Ultra-high-strength casing pipe with resistance to hydrogen sulfide corrosion for oil pipelines and method for its manufacture

Abstract

The present invention discloses an ultra-high-strength jacket pipe with resistance to H2S corrosion for petroleum pipelines, containing Fe and unavoidable impurities as well as the following chemical elements: C: 0.15 - 0.28%, Si: 0.1 - 0.5%, Mn: 0.2% - 0.5%, Cr: 0.4 - 0.8%, Mo: 0.8 - 1.5%, V: 0.15 - 0.3%, Nb: 0.05 - 0.15%, W: 0.2 - 0.6%, Al: 0.01 - 0.05%, Ce: 0.002 - 0.006%, O < O ≤ 0.002%; wherein the mass percentages of Ce and O are further specified as Ce / O = 1 - 3.5. Accordingly, the invention also discloses a method for manufacturing the ultra-high-strength casing pipe described above, which is resistant to H₂S corrosion and suitable for oil pipelines. By appropriately adjusting the composition of the chemical elements, a casing pipe for oil pipelines can be obtained that exhibits both ultra-high strength and good resistance to stress corrosion caused by H₂S.

Description

Technical field

[0001] The invention relates to a steel material and a method for producing it, in particular a casing pipe for an oil pipeline and a method for producing it. State of the art

[0002] Most oil and gas reservoirs developed today contain H2S and are located deep below the Earth's surface, typically in the range of 6000–9000 m. With the increasing development of sulfurous oil and gas wells and the increasing depth of oil and gas exploration, the need for sulfur-resistant steel pipes with a tensile strength of 110 to 130 ksi or more is also growing. These pipes are designed to meet the tensile strength and internal pressure resistance requirements of a pipe string made of jacketed casing when developing a deep, highly acidic oil and gas well.

[0003] Therefore, in the disclosed seamless tubes in the prior art, various technical means are used to improve the resistance of the steel to stress corrosion cracking caused by hydrogen sulfide.

[0004] For example, the Japanese patent entitled “Low-alloy steel” and publication number JP 2004332059 A, published on November 25, 2004, discloses a technical means for reducing amorphous inclusions to improve resistance to stress corrosion caused by hydrogen sulfide.

[0005] For example, the Japanese patent entitled “LOW ALLOY STEEL FOR OIL WELL TUBE HAVING EXCELLENT SULFIDE STRESS CRACKING RESISTANCE” and publication number JP 2005350754 A, published on 22.12.2005, also discloses a technique for controlling the dislocation density and the diffusion coefficient of hydrogen to improve the resistance of a sulfur-resistant steel pipe with a strength of 125 ksi to stress corrosion caused by hydrogen sulfide. Disclosure of the invention

[0006] One object of the invention is to provide an ultra-high-strength casing pipe with resistance to H₂S corrosion for oil pipelines. By appropriately adjusting the composition of the chemical elements, a casing pipe for oil pipelines can be obtained that exhibits both ultra-high strength and good resistance to stress corrosion caused by H₂S.

[0007] To solve this problem, the present invention provides an ultra-high-strength casing pipe with resistance to H₂S corrosion for petroleum pipelines. The casing pipe contains iron and unavoidable impurities, as well as the following chemical elements in mass percentages: C: 0.15 - 0.28%, Si: 0.1 - 0.5%, Mn: 0.2% - 0.5%, Cr: 0.4 - 0.8%, Mo: 0.8 - 1.5%, V: 0.15 - 0.3%, Nb: 0.05 - 0.15%, W: 0.2 - 0.6%, Al: 0.01 - 0.05%, Ce: 0.002 - 0.006%, 0 < O ≤ 0.002%; where Ce / O = 1 - 3.5 applies to the mass percentages of Ce and O.

[0008] Accordingly, the invention also provides an ultra-high-strength jacket pipe with resistance to H2S corrosion for oil pipelines, in which the mass percentages of the elements are: C: 0.15 - 0.28%, Si: 0.1 - 0.5%, Mn: 0.2% - 0.5%, Cr: 0.4 - 0.8%, Mo: 0.8 - 1.5%, V: 0.15 - 0.3%, Nb: 0.05 - 0.15%, W: 0.2 - 0.6%, Al: 0.01 - 0.05%, Ce: 0.002 - 0.006%, O < O ≤ 0.002%; and the residual amount of Fe and other unavoidable impurities, where Ce / O = 1 - 3.5 applies to the mass percentages of Ce and O.

