MX2008005785A - High strength corrosion resistant alloy for oil patch applications - Google Patents

Abstract

A Ni-Fe-Cr alloy having high strength, ductility and corrosion resistance especially for use in deep-drilled, corrosive oil and gas well environments, as well as for marine environments. The alloy comprises in weight%:35-55%Ni, 12-25%Cr, 0.5-5%Mo, up to 3%Cu, 2.1-4.5%Nb, 0.5-3%Ti, up to 0.7%Al, 0.005-0.04%C, balance Fe plus incidental impurities and deoxidizers. The alloy must also satisfy the ratio of (Nb - 7.75 C) / (Al + Ti)=0.5-9 in order to obtain the desired high strength by the formation ofγ'andγ"phases. The alloy has a minimum of 1%by weightγ"phase dispersed in its matrix for strength purposes and a total weight percent ofγ'+γ"phases being between 10 and 30.

Description

ALLOY RESISTANT TO CORROSION. HIGH RESISTANCE FOR APPLICATIONS IN OIL FIELDS BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates generally to corrosion-resistant metal alloys and, more particularly, to nickel-iron-chromium alloy which are particularly useful in corrosive environments of oil and gas wells as well as marine environments where high strength, resistance to corrosion and a reasonable cost are desired attributes.

DESCRIPTION OF THE RELATED TECHNIQUE As older, shallower, and less corrosive oil and gas wells are depleted, higher toughness and corrosion resistant materials are needed to allow deeper drilling, which faces more corrosive environments . In oilfield applications, alloys with increased corrosion resistance and toughness are now required. These increasing demands arise from factors that include: deep wells that involve higher temperatures and pressures; Improved methods of recovery such as steam injection or dioxide carbon (CO2); Increased tube tensions, especially offshore and corrosive constituents in the well including: hydrogen sulfide (H2S), CO2 and chlorides. The selection of materials is especially critical for such sulfurized gas wells - those that contain H2S. Sulfur well environments are highly toxic and extremely corrosive to traditional carbon steel alloys for oil and gas. In some sulfur environments, corrosion can be controlled using inhibitors together with the tubular sections of carbon steel. However, inhibitors involve continuously high costs and are often not reliable at high temperatures. Adding corrosion tolerance to the pipe walls increases the weight and reduces the interior dimensions of the pipe. In many cases, the preferred alternative in terms of life cycle in terms of economy and safety is the use of corrosion-resistant alloys for tubular parts and other well components. These corrosion-resistant alloys eliminate inhibitors, reduce weight, improve safety. Eliminate or minimize reconditioning and reduce idle time. Martensitic stainless steels such as 13% chromium alloys meet the requirements of corrosion resistance and toughness in applications in slightly corrosive oil fields. However, 13% alloys lack the moderate resistance to corrosion and toughness required in low-sulfur gas wells.

Cayard et al., In "Serviceability of 13Cr Tubulars in Oil and Gas Production Environments," published stress corrosion data with sulfur indicating that 13Cr alloys have insufficient corrosion resistance for wells operating in the transition region between environments of sulfur gas and non-sulfurized gas. Additional background of the technique can be found in the patents of E.U.A. Nos. 4,358.51 1 for Smith Jr. et al., And 5,945,067 for Hibner et al. Although slightly corrosive wells are handled by various 13Cr steels, Ni-based alloys are needed for more highly corrosive environments. Among the Ni-based alloys most commonly used for petroleum wells are alloys based on high-Ni austenite such as, for example, alloys 71 8, 725, 825, 925, G-3, C-276, which they provide increased resistance to corrosive sulfur gas environments. However, these alloys mentioned above are also too expensive or do not possess the necessary combination of high tenacity and corrosion resistance. The present invention solves the problems encountered in the prior art by providing an alloy with excellent corrosion resistance to operate in sulfur gas coupled environments with excellent mechanical properties for service in demanding applications in deep oil and gas wells. In addition, the present invention provides a high tenacity and corrosion resistant alloy for use in petroleum field applications at a reasonable cost.

