An experimental gas turbine engine was destroyed as a result of the combustion of its titanium components. It was concluded that a severe surge may have caused interference between rotating and stationary compressor that either directly or indirectly ignited the titanium components. Several engine oil samples (before and after the failure) were analyzed with a Ferrograph, a plasma, an atomic absorption, and an emission spectrometer to see if this information would aid in the engine failure diagnosis. The analyses indicated that a lubrication system failure was not a causative factor in the engine failure. Neither an abnormal wear mechanism nor a high level of wear debris was detected in the engine oil sample taken just prior to the test in which the failure occurred. However, low concentrations (0.2 to 0.5 ppm) of titanium were evident in this sample and samples taken earlier. After the failure, higher titanium concentrations ( 2 ppm) were detected in oil samples taken from different engine locations. Ferrographic analysis indicated that most of the titanium was contained in spherical metallic debris after the failure. The oil analyses eliminated a lubrication system bearing or shaft seal failure as the cause of the engine failure

Jones, W. R., Jr.

English

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https://ntrs.nasa.gov/search.jsp?R=19830004163 2020-03-21T06:42:26+00:00Z
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NASA T	 Maaowrandw 82M
(NASA - 114-82 9 50) FEFFCGBAPHIC AND
	 N83- 12433
SFECIECMETER OIL ANALYSIS FFCE A FAILEL GAS
4UQBINE ENGINE ( NASA)	 15 F HC A02/MF A01	 .`
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	 Unclas	 ^' 4
	
7	 J 1 1 14
Ferrograpl a and Spvc4om4ler
Analysis From a Failed 	 y
.Gas Turbine
	
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Witham R.ones, Jr.
	
X C,
Lewis Research Center
Cleveland, Ohio l
Prepared for the
International Conference on Advances in Ferrography
sponsored by the University College of Swansea
Swansea, United Kingdom, September 22 -24, 1982
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FERROGRAPHIC AND SPECTROMETER OIL ANALYSIS
FROM A FAILED GAS TURBINE ENGINE
by William R. Jones, Jr.
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio
SUMMARY
An experimental gas turbine engine was destroyed a, a result of the com-
bustion of its Ti components. It was concluded that a severe surge may have
caused interference between rotating and stationary compressor parts that
either directly or indirectly ignited the Ti components. Several engine oil
samples (before and after the failure) were analyzed with a Ferrograph, a plas-
ma, an atomic absorption and an emission spectrometer to see if this informa-
tioa would aid in the engine failure diagnosis. The analyses indicated that a
lubrication system failure was not a causative factor in the engine failure.
Neither an abnormal wear mechanis.n nor a high level of wear debris was detect-
ed in the engine oil sample taken just prior to the test in which the failure
occurred. However, low concentrations (0.2 to 0.5 ppm) of Ti were evident in
this sample and samples taken earlier. After the failure, higher Ti concentra-
tions (>Z ppm) were detected in oil samples taken from different engine loca-
tions. FerrQgraphic analysis indicated that most cf the Ti was contained in
spherical metallic debris after the failure. Attempts to pinpoint the failure
initiation site were inconclusive, but the oil analyses did eliminate a lubri-
cation system bearing or shaft seal failure as the cause of the engine failure.
INTRODUCTION
In 1976, an expe, • imental gas turbine engire was being tested as part of
the Full Scale Engine Research Program at the Lewis Research Center. While
exploring a region of fan flutter, the engine appeared to encounter a stall,
caught on fire and was destroyed.
It was concluded that the severe surge may have caused interference be-
tween rotating and stationary compressor parts that either ignited Ti by fric-
tion or caused structural failure with the resulting debris igniting the Ti.
The goals of engine oil analysis are to diagnose the condition of the oil
wetted components (such as bearings and shaft seals) of an engine and to give
early warnings oI any future problems. A variety of different tecnniques
(ref. 1) are being employed to effect these goals. these include spectromet-
ric oil analysis (SOAP) using emission, atomic absorption, and plasma spectro-
meters. These devices measure the concentration of various elemen,s in the oil
(both dissolved and in particulate form) but are not able to distinguish among
the various wear modes that can occur.
Another instrument, the Ferrograph, has been developed which magnetically
separates wear debris from used lubricants onto a glass slide to yield a Ferro-
gram (refs. 2 to 4). Particles range from approximately 0.02 to a few micro-
meters and are arranged according to size on the slide. Individual particles
may be observed with a unique bichromatic microscope (the Ferroscope) or with
a conventional scanning electron microscope.
The objective of this investigation was to determine if analyses of the
engine lubricant using the Ferrograph and various spectrometers would provide
any insight into the diagnosis of the above-mentioned engine failure.
Mr. Vernon Westcott of Foxboro Analytical, Burlington, Massachusetts,
obtained the electron micrographs from the National Engineering Laboratory of
Scotland, East Kilbride, Glasgow.
APPARATUS AND PROCEDURE
Ferrograph
The Ferrograph (refs. 2 to 4) is an instrument used to magnetically pre-
cipitate wear particles from a used oil onto a specially prepared glass slide.
A mixture of 3 ml of used oil and 1 ml of solvent is prepared. This mixture
is then slowly pumped over the slide. A solvent wash and fixing cycle follows
which removes residual oil and permanently attaches the particles to the slide.
The resulting slide with its associated particles is called a Ferrogram.
Energy Dispersive X-ray Analysis
The elemental composition of the different types of wear debris was deter- 	 t
mined using energy dispersive X-ray analysis (EDX). In order to prevent charg-
ing in the scanning electron microscope, the Ferrogram slides were coated with
either a thin layer (2x10- $ m, 200 A) of C or Au.
Spectrometers
Basically, there are two methuus °nr spectrometric oil analysis. One
method uses the emission spectrograph where metallic atoms are excited by an
electric arc to emit characteristic spectra. The intensity of these spectral
lines is uses to measure the metal concentration in the sample. The second
method used the atomic absorption spectrophotometer where the sample is burned
in a flame. The ground state atoms in the flame absorb a portion of a light
beam transmitted through the flame. The amount of light absorbee is a measure
of the metal concentration.
A recent innovation in emission spectrometers is the use of a "plasma" to
excite the sample rather than the traditional arc or spark (ref. 5). This sys-
tem provides a clear background, improved stability, and minimal matrix inter-
ference. The particle size independent technique (ref. 6) involvea mixing the
used lubricant with an acid-solvent mixture in order to dissolve the wear
particles.
RESULTS AND DISCUSSION
There were five oil samples (two prior to failure and three after fail-
ure) analyzed by various techniques. These included two engine oil samples
dated May 27, 1976, and September 10, 1976 (before failure). Three other
samples (after failure) were an engine oil sample dated September 1 A•, 1976, a
sample from the oil cooler and one from the oil filter.
2
Elemental anal sis. - The above samples were spectroscopically analyzed
for Fe, Ag,
	
