H2S stress corrosion resistant steel for petroleum casing pipe and production method of H2S stress corrosion resistant steel

Abstract

The invention provides H2S stress corrosion resistant steel for a petroleum casing pipe and a production method of the H2S stress corrosion resistant steel. The H2S stress corrosion resistant steel comprises the following components: 0.25 to 0.30 percent of C, 0.18 to 0.28 percent of Si, 0.65 to 0.80 percent of Mn, 0.95 to 1.05 percent of Cr, 0.32 to 0.40 percent of Mo, 0.015 to 0.025 percent of Nb, 0.010 to 0.025 percent of Ti, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.26 to 0.32 percent of Ni, 0.20 to 0.36 percent of Cu and the balance of iron and inevitable impurities. Compared with the prior art, chemical components are reasonably designed, and by controlling the continuous casting superheat degree of the large round billet, controlling continuous casting parameters and adjusting the rolling temperature of a steel rolling cogging mill, it is guaranteed that a macrostructure of the steel is free of abnormal and unqualified defects, the segregation control level of components and solidification structures is excellent, the surface state of rolled billets is good, and the quality of finished steel products is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of alloys, and in particular relates to H2S stress corrosion resistant steel for petroleum casing and a production method thereof. Background Art

[0002] H2S stress corrosion resistant oil casing steel is a hot-rolled steel for buried oil and gas pipelines. Through scientific composition design, it can resist the electrochemical corrosion and hydrogen damage caused by H2S pickling gas in the oil and gas pipeline environment. It is a green, environmentally friendly and long-life key field steel material.

[0003] In order to meet the above performance requirements, H2S stress corrosion resistant petroleum casing steel, on the one hand, adds a small amount of alloying elements such as Cr and Mo, which can form a protective corrosion product film on the steel surface to inhibit the corrosion rate; on the other hand, adding micro-alloying elements such as Nb and Ti to form carbides has a strong grain refinement and precipitation strengthening effect, and becomes an irreversible strong trap for hydrogen, which prevents hydrogen accumulation from causing stress damage.

[0004] Due to the large variety of active alloy elements added to the steel, especially Mo, Nb, and Ti, which are highly crack-sensitive elements, transverse cracks are very likely to appear on the surface of the ingot, or cracks during the rolling process; at the same time, this type of steel is rolled using 600mm large round billets, which requires higher process technology control methods for the control of component segregation of the ingot and the uniformity of the solidification structure, as well as the gas escape and thermal stress release during the cooling process of the continuous casting billet and rolled material. In addition, customers have put forward index requirements for the low-multiple quality, gas, and purity of the rolled material according to processing needs. In general, the production according to the existing technology is prone to problems such as surface cracks of the rolled material; low-multiple component / structure segregation; and excessive inclusions. Summary of the invention

[0005] The purpose of the present invention is to provide a H2S stress corrosion resistant oil casing steel and a production method thereof. Through component optimization design, coordinated process optimization and control, the surface of the ingot has no obvious defects such as cracks and pits, and the rolled material has no segregation, looseness, and shrinkage cavity at low magnification; there is no stress crack defect in the rolling and cooling process, and the product performance is improved.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A H2S stress corrosion resistant petroleum casing steel, comprising the following components by mass:

[0008] C is 0.25-0.30%, Si is 0.18-0.28%, Mn is 0.65-0.80%, Cr is 0.95-1.05%, Mo is 0.32-0.40%, Nb is 0.015-0.025%, Ti is 0.010-0.025%, P is ≤0.020%, S is ≤0.010%, Ni is 0.26-0.32%, Cu is 0.20~0.36%, and the rest is iron and unavoidable impurities.

[0009] Preferably, the composition of the H2S stress corrosion resistant petroleum casing steel satisfies: Nb is 0.018-0.022%, and Ti is 0.015-0.020%. Nb and Ti are strong carbide-forming elements that constitute hydrogen traps, so the above contents are controlled.

