Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%

Definitions

• This invention relates to a nickel-base alloy and more particularly to such an alloy and products made therefrom having a unique combination of corrosion resistance and age or precipitation hardenability properties in the heat treated condition and without requiring working below the alloy's recrystallization temperature.
• US-A-3,160,500 relates to a matrix-stiffened alloy described as having high strength containing 55-62% Ni, 7 to 11% Mo, 3 to 4.5% Nb, 20-24% Cr, up to 8% W, 0.1% Max. C, 0.5% Max. Si, 0.5% Max. Mn, 0.015% Max. B, 0.40% Max of a deoxidizer selected from the group consisting of Al and Ti and the balance essentially Fe but not more than 20%.
• percent is given as weight percent (w/o) unless otherwise indicated.
• the alloy is further characterized as having at least about 60 ksi 0.2% YS (414 MN/m2) at room temperature and being essentially non-age hardenable, non-age hardenable being defined in US-A-3,160,500 as a maximum increase in yield strength of 20 ksi (138 MN/m2) when subjected to a heat treatment at a temperature of about 1100 to 1300 F (593.3 - 704.4°C) as compared to the yield strength of the alloy in the annealed condition.
• the total amount of aluminum plus titanium present in the alloy is not to exceed 0.4% "as otherwise the alloys tend to become age hardenable" (Col. 2, lines 45-49).
• Alloys 1-3 exemplifying the claimed subject matter of the patent and two alloys (identified here as Alloys A and B) described as outside the patented invention, are set forth in Table I where the 0.2% YS (ksi, MN/m2) at room temperature in the annealed condition (1900 F (1037.7°C), 1 hour) as reported in the patent are also given.
• Table I it is to be noted that tungsten was reported only in connection with Alloy 2.
• Alloy A was described as being “similar in composition” to Alloy 1 except as indicated (Pat., col. 4, lines 10 & 11).
• Alloy B was characterized as having "age hardened strongly but had a yield strength at room temperature of only 49,500 psi, (341.3 MN/m2) . . . when tested after a 1900 F anneal.”
• Type 625 alloy as well as other compositions of US-A-3,160,500 are characterized by outstanding corrosion resistance particularly resistance to chlorides, sulfides and carbon dioxide, combined with stability at elevated temperatures, this combination of properties was achieved by eliminating age or precipitation hardening for all practical purposes because of the prohibitively long time required at the elevated temperature required for age hardening.
• US-A-3,046,108 describes an age-hardenable nickel alloy containing 0.2 Max. C, 1% Max. Mn, 0.5% Max. Si, 10-25% Cr, 2-5% or 7% Max. Mo, 3-9% Nb + Ta, 0.2-2% Ti, 0.2-2% Al, (Ti + Al ⁇ 2.5%) 0.02% Max. B, 0.5% Max. Zr, 40% Max. Co, 40% Max. Fe and 45-80% Ni + Co with nickel ⁇ 30% and Co ⁇ 40%.
• a preferred composition contains 0.03% C, 0.18% Mn, 0.27% Si, 21% Cr, 0.6% Al, 0.6% Ti, 4% Nb, 3% Mo, 0.009% B, 53% Ni and balance Fe. In a further variation, iron is limited to 20% Max.
• European Patent Application No. 92,397 on the other hand is expressly directed to providing an alloy suitable for use in sour gas wells where corrosion resistance is required to sulfides, carbon dioxide, methane and brine (chlorides) at temperatures up to 300 C.
• This publication suggests that the most likely causes of failure under such conditions are sulfide stress corrosion cracking, chloride stress corrosion cracking, pitting and general corrosion.
• Alloys A-X there are six compositions outside the claimed subject matter of the European application 92,397, Alloys F-L, containing 1.9-3.1% Nb but only Alloy K contains a significant amount of Ti for consideration here.
