 1982-08-18 | Maschf Augsburg Nuernberg Ag | Forming oxide layer on alloy steels |
| GB2093073A (en) * | 1981-02-06 | 1982-08-25 | Maschf Augsburg Nuernberg Ag | A method of producing protective oxide layers |
| GB2097821A (en) * | 1981-05-01 | 1982-11-10 | Atomic Energy Authority Uk | Carbon deposition inhibition |
| GB2190923A (en) * | 1986-05-13 | 1987-12-02 | Nisshin Steel Co Ltd | Metal sheet for sealing to soft glass |
-
1990
- 1990-06-28 GB GB9014419A patent/GB2234530A/en not_active Withdrawn
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1075045A (en) * | 1964-04-02 | 1967-07-12 | Owens Illinois Inc | Oxidation of chromium-contaning alloys |
| GB1205250A (en) * | 1966-10-21 | 1970-09-16 | Toyo Kogyo Kabushiki Kaisha | Heat resistant alloy steel |
| US4266987A (en) * | 1977-04-25 | 1981-05-12 | Kennecott Copper Corporation | Process for providing acid-resistant oxide layers on alloys |
| GB2001677A (en) * | 1977-07-27 | 1979-02-07 | Hultquist G | Oxidising iron-chromium alloys in vacuum |
| GB2092621A (en) * | 1981-02-06 | 1982-08-18 | Maschf Augsburg Nuernberg Ag | Forming oxide layer on alloy steels |
| GB2093073A (en) * | 1981-02-06 | 1982-08-25 | Maschf Augsburg Nuernberg Ag | A method of producing protective oxide layers |
| GB2097821A (en) * | 1981-05-01 | 1982-11-10 | Atomic Energy Authority Uk | Carbon deposition inhibition |
| GB2190923A (en) * | 1986-05-13 | 1987-12-02 | Nisshin Steel Co Ltd | Metal sheet for sealing to soft glass |
Cited By (25)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5674376A (en) | 1991-03-08 | 1997-10-07 | Chevron Chemical Company | Low sufur reforming process |
| US6548030B2 (en) | 1991-03-08 | 2003-04-15 | Chevron Phillips Chemical Company Lp | Apparatus for hydrocarbon processing |
| US5863418A (en) | 1991-03-08 | 1999-01-26 | Chevron Chemical Company | Low-sulfur reforming process |
| US5676821A (en) | 1991-03-08 | 1997-10-14 | Chevron Chemical Company | Method for increasing carburization resistance |
| US5288345A (en) * | 1991-04-26 | 1994-02-22 | Ngk Insulators, Inc. | Method for treating sintered alloy |
| EP0510950A1 (en) * | 1991-04-26 | 1992-10-28 | Ngk Insulators, Ltd. | Treatment of sintered alloys |
| EP0576067A1 (en) * | 1992-06-25 | 1993-12-29 | General Motors Corporation | Hydrogen-water vapour pre-treatment of Fe-Cr-Al alloys |
| US5723707A (en) | 1993-01-04 | 1998-03-03 | Chevron Chemical Company | Dehydrogenation processes, equipment and catalyst loads therefor |
| US5406014A (en) * | 1993-01-04 | 1995-04-11 | Chevron Research And Technology Company | Dehydrogenation processes, equipment and catalyst loads therefor |
| US5593571A (en) | 1993-01-04 | 1997-01-14 | Chevron Chemical Company | Treating oxidized steels in low-sulfur reforming processes |
| USRE38532E1 (en) | 1993-01-04 | 2004-06-08 | Chevron Phillips Chemical Company Lp | Hydrodealkylation processes |
| US5413700A (en) * | 1993-01-04 | 1995-05-09 | Chevron Research And Technology Company | Treating oxidized steels in low-sulfur reforming processes |
| US5405525A (en) * | 1993-01-04 | 1995-04-11 | Chevron Research And Technology Company | Treating and desulfiding sulfided steels in low-sulfur reforming processes |
| US5866743A (en) | 1993-01-04 | 1999-02-02 | Chevron Chemical Company | Hydrodealkylation processes |
| EP0647726A1 (en) * | 1993-10-06 | 1995-04-12 | Messer Griesheim Gmbh | Method for treatment of pieces |
| US6258256B1 (en) | 1994-01-04 | 2001-07-10 | Chevron Phillips Chemical Company Lp | Cracking processes |
| US5575902A (en) | 1994-01-04 | 1996-11-19 | Chevron Chemical Company | Cracking processes |
| US6274113B1 (en) | 1994-01-04 | 2001-08-14 | Chevron Phillips Chemical Company Lp | Increasing production in hydrocarbon conversion processes |
| US6602483B2 (en) | 1994-01-04 | 2003-08-05 | Chevron Phillips Chemical Company Lp | Increasing production in hydrocarbon conversion processes |
| DE19523637A1 (en) * | 1994-12-27 | 1996-07-04 | Mtu Friedrichshafen Gmbh | Corrosion protective layer for substrate against high temp. carburising atmos. |
| US6268067B1 (en) | 1996-04-30 | 2001-07-31 | Surface Engineered Products Corporation | Surfaced alloyed high temperature alloys |
| US6503347B1 (en) | 1996-04-30 | 2003-01-07 | Surface Engineered Products Corporation | Surface alloyed high temperature alloys |
| US6093260A (en) * | 1996-04-30 | 2000-07-25 | Surface Engineered Products Corp. | Surface alloyed high temperature alloys |
| US6419986B1 (en) | 1997-01-10 | 2002-07-16 | Chevron Phillips Chemical Company Ip | Method for removing reactive metal from a reactor system |
| US6551660B2 (en) | 1997-01-10 | 2003-04-22 | Chevron Phillips Chemical Company Lp | Method for removing reactive metal from a reactor system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9014419D0 (en) | 1990-08-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |