JP3470418B2 - High strength austenitic alloy with excellent seawater corrosion resistance and hydrogen sulfide corrosion resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to seawater corrosion resistance and corrosion resistance suitable for use in applications where the outer surface is exposed to seawater during the production or transportation of petroleum and natural gas containing hydrogen sulfide. The present invention relates to a high strength austenitic alloy having hydrogen sulfide corrosiveness.

[0002]

2. Description of the Related Art Seawater corrosion resistance is a passive film on the material surface.
It is determined by the stability of (Cr oxide). When film destruction occurs, Mo, W, N, etc. are said to accelerate the repair of the passive film, and PREW (Pitting Resistance Equ
It is known that the larger ivalent including W), the better the corrosion resistance (CORROSION / 93, NACE Internati
See onal, Paper No. 125 1993. Hereinafter referred to as Document 1). PREW is defined by the following formula.

PREW = [Cr + 3.3 (Mo + 0.5W) + 16N] With respect to hydrogen sulfide corrosion resistance, stress corrosion cracking is a serious corrosion problem under an environment of 200 ° C. or lower.
-Mo-Fe alloy has high corrosion resistance. The reason is that Ni sulfide is first generated on the surface of the material, and then hydrogen sulfide is blocked by Ni sulfide, so Cr oxide is generated under the Ni sulfide. It is believed that Mo promotes its repair when it is released (CORROSION / 84, NACE International, Paper No.206 1
984, see. Hereinafter referred to as Document 2).

JP-A-57-134544 and JP-A-57-2071
No. 42 to No. 207144, JP-A-57-207147, JP-A-57-207148, in the alloy for oil wells, in order to impart stress corrosion cracking resistance in accordance with the temperature conditions of the operating environment. In addition, the range of active ingredients (Ni, Cr, Mo, W) is limited, and Cu and Co are added to enhance the corrosion resistance. However, since N, V and Nb are not added, seawater corrosion resistance There is a problem in strength and strength.

JP-A-57-134544 and JP-A-57-2037
In the alloys for oil wells shown in Nos. 35 to 203737, ordinary cold work finishing and precipitation hardening techniques are used to obtain high strength. JP-A-57-203735 to -20
Although the alloy shown in 3737 has a high N, V and
Since Nb is not added, the strength level may be insufficient. Further, in JP-A-57-134544 and the like, Ni is not considered as an index of corrosion resistance.

JP-A-57-203738 and JP-A-57-2037
In the oil well alloy disclosed in Japanese Patent Publication No. 39, V and Nb
However, since N is not added, there is a problem in seawater corrosion resistance.

JP-A-57-207149, JP-A-57-2071
The alloy for oil wells disclosed in Japanese Patent Publication No. 50 has a N content of 0.05 to 0.25%,
Nb and / or V is contained in an amount of 0.5 to 4%, and stress corrosion resistance and high strength are imparted by cold working finish or precipitation hardening method.

[0008]

In the conventional oil country tubular goods, in consideration of the corrosive fluid (H ₂ S, CO ₂ , Cl ^−, etc.) flowing inside the oil country tubular goods, and even in the case of a corrosion resistant material in a seawater environment, oxygen -Cl ^-
Each alloy design has been based on its corrosion resistance in the environment. However, in the well tube used in the recent offshore oil well, the outer surface is exposed to seawater and the inner surface is in contact with the produced fluid. Further, in consideration of welding, it is necessary to obtain high strength as it is in solution.

An object of the present invention is to provide an austenitic alloy having seawater corrosion resistance, hydrogen sulfide corrosion resistance, and high strength as a solution.

[0010]

The gist of the present invention lies in the following high-strength austenitic alloys.

% By weight, Si: 0.05-1.0%, Mn: 1.5-
10%, Cr: 20-30%, Ni: 20-40%, Al: 0.01-0.5
%, N: over 0.25% and 0.6% or less, Cu: 0.2-2.5%,
Nb: 0.04 to 1.0% , Mo: 0.2 to 4% and W:
0.2 look containing one or two of 8%, the balance being Fe and inevitable impurities, C in the impurity 0.05% is less, P is
A high-strength austenitic alloy excellent in seawater corrosion resistance and hydrogen sulfide corrosion resistance, characterized by satisfying the following conditions (1) to (0.03%) and S (0.01%).
The austenitic alloy described above has V: 0.02 to 1.0% or a rare earth element: 0.001 in place of part of Fe.
~ 0.1%, Y: 0.001-0.20%, Mg: 0.001-0.10% and
And Ca: 0.001 to 0.10% of 1 type (s) or 2 or more types may be contained. When V is included, the following formula, and
Need to be satisfied.

