JP3235383B2 - High Cr-Ni alloy with excellent corrosion resistance in low hydrogen sulfide environment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic high Cr-high Ni alloy, and more particularly to a high Cr-high Ni alloy having excellent corrosion resistance in a low hydrogen sulfide environment.

[0002]

2. Description of the Related Art Materials for oil country tubular goods and oil well flow lines used in the production of crude oil and natural gas containing hydrogen sulfide at a partial pressure of as high as about 10 atm, or materials containing hydrogen sulfide are also used. For example, the hydrogen sulfide corrosion resistance of a steel or an alloy used as a piping material of a desulfurization facility or a geothermal power generation facility in a hydrogen sulfide environment has a temperature of 200.
Below ℃, stress corrosion cracking is the main corrosion,
Ni-Cr-Mo-Fe containing about 0% and high content of Ni
It is known that austenitic austenitic alloys exhibit high corrosion resistance (see JP-A-57-131340 and JP-A-57-131340).
Nos. 134544 and 57-134545).

[0003] For example, the alloy disclosed in Japanese Patent Application Laid-Open No. 57-131340 has Ni, Cr, Mo and W as active ingredients in order to impart stress corrosion cracking resistance in accordance with the temperature conditions of the use environment. Is limited to a predetermined range, and further contains predetermined amounts of Cu and Co. Since these conventional alloys contain expensive Mo or / and W as an essential component, they are expensive. there were.

[0004] Then, the conventional hydrogen sulfide corrosion excellent alloy for OCTG, when used as oil well pipes, H ₂ S contained in the fluid flowing through the tube, CO _2, Cl ^-
Among them, hydrogen sulfide (H ₂ S) and temperature are particularly important factors, and alloys are designed in consideration of this.
In a wet hydrogen sulfide environment, a Ni sulfide film is formed as an outer layer and a Cr oxide film is formed as an inner layer as a corrosion resistant film on the alloy surface, and the formation of a Cr oxide film of the inner layer is promoted by Mo or / and W. This is an alloy that ensures and maintains corrosion resistance. In other words, the outer Ni sulfide coating prevents the entry of hydrogen sulfide into the alloy,
Hydrogen sulfide corrosion resistance is secured and maintained by stably forming the inner Cr oxide film.

However, it has been newly found that when the hydrogen sulfide partial pressure is as low as about 0.1 atm, in the above-mentioned conventional alloy, the Ni sulfide film of the outer layer cannot be sufficiently formed and the corrosion resistance cannot be maintained and secured. And the partial pressure of hydrogen sulfide is 0.1a
There is a strong demand for the development of an inexpensive high Cr-high Ni alloy having excellent resistance to hydrogen sulfide corrosion in an environment as low as about tm and a temperature as low as 150 ° C.

[0006]

SUMMARY OF THE INVENTION The object of the present invention has been made in view of the above circumstances, and the hydrogen sulfide content is as low as about 0.1 atm in partial pressure and the temperature is about 150 ° C. It is an object of the present invention to provide an inexpensive high Cr-high Ni alloy which is excellent in corrosion resistance to hydrogen sulfide under a low hydrogen sulfide environment.

[0007]

The gist of the present invention resides in a high Cr-high Ni alloy having excellent corrosion resistance in the following low hydrogen sulfide environment.

In weight%, Si: 0.05-1.0%, M
n: 0.1 to 1.5%, Cr: 20.0 to 30.0%,
Ni: 20.0 to 40.0%, sol-Al: 0.01
0.3%, Cu: 0.5-5.0 %, REM: 0
0.10%, Y: 0 to 0.20%, Mg: 0 to 0.10
%, Ca: 0 to 0.10 %, and the balance consists of Fe and unavoidable impurities. C, P, and S in the impurities are 0.05% or less, 0.03% or less, and 0.01%, respectively. excellent corrosion resistance in a <br/> Oh Ru low hydrogen sulfide environment below high Cr- high Ni
alloy.

In the above high Cr-high Ni alloy,Is nothing
R may be addedEM, Y, Mg and CaActively attach
Place to addIf you choose one of theseseedAloneOr
2 or moreThe compoundCan be added, but its content
Range is REMabout0.001 to 0.10%, Y
about0.001 to 0.20%, Mgabout
0.001 to 0.10%, Caabout0.001
It is desirably 0.10%.

The present inventors have made the present invention based on the following findings and findings as a result of various experimental studies.