[0009] Many factors influence a material's resistance to hydrogen sulfide stress corrosion. Among them, a carbide containing a metallic element can not only enhance precipitation but also act as a hydrogen trap, reducing hydrogen diffusion within the steel. This contributes to increased resistance to hydrogen sulfide stress corrosion. The interface between the precipitate and the substrate constitutes the primary hydrogen trap, and the size of this interface per unit volume increases with decreasing precipitate size, allowing more hydrogen to be trapped and dispersed. Carbides with a large dimensionality, such as Cr, are particularly effective in this regard. 23C6 can easily precipitate at crystal and lath boundaries to form a diffusion channel for hydrogen, accelerating hydrogen diffusion in the steel and concentrating vulnerable points for cracking. Furthermore, hard Al2O3 inclusions in the steel also represent vulnerable points to hydrogen-induced damage, around which a source of cracking is easily created.

[0010] Based on this, the technical solutions of the invention achieve, on the one hand, a scattered distribution of the existing W₂C carbide within the crystal through the addition of W alloy, due to its enhancement of precipitation and solution annealing. This increases the amount of trapped hydrogen and reduces the susceptibility to cracking under stress corrosion cracking caused by sulfides. On the other hand, the Cr content is reduced to prevent the precipitation of large-dimensional carbides, such as Cr₂. 23The aim is to suppress C6 at the crystal and sheet boundaries, thereby reducing the number of vulnerable points to hydrogen-induced damage. Furthermore, the element Ce is added according to the invention, which reacts with large inclusions, such as Al₂O₃, and alters their shape and size. After vacuum degassing (VD), all large inclusions float to the surface and are then removed. In the steel, CeAlO₃, which has a smaller size and a more regular shape, and its complex inclusions are formed, thus improving resistance to stress corrosion cracking caused by sulfides.

