Patent Application
20240352564
The disclosure relates to the technical field of oil casing used in oil or gas field, in particular to a corrosion-resistant and high toughness oil casing and a method for manufacturing same.
In recent years, with the rapid growth of oil and natural gas demand, international crude oil prices and natural gas prices have also continued to rise. In response to the surging demand, many countries, including China, have stepped up the development of oil and natural gas. In the process of development, the oil and natural gas exploitation environment is becoming more and more harsh, and the development of oil and natural gas wells containing severely corrosive environments such as CO2 and H2S has become the current development trend. However, the ensuing corrosion problem has also become a major factor that seriously restricts the safe and efficient production and transportation of the oil and gas industry.
With the development of oil and gas fields containing seriously corrosive gases such as CO2 and H2S, 13Cr (i.e., the mass content of Cr being about 13%) oil casing with excellent corrosion resistance came into being. However, in high-temperature and corrosive environments, oil casing is required to have excellent resistance to stress corrosion cracking (SCC). In addition, when crude oil or natural gas extracted from wells in a high temperature and well-corrosive environment flows through the well pipe, sulfide stress cracking (SSC) may occur when the temperature of crude oil or natural gas in the well pipe near the surface drops to room temperature. Therefore, oil casing is also required to have excellent resistance to sulfide stress cracking at room temperature. In a high-temperature environment with a temperature of more than 150° C., the corrosion resistance of ordinary 13Cr oil casing drops sharply and cannot meet the current market demand.
On the other hand, when developing oil and gas fields in cold areas and environments containing severely corrosive gases such as CO2 and H2S, the oil casing used in the development requires not only high strength and excellent corrosion resistance (excellent resistance to SCC at high temperature and excellent resistance to SSC at room temperature), but also high toughness at low temperature. Therefore, in order to improve the competitiveness of enterprises, it is urgent to develop an oil casing with high strength, excellent resistance to SCC at high temperature, excellent resistance to SSC at room temperature and high toughness at low temperature, so as to adapt to the increasingly severe exploitation environment.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by embodiments of the present disclosure which provide a corrosion-resistant and high toughness oil casing and a method for manufacturing same.
The purpose of the present application is to provide an oil casing with high strength, excellent resistance to SCC at high temperature, excellent resistance to SSC at room temperature and high toughness at low temperature, so as to solve the problems in the prior art that the corrosion resistance of the existing 13Cr oil casing decreases sharply when the temperature changes, and cannot meet the current market demand.
The technical solution adopted in this application is:
A first aspect of the present disclosure provides a corrosion-resistant and high toughness oil casing, and the oil casing comprises a chemical composition, by mass %, C: 0.01% to 0.04%, Si: 0.1% to 0.8%, Mn: 0.05% to 0.25%, Cr: 11.0% to 14.0%, Mo: 1.5% to 2.8%, Cu: 0.5% to 1.8%, Ni: 3.7% to 5.0%, N: 0.03% to 0.05%, Al: 0.001% to 0.05%, B: 0.001% to 0.005%, Ti: 0.03% to 0.08%, La: 0.07% to 0.35%, Ce: 0.12% to 0.40%, P: 0.013% or less, S: 0.001% or less, and a balance being Fe and inevitable impurities.
The mass % of the chemical composition satisfies the following relationships: [Ni]/[Cu]≥3.0, and 4360≤([Ni]+[Cr]+[Mo])/[B]≤16200, in which, [Ni] represents the mass % of the Ni element, [Cu] represents the mass % of the Cu element, [Cr] represents the mass % of the Cr element, [Mo] represents the mass % of the Mo element, and [B] represents the mass % of the B element.
A microstructure of the oil casing comprises, in terms of volume fraction, 10% to 20% of a ferrite phase, 5% to 20% of a retained austenite phase and the balance of a tempered martensite phase.
The Applicant has carried out a lot of experiments and studies on the corrosion resistance of oil casing in severely corrosive environments containing CO2 and H2S. In addition, the Applicant has also studied the toughness at low temperature of stainless steel. The Applicant has found that an appropriate amount of ferrite can improve the corrosion resistance of steel, but if the ferrite content is too high, the strength of the steel would be reduced. In addition, retained austenite can improve the toughness at low temperature of steel, but excess retained austenite can also reduce the strength of the steel. Therefore, the metallographic microstructure of the oil casing disclosed in this application is composed of ferrite phase with a volume fraction of 10% to 20%, retained austenite phase with a volume fraction of 5.0% to 20% and the balance of a tempered martensite phase, which can ensure that the steel is strong enough on the one hand, and on the other hand, the amount of ferrite phase and retained austenite phase can be properly controlled and adjusted, so as to obtain the oil casing with high strength, excellent corrosion resistance and high toughness at low temperature, so as to meet the current market demand.
The chemical composition described above is the basic chemical composition in the present application. The reasons for limitations on the basic chemical composition and content and design ideas will be described. Hereinafter, mass % is simply referred to as %, unless otherwise noted.
C: 0.01% to 0.04%.