In order to improve the stress corrosion cracking resistance of a high Cr-high Ni alloy in a low hydrogen sulfide environment containing about 0.1 atm of hydrogen sulfide, the effects of various alloy components were examined, By simply increasing the Ni content, the outer Ni sulfide film formed as a two-layer structure on the alloy surface is not densely formed, and the penetration of hydrogen sulfide into the alloy cannot be sufficiently prevented. No effect can be obtained even if the oxide film is promoted by adding Mo or / and W. A new fact that hydrogen sulfide corrosion resistance is drastically improved without setting expensive Mo and / or W, which is contained in the conventional alloy as an essential component, when set in an appropriate range. The mechanism for improving the corrosion resistance to hydrogen sulfide by adding an appropriate amount of Cu is unknown, but is presumed as follows.

That is, Cu is an element that easily forms sulfides more than Ni, and the above-mentioned outer Ni sulfide film formed and formed on the alloy surface in a hydrogen sulfide environment containing a trace amount of hydrogen sulfide is formed by the Cu sulfide. Since the above-mentioned Cu is an element which easily forms a Cu oxide as well as Mo and / or W in an acid environment while improving the penetration resistance of hydrogen sulfide by densification, the Cr oxide film of the inner layer is formed. It is thought that as a result, the corrosion resistance of hydrogen sulfide is remarkably improved as a result of densification of the steel to improve its corrosion resistance.

When one or more of REM (rare earth element), Y, Mg and Ca are selected and added in an appropriate amount as an alloy component, hot workability can be further improved.

[0014]

The function and effect of the components constituting the alloy according to the present invention and the reason why the appropriate content thereof is determined as described above will be described below. In the following,% means wt%.

Si: 0.05 to 1.0% Si is a necessary component as a deoxidizing component, but its effect can be obtained at a content of 0.05% or more. However, when the content exceeds 1.0%, hot workability deteriorates. Therefore, the Si content is determined to be 0.05 to 1.0%. Preferably, it is 0.2 to 0.5%.

Mn: 0.1-1.5% Like Mn, Mn is a necessary component as a deoxidizing component, but its effect is obtained at a content of 0.1% or more. However, when the content exceeds 1.5%, hot workability deteriorates. Therefore, the Mn content is determined to be 0.1 to 1.5%. Preferably, it is 0.5 to 0.75%.

Cr: 20.0 to 30.0% Cr is a component that improves hydrogen sulfide corrosion resistance (mainly stress corrosion cracking resistance) in the presence of other main components Ni and N. However, if the content is less than 20.0%, the effect cannot be obtained. Even if it is reduced to less than 20.0%, hot workability is not improved at all. On the other hand, if the content exceeds 30.0%, the effect is saturated, and no matter how much the S content is reduced, deterioration of hot workability cannot be avoided. Therefore, the Cr content is 20.0-3.
It was determined to be 0.0%. Preferably, 22.0 to 27.0%
It is.

Ni: 20.0 to 40.0% Ni has an effect of improving corrosion resistance to hydrogen sulfide.
If the content is less than 20.0%, the desired effect cannot be obtained. On the other hand, if the content exceeds 40.0%, the effect is saturated, and expensive components increase the cost and impair the economic efficiency. Therefore, the Ni content is determined to be 20.0 to 40.0%. Preferably, it is 22.0 to 30.0%.

Sol-Al: 0.01-0.3% Al is a necessary component as a deoxidizing component, like Si and Mn. Its effect is 0.01% in sol-Al content.
%. However, when the sol-Al content exceeds 0.3%, hot workability deteriorates. Therefore, s
The ol-Al content was determined to be 0.01 to 0.3%. Preferably, it is 0.1 to 0.15%.

Cu: 0.5-5.0% Cu is the most important component in constituting the high Cr-high Ni alloy of the present invention, and the hydrogen sulfide resistance of the alloy in a low hydrogen sulfide environment It has the effect of significantly improving the corrosiveness, but its effect requires a content of 0.5% or more. However, if the content exceeds 5.0%, the effect is saturated, and conversely, the hot workability deteriorates. Therefore, C
The u content was determined to be 0.5 to 5.0%. Preferably 1.
0 to 3.0%.

C: upper limit 0.05% C, when its content exceeds 0.05%, forms coarse carbides with Nb or V in impurities, while forming Cr carbides continuous at grain boundaries. However, since stress corrosion cracking tends to occur at the grain boundaries, the upper limit is set to 0.05%. Preferably, it is 0.03% or less.

P: upper limit 0.03% P is contained as an unavoidable impurity, but if its content exceeds 0.03%, the sensitivity to stress corrosion cracking in a hydrogen sulfide environment is increased. Therefore, the upper limit is set to 0.03% or less. Preferably, it is 0.02% or less.

S: upper limit 0.01% S is contained as an unavoidable impurity like P, but if its content exceeds 0.01%, the hot workability is remarkably deteriorated. Therefore, the upper limit was set to 0.01%.
As described above, when the content of the S component is increased, the hot workability is remarkably deteriorated.
When the workability is reduced to 0007% or less, the hot workability is further improved. Therefore, when hot workability under severe conditions is required, the S content is reduced to 0.0007%.
It is desirable to do the following.

