CA1051858A

CA1051858A - Turbine oil compositions

Info

Publication number: CA1051858A
Application number: CA225,813A
Authority: CA
Inventors: Albert M. Durr (Jr.); Robert A. Krenowicz
Original assignee: Continental Oil Co
Current assignee: ConocoPhillips Co
Priority date: 1974-10-07
Filing date: 1975-04-24
Publication date: 1979-04-03
Also published as: US3926823A

Abstract

Turbine Oil Compositions Abstract of Disclosure Lubricating oil compositions, particularly suit-able for use in steam turbines or gas turbines, are dis-closed. The turbine oil compositions comprise a major amount of a mineral or synthetic hydrocarbon base oil and a minor, but effective, amount of a combination of co-polymer of N-vinyl-2-pyrrolidone and an .alpha.-olefin, triphenyl phosphite or a trialkyl-substituted phenyl phosphite, and benzotriazole or alkyl-substituted benzotriazole. The turbine oil compositions may contain, additionally, a small, but effective, amount of tricresyl phosphate or a partial ester of an alkyl or alkenyl succinic anhydride.

Description

10~1858 Background Field of the Invention The invention is in the field of lubricating oils which are particularly suitable for use in gas turbine engines, including aircraft and automotive, and stationary steam turbine engines.
General Background It is generally recognized that the operating conditions of gas turbine engines expose the lubricant to extreme conditions. In order to be satisfactory, the lubricant must be resistant to oxidation and corrosion at high temperatures. Moreover, the lubricant must be resistant to deposit-formation at high temperatures.
Normally, gas turbine and steam turbine uni*s require different lubricant types, the former synthetic ester-based oils and the latter petroleum oils.
We have found a particular combination of lubricant additives which work in mineral lubricating oils or synthetic hydrocarbon lubricating oils. Furthermore, the lubricant compositions of our invention work in either steam turbines or gas turbines. They are particularly suitable for use in gas turbines. Because of this, our lubricant compositions provide an important advance in the art.
Prior Art Each of the lubricant additives used in our lubricant compositions is known to be useful in lubricating oils. However, we have found that certain synergistic relationships are present in the additives which provide improved results in the combinations used. Moreover, we have found that the lubricant compositions of our invention provide superior performance, particularly when compared to commercially available products.
Brief Summary of the Invention Broadly stated, the present invention is directed to a lubricating oil composition which comprises a major amount of a mineral or synthetic hydrocarbon base oil and an effective amount of a combination of the following materials: (a) copolymer of N-vinyl-2-pyrrolidone and an a-olefin; (b) triphenyl phosphite or a trialkyl-æubstituted phenyl phosphite; (c) benzotriazole or alkyl-sub~tituted benzotriazole.
In further aspects, the lubricating oil com-position contains, additionally, a minor but effective amount of tricresyl phosphate or a partial ester of an alkyl or alkenyl succinic anhydride. The lubricating oil compositions of our invention have properties which render them particularly useful in steam or gas turbines.
Materials Used The base oil can be a conventionally refined mineral lubricating oil or a synthetic hydrocarbon lubri-cating oil. The mineral lubricating oils are well known to those skilled in the art. Both light viscosity (e.g., pale oils) and heavy viscosity (e.g., bright stock) oils can be used. A complet~ description of mineral lubricat-ing oils is provided by Nelson's "Petroleum Refinery Engineering" (McGraw-Hill, New York, 1958).
Suitable synthetic hydrocarbon lubricating oils include di-n-long-chain alkaryls, as described hereinafter, linear mono-olefin oligomers, and a composition consisti~g 105~8S8 essentially of di-n-long-chain alkaryls and tr:ialkyl-substituted tetrahydronaphthalenes.
Linear mono-olefin oligomers, which are suitable as lubricating oils, are described in several U.S. patents, e.g., U.S. 3,382,291, U.S. 3,149,178, and U.S. 3,808,134.
A particularly suitable linear mono-olefin oligomer composition is prepared from ~-olefins containing 6 to 16 carbon atoms, more suitably 8 to 12 carbon atoms, and preferably 10 carbon atoms. The linear mono-olefin oligomer composition contains at least 50 weight percent, more usually at least 60 weight percent, of materials containing 24 to 60 carbon atoms.
The term di-n-long-chain alkaryl refers to materials represented by the formula R ~ A
. Rl~ Al wherein R and Rl are alkyl groups containing from 6 to 18 carbon atoms, more suitably from about 9 to about 15 carbon atoms, and preferably from about 10 to 14 carbon atoms, with the sum of R and Rl being from about 20 to about 28 carbon atoms and wherein A and A1 are hydrogen or a Cl or C2 alkyl group, but preferably are hy~rogen.
Thus, the preferred di-n-long-chain alkaryl is a di-n-alkylbenzene wherein the alkyl group contains from about 10 to about 14 carbon atoms.
The alkyl groups are substantially straight-chain (thus the term n-alkaryls) wherein, preferably, at least 95 percent of the alkyl substituents are bonded to the benzene nucleus through a secondary carbon atom of the respective alkyl groups. While we prefer the term 105~858 "n-alkaryls," other terms such as linear alkaryls or straight-chain alkaryls are equally de~criptive.
A particularly suitable di-n-long-chain alkaryl-trialkyl-substituted tetrahydronaphthalene composition typically contains the following Component: Percent by Weight Di-n-long-chain alkaryls 61-92 Trialkyl-substituted tetrahydro-naphthalenes 5-30 Miscellaneous alkyl aromatics:
Less than 15 Preferably less than 10 . - The composition is also characterized as having the following properties: .
Viscosity index .80-116 Pour point, F -40 to -80 Molecular weight range 350-526 Preferably . 375-480 The di-n-long-chain al~aryls meet the descrip-tion pro~ided in the foregoing.
The trialkyl-substituted tetrahydronaphthalenes can be represented by the formula H R

