JPH0371506B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an austenite alloy for oil well pipes used in the production of oil and natural gas, or line pipes used to transport these, and in particular, _H2S , CO ₂ , Cl ^- in an environment where
It relates to alloys with corrosion resistance. (Conventional Technology) As the environment for producing oil and natural gas increases in H ₂ S and becomes hotter and more pressurized due to deep well drilling, the materials used are also becoming more highly alloyed.
Normally, in high temperature and high pressure environments where H ₂ S exists, Ni
(e.g. 25% or more), Ni-Cr-Mo
-Fe alloys are known to have high corrosion resistance. Also, JP-A No. 61-99656 and JP-A-Sho.
No. 61-99660 "High strength welded steel pipes for line pipes", JP 58-1044 Publication "High strength alloys for oil country tubular goods with excellent stress corrosion cracking resistance", etc. contain corrosive substances in the presence of H ₂ S. alloys used in harsh environments are disclosed. The techniques of JP-A-61-99656 and JP-A-61-99660 set the range of active ingredients (Ni, Cr, Mo, W) so as to impart corrosion resistance,
Furthermore, it relates to welded steel pipes for high-strength line pipes to which rare earth elements, Y, Mg, Ca, and Ti are added to improve hot workability. The objective is to maintain the hot workability of alloy steel pipes by adding rare earth elements and the like. Furthermore, in Japanese Patent Application Laid-open No. 1044/1983, Cr, Mo,
The content of W, Ni, and Mn is adjusted to a range that provides stress corrosion cracking resistance in an H ₂ S environment, and further,
An alloy is disclosed that has improved corrosion resistance by adding Cu and Co, and improves hot workability by adding rare earth elements, Y, Mg, Ca, and Ti. (Problems to be Solved by the Invention) The environmental conditions of oil and gas wells where H ₂ S exists are extremely harsh for the alloys used. For example, not only does the presence of H ₂ S increase the corrosivity of the environment, but also the increased hydrogen ion concentration, temperature, and gas pressure caused by H ₂ S and CO ₂ reduce corrosion resistance. Low-alloy steel suffers general corrosion of up to 10 mm per year, making it unusable. On the other hand, the use of existing high alloys as oil country tubular goods, such as Hastelloy C-276, may be usable in all environments, but the cost and practicality of the oil country tubular goods is low. The present invention is effective in a temperature range of 150°C or higher and lower than 200°C.
The objective is to provide an austenitic alloy with excellent stress corrosion and crevice corrosion resistance in the presence of H ₂ S, CO ₂ and Cl ^- . (Means for solving the problems) The present invention provides general corrosion resistance in the above environment.
It is formed from the basic components of Cr, Ni, and Mo, and the alloy component amounts are set so as to satisfy the conditions that general corrosion does not occur (conditions that the alloy becomes passivated) in the environment in which it is used. However, oil wells containing normal H ₂ S
Since the gas well environment contains chlorine ions, localized corrosion such as pitting corrosion and stress corrosion cracking occurs even in a passive state where general corrosion does not occur. In order for an alloy to be used in an H ₂ S environment, it is necessary to suppress the occurrence of stress corrosion cracking, even among local corrosion. As a result of research, the present inventors have found that stress corrosion cracking resistance can be significantly improved by reducing the shape of inclusions present in the alloy to below a certain size and suppressing the formation of minute δ-ferrite. We have obtained knowledge that it will improve. In this way, after performing treatments to maximize the stress corrosion cracking resistance of the alloy, we set a range of alloy components that would not cause stress corrosion cracking in a given environment. Furthermore, it has been found that by adding Cu, Sn, and Sb under the above conditions, crevice corrosion resistance can be improved. However, the gist of the present invention is that C: 0.03% or less, Si: 0.02% to 1.0%, Mn: 0.02% by weight.