• US-A-4,400,210 and US-A-4,400,211 and Japanese Publication No. 82-203740 December 1982 relate to alloys for making high strength well casing and tubing having improved resistance to stress corrosion cracking in media containing sulfides, chlorides and carbon dioxide such as is encountered in deep wells.
• US-A-4,400,210 and US-A-4,400,211 (Col. 2) assert that "cold working seriously decreases resistance to stress corrosion cracking" but seek to overcome the adverse effect of cold working by the presence of Cr, Ni, Mo and W in the surface layer of a casing or tubing.
• These two U.S. patents and the Japanese publication specify the composition set forth therein as containing 0.5-4% of at least one of Nb, Ti, Zr, Ta, and V.
• European patent application 82-56480 relates to a nickel base alloy having resistance to stress corrosion cracking in contact with water at elevated temperature as in boiling water nuclear reactors or pressurized water reactors.
• the proposed alloy is described as consisting essentially of 15-25% Cr, 1-8% Mo, 0.4-2% Al, 0.7-3% Ti, 0.7-4.5% Nb and the balance Ni, strengthened by gamma prime and/or gamma double prime.
• the gamma prime phase is defined as an intermetallic compound of Ni3(Al, Ti) and the gamma double prime phase as an intermetallic compound of Ni3Nb.
• EP-A-0 066 361 is directed to an age-hardenable nickel-base alloy containing, in weight percent: in which the balance is 45-55% nickel.
• the alloy is described as being good for wrought products, that is, cold rolled strip and extruded tubing for use in tapping deep hydrocarbon fuel reservoirs.
• FR-A-2 277 901 discloses an age-hardenable nickel-base alloy containing, in weight percent: in which the balance is nickel and is directed to a thermal treatment for the alloy defined in time and temperature as a function of the alloy composition so as to control the resulting microstructure.
• the problem to which the application is directed is to provide an age-hardenable nickel-base chromium-molybdenum-containing alloy and articles made therefrom which without being warm or cold worked will have a unique combination of strength and corrosion resistance particularly to pitting and crevice corrosion and resistance to stress corrosion cracking under high stress in severely corrosive environments.
• the alloy and articles made therefrom should have high resistance to pitting and crevice corrosion and to stress corrosion cracking in the presence of chlorides, sulfides and/or carbon dioxide at elevated pressures and temperatures while being hardenable by heat treatment to a 0.2% yield strength greater than 100 ksi (690MN/m2) without the need for working below the recrystallization temperature, that is warm or cold working.
• the alloy and articles made therefrom are moreover to be highly resistant to such corrosion in the chloride-, sulfide-, and carbon dioxide- bearing media at the elevated pressures and temperatures, e.g. up to 500 F (260 C) encountered in deep sour oil and/or gas wells.
• the foregoing problem is solved in accordance with the invention by providing a nickel base, chromium-molybdenum-containing alloy which in weight percent consists essentially of the composition set forth in Table II below.
• the balance of the composition are incidental impurities and at least 57% nickel, the sum of the percent chromium and molybdenum being not greater than 31, and the sum of the percent niobium, titanium and aluminum being such that the total atomic percent thereof is about 3.5 a/o to 5 a/o when calculated as 0.64(w/o Nb) + 1.24(w/o Ti) + 2.20(w/o Al).
• Other elements can be present which aid in making and processing the alloy or which do not objectionably detract from the desired properties.
• the broad range of one or more elements may be used with the preferred ranges of other elements.
• the stated broad maximum or minimum of one or more elements can be used with their preferred maximums or minimums respectively in Table II and hereinafter.
• niobium it is intended by reference to niobium to include the usual amount of tantalum found in commercially available niobium bearing alloys used in making alloying additions of niobium to commercial alloys.
• nickel-base composition in addition to nickel the essential elements are chromium, molybdenum, niobium, titanium and aluminum. Optional elements and the usual incidental impurities may also be present.
• Carbon and nitrogen are not considered to be desirable additions in this composition because each can have an adverse effect upon corrosion resistance and because each interferes with the desired hardening reaction, carbon by tying up niobium and titanium, and nitrogen by tying up titanium.