wherein Rl and R2 contain from 1 to about 13 carbon atom~
each, with the sum of Rl and R2 being from about 6 to about 14 and R3 and R4 contain from 1 to about 16 carbon atoms with the sum of R3 and R4 being from about 9 to about 17. The alkyl groups, Rl, R2, R3, and R4, are 105~858 traight-chain.
The trialkyl-substituted tetrahydronaphthalenes have the same boiling range as the di-n-alkylbenzenes. In addition, they have approximately the same molecular weight.
The vinyl-pyrrolidone ~ a-olefin copolymers which are suitable for use in our invention are characterized as being the reaction product of N-vinyl-2-pyrrolidone and 0.5 to 12 moles of an a-olefin containing 8 to 30 carbon atoms, preferably 18 to 22 carbon atoms. The materials have a molecular weight of about

2,000 to about 20,000, preferably 7,000 to 12,000. Details on the preparation and properties of the copolymers are provided in U.S. Patent Nos. 3,296,134 and 3,423,381. The preferred copolymer is the reaction product of 1 mole of N-vinyl-2-pyrrolidone and 1 mole of a C-20 a-olefin. An example of a commercially available preferred copolymer is "Ganex" V-220*, which is available from GAF Corporation, 140 West 51st Street, New York, New York. This material has the following physical properties:
Physical Form, 25C waxy solid Relative Viscosity (1) 1.007 20 Density (2) .95 Average Molecular Weight (3) 8,600 Softening Point 30C
Melting Range (4) 32-36C
(1) 0.1 g/100 m~ toluene used as solvent 25 (2) gm/cc at 23C

*Trade Mark ~051858

(3) Molecular weight number average determined by High Speed Osmometer in toluene at 25C

(4) Determined on the Mannheim Block Suitable phosphites include triphenyl phosphite and trialkyl-substituted phenyl phosphites, wherein the phenyl moiety has 1 or 2 alkyl substituents, each of which contains 1 to 12 carbon atoms. Examples of the latter-named phosphites which are suitable include triphenyl phosphite, tritolyl phosphite, tricresyl phosphite, tri-hexylphenyl phosphite, tributylphenyl phosphite, and tri-- (mixed mono- and dinonylphenyl) phosphite. Tri-(mixed mono- and dinonylphenyl~ phosphite is particularly suitable.
Suitable triazoles include benzotriazole and alkyl-substituted benzotriazoles having 1 or 2 alkyl groups containing 1 to 10 carbon atoms, preferably 1 carbon atom. Benzotriazole is available under the trade name Cobratec 99 from Sherwin-Williams Chemical. A
particularly suitable alkyl-substituted benzotriazole is tolyltriazole, which is available under the trade name Cobratec TT-100 from Sherwin-Williams Chemical.
Suitable partial esters of an alkyl or alkenyl-succinic anhydride are the products obtained by the reaction of one molar equivalent of a polyhydric alcohol with two molar equivalents of the anhydr.ide. Structurally, these materials are represented by the formula f (O)OH f (OJOH
R-C-H H-C-R
R'-C-H H-C-R' C-(O)OR" (O)C n wherein of the radicals R and R', one is hydrogen and the _her is an alkyl or alkenyl group containin~ from 8 to 15 carbon atoms and R" is the residue of the polyhydric alcohol which generi-cally may contain oxygen, sulfur, or nitrogen in the chain as well as ester substituents, and preferably contains from 3 to 6 carbon atoms. The integer n represents a number from 1 to 4.
In so doing, n includes, in the residue, derivatives of diols, triols, and other polyhydroxy compounds.
A preferred partial ester for use in our invention is represented by the formula 1l 1l f-OH C-OH
R-f-H H-f-R
R'-f-H H-C-R' C -OR" O-C