% ~ 1.0%, Cr: 20% ~ 28%, Ni: 24% ~ 60%,
Mo: 4% to less than 7%, La: 0.1% or less, Al: 0.1
% or less, Ca: 0.03% or less, O: 0.01% or less, P:
0.03% or less, S: 0.01% or less, Cu: 2% or less and/or Sn: 0.15% or less, as necessary.
Sb: Contains one or two of 0.15% or less,
It is an austenitic alloy that is cold-worked and has high cracking resistance in an environment where hydrogen sulfide is present, which is composed of other unavoidable impurities and the balance iron, and which satisfies the conditions of the following formulas. 75≦Cr+2Ni+1.5Mo≦152 Ni+12≧1.5(Cr+Mo) (Al+Ca)/(S+O)≧5 1≦La/[(S+O)−0.05(Al+Ca)]≦20 The present invention will be described in detail below. (Function) Figure 1 shows a 25%Cr-40%Ni-5%Mo-Fe alloy that has been subjected to 20% cold working in a 5% NaCl solution at a temperature of 200°C, PH3, and _H2S partial pressure of 50 atm. The influence of the shape of inclusions on the occurrence of stress corrosion cracking is shown. Incidentally, the inclusion particle size in FIG. 1 is that in the cast structure. In the alloy containing the alloy components of the present invention, which will be described later, the inclusion shape is
Or by adding Ca etc. and their combined addition, etc.
If La is added in a way that does not directly contact the slag after primary deoxidation treatment so that (Al+Ca)≧5(S+O), the shape of inclusions becomes fine as shown in Figure 2. . Incidentally, the particle size of the inclusions shown in FIG. 2 is that in the cast structure. In Figures 1 and 2, in order to obtain an inclusion shape within a range that is effective for stress corrosion cracking resistance, 1≦La/[(S+O)-0.05(Al+Ca)]≦20...(1) It is necessary that La/[(S+O)−0.05
(Al+Ca)] is smaller than 1, inclusions will not be refined, and if it exceeds 20, the refractory will be reduced, and La
This results in the formation of large inclusions containing Also, Mitsushimetal, which is normally used as a deoxidizing agent, is not suitable for the purposes of the present invention. This is because Ce, which exists together with La in Mitsushi Metal, forms large inclusions. Cr−Ni− with controlled inclusion shape as described above
In Mo-Fe alloys, the range of components in which stress corrosion cracking does not occur in the temperature range of 150℃ or higher and lower than 200℃ in an environment where H ₂ S exists is shown in Figure 3 as follows.
It is necessary to use equation (2). In addition, Figure 3 is the 5th
Using the test piece shown in the figure, the fifth example in the example described later.
These are the results of a test similar to that described in the figure. 75≦Cr+2Ni+1.5Mo≦152 ...(2) Furthermore, within the range of the above formula, in order to suppress the formation of fine δ-ferrite and suppress the deterioration of stress corrosion cracking resistance, as shown in Fig. 4. It is necessary that 1.5(Cr+Mo)−12≦Ni...(3). Next, the reasons for limiting the components in the present invention are shown below. C: By precipitating carbides at the grain boundaries, the Cr-deficient layer formed near the grain boundaries is selectively corroded;
In addition, due to corrosion of the carbide itself,
Forms the starting point for stress corrosion cracking. Therefore, when kept in the carbide precipitation temperature range, it is reduced during manufacturing to 0.03% or less, which does not precipitate in a short time. Si: Si is a necessary component as a deoxidizing component. 0.02%
If the value is less than the lower limit, the deoxidizing effect cannot be obtained.
It was set at 0.02%. Even if the content exceeds 1.0%, the effect will be almost saturated, so the upper limit value should be set.