[0024] In addition to the above components, the alloy of the present invention comprises one of the following REM (rare earth element), Y, Mg and Ca.
Species or two or more species can be contained.

REM, Y, Mg and Ca: The upper limit is R
EM, Mg and Ca are 0.10%, and Y is 0.20%. These components have an effect of improving hot workability, so that hot working under severe conditions is necessary and hot working is required. If it is necessary to improve the workability, REM,
One, two or more of Y, Mg and Ca can be selected and contained. However, if the content of any of these components is less than 0.001%, the desired effects due to the above effects cannot be obtained. On the other hand, in the case of REM, Mg and Ca, the content of each component is 0.1
When the content exceeds 0%, and in the case of Y, the content is 0.2%.
If it exceeds 0%, a coarse oxide is generated, which causes deterioration of hot workability. Therefore, the content when these components are contained is 0.001 to 0.10% by REM,
0.001 to 0.20% for Y, 0.001 to 0.
10% and 0.001 to 0.10% for Ca, respectively.

In the alloy of the present invention, the above C, P
And unavoidable impurities other than S, B, Sn, As,
Even if each of Sb, Bi, Pb and Zn is contained in the range of 0.10% or less, the characteristics of the alloy of the present invention are not impaired at all.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Sixteen alloys having the component compositions shown in Table 1 were prepared by using an ordinary electric furnace and an Ar-oxygen decarburizing furnace (A
After melting using an OD furnace, an ingot having a diameter of 500 mmφ was prepared for casting. In Table 1, No. 1 to 1
0 is the alloy of the present invention; 11 to 16 are comparative alloys.

[0028]

[Table 1]

The obtained ingots were heated at 1250 ° C.
Heated to 1200 ° C and hot forged at 1200 ° C
It is formed into a round billet of mφ, formed into a tube having a diameter of 60 mmφ and a wall thickness of 5 mm by a hot extrusion tube method using the obtained billet, and kept at 1100 ° C. for 0.5 hour in the obtained tube →
After water-cooled solution treatment, cold-worked 0.2%
125 ksi grade (125-140 ksi =
After adjusting the strength to 87.75 to 98.28 kgf / mm ² ), a predetermined test piece was sampled and subjected to the next hydrogen sulfide corrosion test. Further, the hot workability was evaluated by examining the presence or absence of flaws on the inner surface of the tube after hot extrusion.

[Hydrogen sulfide corrosion test] Test solution: 0.1 atm H ₂ S-30 atm CO _2-
0.5% CH3 COOH-20% NaCl aqueous solution Test temperature: 150 ° C. Immersion time: 720 hours Applied stress: 125 ksi (87.75 kgf / mm ² ) Test piece: 0.25 of 10 mm width × 2 mm thickness × 75 mm length
mmU notch The results of the hydrogen sulfide corrosion test are shown in Table 1. In the hydrogen sulfide corrosion test, those in which cracking and pitting did not occur were indicated by “○”, and those in which they did occur were indicated by “x”.

As is clear from Table 1, none of the alloys of the present invention has cracks and pitting corrosion in the hydrogen sulfide corrosion test, and is excellent in hydrogen sulfide corrosion resistance. Also, no flaws are generated on the inner surface of the tube after the hot extrusion tube, and the hot workability is excellent.

On the other hand, all of the comparative alloys whose component compositions are out of the range of the present invention show cracks and pitting corrosion in the hydrogen sulfide corrosion test and are inferior in hydrogen sulfide corrosion resistance. In addition, some alloys have flaws on the inner surface of the tube after the hot extrusion tube, and have poor hot workability.

[0033]

According to the present invention, it has high corrosion resistance when used for oil country tubular goods in contact with corrosive fluid of oil wells containing hydrogen sulfide,
Further, since it does not contain Mo and / or W, it is possible to provide an inexpensive high Cr-high Ni alloy, which is extremely large in contributing to the field.

[0034]

Claims (1)

(57) [Claims] (1) Si: 0.05-1.0% by weight, M
n: 0.1 to 1.5%, Cr: 20.0 to 30.0%,
Ni: 20.0 to 40.0%, sol-Al: 0.01
0.3%, Cu: 0.5-5.0 %, REM: 0
0.10%, Y: 0 to 0.20%, Mg: 0 to 0.10
%, Ca: 0 to 0.10 %, and the balance consists of Fe and unavoidable impurities. C, P, and S in the impurities are 0.05% or less, 0.03% or less, and 0.01%, respectively. A high Cr-high Ni alloy excellent in corrosion resistance in a low hydrogen sulfide environment, characterized in that: