[0001] The present invention relates to the use of nickel based alloys which have a combination
of high strength and corrosion resistance.
[0002] Alloys having high strength, for example 689.5 MN/m
2, or advantageously even 1034 MN/m
2, are required in some applications for sustaining stress in load-bearing service
in chemically adverse environments. Some plastic ductility is also needed for enduring
or permitting modest amounts of deformation without sudden fracture, for example to
safeguard against accidental bending, or to enable cold forming to be carried out.
Alloys having this desirable combination of properties are particularly useful for
use in petroleum production tubing for oil wells, in contact with chemically adverse
media such as chlorides, acids and such compounds as hydrogen sulphide. The alloys
must therefore exhibit resistance to corrosive pitting, stress corrosion cracking
and hydrogen embrittlement, as well as high strength.
[0003] The prior art includes numerous disclosures, for example in GB-A-1 385 755 and GB-A-1
514 241, of age-hardenable nickel-iron-chromium alloys that are said to be very resistant
to oxidation at elevated temperatures and to be suitable for fabricated parts such
as aeronautical turbines or turbine casings.
[0004] INCONEL alloy 718, as disclosed and claimed in US―A―3 046 108, is an age-hardenable
high strength alloy for service over a wide temperature range, from -250°C to 700°C,
and offers good resistance to a wide variety of corrosive environments. Since the
alloy also offers excellent stress rupture properties and fatigue strength, it has
been used in down-hole service in oil-wells. However, the alloy has insufficient resistance
to hydrogen embrittlement in the harsh environments found in "sour well" conditions
and, although having high as-cold-drawn strength, has low ductility.
[0005] The present invention is based on the discovery that certain alloy compositions,
developed from alloy 718, have an excellent combination of strength and ductility
in the wrought and age-hardened condition and also excellent resistance to hydrogen
embrittlement and chloride stress cracking.
[0006] According to the invention an alloy consisting, by weight, of from 15 to 22% chromium,
10 to 28% iron, 6 to 9% molybdenum, 2.5 to 5% niobium, 1 to 2% titanium, and up to
1% aluminium, the balance, apart from impurities and incidental elements, being nickel
in a proportion of from 45 to 55% of the alloy, is used in the form of wrought and
age-hardened articles and parts in highly corrosive conditions in sour oil or sour
gas wells or in sulphur dioxide gas scrubbers. Further elements which may be present
in small amounts include up to 0.1 % carbon, up to 0.35% silicon, up to 0.35% manganese,
up to 0.01% boron, and also residual small amounts of cerium, calcium, lanthanum,
mischmetal, neodymium and zirconium such as can remain from additions totalling up
to 0.2% of the furnace charge. Impurities present may include up to 0.5% copper, up
to 0.015% sulphur and up to 0.015% phosphorus.
[0007] Commercial sources of molybdenum and niobium are often associated with tungsten and
tantalum, which may be present at levels of about 0.1% tungsten and 0.1% tantalum.
The tungsten must be controlled at a low level to avoid the formation of undesired
phases such as Laves phase. Although tantalum may be substituted for niobium in equiatomic
percentages, its presence is not desirable because of its high atomic weight.
[0008] The particular combination of the proportions of chromium, iron, molybdenum, niobium,
titanium, aluminium and nickel gives rise to desirable properties of strength, ductility,
fabricability and durability in highly corrosive environments. To optimise these properties,
a preferred composition for use according to the invention contains from 18.5 to 20.5%
chromium, 13.5 to 18% iron, 6.5 to 7.5% molybdenum, 1.3 to 1.7% titanium, 0.05 to
0.5% aluminium, balance (apart from impurities and incidental elements) nickel.
[0009] Advantageously, the titanium and niobium contents of the alloy are closely controlled
such that
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0001)
Preferably the alloy contains 1.3% to 1.7% titanium and 3.6% to 4.4% Nb, and most
preferably 1.5% Ti and 4% Nb.
