An (alpha+beta) titanium alloy useful for oil well tubing and a method of making the same

Abstract

The application discloses a (alpha+beta) titanium alloy for oil well pipe and a preparation method thereof. The alloy is composed of the following components in percentage by mass: Al 5.5-6.75%, V 3.5-4.5%, Mo 0.5-2.3%, Zr 0.5-3%, Nb 0.5-3%, Fe 0.1-0.5%, O 0.1-0.5%, and the rest is Ti and inevitable impurity elements. The alloy element Mo, Zr and Nb is added on the basis of TC4 alloy, the content of Fe and O is controlled, and proper processing technology and heat treatment are combined, so that the 130 ksi titanium alloy oil well pipe is prepared, the yield strength is 850-1000 MPa, the tensile strength is 900-1100 MPa, the elongation is 12-16%, the impact energy of full-size V-shaped notch impact specimen is 30-60 J, and the titanium alloy oil well pipe has good comprehensive performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal materials and oil and gas exploitation industry, and particularly relates to a (alpha + beta) titanium alloy for oil well pipe and a preparation method thereof. BACKGROUND

[0002] With the progress of social science and technology and the gradual increase of energy consumption demand of economic development, the consumption proportion of oil and gas is still at a high level, and the demand for oil well pipe is increasing. At present, the products produced by domestic oil well pipe enterprises have fully covered API Spec 5CT "Casing and Tubing Specification for Petroleum and Natural Gas Industries", and on this basis, a series of non-API oil well pipes capable of being used under more severe conditions have been developed, such as non-API 140 casing, the anti-blast and collapse strength of which has exceeded the API level. Because the oil well pipe is usually applied to the "three high" (high temperature, high pressure and high H2S+CO2+Cl - ) environment, and needs to bear the tensile load of hundreds of tons and the formation collapse pressure, the difficulty of oil and gas resource exploration and development is increasing, and the well completion problem is increasingly prominent, and the core problem is the material selection of the well completion pipe string. The harsh bottom hole temperature, pressure and corrosion conditions require the use of high-strength and corrosion-resistant oil and gas well pipe materials, so the selection of high-temperature and high-pressure oil well materials is an important measure to control the reduction of exploitation cost and solve the well completion problem. With the increasingly severe oil well environment, the development of oil well pipe materials has experienced the stages of low alloy steel, martensitic stainless steel, ferritic-austenitic duplex stainless steel and nickel-based corrosion-resistant alloy.

[0003] China has the first titanium resource reserves, and titanium alloy has the advantages of high specific strength, excellent impact resistance and high economy, which can fully meet the development of oil and gas fields in the "three high" environment, so titanium alloy has become the preferred material in the current oil exploration and development field, and the development of titanium alloy oil well pipe and its production process has become an important technical problem to be solved. TC4 (Ti-6Al-4V) titanium alloy is a typical alpha + beta two-phase titanium alloy, which contains 6wt.% of alpha stabilizing element Al and 4wt.% of beta stabilizing element V, and the usage accounts for more than 50% of all titanium alloys, so TC4 titanium alloy can be used as an important material selection for oil well pipe.

[0004] The TC4 or TC4 ELI alloy oil well pipe does not occur corrosion under the condition of containing sulfur and carbon dioxide, but there are still the following three problems: ① under the condition of matrix acidification, the alloy will occur serious crevice corrosion when the temperature is higher than 85℃; ② under the condition of containing Cl -3) When galvanic corrosion occurs between the titanium alloy as the negative electrode and other metals with lower potential, hydrogen absorption and hydrogen embrittlement problems occur in the titanium alloy, especially in the beta phase of the alloy, the diffusion speed of hydrogen ions is faster, and the hydrogen embrittlement problem is more prominent. In addition, the impact toughness of the commercial oil well pipe material represented by the TC4 alloy is low, the pitting problem and stress corrosion problem in the acid medium are more prominent, and the formed titanium alloy oil pipe cannot improve the performance of the material by deformation heat treatment to meet the performance requirements in different application environments and different drilling sites.

