GB2236113A

GB2236113A - Well equipment alloys

Info

Publication number: GB2236113A
Application number: GB9019277A
Authority: GB
Inventors: Laurence A Jackman; M Daniel Boldy; Arnold L Coffey
Original assignee: Teledyne Industries Inc
Current assignee: TDY Industries LLC
Priority date: 1989-09-05
Filing date: 1990-09-04
Publication date: 1991-03-27
Also published as: GB9019277D0

Abstract

The present invention provides specialty components for high technology wells having improved toughness fabricated from low carbon alloy consisting of Cr 17-21% Ni 50-55% Nb+Ta 4.75-5.5% Mo 2.8-3.3%, Ti 0.65-1.15%, Al 0.2-0.8% not more than 0.025% C, the balance being iron apart from incidental impurities.

Description

SPECIALTY COMPONENTS FOR HIGH TECHNOLOGY WELLS HAVING IMPROVED TOUGHNESS Field of the Invention This invention pertains to the use of certain low carbon iron-containing nickel-base alloys with improved toughness characteristics in the construction of equipment used in extreme environments such as those found in high technology deep sour gas wells.

Backaround Nickel-base superalloys have been under development since prior to the 1930's. Through the years various formulations have been developed for specific applications. One such formulation, alloy 718, is an age hardenable iron-containing nickelbase alloy that provides moderate-temperature high strength as well as good resistance to strain-age cracking in welding. This alloy is described in United States Patent 3,046,108. The chemical composition (weight percent) of alloy 718 is as follows: carbon 0.08 max; manganese, 0.35 maxt silicon, 0.35 max; phosphorus, 0.015 max; sulphur, 0.015 max; chromium, 17.0-21.0; cobalt, 1.0 max; molybdenum, 2.80-3.30; columbium plus tantalum, 4.75-5.50; titanium, 0.65-1.15; aluminum, 0.20-0.80; boron, 0.006 max; copper, 0.30 max; nickel, 50.055.0; iron, remainder. UNS N07718.

The most significant applications of alloy 718 have been in the production of rotating parts for jet aircraft engines, such as forged turbine disks. This is because alloy 718 has the needed high strength at turbine-disk operating temperatures.

Another commercially significant application of alloy 718 has been in high technology oil and gas production systems. This application requires high toughness and resistance to environment-induced cracking, in addition to the high strength and excellent corrosion resistance of nickel base alloys. An alloy's toughness is generally related to that alloy's resistance to cracking and crack propagation. Toughness is measurable by use of notched bar testing such as Charpy (Cv) and precracked specimen testing such as fracture toughness (KIC and K"). Charpy values are typically determined by measuring the energy required to fracture a notched specimen. Standard procedures for determining KIC and K" are described in ASTM E-399 and ASTM E-992, respectively.

During Teledyne Allvac's development of alloy 718 products for high technology oil and gas systems, it was noticed that as section size increased, toughness, as reflected by the Charpy values (Cv), decreased. Consequently, the toughness of large cross section 718 bar was not sufficient to meet the strict requirements for use in the extreme environments associated with high technology wells.

Alloy 718 derives its strength from both solid solution strengthening and precipitation strengtheningt whereas alloys initially used for oil and gas tubulars derived their strength from solid solution strengthening and cold working. The thick wall design of specialty components such as above ground safety valves, subsurface safety valves, packers, and hangers severely limits the use of a cold worked product since the sizes and wall thicknesses are beyond current production capabilities. Furthermore, the limitations of current production techniques preclude thru-wall strength uniformity in a cold worked product having walls with thicknesses greater than about 1 inch.

In the initial effort to achieve uniform high strength in thick walls, and corrosion resistance comparable to the cold reduced alloys used for downhole tubulars, an age hardenable nickel-base alloy, X-750, was used. That alloy was used in the fabrication of specialty components until failures due to environment-induced cracking caused its demise.

Since crack induced failure in such components can be catastrophic, endangering the lives of workers, and may result in the destruction of related equipment, thereby compromising production capacity, the need for age-hardenable alloys with high strength and high toughness is particularly acute in specialty components for deep sour gas wells.

As we focused on the goal of developing an age-hardenable alloy with improved Charpy impact values, and thus increased toughness and resistance to cracking, we considered factors traditionally associated with low Charpy values. For example, we investigated the effect on Cv brought about by the amount of hot work, hot working temperatures, and size effects during heat treatment.

Ultimately, we considered chemistry modifications in alloy 718 to increase Cv. One element that was considered was carbon. We speculated that toughness might be increased by reducing the number and size of carbides. It was recognized, however, that reducing the carbon content of the alloy could be detrimental to toughness due to decreased carbide strengthening at grain boundaries and impaired grain size control.

Moyer had shown that the number and size of carbides could be reduced by decreasing carbon content below O.0108 without degrading high-temperature stressrupture properties. J. M. Moyer, "Extra Low Carbon Allvac 718," Fifth International Symposium of Superalloys (1984). Moyer's work was directed towards improving low cycle fatigue at elevated temperature (above 1000 degrees F) for jet aircraft engines. This, in part, contradicted earlier work by Stroup and Pugliese which showed that reduced carbon superalloys, while having increased strength, exhibited inferior stress-rupture properties.