[0011] In particular, the adjustment of the chemical elements in the ultra-high-strength jacket pipe with resistance to H2S corrosion for oil pipelines according to the invention is based on the following principles: C: In the ultra-high-strength casing pipe according to the invention, which is resistant to H₂S corrosion and used for oil pipelines, C is an important element for ensuring strength and hardenability. If the C content in the steel is less than 0.15%, the strength can only barely reach the level of 125 ksi. Conversely, if the C content in the steel is too high, it is susceptible to cracking during quenching and also tends to precipitate the coarse carbide M. 23 C6 is located at the crystal boundary, which impairs resistance to sulfur. Therefore, in the invention, the mass percentage of element C is controlled between 0.15% and 0.28%. Si: In the ultra-high-strength casing pipe according to the invention, which is resistant to H₂S corrosion and used in oil pipelines, silicon is introduced into the steel by the deoxidizing agent. At a silicon content greater than 0.5%, the tendency of the steel to become brittle at low temperatures is significantly increased. At a content less than 0.1%, the deoxidation effect is reduced. Therefore, in the invention, the mass percentage of silicon is controlled between 0.1% and 0.5%. Mn: Mn exhibits advantageous effects such as increasing the austenite area, improving hardenability, and refining the grains. However, at a Mn content greater than 0.5%, segregation readily occurs during work hardening, and this segregation from the steel impairs the steel's resistance to sulfur. To ensure deoxidation and increase hardenability, the Mn content in the steel should be kept above 0.2%. Based on this principle, the mass percentage of Mn in the ultra-high-strength casing pipe according to the invention, which is resistant to H₂S corrosion and used for oil pipelines, is controlled between 0.2% and 0.5%. Cr: In the ultra-high-strength casing pipe according to the invention, which is resistant to H₂S corrosion and used for oil pipelines, chromium (Cr) is an important element for increasing strength and hardenability, thus effectively increasing the steel's corrosion resistance. However, it is important to understand that the Cr content in the steel should not be too high. Otherwise, an excessively high Cr content leads to the precipitation of the coarse carbide Cr₂. 23 C6 forms at the crystal boundaries during tempering, which negatively affects resistance to stress corrosion cracking caused by hydrogen sulfide. Based on this, the invention controls the mass percentage of element Cr between 0.4% and 0.8%, e.g., between 0.50% and 0.80%. Mo: Mo serves not only to increase strength, stability during tempering, and hardenability, but also to improve the material's resistance to corrosion. At a Mo content greater than 1.5%, coarse carbide precipitates, which negatively affects resistance to stress corrosion cracking caused by hydrogen sulfide. At a content less than 0.8%, it is difficult to guarantee a strength of 125 ksi during high-temperature tempering. Based on this, the mass percentage of the element Mo in the ultra-high-strength jacket pipe according to the invention, which is resistant to H₂S corrosion and used for oil pipelines, is controlled between 0.8% and 1.5%. V: V is an element that effectively refines the grains and enhances precipitation, thus increasing resistance to high-temperature tempering and ensuring a reduced dislocation density in the steel during high-temperature tempering. The fine precipitate phase of V acts as an effective hydrogen trap and can improve resistance to stress corrosion caused by hydrogen sulfide. However, it is important to understand that the V content in the steel should not be too high. Otherwise, an excessively high V content leads to embrittlement after tempering and reduced resistance of the steel to stress corrosion. Based on this, the mass percentage of V in the ultra-high-strength jacket pipe according to the invention, which is resistant to H₂S corrosion and used in oil pipelines, is controlled between 0.15% and 0.3%. Nb: Nb is an element for the effective refinement of grains. The precipitate phase of Nb formed in the austenite region can refine the grains and have a positive effect on the toughness of the steel and its resistance to sulfur. In the ultra-high-strength casing pipe according to the invention, which is resistant to H₂S corrosion and used for oil pipelines, the mass percentage of the element Nb is controlled between 0.05% and 0.15%. W: In the ultra-high-strength casing pipe according to the invention, which is resistant to H₂S corrosion and used for oil pipelines, W is one of the key elements present in the steel in the form of a solid solution or in a precipitated form. The precipitate phase can be evenly distributed throughout the steel, resulting in good reinforcement of the precipitate and improving resistance to high-temperature tempering as well as the material's strength. However, if the W content is too high, the precipitate phase is prone to coarsening and forms vulnerable points for cracking. If the W content is too low, the reinforcement is insufficient, making it difficult to achieve a strength of 125 ksi. Therefore, the mass percentage of the element W is controlled between 0.2% and 0.6%. Aluminum: Aluminum is an element required for the deoxidation of steel, and therefore its introduction into steel production is never entirely avoidable. However, the aluminum content in the steel should not be too high. If the aluminum content in the steel exceeds 0.05%, casting and similar processes will be impaired. Therefore, in the invention, the mass percentage of aluminum is controlled between 0.01% and 0.05%. Ce: In the ultra-high-strength jacket pipe according to the invention, which is resistant to H₂S corrosion and used for oil pipelines, Ce serves to purify the liquid steel, modify inclusions, and enhance precipitation. At high temperatures, Ce readily binds to other elements, such as O, S, etc., forming particles of high-melting-point oxides, sulfides, and oxysulfides. Furthermore, Ce also exhibits good effects in modifying hard inclusions, such as Al₂O₃. If the Ce content in the liquid steel exceeds 20 ppm, it can perform the modifying function to create a small-sized complex inclusion of CeAlO₃ + CaS. After the VD process combined with this, almost all large inclusions float to the surface and can then be removed.This significantly reduces the size of inclusions in the steel, which improves the toughness of the casing pipe and its resistance to cracking under stress corrosion cracking (SSC) caused by hydrogen sulfide. If an excessive amount of ce is present, brittle and hard intermetallic compounds of iron and rare earth metals are formed, reducing the material's resistance to SSC. Furthermore, adding too much ce can easily cause clogging at the outlet, leading to blockage and, in turn, difficulties during casting. Therefore, in the invention, the mass percentage of ce is controlled between 0.002% and 0.006%.

[0012] Furthermore, in the ultra-high-strength jacket pipe according to the invention, which is resistant to H₂S corrosion and suitable for oil pipelines, not only the mass percentage of each element but also the Ce / O ratio is controlled between 1 and 3.5. This is because the oxygen in the steel can form a large Al₂O₃ inclusion with the aluminum, which acts as a strong hydrogen trap in a hydrogen sulfide environment and is prone to fracture due to stress corrosion caused by hydrogen sulfide. The inventor has discovered through research that, at a Ce-to-O ratio greater than 1, Ce can form a particulate inclusion of CeAlO₃, thus refining the inclusions and avoiding the negative impact of the large Al₂O₃ inclusion. If the Ce-to-O ratio exceeds 3.5, casting becomes more difficult. Therefore, the mass percentages of Ce and O are 1 ≤ Ce / O ≤ 3.5.

