Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C30/00—Alloys containing less than 50% by weight of each constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L9/00—Rigid pipes
  • F16L9/006—Rigid pipes specially profiled
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B21/00—Pilgrim-step tube-rolling, i.e. pilger mills
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
  • B21B3/02—Rolling special iron alloys, e.g. stainless steel

Definitions

• the invention relates to a tube to be used in a device for heating of a gas or liquid medium that is transmitted from one end of said tube to the other end thereof while simultaneously being heated such that a chemical reaction occurs.
• the heating can occur for instance by heating the exterior cylindrical tube wall or by providing heating directly through the walls.
• a decomposition of a hydrocarbon occurs.
• the starting materials could be for instance naphta or propane mixed with water vapor.
• the temperature is increased to above 800° C.
• Important products that are being obtained are for instance ethylene and propylene.
• hydrogen gas, methane, butane and other hydrocarbons are being formed.
• the temperature in the furnace can reach 1100- 1200° C -and the tube material temperature in the furnace could be above 1100° C.
• the heating of the furnace room could be obtained by combustion of gases from the cracking process such as hydrogen and methane, and a furnace can be equipped with a large number of gas burners that can be arranged in the floor or in the walls such furnace.
• the tubes that are used in the furnace shall have good shape permanence to heat and shall be able to withstand high temperatures. They must also be resistant towards oxidation and corrosion so as to withstand the atmosphere in the furnace room.
• the carbon potential inside the tubes in the furnace is very high and the tube material should therefor be able to withstand carburization and carbide formation. Minor amounts of sulphur are often being added to the starting material and therefor the tubes must also have good resi-stance towards sulphur and sulphur compounds.
• the present invention relates to a new type of fmned tube to be made of a material that improves resistance towards the environment in furnaces for the cracking of hydrocarbon external to the tube, as well as the particular environmental conditions occurring inside the tube.
• the present invention provides a metal tube for use in furnaces where gas and liquid formed media is being pressed through such tube from its inlet end to its opposite end while being subjected to substantial heating and decomposition therefrom, the metal tube comprising: a body; a smooth outer surface; and an inner surface with a profile; wherein the body is made of a stainless iron-nickel-chromium base alloy comprising, in weight-%: -max 0.08% C, 23-27% Cr, 33-37% Ni, 1.3-1.8% Mn, 1.2-2% Si, 0.08-0.25% N, 0.01-0.15%) rare earth metals, and normal impurities; and the profile comprises a plurality of valleys or recesses, said valleys or recesses extending longitudinally along the tube, and
• Fig. 1 shows a cylinder with a formation in accordance with the invention.
• Fig. 2 shows a cross section of the cylinder embodiment in Fig. 1.
• Fig. 3 shows the weight change during oxidation in air and 1000° C as a function of the exposure time of said tubes.
• Fig. 4 shows schematically how the carburizing profile was measured on rod shaped specimen for analyzing the carbide content.
• Fig. 5 shows the measurement results of the carburizing in terms of area function of carbides.
• a tube 10 is designated having an entry end portion through which a gas formed medium such as hydrocarbon and steam shall be urged towards the exit end portion while undergoing a chemical reaction.
• a gas formed medium such as hydrocarbon and steam shall be urged towards the exit end portion while undergoing a chemical reaction.
• the inner surface 11 of the tube 10 is provided with recesses 13 and ridges 14 of a sinusoidal shaped contour, while the outer surface 16 is substantially smooth or arcuate, see Fig. 2.
• the ridges 14 and the recesses 13 are provided with a rounded profile to avoid fatigue cracks.
• the interiorly provided recesses 13 of the cylinder 10 can be helically provided in the longitudinal direction of said cylinder.
• said tube can be conically shaped from its inlet end to its outlet end.
• the steel material to be selected for such cylinder 10 is a stainless iron-nickel- chromium base alloy with an austenitic structure and otherwise strictly controlled and optimized amounts of alloy constituents.
• the alloy contains, in weight-%, max 0.08% C, 23-27% Cr, 33-37% Ni, 1.3-1.8% Mn, 1.2-2% Si, 0.08-0.25% N, 0.01-0.15% rare earth metals and Fe and normal impurities.
• the amount of rare earth metals are preferably 0.03-0.10% which promotes the formation of a thin elastic adherent oxide film when the material is exposed to oxidizing environment at high temperatures.
• the amount of nitrogen should preferably be 0.13-0.18%, and the amount of silicon should preferably be 1.3-1.8%.