[0012]       [Cr + 3.3 (Mo + 0.5W) + 16N] ≧ 40 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・       [Cr + 3.3 (Mo + 0.5W) + 2Ni] ≧ 70 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・        0.2% proof stress = [50 + 17.8 × (4C + 2N + 2Nb)) ≧ 60 ・ ・ ・ ・ ・        0.2% proof stress = [50 + 17.8 × (4C + 2N + V + 2Nb)] ≧ 60 ・ ・ ・ However, 0.2% proof stress (unit: ksi) is the value in the as-solution state.
Yes ~ The symbol for an element in the formula is the content (heavy weight) of that element.
Amount%).

The new findings on which the present invention is based are as follows.

Seawater corrosion resistance: The above formula is an index relating to seawater corrosion resistance. As shown in Reference 1, local corrosion is the most important corrosion problem in seawater, and by satisfying the formula, corrosion resistance in seawater can be secured.

Hydrogen sulfide corrosion resistance: The above formula is an index relating to hydrogen sulfide corrosion resistance. In a hydrogen sulfide-containing environment, stress corrosion cracking is the most important corrosion problem as shown in Document 2, and by forming Ni sulfide in the outer layer and Cr-O film in the inner layer, corrosion resistance is improved. Can be held. Further, Mo, W and Cu remarkably improve the repairing power of the Cr-O film as the inner layer.

As described above, in the inventions of JP-A-57-134544 and the like, Ni is not included in the index of corrosion resistance. The present inventors have examined the effect of the constituent elements on the stress corrosion cracking resistance of a high N Ni-containing alloy in a hydrogen sulfide environment, and (a) N has almost no effect on the stress corrosion cracking resistance. ,
(B) Ni should also be included in the index of corrosion resistance, (c) Cr,
It was found that Mo and W also improve the stress corrosion cracking resistance. That is, when the formula is satisfied, stress corrosion cracking does not occur in a hydrogen sulfide environment at 150 ° C.

High strength: The above formula (or formula) is an index relating to the strength as a solution. Normal austenitic alloy has a 0.2% proof stress of about 35 kg in the as-solution state.
The strength is low at about / mm2 (50 ksi). A normal alloy that has been strengthened by cold working cannot be used as a strength member because the strength of the normal alloy is greatly reduced if it is welded. When N and Nb (or further V) are added to satisfy the formula (or formula) , it is possible to obtain high strength as a solution because of solid solution strengthening, precipitation strengthening and grain refining effects.

Addition of Cu: Addition of Cu can improve the corrosion resistance in hydrogen sulfide environment, particularly in hydrogen sulfide in a low pH environment of about 3 and seawater environment.

Addition of other alloying components: By adding a certain amount of one or more of rare earth elements, Y, Mg and Ca, hot workability is further improved.

[0020]

The reason why the balance of the chemical composition and the content of the specific component of the alloy of the present invention is limited as described above will be explained below.

Si: 0.05 to 1.0% Si is a necessary component for deoxidation. In order to obtain that effect, the lower limit of the Si content needs to be 0.05%.
On the other hand, if the content exceeds 1.0%, the hot workability deteriorates, so the upper limit was made 1.0%.

Mn: 1.5 to 10% Mn is originally a deoxidizing agent, but it is an element that increases the solid solubility of N, so it is positively added. To obtain this effect, the Mn content must be 1.5% or more. On the other hand, if it exceeds 10%, stress corrosion cracking will occur. Therefore, the range of Mn content was set to 1.5-10%.

Cr: 20-30% Cr is a component which improves seawater corrosion resistance and hydrogen sulfide corrosion resistance (mainly stress corrosion cracking resistance) in the presence of Ni, N, Mo and W. It is also a component that inhibits hot workability. However, even if the content is less than 20%, hot workability will not be improved, and conversely, in order to secure desired seawater corrosion resistance and hydrogen sulfide corrosion resistance,
The lower limit of the Cr content was set to 20% because the Mo and W contents must be increased by that amount, which impairs economic efficiency.
On the other hand, when Cr exceeds 30%, deterioration of hot workability cannot be avoided no matter how much the S content is reduced, so the upper limit was set to 30%.