[0010] The alloy has good workability, both hot and cold, for production into wrought articles
such as cold rolled strip and extruded tubing. Appropriate process treatments may
be used to enhance the strengths of articles manufactured from the alloy. Such treatments
include cold working, age-hardening and combinations of the two. The alloy may be
annealed at a temperature of 871°C to 1149°C, and aged at 593°C to 760°C, or even
816°C. Direct aging treatments of heating the cold-worked alloy at 649°C to 760°C
for from 0.5 to 5 hours directly after cold working are particularly beneficial for
obtaining desirable combinations of high strength and ductility.
[0011] Alloys of the present invention, after appropriate thermomechanical processing exhibit
yield strength (0.2% offset) of in excess of 1034 MN/m
2, with an elongation of 8%, and preferred alloys have strengths of more than 1310
MN/m
2 and elongation of around 15%.
[0012] Some examples will now be given.
Example 1
[0013] Three alloys of the invention and a comparative alloy were prepared. The alloy compositions
are set out in Table I.
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0002)
[0014] Alloy 1 was prepared by vacuum induction melting and was cast to ingot form. Ingots
of alloy 1 were heated at 1121°C for 16 hours for homogenization and then forged flat
from 1121°C. Flats were hot rolled at 1121°C to reduce about 4 mm (0.16 gauge), annealed
at 1066°C for 1 hour and cold rolled to 2.5 mm (0.1 gauge) strip, which was again
annealed at 1066°C for 1 hour. Separate portions of the annealed 2.5 mm strip were
cold rolled different amounts to make 1.57, 1.8 and 2.11 mm sizes (0.062, 0.071 and
0.083 gauge respectively) and then each size (including the 2.5 mm size was again
annealed at 1066°C for 1 hour and cold rolled down to final gauge of about 1.27 mm
(0.05 gauge) resulting in cold work reduction of about 20%, 30%, 40% and 50%.
[0015] Hardenability, including work hardenability and age hardenability, of alloy 1 was
confirmed with hardness measurements, as shown in Table II, on specimens of the 1.27
mm (0.05 gauge) strip before and after heat treatments with temperatures and times
referred to in the Heat Treatment Schedule (Table III).
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0003)
[0016] Annealed hardnesses of 20% CR strip on Rockwell B scale after treatments of 954°C
for hour, 1038°C for 1 hour and 1149°C for hour were 97, 93 and 78. Corresponding
results with 40% CR strip were 23.5 Rc, 94 Rb and 78 Rb.
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0004)
[0017] Tensile specimens about 1.27 mm (0.05 gauge) strip of alloy 1 were evaluated for
mechanical properties at room temperature in preselected thermomechanically processed
conditions, including as cold-rolled conditions and cold-rolled plus heat-treated
conditions, with results set forth in the following Table IV. With cold-worked embodiments
of the alloy of the invention, "direct aging", whereby the alloy is heat treated at
age-hardening temperature directly (without other heat treatment intervening between
cold working and aging) following cold working, gave increased yield strengths of
1034 MN/m
2 and higher, with good retention of ductility; moreover, the 649°C direct age provided
benefits of increase in both strength and ductility exceeding 1103 MN/
M2 and 20% elongation.
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0005)
[0018] The endurance of ductility of alloy 1 in a variety of conditions when subjected to
hydrogen charging was tested by holding restrained 25.4 mm width cold-formed U-bend
specimens at stresses greater than 100% of yield stress while being cathodically charged
in a 5% sulphuric acid solution at 10 milliamps total current for 500-hour periods.
Successful survival throughout the 500-hour charging periods was shown with alloy
1 in twelve processing treatment conditions, as briefly stated below,
ACR 20%, 30%, 40% and 50%;
HT-1 following 20%, 30%, 40% and 50% CR;
20% CR plus HT-8; 20% CR plus HT-9;
20% CR plus HT-10; 20% CR plus HT-11.
[0019] In contrast, two restrained U-bend specimens of 20% cold rolled strip of alloy 1
in conditions resulting from long-time (in these instances, over 16 hours) direct
age treatments HT-5 and HT-6 failed after unsatisfactorily brief survivals of 5 hours
and 2 hours, respectively, when subjected to the same hydrogen charging conditions.
