Metal treatment – Stock – Ferrous
Reexamination Certificate
2002-03-13
2003-11-18
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Ferrous
C148S541000, C148S547000, C420S110000, C420S111000
Reexamination Certificate
active
06648991
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to certain kinds of steel having a higher resistance to corrosion for their application in the manufacture of pipes used for oil and/or gas exploration and production in the petroleum industry. Particularly, the invention refers to a low-carbon steel having an improved resistance to corrosion, which is suitable for applications in the oil industry and particularly in environments containing CO
2
.
BACKGROUND OF THE INVENTION
Corrosion has a wide range of implications on the integrity of materials used in the oil industry. Among the different ways in which corrosion may appear there is the so-called “sweet corrosion” that occurs in the media rich in CO
2
. This is one of the prevailing ways of corrosion that must be faced when producing oil and gas.
The damage produced by corrosion caused by CO
2
has an impact on capital and operational investment, as well as on health, security, and environmental impact. In general terms, 60% of the failures occurring in the oil wells are the result of the corrosion caused by CO
2
. This is mainly due to the poor resistance depicted by the low-alloy carbon steel commonly used in the oil producing industry when faced to this kind of attacks.
It has been shown that, despite the extensive research carried out during the last years in connection with the poor resistance to the corrosion caused by CO
2
observed in the low-alloy carbon steel, this has only led to the over-specification of materials, adversely impacting on the oil and gas production costs.
Carbon steel is usually used in tubes for the production of oil, for example J55, N80 or P110, having the following typical composition ranges: C: 0.20-0.45%; Si: 0.15-0.40%; Mn: 0.60-1.60%; S: 0.03% maximum; P: 0.03% maximum; Cr: 1.60% maximum; Ni: 0.50% maximum; Mo: 0.70% maximum; and Cu: 0.25% maximum.
Corrosion inhibitors have been generally used to offset the corrosive influence of the fluid medium present in an oil exploration and production facility. These inhibitors may be added to the fluid or to the injection water. To that end, filmogenic amines are commonly used. They act by generating a protective film over the metal surface, which protects such surface against the aggressive fluid. They are applied at constant doses of 8-20 mg/l or in weekly batches of 100-200 mg/l. However, these additions largely increase production costs.
As an attempt to counteract the corrosive influence of the fluid media present in an oil production facility, low-alloy carbon steel provided with different kinds of linings such as epoxy-type polymer resins or ceramic linings have been used.
Apart from their cost, these linings are severely damaged by the different tools used while working in the installation inside the well.
Due to the reasons mentioned above herein, the search has recently focused on the production of corrosion-resistant materials, which would make it possible to avoid the addition of such inhibitors and to eliminate pipe-linings.
A proposal was made to use high-chromium steel containing 10% by weight of Cr or more in the manufacture of production tubing. This kind of stainless steel, particularly stainless steel such as AISI420, AISI316, and Duplex (Cr: 22%) with a Cr content going from approximately 12 to 22%, regardless of the fact they have a desirable behavior against corrosion, have a high cost as their main disadvantage. This cost varies between 3 to 15 times the cost of conventional carbon steels.
Therefore, it would be desirable to rely on a steel suitable for the manufacture of cost-effective and corrosion-resistant pipes for the production of oil and/or natural gas.
It is known in the art that a low Cr content (of approximately 3%) is effective in improving the resistance to corrosion of low-alloy steel by means of the creation of a stable protective chromium oxide film. Nevertheless, such beneficial action resulting from the use of chromium could be offset if the carbon concentration and the micro-alloy elements are not modified. Furthermore, said composition should not only be useful to resist corrosion but it should also need to be suitable for the process of manufacturing seamless pipes and to provide high resistance and high tensile strength whenever mechanical stresses are applied. In addition, it should provide good weldability properties, without substantially increasing the cost when compared with conventional carbon steel.
BRIEF SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a low-alloy carbon steel having a chromium content ranging from 1.5 to 4% by weight for the manufacture of the seamless pipes to be used in corrosive oil media, both for exploration and production in the well.
Furthermore, it is an object of the present invention to provide low-alloy carbon steel for the manufacture of seamless pipes for the exploration and the production of oil and/or natural gas having an improved resistance to corrosion, where the steel comprises: 1.5-4.0% by weight of Cr, 0.06-0.10% by weight of C, 0.3-0.8% by weight of Mn, not more than 0.005% by weight of S, not more than 0.015% by weight of P, 0.20-0.35% by weight of Si, 0.25-0.35% by weight of Mo, 0.06-0.9% by weight of V, approximately 0.22% by weight of Cu, approximately 0.001% by weight of Nb, approximately 0.028% by weight of Ti, not more than a total 0 of 25 ppm, with the balance being Fe and unavoidable impurities.
According to a preferred embodiment, the steel is produced following a process that comprises the stages stated below:
the elaboration of a primary melt in an ultra-high power electric furnace, followed by a secondary metallurgy stage with a strong desulfurization, addition of ferroalloys and Cr, and then modification and flotation of inclusions until the specified formulation is obtained;
casting, preferably by continuous casting, followed by
hot-rolling in a continuous roller;
optionally, such hot-rolled steel is subjected to a normalizing thermal treatment;
optionally, said normalized steel is subjected to austenization, followed by quenching and tempering, with a minimum tempering temperature of 490° C.;
optionally, such rolled steel is directly subjected to austenization, quenching, and tempering.
Preferably, the hot-rolling comprises:
a first heating stage conducted at temperatures ranging between 1200-1300° C. for a period of approximately 60 minutes in an atmosphere of combustion gases with an O
2
content from 1 to 1.5%;
an optional second heating stage conducted at a temperature ranging between 850 and 1100° C. for a period of approximately 30 minutes, in an atmosphere of combustion gases with an O
2
content from 1 to 1.5%;
Preferably, the hot-rolling of seamless pipes is carried out in a continuous roller of the floating or restrained mandrel type (Multi-stand Pipe Mill—MPM—or Continuous Mandrel Mill, respectively).
According to one particular embodiment of the present invention, low-alloy carbon steel is provided for the manufacture of the pipes used in the exploration and the production of oil and/or natural gas with an improved resistance to corrosion. This steel containing: 3.3% by weight of Cr, 0.08% by weight of C, 0.47% by weight of Mn, 0.001% by weight of S, 0.014% by weight of P, 0.28% by weight of Si, 0.29% by weight of Mo, 0.52% by weight of V, 0.22% by weight of Cu, 0.001% by weight of Nb, 0.028% by weight of Ti, not more than a total 0 of 25 ppm, with the balance being Fe and unavoidable impurities.
Surprisingly, it has been found that a higher resistance to the corrosion caused by CO
2
can be obtained with respect to the conventional grade carbon steel recommended for the oil industry, also having suitable mechanical properties in terms of tensile strength and weldability.
An aspect of the invention consists of providing low-alloy carbon steel for the manufacture of an oil well casing with an improved resistance to corrosion, wherein such steel contains: 1.5-4.0% by weight of Cr, 0.06-0.10% by weight of C, 0.3-0.8% by weight of Mn, not more than 0.005% by weight of S, not more than 0.015% by weigh
González Juan Carlos
Pérez Teresa Estela
Turconi Gustavo Javier López
Siderca S.A.I.C.
Tolpin Thomas W.
Welsh & Katz Ltd.
Yee Deborah
LandOfFree
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