HYDROGEN EMBRITTLEMENT RESISTANCE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Patent Application No. 63/295,324 filed on December 30, 2021 . The disclosure of the above application is incorporated herein by reference.

FIELD

[0002] The present disclosure relates to nickel-base precipitation hardenable alloys, and particularly to nickel-base precipitation hardenable alloys with improved hydrogen embrittlement resistance.

BACKGROUND

[0003] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0004] Nickel-base precipitation hardenable alloys are used for the manufacture of critical down-hole components in oil field equipment. Such alloys are known to be resistant to chloride-ion stress corrosion cracking, sulfide stress corrosion cracking, and galvanically-induced hydrogen stress corrosion cracking. However, ever increasing resistance to hydrogen embrittlement (HE) is desired. Resistance to hydrogen embrittlement may be evaluated by determining a plastic strain ratio and a plastic strain to failure. As used herein, the phrases “plastic strain to failure” and “plastic strain ratio” refer to the plastic strain to failure and plastic strain ratio as established in NACE Standard TM0198. This standard provides a slow strain rate test for evaluation of Ni-based alloys for resistance to hydrogen-induced stress corrosion cracking (SCC) in simulated oil field production environments at elevated temperatures. More specifically, plastic strain to failure is the maximum plastic deformation in the material before the material breaks. A projection of an elastic line through the stress and strain value at failure is used to determine the amount of strain attributed to sample plastic deformation as the total strain at failure minus the equivalent elastic strain at the failure point. The HE plastic strain ratio is the plastic strain to failure determined from a sample tested in acid divided by the plastic strain to failure determined from a sample tested in an inert environment. [0005] The present disclosure addresses the issue of improved HE resistance of nickel-base precipitation hardenable alloys and other issues related to nickel-base precipitation hardenable alloys for use in oil field environments.

SUMMARY

[0006] This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.

[0007] In one form of the present disclosure, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 7.0% to about 12.0%, Mo from about 6.5% to about 9.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.3% to about 1.3%, Al up to about 0.4%, and balance Ni and incidental impurities, a yield strength greater than or equal to 120 ksi, a plastic strain ratio greater than 0.35, and a plastic strain to failure greater than or equal to 9.0%. In at least one variation the alloy has a Ti content about 0.8% to about 1.1% and an Fe content between about 9.0% to about 12.0%. For example, in at least one variation the alloy has a Ti content between about 0.8% to about 1 .0% and an Fe content between about 10.0% to about 12.0%. In another alternative, the alloy has a Ti content between about 0.4% to about 0.8% and an Fe content between about 10.0% to about 12.0%.

[0008] Although the alloy in one form has a desired plastic strain ratio, i.e., greater than or equal to 0.35, and a plastic strain to failure greater than or equal to 9.0%, the alloy also maintains a desired strength, i.e., greater than or equal to 120 ksi (827 MPa). For example, in at least one variation the alloy has an HE plastic strain ratio greater than or equal to 0.35, a plastic strain to failure greater than 9.0% and the yield strength is between about 120 ksi (827 MPa) and 150 ksi (1034 MPa). Also, in some variations the alloy has a plastic strain ratio greater than or equal to 0.40 and a plastic strain to failure greater than or equal to 10.0%. For example, in at least one variation, the plastic strain ratio is greater than or equal to 0.50 and the plastic strain to failure is greater than or equal to 12.0%.

[0009] In another form of the present disclosure, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 9.0% to about 16.0%, Mo from about 4.5% to about 7.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.4% to about 1.3%, Al up to about 0.4%, and balance Ni and incidental impurities, a yield strength greater than or equal to 120 ksi, a plastic strain ratio greater than or equal to 0.30, and a plastic strain to failure greater than or equal to 8.5%. In at least one variation the alloy has a Ti content about 0.8% to about 1.1 % and an Fe content between about 11.0% to about 16.0%. For example, in at least one variation the alloy has a Ti content between about 0.8% to about 1.0% and an Fe content between about 12.0% to about 16.0%. In another alternative, the alloy has a Ti content between about 0.5% to about 0.8% and an Fe content between about 12.0% to about 16.0%.

[0010] Although the alloy in this form has a desired plastic strain ratio, i.e., greater than or equal to 0.30, the alloy still maintains a desired strength, i.e., greater than or equal to 120 ksi (827 MPa). For example, at least one variation the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.5% and the yield strength is between about 120 ksi (827 MPa) and 150 ksi (1034 MPa). Also, in another form, the alloy has a plastic strain ratio greater than or equal to 0.35 and a plastic strain to failure greater than or equal to 9.0%. In still another form, the plastic strain ratio is greater than or equal to 0.45 and the plastic strain to failure is greater than or equal to 10.0%.