[0013] In the ultra-high-strength jacket pipe according to the invention with resistance to H2S corrosion for oil pipelines, the mass percentages of the individual chemical elements further satisfy at least one of the following conditions: C: 0.18 - 0.25%; Cr: 0.4 - 0.7%; Mon: 0.9 - 1.2%; V: 0.18 - 0.25%; Note: 0.05 - 0.1%; W: 0.2 - 0.5%; Al: 0.015 - 0.04%; Ce: 0.002 - 0.005%.

[0014] Furthermore, the following values ​​apply to the ultra-high-strength jacket pipe according to the invention with resistance to H2S corrosion for petroleum pipelines in the unavoidable impurities S ≤ 0.002%, P ≤ 0.01% and N ≤ 0.008%.

[0015] Furthermore, they are controlled such that S ≤ 0.0015%, P ≤ 0.008% and N ≤ 0.007% apply.

[0016] In the technical solution according to the invention described above, P, S, N and O are harmful impurities. In order to obtain a steel with better properties and higher quality, the levels of P, S, N and O should be kept as low as technically achievable.

[0017] Furthermore, the basic microstructure of the ultra-high-strength jacket pipe according to the invention is made of tempered sorbitol and is resistant to H2S corrosion for petroleum pipelines.

[0018] Furthermore, the ultra-high-strength jacket pipe according to the invention, with resistance to H2S corrosion for petroleum pipelines, has a W2C carbide which is scattered and distributed in the crystals.

[0019] Furthermore, in the microstructure of the ultra-high-strength jacket pipe according to the invention with resistance to H2S corrosion for oil pipelines, the number of alloy precipitate phases having a diameter of more than 200 nm is less than or equal to 5 per 100 µm. 2 , such as 1 to 5 per 100 µm 2 .

[0020] As described above, the precipitation phase of alloys with a large dimension, such as Cr, can 23 C6 precipitates readily at the crystal and lath boundaries to form a diffusion channel for hydrogen, accelerating hydrogen diffusion in the steel and concentrating the points susceptible to cracking. Therefore, the number of alloy precipitates with a diameter greater than 200 nm is less than or equal to 5 per 100 µm. 2 .

[0021] Furthermore, the ultra-high-strength jacket pipe according to the invention, with resistance to H2S corrosion for oil pipelines, has a CeAlO3 inclusion and a CeAlO3+CaS complex inclusion.

[0022] Furthermore, in the ultra-high-strength jacket pipe according to the invention with resistance to H2S corrosion for petroleum pipelines, the size of the CeAlO3 inclusion and the size of the CeAlO3+CaS complex inclusion are ≤ 6 µm.

[0023] Furthermore, the properties of the ultra-high-strength casing pipe according to the invention, with resistance to H2S corrosion for oil pipelines, meet the following conditions: a yield strength of 862 MPa, an impact energy at 0°C ≤ 120 J, and resistance to stress corrosion by H2S K 1SCC ≤ 25 MPa*m 1 / 2 .

[0024] In some embodiments, the yield strength of the ultra-high-strength jacket pipe according to the invention with resistance to H2S corrosion for oil pipelines is in the range of 862 - 930 MPa.

[0025] In some embodiments, the impact energy at 0°C of the ultra-high-strength jacket pipe according to the invention with resistance to H2S corrosion for oil pipelines is in the range of 120 - 160 J.

[0026] In some embodiments, the resistance to stress corrosion due to H2S, i.e. the K 1SCC -value of the ultra-high-strength jacket pipe according to the invention with resistance to H2S corrosion for oil pipelines in the range of 25 - 30 MPa*m 1 / 2 .

[0027] In some embodiments, the ultra-high-strength jacket pipe according to the invention with resistance to H2S corrosion for oil pipelines according to method A from standard NACE TM0177 with solution D, 80% loaded, withstands a nominal yield strength for 720 hours without breakage.

[0028] Accordingly, a further object of the invention is to provide a method for producing the above-described ultra-high-strength jacket pipe with resistance to H2S corrosion for oil pipelines, which has a simple process and low costs.

[0029] To solve this problem, the present invention also provides a method for manufacturing the ultra-high-strength casing pipe described above, which is resistant to H₂S corrosion for oil pipelines. The method comprises the following steps: (1) Melting and continuous casting while maintaining a blank; (2) Heating, drilling, rolling and dimensioning; (3) Quenching: The temperature for austenitizing is in the range of 880 - 920°C, the temperature is held for 30 - 60 min, and then quenching takes place for 40 - 60 min. (4) Tempering: The tempering temperature is in the range of 690 - 720°C, the temperature is held for 50 - 80 min, and then air cooling takes place.

