Alloys or metallic compositions – Ferrous – Nine percent or more chromium containing
Reexamination Certificate
1999-03-31
2001-05-22
Yee, Deborah (Department: 1742)
Alloys or metallic compositions
Ferrous
Nine percent or more chromium containing
C420S069000
Reexamination Certificate
active
06235238
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the use of low alloy steels in applications involving anti-coking properties. Such steels are primarily intended for the manufacture of the elements of apparatus such as reactors, furnaces or conduits or for coating such apparatus primarily used in refining processes or in the petrochemicals industry, such steels having an improved resistance to coking.
The invention also relates to novel compositions of such steels with an improved resistance to coking.
BACKGROUND OF THE INVENTION
The carbonaceous deposit that develops in furnaces when converting hydrocarbons is generally termed coke. This coke deposit is a nuisance in industrial units. The formation of coke on the walls of tubes and reactors causes a reduction in heat exchange, major blockages and thus an increase in pressure drops. In order to keep the reaction temperature constant, it may be necessary to increase the temperature of the walls, which risks damaging the alloy constituting those walls. A reduction in the selectivity of the facilities, and thus a reduction in yield, is also observed.
Japanese application JP-A-03/10 4843 describes a refractory anti-coking steel for an ethylene cracking furnace tube. However, that steel comprises more than 15% of chromium and nickel and at least 0.4% of manganese. That steel was developed to limit coke formation between 750° C. and 900° C. when cracking ethylene. In addition, United States patent U.S. Pat. No. 5,693,155 concerns petrochemical processes using low coking stainless steels. Such steels contain at least 10% of nickel and at least 10% of chromium. Because of those chromium and nickel contents, such steels are more expensive than those of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, good resistance to coking in the production of elements for furnaces, reactors or conduits is obtained by using a steel with a set composition comprising:
at most 0.25% of C;
1.5% to 5% of Si;
4% to 10% of Cr;
0.5% to 2% of Mo;
0.3% to 1% of Mn;
at most 0.03% of S; and
at most 0.03% of P;
the complement to 100% being essentially iron.
The steels used in the invention can further comprise:
at most 0.1% of Nb;
at most 0.40% of V;
at most 0.10% of N;
at most 0.05% of Al and
at most 0.4% of Ni.
More particularly, the invention makes use of a steel comprising:
about 0.1% of C;
from 1.5 to 3% of Si;
about 9% of Cr;
about 1% of Mo;
about 0.5% of Mn and
at most 0.40% of V;
the complement to 100% being essentially iron.
Also the invention can particularly make use of a steel comprising:
about 0.1% of C;
more than 3% up to 5% of Si;
about 9% of Cr;
about 1% of Mo;
about 0.5% of Mn and
at most 0.40% of V,
the complement to 100% being essentially iron.
In accordance with the invention, it is possible to produce some elements intended for the production of furnaces, reactors or conduits in one piece. In such a case the steels can be manufactured using conventional foundry and casting methods, then formed using the usual techniques to produce, for example, sheets, screens, tubes, profiles, ferrules or plates. These semi-finished products can be used to construct the principal parts for furnaces, reactors or conduits, or simply accessory or auxiliary parts thereof.
In the present invention, these steels can also be used in the form of powders to produce coatings on the internal wafs of furnaces, reactors or conduits. Thus the internal walls of a furnace, reactor or conduit are coated using at least one technique selected from co-centrifugation, the plasma technique, PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), an electrolytic technique, an overlay technique and plating.
The apparatus or elements produced using steels with the composition defined above can be used in refining or petrochemical processes carried out at temperatures of 350° C. to 1100° C., for example catalytic or thermal cracking and dehydrogenation.
As an example, during catalytic reforming, which produces a reformate at temperatures of 450° C. to 650° C., a secondary reaction causes coke formation. This coke formation is catalytically activated by the presence of nickel, iron and/or their oxides.
A further application can be dehydrogenation of isobutane which can produce isobutene at temperatures of 550° C. to 700° C.
The invention also relates to novel steels which can be used in the above applications.
These steels are generally defined as comprising:
at most 0.25% of C;
more than 2.5% and up to 5% of Si;
4% to 10% of Cr;
0.5% to 2% of Mo;
0.3% to 1% of Mn;
at most 0.030% of S; and
at most 0.03% of P;
the complement to 100% being essentially iron.
These steels can also comprise:
at most 0.1% of Nb;
at most 0.40% of V;
at most 0.10% of N;
at most 0.05% of Al; and
at most 0.4% of Ni.
In a first variation of the invention, the steel has the following composition:
about 0.1% of C;
more than 2.5% and up to 3% of Si;
about 9% of Cr;
about 1% of Mo;
about 0.5% of Mn;
at most 0.40% of V;
the complement to 100% being essentially iron.
In a further variation of the invention, the steel has the following composition:
about 0.1% of C;
more than 3% to 5% of Si;
about 9% of Cr;
about 1% of Mo;
about 0.5% of Mn;
at most 0.40% of V;
the complement to 100% being essentially iron.
The entire disclosure of all applications, patents and publications, cited above and below, and of corresponding French application 98/04088, filed Mar. 31, 1998, are hereby incorporated by reference.
REFERENCES:
patent: 1456088 (1923-05-01), Armstrong
patent: 3455681 (1969-07-01), Moskowitz et al.
patent: 4141724 (1979-02-01), Brickner et al.
patent: 4790977 (1988-12-01), Daniels et al.
patent: 0 338 133 (1989-10-01), None
patent: 627628 (1927-10-01), None
patent: 461 251 (1937-02-01), None
Lecour Philippe
Longaygue Xavier
Ropital François
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Yee Deborah
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