[0011] In yet another form of the present disclosure, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 15.0% to about 21.0%, Mo from about 3.0% to about 4.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.5% to about 1 .3%, Al up to about 0.4%, Cu from about 0.5% to about 3.0%, and balance Ni and incidental impurities. This alloy has a yield strength greater than or equal to 140 ksi, a plastic strain ratio greater than or equal to 0.30, and a plastic strain to failure greater than or equal to 8.0%. In at least one variation of this alloy, the Ti content is about 0.8% to about 1.1 % and the Fe content is between about 16.0% to about 21.0%. For example, in at least one variation, the alloy has a Ti content between about 0.8% to about 1 .0% and an Fe content between about 17.0% to about 20.0%. In another alternative, the alloy has a Ti content between about 0.5% to about 0.8% and an Fe content between about 18.0% to about 21.0%.

[0012] Although this alloy has a desired plastic strain ratio, i.e., greater than or equal to 0.5, the alloy still maintains a desired strength, i.e., greater than or equal to 140 ksi (965 MPa). For example, in at least one variation the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.0% and the yield strength is between about 140 ksi (965 MPa) and 170 ksi (1172 MPa). Also, in some variations, this alloy has a plastic strain ratio greater than or equal to 0.35 and a plastic strain to failure greater than or equal to 9.0%. In yet another form, the plastic strain ratio is greater than or equal to 0.45 and the plastic strain to failure is greater than or equal to 10.0%.

[0013] While not being bound to any particular theory, it is believed that a careful balance of Ti and Fe results in an alloy that provides high strength and is resistant to hydrogen embrittlement.

[0014] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DETAILED DESCRIPTION

[0015] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0016] Referring to Table 1 below, Unified Numbering System (UNS) composition specifications for nine (9) nickel-based (Ni-base) precipitation hardenable alloys are shown.

Table 1

[0017] The alloys shown in Table 1 are known to be used in a variety of industries and applications, some of which include down-hole components in oil field equipment, and for which enhanced HE resistance is desired. Alloys falling within the UNS specifications shown in Table 1 were subjected to HE testing (see Paper No. 13284, CORROSION 2019 Conference Proceedings; incorporated herein by reference). Also, the inventors performed a statistical analysis of the compositions of the alloys in Table 1 and discovered that the HE resistance of these alloys showed a trend of enhanced HE resistance as a function of decreasing Ti content and increasing Fe content. Particularly, the plastic strain ratio for the alloys was discovered to obey the following relationship based on statistical modeling:

Plastic strain ratio = 0.3461 + 0.016572*Fe - 0.2022*Ti (1 ) with a Coefficient of Determination (R ² ) equal to 0.997 and Fe, Ti in weight percent (wt.%). As noted from relationship (1 ) above, reducing the Ti content and increasing the Fe content increases the plastic strain ratio and thereby enhances HE resistance.

[0018] Referring now to Table 2, four Ni-based alloys with varying amounts of chromium, iron, molybdenum, niobium, titanium and aluminum are shown. Particularly, specific alloys generally falling within the UNS N07716, UNS N07718, UNS N09925, and UNS N09945 composition ranges are shown in Table 2. It should be understood that the compositions of the alloys shown in Table 2 were obtained from Paper No. 4248 in the CORROSION 2014 Conference Proceedings (incorporated herein by reference) and may not include all of the alloying elements in the UNS specifications listed in the table.

Table 2

[0019] The alloys in Table 2 were subjected to HE testing (see Paper No. 4248, CORROSION 2014 Conference Proceedings). Also, a statistical analysis of the compositions of the alloys in Table 2 and the HE resistance of these alloys similarly showed a trend of enhanced HE resistance as a function of decreased Ti content and increased Fe content. Particularly, the reduction in area ratio for testing in an HE environment to testing in an inert environment was discovered to obey the following relationship based on statistical modeling:

Reduction in area ratio = 0.6348 + 0.01274*Fe - 0.1530*Ti (2) with R ² equal to 0.779.

[0020] Referring now to Table 3, seven (7) Ni-based precipitation hardenable alloys with varying amounts of chromium, iron, molybdenum, niobium, titanium and aluminum are shown. Particularly, specific alloys generally falling within the UNS N07725, UNS N07716, and UNS N07718 composition ranges are shown in Table 3. It should be understood that the compositions and names of the alloys shown in Table 3 were obtained from Paper No. 11114 in the CORROSION 2018 Conference Proceedings (incorporated herein by reference) and may not include all of the alloying elements provided in a corresponding UNS specification.