[0030] Furthermore, in step (1) of the inventive method for production during casting, the degree of superheating of the liquid steel is controlled in the range of 40°C - 50°C and the drawing speed during continuous casting is controlled in the range of 1.5 - 1.8 m / min.

[0031] The addition of ce according to the invention leads to an increase in the viscosity of the liquid steel and thus to a deterioration in its flowability. To ensure the flowability of the liquid steel and to avoid blockage at the outlet due to clogging during casting, a high degree of superheating and a low drawing speed are preferably maintained during continuous casting. Therefore, in preferred embodiments of the invention, the degree of superheating of the liquid steel is controlled in the range of 40°C to 50°C and the drawing speed during continuous casting is controlled in the range of 1.5 to 1.8 m / min.

[0032] Furthermore, in step (2) of the inventive manufacturing process, the temperature is increased to a holding temperature of 1200 - 1280°C.

[0033] Furthermore, in step (2) of the inventive manufacturing process, the temperature for the bore is controlled in a range of 1150 - 1250°C.

[0034] Furthermore, in step (2) of the inventive method for manufacturing, the temperature for finished rolls is controlled in a range of 880 - 940°C.

[0035] Furthermore, in step (2) of the inventive manufacturing process, the temperature for dimensioning is controlled in a range of 840 - 910°C.

[0036] The ultra-high-strength jacket pipe according to the invention, with resistance to H2S corrosion for oil pipelines, and the method for manufacturing it, have the following advantages and favorable effects.

[0037] In the ultra-high-strength casing pipe according to the invention, which is resistant to H2S corrosion for oil pipelines, the number of large precipitate phases of the alloy can be controlled by appropriately adjusting the composition of the alloying elements, and at the same time the inclusions can be modified to reduce their size, resulting in a casing pipe for oil wells that has both ultra-high strength and good resistance to stress corrosion by H2S.

[0038] The ultra-high-strength casing pipe according to the invention, with resistance to H2S corrosion for oil pipelines, achieves a strength of 125 ksi, a yield strength ≤ 862 MPa, an impact energy at 0°C ≤ 120 J, and resistance to stress corrosion by H2S K 1SCC ≤ 25 MPa*m 1 / 2 , and no fracture according to method A of standard NACE TM0177 with solution D, 80% loaded, at a nominal yield strength for 720 hours.

[0039] The ultra-high-strength casing pipe according to the invention, with resistance to H2S corrosion for oil pipelines, can be used for the development of oil or gas in a hydrogen sulfide-containing source with an extreme depth of more than 9000 meters, which is of very important importance. Detailed descriptions

[0040] The following section explains and describes in more detail the ultra-high-strength casing pipe according to the invention, which is resistant to H₂S corrosion and is used for oil pipelines, and the method for manufacturing it, in connection with specific embodiments. However, this explanation and description do not constitute a limitation of the technical solutions according to the invention. Examples 1-6 and comparative examples 1-8

[0041] The ultra-high-strength jacket pipes with resistance to H2S corrosion for oil pipelines according to examples 1-6 and the comparison jacket pipes according to comparison examples 1-8 were manufactured using the following steps: (1) The chemical composition shown in Table 1 was melted, refined in a ladle furnace (LF), processed under vacuum in a vacuum forming (VD) furnace, and continuously cast to obtain a blank. In both the LF and VD furnace processes, pure ce or a ce alloy was added to the liquid steel, argon was blown, the steel was allowed to stand for more than 5 minutes, and then continuously cast. During casting, the degree of superheating of the liquid steel was controlled in the range of 40–50°C, and the drawing speed during continuous casting was controlled in the range of 1.5–1.8 m / min. (2) Heating: The temperature was increased to a holding temperature of 1200 - 1280°C. (3) Drilling: The temperature for drilling was controlled in a range of 1150 - 1250°C. (4) Rolls: The temperature for finishing rolls was controlled in a range of 880 - 940°C. (5) Sizing: The temperature for sizing was controlled in a range of 840 - 910°C, and a pipe of φ177.8*12.65 mm was obtained. (7) Quenching: The temperature for austenitizing was in the range of 880 - 920°C, the temperature was held for 40 - 60 min, and then quenching took place. (8) Tempering: The tempering temperature was in the range of 690 - 720°C, the temperature was held for 50 - 80 min, and then air cooling took place.

