Seamless steel pipe for oil extraction pump and preparation method thereof

Abstract

The present invention relates to seamless steel pipes for oil extraction pumps, which comprise the following components by mass percentage: C: 0.05 - 0.10%; Si: 0.20 - 0.40%; Mn: 0.60 - 1.00%; Cr: 7.00 - 8.00%; Mo: 1.30 - 1.50%; Al: 0.005 - 0.045%; Cu: 0.30 - 0.50%; P: 0.010 - 0.020%; S: 0 - 0.010%; the balance is Fe; the heat treatment method during the preparation of the steel pipe is as follows: the steel pipe is loaded into a continuous heating furnace, the total length of the heat treatment furnace is 45 meters, the first 20 meters is the heating section, and the last 25 meters is the isothermal heat preservation section; among them, the heating section is at 850 - 870°C and the heat preservation is ≥ 0.5 hour; the isothermal heat preservation section is at 750 - 770°C and the heat preservation is ≥ 1 hour; the hardness value of the steel pipe of the present invention can be reduced to about 150 HBW, and the production efficiency is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel pipes for oil production and their preparation methods, and particularly relates to seamless steel pipes for oil pumps and their preparation methods. Background Art

[0002] With the continuous change of the oilfield geological environment, the accessories for oil extraction have also been reformed and upgraded accordingly. Oil pumps are widely used in oilfield pumping operations. When the use environment is a high-temperature and highly corrosive (hydrogen sulfide) environment, ordinary carbon steel pipes can no longer meet the on-site operation requirements. Therefore, it is necessary to add appropriate alloys to the carbon steel pipes to match the use performance.

[0003] However, conventional heat treatment is generally normalizing in a high-temperature furnace and tempering in a low-temperature furnace. The defects of this process are long heat treatment time, high energy consumption, and high hardness of the steel pipe after heat treatment, which is not conducive to subsequent processing, especially cold processing.

[0004] The annealing process usually uses a trolley furnace. The defects of this process are slow production rhythm. The steel pipe needs to be cooled in the furnace to a certain temperature before it can be taken out of the furnace, and continuous production cannot be achieved at the same time. In addition, when using a trolley furnace for heat treatment, since the steel pipe does not move during heat treatment, it is difficult to ensure the straightness and roundness of the steel pipe, which has a great impact on subsequent use. Summary of the Invention

[0005] The purpose of the present invention is to provide.

[0006] The present invention solves its technical problems by adopting the following technical solutions:

[0007] A seamless steel pipe for an oil pump, comprising the following components in mass percentage:

[0008] C: 0.05 - 0.10%; Si: 0.20 - 0.40%; Mn: 0.60 - 1.00%; Cr: 7.00 - 8.00%; Mo: 1.30 - 1.50%; Al: 0.005 - 0.045%; Cu: 0.30 - 0.50%; P: 0.010 - 0.020%; S: 0 - 0.010%; the balance is Fe.

[0009] The addition of Cr can significantly improve the oxidation resistance and corrosion resistance of the steel, and at the same time exists in the form of Cr3(C, N) or Cr 23 C6 in the steel, which improves the creep strength of the steel. However, too high a content of Cr not only increases the cost, but also significantly increases the room-temperature tensile strength and hardness. Therefore, the content of Cr is controlled at about 7.00 - 8.00%;

[0010] Mn has the function of deoxidization, which can improve the purity of steel. By controlling the Mn content between 0.60% and 1.00%, while increasing the strength of the steel pipe, it also plays a certain role in the wear resistance of the steel pipe.

[0011] Mo refines the grains of steel, improves hardenability and hot strength properties, and maintains sufficient strength and creep resistance at high temperatures.

[0012] Cu enables low-alloy structural steel and rail steel to obtain excellent atmospheric corrosion resistance, and is also beneficial to improving the strength, wear resistance and yield ratio of steel, and has no adverse effect on the weldability of steel, and can improve its corrosion resistance in acidic media.