Table 3

[0021] The alloys in Table 3 were subjected to HE testing (see Paper No. 11114, CORROSION 2018 Conference Proceedings). Also, a statistical analysis of the compositions of the alloys in Table 3 and the HE resistance of these alloys similarly showed a trend of enhanced HE resistance as a function of decreasing Ti content. Particularly, the reduction in fracture load for the alloys testing in an HE environment versus testing in an inert environment was discovered to obey the relationship based on statistical modeling:

% Reduction in Fracture Load = -43.4 + 52.24*Ti (3) with R ² equal to 0.876 and a higher value (i.e., less negative) of a reduction in fracture load indicating a higher HE resistance. As shown by relationship (3), the contribution of Fe was statistically irrelevant with respect to the % Reduction in Fracture Load for the alloys shown in Table 3.

[0022] It should be understood that the results of the analyses show an increase in HE resistance with a decrease in Ti alloy content in Ni-based precipitation hardenable alloys. Accordingly, new Ni-based precipitation hardenable alloys with reduced Ti content and increased Fe and increased HE resistance have been developed according to the teachings herein.

[0023] Additional testing was pursued to further develop the influence of Ti, Fe, and yield strength (YS) on the HE resistance of precipitation hardened nickel alloys. Referring now to Table 4 below, the composition of the tested nickel-based (Ni-base) precipitation hardenable alloys are shown. A combination of commercial and laboratory alloys are included.

Table 4

[0024] The laboratory melted alloys in Table 4 were fabricated from 4- inch diameter 50-pound vacuum induction (VIM) melted ingots in the form of 0.625” diameter hot-rolled rod product. The homogenized and hot-rolled rod samples were annealed at 1900°F. Age-hardening was performed at 1350°F for 8 hours with a furnace cool at 100°F per hour to 1150°F with a hold for 8 hours followed by air cooling. Production melted alloys were fabricated from commercial VIM-melted material. VIM electrodes at 18” diameter were vacuum arc re-melted (VAR) to 20” diameter and forged to finished diameter between 5 and 10” in diameter with a gyro-rotational forging machine (GFM). As shown in Table 5 below, the finished rods were annealed between 1850-1900°F. Age-hardening was performed at between 1300-1365°F for 5.5-8 hours with furnace cool at 50-100°F per hour to 1150°F with hold for 5.5-12 hours followed by air cooling.

Table 5

[0025] The alloys in Table 5 were subjected to tensile strength and

Charpy impact testing. Table 6 below summarizes the test results per heat:

Table 6

[0026] The alloys in Table 5 were further subjected to HE resistance testing. The HE resistance of each variant was tested per NACE TM0198 Method C slow strain rate testing procedure. The slow strain rate test incorporates a slow, dynamic strain applied at a constant extension rate. It evaluates resistance to hydrogen induced stress cracking. Table 7 summarizes the HE resistance average test results per heat. (Blank or no values indicate no test was completed for that alloy).

Table 7

[0027] All samples were examined with light optical microscopy to confirm the microstructure met the requirements defined in API6A CRA Annex A, Reference Microstructures, and were free of significant grain boundary or intragranular precipitation. It has been shown that such microstructures are prone to intergranular fracture under in HE conditions. Such microstructures were excluded from the current study to isolate the influence of Ti and Fe, and yield strength, on HE performance without the additional influence of significant grain boundary precipitation.

[0028] Through data analysis including single and multi-variable regression models and cross-validation, it was determined that Ti content, Fe content, and yield strength each have an influence in HE resistance. In particular, over the yield strength range of 120-170 ksi, lower Ti content and higher Fe content correspond with increased HE resistance.

[0029] The results from testing were evaluated and used to guide the claim ranges contained herein. Table 8 below shows a summary of composition ranges, plastic strain ratios and yield strengths for the new alloys according to the present disclosure.