• carbon is limited to no more than 0.1% and preferably to no more than 0.03% or better yet to no more than 0.02%.
• Nitrogen is limited to no more than 0.04% or even to a maximum of 0.03% and is preferably limited to no more than 0.01%.
• the hardener elements, niobium and titanium are present in the larger amounts indicated by their ranges. While better results can be attained with extremely low levels of carbon present, e.g. less than 0.005% or less than 0.003%, the cost of reducing carbon below 0.01% makes that a practical minimum for carbon when the added cost would not be warranted.
• Manganese may be present in amounts up to 5% but it is preferably kept low, to no more than 2%, better yet to no more than 0.5% or even no more than 0.2%, because manganese increases the tendency for grain boundary precipitation and reduces intergranular corrosion resistance, and pitting and crevice corrosion resistance.
• the larger amounts of manganese when present are at the expense of the larger amounts of iron contemplated in this alloy.
• silicon While silicon may be present it is preferably kept low because it promotes the formation of unwanted Laves phase and excessive amounts of silicon can affect weldability and hot workability. Thus, silicon is limited to no more than 1%, preferably no more than 0.5% and better yet no more than 0.2%. Phosphorus and sulfur are considered impurities in this alloy because both adversely affect hot workability and cleanliness of the alloy and promote hydrogen embrittlement. Therefore, phosphorus and sulfur are kept low, less than 0.03% each. Preferably phosphorus is limited to 0.015% Max. and sulfur to 0.010% Max.
• cobalt contributes to corrosion resistance when present in this composition and to that end may replace nickel on a weight-for-weight basis.
• the cost of cobalt is now and is expected to continue to be greater than nickel so that the extent of the benefit gained from a given addition of cobalt must be weighed against the cost thereof. For that reason, cobalt is limited to a maximum of 5% and nickel is at least 57%, better yet at least 59% nickel is present.
• tungsten can be substituted for its equivalent percent molybdenum, that is 2% by weight tungsten for each 1% by weight molybdenum replaced, when it may be beneficial but at least 7% molybdenum must be present.
• Boron up to a maximum of 0.02% may be present in this alloy. Even though many of the advantages of the present alloy can be attained without a boron addition, it is preferred for consistent best results that a small amount of boron of 0.001% to 0.006% Max. be present. Also to aid in refining the alloy, up to 0.50% Max. preferably not more than 0.08% Max. zirconium may be present and from a few hundredths up to about a tenth of a percent of other elements such as magnesium, calcium or one or more of the rare earths may be added.
• Copper may be present in this alloy when it may be exposed to sulfuric acid-bearing media or it is desired to ensure maximum resistance to chloride and sulfide stress corrosion cracking at elevated temperature when its adverse effect, if any, on pitting, crevice and intergranular corrosion resistance can be tolerated. To that end, up to 3%, preferably no more than 2.0%, copper may be present.
• Iron also is not an essential element in this composition and, if desired, may be omitted. Because commercially available alloying materials contain iron it is preferred to reduce melting costs by using them. It is also believed that iron contributes to resistance to room temperature sulfide stress-cracking. Thus, up to 20% Max. iron may be present but 2% to no more than 14% is preferred.
• Chromium, molybdenum, niobium, titanium, aluminum and nickel are critically balanced to provide the uniquely outstanding combination of strength and corrosion resistance properties characteristic of the alloy provided by the present invention.
• the maximum tolerable molybdenum is proportionately reduced on a one-for-one weight percent basis from 12% to 7%. Because the larger amounts of chromium ( ⁇ 22%) or molybdenum (>11%) may result in the precipitation of deleterious phases, they are preferably avoided with 57% nickel or better yet 59% nickel is preferred.
• the elements niobium, titanium, and aluminum take part in the age hardening reaction by which the present composition is strengthened by heat treatment and without requiring warm or cold working.