It was set at 1.0%. Mn: Like Si, the Mn component has a deoxidizing effect. 0.02
%, the deoxidizing effect cannot be obtained, so the lower limit was set at 0.02%. This component has almost no effect on stress corrosion cracking resistance, and the effect reaches saturation when added in excess of 1.0%, so its upper limit was set at 1.0%. P: Segregates at grain boundaries, deteriorating hot workability and stress corrosion cracking resistance. If the content is 0.03% or less, there is no practical effect. For this reason, it was specified as 0.03% or less. Ni: In an environment where H ₂ S exists, Ni is a main element that forms a passive state together with Cr and suppresses the formation of δ-ferrite as an austenite forming element. In order to suppress the formation of δ-ferrite corresponding to ferrite-forming elements (Cr, Mo),
From the formula Ni+12≧1.5 (Cr+Mo), as the lower limit amount
24% is necessary, and addition of more than 60% is not necessary in order to suppress the formation of δ-ferrite even if the ferrite-forming element is at the upper limit. For this reason, it was set at 24% or more and 60% or less. Cr: A main element that forms a passive film, and in the environment shown in Figures 3 and 4 where H ₂ S exists, it does not show any effect if it is less than 20%. Also, even if it is added in excess of 28%,
Within the range shown in FIG. 3, the effect is saturated and δ-ferrite is produced, deteriorating the stress corrosion cracking resistance. For this reason, we set the lower limit to 20% and the upper limit to 28%.
And so. Mo: Suppresses the initiation and propagation of stress corrosion cracking by suppressing active dissolution. In an H ₂ S environment of 150°C or higher, addition of less than 4.0% has little effect, and
Addition of 7.0% or more forms δ-ferrite,
On the contrary, it deteriorates stress corrosion cracking resistance. For this reason, the lower limit was set to 4.0% and the upper limit was set to less than 7.0%. Al, Ca: Added as deoxidizers. Therefore, it is not added in an amount exceeding the upper limit required for deoxidation. Al and Ca
The component amount after addition is (Al + Ca) ≧ 5 (O + S)
It is added so that Al is 0.1%, Ca is 0.03
If added in excess of %, stress corrosion cracking resistance will deteriorate. Therefore, the upper limits of Al and Ca were set to 0.1% and 0.03%, respectively. La: Refines inclusions in steel. However, it is not effective when the O and S contents are high. Therefore, Al, Ca,
Alternatively, by a combination of these or other means, the molten alloy is deoxidized and desulfurized so that (Al + Ca) ≧ 5 (O + S), and La is deoxidized so that it does not come into contact with the slag as a deoxidation product. It is necessary to add The effect of La on making inclusions finer is
It is effective within the range of formula (1), and saturates when La exceeds 0.07%, regardless of the limitations of formula (1). Also,
Addition of La also has the effect of improving pitting corrosion resistance. The effect on pitting corrosion resistance is saturated at approximately 0.1%.
For the above reasons, the upper limit was set at 0.1%. Furthermore, the effect of La can be replaced by Mg, but its effect is smaller than that of La. S: S generates sulfide inclusions and becomes the starting point of corrosion and stress corrosion cracking, so it must be kept at 0.01% or less. O: Since O forms oxide inclusions and becomes the starting point of stress corrosion cracking, it is necessary to reduce it to 0.01% or less. The above are the basic components of the present invention, but in addition to these, the following elements may also be contained as necessary. Cu: Has the effect of suppressing the occurrence of crevice corrosion. However, the effect saturates when it exceeds 2%. Therefore, it is selectively added within a range of 2% or less. Sn, Sb: Adding one or two of these has the effect of suppressing the occurrence of crevice corrosion. However, the effect saturates when each exceeds 0.15%. Moreover, if it exceeds 0.2%, stress corrosion cracking resistance will deteriorate. For this reason, each upper limit was set at 0.15%. When the alloy of the present invention is used as oil country tubular goods in oil and gas well environments, it is required to provide strength. Usually, methods such as work hardening, precipitation hardening, and solid solution hardening are used to impart strength. Among these, precipitation hardening is a method that imparts strength by precipitating fine precipitates, but it is difficult to precipitate fine precipitates uniformly, and when large precipitates are formed, the aforementioned interference occurs. It becomes the starting point of stress corrosion cracking, just like other materials. Therefore, in the present invention, precipitation hardening is not used. Next, solid solution hardening, as in the present invention, has a small effect on the amount of added alloy in the case of high alloys, and is therefore difficult to employ as a strengthening method. In view of the above, the present invention provides strength through work hardening. Excessive work hardening deteriorates the stress corrosion cracking resistance, but cold working up to 30% does not change the stress corrosion cracking resistance. Therefore, in the present invention, in order to add strength, the stress corrosion cracking resistance is reduced by 30% after the final heat treatment. % or less. Next, the alloy of the present invention will be explained using examples while comparing with comparative examples and conventional examples. (Example) Alloys having the respective compositions shown in Table 1 were manufactured by the following steps, and alloy material 1 of the present invention was produced.
