JPH0450366B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides excellent stress corrosion cracking resistance (hereinafter referred to as "SCC resistance") under a corrosive environment, particularly under a sour gas environment ( _H2S - _CO2 -Cl-containing environment). )
and a method for manufacturing an oil well tubular member having hydrogen cracking resistance. (Prior Art) In recent years, there has been a demand for deeper oil wells and for drilling wells in sour gas environments, and Ni-based alloys and the like having high strength and high corrosion resistance are being used for such oil wells. It is well known that the corrosion resistance performance of these Ni-based alloys can be improved mainly by increasing the contents of Cr, Mo, and W. An alloy composition system suitable for the corrosive environment is selected. Furthermore, in terms of strength, high strength of 77 Kgf/mm ² or more or 91 Kgf/mm ² or more is often required at 0.2% yield strength, whereas oil well tubular members such as tubing, liners, and casings High strength is often achieved through cold working. However, with conventional manufacturing methods, it is known that stress corrosion cracking (SCC) and hydrogen cracking susceptibility in a sour gas environment increases significantly as the degree of working (cross section or wall thickness reduction rate) increases during cold working. From the perspective of ensuring corrosion resistance, the degree of cold working had to be limited, and therefore there was a limit to the strength. Furthermore, the Ni-based alloy used in this environment is mainly used as a polycrystalline body consisting of an austenite phase, but in conventional methods, elements effective in improving corrosion resistance such as Cr, Mo, and W tend to segregate, resulting in a homogeneous structure. This requires solution treatment at high temperatures, which results in coarsening of austenite grains.
In such situations, even if the alloy system contains sufficient alloying elements and forms a strong corrosion-resistant film in a static state, once stress is applied, local stress concentration tends to occur. Stable durability
It becomes impossible to demonstrate SCC properties. The presence of SCC is the biggest material factor that causes variations in corrosion resistance in a sour gas environment, even for members with the same composition, and this is due to a decrease in the set value of the allowable limit stress in material design. Alternatively, the use of overgrade materials is a factor that creates a disadvantageous situation in terms of cost. (Problems to be Solved by the Invention) An object of the present invention is to provide a method for manufacturing a tubular member for oil wells that has excellent SCC resistance and hydrogen cracking resistance in a corrosive environment such as a sour gas environment. . (Means for Solving the Problems) In order to achieve the above object, the present inventors conducted detailed research on material factors that affect SCC resistance and hydrogen cracking resistance in a sour gas environment. By adjusting the microstructure through optimization, it is now possible to improve corrosion performance, which was previously possible only by adding alloying elements, and even with the same composition system, optimization of the manufacturing process The present invention was completed based on the discovery that SCC resistance and hydrogen cracking resistance can be significantly improved. In other words, from a fracture mechanics perspective, microstructural refinement is extremely effective as a method to reduce stress concentration, which is a factor in SCC, but when the component system is manufactured using conventional manufacturing methods, uniform fine grains cannot be obtained. was extremely difficult. After examining the cause in detail, we obtained the following findings. Unlike carbon steel, low alloy steel, etc., transformation cannot be used. In unstable austenite such as stainless steels such as SUS304, once deformation-induced transformation occurs, fully austenitic systems that can utilize the reverse transformation do not undergo deformation-induced transformation. High Ni austenite matrix is prone to segregation of alloying elements Cr, Mo, W, Nb, Ti, etc.
High-temperature heat treatment is required to homogenize the structure, which tends to cause coarse grains and mixed grains. The simplest methods for solving the above problem are the powder metallurgy method and the ultra-rapid solidification method, but both are unsuitable for manufacturing tubular members for oil wells in terms of cost or manufacturable dimensions. Therefore, after studying these in more detail, we found that even with conventionally known component systems, it is possible to achieve a uniform and fine structure, and by optimizing the manufacturing process, we can achieve extremely good optimization of corrosion resistance even with the same component system. It was found that the obtained tissue was In other words, the cross-sectional reduction rate of the raw pipe obtained by specified hot working etc. is 35 in the temperature range of 200℃ or less.