, r, u, Mg, Ni, Si, and Ti by routine emission spectrographic
techniques (SOAP) (ref. 1) and by a plasma spectroscopic technique (ref. 5).
Results for these analyses are shown in table I. In the two samples taken be-
fore the failure, low concentrations of Fe, A1, Cu, Si, and Ti were detected.
There is nothingunusual in thesi results. In the September 14, 1976, engine
oil sample taken after failure, there are definite increases in the concentra-
tions of Fe, Al, Cr, Ni, Si, and Ti. Similar increases were noted for the two
other "after failure" samples.
Since the ordinary emission spectroscopic techniques are somewhat depen-
dent on the particle size of the debris present in the sample, a special atom-
ic absorption technique (particle size independent) was used for Ti analysis
(ref. 6). Analytical results for four samples using this technique appear in
table II. Higher Ti concentrations were detected in all four samples compared
to the plasma spectrometer results of table I. This technique is considered to
be more accurate than the plasma emission analysis.
Ferrographic analysis (before failure). - Oil samples were also analyzed
using the Ferrograph and selected areas of Ferrograms were further analyzed in
a scanning electron microscope. An electron micrograph of wear debris from the
engine oil sample (September 10, 1976) appears in figure 1(a). A typical par-
ticle (A) is analyzed by X-ray dispersive energ,, analysis (EDX) in figure 1(b).
Particle A is predominantly Ti and Fe with lesser mounts of Cr, Mn, and Ni.
It saould be noted that in any small particle analysis using EDX, there may be
surrounding particle interference. This means that contributions to some of
the EDX peaks may be from surrounding or underlying particles or substrate
since the analyzing depth or volume may, in some cases, be greater than the
size of the analyzed particle.
The particle morphology of figure 1(a) is essentially that of normal rub-
bing wear particles (a benign form of wear) (refs. 7 and 8). However, there
were spherical particles evident in the prefailure sample and an electron
micrograph appears in figure 2(a). EDX analysis of the spheres appears in
figure 2(b) and the background analysis of the glass Ferrogram appears in fig-
ure 2(c). The presence of Au is due to the evaporated Au film to prevent
charging in the SEM. These spheres are essentially pure Fe. No other elements
(besides the background elements) are detected by EDX. These large 10- to
15-um-diameter spheres are probably contaminants in the oil. Spherical parti-
cles have been related to bearing fatigue (refs. 7-1U), but spheres from fa-
tigue are usually much smaller (1 to 5 um in diameter) and have analyses simi-
lar to the bearing steel. Large spheres have been associated with cavitation
erosion (ref. 8) and grinding (ref. 11).
Essentially the same area on the Ferrogram that appears in figure 2(a) is
mapped for the distribution of Fe, Ti, Cu, and Si in figures 3(b) to (e). As
can be seen, the majority of the particles contain Fe, while one particle con-
tains Ti. Most of the Si and Cu is from the background.
Ferrographic analysis (after failure). - Figure 4 shows the type of parti-
cles present in the oil taken from the oil filter after the failure. As can be
seen, the majority are spherical or spheroidal in nature. In reflected white
light, the spherical particles have a variety of colors from white, to straw-
colored, to deep blue. There is also evidence of tear-shaped or globular par-
1
s
ticles. These shapes, combined with the variety of colors, are indicative of
a high-temperature melting and resolid Jication process. These particles are
shown at higher magnification in figure 5.
Electron micrographs of debris from the engine oil sample (September 14,
1976) show similar particle types. These are shown in figure 6(a) with an ac-