[0013] The preparation method of seamless steel pipe for oil production pump includes the following steps:

[0014] Tube rolling: Tube billet heating → Piercing → Hot rolling → Stretch reducing sizing → Cooling bed. The final rolling temperature of the tube rolling out of the stretch reducing mill is greater than 920 °C to complete a phase transformation process of the steel pipe, and a heat preservation cover is added to the cooling bed for slow cooling.

[0015] Heat treatment: The steel pipe after tube rolling is loaded into a continuous heating furnace. The total length of the heat treatment furnace is 45 meters. The first 20 meters is the heating section, and the last 25 meters is the isothermal heat preservation section. Among them, the heating section is 850 - 870 °C, and the heat preservation is ≥ 0.5 hours; the isothermal heat preservation section is 750 - 770 °C, and the heat preservation is ≥ 1 hour.

[0016] Furthermore, when the steel pipe enters the cooling bed with a heat preservation cover for slow cooling, the cooling rate ≤ 2000 °C / h to obtain a ferrite + carbide + martensite structure.

[0017] Furthermore, the yield strength of the seamless steel pipe after heat treatment at room temperature ≥ 255 MPa; the tensile strength ≥ 500 MPa; the hardness ≤ 160 HBW.

[0018] The advantages and positive effects of the present invention are:

[0019] 1), When conventional steel pipes are produced, normal normalizing + tempering heat treatment is adopted, and the hardness is often about 220 HBW. However, when the treatment method of this invention patent is adopted, the hardness value can be reduced to about 150 HBW, thus providing convenience for subsequent processing.

[0020] 2), The present invention greatly improves production efficiency; the qualified rate of hardness index of the conventional normalizing + tempering heat treatment process is very low, and only the full annealing process can meet the requirements, but it requires a long heat preservation time, so the production efficiency is low. Usually, it takes more than 10 hours to heat treat a furnace of steel pipes, while adopting the process method of the present invention, it takes at most 3 hours to heat treat a furnace of steel pipes, and the production rate is greatly improved. Specific embodiments

[0021] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other.

[0022] Embodiment 1

[0023] The seamless steel pipe for oil production pump provided in this embodiment comprises the following components in mass percentage:

[0024] C: 0.05 - 0.10%; Si: 0.20 - 0.40%; Mn: 0.60 - 1.00%; Cr: 7.00 - 8.00%; Mo: 1.30 - 1.50%; Al: 0.005 - 0.045%; Cu: 0.30 - 0.50%; P: 0.010 - 0.020%; S: 0 - 0.010%; the balance is Fe.

[0025] The addition of Cr can significantly improve the oxidation resistance and corrosion resistance of the steel. At the same time, it exists in the form of Cr3(C, N) or Cr 23 C6 in the steel, improving the creep strength of the steel. However, too high a content of Cr not only increases the cost, but also significantly increases the room temperature tensile strength and hardness. Therefore, the content of Cr is controlled at about 7.00 - 8.00%;

[0026] Mn has the function of deoxidizing, improving the purity of the steel. Controlling the content of Mn between 0.60 - 1.00% can improve the strength of the steel pipe and also play a certain role in the wear resistance of the steel pipe;

[0027] Mo refines the grains of the steel, improves the hardenability and thermal strength performance, and maintains sufficient strength and creep resistance at high temperatures;

[0028] Cu enables low-alloy structural steel and rail steel to obtain excellent atmospheric corrosion resistance, and is also beneficial to improving the strength, wear resistance and yield ratio of the steel, and has no adverse effect on the weldability of the steel, and can improve its corrosion resistance in acidic media.

[0029] The preparation method of the seamless steel pipe for oil production pump comprises the following steps:

[0030] Tube rolling: Tube billet heating → Piercing → Hot rolling → Stretch reducing sizing → Cooling bed. The final rolling temperature of the tube rolling out of the stretch reducing mill is greater than 920 °C to complete a primary phase transformation process of the steel pipe, and a heat preservation cover is added to the cooling bed for slow cooling;

[0031] Heat treatment: The steel pipe after tube rolling is loaded into a continuous heating furnace. The total length of the heat treatment furnace is 45 meters, the first 20 meters is the heating section, and the last 25 meters is the isothermal heat preservation section; among them, the heating section is 850 - 870 °C and the heat preservation is ≥ 0.5 hours; the isothermal heat preservation section is 750 - 770 °C and the heat preservation is ≥ 1 hour.