C is a chemical element which is precipitated as carbide during tempering, and increases the content of the tempered martensite phase in stainless steel and the strength. However, when the C content is too high, the resistance to SSC may deteriorate significantly. Therefore, the C content is limited to the range of 0.01% to 0.04%, or preferably 0.02% to 0.04%.
Si: 0.1% to 0.8%.
Si is a chemical element which functions as a deoxidizer, and the Si content is too low to have the effect of deoxidization. However, when the Si content exceeds 0.8%, the corrosion resistance and hot workability of the oil casing are significantly reduced. Therefore, the Si content is limited to the range of 0.1% to 0.8%, or preferably 0.1% to 0.5%.
Mn: 0.05% to 0.25%.
Mn is a chemical element which improves the toughness, strength and hot workability of steel. If the Mn content is too high, the austenite phase may remain too much after quenching and tempering, resulting in a decrease of the strength. And, if the Mn content is too high, the resistance to SSC and SCC may greatly decrease. Therefore, the Mn content is limited to the range of 0.05% to 0.25%, or preferably 0.05% to 0.20%.
Cr: 11.0% to 14.0%.
Cr is a chemical element which forms a protective film to improve corrosion resistance. However, in the case where the Cr content is too low, it is difficult to realize such an effect. On the other hand, in the case where the Cr content is too high, the volume fraction of the ferrite phase exceeds 20%, which is not good for the strength of the oil casing. Therefore, the Cr content is limited to the range of 11.0% to 14.0%, or preferably 11.5% to 13.0%.
Mo: 1.5% to 2.8%.
Mo improves the resistance to SSC, and the nanoscale precipitates of both Mo and Cr at the same time better improves the resistance to SCC at high temperature of the steel. However, in the case where the Mo content is too high, it is easy to generate more ferrite phase, which reduces the strength of the steel. Moreover, since Mo is an expensive element, in the case where the Mo content is more than 2.8%, there is a significant increase in production costs, which causes economic burden to enterprises. Therefore, the Mo content is limited to the range of 1.5% to 2.8%, or preferably 1.5% to 2.6%.
Cu: 0.5% to 1.8%.
Cu is able to stabilize the protective film formed by Cr to improve the resistance to SSC. In addition, Cu is precipitated as fine Cu particles when tempering to improve the strength of the steel. However, in the case where the Cu content is too high, the martensite phase transformation may not be sufficient during the process of quenching, which causes too much amount of the retained austenite phase, and reduces the strength of the steel. Therefore, the Cu content is limited to the range of 0.5% to 1.8%, or preferably 1.0% to 1.6%.
Ni: 3.7% to 5.0%.
Ni is able to stabilize the protective film formed by Cr to improve the resistance to SSC and improves the strength of the steel. In addition, in the process of tempering, Ni promotes the formation of retained austenite phase at room temperature to improve the toughness at low temperature. However, in the case where the Ni content is too high, the stability of tempered martensite phase is reduced and the strength of the steel is reduced. Therefore, the Ni content is limited to the range of 3.7% to 5.0%, or preferably 3.7% to 4.8%. Furthermore, in order to obtain oil casing with high strength, excellent corrosion resistance and high toughness at low temperature, the mass % of Ni content and Cu content satisfies the following relationships: [Ni]/[Cu]>3.0, where [Ni] represents the mass % of the Ni element, and [Cu] represents the mass % of the Cu element.
N: 0.03% to 0.05%.
N can form carbonitrides with C. The pinning effect of precipitated carbonitrides refines the grains, thereby improving strength and corrosion resistance. However, in the case where the N content is more than 0.05%, there is a decrease in the toughness and corrosion resistance. Therefore, the N content is limited to the range of 0.03% to 0.05%, or preferably 0.03% to 0.04%.
Al: 0.001% to 0.05%.
Al is a chemical element which functions as a good deoxidizer and fine grains, which can improve the toughness at low temperature and the oxidation resistance of the oil casing. However, in the case where the Al content is too high, there is a significant increase in the amount of non-metallic inclusions in oil casing, which has a negative effect on the toughness of steel. Therefore, the Al content is limited to the range of 0.001% to 0.05%, or preferably 0.001% to 0.04%.
B: 0.001% to 0.005%.
B increases the hardenability of steel, reduces deformation and improves the resistance to SSC. The appropriate addition of B can save other relatively rare metals, such as Ni, Cr and Mo. 0.001% of B element can replace 1.6% of Ni, 0.3% of Cr or 0.2% of Mo. However, in the case where the B content is too high, there is a tendency to promote tempered brittleness and reduce the toughness at low temperature of the steel. Therefore, the B content is limited to the range of 0.001% to 0.005%, or preferably 0.001% to 0.003%. Considering the toughness at low temperature, corrosion resistance and cost of steel, the mass % of Ni, Cr, Mo and B contents satisfies the following relationships: 4360≤([Ni]+[Cr]+[Mo])/[B]≤16200, in which, [Ni] represents the mass % of the Ni element, [Cr] represents the mass % of the Cr element, [Mo] represents the mass % of the Mo element, and [B] represents the mass % of the B element.
Ti: 0.03% to 0.08%.