[0005] The existing extruded pipe material TC4S (yield strength 855 MPa, tensile strength 950 MPa) of the domestic Baotitan Group only meets the 110 steel grade of API 5CT-2011. The 930 MPa grade ultra-high strength Ti-Al-V-Zr-Mo titanium alloy pipe material for drill pipes is newly developed by China Petroleum and Natural Gas Group Co., Ltd. The test shows that the yield strength of the alloy is greater than 933 MPa, the tensile strength is greater than 1051 MPa, the elongation is greater than 10%, and the impact energy is greater than 60 J, which meets the mechanical property standard requirements of 135 Ksi strength grade drill pipes in API-5DP.

[0006] The titanium alloy oil well pipe material system above 120 ksi is missing in China, and the relationship between the strength and toughness of the titanium alloy oil well pipe material above 120 ksi and the organization control is not clear. A large increase in strength will inevitably sacrifice plasticity, and it cannot be determined which microstructure or mixed structure is beneficial to the balance of strength and plasticity. The systematic research on the alloy composition design, microstructure control and performance of related materials is still blank. At the same time, the formed oil well pipe body part cannot be regulated by plastic deformation to improve the performance of the material, and can only be regulated by heat treatment to improve the performance of the microstructure, which makes it more difficult to regulate the microstructure of the pipe body. SUMMARY

[0007] The purpose of the present application is to overcome at least one of the deficiencies of the prior art, and to provide a (alpha+beta) titanium alloy for oil well pipes and a preparation method thereof.

[0008] The technical scheme adopted by the present application is:

[0009] In a first aspect, the present application provides a (alpha+beta) titanium alloy for oil well pipes, the composition of the alloy is as follows in mass percentage: Al 5.5% to 6.75%, V 3.5% to 4.5%, Mo 0.5% to 2.3%, Zr 0.5% to 3%, Nb 0.5% to 3%, Fe 0.1% to 0.5%, O 0.1% to 0.5%, and the balance is Ti and inevitable impurity elements.

[0010] In some examples, the alloy composition comprises, in mass percentage, Al 6%, V 4%, Mo 0.5%-1%, Zr 0.5%-2%, and Nb 0.5%-3%.

[0011] In some examples, the alloy composition comprises impurity elements C, Cu, Ni, B, and Y.

[0012] In some examples, the alloy composition comprises, in mass percentage, Al 6%, V 4%, Mo 1%, Zr 2%, and Nb 3%.

[0013] In some examples, the titanium alloy has a yield strength of 850-1000 MPa, a tensile strength of 900-1100 MPa, an elongation of 12-16%, and an impact energy of 30-58 J for a full-size V-notch impact specimen.

[0014] In a second aspect, the method for preparing the (α+β) titanium alloy provided in the first aspect comprises the following steps:

[0015] 1) batching: ingredients are prepared according to the composition of each element, mixed uniformly, and pressed into a billet;

[0016] 2) melting: the billet of step 1) is subjected to at least 2 times of vacuum melting, and cooled to obtain a (α+β) titanium alloy ingot for oil well pipes;

[0017] 3) heat treatment: the (α+β) titanium alloy ingot obtained in step 2) is subjected to forging, extrusion, and warm rolling, a protective coating is brushed on the surface of the obtained material, and then solid solution heat treatment and aging heat treatment are performed or not performed.

[0018] In some examples, the operation condition of the solid solution heat treatment is 800-1000 ℃ for 0.5-4 h.

[0019] In some examples, the operation condition of the aging heat treatment is an aging temperature of 300-650 ℃ and a holding time of 4-8 h.

[0020] In some examples, the protective coating is chromium oxide, aluminum oxide, or boron nitride, and the brushing thickness is 0.1-1 mm.

[0021] In some examples, the melting temperature of step 2) is 1600-1700 ℃, the number of melting is 2-3 times, and the vacuum degree during melting is ≤1.33×10-2 Pa.