[0020] Good resistance to contact with acid chloride media at elevated temperature was confirmed
with evaluations of weight loss and visual appearance of specimens of alloy 1 of 10.2
cm x 7.62 cm in the 40% cold-rolled condition. Two specimens were immersed in aqueous
10% FeCl
3+0.5 HCI solutions at 66°C for 24 hours. The weight losses were satisfactorily low
values of 0.03 and 0.52 mg/cm
2. Visual inspection for appearances of pitting showed that only one pit occurred and
confirmed that the alloy metal provided good resistance to the acid media.
[0021] Capability of the alloy to provide resistance against stress-corrosion cracking was
shown by satisfactory survival of a cold formed, restrained, U-bed specimen of 50%
cold-rolled alloy 1 during a 720- hour exposure in boiling 42% MgC1
2.
Example 2
[0022] Alloy 2 and alloy 3 were air induction melted and centrifugally cast with protection
of an argon shroud in a metal mould having a 10.8 cm I.D. and 1300 rpm rotation speed
to produce cast centrifugally solidified tube shells of alloy 2 and 3. Cast dimensions
were 10.8 cm O.D. and 1.9 cm wall thickness. The shell was cleaned up to 10.2 cm O.D.
and 1.11 cm wall thickness.
[0023] A leader tube was welded onto the shell and processing proceeded as follows. The
tube shell was annealed at 1149°C, pickled and cold drawn (about 15.8%) to 9.525 cm
O.D. x 0.99 cm wall, re-annealed at 1149°C and pickled, then cold drawn to 8.89 cm
O.D. x 0.889 cm wall (also 15.8% reduction), re-annealed at 1149°C and pickled, then
tube reduced to 6.668 cm O.D. x 0.762 cm wall (about 36.7% reduction in area).
[0024] Mechanical properties were determined with sub-size round bar specimens taken longitudinally
from the tube wall and are set out in Table V.
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0006)
[0025] Good combinations of strength and ductility are achieved with cold-worked and direct-aged
articles of alloys 2 and 3, especially with one to two hour direct ages at 704°C to
760°C.
[0026] A transverse specimen taken from the extruded and 704°C direct aged product of alloy
3 was of ASTM grain size No. 3
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0007)
; optical microscopy of the specimen showed an absence of intergranular carbides and
indicated that the extruded, cold-reduced and heat-treated microstructure did not
contain any intragranular phases resolvable at 1000x.
Example 3
[0027] Alloys 2, 3 and E were melted, and centrifugally cast to tube shells and processed
to 6.67 cm O.D. tube with 0.762 cm wall thickness by the process described in Example
2. Table VI compares chloride stress corrosion cracking data for these alloys at 177°C
and 204°C. The alloy samples were prepared as stressed C-ring specimens and subjected
to a simulated deep sour gas well environment comprising a 25% solution of sodium
chloride plus 0.5% acetic acid and 1 g/I sulphur, the solution saturated with hydrogen
sulphide to an H
2S overpressure of 861 KN/m
2.
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0008)
[0028] The test conditions chosen for alloy E were those considered to be less prone to
hydrogen embrittlement than the cold worked+aged samples of alloys 2 and 3. Despite
testing at lower stress the comparative alloy failed earlier than alloys of the invention.
[0029] Hydrogen embrittlement tests were carried out on stressed c-ring specimens of the
alloy coupled to steel in solution of 5% sodium chloride+0.5% acetic acid, saturated
with hydrogen sulphide. Results are shown in Table VII.
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0009)
[0030] The room temperature tensile data corresponding to the above corrosion data is summarised
in Table VIII.
![](https://data.epo.org/publication-server/image?imagePath=1990/41/DOC/EPNWB2/EP82301929NWB2/imgb0010)
[0031] It will be observed that the commercial alloy E has very high as cold drawn strength
and low ductility, and this was why alloy E was tested in corrosion tests at a stress
less than 100% of RT yield strength.
[0032] It will be noted from the comparison between alloys 2, 3 of the present invention
and the commercial alloy E that the special correlation of composition of the present
invention gives rise to enhanced corrosion resistance in respect of chloride stress
corrosion cracking and hydrogen embrittlement. At the same time however the alloys
of the invention exhibit a desirable combination of strength and ductility.