[0010] The composition of the H2S stress corrosion resistant petroleum casing steel also satisfies As+Sn+Pb+Sb+Bi≤0.035%, wherein Sn≤0.015%, Sb≤0.010%, As≤0.020%, Pb≤0.003%, and Bi≤0.005%; the above elements are five harmful elements.

[0011] The various inclusions of the H2S stress corrosion resistant petroleum casing steel are all ≤1.0 level.

[0012] A production method for H2S stress corrosion resistant oil casing steel includes the following process flow: converter → LF refining → RH furnace → continuous casting → continuous casting billet entering pit for slow cooling → heating → billet opening and continuous rolling → bar entering pit for slow cooling → inspection, finishing and storage after exiting pit.

[0013] The converter: high-drawing supplementary blowing, controlling the steel composition to 0.06%≤C≤0.12%, P≤0.011%; adding 4-4.5kg / t of lime and 0.8-0.9kg / t of slag reducing agent after steel tapping, adding 3-3.5kg / t of bearing steel refined slag after steel tapping; ensuring that the LF inlet temperature is ≥1520°C.

[0014] The LF refining outside the furnace: refining cycle 35-40min, soft blowing time ≥15 minutes, adding lime and slag-removing agent to adjust the white slag, adding silicon carbide and slag-removing agent for diffusion deoxidation, and requiring the slag to have good fluidity.

[0015] The RH furnace: a double-station RH furnace is used, argon is used as the lifting gas throughout the process, the vacuum degree is ≤67Pa, and it is maintained for more than 15 minutes. The hydrogen content of each furnace out of the station is ≤1.5ppm, the oxygen content is ≤5ppm, and the soft blowing time after feeding the calcium line is greater than 15min.

[0016] The continuous casting: the tundish superheat of the continuous casting furnace is ≤30℃, the casting speed is 0.26-0.28m / min; the water volume of the crystallizer is 3600L / min, and the water volume of the secondary cooling is 0.15L / min. Make good use of the three-stage electric stirring configuration and optimize the parameter design: the crystallizer electric stirring current is 240A, the frequency is 2Hz; the terminal electric stirring current is 650A, the frequency is 6Hz; the secondary cooling electric stirring current is 150A, the frequency is 3Hz.

[0017] The continuous casting is a continuous casting of a large round billet with a diameter of 600 mm. The main physical indicators of the protective slag used in the process are as follows: viscosity 0.90-1.10, basicity 1.00-1.25, melting point 1170-1230°C.

[0018] The continuous casting process of "large ladle-intermediate ladle-finisher" is carried out under gas protection throughout the casting process;

[0019] The continuous casting billet is slowly cooled in the pit: the billet is slowly cooled in the pit with a heat preservation cover, and the cover is opened after 72 hours, and the billet is taken out of the pit at a temperature less than 150°C;

[0020] The hot rolling process is as follows: the cold billet is charged with steel, and the time in the furnace is 7.5 hours; the temperature in the soaking section is 1270° C.; the billet must be descaled by high-pressure water after it is taken out of the furnace.

[0021] The specific steps of the slab opening and continuous rolling are as follows: the temperature of the slab opening machine is 1080±15°C, and the continuous rolling temperature is greater than 900°C;

[0022] The bars are put into the pit for slow cooling: the rolled materials (bars) are collected quickly, the rolled materials are put into the pit for slow cooling at a temperature of >400℃, the time is ≥36 hours and the rolled materials are taken out of the pit at a temperature of ≤150℃.