Due to the strong binding force between Ti and C, the generated titanium carbide can prevent grains growth, refine grains, and increase the toughness of oil casing at low temperature. In addition, an appropriate amount of Ti improves the corrosion resistance of oil casing. However, in the case where the Ti content is too high, TiN is formed, resulting in a sharp decrease in the resistance to SSC. Therefore, the Ti content is limited to the range of 0.03% to 0.08%, or preferably 0.04% to 0.06%.
La: 0.07% to 0.35%, Ce: 0.12% to 0.40%.
The appropriate content of rare earth elements La and Ce can purify the molten steel, and change the composition, morphology, distribution and properties of the inclusions in the steel, so as to improve the toughness and processing performance of the steel. However, the cost of rare earth elements is high, therefore, the rare earth element La content is limited to the range of 0.07% to 0.35%, and the Ce content is limited to the range of 0.12% to 0.40%.
P: 0.013% or less.
P is a chemical element which is present in steel as an inevitable impurity that reduces the toughness and resistance to SSC. The relatively high P concentration in the grain boundary reduces the binding force of the grain boundary, which seriously weakens the impact toughness at low temperature of the steel. In particular, in the case where the P content exceeds 0.013%, the toughness and resistance to SSC are rapidly decreased. Therefore, the P content is limited to 0.013% or less.
S: 0.001% or less.
S is a chemical element which is present in steel as an inevitable impurity that reduces the toughness and resistance to SSC. In particular, in the case where the S content exceeds 0.001%, the toughness and resistance to SSC are rapidly decreased. Therefore, the S content is limited to 0.001% or less.
The application also provides a corrosion-resistant and high toughness oil casing, which further comprises by mass %, W: 0.01% to 1.3% and V: 0.06% to 0.1%.
W is a chemical element which may be contained in oil casing or not be contained. When W is contained, W, Mo, and Cr can better improve the resistance to SCC at high temperature of the steel. In addition, special compounds formed by W and C significantly refine the grain and improve the strength and toughness of the steel. However, in the case where the W content exceeds 1.3%, there is too much ferrite phase in the steel, which significantly reduces the strength of the steel. Therefore, the W content is limited to the range of 0.01% to 1.3%.
V is a chemical element which may be contained in oil casing or not be contained. When V is contained, V, N and C are precipitated as a fine precipitate. The pinning effect of the precipitate refines the grains, thereby improving the strength. However, in the case where the V content is too high, there is a decrease in the corrosion resistance to SSC and toughness at low temperature. Therefore, the V content is limited to the range of 0.06% to 0.1%.
The application also provides a corrosion-resistant and high toughness oil casing, which further comprises by mass %, one or two elements selected from Ca: 0.0001% to 0.005% and Mg: 0.0001% to 0.005%.
Ca and Mg are both chemical elements which may be contained in oil casing or not be contained. When Ca and/or Mg are/is contained, there is an increase in hot workability of the steel. However, in the case where the Ca and/or Mg content is too high, large oxides may be formed, which reduces the corrosion resistance to SSC. Therefore, the Ca content is limited to the range of 0.0001% to 0.005%, and the Mg content is limited to the range of 0.0001% to 0.005%.
Also encompassed by the present disclosure is a method for manufacturing the oil casing, which may include the following a smelting and casting process, a steel pipe making process and a heat treatment process.
A smelting and casting process: preparing raw materials according to the mass % of the chemical composition, and performing a smelting in an electric furnace, a ladle refining, a vacuum degassing and a curved continuous casting on the raw materials in sequence to obtain a billet.
A steel pipe making process: heating the billet to obtain a hot billet; piercing the hot billet to obtain a hollow shell having an outer diameter of 300 millimeters (mm) to 302 mm; rolling the hollow shell in a Premium Quality Finishing mill to form a shell having an outer diameter of 264 mm to 266 mm; and performing a slight stretch reducing and a cooling in a walking beam cooler on the shell to obtain an as-rolled steel pipe.
A heat treatment process: heating the as-rolled steel pipe to 980° C. to 1030° C. for 15 min to 25 min, air-cooling or water-cooling the heated steel pipe to 80° C. to 100° C. for quenching; then, heating the quenched steel pipe to 650° C. to 700° C. for 20 min to 40 min, air-cooling the heated quenched steel pipe for tempering.