[0022] The present application has the following beneficial effects:

[0023] The application adds alloy elements Mo, Zr and Nb to TC4 alloy, controls Fe and O contents, combines with proper processing technology and heat treatment, and prepares 130ksi grade titanium alloy oil well pipe with good comprehensive performance.

[0024] The yield strength of the (alpha+beta) titanium alloy prepared in the application is 850MPa-1000MPa, the tensile strength is 900MPa-1100MPa, the elongation is 12-16%, and the impact energy of the full-size V-notch impact sample is 30-60J.

[0025] The alloying effect of the selected Al, V, Mo, Zr and Nb elements in Ti forms (alpha+beta) titanium alloy, and under the condition of reasonable component ratio, the performance of the alloy is regulated and controlled through different processing and heat treatment processes, the mechanical performance of the alloy meets the requirement of the 135Ksi strength level drill pipe in API-5DP, and the plasticity is further improved to more than 13%, and the performance is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is the DSC curve diagram of Example 1.

[0027] Figure 2 It is the metallographic picture of Example 1 after quenching after holding at 935 DEG C.

[0028] Figure 3 It is the metallographic picture of Example 1 after quenching after holding at 940 DEG C. DETAILED DESCRIPTION

[0029] The following disclosure provides many different embodiments or examples for implementing the different aspects of the application. The element composition of the alloy in each example and comparative example is shown in Table 1 below, the Fe content is 0.1%-0.5%, the O content is 0.1%-0.5%, and the rest is Ti and inevitable impurity elements. Comparative example 1 is TC4 alloy, and comparative example 2 does not add Nb.

[0030] Table 1

[0031]

[0032] The preparation and heat treatment method of the (alpha+beta) titanium alloy of each example and comparative example are as follows:

[0033] 1, batching: Al, Nb and Mo intermediate alloy are respectively prepared according to the composition of the alloy, zero-grade sponge Ti and sponge Zr are mixed uniformly; the purity of the sponge Zr is greater than or equal to 99.9%.

[0034] 2. Melting: The prepared raw materials are pressed into electrodes on a hydraulic press and are subjected to three times of melting in a vacuum self-consumption arc furnace. During the melting, the vacuum degree in the furnace is controlled to be less than or equal to 10 -2 Pa, and the furnace temperature is about 1600°C, to obtain an alloy ingot. After being cooled sufficiently, samples are taken for differential thermal analysis and metallographic analysis, the β→α phase transition temperature of the alloy is measured, and whether the ingot has composition segregation is analyzed by a chemical method. Then, the surface of the ingot is turned to remove the outer oxide layer and the necking.

[0035] 3. Open-die forging: Before forging, the surface of the ingot is brushed with a layer of chromium oxide to reduce oxidation and hydrogen absorption. After being naturally air-dried, the ingot is heated in a gas furnace or an electric resistance furnace and is subjected to multiple times of forging on a 10000-ton open-die forging machine. After being completed, the ingot is air-cooled to room temperature to obtain a forged bar. Samples of the forged bar are taken for the β→α phase transition temperature and composition detection of the alloy. After the forged bar is machined, an extrusion blank is obtained.

[0036] 4. Extrusion: A layer of steel sleeve and copper sleeve is successively wrapped on the outer surface and the inner hole surface of the extrusion blank as a lubricating layer during extrusion. Subsequently, the extrusion blank is heated to 800-1000°C in an electric resistance furnace and is subjected to pipe extrusion. During the extrusion, graphite, MoS2, etc. are sprayed on the surface of the work die for lubrication. After being put into an extrusion cylinder, the extrusion blank is covered with an extrusion pad. After the extrusion is completed, the extrusion blank is air-cooled, and then is pickled and straightened. The obtained extruded pipe has an outer diameter of and a wall thickness of 14.5mm.