[0032] Among them, when the steel pipe enters the cooling bed and is slowly cooled with a heat preservation cover, the cooling rate ≤ 2000 °C / h, and a ferrite + carbide + martensite structure is obtained; the yield strength of the seamless steel pipe after heat treatment at room temperature ≥ 255 MPa; the tensile strength ≥ 500 MPa; the hardness ≤ 160 HBW.

[0033] Example 2

[0034] Using the process method in Example 1, a number of seamless steel pipes for oil extraction pumps are prepared, and their specific chemical compositions are shown in the following table (wt%):

[0035] Specimen C Si Mn P S Cr Mo Cu Al 1 0.05 0.2 0.6 0.010 0.005 7.0 1.30 0.30 0.005 2 0.08 0.3 0.8 0.015 0.008 7.5 1.40 0.40 0.020 3 0.10 0.4 1.0 0.020 0.010 8.0 1.50 0.50 0.045 4 0.05 0.2 0.6 0.010 0.005 7.0 1.30 0.30 0.005 5 0.08 0.3 0.8 0.015 0.008 7.5 1.40 0.40 0.020 6 0.10 0.4 1.0 0.020 0.010 8.0 1.50 0.50 0.045

[0036] After removing the above components from the steel pipe, the remaining component is iron.

[0037] The above steel pipe is heat-treated according to the following heat treatment process:

[0038]

[0039] For specimens 7 and 8 with the same components as specimens 2 and 3, a normalizing + tempering heat treatment process is adopted:

[0040]

[0041] The tensile and hardness properties of the seamless steel pipe after the heat treatment process of the above specimens 1-6 all meet the design requirements, as follows:

[0042] Specimen Yield strength (MPa) Rp0.2 Tensile strength (MPa) Hardness (HBW) 1 280 545 147 2 275 545 144 3 265 530 140 4 275 540 151 5 275 540 146 6 280 530 142

[0043] For specimens 7 and 8 with the same components as specimens 2 and 3, a normalizing + tempering heat treatment process is adopted, and the results are as follows:

[0044]

[0045]

[0046] The above examples have described the present invention in detail, but the content described is only the preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the present invention application should still fall within the scope covered by the patent of the present invention.

Claims

1. A method for preparing seamless steel pipes for sucker rods, characterized in that, The seamless steel pipe for sucker rod pump comprises the following components in mass percentage: C: 0.05 - 0.10%; Si: 0.20 - 0.40%; Mn: 0.60 - 1.00%; Cr: 7.00 - 8.00%; Mo: 1.30 - 1.50%; Al: 0.005 - 0.045%; Cu: 0.30 - 0.50%; P: 0.010 - 0.020%; S: 0 - 0.010%; the balance is Fe; The preparation method comprises the following steps: Tube rolling: Tube blank heating → Piercing → Hot rolling → Stretch reducing sizing → Cooling bed. The final rolling temperature of the tube rolling when leaving the stretch reducing mill is greater than 920 °C to complete a primary phase transformation process of the steel pipe, and a heat preservation cover is added to the cooling bed for slow cooling; Heat treatment: The steel pipe after tube rolling is loaded into a continuous heating furnace. The total length of the heat treatment furnace is 45 meters, with the first 20 meters being the heating section and the last 25 meters being the isothermal heat preservation section; among them, the heating section is at 850 - 870 °C and the heat preservation is ≥ 0.5 hour; the isothermal heat preservation section is at 750 - 770 °C and the heat preservation is ≥ 1 hour.

2. The preparation method of the seamless steel pipe for the oil pump according to claim 1, characterized in that, When the steel pipe enters the cooling bed and a heat preservation cover is added for slow cooling, the cooling rate ≤ 2000 °C / h to obtain a ferrite + carbide + martensite structure.

3. The preparation method of the seamless steel pipe for the oil pump according to claim 1, characterized in that The yield strength of the seamless steel pipe after heat treatment at normal temperature ≥ 255 MPa; the tensile strength ≥ 500 MPa; the hardness ≤ 160 HBW.

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