In the present application, raw materials are prepared according to the mass % of the chemical composition of the oil casing. The raw materials are successively subjected to the smelting and casting process, the steel pipe making process and the heat treatment process to prepare the corrosion-resistant and high toughness oil casing with excellent comprehensive performance. In the heat treatment process, the as-rolled steel pipe is heated to a temperature above the Ac3 phase transition (Ac3: the final temperature at which it is converted into austenite phase when heated) for 15 min to 25 min, and then cooled to a cooling temperature below 100° C. for quenching. As a result, a miniaturized and highly toughened martensitic phase is obtained. If the quenching temperature is lower than the Ac3 phase transition, it is difficult to heat the as-rolled steel pipe to the austenite single-phase domain, and a sufficient martensite phase is not obtained in the subsequent cooling process, which causes that the high strength oil casing cannot be obtained. Therefore, the quenching temperature is limited to above the Ac3 phase transition, or preferably 980° C. to 1030° C. Then, the quenched oil casing is tempered. During tempering treatment, it is heated below the Ac1 phase transition (Ac1: the temperature at which pearlite phase converts to austenite phase when heated) and is kept for at least 10 min, and then air-cooled. If the tempering temperature is higher than the Ac1 phase transition, the formation of the austenite phase cannot be ensured, and the toughness at low temperature cannot be guaranteed. Therefore, the tempering temperature is limited to below the Ac1 phase transition, or preferably 650° C. to 700° C. Understandably, the Ac3 phase transition (° C.) and Ac1 phase transition (° C.) described above can be determined by the expansion method. The expansion method comprises: performing a temperature history of heating and cooling on a test piece, and determining the phase transition according to the small displacements of expansion and contraction. The phase transition is determined using a Formaster phase transition dilatometer or a Gleeble thermal simulation testing machine.
In the quenching treatment, the as-rolled steel pipe is heated to 980° C. to 1030° C. for 15 min to 25 min. The dissolved residue of carbide is reduced and the phase grains are refined under the condition of the preferable quenching temperature and holding time. In the tempering treatment, the quenched steel pipe is heated to 650° C. to 700° C. for 20 min to 40 min. The internal stress of martensite phase is removed under the condition of the preferable tempering temperature and holding time, which ensures the formation of austenite phase with corresponding volume fraction, and contributes to the formation of oil casing with high toughness at low temperature. The preferable quenching and tempering temperature and holding time can ensure the formation of oil casing with high strength, small deviation, excellent corrosion resistance and high toughness at low temperature.
As an embodiment of the present application, the process of rolling the hollow shell in the Premium Quality Finishing mill comprises: spraying borax into the hollow shell, and then spraying nitrogen, a pressure of the spraying nitrogen being 3 bar to 8 bar, and a time of spraying borax being 5 s to 12 s.
In the steel pipe making process, when the hot billet is pierced to produce hollow shell, due to the oxide layer formed by the contact between the surface of the hot billet and oxygen, too much and too thick oxide layer affects the qualification rate of the product in the subsequent pipe rolling process, and affects the life of internal deformation tools, such as plug or mandrel during rolling, so the oxide layer needs to be removed during rolling. In the present application, borax is continuously sprayed into the hollow shell to remove the oxide layer, and then nitrogen is sprayed at high speed to blow the oxide in the oxide layer away. On the other hand, a part of the oxide forms an anti-oxidation film, which prevents the re-oxidation of the hollow shell, improves product quality, prolongs the life of the internal deformation tools during rolling, and reduces the rolling pressure and energy consumption. The efficiency of the removal of oxide layer may be improved and the amount of borax and nitrogen may be saved under the conditions of the preferable pressure of the spraying nitrogen and time of spraying borax.
As an embodiment of the present application, in the quenching process, a rate of air-cooling is 5° C./min to 20° C./min; or a rate of water-cooling is 10° C./s to 65° C./s.
It should be noted that in the quenching process, the cooling method may not be limited specifically. Conventional air-cooling or water-cooling well known to those skilled in the art may be adopted. The cooling rate may not be limited specifically. There is a decrease of the precipitation of coarse carbides using the above-mentioned preferable cooling rate, which ensures the performance of the steel pipe and conducive to obtaining the oil casing with high strength and small deviation, excellent corrosion resistance and high toughness at low temperature.
As an embodiment of the present application, the process of ladle refining comprises: adding lime, fluorite and calcium carbide into the ladle for slagging, then refining in a gradual temperature rising mode, a time of the refining being 60 min to 70 min.
The addition of lime, fluorite and calcium carbide to the ladle for slagging is conducive to further desulfurization and adsorption of inclusions, and to improve the resistance to SSC of oil casing.
As an embodiment of the present application, in the process of curved continuous casting, a speed of casting is 2.8 m/min to 3.2 m/min, a vibration frequency of a mold is 163 min−1 to 178 min−1, an amplitude of the mold is 10.0 mm to 10.3 mm, and a negative slip rate is 30% to 32%.
In the process of curved continuous casting, as the speed of casting increases, high requirements are placed on the vibration parameters of the mold. The slags and bubbles in the molten steel float up under the preferable vibration parameters of the mold in the present application, which reduces the slags, pores and cracks on the surface of the billet. The separation of the billet shell and the inner wall of the mold becomes more stable by controlling the vibration frequency and amplitude of mold, which avoids the adhesion of the billet shell and the mold in the vibration process, the generation of cracks on the surface of the billet and the harmful effect on the quality of the final finished oil casing.
As an embodiment of the present application, the steel pipe making process comprises: heating the billet to 1220° C. to 1260° C. and holding the temperature for 90 min to 110 min to obtain the hot billet; and a temperature of piercing the hot billet is 1150° C. or more.
The billet is heated, and the internal microstructure of the heated billet is more uniform, and the thermal piercing is matched at a temperature of not less than 1150° C. to control the piercing process parameters, so as to obtain a hollow shell with uniform pipe diameter and uniform mechanical properties, so as to ensure the quality of the shell of subsequent rolling.