wherein of R and R', one represents hydrogen and the other a branched chain dodecenyl group and R" i5 an alkylene group of 3 to 6 carbon atoms.
A commercially available partial ester which can be used in our invention is "Hitec" E-536*, available from Edwin Cooper Company, St. Louis, Missouri, The preparation of and additional information concerning these partial esters are provided by U~S. Patent No. 3,117,091.
~ricresyl phosphate is a well known chemical, ~eing represented by the formula (C6H4Me) PO4. Any high quality, commercially available tricresyl phosphate can be used.

*Trade Mark 105185~

Amounts of Materials Ust~d The amounts of the various materials used in the turbine oil compositions of our invention are shown below, in both suitable and preferred ranges.
AMOUNT
(WEIG~IT PERCENT) Material Copolymer of N-vinyl-2-pyrrolidone and ~-olefin 0.1-1.0 0.2-0.6 Phosphite 0.05-1.5 0.1-1.0 Triazole 0.002-0.1 0.01-0.04 Tricresyl Phosphate* 1-15 3-8 Partial Ester of Alkyl or Alkenyl Succinic Anhydride*0.01-0.15 0.04-0.08 *Each material i8 used in only one aspect of our invention.
As is implied, the balance of the composition is the base lubricating oil, it being understood that other conventional lubricant additives can be included, if desired.
Use of Other Materials in Our Invention In describing our invention, we have shown only the essential materials which are used therein. It is to be understood that other conventional lubricating oil additives can be used in the composition, if desired.
Examples of other such materials include, but are not limited to, antifoam agents, pour point depressants, viscosity and viscosity index improvers, and dyes.

In order to disclose the nature of the present invention still more clearly, the following examples, both illustrative and comparative, will be given. It is to be understood that the~invention is not to be limited to the .
_g_ ' , specific conditions or details set forth in these examples except insofar as such limitations are ~pecifie~ in the appended claims.
Test Methods The test methods used to evaluate the various compositions, both illustrative and comparative, were the following:
(1) Federal Test Method 5308.6 of Standard 791 b.
(2) Rotary Bomb Oxidation Test ASTM-D-2272 (3) ASTM-D-943 Oxidation Test (4) Heat Stability Test Inasmuch as the first three tests are standard, published tests, it is not believed necessary that they be described in detail herein.
Since the data from the Federal Test Method 5308.6 was used more consistently, this test will be described in some detail. Usually in this test, the only values obtained are oil viscosity change, acid number change, and the weight loss of the metal test specimens.
In addition to these values, we obtained the amount of solids deposited or formed during the test. This value is expressed as milligrams of solids per 100 grams of oil sample. In our opinion, this value is a good indicator of the tendency to cause residues in operation of a turbine, 2~ which, in turn, can impair performance.
A description of Federal Test Method $303.6 follows:
A 100-ml test sample, on which viscosity in centistokes at 100F and neutralization number have been measured, is subjected to a temperature of 347F for a 105~858 period of 72 hours in the presence of 5 liters of air per hour and polished, cleaned, weighed copper, silver, steel, magnesium, and aluminum coupons held rigidly in a specific arrangement.
The test apparatus consists of a test tube (to contain the test sample) which is fitted with vertical water-cooled condenser and air-delivery tube extending to within 1/8" of the bottom of the test tube. The tube is submerged its entire length except for the joint and condenser in a constant temperature bath at test tempera-ture.
At the end of the test period specified, these observations and measurements are made and recorded:
(a) Condenser deposits (liquid or solid) appearance.
(b) Viscosity change, % viscosity change from original at 100F, centistokes and neutralization number change from original are determined on filtered oil.
(c) Deposits or solids contalned in oil sample, in test cell, and on coupons are collected on a filter paper and their weight determined to the nearest 0.1 mg.
(d) Metal coupons are washed and weighed to establish loss or gain to the nearest 0.1 mg.
(e) Deposits adhering to test cell after scraping and washing are rated for appearance in vapor, oil-air interface, and bottom of test cell.
A heat stability test was used to measure Cu-Pb bearing corrosion. Briefly, this test can be described as follows:

1~51858 A copper-lead faced steel coupon, 1 x 3", is cleaned in accordance with the established procedure and we~ghed. Two hundred milliliters of test sample is placed in a 400 ml tall form beaker. The test coupon is placed in the beaker, which is then covered with a watch glass, and placed in a 250F oven for 96 hours. At the end of the specified period of time, the beaker is removed and allowed to cool. The coupon is removed, washed with hexane, dried, and weighed.
In the following example~ the materials used were as follows. Base oils "X" and "Y" were mineral lubricating oils. Base oil "X" was a bright stock having a viscosity of 155 SSU at 210F, while base oiL ~yl~ was a pale oil having a viscosity of 170 SSU at 100F. Base oil "Z" was a synthetic hydrocarbon lubricant consisting essentially of di-n-alkylbenzenes and trialkyl-substituted tetrahydronaphthalenes. The alkyl groups of the di-n-alkylbenzenes were predominantly C13. This base oil contained about 75 percent di-n-alkylbenzenes and about 20 20 percent trialkyl-substituted tetrahydronaphthalenes.
It had the following physical properties:
Viscosity, centistokes 210F 5.06 100F 29.12 -40F 9,169 Viscosity Index 111 Pour Point, F -70 The materials, other than base oils, used in the composition were as follows:
Copc,lymer "Ganex" V-220 Triazole "Cobratec" 99~
Phosphite Uniroyal Chemicals "Polygard" -a tri (mixed mono- and dinonyl-phenol phosphite Partial Ester "Hitec" E-536 ~
Antifoam agent A commercially available silicone The amounts of the various mat.erials used in the compositions tested, stated in weight percent, were as follows:
COMPOSITION NO
Material A B C D E F
Copolymer 0.80 - O.40 0.40 0.40 0.40 Triazole 0.02 0.02 0.02 0.02 0.02 0.02 Phosphite - 1.50 0.75 0.75 0.75 0.75 Antifoam 0.10 0.10 0.10 0.10 0.10 0.10 Tricresyl Phosphate 5.00 5.00 5.00 Partial Ester 0.06 Base Oil "X" 6.006.00 6.00 6.00 Base Oil "Y" 93.73 93.67 Base Oil "Z" 93.0892.3892.7387.73 The results of the tests conducted on the various compositions are shown in the table which follows.

rr J~ mul~

10518~8 X ~ ~~ O L) ~I N ~ r l J ~ O
O ~
.. . ~D . .... O ~ O O O I ~ O ~1 I` NO N 1~ + + + + + ~ +
1~

o ~ ~ a~ r o ~D . O ~1 0 0 0 N O ~1 ~r 1` ~1 o 1--1`1 + + + + +
rL~

o ~ O ~a ~ ~1 ~ o _I a .o 1` 1` . . a.) ~ . . ~D
. . O . O O O O O ~ CO O
. ~ O U~ ~I O ~ ~ I I + ~ I I
z al ~ ~
o .,, O ~ ~n o .o co ~ . ~
. . . .~. . . _10000 ~ 00 0 ~r~ o~r~r l + + +
CJ C~

1~ In CO 11'~ 0 ~ ~r N ~ O ~ O ~ ~ _I U') ~ . O O
1o ~P ~ + I + + +
ml ~ +

~D O ~ . ~ ~ .. .
~ . . .,~ o . . ooooo :~: Z
~ r co co l + + + +
A I ~ ~ -~

o O o 0 S~rl ,a ~ p J~ 6q OD O ~ S: ~ O tn o :~
O I I ~ ~1 ~ U
u~o O ~ ~O ~ t~ ~ o ~
I tnJ O ~1 0 U O O O q~ 1 U O ~
z z 0 ~ ~ m ~ ~
0 1 0 ~~ o ~ o ~ la ~ 1 ~ Q ~ U) 0~ æ ~