• This invention in part stems from the discovery that the elements niobium and titanium together with smaller amounts of aluminum in the critical proportions specified herein in relation to each other and to the elements chromium, molybdenum and nickel provide a high 0.2% yield strength combined with a high level of corrosion resistance suitable for use under a wide variety of conditions and, when balanced as indicated to be preferred herein, provide a composition suitable for use under the rigorous conditions to be encountered in deep sour wells.
• compositions strengthened primarily with niobium and titanium differ from those strengthened with titanium or titanium and aluminum in that the titanium and the titanium plus aluminum strengthened material showed extensive intergranular precipitation of chromium-rich carbides (M23C6) during aging which occurred independent of the chromium and molybdenum content.
• the hardener elements niobium, titanium and aluminum must be carefully balanced if the high strength of this composition provided by the age hardening reaction is not to result in an unwanted reduction in corrosion resistance. While the broad range for niobium has been stated as 2-6% and for titanium 0.50-2.5%, for better corrosion resistance a preferred niobium range is 2.5-5% or better yet 2.75-4.25% and a preferred titanium range is 0.6 to 2% or even better yet 0.7 to 2.0%.
• the total hardener content should range from 3.5 a/o up to 5 a/o and better yet should not exceed 4.5 a/o for a better all around combination of properties as described herein.
• nickel should be increased whenever the hardener content is increased with the ratio of the atomic percent increase in nickel to the atomic percent increase in hardener content being 3 to 1 to compensate for the additional nickel removed from the alloy matrix. In this way, the adverse effect of undesired phases, such as sigma phase, and their attendant adverse effect can be avoided.
• aluminum is beneficial in stabilizing the desired intragranular precipitate and relatively small amounts are found advantageous. It has also been noted that above 0.25%, that is at 0.35% and above, aluminum does not appear to add to but rather to detract from the yield strength at room temperature. Therefore, while up to about 1% aluminum can be present, for better results, particularly higher yield strength, aluminum is limited to no more than 0.5%. In this regard, it is also to be noted that when the larger amounts of aluminum objectionably affect the room temperature yield strength, the strength of the composition can be increased by using a lower solution or a higher primary aging temperature. Also, if the tolerable maximum amounts of niobium and/or titanium are not already present then one or both may be increased. Therefore, aluminum amounts in excess of 0.35% (0.77 a/o) are not to be included in atomic percent determinations throughout this specification but only insofar as room temperature yield strength is concerned.
• the alloy of this invention can be melted and hot worked using techniques that are well known and conventionally used in the commercial production of nickel-base alloys.
• a double melting practice is preferred such as melting in the electric arc furnace plus argon-oxygen decarburization or vacuum induction melting, to prepare a remelt electrode followed by remelting, e.g. consumable remelting.
• Deoxidation and desulfurization with magnesium and/or calcium when used contributes to hot workability.
• Additions of rare earths, e.g. in the form of misch metal which is primarily a mixture of cerium and lanthanum, or yttrium may also be beneficial.
• Small amounts of boron and/or zirconium also stabilize grain boundaries and may contribute to hot workability.
• the elements present in this composition are balanced to provide an austenitic microstructure in which the strengthening elements niobium, titanium and aluminum react during appropriate heat treatment with nickel to form one or more strengthening phases in the form of an intragranular precipitate by age or precipitation hardening.
• the composition of those phases is generalized as Ni3(Nb,Ti,Al) and may include gamma prime and/or gamma double prime.
• the age-hardenable corrosion resistant nickel-base chromium, molybdenum, niobium, titanium and aluminum alloy of the present invention is readily fabricated into a wide variety of parts following practices utilized in connection with other nickel base alloys. It is well suited to be produced in the form of billets, bars, rod, strip and plate as well as a variety of semi-finished and finished articles for use where its outstanding combination of strength and corrosion resistance in the heat treated condition is desired without requiring working below the recrystallization temperature. Homogenization and hot working is carried out from a temperature of 2050-2200 F (about 1120-1200 C). When required following hot working, solutioning and recrystallization is carried out by heating to a solution treating temperature of 1800-2200 F (980 - 1200 C).