Table 8

[0030] In one form of the present disclosure, shown as “A- New Alloy 725” in Table 8, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 7.0% to about 12.0%, Mo from about 6.5% to about 9.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.3% to about 1 .3%, Al up to about 0.4%, and balance Ni and incidental impurities and a plastic strain ratio greater than or equal to 0.35 or a plastic strain to failure of greater than or equal to 9.0 percent. In some variations the alloy has a Ti content between about 0.8% to about 1 .1 %, while in other variations the alloy has a Ti content between about 0.8% to about 1 .0%. In at least one variation the alloys has a Ti content about 0.8% to about 1 .1 % and an Fe content between about 9.0% to about 12.0%. For example, in at least one variation the alloy has a Ti content between about 0.8% to about 1 .0% and an Fe content between about 10.0% to about 12.0%. Also, additional alloying elements such as B, C, Co, Mn, P, Si, and S can be present in amounts corresponding to the UNS N07725 specification and/or normal melting practices for making Ni-based precipitation hardenable alloys while remaining within the scope of the present disclosure. [0031] Although the alloy has a desired plastic strain ratio, i.e., greater than or equal to 0.35, the alloy also maintains a desired strength, i.e., greater than or equal to 120 ksi (827 MPa). That is, even with Ti reduced to lower levels within or below the Ti range for UNS N07725, the alloy still has a desired yield strength for down-hole components in oil field production. For example, in at least one variation the alloy has a plastic strain ratio is greater than or equal to 0.35 and the yield strength is between about 120 ksi (827 MPa) and 150 ksi (1034 MPa). In one form, the alloy has a plastic strain ratio is greater than or equal to 0.3 and the yield strength is between about 130 ksi (896 MPa) and 150 ksi (1034 MPa). In another form, the alloy has a plastic strain ratio greater than or equal to 0.35, a plastic strain ratio greater than or equal to 9.0% and the yield strength is between about 140 ksi (965 MPa) and 150 ksi (1034 MPa). Also, in some variations the alloy has a plastic strain ratio greater than or equal to 0.40 and a plastic strain to failure greater than or equal to 10.0%. For example, in at least one variation, the plastic strain ratio is greater than or equal to 0.50 and the plastic strain to failure is greater than or equal to 12.0%.

[0032] In another form of the present disclosure, represented by B- New Alloy 735 in Table 8, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 9.0% to about 16.0%, Mo from about 4.5% to about 7.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.4% to about 1 .3%, Al up to about 0.4%, and balance Ni and incidental impurities and a plastic strain ratio greater than or equal to 0.3 or a plastic strain to failure of greater than or equal to 8.5 percent. In one form, the alloy has a Ti content between about 0.8% to about 1 .1 %, while in other variations the alloy has a Ti content between about 0.8% to about 1.0%. In at least one variation the alloy has a Ti content about 0.8% to about 1.1 % and an Fe content between about 14.0% to about 17.0%. In still another form, the alloy has a Ti content between about 0.8% to about 1 .0% and an Fe content between about 15.0% to about 17.0%. Also, additional alloying elements such as B, C, Co, Mn, P, Si, and S can be present in amounts corresponding to normal melting practices for making Ni-based precipitation hardenable alloys while remaining within the scope of the present disclosure.

[0033] Although the alloy has a desired plastic strain ratio, i.e., greater than or equal to 0.30, the alloy still maintains a desired strength, i.e., greater than or equal to 120 ksi (827 MPa). For example, in at least one variation the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.5% and the yield strength is between about 120 ksi (827 Mpa) and 150 ksi (1034 Mpa). In one form, the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.5%, and the yield strength is between about 130 ksi (896 Mpa) and 150ksi (1034 Mpa). In yet another form, the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.5% and the yield strength is between about 140 ksi (965 Mpa) and 150 ksi (1034 Mpa). In another form, the alloy has an HE plastic strain ratio greater than or equal to 0.35 and a plastic strain to failure greater than or equal to 9.0%. In yet another form, the plastic strain ratio is greater than or equal to 0.45 and the plastic strain to failure is greater than or equal to 10.0%.

[0034] In still another form of the present disclosure corresponding to C- New Alloy 945X in Table 8, a Ni-based precipitation hardenable alloy has a composition, in wt.% of Cr from about 18.0% to about 23.0%, Fe from about 15.0% to about 21 .0%, Mo from about 3.0% to about 4.5%, Nb from about 3.2% to about 5.2%, Ti from about 0.5% to about 1 .3%, Al up to about 0.4%, Cu from about 0.5% to about 3.0%, and balance Ni and incidental impurities and a plastic strain ratio greater than or equal to 0.3 or a plastic strain to failure of greater than or equal to 8.0 percent. In one form, the alloy has a Ti content between about 0.8% to about 1.1%, while in another form, the alloy has a Ti content between about 0.8% to about 1 .0%. In at least one variation, the alloy has a Ti content about 0.8% to about 1.1 % and an Fe content between about 19.0% to about 22.0%. In yet another form, the alloy has a Ti content between about 0.8% to about 1.0% and an Fe content between about 20.0% to about 22.0%. Also, additional alloying elements such as B, C, Co, Mn, P, Si, and S can be present in amounts corresponding to the UNS N09946 specification and/or normal melting practices for making Ni-based precipitation hardenable alloys while remaining within the scope of the present disclosure.

