Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2003-02-11
2003-09-23
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C138S143000, C138S178000, C148S327000, C148S427000, C148S442000, C420S043000, C420S097000, C420S128000, C420S442000, C420S452000, C420S584100, C428S615000, C428S636000, C428S637000, C428S638000, C428S679000, C428S680000, C428S681000, C428S682000, C428S683000, C428S684000
Reexamination Certificate
active
06623869
ABSTRACT:
TECHNICAL FIELD
This invention relates to a metallic material, which is a high Cr-high Ni—Fe alloy, and a double- or multi-layer metallic material, and a metal tube or pipe made thereof, which each could be used as a container, a reforming tube, a part or the like, exposed to a high-temperature atmosphere in a heat exchanger type reforming unit for hydrocarbon or waste heat recovery system or the like, in a petroleum refinery or petrochemical plant, for instance.
BACKGROUND ARTS
Demand for gases capable of serving as clean energy fuels, for example hydrogen and methanol, is expected to grow very rapidly in the future. To meet such demand, larger-sized reforming units for hydrocarbon further improved in heat efficiency and still more suited for mass production are required. Even in reforming units for hydrocarbon in existing petroleum refining or petrochemical plants, in ammonia production plants, hydrogen production plants or other plants in which petroleum or the like is used as the raw material, the number of heat exchangers in use for waste heat recovery is increasing so that the energy efficiency is continuing to increase.
For efficient utilization of the heat of such high-temperature gases, it is important to carry out heat exchange in a temperature range of 400-700° C., which is lower than the range so far taken into consideration. Thus, corrosion caused by carburizing of high Cr-high Ni—Fe alloy metallic materials, used in reforming tubes, heat exchangers and the like in this temperature range is now a problem.
Usually, in such reactors as mentioned above, a reaction gas, namely a gas containing H
2
, CO, CO
2
, H
2
O and hydrocarbons, such as methane, could be in contact with metallic materials, such as reforming tubes, at a temperature of about 1,000° C. or above. In this temperature range, an element or elements which have a greater oxidation tendency than Fe, Ni and the like are oxidized selectively on the metallic material surface, and corrosion is prevented by the formation of compact oxide films, such as Cr oxide and/or Si oxide. In parts where the temperature is relatively low, such as in heat exchanging parts, however, the diffusion of elements from the inside to the surface of the metallic material becomes insufficient, so that the formation of oxide films, effective in preventing corrosion is delayed, with the result that C atoms are adsorbed on the metallic material surface from the gas and thus C penetrates into the metallic material and causes carburizing.
When the carburizing progresses in such an environment and a carburizing layer, containing carbides of Cr, Fe and/or the like is formed, the volume of that portion expands and develops a tendency to cause microcracks. Furthermore, when C penetrates into a metallic material and the formation of carbides reaches a point of saturation, a metal powder, resulting from decomposition of the carbides, peels off from the metallic material surface and corrosion/wear, called metal dusting, appears. Further, the metal dust, resulting from such peeling, acts as a catalyst and promotes the precipitation of carbon on the metallic material surface. As such wear and/or tube/pipe clogging by precipitation of carbon advances, trouble may occur in a unit or plant, possibly leading to a shutdown. Therefore, due consideration must be given in selecting the material for constructing the unit.
Various measures have been attempted to prevent metal dusting, up to this time. In Japanese laid-open patent application (JP Kokai) H09-78204, for instance, there is disclosed of an invention relating to a Fe-based alloy containing not less than 24% (by weight; hereinafter the same shall apply unless otherwise specified) of Cr and not less than 35% of Ni, a Ni-based alloy containing not less than 20% of Cr and not less than 60% of Ni, and a material derived from such a Fe-based alloy or Ni-based alloy by further addition of Nb, since Fe-based or Ni-based alloys containing 11-60% of Cr are excellent in metal dusting resistance in atmospheric gases containing H
2
, CO, CO
2
and H
2
O at 400-700° C. Generally, however, mere increases in Cr and/or Ni content in Fe-based or Ni-based alloys will not bring about any satisfactory carburizing-inhibiting effect. Therefore, it is necessary to take other measure to still further prevent metal dusting.
The method or technology disclosed in JP Kokai H11-172473 consists in preventing corrosion, for “high-temperature alloys” containing iron, nickel and chromium, resulting from metal dusting, by causing one or more metals of the groups VIII, I
B
, IV and V of the periodic table of the elements or a mixture thereof, to adhere to the surface by conventional physical or chemical means and annealing the same in an inert atmosphere, for the formation of a thin layer which has a thickness of 0.01 to 10 &mgr;m. Thin layers made of Sn, Pb, Bi and the like are allegedly highly effective, among others. This method is initially effective but, when the thinlayer is peeled off after a long period of use, the effect is lost.
Further, a method comprising adding H
2
S to the atmospheric gas is also conceivable. However, since H
2
S may possibly markedly decrease the activity of the catalyst used for hydrocarbon reforming, the application of such method is restricted. As discussed above, in spite of various investigations, a metallic material capable of satisfactorily inhibiting metal dusting is not available at this time.
DISCLOSURE OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a metallic material, which is a high Cr-high Ni—Fe alloy, and a double- or multi-layer metallic material, and a metal tube or pipe made thereof, each of which shows good corrosion resistance in an environment in which metal dusting readily occurs, for example in a gaseous atmosphere containing H
2
, CO, CO
2
, H
2
O and hydrocarbons, among others.
The gist of the present invention is summarized below:
(I) A metallic material having metal dusting resistance which comprises, in mass %, C: not more than 0.2%, Si: 0.01-4%, Mn: 0.05-2%, P: not more than 0.04%, S: not more than 0.015%, Cr: 10-35%, Ni: 30-78%, Al: not less than 0.005% but less than 4.5%, N: 0.005-0.2%, and one or both of Cu: 0.015-3% and Co: 0.015-3%, with the balance substantially being Fe, and of which the fn1 value defined by the formula (1) given below is not less than 50:
fn1=40Si+Ni+5Al+40N+10(Cu+Co) (1),
wherein, in the above formula (1) , the symbols of the elements represent the contents, in mass %, of the elements in the metallic material.
(II) The metallic material having metal dusting resistance as described above under (I) , which is intended for use in an atmosphere at 1,000° C. or below, in which the total content of hydrocarbons, CO and H
2
is not less than 25% by volume and the total content of hydrocarbons and CO is not less than 1% by volume.
(III) A double- or multi-layer metallic material comprising one layer or a plurality of layers made of the metallic material, having metal dusting resistance as described above under (I) , with at least one of the outermost layers being a layer of the above-mentioned metallic material, having metal dusting resistance.
(IV) A metal tube or pipe of which the material is the metallic material having metal dusting resistance as described above under (I).
(V) A double- or multi-layer metal tube or pipe of which the material is the double- or multi-layer metallic material, as described above under (III), with the outer surface being a layer of the metallic material having metal dusting resistance.
In order to increase the metal dusting resistance of the metallic material, having metal dusting resistance as described above under (I), it is possible to cause at least one of the group (a) components specified below to be included in lieu of part of Fe of that metallic material.
(a) Mo: 0.05-10%, Ta: 0.05-5%, W: 0.05-5%, Ti: 0.01-3%, V: 0.01-1%, Zr: 0.01-3%, Nb: 0.01-3% and Hf: 0.01-1%.
In cases where at least one of the above group (a) components
Nishiyama Yoshitaka
Otsuka Nobuo
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