• An optimum solution treating temperature is 1900 F (1038 C) and preferably should be no higher than 1950 F (1065 C) because higher temperature tends to reduce strength and pitting and crevice corrosion resistance, and to increase intergranular precipitation during the aging heat treatment.
• Lower solution treating temperatures than the recrystallization temperature are preferably not used to avoid an adverse effect on corrosion resistance and microstructure though higher strength may result. While care is to be exercised in selecting the solution and aging treating temperatures, the temperatures to be used for optimum results are readily determined.
• a single step age hardening heat treatment may be used if desired but to provide optimum strength and corrosion resistance a two-step aging treatment is preferred.
• the initial or primary aging treatment can be at 1250 F (677 C) to 1450 F (788 C), preferably between 1300 and 1400 F (700 - 760 C), e.g. 1350 F (732 C), followed by secondary aging at 1100 - 1250 F (590 - 675 C). It is to be noted that in this composition, the use of higher primary aging temperatures result in increased strength but contributes to intergranular precipitation.
• Table III The examples set forth in Table III are exemplary of the present invention and in addition to the amounts indicated under each element contained from 0.001-0.006% boron. Other elements when present in more than what is considered a residual or incidental amount in keeping with good commercial practice are indicated in the footnote to the table.
• Examples 1-45 were vacuum induction melted as small laboratory heats and, unless otherwise noted, contained ⁇ 0.2% manganese, ⁇ 0.2% silicon, ⁇ 0.015% phosphorus, ⁇ 0.010% sulfur, and ⁇ 0.01% nitrogen. An addition of 0.05% magnesium was made to each to complete desulphurization and/or deoxidation before being cast as an ingot.
• the ingots were homogenized at 2185 F (1195 C) for an extended period (60-70 hours) and then forged from a starting temperature of 2100 F (1150 C), with intermediate reheats as required, to bars 0.75 in ⁇ 1.25 or 1.5 in (1.9 ⁇ 3.2 or 3.8 cm). Sections of forged bar from each example were then formed into 0.125 in (0.32 cm) thick strip.
• Tensile and corrosion test specimens were prepared from bar and/or strip material of the examples and heats of Tables III and IIIA and were tested in the solution treated (recrystallized) plus age hardened condition unless otherwise stated.
• Room temperature tensile and hardness data are set forth in Tables IV and IVA.
• the 0.2% yield strength (“0.2% YS") is given as the average of two tests in “ksi” and “(MN/m2)" as is also the ultimate tensile strength ("UTS").
• the percent elongation in four diameters or widths depending on whether from bar or strip specimens is indicated as "El.(%)".
• the percent reduction in area is indicated as "RA(%)”.
• the average room temperature hardness on the Rockwell C scale is indicated as "HRC”.
• the alloy of the present invention in the solution treated and age hardened condition is brought to a high yield strength with a minimum hardener content (Nb+Ti+Al) of 3.5 a/o without requiring warm or cold working for that purpose.
• Yield strengths greater than 100 ksi (690 MN/m2), that is at least 105 ksi (723.9 MN/m2) are consistently provided with hardener contents greater than 3.5 a/o with niobium ⁇ 3.0 w/o.
• the minimum weight percent titanium is proportionately increased from 0.8 w/o to 2.0 w/o, that is, a reduction of a predetermined amount in the niobium content should be accompanied by 1.2 times that amount of an increase in the weight percent titanium present in the alloy.
• a reduction of a predetermined amount in the niobium content should be accompanied by 1.2 times that amount of an increase in the weight percent titanium present in the alloy.
• only up to 0.35 w/o (0.77 a/o) aluminum is present.