[0042] It should be noted that the chemical compositions and the configurations of the processes involved in the ultra-high-strength casing pipes with resistance to H₂S corrosion for oil pipelines according to Examples 1-6 of the invention meet the requirements of the invention's configuration. However, the chemical element content of Comparative Examples 1-8 does not meet the requirements of the invention.

[0043] Table 1 summarizes the mass percentages of the individual chemical elements of the ultra-high strength jacket pipes with resistance to H2S corrosion for oil pipelines according to examples 1 - 6 and the comparison jacket pipes according to comparison examples 1 - 8.

[0044] Table 2 summarizes the specific process parameters in the process steps described above for the ultra-high-strength jacket pipes with resistance to H2S corrosion for oil pipelines according to examples 1 - 6 and for the comparison jacket pipes according to comparison examples 1 - 8. Table 2. number Degree of superheat (°C) Drawing speed in continuous casting (m / min) Holding temperature (°C) Temperature for drilling (°C) Temperature for finished rollers (°C) Temperature for dimensioning (°C) Austenitizing temperature (°C) Time required to maintain quenching temperature (min) Tempering temperature (°C) Time required to maintain temperature (min) Example 1 40 1,6 1210 1190 900 880 900 50 690 50 Example 2 42 1,8 1220 1200 910 840 890 30 700 60 Example 3 50 1,7 1240 1210 930 870 910 60 720 60 Example 4 45 1,5 1230 1190 920 900 880 60 710 80 Example 5 48 1,6 1200 1250 940 890 920 40 700 70 Example 6 45 1,7 1280 1150 880 910 880 40 715 70 Comparative example 1 40 1,6 1210 1190 900 880 900 50 690 50 Comparative example 2 40 1,6 1210 1190 900 880 900 50 690 50 Comparative example 3 42 1,8 1220 1200 910 840 890 30 700 60 Comparative example 4 50 1,7 1240 1210 930 870 910 60 710 60 Comparative example 5 45 1,5 1230 1190 920 900 880 60 720 80 Comparative example 6 48 1,6 1200 1250 940 890 920 40 700 70 Comparative example 7 45 1,7 1280 1150 880 910 880 40 705 70 Comparative example 8 46 1,7 1240 1210 930 870 910 60 710 60

[0045] Samples were taken from the ultra-high-strength casing pipes with resistance to H₂S corrosion for oil pipelines according to Examples 1–6 and from the comparison pipes according to Comparison Examples 1–8, and the properties of the pipes were measured, the results of which are listed in Table 3. The associated procedures for measurements and tests are described below. (1) Microstructure observation: The sample is polished. The inclusions are observed using an optical microscope. The sample undergoes microstructure analysis using an EVO MA25 scanning electron microscope and a JEM 2100F transmission electron microscope. The type of carbide is determined by analyzing the electron diffraction spectrum of the carbide. The size of the carbide is measured using the transmission electron microscope. The size of the inclusions is determined using the scanning electron microscope. The type of inclusions is determined by analysis using an energy-dispersive spectrometer (EDS). The diameters and number of alloy precipitates are determined using the scanning electron microscope. (2) Tensile test: The tensile strength is measured at normal temperature in accordance with standard GB / T 228.1-2000 to obtain the yield strength. (3) Impact test: The measurement of impact energy at 0°C is carried out in accordance with standard GB / T 229-2007 procedure for the Charpy impact test using a pendulum hammer for metallic material. (4) Determination of the K 1SCC -Values: The determination is carried out according to procedure D from the standard NACE TM0177-2016. (5) Measurement of resistance to sulfur: The measurement of resistance to sulfur is carried out in accordance with method A of standard NACE TM0177-2016 using solution D, loaded 80%, at a nominal yield strength (862 MPa) for 720h.

[0046] Table 3 summarizes the results of the tests for examples 1 - 6 and the comparison examples 1 - 8. Table 3. number Yield strength Rt0.7(MPa) Percussion work in the transverse direction (0°C, J) K 1SCC (MPa*m 1 / 2 ) Number of alloy precipitation phases with a diameter greater than 200 nm ( / 100 µm) 2 ) Maximum dimensions of the CeAlO3 inclusion and CeAlO3+CaS complex inclusion (µm) Procedure A according to standard NACE TM0177 (D solution, loaded 80% * 862 MPa, 720h) Example 1 896 153 27,6 3 4 no fracture Example 2 920 145 28,1 2 5 no fracture Example 3 925 145 27,9 4 3 no fracture Example 4 890 146 26,5 3 2 no fracture Example 5 870 159 27,4 1 1 no fracture Example 6 895 140 26,6 2 4 no fracture Comparison example 1 778 189 27,1 3 3 fracture Comparison example 2 965 110 21,1 22 3 fracture Comparison example 3 784 185 26,5 4 2 fracture Comparison example 4 968 76 20,2 20 4 fracture Comparison example 5 870 125 23,1 25 5 fracture Comparison example 6 920 110 23,5 18 4 fracture Comparison example 7 880 140 22,8 3 105 fracture Comparison example 8 890 145 23,2 30 56 fracture