As an embodiment of the present application, in the process of rolling the hollow shell in the Premium Quality Finishing mill, an amount of hollow shell feeding is 62 mm to 113 mm, a roll speed is 20 rpm to 40 rpm, and a wind pressure is 5.2 bar to 6.3 bar.
The Premium Quality Finishing mill is adopted to roll the hollow shell in the present application. The generation of internal cracks is significantly inhibited and the grains are fully broken under the preferable parameters, so as to obtain a shell with fine grains.
In the present application, based on the 13Cr series oil casing, the Applicant has deeply studied the effects of various alloying elements and metallographic microstructure on the resistances to SSC and SCC in corrosive environments containing CO2 and H2S, as well as the toughness at low temperature. The results show that by reasonably adjusting the contents of C, Mn, Cr, Mo, Cu, Ni, N, Al, B, Ti and the rare earth elements La and Ce, and appropriately adjusting the amount of retained austenite phase while generating tempered martensite phase in the metallographic microstructure through quenching and tempering to determine the volume fraction of ferrite phase, retained austenite phase and tempered martensite phase, the oil casing is obtained with high strength, excellent resistances to SSC and SCC in corrosive environments containing CO2 and H2S.
Ni promotes the formation of retained austenite phase after quenching and tempering, especially after tempering. Therefore, Ni may improve the toughness at low temperature. In addition, Cu is precipitated as fine Cu particles when tempering to improve the strength of the steel. Therefore, by adjusting the Ni content and Cu content, it is possible to obtain an oil casing with high strength and excellent toughness at low temperature.
The oil casing provided in this application has a high strength of yield strength of 862 MPa or more and tensile strength of 920 MPa or more, and the maximum corrosion rate is 0.0442 millimeters/annually (mm/a) at high temperature of 150° C. or more, and no cracks are generated in the resistance to SSC evaluation test. The oil casing provided in this application has good resistance to SCC at high temperature and resistance to SSC at room temperature in severe corrosive environments containing CO2 and H2S, and still has an absorption energy of 100 J or more under low temperature of minus 50° C. or below, and has very good toughness, which can meet the needs of oilfields in harsh corrosive environments such as extreme cold and high temperature, and has broad market prospects.
In order to make the purpose, technical solution and advantages of the present application more clearly understood, further details are described in conjunction with the embodiments in the present application. It should be understood that the specific embodiments described herein are only used to interpret the present application and are not intended to limit the present application.
In order to better illustrate the present application, further details are given below through specific embodiments.
The example of the present application provided a corrosion-resistant and high toughness oil casing which included a chemical composition, by mass %, C: 0.01%, Si: 0.5%, Mn: 0.05%, Cr: 11.0%, Mo: 2.6%, Cu: 0.7%, Ni: 3.7%, N: 0.03%, Al: 0.001%, B: 0.002%, Ti: 0.03%, La: 0.07%, Ce: 0.12%, P: 0.013%, S: 0.001%, and the balance being Fe and inevitable impurities. The mass % of the chemical composition satisfied the following relationships: [Ni]/[Cu]=5.2, and ([Ni]+[Cr]+[Mo])/[B]=8650.
The method for manufacturing the oil casing included the following smelting and casting process, steel pipe making process and heat treatment process.
A smelting and casting process: the alloy and steel scrap were as raw materials, and the raw materials were performed a smelting in an electric furnace, a ladle refining, a vacuum degassing and a curved continuous casting in sequence to obtain a billet.
In the process of ladle refining, lime, fluorite and calcium carbide were added into the ladle for slagging. The refining was performed in a gradual temperature rising mode, a time of the refining being 60 min. In the process of curved continuous casting, a speed of casting was 2.8 m/min, a vibration frequency of a mold was 163 min−1, an amplitude of the mold was 10.0 mm, and a negative slip rate was 30%.
A steel pipe making process: the billet was heated to 1220° C. for 90 min to obtain a hot billet. The hot billet was pierced at the temperature of 1150° C. or more to obtain a hollow shell having an outer diameter of 300 mm. The hollow shell was rolled in a Premium Quality Finishing mill to form a shell having an outer diameter of 264 mm. A slight stretch reducing and a cooling in a walking beam cooler were performed on the shell to obtain an as-rolled steel pipe with φ244.48 mm×11.99 mm.
In the process of rolling the hollow shell in a Premium Quality Finishing mill, the borax was sprayed into the hollow shell, and then the nitrogen was sprayed. A pressure of the spraying nitrogen was 3 bar, and a time of spraying borax was 5 s.
In the process of rolling the hollow shell in the Premium Quality Finishing mill, an amount of hollow shell feeding was 62 mm, a roll speed was 20 rpm, and a wind pressure was 5.2 bar.
A heat treatment process: the as-rolled steel pipe was heated to 980° C. for 15 min. The heated steel pipe was air-cooled to 80° C. for quenching with a rate of air-cooling being 5° C./min. Then, the quenched steel pipe was heated to 650° C. for 20 min. The heated quenched steel pipe was air-cooled for tempering to obtain the corrosion-resistant and high toughness oil casing.