• niobium and titanium are adjusted proportionately in relation to each other so that as the percent by weight niobium is decreased from 3.9 w/o to 3.0 w/o the minimum weight percent titanium is increased proportionately from 0.50 w/o to 1.1 w/o, that is, the ratio of an increase in titanium to a decrease in niobium is equal to 2/3. As the weight percent niobium is decreased from 3.0% to 2.75% the minimum weight percent titanium is increased proportionately from 1.1% to 1.6%, that is, a ratio of an increase in titanium to the accompanying decrease in niobium of 2.
• the weight percent niobium is decreased from 4.5 w/o to 3.5 w/o the weight percent titanium is increased proportionately from 0.50 to 1.5 w/o, then a minimum 0.2% yield strength of 140 ksi (about 965 MN/M2) is attainable.
• the carbon content exceeds 0.03%, the effect of carbon on strength can be offset by increasing hardener content, particularly niobium, so as to compensate for the amount tied up by carbon and thereby rendered unavailable for the desired hardening reaction. Because carbon tends toward increased intergranular precipitation and an attendant reduction in corrosion resistance, the higher carbon contents contemplated herein, e.g. greater than 0.06% are to be avoided when its affect on corrosion resistance cannot be tolerated.
• Example 23 illustrates that with 0.06% carbon the average yield strength was 99.5 (101.0 and 98.0) ksi.
• the strength of Ex. 23 can be increased by increasing the hardener content or by using a lower solution treating temperature, the Al heat treatment.
• processing of the material should be such as to provide a grain size in the age hardened material of about ASTM 5 or finer.
• V-notch Charpy impact strength 40 ft-lb (54.2 J)
• a maximum of about 11% molybdenum is preferred with about 16-18% chromium.
• the maximum molybdenum is proportionately reduced from 11% to 9%, and as chromium is increased from 22.0% to 24%, %Cr + %Mo ⁇ 31.
• Ex. 36 specimens had a V-notch Charpy impact strength of 34.5 ft-lb (46.8 J) as heat treated B1 and 23.5 ft-lb (31.9 J) exposed.
• Heats 910, 914 and 967 (%Cr + %Mo > 31) as B1 heat treated had impact strengths, respectively, of 66.5 ft-lb (90.2 J), 30.5 ft-lb (41.4 J) and 42 ft-lb (56.9 J), and in the exposed condition they had, respectively, 33.5 ft-lb (45.4 J), 17 ft-lb (23 J) and 24.5 ft-lb (33.2 J).
• the preferred composition of the present invention as set forth in Table II hereinabove is characterized by a minimum Charpy V-notch impact strength of 40 ft-lb (54.2 J).
• Molybdenum is about four times as effective as chromium (in weight percent) in improving pitting and crevice corrosion resistance when tested at 40 C in 6% ferric chloride (FeCl3) plus 1% hydrochloric acid (HCl).
• a preferred composition provides a higher level of resistance in FeCl3-HCl, that is, an average weight loss of no more than 1 mg/cm2 when tested with a standard crevice (ASTM G-48) at 40 C for 72 hours.
• ASTM G-48 standard crevice
• this composition there is preferably a minimum of 17% chromium and the percent chromium plus four times the percent molybdenum is not less than 52%.
• This preferred composition also consistently provides freedom from the onset of pitting below the temperature at which the test medium boils, 100 C, however, no more than 11% molybdenum should be used with 17% chromium. From the worst case data obtained with the crevice corrosion test specimens exposed at 55 C, it is apparent good pitting and crevice corrosion resistance is preferably maintained with a minimum of 59% nickel and by limiting the molybdenum content to no more than 10%.
• the molybdenum and chromium contents are also preferably balanced in relation to each other so that at 16% chromium the molybdenum is 8.5-10%.
• the minimum weight percent of molybdenum preferred is proportionately reduced to 7.0% but the maximum remains at 10%.
• the preferred weight percent molybdenum is 7-10% but not greater than [31 -(% Cr)].
• the chromium weight percent is increased from 18.0% to 20.5% the preferred minimum weight percent molybdenum is proportionately reduced from 8.5% to 8.0% and the preferred maximum weight percent is proportionately reduced to 9.4%.