[0023] The design ideas of the present invention are as follows: the present invention performs component optimization design: in addition to conventional chemical corrosion resistant elements such as Cr, Ni and Mo, Nb and Ti microalloying elements are designed to be matched to manufacture hydrogen traps to ensure the material's resistance to hydrogen sulfide stress corrosion cracking; large round billet component segregation control: three-stage electromagnetic stirring technology is adopted to reduce component and solidification structure segregation; molten steel purity control: deoxidation slag making process requirements are strictly regulated, and the "large ladle-intermediate ladle-finisher" continuous casting process is used for gas protection during the entire process to reduce secondary oxidation of molten steel; multi-alloy large round billet surface quality control: large round billet peritectic steel protective slag is adopted, continuous casting weak cooling process, constant drawing speed, constant liquid level, and constant temperature superheat control are used; O and H gas control: RH high vacuum degassing for 15 minutes, and the billet is quickly collected and slowly cooled in the pit after it is off the line; heating rolling process: the heating and soaking section temperature, billet opening and rolling start temperature are designed to reduce the problem of strong rolling crack sensitivity of large round billets containing Nb and Ti steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The low-magnification structure of the 1# rolled material in Example 1 is free of general point segregation defects;

[0025] Figure 2 The low-magnification structure of the 2# rolled material in Example 1 is free of general point segregation defects;

[0026] Figure 3 This is the macrostructure of the 3# rolled material of comparative example 1, with a level 1 general point segregation defect;

[0027] Figure 4 This is the macrostructure of the 4# rolled material of comparative example 1, with a level 1 general point segregation defect;

[0028] Figure 5 The surface of the rolled billet in Example 1 is completely free of iron oxide scale;

[0029] Figure 6 For Comparative Example 2, the surface of the rolled billet has iron oxide scale that cannot be completely removed. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] A H2S stress corrosion resistant petroleum casing steel, comprising the following components by mass:

[0033] C is 0.28%, Si is 0.23%, Mn is 0.68%, Cr is 1.00%, Mo is 0.335%, Nb is 0.018%, Ti is 0.017%, P is ≤0.020%, S is ≤0.010%, Ni is 0.28%, Cu is 0.27%, and the rest are iron and unavoidable impurities. The five harmful elements are controlled as: As+Sn+Pb+Sb+Bi≤0.035%, among which Sn≤0.015%, Sb≤0.010%, As≤0.020%, Pb≤0.003%, and Bi≤0.005%.

[0034] Comparative Example 1

[0035] A H2S stress corrosion resistant petroleum casing steel, comprising the following components by mass:

[0036] C is 0.29%, Si is 0.24%, Mn is 0.68%, Cr is 0.98%, Mo is 0.340%, Nb is 0.020%, Ti is 0.018%, P is ≤0.020%, S is ≤0.010%, Ni is 0.27%, Cu is 0.28%, and the rest are iron and unavoidable impurities. The five harmful elements are controlled as: As+Sn+Pb+Sb+Bi≤0.035%, among which Sn≤0.015%, Sb≤0.010%, As≤0.020%, Pb≤0.003%, and Bi≤0.005%.

[0037] Comparative Example 2

[0038] A H2S stress corrosion resistant petroleum casing steel, comprising the following components by mass:

[0039] C is 0.28%, Si is 0.23%, Mn is 0.69%, Cr is 1.01%, Mo is 0.330%, Nb is 0.018%, Ti is 0.019%, P is ≤0.020%, S is ≤0.010%, Ni is 0.29%, Cu is 0.27%, and the rest are iron and unavoidable impurities. The five harmful elements are controlled as: As+Sn+Pb+Sb+Bi≤0.035%, among which Sn≤0.015%, Sb≤0.010%, As≤0.020%, Pb≤0.003%, and Bi≤0.005%.

[0040] Comparative Example 3

[0041] A steel for petroleum casing resistant to H2S stress corrosion comprises the following components by mass: the same components as those in Example 1.

[0042] The production methods of Example 1 and Comparative Examples 1-3 for H2S stress corrosion resistant petroleum casing steel are as follows:

[0043] The process includes the following: 120t converter → LF refining → RH furnace → continuous casting → continuous casting billet entering the pit for slow cooling → heating → billet opening and continuous rolling → bars entering the pit for slow cooling → inspection, finishing and storage after leaving the pit.

[0044] The converter: high-drawing supplementary blowing, controlling the steel composition to 0.06%≤C≤0.12%, P≤0.011%; adding 500kg / furnace of lime and 100kg / furnace of slag-reducing agent after steel tapping, adding 400kg of bearing steel refined slag after steel tapping; ensuring that the LF inlet temperature is ≥1520°C.