A microstructure of the oil casing included, in terms of volume fraction, 10% of a ferrite phase, 5% of a retained austenite phase and 85% of a tempered martensite phase.
The method for determining the volume fraction of ferrite phase included the following processes.
A test-piece was cut out from the prepared oil casing for observation of its microstructure. A cross-section (i.e., the observation surface) was ground on the surface of the test-piece. The ground observation surface was etched with a mixture of aqua regia and glycerin. The volume fraction (vol. %) of ferrite phase was determined according to the standard JIS G 0555:2003 “method for determining non-metallic inclusions in steel”.
The method for determining the volume fraction of retained austenite phase included the following processes.
A test-piece was cut out from the prepared oil casing for observation of its microstructure. The test-piece was ground to determine the volume fraction of retained austenite phase (γ phase) by X-ray diffraction. The X-ray integral intensities of the (200) and (211) surfaces of the ferrite (α phase), the (200), (220) and (311) surfaces of the retained austenite (γ phase) were measured, and the volume fraction Vγ (6 in total) of retained austenite of each surface was calculated using the following formula:
In which, Iα represented the integral intensities of the α phase, and Iγ represented the integral intensities of the γ phase. Rα represented the crystallography theory calculation of the α phase, and Rγ represented the crystallography theory calculation of the γ phase. The mean value of the volume fraction Vγ of each surface was defined as the volume fraction (vol. %) of retained austenite.
The method for determining the volume fraction of tempered martensite phase was: the volume fraction of retained austenite phase=100%−(the volume fraction of ferrite phase+the volume fraction of retained austenite phase).
The tensile testing was carried out in accordance with API Spec 5CT Casing and Tubing, and the random sampling method was used to take samples from the oil casings prepared in Example 1 to analyze the yield strength and tensile strength.
The charpy impact test was carried out at minus 60° C. in accordance with the standard ASTM E23 to determine the absorbed energy (J). The statistical results of the determined yield strength, tensile strength and absorbed energy were shown in Table 1.
The oil casing specimen prepared in Example 1 was placed in an autoclave for corrosion test. The composition of the corrosion solution included Na++K+11350 mg/L, Cl−17495 mg/L, HCO3−1312 mg/L and SO42−1663 mg/L. The flow rate was 1.5 m/s, the temperature was 150° C., the test time was 168 h, the total pressure of the gas was 30 MPa, the partial pressure of CO2 was 1 MPa, and the corrosion rate measured was 0.0432 mm/a.
According to the NACE TM0177-2005 standard, the SSC performance evaluation test was carried out on the oil casing prepared in Example 1. And the SSC corrosion test was carried out by using the A method (standard tensile method). The pH of the test solution was 4.0, the partial pressure of H2S was 3 kPa, the impregnation time was 720 h, and the loading stress was 706.4 MPa. The tensile surface of the sample was observed with a microscope with a magnification of ×10, and there were no cracking surfaces.
The example of the present application provided a corrosion-resistant and high toughness oil casing which included a chemical composition, by mass %, C: 0.03%, Si: 0.1%, Mn: 0.15%, Cr: 13.0%, Mo: 1.5%, Cu: 1.6%, Ni: 5.0%, N: 0.04%, Al: 0.04%, B: 0.003%, Ti: 0.05%, La: 0.12%, Ce: 0.24%, P: 0.011%, S: 0.0009%, W: 0.7%, V: 0.06% and the balance being Fe and inevitable impurities. The mass % of the chemical composition satisfied the following relationships: [Ni]/[Cu]=3.1, and ([Ni]+[Cr]+[Mo])/[B]=6500.
The method for manufacturing the oil casing included the following smelting and casting process, steel pipe making process and heat treatment process.
A smelting and casting process: the alloy and steel scrap were as raw materials, and the raw materials were performed a smelting in an electric furnace, a ladle refining, a vacuum degassing and a curved continuous casting in sequence to obtain a billet.
In the process of ladle refining, lime, fluorite and calcium carbide were added into the ladle for slagging. The refining was performed in a gradual temperature rising mode, a time of the refining being 65 min. In the process of curved continuous casting, a speed of casting was 3.0 m/min, a vibration frequency of a mold was 170 min−1, an amplitude of the mold was 10.2 mm, and a negative slip rate was 31%.
A steel pipe making process: the billet was heated to 1242° C. for 100 min to obtain a hot billet. The hot billet was pierced at the temperature of 1150° C. or more to obtain a hollow shell having an outer diameter of 301 mm. The hollow shell was rolled in a Premium Quality Finishing mill to form a shell having an outer diameter of 265 mm. A slight stretch reducing and a cooling in a walking beam cooler were performed on the shell to obtain an as-rolled steel pipe with φ244.48 mm×11.99 mm.
In the process of rolling the hollow shell in a Premium Quality Finishing mill, the borax was sprayed into the hollow shell, and then the nitrogen was sprayed. A pressure of the spraying nitrogen was 5 bar, and a time of spraying borax was 8 s.
In the process of rolling the hollow shell in the Premium Quality Finishing mill, an amount of hollow shell feeding was 83 mm, a roll speed was 30 rpm, and a wind pressure was 5.8 bar.
