JPS629661B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an alloy for oil country tubular goods that has excellent corrosion resistance, particularly stress corrosion cracking resistance. In recent years, there has been a marked trend toward deeper oil and natural gas wells, and the produced gas is increasingly containing corrosive substances such as wet hydrogen sulfide, carbon dioxide gas, and chlorine ions. As the usage conditions for oil country tubular goods become more severe along with this trend, countermeasures against corrosion will become even more important for stable operation. The most common method to prevent corrosion of oil country tubular goods is to add a corrosion suppressant called an inhibitor, but in some cases, such as in offshore oil wells, this method is often not effective. To deal with this situation, there has been a recent trend toward using higher-grade corrosion-resistant materials, including stainless steel.
Consideration has also begun to be given to the use of high alloy steels such as Incoloy and Hastelloy (both trade names). However, for now, H ₂ S−CO ₂ −Cl ⁻
The details of the oil well environment, such as its corrosion behavior, have not been sufficiently elucidated, and the relationship between corrosion and steel composition in this environment has only been investigated through field tests to determine the suitability of existing high-alloy steels. There has only been a level of research conducted to confirm this. The present invention uses this highly corrosive H ₂ S
The object of the present invention is to provide a steel for oil country tubular goods that exhibits excellent durability under -CO ₂ -Cl ^- oil well environments, particularly in adverse environments of 200°C or less. In other words, the gist of the present invention is that C0.1
% or less, Si1.0% or less, Mn2.0% or less, P0.030% or less, S0.005% or less, Al 0.5% or less, Cr22.5~30
%, Ni exceeding 28% and not more than 60%, containing one or both of Mo and W within a range that satisfies the following formula, and containing or not containing one or two of Cu1% and Co2% or less, Furthermore, in some cases, one or more of rare earth elements (hereinafter referred to as REM) 0.10% or less, Y 0.20% or less, Mg 0.10% or less, Ca 0.10% or less, and Ti 0.5% or less are added. Cr (%) + 10Mo (%) + 5W (%) ≧70%...4%≦Mo (%) + 1/2W (%) < 8%...... According to detailed experiments and research by the inventors, H ₂ S
The main type of corrosion in the −CO ₂ −Cl ⁻ environment is stress corrosion cracking, but the behavior of stress corrosion cracking in this case is completely different from that of stainless steel in general, and is different from that of general stainless steel. stress corrosion cracking
While this is deeply related to the presence of Cl ^- , it has become clear that in the oil well environment mentioned above, the influence of H ₂ S is greater than that of Cl ^- . On the other hand, steel pipes used for practical use as oil country tubular goods are generally cold-worked to improve their strength, but the present invention also shows that cold working significantly impairs the resistance to stress corrosion cracking. This was revealed from their research. Based on these research results, the present inventors conducted experiments with the intention of developing a cold-worked material that has high resistance to stress corrosion cracking in the presence of H ₂ S.
As a result of further research, it was found that _the
This led to the development of an alloy material that can be used as a cold-worked material that exhibits outstanding durability even in corrosive environments with operating temperatures below 200°C. Elution (corrosion) of alloys in H ₂ S−CO ₂ −Cl ⁻ environment
depends on the amounts of Cr, Ni, Mo and W. In other words, corrosion resistance is ensured by a surface film made of these elements, and the balance of content of these elements in this surface film is the most important factor that influences corrosion resistance. Regarding stress corrosion cracking in the above oil well environment, Mo is 10 times more effective than Cr, and W is 5 times more effective than Cr, and both Mo and W satisfy the above formula. In addition, experiments by the present inventors have shown that if Cr is in the range of 22.5 to 30% and Ni is in the range of more than 28% but less than 60%, a corrosion-resistant film with excellent resistance to stress corrosion cracking can be obtained. It became clear. Further, Ni has the effect of increasing corrosion resistance in terms of structure, and the above range of Ni takes this point into consideration. FIG. 1 shows the relationship between stress corrosion cracking resistance, Cr (%) + 10Mo (%) + 5W (%), and Ni content under the above-mentioned oil well environment. This data is based on Cr-Ni-Mo system or Cr-Ni system with various addition amounts of component elements.