[0035] Although the alloy has a desired plastic strain ratio, i.e., greater than or equal to 0.3, the alloy still maintains a desired strength, i.e., greater than or equal to 140 ksi (965 MPa). For example, in at least one variation the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.0% and the yield strength is between about 140 ksi (965 MPa) and 170 ksi (1172 MPa). In one form, the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.0%, and the yield strength is between about 145 ksi and 170 ksi (1172 MPa). In yet another form, the alloy has a plastic strain ratio greater than or equal to 0.30, a plastic strain to failure greater than or equal to 8.0% and the yield strength is between about 150 ksi (1034 MPa) and 170 ksi (1172 MPa). In still another form, the alloy has a plastic strain ratio greater than or equal to 0.35 and a plastic strain to failure greater than or equal to 9.0%. In another form, the plastic strain ratio is greater than or equal to 0.45 and the plastic strain to failure is greater than or equal to 10.0%.

[0036] It should be understood from the compositions disclosed herein according to the present disclosure, HE resistance measures (i.e. plastic strain to failure or plastic strain ratio) and strengths (i.e., yield strengths) for the new alloys discussed above, a critical range of Ti is desired. That is, a critical range of Ti in the alloys has been discovered such that a desired HE resistance is provided or exceeded, while a desired level of yield strength is provided or exceeded. Particularly, for Ti levels less than the minimum values shown in Table 8 above, the alloys have an undesirable (e.g., low) yield strength and for Ti levels greater than the maximum values shown in Table 8, the alloys have an undesirable (e.g., low) HE resistance. In some variations of the present disclosure, a critical range of Ti and a critical range of Fe are desired. That is, a critical range of Ti and a critical range of Fe in the alloys have been discovered such that a desired HE resistance is provided or exceeded, a desired level of yield strength is provided or exceeded, and alloying elements such as Mo and Cr remain generally in solid solution, i.e., undesirable Mo- and/or Cr-rich precipitates (e.g., sigma phase) are not present in the new alloys. In at least one variation of the present disclosure there is a synergistic effect between Ti and Fe that provides a combination a high HE resistance, desired yield strength and desired microstructure with reduced or no undesirable Mo- and/or Cr-rich precipitates.

[0037] It should also be understood that the compositions of the alloys shown in Table 8 include all incremental values between the minimum alloying element composition and maximum alloying element composition values listed above. That is, a minimum alloying element composition value for any of the alloys shown in Table 8 can range from the minimum value to the maximum value shown in the table. Likewise, the maximum alloying element composition value for any of the alloys shown in Table 8 can range from the maximum value shown to the minimum value shown in the table. For example, the minimum Ti content for the A- New Alloy 725 can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 , 1.2, or 1.3, and any value between these incremental values, and the maximum Ti content for the A- New Alloy 725 can be 1 .3, 1.2, 1.1 , 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, or 0.3, and any value between these incremental values.

[0038] Similarly, the yield strength of the alloys shown in Table 8 include all incremental values between the minimum yield strength and maximum yield strength values listed above. That is, a minimum yield strength value for any of the alloys shown in Table 8 can range from the minimum yield strength value to the maximum yield strength value shown in the table. Likewise, the maximum yield strength value for any of the alloys shown in Table 8 can range from the maximum yield strength value shown to the minimum yield strength value shown in the table.

[0039] Similarly, the plastic strain ratio of the alloys shown in Table 8 include all incremental values between the minimum plastic strain ratio and maximum plastic strain ratio values listed above. That is, a minimum plastic strain ratio value for any of the alloys shown in Table 8 can range from the minimum plastic strain ratio value to the maximum plastic strain ratio value shown in the table.

[0040] Similarly, the HE plastic strain of the alloys shown in Table 8 include all incremental values between the minimum plastic strain to failure and maximum plastic strain to failure values listed above. That is, a minimum plastic strain value for any of the alloys shown in Table 8 can range from the minimum plastic strain value to the maximum plastic strain value shown in the table.

[0041] Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or "approximately" in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability.

[0042] As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

[0043] The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.