[0047] Table 3 shows that the ultra-high-strength jacket pipes according to the invention with resistance to H2S corrosion for oil pipelines according to Examples 1 - 6 each have a yield strength ≥ 870 MPa, an impact strength at 0°C ≥ 140J, and resistance to stress corrosion by H2S K 1SCC ≥ 26.5 MPa*m 1 / 2 , and exhibit no fracture according to Method A of standard NACE TM0177 with solution D, 80% loaded, at a nominal yield strength for 720 hours.

[0048] Observation of the samples of H₂S-resistant casing pipes for oil pipelines, as shown in Examples 1-6, reveals that the basic microstructure is composed of tempered sorbitol and exhibits both a W₂C carbide scattered throughout the crystals and CeAlO₃ inclusions as well as CeAlO₃+CaS complex inclusions, with the size of the CeAlO₃ inclusions and CeAlO₃+CaS complex inclusions being less than 6 µm. Furthermore, the number of alloy precipitates with a diameter greater than 200 nm is less than or equal to 4 per 100 µm. 2 .

[0049] In contrast, the chemical elements of comparative examples 1-8 do not meet the design specifications of the invention, while the processes for their production essentially comply with the requirements of the invention. From this, it can be deduced that: Since the C content in the steel according to Comparative Example 1 falls below the criterion of the invention, the steel is not qualified with regard to the strength of the steel of 125 ksi or in the test according to Method A from Standard NACE TM0177.

[0050] Since the C content in the steel according to comparative example 2 exceeds the criterion of the invention, many alloy precipitate phases exist that have a diameter of more than 200 nm, which reduces the resistance to sulfur.

[0051] Since the Mo and V content in the steel according to comparative example 3 falls below the criterion of the invention, the steel is not qualified with regard to the strength of the steel of 125 ksi or in the test according to method A from standard NACE TM0177.

[0052] Since the Mo and V content in the steel according to comparative example 4 exceeds the criterion of the invention, many alloy precipitate phases exist that have a diameter of more than 200 nm, which reduces the resistance to sulfur and the impact strength.

[0053] Since the steel according to Comparative Example 5 does not contain W and the Cr content exceeds the criterion of the invention, there are many alloy precipitate phases that have a diameter of more than 200 nm, so that it is not qualified with regard to resistance to sulfur.

[0054] Since the W content in the steel according to comparative example 6 exceeds the criterion of the invention, there are many alloy precipitation phases that have a diameter of more than 200 nm, so that it is not qualified with regard to resistance to sulfur and impact strength.

[0055] Since the steel in comparison example 7 does not contain Ce, it has large inclusions and is therefore not qualified with regard to resistance to sulfur.

[0056] Since the Ce / O ratio in the steel according to comparative example 8 exceeds the criterion of the invention, there are many alloy precipitation phases with a diameter of more than 200 nm and large inclusions, so that it is not qualified with regard to resistance to sulfur.

[0057] It can be seen from this that with the technical solutions according to the invention a casing pipe for oil pipelines can be obtained which has both ultra-high strength and good resistance to stress corrosion caused by H2S.

[0058] It should be noted that the combination of technical features of the invention is not to be limited to the combinations specified in the claims of the invention or to the combinations specified in the specific embodiments, and that all specified technical features of the invention can be freely combined or assembled with one another as long as they do not contradict each other.