- Molten Mo-W alloy, forge and stretch, and 7mm
After hot-rolling to a thickness, it is held at 1050℃ for 30 minutes and then water-cooled, which is a solid solution treatment.
Based on the results of a stress corrosion cracking test on specimens 2 mm thick, 10 mm wide, and 75 mm long taken perpendicular to the rolling direction from the plate material obtained after 30% cold working.
For the stress corrosion cracking test, a tensile stress equivalent to 0.2% proof stress was applied to the above specimen using the three-point support beam jig shown in Figure 2, and the specimen was heated with H2S at 10 atm _H2S and CO2 at ₁₀ atm. A method was used in which the specimens were immersed in a 20% NaCl solution (temperature 200°C) saturated with _2S and _CO2 for 1000 hours, and the presence or absence of cracking was observed. In the figure, ○: No cracking, ×: Cracking. As is clear from the figure, Cr (%) + 10Mo (%) +
If 5W (%) is less than 70% or Ni is less than 28%, stress corrosion cracking resistance is insufficient. By the way,
The reason for setting Ni to 60% or less is that even if the Ni content exceeds this value, no improvement in effectiveness will be observed, and this will only lead to economic disadvantage. In addition, the reason for limiting the characteristic components of the alloy of the present invention is that Cr is a component that increases stress corrosion cracking resistance, but it deteriorates hot workability, so it must be kept at 30% or less, but 22.5 Even if it is less than %, hot workability is hardly improved, and the formula Cr (%) + 10Mo
(%)+5W(%)≧7%, the amount of Mo and W added increases as the amount of Cr decreases, which is only economically disadvantageous. Both Mo and W are essential components for improving stress corrosion cracking resistance, and the reason for specifying Mo (%) + 1/2 W (%) is that W has an atomic weight approximately twice that of Mo. , same weight%
However, if this amount is less than 4%, the formula cannot be satisfied when Cr≦30%, and similarly, if the content exceeds 8%, it will lead to an increase in cost. Just 200℃
It is virtually unnecessary in the following H ₂ S−CO ₂ −Cl ⁻ environment. Next, the other basic components of the alloy of the present invention will be briefly described. C: There is no problem if it is 0.10% or less, but if it exceeds 0.10%, intergranular stress corrosion cracking tends to occur. Si: Necessary as a deoxidizing agent, but if it exceeds 1.0%, hot workability deteriorates. Mn: This is a deoxidizing component and has almost no adverse effect on stress corrosion cracking resistance, so Mn was allowed up to 2.0%. P: 0.030% as it increases stress corrosion cracking susceptibility
The following was made. S: 0.005 as it significantly deteriorates hot workability.
% or less. Al: Effective as a deoxidizing component and can be added up to 0.5%. Furthermore, as a selective ingredient used as required.
Cu is an element that improves corrosion resistance, but if it exceeds 1%, it adversely affects hot workability. Similarly, Co is an effective element for improving corrosion resistance and solid solution strengthening, and at 2%
The following effects are sufficient. Also REM, Y,
Addition of Mg, Ca, and Ti in appropriate amounts is effective in improving hot workability, but if they are added in excess, hot workability decreases again. This is the reason for limiting each upper limit value. Next, the effects of the present invention will be explained in detail with reference to Examples. A pipe with a size of 60 mm outer diameter x 4 mm thickness was produced from an alloy having the components (1) to (24) shown in Table 1, and was subjected to 20% cold working to increase its strength and make it into an oil country tubular product. A length (20 mm) of the pipe with a notch at a central angle of 60° was taken from this oil country tubular goods as a test piece, set as shown in Figure 3, and bolted to the outer surface of the pipe with a 0.2% yield strength. A tensile stress equivalent to H ₂ S−10 atm CO ₂ was applied and the H ₂ S partial pressure was varied.
-20% NaCl solution (temperature: 200°C) for 1000 hours, and the presence or absence of stress corrosion cracking was investigated. The results are summarized in Table 2.