Ni: 20-40% Ni has the effect of improving the hydrogen sulfide corrosion resistance, but if the content is less than 20%, the desired excellent hydrogen sulfide corrosion resistance cannot be secured. On the other hand, even if it exceeds 40%, the effect of further improving the hydrogen sulfide corrosion resistance does not appear. Therefore, considering economic efficiency, the range of Ni content is 20
-40%.

Al: 0.01-0.5% Al is necessary for deoxidation. Al to get that effect
The lower limit of the content is 0.01%. On the other hand, the Al content is 0.5
If it exceeds%, the hot workability deteriorates. Therefore, the proper content of Al is 0.01 to 0.5%.

N: more than 0.25% and not more than 0.6% N has the effect of notably improving seawater corrosion resistance, but also improving the strength of the alloy by solid solution strengthening. However, if the N content is 0.25% or less, the desired high strength cannot be obtained. On the other hand, if it exceeds 0.6%, nitrogen does not form a solid solution sufficiently to form Cr nitrides and deteriorate the corrosion resistance of the alloy. Therefore, the range of the N content is set to exceed 0.25% and to 0.60%.

Cu: 0.2 to 2.5% Cu has the effect of improving the corrosion resistance especially in acidic (about pH 3) hydrogen sulfide and seawater environments. If it is less than 0.2%, it has no effect. On the other hand, if Cu exceeds 2.5%, the hot workability deteriorates, so the upper limit was made 2.5%.

In the alloy of the present invention, Nb content of 0.04 to 1.0% (or
Further contains V of 0.02 to 1.0%).

Nb: 0.04 to 1.0% (or V: 0.02
~ 1.0%) Nb has solid solution strengthening, precipitation strengthening and grain refining effects.
Required as it has the effect of improving the strength of the solution
It is contained as an additional element . If Nb is less than 0.04%, the above effect cannot be obtained. Since V also has the same effect as Nb,
As an optional additional element, it may be contained together with Nb,
If V is less than 0.02%, the effect of addition cannot be obtained. on the other hand,
If both V and Nb exceed 1.0%, the ductility and toughness of the steel deteriorate, and the hot workability also deteriorates.

Mo: 0.2 to 4%, W: 0.2 to 8% As described above, these components have the function of improving the resistance to seawater corrosion and the resistance to hydrogen sulfide corrosion in the presence of N, Ni and Cr. There is. However, if the content of both Mo and W is less than 0.2%, the effect is small. On the other hand, when the Mo content exceeds 4% and the W content exceeds 8%, further improvement in corrosion resistance does not appear in a hydrogen sulfide environment at a temperature of 150 ° C or lower.
Therefore, in consideration of economic efficiency, the upper limits when these are contained are 4% for Mo and 8% for W.

The alloy of the present invention may comprise, in addition to the components described above, the balance of Fe and inevitable impurities. Typical unavoidable impurities are C, P and S, and these are below the permissible upper limit values below, and it is preferable that they are as small as possible.

C is an unavoidable impurity that deteriorates the stress corrosion cracking resistance. If the content exceeds 0.05%, stress corrosion cracking easily occurs at the grain boundary. Also, Nb (or more
When V) is present, these coarse carbides are generated and continuous carbides are generated at the grain boundaries, so that stress corrosion cracking easily occurs at the grain boundaries. Therefore, C
The upper limit of the content is 0.05%.

P: 0.03% or less P as an unavoidable impurity has a function of deteriorating the stress corrosion cracking resistance in a hydrogen sulfide environment if its content exceeds 0.03%, so the upper limit is set to 0.03%. It was

S: 0.01% or less S as an unavoidable impurity has a function of deteriorating the hot workability when its content exceeds 0.01%, so that the upper limit is set to 0.01% and the hot workability is degraded. Need to be prevented. As described above, when the S component has a large content, it has an effect of deteriorating the hot workability, but the content is 0.0007
%, The hot workability is further improved. Therefore, when hot workability under severe conditions is required, the S content is preferably 0.0007% or less.

The alloy of the present invention may further contain one or more selected from the following rare earth elements, Y, Mg and Ca, in addition to the components described above. The effects and desirable contents of these optional addition components are as follows.

Rare earth elements, Y, Mg and Ca: Since these components have the effect of further improving hot workability,
If hot workability is performed under severe conditions, it is contained as necessary. The desirable lower limit of each content is 0.001% when positively obtaining the effect of improving hot workability.