~ ~ ~ dP Z Z C~
- l A brief study of the results in the preceding table indicates the following. Composition C (which corresponds to the broad aspect of our invention~ as compared to Compositions A and B shows (a) better viscosity than A, (b) better neutralization number than A, (c) better corrosion than B, and (d) better Cu-Pb bearings than B.
Composition D which corresponds to Composition C but contains additionally tricresyl phosphate, shows better overall results than Composition C except for deposits.
Composition E is similar to Composition D except that pale oil has been substituted for the synthetic hydrocarbon oil. As compared to CoMposition D, Composition E shows better viscosity results but higher deposits. Composition F
corresponds to Composition E but contains additionally a partial ester. As compared to Composition E, Composition F shows better neutralization number, better RBOT, better Cu-Pb bearings, but higher deposits.
For purposes of comparison, we provide below the results of tests on a commercial high temperature oil and a typical steam turbine oil. Both used a mineral oil as the base oil.

Commercial Typical High Steam Temperature Turbine Oil _ Oil Results: FTM 5308.6-72 Hr.
Original Viscosity, CS @ 100F 31.80 34.87 Final Viscosity, CS @ 100F 33.66 47.95 Viscosity Change +1.86 13.08 ~ Viscosity Change +5.85 +37.51 Original Neut. No. .15 .06 Final Neut. No. 1.92 +5.41 Neut. No. Increase 1.77 +5.35 Corrosion, mgs/coupons Silver +1.9 +2.0 Copper +0.4 +0-3 Steel +1.2 ~1.0 Magnesium +1.7 +2.1 Aluminum +1.9 +1.7 Deposits (Filtered) Mg/100 gms. 2,140 1,231 RB~T @ 150C-Minutes 40 405 Inspection of the test re~ults for the two commercial oils shows that over all they were inferior to all of the compositions tested, including A and B. While the commercial high temperature oil gave a good RBOT
result, it gave extremely high deposits.
Thus, having described the invention in detail, it will be understood by those skilled in the art that-certain variations and modifications may be made without departing from the spirit and scope of the invention as defined herein and in the appended claims.
We claim:

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A turbine oil composition comprising a major amount of a mineral or synthetic hydrocarbon base lubricating oil and the following combination of materials in the amounts specified, as weight percent of total composition:
(a) about 0.1 to about 1.0 - copolymer of 1 mole N-vinyl-2-pyrrolidone and 0.5 to 12 moles of an .alpha.-olefin containing 8 to 30 carbon atoms; said co-polymer having a molecular weight from about 2000 to about 20,000.
(b) about 0.05 to about 1.5 - triphenyl phosphite or trialkyl-substituted phenyl phosphite, wherein the phenyl moiety has 1 or 2 alkyl groups, each of which contains 1 to 12 carbon atoms; and (c) about 0.002 to about 0.1 - benzotriazole or alkyl-substituted benzotriazole having 1 or 2 alkyl groups containing 1 to 10 carbon atoms.

2. The turbine oil composition of Claim 1 wherein the base lubricating oil is a mineral oil.

3. The turbine oil composition of Claim 2 wherein it contains from about 1 to about 15 weight percent tricresyl phosphate.

4. The turbine oil composition of Claim 2 wherein it contains from about 0.01 to about 0.15 weight percent of a partial ester of an alkyl or alkenyl succinic anhydride, which is represented by the formula:

wherein of the radicals R and R', one is hydrogen and the other is an alkyl or alkenyl group containing from 8 to 15 carbon atoms, and R" is a residue of a polydric alcohol containing from 3 to 6 carbon atoms and n is an integer of at least one but less than five.

5. The turbine oil composition of Claim 1 wherein the base lubricating oil is a synthetic hydro-carbon lubricant which is selected from the group con-sisting of di-n-long-chain alkaryls, linear mono-olefin oligomers, and a composition consisting essentially of di-n-long-chain alkaryls and trialkyl-substituted tetrahydro-naphthalenes, wherein (a) the term di-n-long-chain alkaryls refers to materials represented by the formula wherein R and R1 are substantially straight-chain alkyl groups containing from 6 to 18 carbon atoms, with the sum of R and R1 being from about 20 to about 28 and wherein A
and A1 are hydrogen or a C1 or C2 alkyl group, (b) the term linear mono-olefin oligomer refers to materials prepared from .alpha.-olefins containing 6 to 16 carbon atoms and which contain at least 50 weight percent of materials containing 24 to 60 carbon atoms, and (c) the term trialkyl-substituted tetrahydronaph-thalene refers to materials represented by the formula wherein R1 and R2 are straight-chain alkyl groups con-taining from 1 to about 13 carbon atoms each, with the sum of R1 and R2 being from about 6 to about 14, and wherein R3 and R4 are straight-chain alkyl groups containing from about 1 to about 16 carbon atoms, with the sum of R3 and R4 being from about 9 to about 17.