Stroup and Pugliese, "How Low-Carbon Contents Affect Superalloys," Metal Progress, (February, 1978) 96100. Stroup and Pugliese had also shown that reduced carbon superalloys exhibited significant notch weakness, i.e., decreases in carbon levels could be detrimental to toughness. In summary, the information regarding carbon content was contradictory, and furthermore there was no specific data on the influence of carbon content on toughness.

The Invention We have recently discovered that reducing the carbon level of alloy 718 significantly below conventional levels provides an unexpected advantage, that is, enhancing toughness and thus resistance to cracking, as reflected by improved Charpy impact values (Cv) and fracture toughness values (uke) It is possible that these low carbon 718 alloys have the added advantage of improved resistance to environment-induced cracking. For present purposes, a low carbon 718 alloy is one in which the carbon concentration is no more than 0.025 weight percent. Preferably, the carbon concentration will be no more than about 0.020 weight percent, and most desirably about 0.015 weight percent.Lower carbon concentrations may provide additional benefit, however, the presently preferred concentrations result from considerations of commercial and practical processing limitations.

The improved Cv exhibited by these low carbon formulations of alloy 718 makes them suitable for a number of uses for which the standard alloy 718 was heretofore only marginally acceptable or unacceptable. Among such uses is the application of low carbon 718 in the construction of specialty components used in high technology wells.

Specialty components are those components in high technology wells that are traditionally constructed of metal, but which due to the specialized shape of these components are not amenable to construction from cold worked tubulars.

For example, the size and wall thicknesses needed are beyond current production capabilities for cold worked tubulars. Furthermore, thru-wall strength uniformity is not obtainable for tubulars with wall thicknesses required by these specialty components.

By way of example, these metal specialty components include subsurface safety valve body components (Figures 1-3), tubing hangers, and packers, as well as above ground safety valves.

The present invention thus provides specialty components for high technology wells formed from an alloy consisting essentially of 17 to 21 weight percent chromium, 50 to 55 weight percent nickel, 4.75 to 5.50 weight percent columbium plus tantalum, 2.8 to 3.3 weight percent molybdenum, 0.65 to 1.15 weight percent titanium, 0.2 to 0.8 weight percent aluminum, not more than 0.025 weight percent carbon, and the balance essentially iron and incidental impurities.

Furthermore, the present invention provides a method for improving toughness in specialty components for high technology wells comprising fabricating such metal specialty components from an alloy consisting essentially of 17 to 21 weight percent chromium, 50 to 55 weight percent nickel, 4.75 to 5.50 weight percent columbium plus tantalum, 2.8 to 3.3 weight percent molybdenum, 0.65 to 1.15 weight percent titanium, 0.2 to 0.8 weight percent aluminum, not more than 0.25 weight percent carbon, and the balance essentially iron and incidental impurities and using said specialty components in high technology well applications.

EXAMPLE Low Carbon 718 Alloy A heat (&num;6439-1) of low carbon 718 alloy was melted, the chemical composition of which was 17.38 weight percent chromium, 52.10 weight percent nickel, 5.11 weight percent columbium plus tantalum, 2.89 weight percent molybdenum, 0.97 weight percent titanium, 0.52 weight percent aluminum, 0.015 weight percent carbon, and the balance iron and incidental impurities. See Table 4.

Tables 1-4 present comparative data for the low carbon material of the present invention with the standard (approximately 0.035 weight percent carbon) production material. Average transverse Charpy and Kee values increased substantially for low carbon material. Table 4 presents the chemical compositions of all the heats referred to in Tables 1-3. All of the standard alloy 718 heats have carbon levels of 0.034 or more. TABLE 1 TENSILE PROPERTIES Test Carbon .2% YS, Temperature Heat No. Dia., In.Wt., % UTS, Ksi Ksi EL % RA% Room 6439-1 6.0 .016 180.3 139.0 27.5 41.3 Room 6439-2 9.0 .016 184.5 140.2 25.3 34.7 Room 6439-3 10.0 .016 178.9 130.8 28.0 36.9 Room 6439-1 11.5 .016 188.2 138.4 26.1 40.7 Room 5403-1 6.0 .035 179.5 135.2 30.0 49.0 Room 3953-1 6.0 .034 175.4 126.8 30.2 47.5 Room 2810-3 7.5 .039 175.9 129.3 26.5 40.2 Room 1946-3 8.0 .042 176.4 129.2 28.0 38.5 Room 1564-3 8.0 .043 177.1 131.8 28.0 40.0 Room 6496-1 12.0 .037 172.2 117.0 31.6 47.6 250 F 6439-1 6.0 .016 168.6 120.3 32.0 46.5 250 F 6439-1 6.0 .016 168.0 119.9 30.8 46.2 250 F 6439-1 6.0 .016 167.1 120.5 29.2 43.6 250 F 6439-1 6.0 .016 167.3 120.1 28.0 40.7 250 F 5403-1 6.0 .035 166.1 120.3 30.1 45.4 250 F 5403-1 6.0 .035 167.8 124.5 29.4 40.6 250 F 5403-1 6.0 .035 166.4 119.7 32.3 49.4 250 F 5403-1 6.0 .035 165.1 119.9 31.2 50.5 TABLE 2 O"F CHARPY IMPACT Carbon, Energy, Lateral Heat No. ..... In. Wt., % ft/lbs Expansion. mils 6439-1 6.0 .016 59.0 30.0 59.0 38.0 59.0 30.0 6439-2 9.0 .016 52.0 32.0 54.0 30.0 54.0 30.0 6439-3 10.0 .016 60.0 32.0 60.0 32.0 62.0 32.0 6439-1 11.5 .016 59.0 30.0 55.0 28.0 55.0 30.0 3953-1 6.0 .034 37.0 24.0 38.0 24.0 39.0 24.0 5403-1 6.0 .035 43.0 24.0 44.0 28.0 52.0 26.0 2810-3 7.5 .039 36.0 20.0 36.0 19.0 37.0 20.0 1946-3 8.0 .042 32.0 21.0 32.0 20.0 32.0 20.0 1564-3 8.0 .043 35.0 18.0 35.0 20.0 37.0 18.0 6496-1 12.0 .037 37.5 22.0 38.0 22.0 40.0 22.0 TABLE 3 FRACTURE TOUGHNESS