BRIEF DESCRIPTION OF THE INVENTION Briefly, the present invention relates to a Ni-Fe-Cr alloy containing small amounts of Mo and Cu having related and controlled amounts of Nb, Ti, Al and C in order to develop a unique microstructure to provide a minimum deformation limit of 120 ksi. In general, the alloy has a ratio of (Nb - 7.75 C) / (A1 + Ti) in the range of 0.5 to 9. In the preceding calculation, 7.75 x the weight percent of carbon corrects the differences in atomic weight between carbon (atomic weight 12.01) and those of Nb (atomic weight 92.91). In other words, 7.75 x percent by weight of C takes that many percent by weight of Nb from the matrix and is not available to form precipitation hardening phases. When the value of the ratio of 0.5 to 9 is satisfied, the alloy will have a combination of phase? "(Double prime range) and phase? ' (raw range) as reinforcement phase with a minimum of 1% by weight of phase? " present and a weight percent interval of? +? "from 10 to 30 and preferably a weight percent range of 12-25, when the ratio is 0.5 to 8 and even narrower when the ratio is 0.5 to 6, determined by ThermoCalc. obtained by annealing and aging hardening conditions which provides an attractive combination of impact resistance, ductility and corrosion resistance to allow the material of the invention to be used in applications in corrosive oil and gas wells containing gaseous mixtures of carbon dioxide (CO2) and hydrogen sulfide (H2S) typically found in sulfur well environments. The material of the invention is also useful in marine applications where toughness, resistance to corrosion in costs are important factors in relation to the selection of the material. This specification describes all compositions in percent by weight, unless specifically expressed in another sense. The alloy of the present invention preferably comprises, in percentages by weight, the following constituents: 38-55% Ni, 12-25% Cr, 0.5-5% Mo, 0-3% Cu, 2-4.5% of Nb, 0.5-3% of Ti, 0-0.7% of Al, 0.005-0.04% of C, the rest of Fe plus minor impurities and deoxidizers. The Fe content of the alloy is between about 16-35%. The annealing and aging hardening conditions used in relation to the alloy of the invention are as follows. Annealing is performed in a temperature range between 954 ° C (1750 ° F) and 1 121 ° C (2050 ° F). Aging is preferably carried out in a two-stage process. The upper temperature is in the range of 690 ° C (1275 ° F) to 760 ° C (1400 ° F) and the lower temperature is in the range of 565 ° C (1050 ° F) to 677 ° C (1250 ° F) ). A unique aging temperature is also possible at any temperature interval but it significantly extends the aging time and it may result in slightly lower toughness or ductility as well as a general increase in the cost of heat treatment.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a photograph of a diffraction pattern using a transmission electron microscopy (TEM) instrument of heat treated alloy # 1 using procedure B showing the alloy matrix and the dots in phase? '; and Figure 2 is a photograph of a diffraction pattern using a TEM instrument of alloy # 7 heat treated according to procedure C showing the alloy matrix as well as the points in phase? ' Y ?" .

DETAILED DESCRIPTION OF THE INVENTION As stated in the forng, the chemical compositions set forth herein are in percentages by weight. According to the present invention, the alloy contains about 38-55% Ni, 12-25% Cr, 0.5-5% MO, 0-3% Cu, 2-4.5% Nb, 0.5-3% of Ti, 0-0.7% of Al, 0.005-0.04% of C, the rest of Fe plus minor impurities and deoxidants. Ni modifies the Fe-based matrix to provide a stable austenitic structure, which is essential for good thermal stability and susceptibility to formation.