[0045] The LF refining outside the furnace: refining cycle 35-40min, soft blowing time ≥15 minutes, adding lime and slag-removing agent to adjust the white slag, adding silicon carbide and slag-removing agent for diffusion deoxidation, and requiring the slag to have good fluidity.

[0046] The RH furnace: a double-station RH furnace is used, argon is used as the lifting gas throughout the process, the vacuum degree is ≤67Pa, and it is maintained for more than 15 minutes. The hydrogen content of each furnace out of the station is ≤1.5ppm, the oxygen content is ≤5ppm, and the soft blowing time after feeding the calcium line is greater than 15min.

[0047] The continuous casting: the tundish superheat of the continuous casting furnace is ≤30℃, the casting speed is 0.26-0.28m / min; the water volume of the crystallizer is 3600L / min, and the water volume of the secondary cooling is 0.15L / min. Make good use of the three-stage electric stirring configuration and optimize the parameter design: the crystallizer electric stirring current is 240A, the frequency is 2Hz; the terminal electric stirring current is 650A, the frequency is 6Hz; the secondary cooling electric stirring current is 150A, the frequency is 3Hz;

[0048] The continuous casting is a continuous casting of a large round billet with a diameter of 600 mm. The main physical indicators of the protective slag used in the process are as follows: viscosity 0.90-1.10, basicity 1.00-1.25, melting point 1170-1230°C.

[0049] The continuous casting process of "large ladle-intermediate ladle-finisher" is carried out under gas protection throughout the casting process;

[0050] The continuous casting billet is slowly cooled in the pit: the billet is slowly cooled in the pit with a heat preservation cover, and the cover is opened after 72 hours, and the billet is taken out of the pit when the temperature is less than 150°C;

[0051] The hot rolling process: the cold billet is charged with steel, and the furnace time is 7.5 hours; the temperature of the soaking section is 1270°C. The billet must be descaled by high-pressure water after it comes out of the furnace.

[0052] The specific steps of the slab opening and continuous rolling are as follows: the temperature of the slab opening machine is 1080±15°C, and the continuous rolling temperature is greater than 900°C;

[0053] The bars are put into the pit for slow cooling: the rolled materials (bars) are collected quickly, the rolled materials are put into the pit for slow cooling at a temperature of >400℃, the time is ≥36 hours and the rolled materials are taken out of the pit at a temperature of ≤150℃.

[0054] Table 1 shows the main production process parameters of the embodiments and comparative examples.

[0055]

[0056]

[0057] The process conditions not mentioned in Table 1 are the same as those in Example 1 for Comparative Examples 1-3.

[0058] Depend on Figure 1-Figure 4 It can be seen that the macrostructure of the H2S stress corrosion resistant oil casing steel prepared in the embodiment of the present invention has no general pitting segregation defects, while the macrostructure of the H2S stress corrosion resistant oil casing steel prepared in comparative example 1 has general pitting segregation, which does not meet the user's technical requirements.

[0059] Depend on Figure 5-Figure 6 It can be seen that the H2S stress corrosion resistant petroleum casing steel prepared in the embodiment of the present invention is very cleanly descaled by heating the blank with water, while the H2S stress corrosion resistant petroleum casing steel prepared in comparative example 2 has a large amount of iron oxide scale on the surface that has not been completely removed.

[0060] The inclusions of the products of Example 1 and Comparative Examples 1-3 were detected, and the results are shown in Table 2.

[0061] Table 2 Inclusion control of examples and comparative examples

[0062]

[0063]

[0064] From the inclusion control of the products of the embodiment and comparative examples 1-3 in Table 2, it can be seen that the various inclusion indicators of the embodiment are all ≤1.0 level, while comparative examples 1 and 3 both have 1.5 level inclusion types, especially comparative example 3 has a significantly improved inclusion level after the protective slag indicator is changed.