[0037] 5. Warm rolling: The extruded titanium pipe after being pickled and straightened is subjected to pilger rolling to finally obtain a rolled pipe . Subsequently, the rolled pipe is machined using a wire cutting machine, and samples are cut from the rolled pipe for mechanical property detection. The specific detection results are shown in Table 2 corresponding to the data of the warm rolling state. The rest is used for the following solid solution heat treatment.

[0038] 6. Solid solution heat treatment: After the surface of the pipe is smeared with a layer of chromium oxide, the pipe is put into a box-type electric resistance furnace for solid solution treatment. Different solid solution temperatures are selected to investigate their effects on the properties of the alloy. After being kept for a certain time, the pipe is air-cooled. The solid solution heat treatment conditions are 800-1000°C for 0.5h-4h, and air-cooling.

[0039] 7. Aging heat treatment: The aging is performed in a box-type electric resistance furnace, and the pipe is air-cooled after being kept for a certain time. The aging treatment system is: aging temperature 300-650°C, and keeping time 4h-8h.

[0040] The samples of the forged bar are taken for the β→α phase transition temperature, composition detection results, and the specific data of the properties of the titanium alloy under different processing and heat treatment states are shown in the following examples. Due to the limitation of the wall thickness of the pipe, the impact energy test sample of the rolled pipe can be 3 / 4 size (7.5*10*55mm), which can be converted into full-size sample impact energy by 80%.

[0041] Example 1

[0042] The component detection results of this example are shown in Table 2, and the performance data of the titanium alloy prepared in different processing and heat treatment states are shown in Table 3. It can be seen from Table 3 that the β→α phase transition temperature of the alloy is about 940℃ according to the preliminary judgment of the DSC curve, and the phase transition temperature of the alloy is 937℃ in combination with the metallographic pictures (500 times) obtained after holding at 935℃ Figure 1 Figure 2 ), 940℃ Figure 3 ) for 45 min and then quenching.

[0043] Table 2 ICP component inspection results

[0044] Al V Mo Zr Nb Fe Ti 6.49 3.87 0.47 1.50 1.00 0.088 bal.

[0045] Table 3 Performance data of the titanium alloy prepared in Example 1 in different processing and heat treatment states

[0046]

[0047] Example 2:

[0048] The performance data of the titanium alloy prepared in this example in different processing and heat treatment states are shown in Table 4. According to the DSC curve and the metallographic method, the phase transition temperature of the alloy is 960℃.

[0049] Table 4 Performance data of the titanium alloy prepared in Example 2 in different processing and heat treatment states

[0050]

[0051] Example 3:

[0052] The performance data of the titanium alloy prepared in this example in different processing and heat treatment states are shown in Table 5. According to the DSC curve and the metallographic method, the phase transition temperature of the alloy is 930℃.

[0053] Table 5 Performance data of the titanium alloy prepared in Example 3 in different processing and heat treatment states

[0054]

[0055] Example 4:

[0056] The performance data of the titanium alloy prepared in this example in different processing and heat treatment states are shown in Table 6. According to the DSC curve and the metallographic method, the phase transition temperature of the alloy is 920℃.

[0057] Table 6 Performance data of the titanium alloy prepared in Example 4 in different processing and heat treatment states

[0058] ​

[0059] Example 5

[0060] The performance data of the titanium alloy prepared in this example in different processing and heat treatment states are shown in Table 7. According to the DSC curve and metallographic method, the phase transition temperature of the alloy is determined to be 925℃.

[0061] Table 7 Performance data of the titanium alloy prepared in Example 5 in different processing and heat treatment states

[0062]

[0063] Example 6

[0064] The performance data of the titanium alloy prepared in this example in different processing and heat treatment states are shown in Table 8. According to the DSC curve and metallographic method, the phase transition temperature of the alloy is determined to be 907℃.

[0065] Table 8 Performance data of the titanium alloy prepared in Example 6 in different processing and heat treatment states

[0066]

[0067] Example 7

[0068] The performance data of the titanium alloy prepared in this example in different processing and heat treatment states are shown in Table 9. According to the DSC curve and metallographic method, the phase transition temperature of the alloy is determined to be 890℃.