Nickel (Ni) is one of the main elements which forms the phase? ' NI3AI type, which is essential for high tenacity. In addition, a minimum of about 35% Ni is required to have a good resistance to aqueous stress corrosion. Instead of a high content of Ni increase the cost of the metal. The Ni range is broadly defined as 35-55%, and, more preferably, the Ni content is 38-53%. Chromium (Cr) is essential for corrosion resistance. A minimum of about 12% Cr is needed for an aggressive corrosive environment, but more than 25% of Cr tends to result in formation of a-Cr and sigma phases which are detrimental to the mechanical properties. The broad range of Cr is defined as 12-25% and more preferably Cr is 16-23%. Molybdenum (MO) is present in the alloy. It is known that an addition of Mo increases the resistance to pitting corrosion. The addition of Mo also increases the strength of Ni-Fe alloys by substitution of a solid reinforcement solution since the atomic radius of Mo is much higher than that of Ni and Fe. However, an amount greater than about 8% of Mo tends to form a phase in μ of type M? 7 (Ni, Fe, Cr) 6 unwanted or a phase s (sigma) ternary with Ni, Fe and Cr. These phases degrade the susceptibility to work. In addition, it is expensive, and higher contents of Mo unnecessarily increase the cost of alloy. The range of Mo is broadly defined as 0.5-5% and more preferably the Mo content is 1.0-4.8%. Copper (Cu) improves corrosion resistance in non-oxidizing corrosive environments. The synergistic effect of Cu and Mo is recognized to counteract corrosion in typical applications in oil fields where there are acid reducing environments containing high concentrations of chlorides. The Cu range is broadly defined as 0-3% and more preferably the Cu content is 0.2-3%. Additions of aluminum (Al) result in the formation of a phase? ' type Ni3 (Al) which contributes to a high tenacity. Some minimum content of Al is required to activate the formation of? . In addition, the toughness of an alloy is proportional to the volume fraction of? . Instead of this, high volume fractions of? , however, result in degradation in susceptibility to hot working. The range of aluminum is broadly defined as 0-0.7% and more preferably the Al content is 0.01 -0.7%. Titanium (Ti) is incorporated in Ni3 (Al) to form a phase? ' of type Ni3 (AlTi) which increases the volume fraction of the phase? ' and therefore the tenacity of the alloy. The reinforcement power of? ' is also increased by a mismatch of the grid between? and the matrix. Titanium tends to increase the separation of the lattice from? . The synergistic increase in Ti and a decrease in Al is known to increases tenacity by increasing the lack of coincidence in the grid. The contents of Ti and Al have been optimized in the present to maximize this lack of coincidence of the grid. Another important benefit of Ti is that it links the N present as TiN. A decrease in the N content in the matrix improves the susceptibility to hot working of the alloy. Excessively large amounts of Ti generate phase precipitation? Type N3Ti unwanted but degrades the susceptibility to work and hot ductility. The wide range of titanium is 0.5-3% and more specifically the Ti content is 0.6-2.8%. Niobium (Nb) reacts with Ni3 (AlTi) to form a phase? ' of type Ni3 (AlTiNb) which increases the volume fraction of the phase? ' and therefore tenacity. It has been found that a particular combination of Nb, Ti, Al and C results in the formation of phases? and? "which greatly increases tenacity.The ratio of (Nb - 7.75 C) / (A1 + Ti) is in the range of 0.5 to 9 to obtain the high tenacity desired., the alloy must have a minimum of 1% by weight of "as the reinforcement phase." In addition to this reinforcing effect, Nb binds to C as NbC, thereby decreasing the C content in the matrix. The carbide formation of Nb is greater than that of Mo and Cr. Consequently, Mo and Cr are retained in the matrix in the form of elements, which is essential for corrosion resistance. and Cr present the tendency to form in the grain boundaries, while NbC is formed in the whole structure. The elimination / minimization of Mo and Cr carbides improves ductility. An excessively large Nb content tends to form an undesired phase s and excessive amounts of NbC and β ", which are detrimental to processability and ductility.The niobium range is broadly 2.1 .4.5% and Most preferably the Nb content is 2.2-4.3% Iron (Fe) is an element which constitutes the substantial balance in the described alloy.A rather high Fe content in this system tends to decrease the thermal stability and corrosion resistance It is recommended that the Fe does not exceed 35% In general, the Fe content is 16-35%, more preferably between 18-32% and even more preferably between 20-32%. 32% In addition, the alloy contains minor amounts of Co, Mn, Si, Ca, Mg and Ta In the following the description includes examples of alloys to further illustrate the invention Table 1 shows the chemical compositions of different alloys Eve The alloys 1-5 have compositions containing Nb below the range of the invention. Table 2 shows the conditions of annealing and hardening by aging. The mechanical properties determined after annealing and hardening by aging are included in tables 3 and 4.

Comparison of properties shows that the strain limits that are included in table 3 are in the range of 107 to 1 16 ksi for alloys 1 -5 and the strain limits included in table 4 are in the range of 125 to 145 ksi for alloys 6-10 of the present invention.

Table 1 Note: alloys 1, 2 and 6-9 merge into VIM and alloys 3 -5 and 10 merge into VIM + VAR. VIM means merger by Vacuum induction and VAR means vacuum arc refusion.

Table 2 WQ = cooling with water, FC = cooling in oven at 100 ° F / hour, AC = cold air.

Table 3 Mechanical properties at room temperature. Impact and hardness are the averages of three test data. The numbers 1 and 2 are VIM alloys of 50 pounds and 3 to 5 are VIM + VAR heats of 135 pounds.

YS = deformation limit 0.2%, UTS = tenacity at the final tension, ROA = area reduction.

Table 4 Mechanical properties at room temperature. Impact and hardness are the averages of three test data. Numbers 6 to 9 are 50-pound VIM alloys and number 10 are 135-pound VIM + VAR alloys.

