JPS629660B2 - - 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 introduce 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 corrosion behavior in the oil well environment have not yet been fully elucidated, and the suitability of existing high-alloy steels has only recently been tested regarding the relationship between corrosion and steel composition in this environment. It's just a matter of time. The present invention uses this highly corrosive H ₂ S
The purpose of the present invention is to provide an alloy for oil country tubular goods that exhibits excellent durability even in the -CO ₂ -Cl ^- oil well environment. 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, Ni35~60%,
Cr22.5 to 35% contains one or both of Mo and W within a range that satisfies the following formula, and Cu1
%, and in some cases rare earth elements (hereinafter referred to as REM) 0.10% or less, Y0.20%
Below, stress corrosion cracking resistance characterized by containing one or more of the following: Mg 0.10% or less, Ca 0.10% or less, Ti 0.5% or less, and the remainder being substantially Fe. Excellent alloy for oil country tubular goods, Cr (%) + 10Mo (%) + 5W (%) ≧50%... 1.5%≦Mo (%) + 1/2W (%) < 4%...... According to detailed experiments and research by the inventors, H ₂ S
The main type of corrosion in a -CO ₂ -Cl ^- environment is stress corrosion cracking, but the behavior of stress corrosion cracking in this case is completely different from that of general austenitic stainless steel. While general stress corrosion cracking is deeply related to the presence of Cl ^- , in the oil well environment mentioned above, Cl ^-
However, it has become clear that the influence of H ₂ S is even greater than that. On the other hand, steel pipes used for practical use as oil country tubular goods are generally subjected to cold working to improve their strength, but it is also true that cold working significantly reduces the resistance to stress corrosion cracking mentioned above. This was discovered through research by the inventors. 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.
Further research has resulted in an environmental temperature of 150
This led to the development of a relatively inexpensive alloy that exhibits extremely good durability as a cold-worked material even under high concentration H ₂ S at temperatures below ℃. The elution rate (corrosion rate) of the alloy in the H ₂ S−CO ₂ −Cl ⁻ environment depends on the amounts of Cr, Ni, Mo, and W.
Corrosion resistance is maintained by the surface film made of these elements. These elements also increase its resistance to stress corrosion cracking, especially Mo.
has a 10 times effect on Cr as shown in the formula,
In addition, W has twice the effect of Mo, and if Mo and W satisfy the above formula and the Ni content is in the range of 35 to 60% and the Cr content is in the range of 22.5% to 35%, stress corrosion will occur. Experiments conducted by the present inventors have revealed that a surface film having excellent resistance to oxidation can be obtained. Note that Ni not only has an effect on the surface film, but also has the effect of increasing stress corrosion cracking resistance structurally, and the range of the Ni amount was determined with this point in mind. FIG. 1 shows the relationship between stress corrosion cracking resistance, Cr (%) + 10Mo (%) + 5W (%), and the amount of Ni under the above-mentioned oil well environment. This data was obtained by melting Cr-Ni-Mo or Cr-Ni-Mo-W alloys with various addition amounts of component elements, and making them 7 mm thick by forging and hot rolling. After that, at 1050℃
A solution treatment of holding for 30 minutes and cooling with water is carried out, followed by 30% cold working for the purpose of improving strength, and from the obtained steel plate, 2 mm thick, 10 mm wide,
Based on the results of stress corrosion cracking tests taken on 75mm long test pieces. As a stress corrosion cracking test,
Using the three-point support beam jig shown in Figure 2, a tensile stress equivalent to 0.2% proof stress was applied to the above test piece.
The sample was immersed for 1000 hours in a 20% NaCl solution (temperature 150°C) saturated with H ₂ S and CO ₂ at 10 atm H ₂ S and 10 atm CO ₂ and observed for cracking. In the figure, O: No cracking, ×: Cracking. As is clear from the figure, Cr (%) + 10Mo (%) +
If 5W (%) is less than 50% or Ni is less than 35%, 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 present alloy is that Cr is a component that increases stress corrosion cracking resistance, but it deteriorates hot workability, so it must be kept at 35% or less, but 22.5 Even if it is less than %, hot workability is hardly improved, and the formula Cr (%) +
Due to the regulation of 10Mo (%) + 5W (%) ≧50%, as the amount of Cr decreases, the amounts of Mo and W added increase, which is only economically disadvantageous. Mo and W
Both are essential components for improving stress corrosion cracking resistance, and the formula for Mo (%) + 1/2 W (%) is that W has approximately twice the atomic weight of Mo, and is approximately 1 times more effective in terms of effectiveness. /2
This is because if this amount is less than 1.5%, the formula cannot be satisfied when Cr≦35%, and similarly, although a content exceeding 4% leads to an increase in cost, It is virtually unnecessary in a H ₂ S−CO ₂ −Cl ⁻ environment below 150°C. Next, the reasons for limiting the other basic components of the steel of the present invention are as follows. C: If it is 0.10% or less, it does not affect stress corrosion cracking, 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 little effect on stress corrosion cracking, so Mn was allowed up to 2.0%. P: 0.030 as P increases susceptibility to stress corrosion cracking.
% or less. S: S is an element that significantly deteriorates hot workability, so it is limited to 0.005% or less. Al: Al is effective as a deoxidizing component and can be contained up to 0.5%. Furthermore, as a selective ingredient used as required.
Cu is an element that increases corrosion resistance, but if it exceeds 1%, hot workability deteriorates, so it is limited to 1% or less. Furthermore, when REM, Y, Mg, Ca, and Ti are added in appropriate amounts, hot workability is significantly improved. However, when added in excess, hot workability deteriorates again. Next, the effects of the present invention will be explained in detail with reference to Examples.
A pipe with an outer diameter of 60 mm and a wall thickness of 4 mm was manufactured from an alloy having the components (1) to (21) 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 of 20 mm is obtained by cutting out the 60° central angle from this OCTG.
mm tube was taken as a test piece, a tensile stress equivalent to 0.2% proof stress was applied to the outer surface of the tube using bolts and nuts as shown in Figure 3, and this was applied to H2S with various _H2S partial pressures. ₂ S − 10 atm CO ₂ − 20% NaCl solution (temperature:
(150℃) for 1000 hours, and the presence or absence of stress corrosion cracking was investigated. The results are summarized in Table 2.