[0033] Alloys of the present invention are useful for tubes, vessels, casings and supports,
needed for sustaining heavy loads and shocks in rough service while exposed to corrosive
media, and particularly for production tubing to tap deep natural reservoirs of hydrocarbon
fuels. In deep oil or gas well service, possibly in off-shore installations, the alloys
are beneficial for resistance to media such as hydrogen sulphide, carbon dioxide,
organic acids and concentrated brine solutions sometimes present with petroleum. Also,
the alloys provide good resistance to corrosion in sulphur dioxide gas scrubbers and
are useful for seals, ducting, fans and stack lines in such environments. Articles
of the alloy can provide useful strength at elevated temperatures up to 648°C and
possibly higher.
1. The use of an alloy consisting, by weight, of from 15 to 22% chromium, 10 to 28%
iron, 6 to 9% molybdenum, 2.5 to 5% niobium, 1 to 2% titanium, up to 1% aluminium,
up to 0.1 % carbon, up to 0.35% silicon, up to 0.35% manganese, up to 0.01 % boron,
with or without residual amounts not exceeding 0.2% in total of cerium, calcium, lanthanum,
mischmetal, magnesium, neodymium and zirconium, the balance, apart from impurities,
being nickel in a proportion of from 45 to 55% of the alloy, in highly corrosive conditions
in sour oil or sour gas wells or in sulphur dioxide as scrubbers in the form of wrought
and age-hardened articles and parts.
2. The use for the purpose of claim 1 of an alloy as defined therein in which the
amount of titanium and niobium are correlated according to the relationship:
3. The use for the purpose of claim 1 of an alloy as defined in claim 2 containing
1.3 to 1.7% titanium and 3.6 to 4.4% niobium.
4. The use for the purpose of claim 1 of an alloy as defined in any preceding claim
that contains from 18.5 to 20.5% chromium, 13.5 to 18% iron, 6.5 to 7.5% molybdenum,
1.3 to 1.7% titanium and 0.05 to 0.5% aluminium.
5. The use for the purpose of claim 1 of an alloy as defined in any preceding claim
that has been hot- or cold-worked and heat treated to develop a yield strength (0.2%
offset) in excess of 1034 MN/m2 and an elongation greater than 8%.
6. The use for the purpose of claim 1 of an alloy as defined in claim 5 that has been
heat treated by annealing at a temperature in the range 871 to 1149°C and aging at
a temperature in the range 593 to 816°C.
7. The use for the purpose of claim 1 of an alloy as defined in claim 5 that has been
cold-worked and aaed thereafter at a temoerature in the ranae 649 to 760°C for from
0.5 to 5 hours.
8. The use of an alloy as defined in any preceding claim for wrought and age-hardened
production tubing for deep sour oil and gas wells
1. Verwendung einer Legierung, welche in Gewichtsprozent aus 15 bis 22% Chrom, 10
bis 28% Eisen, 6 bis 9% Molybdän, 2,5 bis 5% Niob, 1 bis 2% Titan, bis zu 1 % Aluminium,
bis zu 0,1% Kohlenstoff, bis zu 0,35% Silizium, bis zu 0,35% Mangan, bis zu 0,01 %
Bor, und gegebenenfalls verbleibenden Restbeständen von insgesamt 0,2% Cer, Kalzium,
Lanthan, Mischmetall, Magnesium, Neodym und Zirkon besteht, wobei der Rest, abgesehen
von Verunreinigungen, Nickel mit einem Anteil von 45 bis 55% der Legierung ist, in
hochkorrosiven Bedingungen in sauren ÖI- oder sauren Gasquellen oder in Schwefeldioxidgaswaschern,
in Form von geschmiedeten und alterungsgehärteten Gegenständen und Teilen.
2. Verwendung einer Legierung nach Anspruch 1 für den dort definierten Zweck, wobei
zwischen den Anteilen an Titan und Niob die folgende Beziehung besteht:
3. Verwendung einer Legierung nach Anspruch 2 für den Zweck nach Anspruch 1, mit der
Maßgabe, daß sie 1,3 bis 1,7% Titan und 3,6 bis 4,4% Niob enthält.