% plastic working, then heated just above the recrystallization temperature, held for a predetermined time, and then cooled at a cooling rate faster than air cooling, which is repeated once or twice, to form M ₂₃ C ₆ type and M ₆ C type. Mold (M: Cr, Mo,
Fe, etc.) It is possible to create a fine austenite single-phase structure with an average grain size of 20 μm or less without forming carbides. Furthermore, when one or more of Ti and Nb is added, M'C type (M':Ti, Nb) carbides of 500 Å or less are further uniformly dispersed within the austenite grains in the above process, which also improves strength. It was found that by creating such a structure, the SCC resistance and hydrogen cracking resistance in a sour gas environment were significantly improved even if the compositions were the same. Here, the gist of the present invention is as follows: In weight%, C: 0.05% or less, Si: 1.0% or less, Mn: 2.0% or less, Ni: 30 to 60%, Cr: 15 to 30%, Mo: 1.5 to 12%, Cu: 0.01 to 3.0%, and optionally at least one of Ti: 0.01 to 2.0% and Nb: 0.01 to 2.0%, with the balance consisting of Fe and incidental impurities. A heating process in which plastic working with a cross-section reduction rate of 35% or more is applied in the temperature range from ℃ to room temperature, then heated and held just above the recrystallization temperature, cooled at a cooling rate higher than air cooling, and then cold worked.
This is a method for manufacturing a sour gas resistant tubular member for oil wells, which is characterized by performing cooling and processing one or more times. The above-mentioned "raw pipe" may be manufactured by performing hot processing such as hot extrusion after welding, or may be a hollow billet made by casting into a hollow cylindrical shape. In the present invention, "area reduction rate of 35% or more" is specified, and the upper limit is not particularly limited, but the higher the degree of processing, the better, and can be appropriately determined depending on the product dimensions, etc. In addition, "just above the recrystallization temperature" means above the recrystallization temperature,
Recrystallization temperature + 150℃ or less. (Function) Next, the reason why the alloy components and manufacturing conditions are limited as described above in the present invention will be explained in detail below. Note that unless otherwise specified, "%" means "% by weight." Chemical composition C: For C > 0.05%, M ₂₃ C ₆ type and M ₆ C type (M:
The amount of carbides (Mo, Cr, W, etc.) increases significantly, resulting in deterioration of ductility and toughness. Preferably, C≦
However, when C≦0.010%, ductility, toughness, and corrosion resistance are further improved. Si: Si is usually added because it is effective as a deoxidizing agent, but when added in large amounts, it forms intermetallic compounds that are unfavorable for ductility and toughness, such as σ, P, and Laves phases (hereinafter collectively referred to as "TCP phases"). It becomes easier to generate. Furthermore, when Si > 1.0%, micro-segregation during solidification is promoted, and the above-mentioned M ₆ C type carbide and P
The effect of significantly promoting phase formation was observed.
Si≦1.0%, but when Si≦0.50%, the effect of suppressing grain boundary precipitation of carbides is added, improving ductility, toughness,
Corrosion resistance is dramatically improved. Mn: Mn is usually added as a desulfurization agent, but it may promote TCP phase formation, so Mn≦2.0%. Ni: The alloy in the present invention contains elements Mo, Cr, which have good solid solution strengthening and work hardening ability, in the Ni matrix.
Basically, it is strengthened by adding W, Nb, etc. However, since adding a large amount of the above elements leads to destabilization of austenite, it is necessary to have an amount of Ni sufficient to stabilize the austenite base, and for this purpose Ni≧30%. Ni itself improves work hardening ability, but if it exceeds 60%, hydrogen cracking resistance deteriorates, so Ni≦60%. Cr: Improves corrosion resistance and strength together with Mo. This effect becomes noticeable when Cr≧15%, but when it exceeds 30%, hot workability decreases and TCP phase is more likely to be generated. Mo(W): Significantly improves strength and corrosion resistance, especially pitting corrosion resistance, in coexistence with Cr. In the environment targeted by the present invention, this effect becomes remarkable when Mo≧1.5%, but as with Cr, adding a large amount destabilizes the austenite matrix, so Mo≦12% is selected. Mo may be partially replaced by W, in which case Mo+1/
It is sufficient if 2W≧1.5% and Mo+1/2W≦12%. Cu: Under the target environment of the alloy system according to the present invention
Along with Cr, Mo, and W, Cu is extremely effective in improving corrosion resistance. For this purpose, Cu≧0.01% is required, but the effect is saturated when it exceeds 3%.
0.01%≦Cu≦3.0%. Ti: Ti is an optional component added as desired. It is effective in stabilizing trace amounts of C, but when Ti>2.0%
0.01≦Ti≦2.0% because TCP phase is easily generated