【table】

[Table] In areas where the partial pressure of H ₂ S is relatively low, some comparative examples (12) to (21) made of conventional steels do not exhibit stress corrosion cracking. As the partial pressure of H ₂ S increases, it decreases, and when the partial pressure of H ₂ S becomes 20
When it reaches atmospheric pressure, it disappears. However, in steels (1) to (11) made of the steels of the present invention, no cracking was observed even under an H ₂ S partial pressure of 20 atmospheres, proving the effectiveness of the steels of the present invention against stress corrosion cracking. By the way, comparative example
Since Ni in (12) and Cr+10Mo+5W in Comparative Example (13) are below the range of the present invention, stress corrosion cracking resistance is insufficient. Comparative steel (14) has too high Cr content, (15) has too high S content, and (16)
(17) has poor hot workability due to excessively high levels of selected components among Cu, REM, Y, Ca, Mg, and Ti, resulting in cracks occurring during billet production, making pipe production virtually impossible. It was possible. 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 (%) +
Figure 2 is a diagram showing the influence of 5W (%) on stress corrosion cracking resistance, Figure 2 is a diagram showing a stress corrosion cracking tester for plate specimens, and Figure 3 is a diagram showing a tubular specimen.

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,
Stress-corrosion resistant, characterized by containing 35 to 60% Ni, 22.5 to 35% Cr, and one or both of Mo and W within a satisfying range, with the remainder essentially consisting of Fe. Alloy for oil country tubular goods with excellent crackability. Cr (%) + 10Mo (%) + 5W (%) ≧ 50% ...... 1.5% ≦ Mo (%) + 1/2W (%) < 4% ...... 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 35 to 60% Ni, 22.5 to 35% Cr, one or both of Mo and W within a range that satisfies the following formula, further contains 1% or less of Cu, and the remainder is substantially
An alloy for oil country tubular goods with excellent stress corrosion cracking resistance, characterized by being made of Fe. Cr (%) + 10Mo (%) + 5W (%) ≧ 50% ...... 1.5% ≦ Mo (%) + 1/2W (%) < 4% ...... 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 35 to 60% Ni, 22.5 to 35% Cr, and one or both of Mo and W within a range that satisfies the following formula, and further contains rare earth elements of 0.10% or less, Y0.20% or less, and Mg0. 10% or less, Ca 0.10% or less, Ti 0.5% or less, and the remainder is substantially Fe for oil country tubular goods with excellent stress corrosion cracking resistance. alloy. Cr (%) + 10Mo (%) + 5W (%) ≧ 50% ...... 1.5% ≦ Mo (%) + 1/2W (%) < 4% ...... 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 35 to 60% Ni, 22.5 to 35% Cr, and one or both of Mo and W within a range that satisfies the following formula, and further contains 1% or less of Cu, 0.10% or less of rare earth elements, and Y0.20. % or less, Mg 0.10% or less, Ca 0.10% or less, and Ti 0.5% or less. Excellent alloy for oil country tubular goods. Cr (%) + 10Mo (%) + 5W (%) ≧ 50%…… 1.5% ≦ Mo (%) + 1/2W (%) < 4% ………