4. Verwendung einer Legierung nach einem der vorhergehenden Ansprüche für den Zweck
nach Anspruch 1, mit der Maßgabe, daß sie 18,5 bis 20,5% Chrom, 13,5 bis 18% Eisen,
6,5 bis 7,5% Molybdän, 1,3 bis 1,7% Titan und 0,05 bis 0,5% Aluminium enthält.
5. Verwendung einer Legierung nach einem der vorhergehenden Ansprüche für den Zweck
nach Anspruch 1, mit der Maßgabe, daß sie kalt oder warm verformt und wärmebehandelt
wurde, um eine Streckgrenze (0,2% Verformung) oberhalb 1034 MN/m2 und eine Bruchdehnung von über 8% zu erzielen.
6. Verwendung einer Legierung nach Anspruch 5 für den Zweck nach Anspruch 1, mit der
Maßgabe, daß sie durch Glühen bei einer Temperatur im Bereich von 871 bis 1149°C und
Altern bei einer Temkperatur im Bereich von 593 bis 816°C wärmebehandelt wurde.
7. Verwendung einer Legierung nach Anspruch 5 für den Zweck nach Anspruch 1, mit der
Maßgabe, daß sie kalt verformt und dann bei einer Temperatur im Bereich von 649 bis
760°C während 0,5 bis 5 Stunden gealtert wurde.
8. Verwendung einer Legierung nach einem der vorhergehenden Ansprüche für geschmiedete
und alterungsgehärtete Förderrohre für tiefe saure Öl- und Gasquellen.
1. Utilisation d'un alliage comprenant, en poids, de 15 à 22% de chrome, de 10 à 28%
de fer, de 6 à 9% de molybdène, de 2,5 à 5% de niobium, de 1 à 2% de titane, jusqu'à
1 % d'aluminium, jusqu'à 0,1% de carbone, jusqu'à 0,35% de silicium, jusqu'à 0,35%
de manganèse, jusqu'à 0,01 % de bore, avec ou sans quantités résiduelles ne dépassant
pas 0,2% au total de cérium, calcium, lanthane, mischmetale, magnésium, néodymium
et zirconium, le complément étant, outre les impuretés, le nickel en une proportion
de 45 à 55% de l'alliage, sous la forme d'articles et de pièces travaillés et durcis
par vieillissement dans des conditions extrêmement corrosives, dans des puits de pétrole
acide ou de gaz acide ou dans des épurateurs à l'anhydride sulfureux.
2. Utilisation selon la revendication 1 d'un alliage tel que défini dans celle-ci,
selon laquelle les quantités de titane et de niobium sont en corrélation conformément
à la relation:
3. Utilisation selon la revendication 1 d'un alliage tel que défini dans la revendication
2, contenant 1,3 à 1,7% de titane et 3,6 à 4,4% de niobium.
4. Utilisation selon la revendication 1, d'un alliage tel que défini dans l'une quelconque
des revendications précédentes qui contient de 18,5 à 20,5% de chrome, de 13,5 à 18%
de fer, de 6,5 à 7,5% de molybdène, de 1,3 à 1,7% de titane et de 0,05 à 0,5% d'aluminium.
5. Utilisation selon la revendication 1, d'un alliage tel que défini dans l'une quelconque
des revendications précédentes, qui a été travaillé à chaud ou écroui et traité par
la chaleur pour obtenir une limite élastique (0,2% de formation de plus de 1034 MN/m2 et un allongement de plus de 8%.
6. Utilisation selon la revendication 1, d'un alliage tel que défini dans la revendication
5 qui a été thermiquement traité par recuit à une température entre 871 et 1149°C
et par vieillissement à une température de 593 à 816°C.
7. Utilisation selon la revendication 1, d'un alliage tel que défini dans la revendication
5 qui a été écroui et ensuite vieilli à une température de 649 à 760°C pendant 0,5
à 5 heures.
8. Utilisation d'un alliage selon l'une quelconque des revendications précédentes
pour la production par forgeage et durcissement par vieillissement de tubes pour les
puits profonds et acides de pétrole et du gaz.