YS = deformation limit 0.2%, UTS = tenacity at the final tension, ROA = area reduction. Table 5 shows ratios of (Nb - 7.75 C) / (A1 + Ti) limit of average deformation and calculated as% by weight of percentages of? and? "The calculations are made using a program based on ThermoCalcM R. It is surprising to note that only the alloys of the ratio (Nb - 7.75 C) / (A1 + Ti) greater than 0.5 have a higher deformation limit of 120 ksi Furthermore, only these alloys (6-1 0) are predicted to have the presence of a reinforcement phase 1? " . The experimental analysis at the low deformation limit (alloy # 1) and high deformation limit (alloy # 7) of the material confirms the absence or presence of? ", See figures 1 and 2. The additional striations observed in the figure 2 are generated by the presence of precipitates? " . Corrosion tests show that alloy # 10 has a ratio (Nb -7.75) / (Al + Ti) of 1.76 and an average strain of 136.5 ksi, which also has a good resistance to corrosion in applications of oil field type, see table 6.

Table 5 Proportions of percentage by weight of hardening elements, averages measured with deformation limit of 0.2% »and calculated amount of reinforcement phases, determined by ThermoCalc.

All alloy samples are annealed and aged as indicated in Tables 2-4.

Table 6 Slow voltage rate corrosion test results. The test is performed at 149 ° C (300 ° F) in 25% NaCl without air, under CO2 at 2.7 MPa (400 psig and H2S 2.7 MPa (400 psig), time to failure (TTF),% elongation (EL ), and% area reduction (RA) and its ambient / air ratios are included in the following: This is a # 10 alloy with heat treatment C.

It will be noted in table 5 that alloys 1-5 do not satisfy the formula: (Nb -7.75 C) = 0.5-9 (Al + TÍ) and therefore do not reach the desired minimum deformation limit of 120 ksi. Alloys 1 -5 have average strain limits between 109-1,15 ksi. On the other hand, alloys 6-10 agree with the present invention are observed in table 5 and present values calculated which satisfy the previous formula and generate limits of average deformation between 126-144 ksi. When the calculated value of the above formula is within the desired range of 0.5-9 of According to the present invention, there is present in the alloy matrix a minimum of 1% by weight of phase? ", together with the phase? ' and the% in total weight of the phases? ' +? "between approximately 10 to 30% is present, which takes into consideration the increased strain limit which exceeds the desired minimum 120 ksi. It will be noted in Table 5 that alloys 1-5, which do not satisfy the above formula, do not contain phase? ", While alloys 6-10 of the present invention contain 2.6-6.6% by weight of phase?" along with 8. 1 - 12.2% phase? ' in the matrix. The alloy of the present invention preferably contains 1-10% by weight of phase? "The sum of% by weight of? ' +? " it is between 10 and 30, preferably between 12 and 25. The alloy 10 of the present invention is prepared and subjected to a slow stress rate corrosion test. The test is carried out at a temperature of 149 ° C (300 ° F) in 25% NaCl without air under CO2 2.7 MPa (400 psig) and H2S 2.7 MPa (400 psig). A comparative test on alloy 10 in an air environment is also carried out. The results of the test are established in table 6 above. It will be noted that alloy 10 in the harsh environment shows a time to failure ratio (TTF) of about 0.85 compared to alloy 10 in air with a similar% elongation (EL) ratio. The% reduction in area ratio (RA) is 0.79. These data indicate that the alloys of the present invention provide excellent corrosion resistant properties and meet the standards suggested in the industry when subjected to a very strong sulfur gas well environment. Therefore, according to the present invention, the Ni-Fe-Cr alloy system is modified with additions of Mo and Cu to improve the resistance to corrosion. Additionally, the additions of Nb, Ti, Al and C are optimized to produce a fine dispersion of the phases? and "in the matrix to provide high tenacity." In this manner, the present invention provides a ductile, high tenacity alloy with high impact strength and corrosion resistant designed primarily for the manufacture of bars, tubing and similar shapes. for applications in gas or oil wells Table 7 below provides the currently preferred ranges of the elements constituting the alloy of the invention together with a currently preferred nominal composition.

Table 7 * more minor impurities and deoxidizers In addition to satisfying the constitutive ranges established in table 7, the alloy of the invention must satisfy the equation: (Nb -7.75 C) 0.5-9 (Al + Ti) to ensure that the alloy matrix contains a mixture of phases? ' and y "with a minimum of 1% by weight of phase?" and one percent in Total weight of? ' and? "between 10 and 30 present, for reinforcement purposes.

Although the fusion to the air is satisfactory, the alloy of present invention is preferably prepared using a VIM practice or a VIM + VAR fusion practice to ensure the cleaning of the ingot.