On the other hand, rare earth elements are 0.1%, Y is 0.2%,
When Mg exceeds 0.10% and Ca exceeds 0.10%, the above effect is saturated.

In addition to the above chemical composition, the alloy of the present invention must satisfy the balance condition of the content of the components represented by the following formulas- (or formulas and) .

[Cr + 3.3 (Mo + 0.5W) + 16N] ≧ 40 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ [Cr + 3.3 (Mo + 0.5W) + 2Ni] ≧ 70 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 0.2 % Proof strength = [50 + 17.8 × (4C + 2N + 2Nb )] ≧ 60 ・ ・ ・0.2% proof strength = [50 + 17.8 × (4C + 2N + V + 2Nb)] ≧ 60 ・ ・ ・ However, 0.2% proof strength (unit: ksi) is a solution The value as it is.

If the value on the left side of the equation is less than 40, the desired seawater corrosion resistance cannot be secured. The lvalue of the expression is
If it is less than 70, desired hydrogen sulfide corrosion resistance cannot be secured. If the value on the left side of the formula (or formula) is less than 60, the desired 0.2% proof stress (60 ksi or more) in the as-solution state cannot be obtained.

In this alloy of the present invention, B, Sn, As, Sb, Bi, Pb and Zn are each inevitable impurities.
The inclusion of 0.1% or less does not impair the above properties of the alloy of the present invention.

[0042]

EXAMPLES Steels having chemical compositions shown in Tables 1, 2 and 3 were melted in an ordinary electric furnace, and an Ar-oxygen decarburization furnace (AOD furnace) was used for the purpose of controlling nitrogen content and desulfurization. After being melted, it was cast into an ingot having a diameter of 500 mm.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

Next, these ingots were hot forged at a temperature of 1200 ° C. to manufacture a billet having a diameter of 150 mmφ. At this time, for the purpose of evaluating hot workability, it was observed whether or not the billet had cracks, and subsequently, a tube having a diameter of 60 mm and a wall thickness of 5 mm was manufactured from the billet by hot extrusion. Furthermore, these tubes were subjected to solution treatment at 1100 ° C.

Test pieces were processed from the thus obtained pipes, and seawater corrosion resistance, hydrogen sulfide corrosion resistance and tensile test were conducted. Below, each test condition and the size of the test piece are shown.

(A) Tensile test test temperature: Normal temperature test piece: 4.0 mmφ and parallel part length 20 mm (B) Seawater corrosion resistance test Ferric chloride test according to ASTM G48 Test temperature: 60 ° C Test piece: 30 mm square , Thickness 3mm (C) Hydrogen sulfide corrosion resistance test solution: 20% NaCl + 0.5% CH ₃ COOH, 10atmH ₂ S + 10at
mCO ₂ Test temperature: 150 ° C Immersion time: 720 hours Additional stress: Actual 0.2% Proof strength 100% Specimen: Width 10 mm × thickness 2 mm × length 75 mm (0.25 at center)
mm U notch) Table 3 shows the results of these tests and the evaluation results of hot workability. In addition, ◯ indicates that cracking and pitting did not occur, and x indicates that occurred.

From the results shown in Table 3, it is clear that the alloy of the present invention satisfying the chemical composition defined by the present invention, and further satisfying the equations and formulas have both seawater corrosion resistance and hydrogen sulfide corrosion resistance. . On the other hand, it is understood that none of the comparative alloys whose chemical compositions or formulas are out of the ranges defined by the present invention show sufficient corrosion resistance. Further formula
In the alloy of the present invention which also satisfies (or the formula), it is clear that 0.2% proof stress becomes 60 ksi or more in the as-solution state, and desired high strength can be obtained.

[0050]

INDUSTRIAL APPLICABILITY The alloy of the present invention is suitable for oil well pipes whose outer surface is exposed to seawater and whose inner surface is in contact with corrosive fluid such as hydrogen sulfide.
ksi or more).