~21, comparative alloy materials 1 to 4, and conventional alloy material 1
I got ~3. Conventional alloy material 1 is based on Incolloy825, conventional alloy material 2 is based on DIN14462, and conventional alloy material 3 is based on JIS.
Each has a composition corresponding to SUS316C. [Process] Melting: Adjust ingredients and melt in an electric furnace. ↓ Refining: Deoxidation, desulfurization, and composition adjustment are performed using an AOD furnace. ↓ Steel extraction: La is added in a ladle. ↓ Construction ingot: 2 to 4 tons of steel ingot. ↓ Forging: Forging into a billet that has the shape required for the next process. ↓ Pipe making: The raw pipe is made using the hot extrusion method. ↓ Annealing: Solution annealing in the temperature range of 1050 to 1110℃. After annealing, the surface is finished by pickling, etc. ↓ Cold working: Using cold cables, the wall thickness is reduced by 30% or less according to the predetermined strength level. Next, the present invention alloy material 1 obtained from this result
~21, comparative alloy materials 1 to 4, and conventional alloy material 1
A force 1.2 times the 0.2% proof stress was applied to the test piece as shown in the front view in Figure 5, and 50 atm was applied to the test piece in this state.
In _H2S -5% NaCl solution (PH=3, temperature 200℃)
A stress corrosion cracking test was conducted by immersion for 330 hours, and the presence or absence of stress corrosion cracking after the test was investigated. In Fig. 5, 2 is the main body of the four-point support bending jig;
3 is a push-in screw for causing the test piece 1 to bend; 4 is a support rod for supporting the test piece 1 and applying the force of the push-in screw 3 to the test piece 1;
The push-in screw 3 is pushed in to cause bending deformation in the test piece 1, and the resulting tensile stress is transferred to the test piece 1.
The stress corrosion cracking resistance of the test piece 1 in the test environment is determined by exposing the test piece 1 and the four-point support bending jig to the test environment under the same conditions. Furthermore, test specimens 1 and ^1a as shown in the front view in FIG. A crevice corrosion cracking test was conducted by immersing the sample in an atmospheric pressure _H2S -5% NaCl solution (PH=3, temperature 200°C) for 120 hours, and the presence or absence of crevice corrosion after the test was investigated. In Table 1, ○ marks indicate no occurrence, and △ marks indicate microcorrosion occurrence.
The x mark indicates that cracks and crevice corrosion occurred.

【table】

【table】

[Table] From the results shown in Table 1, comparative alloy materials 1 to 4
are inferior in at least one of the properties of stress corrosion cracking resistance and crevice corrosion resistance, whereas the present invention alloy materials 1 to 21 all have poor stress corrosion cracking resistance and crevice corrosion resistance. Moreover, it is clear that it has even better properties than conventional alloy materials 1 to 3. (Effects of the Invention) As mentioned above, the alloy of the present invention has excellent stress corrosion cracking resistance and excellent crevice corrosion resistance, so it can be used in harsh environments where these properties are required. It exhibits extremely excellent performance as a steel pipe material for oil and natural gas extraction.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the grain size of inclusions and load stress/yield stress regarding stress corrosion cracking properties of alloys.
Figure 2 shows the particle size of inclusions and La (%)/[S (%) + O
(%) - 0.05 (Al (%) + Ca (%)) Figure 3 shows the relationship between stress corrosion cracking resistance of the alloy.