shall be. Nb: Like Ti, Nb is also an optional component that can be added as desired. Nb significantly improves the corrosion resistance performance of the alloy system according to the present invention in the target environment. Furthermore, like Ti, it has a stabilizing effect on C, and also contributes to increasing strength. For this purpose, Nb≧0.01%, but if it exceeds 2.0%, TCP phase tends to be generated, so 0.01≦Nb≦2.0. Other Component Elements There is no need to specify other component elements in order to achieve the purpose of the present invention, but since the same effect as when normally added can be obtained, they can be added within the following range. Al: Usually added to Ni-based alloys as an effective deoxidizer. Addition of a large amount of Yadashi promotes TCP phase formation, so Al≦1.0%. V, Ta, Zr, Hf: Like Ti, etc., they are effective in stabilizing C, but if each exceeds 1%, TCP phase is likely to be generated.
V, Ta, Zr, Hf≦1.0%. N: If a large amount of N is added, coarse nitrides are formed, which deteriorates ductility and toughness, so N≦0.050%. P, S: P and S are impurities that are inevitably mixed in, and if they exist in large amounts in the alloy, they reduce hot workability due to grain boundary segregation and also deteriorate corrosion resistance, so P≦0.030%, S≦0.0050%. Co: Co is effective in improving hydrogen cracking resistance. 5.0%
If the Co
≦5.0%. REM, Ms, Ca, Y: These improve hot workability by adding at least one small amount of 0.10% and 0.10%, respectively.
%, 0.10%, and 0.20%, conversely, low melting point compounds tend to be produced and processability deteriorates. Others: Trace amounts of B, Sn, Zn, Pb, etc. do not affect the properties of the alloy obtained by the present invention, so up to 0.10% of each is allowed as impurities.
If this upper limit is exceeded, workability or corrosion resistance will deteriorate. According to the present invention, a raw pipe is made from an alloy within the above-mentioned composition range. The method for obtaining the blank tube may be a hot extrusion method such as the Eugene Ségiurne method or the Erhard push bench method after a normal ingot is subjected to a blooming process, or an inclined rolling method such as the plug mill method or mandrel mill method. Alternatively, a raw pipe directly cast into a hollow cylindrical mold may be used, and the raw pipe produced in this way can be manufactured with or without soaking. Next, the raw pipe obtained above is subjected to cold plastic working in a temperature range of 200° C. or lower, and further heated to just above the recrystallization temperature, and the following conditions are preferable. Cold plastic working When the temperature of cold plastic working exceeds 200℃, defects (dislocations, etc.) introduced by plastic deformation begin to actively interact with solute atoms, which inhibits uniform deformation. Ru. Therefore, the temperature should be 200℃ or less.
Generally, it is sufficient to carry out the reaction at a temperature in the range of room temperature to 100°C.
Similarly, when the degree of working is 35% or more in terms of area reduction rate, recrystallization nuclei are generated everywhere due to interaction between dislocations, making it possible to refine grains. Therefore, it should be 35% or more. Preferably it is 50% or more. Liquefaction treatment The temperature of solution treatment is just above the recrystallization temperature. In general, it is preferable that the temperature be higher than the recrystallization temperature and as close to the recrystallization temperature as possible, but approximately 150℃ below the recrystallization temperature.
It is permissible up to a moderately high temperature range. In the conventional method, M ₂₃ C ₆ and M ₆ C are formed locally just above the recrystallization temperature because the grain refinement by cold plastic working as described above is not sufficient, making it difficult to make the structure uniform. According to the present invention, uniformity is possible. Similarly, regarding holding time, heating/cooling speed, rapid heating,
Although cooling and short-term holding are generally desirable, there is no problem with normal conditions obtained with conventional equipment. Such solution treatment is followed by cold working, and the degree of working is not particularly limited as long as the shape of the final product can be obtained. If necessary, the solution treatment and subsequent cold working are repeated one or more times. Next, the present invention will be further explained by examples. Example After preparing each alloy having the chemical composition shown in Table 1, raw pipes were made by the methods (A) to (C) shown in Table 2, and the fine grain processes (A) to The pipe is made using the method (D) and the yield strength is 70-100Kgf/ at 0.2% proof stress (room temperature).
The desired strength of mm ² was obtained. The recrystallization temperature of these materials was 850-980°C. Next, tensile and corrosion test pieces were taken from this material, and various tests were conducted in the following manner. The results are summarized in Table 1. The material used in the hydrogen cracking test was subjected to a long-term heat treatment at 300°C for 1000 hours before being subjected to the test.

