KR900007118B1 - Corrosion resistant nickel base alloy - Google Patents

Abstract

A nickel base alloy, having an excellent hot and cold workability and superior corrosion resistance to a variety of media including deep sour gas well environments, consists of 27-33 wt.% chromium, 8-12 wt.% molybdenum, 1-4 wt.% tungsten, up to 1.5 wt.% iron, up to 12 wt.% cobalt, up to 0.15 wt.% carbon, up to 1.5 wt.% aluminium, up to 1.5 wt.% titanium, up to 2 wt.% niobium and residual amt. of nickel.

Description

Corrosion Resistance Nickel Alloy

FIELD OF THE INVENTION The present invention relates to corrosion resistant nickel base alloys, particularly to improved hot and cold workable nickel alloys which are particularly suitable for use in sour gas welds that are highly corrosion resistant and highly corrosive under a wide range of corrosion conditions. About

Most alloys commercially used in applications requiring good corrosion resistance are nickel alloys. Such alloys generally contain relatively large amounts of chromium and molybdenum and also usually contain significant amounts of iron, copper or cobalt.

Well-known corrosion-resistant nickel alloys used in various corrosive applications, such as alloy C-276, consist of about 15 5% chromium, 15.5% molybdenum, 3.5% tungsten, 6% iron, 2% cobalt and residual nickel It has a nominal composition.

Other known corrosion resistant alloys are alloy B-2 having a nominal composition consisting of about 28% molybdenum, 1% chromium, 2% iron, 1% cobalt, and the balance nickel, about 21.5% chromium, 9% Molybdenum, 4% iron, 3 6% niobium, and alloy 625 containing the balance of nickel, and about 19% chromium, 3% molybdenum, 9% iron, 5 1% niobium, and the balance nickel Alloy 718 containing

One of the most severe corrosive environments for corrosion-resistant nickel alloys is found in deep sour gas well operations, in which case casings, pipes and other parts are subjected to high concentrations of hot and humid hydrogen sulphide, brine and carbon dioxide under high and high pressure conditions. easy

To date, this industry has relied on commercially available corrosion resistant nickel alloys as described above. However, these alloys were not fully satisfied under the severe conditions found in sour gas well operations. On the other hand, although a highly corrosion resistant feature alloy has been developed, such an alloy is quite expensive because of its high cobalt content.

Therefore, in the present invention, nickel alloys having excellent corrosion resistance were found for a wide range of corrosion conditions ranging from oxidation conditions to reduction conditions. The nickel alloys are particularly used in tests designed to simulate the extremely severe corrosion environments found in sour gas purification operations. Good performance. In addition to this, the alloy exhibits excellent hot and cold workability and relatively low content of expensive alloying elements.

These and other beneficial properties are obtained according to the invention in nickel alloys which are in a tight balance of chromium, molybdenum and tungsten in the following weight percent ranges.

Such a tightly balanced nickel alloy of chromium, molybdenum and tungsten has superior corrosion resistance in various solutions compared to other commercially available corrosion resistant alloys including alloys C-276, B-2, alloy 718 and alloy 625. Indicates. Moreover, based on the cost of the metals contained in the alloy, the alloy according to the invention is less expensive than other commercial nickel alloys with poor corrosion resistance.

The alloy of the present invention can be easily hot worked to be formed into various shapes desired, and also exhibits excellent cold workability so that high strength can be imparted to the final product by cold working.

In practicing the present invention, beneficial results indicate that the alloy has about 27-33% chromium, about 8-12% molybdenum, about 0-4% tungsten, up to about 1.5% iron, up to about 12% cobalt, E) obtained mainly when composed of up to about 0.15% carbon, up to about 1.5% aluminum, up to about 1.5% titanium, up to about 2% niobium, and the balance nickel. In addition to the above-mentioned elements, the term "consisting mainly of" may also mean that the alloy may also contain additional impurities and other unlisted elements that do not substantially affect the basic and novel properties of the alloy, in particular the corrosion resistance of the alloy. Means

Chromium is an essential element in the alloy of the present invention because it increases the corrosion resistance contributed by the alloy. It was shown from the tests that the chromium is optimal at about 31% of the composition. More than about 33% of chromium deteriorates hot workability and corrosion resistance. Also, corrosion resistance deteriorates at about 27% or less of chromium.

The presence of molybdenum improves corrosion resistance. The optimum content of molybdenum of about 10% is considered to have the lowest corrosion rate in the tested solution. If the molybdenum content is reduced to about 8% or less, the viscosity and crevice corrosion increase significantly. The same phenomenon occurs when molybdenum increases above about 12%, with hot and cold workability significantly reduced.

Tungsten is generally not included in commercial alloys developed for corrosion resistance applications. Tungsten is usually present in applications where strength is most important, especially at high temperatures, and is generally not considered to exhibit any beneficial effect on corrosion resistance. However, in the alloy of the present invention, the presence of tungsten significantly increases the corrosion resistance. okay. Corrosion tests have shown that the absence of tungsten results in a very high corrosion rate, while a tungsten content of more than about 4% causes corrosion of the material at high rates in some solutions and makes the alloy more difficult to hot work. .