【table】

[Table] The table above shows the occurrence of cracking during hot working.
None is also listed.
In Table 2, where the partial pressure of H ₂ S is relatively low, comparative examples (21) to 1 made of conventional steel are used.
(24) also shows no stress corrosion cracking, but it disappears when the H ₂ S partial pressure becomes 1 atm or more. However, those made of the steel of the present invention (1) to (14)
No cracking was observed even under an H ₂ S partial pressure of 20 atmospheres, proving the effectiveness of the steel of the present invention against stress corrosion cracking. By the way, comparative example (15) is Ni
However, similarly (16) is Cr (%) + 10Mo (%) + 5W
Since the value of (%) is below the range of the present invention, stress corrosion cracking resistance is insufficient at an environmental temperature of 200°C. In addition, comparative example (17) has too high Cr, so (18)
In addition, (19) and (20) have too high a selected component of Cu, REM, Y, Ca, Mg, or Ti, resulting in poor hot workability and problems during billet production. Cracks appeared, making it virtually impossible to manufacture the tube. As is clear from the above description, the alloy of the present invention is
It is a material that can produce cold-worked materials that exhibit stress corrosion cracking resistance that far exceeds that of conventional high-alloy steel in the highly corrosive H ₂ S−CO ₂ −Cl ^- oil well environment, so the conditions It exhibits excellent durability when used in harsh conditions for oil country tubular goods.

[Brief explanation of the drawing]

Figure 1 shows Ni and Cr (%) + 10M (%) +
A chart showing the influence of 5W (%) on stress corrosion cracking resistance. Figure 2 shows a stress corrosion cracking tester using a plate as a test piece, and Figure 3 shows a stress corrosion cracking test piece for a tubular body.

Claims (1)

[Claims] 1 C0.1% or less, Si1.0% or less, Mn2.0% or less,
P0.030% or less, S0.005% or less, Al 0.5% or less,
It is characterized by containing 22.5 to 30% Cr, more than 28% Ni to 60% or less, and one or both of Mo and W within a range that satisfies the following formula, with the remainder essentially consisting of Fe. An oil country tubular alloy with excellent stress corrosion cracking resistance. Cr (%) + 10Mo (%) + 5W (%) ≧ 70%...... 4% ≦ Mo (%) + 1/2W (%) < 8%... 2 C0.1% or less, Si1.0% or less, Mn2.0% or less,
P0.030% or less, S0.005% or less, Al 0.5% or less,
Contains 22.5 to 30% Cr, more than 28% Ni but less than 60%, one or both of Mo and W within a range that satisfies the following formula, and less than 1% Cu and less than 2% Co.
1. An alloy for oil country tubular goods having excellent stress corrosion cracking resistance, characterized in that it contains one or both of the following elements, and the remainder is substantially composed of Fe. Cr (%) + 10Mo (%) + 5W (%) ≧ 70%...... 4% ≦ Mo (%) + 1/2W (%) < 8%... 3 C0.1% or less, Si1.0% or less, Mn2.0% or less,
P0.030% or less, S0.005% or less, Al 0.5% or less,
Contains 22.5 to 30% Cr, more than 28% Ni to 60% or less, contains either or both of Mo and W within a range that satisfies the following formula, and further contains 0.10% or less of rare earth elements,
Y0.20% or less, Mg0.10% or less, Ca0.10% or less,
An alloy for oil country tubular goods having excellent stress corrosion cracking resistance, characterized by containing one or more of Ti at 0.5% or less, and the remainder being substantially Fe. Cr (%) + 10Mo (%) + 5W (%) ≧70%...... 4%≦Mo (%) + 1/2W (%) <8%...... 4 C0.1% or less, Si1.0% or less, Mn2.0% or less,
P0.030% or less, S0.005% or less, Al 0.5% or less,
Contains 22.5 to 30% Cr, more than 28% Ni but less than 60%, and one or both of Mo and W within a range that satisfies the following formula, and contains less than 1% Cu and less than 2% Co.
Contains one or more of rare earth elements 0.10% or less, Y0.20% or less, Mg 0.10% or less, Ca 0.10% or less, Ti 0.5% or less, and the remainder is an oil country tubular alloy with excellent stress corrosion cracking resistance, which is essentially composed of Fe. Cr (%) + 10Mo (%) + 5W (%) ≧ 70%...... 4% ≦ Mo (%) + 1/2W (%) < 8%...