[0059] It should also be noted that the embodiments mentioned above represent only specific embodiments of the invention. Naturally, the present invention is not limited to the embodiments mentioned above. Changes or modifications that a person skilled in the art can readily deduce from the disclosure of the invention, or that are easily imaginable to him or her, are intended to be included within the scope of protection of the invention. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2004332059 A

[0004] JP 2005350754 A

[0005] Cited non-patent literature

[0000] GB / T 228.1-2000

[0045] GB / T 229-2007

[0045]

Claims

[1] Ultra-high strength casing pipe with resistance to H2S corrosion for petroleum pipelines containing Fe and unavoidable impurities, characterized by , that the ultra-high-strength casing pipe for oil pipelines further contains the following chemical elements in mass percentage: C: 0.15 - 0.28%, Si: 0.1 - 0.5%, Mn: 0.2% - 0.5%, Cr: 0.4 - 0.8%, Mo: 0.8 - 1.5%, V: 0.15 - 0.3%, Nb: 0.05 - 0.15%, W: 0.2 - 0.6%, Al: 0.01 - 0.05%, Ce: 0.002 - 0.006%, 0 < O ≤ 0.002%; where Ce / O = 1 - 3.5 applies to the mass percentages of Ce and O. [2] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 1, characterized by , that in the ultra-high-strength casing pipe for oil pipeline the mass percentages of the elements are: C: 0.15 - 0.28%, Si: 0.1 - 0.5%, Mn: 0.2% - 0.5%, Cr: 0.4 - 0.8%, Mo: 0.8 - 1.5%, V: 0.15 - 0.3%, Nb: 0.05 - 0.15%, W: 0.2 - 0.6%, Al: 0.01 - 0.05%, Ce: 0.002 - 0.006%, O < O ≤ 0.002%; and the residual amount of Fe and other unavoidable impurities, where Ce / O = 1 - 3.5 applies to the mass percentages of Ce and O. [3] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 1 or 2, characterized by that in the ultra-high-strength casing pipe for oil pipelines, the mass percentages of the chemical elements continue to meet at least one of the following conditions: C: 0.18 - 0.25%; Cr: 0.4 - 0.7%; Mon: 0.9 - 1.2%; V: 0.18 - 0.25%; Note: 0.05 - 0.1%; W: 0.2 - 0.5%; Al: 0.015 - 0.04%; Ce: 0.002 - 0.005%. [4] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 1 or 2, characterized by, that the unavoidable impurities S ≤ 0.002%, P ≤ 0.01% and N ≤ 0.008% apply. [5] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 1 or 2, characterized by , that the basic microstructure of the ultra-high-strength casing pipe for oil pipelines is formed from tempered sorbitol. [6] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 1 or 2, characterized by , that the ultra-high-strength casing pipe for oil pipeline contains a W2C carbide which is scattered throughout the crystals. [7] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 1 or 2, characterized by , that in the microstructure of the ultra-high-strength casing pipe for oil pipelines, the number of alloy precipitation phases with a diameter greater than 200 nm is less than or equal to 5 per 100 µm2. [8] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 1 or 2, characterized by that the ultra-high-strength casing pipe for oil pipeline has a CeAlO3 inclusion and a CeAlO3+CaS complex inclusion. [9] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 8, characterized by that the CeAlO3 inclusion and the CeAlO3+CaS complex inclusion each have a size of ≤ 6 µm. [10] Ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipeline according to claim 1 or 2, characterized by , that the ultra-high-strength casing pipe for oil pipelines has the following properties: a yield strength ≥ 862 MPa, an impact energy at 0°C ≥ 120 J, and a resistance to stress corrosion by H2S K1SCC ≥ 25 MPa*m1 / 2. [11] Method for producing an ultra-high-strength casing pipe with resistance to H2S corrosion for oil pipelines according to any one of claims 1-10, characterized by that the procedure includes the following steps: Melting and continuous casting while preserving a blank; Heating, drilling, rolling and dimensioning; Quenching: Austenitize at a temperature of 880 - 920°C, hold the temperature for 30 - 60 min, and quench; Tempering: The tempering temperature was in the range of 690 - 720°C, the temperature was held for 50 - 80 minutes, and then air cooling took place. [12] Method for production according to claim 11, characterized by , that in step (1) during casting the degree of superheating of the liquid steel is controlled in the range of 40°C - 50°C and the drawing speed during continuous casting is controlled in the range of 1.5 - 1.8 m / min. [13] Method for production according to claim 11, characterized by, that in step (2) the temperature is increased to a holding temperature of 1200 - 1280°C. [14] Method for production according to claim 11, characterized by , that in step (2) the temperature for drilling is controlled in a range of 1150 - 1250°C. [15] Method for production according to claim 11, characterized by , that in step (2) the temperature for finishing rolls is controlled in a range of 880 - 940°C; and / or in step (2) the temperature for dimensioning is controlled in a range of 840 - 910°C.