6. The turbine oil composition of Claim 5 wherein it contains from about 1 to about 15 weight percent tricresyl phosphate.

7. The turbine oil composition of Claim 6 wherein (a) the amount of said copolymer is about 0.2 to about 0.6 weight percent, (b) the amount of said phosphite is about 0.5 to about 1.0 weight percent, and (c) the amount of said triazole is about 0.01 to about 0.04 weight percent.

8. The turbine oil composition of Claim 5 wherein it contains from about 0.01 to about 0.15 weight percent of a partial ester of an alkyl or alkenyl succinic anhydride, which is represented by the formula:

wherein of the radicals R and R', one is hydrogen and the other is an alkyl or alkenyl group containing from 8 to 15 carbon atoms, R" is a residue of a polydric alcohol containing from 3 to 6 carbon atoms, and n is an integer of at least one but less than five.

9. A turbine oil composition comprising a major amount of a mineral or synthetic hydrocarbon base lubricating oil and the following combination of materials in the amounts specified, as weight percent of total composition:
(a) about 0.2 to about 0.6 - copolymer of about 1 mole of N-vinyl-2-pyrrolidone and about 1 mole of a C-20 .alpha.-olefin; said co-polymer having a molecular weight from about 2000 to about 20,000.
(b) about 0.1 to about 1.0 - triphenyl phosphite or tri (mixed mono- and dinonylphenyl) phosphite; and (c) about 0.01 to about 0.04 - benzotriazole or tolyltriazole.

10. The turbine oil composition of Claim 9 wherein the base lubricating oil is a mineral oil.

11. The turbine oil composition of Claim 10 wherein it con-tains from about 3 to about 8 weight percent tricresyl phosphate.

12. The turbine oil composition of Claim 11 wherein it con-tains from about 0.04 to about o.o8 weight percent of a partial ester of succinic anhydride which is represented by the formula:
wherein of R and R' one represents hydrogen and the other a branched chain dodecenyl group and R" is an alkylene group of 3 to 6 carbon atoms.

13. The turbine oil composition of Claim 9 wherein the base lubricating oil is a synthetic hydrocarbon lubricant which is selected from the group consisting of di-n-long-chain alkaryls, linear mono-olefin oligomers, and a composition consisting essentially of di-n-long-chain alkaryls and trialkyl-substituted tetrahydronaph-thalenes, wherein (a) the term di-n-long-chain alkaryls refers to materials represented by the formula wherein R and R1 are substantially straight-chain alkyl groups containing from 6 to 18 carbon atoms, with the sum of R and R1 being from about 20 to about 28 and wherein A and A1 are hydrogen or a C1 or C2 alkyl group, (b) the term linear mono-olefin oligomer refers to materials prepared from .alpha.-olefins containing 6 to 16 carbon atoms and which contain at least 50 weight percent of materials containing 24 to 60 carbon atomæ, and (c) the term trialkyl-substituted tetrahydronaph-thalenes refers to materials represented by the formula wherein R1 and R2 are straight-chain alkyl groups con-taining from 1 to about 13 carbon atoms each, with the sum of R1 and R2 being from about 6 to about 14, and wherein R3 and R4 are straight-chain alkyl gxoups con-taining from about 1 to about 16 carbon atoms, with the sum of R3 and R4 being from about 9 to about 17.

14. The turbine oil composition of Claim 13 wherein it contains from about 3 to about 8 weight percent tricresyl phosphate.

15. The turbine oil composition of Claim 14 wherein the base lubricating oil is a composition consist-ing essentially of di-n-long-chain alkaryls, which are present in an amount of 61 to 92 weight percent, and trialkyl-substituted tetrahydronaphthalenes which are present in an amount of 5 to 30 weight percent.

16. The turbine oil composition of Claim 13 wherein it contains from about 0.04 to about 0.08 weight percent of a partial ester of succinic anhydride which is represented by the formula wherein of R and R' one represents hydrogen and the other a branded chain dodecenyl group and R" is an alkylene group of 3 to 6 carbon atoms.

17. The turbine oil composition of Claim 16 wherein the base lubricating oil is a composition consisting essentially of di-n-long-chain alkaryls, which are present in an amount of 61 to 92 weight percent, and trialkyl-substituted tetrahydronaphthalenes which are present in an amount of 5 to 30 weight percent.