• the minimum weight percent molybdenum is proportionately reduced from 8.0 to 7.7% and the maximum weight percent molybdenum is preferably reduced so that with a chromium content of 22.0%, the maximum molybdenum is 8.2%.
• a minimum of 0.8% to 0.9% titanium is required to attain the outstanding crevice corrosion resistance at 55° C.
• a minimum of 1.1% Ti and of 2.75% Nb is preferred.
• Room temperature sulfide stress cracking test specimens were prepared from strip which, after heat treatment had been heated at 550 F (287.8 C) for 30 days and air cooled to simulate deep well aging (well aged).
• Longitudinal U-bend test specimens 3-7/8 ⁇ 3/8 ⁇ 1/8 in (9.8 ⁇ 1 ⁇ .3 cm) from well aged strip were machined to a 120 grit surface finish and bent in accordance with ASTM G-30 (Fig. 5) to a 1 in (2.54 cm) inside diameter.
• a steel bolt was attached to each leg of each U-bend specimen using nuts and washers at each end.
• transverse specimens were also prepared and processed as described in connection with the U-bend test specimens except that the transverse specimens were about 1-3/8 in (3.5 cm) long and while exposed to the test solution each specimen was anchored at its opposite ends in engagement with iron sleeves and bent to a predetermined deflection by a force applied midway between its ends. After cleaning the specimens were exposed to the solution specified in NACE Test Method TM-01-77 (approved July 1, 1977). Each specimen was examined at 20 ⁇ magnification for cracks after intervals of 240, 504, 648, and 1000 hours. The time after which cracking was detected or "NC" for no cracks is indicated in Table VI and VIA under "NACE".
• the U-bend data is grouped as longitudinal specimens under "Long.” and the transverse specimens under “Trans.” in Tables VI and VIA.
• “longitudinal” and “transverse” serve to identify the axis of the specimen in relation to the direction in which the parent material, from which the specimen was prepared, was worked.
• the NACE TM-01-77 test data in Tables VI and VIA show that the present composition is resistant to sulfide stress-cracking at room temperature. For best results, the highest levels of molybdenum, niobium and titanium should be avoided. In this regard, 24% chromium is used with 7% molybdenum. As the amount of chromium is decreased from 23%, the maximum amount of molybdenum can be increased from 8%, with the ratio of the reduction in the chromium weight percent to the increase in the tolerable molybdenum weight percent being equal to about 2.
• a decrease in chromium content from about 22% to 20% results in an increase from 8.5% to about 9.5% in the maximum amount of molybdenum that is preferably used when optimum resistance to sulfide stress-cracking is desired. Also indicated is a reduction to 16% chromium when the molybdenum content is at about 11.5%.
• aluminum is held to its preferred range for this purpose, the amount of niobium and titanium should be carefully controlled. With 4.5% niobium present, titanium should not be greater than about 0.50%. As the weight percent niobium is reduced from 4.5% to about 3.0%, the maximum amount of titanium present can be proportionately increased to 2.0%.
• the maximum weight percent of niobium is 4.25% with which no more than 0.50% titanium is used.
• the maximum weight percent titanium is proportionately increased from 0.50% to 1.75%.
• the ratio of an increase in the weight percent of titanium to the accompanying decrease in niobium is 1.0 in both these instances.
• the present alloy and age hardened products made therefrom have good resistance to chloride stress-cracking as demonstrated by exposure to the severe environment of boiling 45% MgCl2. With nickel below 60%, the lower chromium and molybdenum contents provide better results.
• nickel With nickel below 60%, the lower chromium and molybdenum contents provide better results.
• nickel Preferably, with a hardener content of 4.0 a/o at least 60% nickel should be present. And as the hardener content is increased above 4.0 a/o or decreased, the minimum nickel to be present is correspondingly increased or decreased above or below 60% with the amount of the change in nickel content being three times the change in hardener content.
• the nickel content should be correspondingly increased or decreased by 1.5 a/o.
