Classifications

• • 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
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/14—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying for coating elongate material
  • C23C4/16—Wires; Tubes
• • 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
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/18—After-treatment
• • 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
  • F16L58/00—Protection of pipes or pipe fittings against corrosion or incrustation
  • F16L58/02—Protection of pipes or pipe fittings against corrosion or incrustation by means of internal or external coatings
  • F16L58/04—Coatings characterised by the materials used
  • F16L58/08—Coatings characterised by the materials used by metal
• • 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
  • F16L58/00—Protection of pipes or pipe fittings against corrosion or incrustation
  • F16L58/02—Protection of pipes or pipe fittings against corrosion or incrustation by means of internal or external coatings
  • F16L58/04—Coatings characterised by the materials used
  • F16L58/10—Coatings characterised by the materials used by rubber or plastics
  • F16L58/1054—Coatings characterised by the materials used by rubber or plastics the coating being placed outside the pipe
  • F16L58/1072—Coatings characterised by the materials used by rubber or plastics the coating being placed outside the pipe the coating being a sprayed layer

Definitions

• This invention concerns tubes for environments, where the tubes are exposed to high temperatures and aggressive environments.
• the invention also concerns ways of manufacturing such tubes and the use of such tubes.
• tubes according to this invention are radiant tubes for the treatment, melting and heating of metallic and ceramic materials, tubes for heat exchangers and recuperators as well as thermocouple protection tubes for the measurements of high temperatures using thermocouples.
• Radiant tubes are used in industrial furnaces, which are used for many different purposes and with varying atmospheres in the furnaces. Radiant tubes in furnaces are constantly exposed to corrosive atmospheres of different kinds. Oxidizing environments are common as well as strongly carburizing and sulphur containing environments. The temperature conditions can be unsuitable for the service life o the tubes. Both a very high temperature as well as specific temperature intervals below the highest temperature of application, can cause corrosion damages as well as other damages to quickly appear on the tubes. Both temperature conditions as well as other conditions can vary in a furnace, in continous furnaces are, for example, often the temperature lower in the inlet part ofthe furnace.
• NiCr- and NiCrFe-alloys have limited service lives.
• NiCr- and FeNiCr-alloys are alloyed with Si (silicon) to receive a surface layer of Si ⁇ 2 as protection to attacks from a corrosive atmosphere.
• FeCrAl-alloys have been used for radiant tubes, among other things due to the advantageous properties of these alloys in strongly carburizing and sulphur containing atmospheres.
• the FeCrAl-alloys contain aluminium, which forms a layer of a thin aluminium oxide, which has a good resistance in most ofthe furnace atmospheres that are common today.
• the protecting aluminium oxide layer which forms on the surface do efficiently protect the base material from most corrosive environments.
• the FeCrAl-alloys spontanously form aluminium oxide if the temperature is high enough and if the atmosphere contains oxygen.
• the protecting aluminium oxide layer there are applications where this is not enough and as a result not even FeCrAl-tubes display enough good properties.
• the formation and the preservation ofthe protecting layer also require that the radiant tubes are surrounded by an atmosphere containing a high enough oxygen content.
• NiCr-, FeNiCr- and FeCrAl-alloys can be used in many applications and in different atmospheres, but in certain applications, a satisfactorily service life of tubes in these alloys are not achieved.
• the present invention makes it possible to avoid quick failures in furnaces and other applications with, for other tubes, an unsuitable atmosphere and/or temperature. This is also of increasing interest in continous heat treatment processes, where a production stop is of great disadvantage in planning and costs. This invention makes it possible to work with longer periods between production stops for maintenance works.
• the purpose ofthe present invention is that during certain special conditions concerning for example atmospheres or temperature ranges, to achieve a prolonged service life for tubes.
• This purpose is achieved by the present invention, which concerns tubes with a coating which reinforces the protective oxide layers with, primarily, aluminium oxide.
• the invention concerns also ways of manufacturing such tubes as well as the use of such tubes.
• a surface layer of aluminium and/or aluminium oxide is brought onto the tube, whereafter the tube is heat treated at about 1050 C at enough long time, whereby the aluminium oxide layer on the FeCrAl-alloys are improved and the NiCr- and FeNiCr-alloys are given an aluminium oxide layer as protection in corrosive environments.
• the purpose ofthe coating is to significantly increase the service life for critical applications and at increased service temperatures for tubes in these alloys. The good properties ofthe aluminium oxide are in this way utilized in most atmospheres where these alloys earlier could not be used.
• Tubes according to this invention give advantages in many different areas of applications, among which the following examples can be given:
• thermoelements used to measure the temperature of metal melts of aluminium and zinc.
• the tubes are lowered into the melt for a shorter or a longer period of time.
• the coatmg is performed with a thick aluminium oxide layer followed by a preoxidation.
• the tubes both NiCr-, FeNiCr- and FeCrAl-tubes, with a thick aluminium oxide layer and perform a preoxidation afterwards, the protection and therefore also the service life, are significantly improved.
• the purpose of this invention is to improve the aluminium oxide layer of the FeCrAl-alloys and to give the NiCr- and FeNiCr-alloys an aluminium oxide layer, as protection in a corrosive environment.
• the purpose ofthe coating is to significantly increase the service life in critical applications as well as increased service temperatures for the NiCr- and FeNiCr-alloys.
• tubes for the use at high temperatures or any other aggressive environment are coated with a coating of a layer of aluminium and aluminium oxide with a thickness of at least 0,3 mm, on the outside ofthe tube.
• a coating of a layer of aluminium and aluminium oxide with a thickness of at least 0,3 mm on the outside ofthe tube.
• it is suitable to coat the tube with many layers and perform an oxidation of every coated layer before next layer is put on usually the coating is made with 2 or 3 layers to a layer thickness of 0,3-0,7 mm, preferable ca 0,5 mm.
• Suitable methods for coating are flame spraying, high velocity spraying, plasma spraying or other ways of thermal spraying or a combination of these methods.
• the material which is put on is aluminium or possibly a mixture of aluminium and aluminium oxide.
• aluminium also means alloys of aluminium with small amounts of alloy additions, preferably less than 5 weight percent.
• a substantial amount ofthe coating material oxidizes, and the coating often contains a large amount of aluminium oxide.
• a heat treatment is performed, which causes the coatmg material to completely transform into aluminium oxide. This treatment means heating to ca 1050 C during at least four hours. This procedure gives an aluminium oxide layer, which is not sensitive to mechanical damage and which stays on also at low temperatures, where one cannot expect spontanous aluminium oxide formation to occur.
• FIG. 1-2 One example of the use of a tube according the mvention is shown in figures 1-2, which showns a dosing furnace for melted aluminium.
• Figure 1 is a side view ofthe cross section ofthe furnace.
• FIG. 1 shows the furnace from above with the cover removed.
• the tube consists, according to the invention, by a high temperature alloy, on which a 0,5 mm thick surface layer has been put on, distributed on two separate layers, according to the desription above.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Physics & Mathematics (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Rigid Pipes And Flexible Pipes (AREA)
• Laminated Bodies (AREA)
• Coating By Spraying Or Casting (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=20284951

Family Applications (1)

Country Status (3)

Family Cites Families (3)

• 2001
  • 2001-07-27 SE SE0102626A patent/SE522102C2/sv not_active IP Right Cessation
• 2002
  • 2002-07-26 WO PCT/SE2002/001418 patent/WO2003012168A1/en not_active Ceased
  • 2002-07-26 EP EP02751943A patent/EP1423554A1/de not_active Withdrawn

Non-Patent Citations (1)

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