[0065] From the above content combined with the data in Table 1, it can be seen that the present invention, on the basis of reasonable design of chemical composition, controls the superheat of continuous casting of large round billets in production process; optimizes the three-stage electric stirring parameters of crystallizer-end-second cooling, and selects protective slag with suitable physical performance indicators; at the same time, adjusts the rolling temperature of the steel rolling mill to ensure that the steel macrostructure has no abnormal and unqualified defects, the solidification structure segregation and inclusion control level are excellent, and the surface state of the rolled billet is good, thereby improving the quality of the finished steel product.

[0066] The composition design of the present invention meets the requirements of product resistance to H2S stress corrosion and the needs of subsequent heat treatment process of steel pipes; the smelting process design meets the technical requirements of product gas and purity, H≤1.5ppm, and the highest level of various inclusions is 1.0; the large round billet continuous casting process and protective slag index design meet the requirements of billet composition and solidification structure uniformity, the billet surface has no obvious defects such as cracks and pits, and the rolled material has no segregation, looseness, and shrinkage cavity at low magnification; the heating and slow cooling system design is reasonable, and no stress crack defects occur during the rolling and cooling process.

[0067] The underlined data above do not meet the requirements of the present invention.

[0068] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A steel for petroleum casing resistant to H2S stress corrosion, characterized in that: The H2S stress corrosion resistant petroleum casing steel comprises the following 100% components by mass: C is 0.25-0.30%, Si is 0.18-0.28%, Mn is 0.65-0.80%, Cr is 0.95-1.05%, Mo is 0.32-0.40%, Nb is 0.015-0.025%, Ti is 0.010-0.025%, P is ≤0.020%, S is ≤0.010%, Ni is 0.26-0.32%, Cu is 0.20~0.36%, and the rest is iron and unavoidable impurities.

2. The H2S stress corrosion resistant petroleum casing steel according to claim 1, characterized in that: The composition of the H2S stress corrosion resistant petroleum casing steel meets the following requirements: Nb is 0.018-0.022% and Ti is 0.015-0.020%.

3. The H2S stress corrosion resistant petroleum casing steel according to claim 1, characterized in that: The various inclusions of the H2S stress corrosion resistant petroleum casing steel are all ≤1.0 level.

4. A method for producing H2S stress corrosion resistant petroleum casing steel according to any one of claims 1 to 3, characterized in that: The production method comprises the following process flow: converter → LF refining outside the furnace → RH furnace → continuous casting → continuous casting billet entering the pit for slow cooling → heating → billet opening and continuous rolling → bar entering the pit for slow cooling → inspection, finishing and storage after exiting the pit.

5. The production method according to claim 4, characterized in that: The RH furnace: the air density is ≤67Pa, maintained for more than 15 minutes, the hydrogen content of each furnace out of the station is ≤1.5ppm, the oxygen content is ≤5ppm, and the soft blowing time after feeding the calcium line is greater than 15min.

6. The production method according to claim 4, characterized in that: The continuous casting: the overheating degree of the tundish in the continuous casting furnace is ≤30°C.

7. The production method according to claim 4 or 6, characterized in that: The continuous casting: three-stage electric stirring control crystallizer electric stirring current is 240A, frequency is 2Hz; end electric stirring current is 650A, frequency is 6Hz; second cooling electric stirring current is 150A, frequency is 3Hz.

8. The production method according to claim 4, characterized in that: The continuous casting adopts the protective slag with main physical indicators: viscosity 0.90-1.10, basicity 1.00-1.25, melting point 1170-1230°C.

9. The production method according to claim 4, characterized in that: The hot rolling process includes: charging the cold billet with steel, and keeping the steel in the furnace for 7.5 hours; and the temperature in the soaking section is 1270°C.

10. The production method according to claim 4, characterized in that: The specific process of the slab opening and continuous rolling is as follows: the temperature of the slab entering the slab opening machine is 1080±15°C, and the continuous rolling temperature is greater than 900°C.

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