A heat treatment process: the as-rolled steel pipe was heated to 1000° C. for 20 min. The heated steel pipe was air-cooled to 90° C. for quenching with a rate of air-cooling being 12° C./min. Then, the quenched steel pipe was heated to 680° C. for 30 min. The heated quenched steel pipe was air-cooled for tempering to obtain the corrosion-resistant and high toughness oil casing.
A microstructure of the oil casing included, in terms of volume fraction, 15% of a ferrite phase, 20% of a retained austenite phase and 65% of a tempered martensite phase.
The methods for determining the volume fraction of ferrite phase, retained austenite phase and tempered martensite phase were the same as Example 1.
The tensile testing was carried out in accordance with API Spec 5CT Casing and Tubing, and the random sampling method was used to take samples from the oil casings prepared in Example 2 to analyze the yield strength and tensile strength.
The charpy impact test was carried out at minus 50° C. in accordance with the standard ASTM E23 to determine the absorbed energy (J). The statistical results of the determined yield strength, tensile strength and absorbed energy were shown in Table 2.
The oil casing specimen prepared in Example 2 was placed in an autoclave for corrosion test. The composition of the corrosion solution included Na++K+11350 mg/L, Cl−17495 mg/L, HCO3−1312 mg/L and SO42−1663 mg/L. The flow rate was 1.5 m/s, the temperature was 160° C., the test time was 168 h, the total pressure of the gas was 30 MPa, the partial pressure of CO2 was 2 MPa, and the corrosion rate measured was 0.0442 mm/a.
According to the NACE TM0177-2005 standard, the SSC performance evaluation test was carried out on the oil casing prepared in Example 2. And the SSC corrosion test was carried out by using the A method (standard tensile method). The pH of the test solution was 4.0, the partial pressure of H2S was 3 kPa, the impregnation time was 720 h, and the loading stress was 714.5 MPa. The tensile surface of the sample was observed with a microscope with a magnification of ×10, and there were no cracking surfaces.
The example of the present application provided a corrosion-resistant and high toughness oil casing which included a chemical composition, by mass %, C: 0.04%, Si: 0.5%, Mn: 0.25%, Cr: 14.0%, Mo: 2.6%, Cu: 1.2%, Ni: 4.8%, N: 0.05%, Al: 0.015%, B: 0.004%, Ti: 0.08%, La: 0.34%, Ce: 0.40%, P: 0.01%, S: 0.001%, Ca: 0.0001%, Mg: 0.0001% and the balance being Fe and inevitable impurities. The mass % of the chemical composition satisfied the following relationships: [Ni]/[Cu]=4.0, and ([Ni]+[Cr]+[Mo])/[B]=5350.
The method for manufacturing the oil casing included the following smelting and casting process, steel pipe making process and heat treatment process.
A smelting and casting process: the alloy and steel scrap were as raw materials, and the raw materials were performed a smelting in an electric furnace, a ladle refining, a vacuum degassing and a curved continuous casting in sequence to obtain a billet.
In the process of ladle refining, lime, fluorite and calcium carbide were added into the ladle for slagging. The refining was performed in a gradual temperature rising mode, a time of the refining being 70 min. In the process of curved continuous casting, a speed of casting was 3.2 m/min, a vibration frequency of a mold was 178 min−1, an amplitude of the mold was 10.3 mm, and a negative slip rate was 32%.
A steel pipe making process: the billet was heated to 1260° C. for 110 min to obtain a hot billet. The hot billet was pierced at the temperature of 1150° C. or more to obtain a hollow shell having an outer diameter of 302 mm. The hollow shell was rolled in a Premium Quality Finishing mill to form a shell having an outer diameter of 266 mm. A slight stretch reducing and a cooling in a walking beam cooler were performed on the shell to obtain an as-rolled steel pipe with φ244.48 mm×11.99 mm.
In the process of rolling the hollow shell in a Premium Quality Finishing mill, the borax was sprayed into the hollow shell, and then the nitrogen was sprayed. A pressure of the spraying nitrogen was 8 bar, and a time of spraying borax was 12 s.
In the process of rolling the hollow shell in the Premium Quality Finishing mill, an amount of hollow shell feeding was 113 mm, a roll speed was 40 rpm, and a wind pressure was 6.3 bar.
A heat treatment process: the as-rolled steel pipe was heated to 1030° C. for 25 min. The heated steel pipe was water-cooled to 90° C. for quenching with a rate of water-cooling being 30° C./s. Then, the quenched steel pipe was heated to 700° C. for 40 min. The heated quenched steel pipe was air-cooled for tempering to obtain the corrosion-resistant and high toughness oil casing.
A microstructure of the oil casing included, in terms of volume fraction, 15% of a ferrite phase, 10% of a retained austenite phase and 75% of a tempered martensite phase.
The methods for determining the volume fraction of ferrite phase, retained austenite phase and tempered martensite phase were the same as Example 1.
The tensile testing was carried out in accordance with API Spec 5CT Casing and Tubing, and the random sampling method was used to take samples from the oil casings prepared in Example 3 to analyze the yield strength and tensile strength.