The optimum tungsten content at the 10% molybdenum level appears to be about 2%, but replacing some or all of the tungsten with additional molybdenum, for example, provides good corrosion resistance in some test media (see Table 1 alloy M).

Alloys also typically contain carbon at levels up to about 0.15% as incidental impurities or as intentional additives to form stable carbides. Preferably the carbon level should be maintained at a maximum level of about 0.08% by weight, in particular up to about 0.04%.

Cobalt and nickel are generally believed to be interchangeable and provide similar properties to the alloy. Test results showed that substitution of cobalt for some of the nickel content did not adversely affect the corrosion resistance and processing properties of the alloy.

Cobalt may therefore be included in the alloy, if desired, even at levels up to about l2% by weight. However, cobalt is currently expensive, so the substitution of cobalt instead of nickel is not economically interesting.

Aluminum may be present in small amounts to act as a deoxidation material. However, the addition of a large amount of aluminum adversely affects the processing of the alloy. Aluminum is preferably present in amounts up to about 1.5% by weight 6, in particular up to about 0.25% by weight.

Titanium and niobium may also be present in small amounts to act as a mono-former. These elements preferably contain up to about 1.5 weight percent tidan and up to about 2 weight percent niobium, most preferably at levels up to about 0.40 weight percent. However, it has been found that addition of these elements in significant amounts has a detrimental effect on hot workability.

The alloy according to the invention may also contain small amounts of other elements as impurities in the raw materials used or as intentional additives for improving certain properties as is well known in the art. For example, traces of magnesium, cerium, lanthanum, yttrium or mischmetal may be contained as desired to impart processability. Tests have shown that magnesium can be tolerated up to about 0.10%, preferably 0.07%, with no significant loss of corrosion resistance. Boron may preferably be added up to about 0.005% to impart high temperature strength and toughness. Alternatively, it may be present at levels up to about 2% without adversely affecting the workability, but it was not observed that even when tantalum is present at this level, it has a good effect on the corrosion resistance and workability of the alloy. Similarly, vanadium may be present up to about 1% and zirconium may be present up to 0.1%.

A large amount of iron lowers the corrosion resistance of the alloy. Iron can be tolerated at levels up to about 1.5%, but its corrosion resistance is significantly lower at higher levels. Copper, manganese, and silicon may be acceptable when present in small amounts or as impurities. However, it has been found that when a significant amount is added as an alloying element to the basic composition of the alloy, these elements lower the corrosion resistance of the alloy, reduce the processability of the alloy, or reduce these two properties. It is significantly worse when present at a level of 5% or more, or at a level of about 2% or more of manganese. Silicon is preferably maintained at a level of 1% or less

The following examples illustrate a number of feature alloy compositions according to the present invention and compare the corrosion resistance of the alloys according to the present invention with other known corrosion resistant nickel alloys.

Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1

Heat of several alloy compositions according to the present invention was prepared, and the chemical composition of these alloys is shown in the alloy of Table 1. The percentages (1%) shown in Table 1 are by weight based on the total composition and represent the nominal composition, ie the amount of each of the elements as refreshed to dissolve. Test specimens of various types of cold worked and annealed (about 4 square inches of surface area are prepared, quantified, and subjected to corrosion tests in various test solutions, and then the samples are dried, immersed again, and the weight loss (g) is measured. This was converted to mil / year.

Test 1 is a standard test method for measuring corrosion resistance and crevice corrosion using ferric chloride solution. The test piece was immersed in 10% by weight ferric chloride solution at 50 ° C. for 72 hours. This test method is similar to the ASTM test method except that ASTM rat test method G48-76 uses 6% by weight of ferric chloride.

In test 2, the samples were immersed in boiling aqueous solution of 10% sodium chloride and 5% jade chloride for 24 hours.

Test 3 is a standard test method (ASTM test method G 28-72) for the detection of susceptibility to intergranular corrosion in chromium-containing alloys with high nickel content. In this test, the samples were immersed in a solution of Methanol-50% sulfuric acid, which was boiled for 24 hours.

In test 4 the samples were immersed in 65% nitric acid boiling for 24 hours.

TABLE 1

For comparison purposes, several commercially available corrosion resistant alloys (Alloy B-2, Alloy C-276, Alloy 718 and Alloy 625) were tested in the same manner and these test results are also listed in Table 1.

From these test results, it can be seen that, except for a few, the alloys of the present invention are superior in corrosion resistance compared to the commercially available corrosion resistant alloys described above under these test conditions.

Example 2

Two of the alloys of Example 1 were reduced by 70% cold section on the rolling mill. Samples of alloy C-276 were similarly reduced. The alloy was then tested in the test solution and the results are shown in Table 2.