Claims (4)

(57) [Claims] 1. By weight%, Si: 0.05-1.0%, Mn: 1.5-
10%, Cr: 20-30%, Ni: 20-40%, Al: 0.01-0.5
%, N: over 0.25% and 0.6% or less, Cu: 0.2-2.5%,
Nb: 0.04 to 1.0%, Mo: 0.2 to 4% and W:
Look containing one or two of from 0.2 to 8%, the remaining part consists of Fe and unavoidable impurities, C in the impurity 0.05% is less, P is
0.03% or less, S is 0.01% or less, and the following formula ~
A high-strength austenitic alloy excellent in seawater corrosion resistance and hydrogen sulfide corrosion resistance, which is characterized by satisfying the above conditions. [Cr + 3.3 (Mo + 0.5W) + 16N] ≧ 40 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ [Cr + 3.3 (Mo + 0.5W) + 2Ni] ≧ 70 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 0.2% proof strength = [50 + 17.8 × (4C + 2N + 2Nb )] ≧ 60 …… However, 0.2% proof stress (unit: ksi) is the value as solutionized. 2. Si: 0.05-1.0%, Mn: 1.5- by weight%
10%, Cr: 20-30%, Ni: 20-40%, Al: 0.01-0.5
%, N: over 0.25% and 0.6% or less, Cu: 0.2-2.5%,
Nb: 0.04 to 1.0%, Mo: 0.2 to 4% and W:
One or two of 0.2 to 8%, and rare earth elements: 0.
001 to 0.1%, Y: 0.001 to 0.20%, Mg: 0.001 to 0.10%
And Ca: contains 0.001 to 0.10% of one or more kinds
Look, the balance consisting of Fe and unavoidable impurities, the C in impurities
0.05% or less, P is 0.03% or less, S is 0.01% or less,
A high-strength austenitic alloy excellent in seawater corrosion resistance and hydrogen sulfide corrosion resistance, which is characterized by satisfying the following conditions. [Cr + 3.3 (Mo + 0.5W) + 16N] ≧ 40 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ [Cr + 3.3 (Mo + 0.5W) + 2Ni] ≧ 70 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 0.2% proof strength = [50 + 17.8 × (4C + 2N + 2Nb )] ≧ 60 …… However, 0.2% proof stress (unit: ksi) is the value as solutionized. 3. By weight%, Si: 0.05-1.0%, Mn: 1.5-
10%, Cr: 20-30%, Ni: 20-40%, Al: 0.01-0.5
%, N: over 0.25% and 0.6% or less, Cu: 0.2-2.5%,
Nb: 0.04 to 1.0%, V: 0.02 to 1.0%, Mo: 0.
2 to 4% and W: 0.2 to 8% of one or two
IncludingOnly the restIs Fe and inevitable impurities, and C in the impurities
Is 0.05% or less, P is 0.03% or less, and S is 0.01% or less.
And the following formula,andTo satisfy the conditions of
Highly characterized by excellent seawater corrosion resistance and hydrogen sulfide corrosion resistance
Strength austenitic alloy.       [Cr + 3.3 (Mo + 0.5W) + 16N] ≧ 40 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・       [Cr + 3.3 (Mo + 0.5W) + 2Ni] ≧ 70 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・        0.2% proof stress = [50 + 17.8 × (4C + 2N + V + 2Nb)] ≧ 60 ・ ・ ・ However, the 0.2% proof stress (unit: ksi) is the value as solutionized. 4. Si: 0.05-1.0%, Mn: 1.5-by weight%
10%, Cr: 20-30%, Ni: 20-40%, Al: 0.01-0.5
%, N: over 0.25% and 0.6% or less, Cu: 0.2-2.5%,
Nb: 0.04 to 1.0%, V: 0.02 to 1.0%, Mo: 0.
2 to 4% and W: 0.2 to 8% of 1 or 2seed,
FurtherRare earth elements:0.001~ 0.1%, Y:0.001~ 0.20%,
Mg:0.001~ 0.10% and Ca:0.001~ 0.10%One kind of
Includes two or more, The balance consists of Fe and inevitable impurities,
Impurity C is 0.05% or less, P is 0.03% or less, S is 0.01
% Or less and the following formula,andSatisfies the conditions
Resistance to seawater corrosion and hydrogen sulfide corrosion
Excellent high strength austenitic alloy.       [Cr + 3.3 (Mo + 0.5W) + 16N] ≧ 40 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・       [Cr + 3.3 (Mo + 0.5W) + 2Ni] ≧ 70 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・        0.2% proof stress = [50 + 17.8 × (4C + 2N + V + 2Nb)] ≧ 60 ・ ・ ・ However, the 0.2% proof stress (unit: ksi) is the value as solutionized.