[0069] Table 9 Performance data of the titanium alloy prepared in Example 7 in different processing and heat treatment states

[0070]

[0071] Comparative Example 1

[0072] The performance data of the titanium alloy prepared in this example in different processing and heat treatment states are shown in Table 10. According to the DSC curve and metallographic method, the phase transition temperature of the alloy is determined to be 978℃. Without adding Mo, Zr, Nb, the performance of the alloy is not as good as that of the examples.

[0073] Table 10 Performance data of the titanium alloy prepared in Comparative Example 1 in different processing and heat treatment states

[0074]

[0075] Comparative Example 2

[0076] The performance data of the titanium alloy prepared in the example in different processing and heat treatment states are shown in Table 11. According to the DSC curve and metallographic method, the phase transition temperature of the alloy is determined to be 967℃. The strength of the alloy is low due to the small addition of Mo and Zr; and the impact energy is low due to the absence of Nb.

[0077] Table 11 Performance data of the titanium alloy prepared in Comparative Example 2 in different processing and heat treatment states

[0078]

[0079] In summary, increasing the contents of Mo, Zr and Nb can reduce the β phase transition temperature of the alloy. Compared with Comparative Example 2, the addition of Mo and Zr in Comparative Example 1 can enhance the yield strength and tensile strength of the alloy; and compared with Comparative Example 2, the addition of Nb in Example 1 can improve the plasticity and impact resistance of the alloy.

[0080] The above is a further detailed description of the present application, which should not be considered as a limitation on the specific implementation of the present application. For those skilled in the art to which the present application belongs, simple deductions or replacements without departing from the concept of the present application are within the protection scope of the present application.

Claims

1. An (α+β) titanium alloy useful for oil country tubular goods, characterized in that, The alloy has the following composition in percentage by mass: Al 5.5-6.75%, V 3.5-4.5%, Mo 0.5-2.3%, Zr 0.5-3%, Nb 0.5-3%, Fe 0.1-0.5%, O 0.1-0.5%, and the rest is Ti and inevitable impurities, and the preparation method comprises the following steps: 1) batching: the components are mixed according to the element composition, and then pressed into a blank; 2) melting: the blank of step 1) is subjected to at least two vacuum melting, and then cooled to obtain a (alpha+beta) titanium alloy ingot for oil well pipe; 3) heat treatment: the (alpha+beta) titanium alloy ingot obtained in step 2) is subjected to forging, extrusion and warm rolling, and then a protective coating is brushed on the surface of the obtained material, and then solid solution heat treatment and aging heat treatment are carried out, the operation conditions of the solid solution heat treatment are: solid solution treatment at 800-1000 ℃ for 0.5-4 h, and the operation conditions of the aging heat treatment are: aging temperature is 300-650 ℃, and the holding time is 4-8 h.

2. The titanium alloy of claim 1, wherein In the alloy composition, Al, V, Mo, Zr and Nb are 6%, 4%, 0.5-1%, 0.5-2% and 0.5-3% respectively in percentage by mass.

3. The titanium alloy of claim 1, wherein The impurities in the alloy composition are C, Cu, Ni, B and Y.

4. The titanium alloy of claim 1, wherein In the alloy composition, Al, V, Mo, Zr and Nb are 6%, 4%, 1%, 2% and 3% respectively in percentage by mass.

5. The titanium alloy of claim 1, wherein The titanium alloy has a yield strength of 850-1000 MPa, a tensile strength of 900-1100 MPa, an elongation of 12-16%, and an impact energy of 30-58 J for a full-size V-notch impact specimen.

6. The titanium alloy of claim 1, wherein The protective coating is chromium oxide, aluminum oxide or boron nitride, and the brushing thickness is 0.1-1 mm.

7. The titanium alloy of claim 1, wherein The temperature of the smelting of step 2) is 1600-1700℃, the number of smelting is 2-3 times, the vacuum degree during smelting is ≤1.33×10 -2 Pa.

Images