TABLE 2

As is evident from these tests, the alloy of the present invention was significantly superior in corrosion resistance compared to Alloy C-276 in the test solution when compared under cold reduction conditions.

Example 3

Corrosion investigations designed to evaluate the performance of two alloy test specimens (alloys N and alloy O) according to the present invention in the hydrogen sulfide environment (tests A, B and C) and simulated scrubber environment (test D) of corrosive sour gas wells in oil fields Was performed. Alloys N and O had the following nominal chemical compositions. 31% Cr, 10% Mo, 2% W, 0.40% Cb, 0.25% Ti, 0.25% Al, 0.001% (max) B, 0.10% (max) Fe, 0.10% (max) Cu, 0.04% C, 0.015% (max) S, 0.25% (max) Co, 0.015% (max) P, 0.10% (max) Ta, 0.10% (max) Zr, 0.10% (max) Mn, 0.10% (max) V, 0.2596 Si (max), residual amount of nickel.

For comparison purposes, test pieces of alloy C-276 were evaluated under similar conditions. All three materials were investigated under aging and non-aging conditions of 500 ° F (260 ° C) after one-way cold working.

The mechanical properties of the three alloy test specimens are shown in Table 3.

TABLE 3

Mechanical properties of materials evaluated in corrosion investigation

Three materials were investigated in four environments as follows:

All embrittlement tests were carried out using a 4.375 inch × 0.25 inch × 0.094 inch beam test piece stressed at three point curvature. The non-ageing materials were stressed to their respective strengths of 80 and 100%. Aged samples of 50 hours at 260 ° C. were stressed up to their proof strength of 100%,

Unstressed, cracked specimens of 2 inches x 0.625 inches x 0.062515 inches were used for the weight loss test due to corrosion. Test A-C was run for 28 days. In the test specimens were irradiated and weighed at the end of 24 hours, 72 hours and 168 hours.

A test specimen stressed to a stress corrosion cracking of 80 or 100% in NACE solution (5% NaC1 and 0.5% CH ₃ COOH saturated with 100% H ₂ S gas) at test A-24 ° C was Exposed for days. All specimens were recovered in an unbroken sieve without showing any signs of visual corrosion.

(Hydrogen embrittlement in NACE solution of test B-24。C)

Beam specimens stressed to 80 or 100% yield were placed in a NACE solution for 28 days with a steel couple. All beam specimens were recovered in an unbroken sieve.

(Hydrogen embrittlement in 5% H ₂ SO ₄ + 1mg / I sodium arsenite in test C-24。C)

The nickel-chromium wires were spot welded to the ends of the beams stressed to a strength of 80 or 100%. The beam specimens were then placed in test solution and negatively charged with hydrogen at a current of 25 mA / cm ² . At the end of the 13th day, alloy C-276 was defective under stress conditions at 100% yield strength. Alloy C-276 was found to be defective after 21 days under non-aging conditions stressed up to 100% yield. Test pieces of alloys N and O were recovered in an unbroken sieve at the end of 28 days of testing.

(Weight loss due to corrosion in Test D- "Greendes" solution (boiling 1% H ₂ SO ₄ + 3% HC1 + 1% FeCl ₃ + 1% CuCl ₃ ))

Weight loss test pieces due to corrosion of each material were weighed, uniformed and placed in a "Greendes" solution. The test pieces were washed and reweighed after 24 hours, 72 hours, and 168 hours. The specimens of alloys N and O had significantly less weight loss due to corrosion than the specimens of alloy C-276, as shown in Table 4.

TABLE 4

As can be seen from these test results, the performance of the alloy of the present invention under simulated dielectric hydrogen sulfide environment is equal to or better than that of alloy C-276, and the performance of the alloy of the present invention under simulated scrubber environment ("Greendes") test conditions. Corrosion resistance is obviously better than alloy C-276

Example 4

A one-sided test is performed to investigate the effect of varying the amounts of chromium, olivedene, tungsten, copper and iron on corrosion resistance. The basic red lead alloy composition (heat 367) was as follows. That is, for 31% Cr, 10% Mo, 2% W, 0.02% C, 0.25% Ti, 0.25% Al, 0.40% Cb, residual Ni, elemental chromium, molybdenum, tungsten, copper and iron. Heat is produced by keeping all other characteristic elements constant while varying the amount of elements.

The test pieces were prepared and tested in Example 1 under the conditions of Test # 2 and Test # 3. The results are shown in Table 5.

TABLE 5

nt-not tested

*-Test not possible due to specimen splitting due to lack of workability

Claims (1)

Nickel alloys with good hot and cold workability and excellent corrosion resistance to various media including deep sour gas well environments, 31% chromium, 10% molybdenum, 2% tungsten, up to 1.5%, up to 4% Corrosion-resistant nickel alloy consisting of cobalt, up to 0.08% carbon, up to 0.25% aluminum, up to 0.40% titanium, up to 0.40% niobium, and residual nickel