Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Patent
1995-10-26
1997-04-15
Zimmerman, John
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
428685, 138143, 420 52, 420 53, 4205861, B32B 1518, C22C 3844, C22C 3848
Patent
active
056208057
DESCRIPTION:
BRIEF SUMMARY
This application was filed under 35 U.S.C. 371 PCT/JP95/00382, Mar. 8, 1995.
FIELD OF THE INVENTION
The present invention relates to an alloy for a steel tube used in an environment like in a boiler where fuel containing V, Na, S and Cl, for example, crude oil, heavy oil, tar or coal, is burnt on in a refuse incineration environment. The present invention also relates to a multilayer steel tube which exhibits high hot corrosion resistance and high hot erosion resistance in the presence of V.sub.2 O.sub.5, Na.sub.2 SO.sub.4, NaCl, and the like formed in such an environment.
BACKGROUND OF THE INVENTION
In a combustion environment like in a boiler where crude oil, heavy oil, and the like are used as fuel or in refuse incineration, V.sub.2 O.sub.5, Na.sub.2 SO.sub.4, NaCl, KCl and CaSO.sub.4 present in the fuel or formed during combustion adhere to corrosion products such as oxidized scales, and deposit thereon to form a molten salt environment. As a result, a type of corrosion termed vanadium attack and hot corrosion takes place.
Literature on related techniques (e.g., Corrosion, 42, 568 (1986); Iron and Steel, 67, 996 (1981)) illustrates that alloy components such as Cr and Ni have a corrosion resistance to a certain degree to such types of corrosion, particularly to vanadium attack. Moreover, Unexamined Japanese Patent (Kokai) No. 58-177438 discloses an austenitic stainless steel having an improved high temperature corrosion resistance.
On the other hand, many processes are known for producing a double layer tube. For example, there is a process for producing a welded multilayer steel tube, wherein a cladding alloy is temporarily bonded to a carbon steel or low alloy steel, the bonded material is further hot rolled to give a so-called clad steel sheet or plate, and the sheet or plate is subjected to submerged arc welding. There is also a conventional process for producing a multilayer steel tube, wherein a final product is directly clad with a metal. For example, Unexamined Japanese Patent Publication (Kokai) No. 61-223106 discloses a process for directly producing a final product, a multilayer steel tube, comprising cladding a metal material with high alloy powder by hot isostatic pressing. Furthermore, Unexamined Japanese Patent Publication (Kokai) No. 64-17806 discloses a process for producing a multilayer steel tube, though the method for producing a multilayer billet is not clearly described.
DISCLOSURE OF THE INVENTION
When tar, coal, heavy oil, or the like, or combustible refuse containing plastics is used as fuel in installations such as a thermal power plant where fossil fuel or combustible refuse is burnt as an energy source, the combustion products of such a fuel, etc. often contain large amounts of V, Na, S and Cl. Low-melting-point compounds containing V.sub.2 O.sub.5, Na.sub.2 SO.sub.4, NaCl, etc. are, therefore, formed on the surface of the furnace wall tubes, steam superheater tubes, etc. of the thermal power plant or combustion installation. As a result, the scales formed on the tube surface are fused to cause hot corrosion, and the furnace wall tubes, steam superheater tubes, etc., are destroyed during the operation of the thermal power plant or combustion installation over a long period of time.
Furthermore, when coal burning boilers, or refuse incinerators and thermal power plants of the fluidized bed furnace bed type are used, hot erosion caused by combustion ash and fluid sand takes place on the surface of the furnace wall tubes, steam superheater tubes, etc. to promote hot corrosion.
An object of the present invention is to provide, at low cost, an alloy exhibiting a high corrosion resistance and a high erosion resistance in a high temperature combustion environment where V.sub.2 O.sub.5, Na.sub.2 SO.sub.4, NaCl, and the like are present, and a multilayer steel tube comprising the alloy.
As the result of carrying out research on materials suited to a high temperature combustion environment where V.sub.2 O.sub.5, Na.sub.2 SO.sub.4, NaCl, KCl and CaSO.sub.4 are formed during co
REFERENCES:
patent: 4463061 (1984-07-01), Otoguro et al.
patent: 4505232 (1985-03-01), Usami et al.
patent: 5103870 (1992-04-01), Ishii et al.
Rapp, Robert A.; "Chemistry & Electrochemistry of the Hot Corrosion of Metals", Corrosion, vol. 42, No. 10, Oct. 1986, pp. 568-577.
Yoshiba, Masayuki et al., "Hot Corrosion Behavior of Heat Resisting Alloys"; Iron & Steel, vol. 67, No. 7, 1981, pp. 156-165.
Ishitsuka Tetsuo
Nose Koichi
Ogawa Hiroyuki
Nippon Steel Corporation
Zimmerman John
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