【table】

【table】

[Table] The test procedures were as follows. Tensile test Temperature: Room temperature Test piece: 4.0mmφ, GL=20mm Stress corrosion cracking test Corrosion resistant solution: 20% NaCl-1g/S-(0.1,
1, 10) atmH ₂ S−20atm CO ₂ Temperature: 250℃ Immersion time: 500h Test piece: 10w×2t×75 R0.25U with notch,
Added stress 1σy Hydrogen cracking resistance test NACE conditions: 5%NaCl−0.5%CH ₃ COOH−
1atmH ₂ S 25℃ Test piece: Carbon steel coupling, 10w×2t×75
R0.25U with notch, added stress 1σy Figure 1 shows alloy No. 1 in Table 1, which was made with the method (A) and then subjected to cold drawing rate of 20 to 80 using the grain refining method (A).
%, and shows the structure after solution treatment and corrosion resistance performance by SSRT. By cold plastic working of 35% or more, the average grain size becomes less than 20μm,
Furthermore, the corrosion resistance performance is also good. Note that the SSRT test was conducted at 150°C in the air and in a _H2S environment (25% NaCl-1g/-S,
7 atmH ₂ S) at a strain rate ε・=1×10 ^-7 S ^-1 , and evaluation was made by the ratio of the rupture time in the air and in the H ₂ S environment. (Effects of the Invention) As described above, according to the present invention, by uniformly refining the structure, corrosion resistance can be dramatically improved even in the same component system.

[Brief explanation of the drawing]

The accompanying drawings are graphs showing the results of embodiments of the present invention.

Claims (1)

[Claims] 1% by weight: C: 0.05% or less, Si: 1.0% or less, Mn: 2.0% or less, Ni: 30-60%, Cr: 15-30%, Mo: 1.5-12%, An alloy tube with a composition of Cu: 0.01 to 3.0%, balance Fe and incidental impurities is subjected to plastic working with a cross-section reduction rate of 35% or more in the temperature range from 200℃ to room temperature, and then heated and heated just above the recrystallization temperature. Heating, which involves holding, cooling at a cooling rate faster than air cooling, and then cold processing.
A method for manufacturing a tubular member for sour gas oil wells, which is characterized by performing cooling and processing one or more times. 2% by weight: C: 0.05% or less, Si: 1.0% or less, Mn: 2.0% or less, Ni: 30-60%, Cr: 15-30%, Mo: 1.5-12%, Cu: 0.01-3.0% , plus Ti: 0.01~2.0% and Nb: 0.01~2.0%
An alloy material tube containing at least one of・Heating that involves holding, cooling at a cooling rate faster than air cooling, and then cold processing.
A method for manufacturing a tubular member for sour gas oil wells, which is characterized by performing cooling and processing one or more times.