Figure 4 shows the relationship between Ni content and Cr (%) + 2Ni (%) + 1.5Mo (%).
A diagram showing the relationship between Ni content and Cr (%) + Mo (%), and FIGS. 5 and 6 are front views showing aspects of a stress corrosion cracking test and a crevice corrosion test, respectively. 1, 1a... Test piece, 2... 4-point support bending jig main body, 3... Push-in screw, 4... Support rod.

Claims (1)

[Claims] 1 C: 0.03% or less Si: 0.02% or more, 1.0% or less Mn: 0.02% or more, 1.0% or less Cr: 20% or more, 28% or less Ni: 24% or more, 60% Mo: 4% or more, less than 7% La: 0.1% or less Al: 0.1% or less Ca: 0.03% or less O: 0.01% or less P: 0.03% or less S: 0.01% or less Consists of other unavoidable impurities and the balance iron, and ,
An austenitic alloy that is cold-worked and has high cracking resistance in an environment where hydrogen sulfide is present, which satisfies the conditions of each formula below. 75≦Cr+2Ni+1.5Mo≦152 Ni+12≧1.5 (Cr+Mo) (Al+Ca)/(S+O)≧5 1≦La/[(S+O)−0.05(Al+Ca)]≦20 2 C in weight%: 0.03% or less Si: 0.02 % or more, 1.0% or less Mn: 0.02% or more, 1.0% or less Cr: 20% or more, 28% or less Ni: 24% or more, 60% or less Mo: 4% or more, less than 7% Cu: 2% or less La: 0.1 % or less Al: 0.1% or less Ca: 0.03% or less O: 0.01% or less P: 0.03% or less S: 0.01% or less Consists of other unavoidable impurities and the balance iron, and
An austenitic alloy that is cold-worked and has high cracking resistance in an environment where hydrogen sulfide is present, which satisfies the conditions of each formula below. 75≦Cr+2Ni+1.5Mo≦152 Ni+12≧1.5 (Cr+Mo) (Al+Ca)/(S+O)≧5 1≦La/[(S+O)−0.05(Al+Ca)]≦20 3 C in weight%: 0.03% or less Si: 0.02 % or more, 1.0% or less Mn: 0.02% or more, 1.0% or less Cr: 20% or more, 28% or less Ni: 24% or more, 60% or less Mo: 4% or more, less than 7% La: 0.1% or less Al: 0.1 % or less Ca: 0.03% or less O: 0.01% or less P: 0.03% or less S: 0.01% or less Contains one or two of Sn: 0.15% or less, Sb: 0.15% or less, and other unavoidable impurities and the balance iron An austenitic alloy that is cold-worked and has high cracking resistance in an environment where hydrogen sulfide is present, and is characterized by satisfying the conditions of the following formulas. 75≦Cr+2Ni+1.5Mo≦152 Ni+12≧1.5 (Cr+Mo) (Al+Ca)/(S+O)≧5 1≦La/[(S+O)−0.05(Al+Ca)]≦20 4 C in weight%: 0.03% or less Si: 0.02 % or more, 1.0% or less Mn: 0.02% or more, 1.0% or less Cr: 20% or more, 28% or less Ni: 24% or more, 60% or less Mo: 4% or more, less than 7% Cu: 2% or less La: 0.1 Contains one or two of the following: % or less Al: 0.1% or less Ca: 0.03% or less O: 0.01% or less P: 0.03% or less S: 0.01% or less Sn: 0.15% or less, Sb: 0.15% or less, and others An austenitic alloy that is cold-worked and has high cracking resistance in an environment where hydrogen sulfide is present, which is composed of unavoidable impurities and a balance of iron, and which satisfies the conditions of the following formulas. 75≦Cr+2Ni+1.5Mo≦152 Ni+12≧1.5 (Cr+Mo) (Al+Ca)/(S+O)≧5 1≦La/[(S+O)−0.05(Al+Ca)]≦20