The charpy impact test was carried out at minus 50° C. in accordance with the standard ASTM E23 to determine the absorbed energy (J). The statistical results of the determined yield strength, tensile strength and absorbed energy were shown in Table 3.
The oil casing specimen prepared in Example 3 was placed in an autoclave for corrosion test. The composition of the corrosion solution included Na++K+11350 mg/L, Cl−17495 mg/L, HCO3−1312 mg/L and SO42−1663 mg/L. The flow rate was 1.5 m/s, the temperature was 160° C., the test time was 170 h, the total pressure of the gas was 30 MPa, the partial pressure of CO2 was 2 MPa, and the corrosion rate measured was 0.0412 mm/a.
According to the NACE TM0177-2005 standard, the SSC performance evaluation test was carried out on the oil casing prepared in Example 3. And the SSC corrosion test was carried out by using the A method (standard tensile method). The pH of the test solution was 3.0, the partial pressure of H2S was 4 kPa, the impregnation time was 720 h, and the loading stress was 810 MPa. The tensile surface of the sample was observed with a microscope with a magnification of ×10, and there were no cracking surfaces.
Through the above performance testing results, it can be seen that in Examples 1 to 3, the chemical composition ratio of the oil casing is appropriate, [Ni]/[Cu] is 3.0 or more, and 4360≤([Ni]+[Cr]+[Mo])/[B]≤16200. Therefore, the microstructure of Examples 1 to 3 is composed of ferrite phase, retained austenite phase and tempered martensite phase, and the volume fraction of ferrite phase is 10% to 20%, and the volume fraction of retained austenite phase is 5.0% to 20%. The oil casing prepared by reasonable chemical composition and preparation process in this application has a yield strength of 862 MPa or more and a tensile strength of 920 MPa or more. In addition, the absorbed energy in low temperature environment is 100 J or more, and the toughness is high. In addition, the maximum corrosion rate is 0.0442 mm/a at a temperature of 150° C. or more, and the resistance to SCC at high temperature is good. The resistance to SSC is excellent because there were no cracking surfaces in the resistance to SSC testing.
The comparative example provided an oil casing which included a chemical composition, by mass %, C: 0.01%, Si: 0.5%, Mn: 0.05%, Cr: 11.0%, Mo: 2.6%, Cu: 1.6%, Ni: 3.7%, N: 0.03%, Al: 0.001%, B: 0.004%, Ti: 0.03%, La: 0.07%, Ce: 0.12%, P: 0.013%, S: 0.001%, and the balance being Fe and inevitable impurities. The mass % of the chemical composition satisfied the following relationships: [Ni]/[Cu]=2.3, and ([Ni]+[Cr]+[Mo])/[B]=4325.
The method for manufacturing the oil casing, the conditions and processes of performance testing were the same as Example 1.
A microstructure of the oil casing prepared in Comparative Example 1 included, in terms of volume fraction, 16% of a ferrite phase, 3% of a retained austenite phase and 81% of a tempered martensite phase.
The ratio of Ni content to Cu content [Ni]/[Cu]in Comparative Example 1 is less than 3.0, so the absorbed energy in low temperature environment is less than 100 J, and the toughness is poor.
The comparative example provided an oil casing which included a chemical composition the same as Example 1. The smelting and casting process and steel pipe making process in manufacturing the oil casing were the same as Example 1, and only the heat treatment process was different from Example 1.
The heat treatment process in Comparative Example 2: the as-rolled steel pipe was heated to 750° C. for 25 min. The heated steel pipe was water-cooled to 90° C. for quenching with a rate of water-cooling being 30° C./s. Then, the quenched steel pipe was heated to 630° C. for 40 min. The heated quenched steel pipe was air-cooled for tempering to obtain the oil casing.
A microstructure of the oil casing prepared in Comparative Example 2 included, in terms of volume fraction, 42% of a ferrite phase, 3% of a retained austenite phase and 55% of a tempered martensite phase.
The conditions and processes of performance testing in Comparative Example 2 were the same as Example 1.
The quenching temperature in Comparative Example 2 is lower than the Ac3 phase transition and cannot achieve to the austenite single-phase domain, so the sufficient martensite microstructure may not be obtained in subsequent cooling process. The tempering temperature is higher than the Ac1 phase transition, which cannot ensure the formation of austenite phase. The obtained oil casing has low strength. The maximum yield strength is 732 MP, and the maximum tensile strength is 768 MPa. In addition, the absorbed energy in low temperature is less than 100 J, and the toughness is poor. In addition, the resistance to SCC at high temperatures in Comparative Example 2 is poor, and there were cracking surfaces in the resistance to SSC testing, and the resistance to SSC is poor.
The above-mentioned embodiments are only used to illustrate the technical solutions of the disclosure, but not to limit the disclosure. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included within the protection scope of the present application.
This application is a continuation of International Application No. PCT/CN2023/089649, filed on Apr. 21, 2023 and entitled “corrosion-resistant and high toughness oil casing and method for manufacturing same”. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2023/089649 | Apr 2023 | WO |
| Child | 18671752 | US |