• a further improvement can be achieved by providing a chromium oxide layer on the inner tube surfaces which will prevent the diffusion of carbon into the material by oxidation of said tubes before they are put into usage.
• Fig. 3 illustrates the results of a study of the tendency toward oxide flaking in tubes made of Sanicro 39 type material according to the invention put in relation to some conventional materials that are being used in corresponding applications.
• this study included both forged and cast alloys which are well established materials for cracker tubes in ethylene furnaces, for instance a material marketed by International Nickel Inc. under the designation LNCO 803, one material marketed by Sumitomo Metals Ltd under designation HK4M and a cast alloy with designation HP45-Nb.
• LNCO 803 a material marketed by International Nickel Inc. under the designation LNCO 803
• HK4M one material marketed by Sumitomo Metals Ltd under designation HP45-Nb.
• the diagram in Fig. 3 shows the weight change during oxidation in air at 1000D C as a function of the exposure time for the tubes. As appears from the diagram in Fig. 3 the obtained result shows that the oxides being formed more easily come apart from these reference materials when compared with the material Sanicro 39 selected according to the invention.
• the carburizing tests were carried out so as to be similar to the ethylene environment present in the aforementioned cracker applications by providing shifting carburizing and oxidizing environments.
• the carburizing occurred in a gas mixture comprising carbon monoxide, hydrogen gas and methane in a mixture which was at a temperature of 1050° C and gave an oxygen potential corresponding to 10-15 atm and a carbon activity > 1.
• the time period for the carburizing/oxidizing cycle varied bet- ween 135-140 hours.
• the total testing time was 1104 hours corresponding with 8 cycles as set forth above.
• the temperature was kept constant at 1050° C during the entire first test.
• the geometry of the test rods was 8 mm x 8 mm x 20 mm.
• the test rods were taken out and a cross section thereof was studied by looking upon how the area fraction of carbides varied along a selected line.
• the cross section of said test rods had a square shaped outer surface and with this test rod design it was found that the carbonizing was much depending on where on this outer surface the measurement was made. Areas close to corners and edges appeared to be more sensitive to carbonizing than those surfaces that were planar.
• Fig. 4 it is shown the position of the lines that are analyzed in the cross section of the test rod.
• the first line (Prof 10) was located 0.8 mm (10% of the edge length) into the material along the outer surface.
• the second line (Prof 50) was located 4 mm from a corner whilst being extended through the center of the test rod.
• Fig. 4 it is schematically shown how carburizing varies depending on whether the location is close to an edge or extending far into a planar surface.
• This figure also schematically shows how the carburizing depth varies depending on the distance from a corner.
• the grey marked area represents the carburized area and the white field represents the noncarburized area. It should be noted that the carbonizing depth is larger in the corners of the test rod.
• Fig. 5 the results from the area fraction analysis of carbides are presented.
• the x-axis represents the distance from the start point at one outer surface (0-8 mm) and the y-axis shows the measured area fraction of carbides (%).
• the diagram shows that Sanicro 39 and HP45-Nb are not affected by carburizing from planar surfaces (Prof 50) and out of these two Sanicro 39 appeared with the best resistance towards carburizing in the area close to the corners or the edges (prof 10).
• the alloy 803 was affected by massive carburizing in the comer areas and also appeared with strong carburizing on the planar surfaces.
• the alloy HK4M was subjected to carburizing to its maximum through the entire material.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• General Engineering & Computer Science (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Rigid Pipes And Flexible Pipes (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Manufacture And Refinement Of Metals (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 2000
  • 2000-11-24 SE SE0004336A patent/SE0004336L/sv unknown
• 2001
  • 2001-11-23 BR BR0115397-8A patent/BR0115397A/pt not_active Application Discontinuation
  • 2001-11-23 EA EA200300603A patent/EA004604B1/ru not_active IP Right Cessation
  • 2001-11-23 WO PCT/SE2001/002602 patent/WO2002042510A1/en not_active Application Discontinuation
  • 2001-11-23 JP JP2002545210A patent/JP2004514788A/ja active Pending
  • 2001-11-23 EP EP01997570A patent/EP1339890A1/en not_active Withdrawn
  • 2001-11-23 KR KR10-2003-7006638A patent/KR20030051833A/ko not_active Application Discontinuation
  • 2001-11-23 CA CA002426882A patent/CA2426882A1/en not_active Abandoned
  • 2001-11-26 US US09/991,703 patent/US20020096318A1/en not_active Abandoned
• 2003
  • 2003-05-23 NO NO20032334A patent/NO20032334D0/no not_active Application Discontinuation

Non-Patent Citations (1)

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