• copper also contributes to stress-cracking resistance in boiling MgCl2 and for this purpose it is desirable to include up to 3% copper to compensate for lower nickel than 60% or when the hardener content is greater than 4.0 a/o. Up to 2.0% copper is effectively used in compositions containing 60% nickel and above.
• the specimens were ground to 120 grit finish, bent to 1 in (2.54 cm) inside diameter and were stressed.
• Tables VII-IX the number of hours of exposure following which the specimen showed a stress crack or NC for no crack is given.
• the examples of the present invention and of the heats in Tables VII-IX were exposed to saturated (25%) sodium chloride, 0.5 g/l elemental sulfur and 1300-1440 psig partial pressure of hydrogen sulfide test medium under three different conditions. As indicated in Table VII, the examples and heats there listed were tested for 648h at 400 F (204.4 C) made up of two 160h periods and one period of 328h and if no cracks were observed the test was continued for 328h at 450 F.
• the autoclave test data demonstrate the outstanding resistance to corrosion and stress cracking under extremely severe conditions. Analysis of the data shows that in this composition molybdenum in weight percent is about four times as effective as chromium in improving resistance to stress cracking as measured in the autoclave test in the 400-450 F temperature range. For best resistance to cracking in the 400-450 F range, the percent chromium plus four times the percent molybdenum should not be less than 47%, that is, % Cr + 4(%Mo) ⁇ 47% Eq.
• the percent chromium plus four times the percent molybdenum should not be less than 49.5%, that is, % Cr + 4(%Mo) ⁇ 49.5% Eq. 4
• the percent chromium plus the percent molybdenum should not be less than 30%, that is, % Cr + % Mo ⁇ 30% Eq. 5
• the hardener content is preferably no greater than 4.5 a/o. For exposures at temperatures below 500 F a hardener content up to 5 a/o gives good resistance to stress-cracking.
• aluminum is preferably no more than 0.35% (no more than 0.77 a/o) to maximize strength. Copper also contributes to improved resistance to stress cracking in the autoclave test and for this purpose up to 3% can be used. As hardener content is increased above 4.0 a/o, copper preferably up to 2.0% is used effectively in improving resistance to stress cracking in the autoclave test.
• Example 46 was prepared using a double melting practice as a heat weighing about 10,000 pounds (4,545.5 kg) and forged to 4 in (10.16 cm) round bar which was heat treated.
• the composition of Example 46 is set forth in Table X.
• the composition of Heat A, representative of commercial Type 625 alloy (also about a 10,000 lb heat) is also given in Table X. Each contained less than 0.01% phosphorus and less than 0.01% sulfur. Though not indicated, Heat A also contained about 0.004% boron.
• the alloy of the present invention by its unusual combination of strength and corrosion resistance properties is well suited for a wide variety of uses in the chemical, petroleum and nuclear industries.
• the alloy lends itself to the production of a large variety of sizes and shapes.
• Intermediate products in any desired form such as billets, bars, strip and sheet as well as powder metallurgy products can be provided from which an even wider range of finished products can be made.
• the compositions set forth herein are advantageously used to provide parts for use in the exploration for, and exploitation of, petroleum products such as those intended for exposure under stress and/or under elevated temperatures.
• such parts include subsurface safety valves, hangers, valve and packer components, and other parts used above or below ground.

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• 1987
  • 1987-05-19 IL IL82587A patent/IL82587A0/xx unknown
  • 1987-05-26 CA CA000538031A patent/CA1336945C/en not_active Expired - Lifetime
  • 1987-05-26 NO NO872215A patent/NO872215L/no unknown
  • 1987-05-26 EP EP87107651A patent/EP0247577B1/en not_active Expired - Lifetime
  • 1987-05-26 DE DE8787107651T patent/DE3773261D1/de not_active Expired - Lifetime
  • 1987-05-27 JP JP62131042A patent/JP2729480B2/ja not_active Expired - Fee Related
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