Test Carbon, Temperature Heat &num; Diameter, In. Wt. % Kee, Ksi/In.

0 F 6439-1 6.0 .016 292.3 291.1 292.4 0 F 6439-2 9.0 .016 268.0 261.3 259.9 0 F 6439-3 10.0 .016 315.1 329.0 323.1 0 F 6439-1 11.5 .016 303.7 307.3 307.6 0 F 5403-1 6.0 .035 248.2 257.5 237.5 0 F 3953-1 6.0 .034 206.2 215.1 213.6 TABLE 4 CHEMISTRY. WT% Heat No. C Cr Ni Cb+Ta Mo Ti Al 6439-1,2,3 .016 17.38 52.10 5.11 2.89 .97 .52 5403-1 .035 17.39 51.99 5.15 2.91 .96 .51 3953-1 .034 17.31 52.19 5.15 2.86 .90 .53 2810-3 .039 17.77 51.74 5.13 3.23 .95 .51 1946-3 .042 17.51 52.20 5.12 2.94 1.00 .59 1564-3 .043 17.54 52.35 5.13 2.88 .95 .55 6496-1 .037 17.32 52.07 5.12 2.97 .92 .54

Claims

WHAT IS CLAIMED IS

1. Specialty components for high technology well equipment formed from an alloy consisting essentially of 17 to 21 weight percent chromium, 50 to 55 weight percent nickel, 4.75 to 5.50 weight percent columbium plus tantalum, 2.8 to 3.3 weight percent molybdenum, 0.65 to 1.15 weight percent titanium, 0.2 to 0.8 weight percent aluminum, not more than 0.025 weight percent carbon, and the balance essentially iron and incidental impurities.

2. The specialty components of claim 1 wherein the carbon content is about 0.015 weight percent.

3. A specialty component according to claim 1 which comprises a subsurface safety valve.

4. A specialty component according to claim 1 which comprises a subsurface packer.

5. A specialty component according to claim 1 which comprises a tubing hanger.

6. A specialty component according to claim 1 which comprises an above ground safety valve.

7. Specialty components for high technology well equipment formed from an alloy consisting essentially of about 18 weight percent chromium, about 52 weight percent nickel, about 5 weight percent columbium plus tantalum, about 3 weight percent molybdenum, about 1 weight percent titanium, about 0.5 weight percent aluminum, not more than 0.025 weight percent carbon, and the balance essentially iron and incidental impurities.

8. A method for improving toughness in specialty components for high technology well equipment comprising fabricating metal specialty components from an alloy consisting essentially of 17 to 21 weight percent chromium, 50 to 55 weight percent nickel, 4.75 to 5.50 weight percent columbium plus tantalum, 2.8 to 3.3 weight percent molybdenum, 0.65 to 1.15 weight percent titanium, 0.2 to 0.8 weight percent aluminum, not more than 0.025 weight percent carbon and the balance essentially iron and incidental impurities and using said specialty components in well equipment applications.

9. The method according to claim 8 wherein the step of fabricating metal specialty components comprises fabricating said components from an alloy having a carbon content of about 0.015 weight percent.

10. The method according to claim 8 wherein the step of fabricating metal specialty components comprises fabricating said components from an alloy consisting essentially of about 18 weight percent chromium, about 52 weight percent nickel, about 5 weight percent columbium plus tantalum, about 3 weight percent molybdenum, about 1 weight percent titanium, about 0.5 weight percent aluminum, not more than 0.025 weight percent carbon, and the balance essentially iron and incidental impurities.