The final heat treatment method of the present invention comprises a first solution annealed by heating between 954 ° C (1750 ° F) to 1 121 ° C (2050 ° F) for a time from about 0.5 to 4.5 hours, preferably for 1 hour followed by quenching in water or cooling with air. The product is then allowed to age preferably by heating to a temperature of at least about 691 ° C (1275 ° F) and is maintained at a temperature for a time between about 6-10 hours to precipitate the? and? ", optionally by a second treatment with heat and aging at about 565 ° C (1050 ° F) at 677 ° C (1250 ° F) and maintained at that temperature to carry out a secondary aging step for about 4 hours. at 12 hours, preferably for a time of about 8 hours.The material after aging is allowed to cool in air to room temperature to obtain the desired microstructure and maximize the reinforcement? Y ?" . After dealing with heat in this manner, the desired microstructure consists of a further matrix? and a minimum of 1% of? "In general, the weight percent of? +? " is between 10 and 30, and preferably between 12 and 25. Although specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to the details may be developed taking into consideration the general teachings of this description. The presently preferred embodiments described herein are to be understood only as illustrative and not limiting as to the scope of the invention, which is determined by the entire scope of the appended claims and any and all equivalents thereof.

Claims (15)

1 . An alloy resistant to corrosion of high tenacity characterized in that it comprises in weight percent: 35-55% »Ni, 12-25% Cr, 0.5-5% Mo, up to 3% Cu, 2. 1 -4.5% Nb, 0.5-3% of you, up to 0.7% of Al, 0.005-0.04% of C, the rest of Fe plus minor and deoxidizing impurities and where the alloy satisfies the equation: (JV "-7-75) = 0.5 Q 9 (Al + Ti) the alloy contains a mixture of phases? ' Y ?" with a minimum of 1% by weight of? "and has a minimum deformation limit of 120 ksi when it is in an aged and aged condition.

2. The alloy according to claim 1, characterized because the total weight percent of? ' +? "is from 10 to 30 per hundred.

3. The alloy according to claim 1, characterized in that it contains 16-35% Fe.

4. The alloy according to claim 1, characterized because it contains 38-53% Ni, 16-23% Cr, 1 -4.8% Mo, 0. 2-3.0% Cu, 2.2-4.3% Nb, 0.6-2.8% Ti, 0.01 -0.7% Al and 0.005-0.03% C.

5. The alloy according to claim 4, characterized in that it contains a mixture of phases? ' and? "with a minimum of 1% by weight of phase?" and percent in total weight of? +? "from 10 to 30 present.

6. The alloy according to claim 1, characterized in that it contains 38-52% Ni, 18-23% Cr, 1 -4.5% Mo, 0. 5-3% of Cu, 2.5-4% of Nb, 0.7-2.5% of Ti, 0.05-0.7% of Al and 0.005-0.025% of C.

7. The alloy according to claim 6, characterized in that it contains a total weight percent of phases? +? "from 10 to 30 presents.

8. The alloy according to claim 1, characterized in that it contains between 1-10% by weight of phase? ".

9. The alloy according to claim 1, characterized in that it is in the form of a tube or bar for use in a environment of oil or gas well or in a marine environment.

10. A process for manufacturing a corrosion resistant, high tenacity alloy, characterized in that it comprises the steps of: providing an alloy consisting essentially of weight percent: 35-55% Ni, 12-25% Cr, 0.5-5% of Mo, up to 3% of

Cu, 2.1 -4.5% Nb, 0.5-3% Ti, up to 0.7% Al, 0.005-0.04% C, the rest of Fe plus minor and deoxidizing impurities and where the alloy satisfies the equation: and heat treating the alloy by annealing and at least one hardening step by aging so that the alloy contains a mixture of phases? and? "within a minimum of 1% by weight of phase?" and has a minimum deformation limit of 120. eleven . The method according to claim 10, characterized in that it includes two stages of aging hardening.

12. The procedure in accordance with the claim 10, characterized in that the annealing step is carried out between 954 ° C (1 750 ° F) at 1 121 ° C (2050 ° F) and the hardening by aging is in two stages of aging that are carried out at 691 ° C (1275 ° F) at 760 ° C (1400 ° F) and 565 ° C (1050 ° F) at 677 ° C (1250 ° F).

13. The process according to claim 12, characterized in that the annealing step is followed either by rapid cooling in air or water and the first stage of aging is followed by an oven cooling to a second aging temperature, followed by cooling with air.

14. The method according to claim 10, characterized in that the alloy contains 1% by total weight of phases? and? "from 10 to 30 presents.

15. The method according to claim 10, characterized in that it includes the step of shaping the alloy in the form of a tube or bar for use in a gas or oil well environment or in a marine environment.