companying EDX analysis in figure 6(b). The particles are predominantly Ti and
Fe with lesser amounts of Cr and Ni.
Another micrograph of debris from engine sample (September 14, 1976) is
shown in figure 7(a). X-ray distribution maps for Ti, Fe, Ni, Cr and Si appear
in figures 7(b) through (f), respectively. In support of the previous figure,
the debris consists of Ti and Fe with small amounts of Ni and Cr. The Si is
,-._sentially from the Ferrogram slide.
Wear severit index. - A parameter, the wear severity index, has been ad-
vocated by Bowen and Westcott (ref. 7). This parameter is calculated from op-
tical density measurements made at the entry position of the Ferrogram (k)
and at the 50-mm position (A S). These are the areas covered by the large
and small particles. Their sum (A, +) yields the general level of wear,
while their difference (
	 - AS ) gives n indication of abnormality. These two
quantities multiplied tother (AE + AS )(At - AS ) yield the wear severity index
A^ - AS, usually abbreviated IS.
IS values for all of the oil samples, including the mean and standard
deviaLJ on of six engine samples from 1974, are shown in figure 8. The IS
increased from about 10 to 140 from the May 27, 1976, sample to the September
10, 1976 sample. Although this is a large increase prior to failure, it is
not significant when compared to the range of IS values obtained from this
engine in the past (i.e., 1974 samples). After failure, IS values increase
dramatically. This, of course, is expected. An especially large value was
obtained from the oil filter sample.
Failure initiation site. - One of the more plausible faiiure modes was the
ignition of i by friction between moving an.i stationary components in the high
pressure compressor. There were two poss;`iiities: (1) rotor/ shroud source
in which the Ti rotor blades would interfere with their shrouds (Metro 301, an
abradable Ni-Cr-Fe alloy); and (2) a stator/spacer source in which the Ti
knife e'ges on the spacers interfere with tht labyrinth seal materia l (AMS 430,
a sta.niess steel).
These types of failures would generate debr i s in the gas path of the en-
gine. Conceivably, this debris could enter the bearing compartments through
the seals and eventually find its way into the lubrication system.
It was hoped that analysis of this debris might indicate the location of
the high speed rub. The nominal composition cf the shroud material (Metro 301)
is 69 percent Ni, 14 percent Cr, 8 percent Fe, 5.5 percent BN and 3.5 percent
Al. The labyrinth seal material is AMS 430 which has a composition of 83 per-
cent Fe, 17 percent Cr and 1 percent Mn. Examining many particles by EDX after
-allure (such as in fig. 7) was inconclusive. No analysis exactly matched the
above compositions. This is not surprising considering the manner in which the
4
particles were formed. In addition, the particle analysis from figure 6(b) is
very similar to the analysis of the particle in figure 1(b) which was from a
sample taken prior to the failure. There definitely were Ti-containing parti-
cles in the engine lubricant prior to the engine failure.
CONCLUDING REMARKS
It was concluded that a failure in the lubrication system was not involved
and, therefore, did not contribute to the engine failure. Attempts to pinpoint
the possible failure initiation site in the high pressure compressor were in-
conclusive.
SUMMARY OF RESULTS
The Ferrograph, an emission spectrometer, a plasma spectrometer and an
atomic absorption spectrophotometer were used to analyze engine oil samples
from a failed gas turbine engine. The major results are summarized as follows:
1. No abnormal wear mechanisms nor high levels of wear were detected in
engine oil samples taken prior to engine failure.
2. However, low concentration; of Ti (0.2 to 0.5 ppm) were evident in the
engine oi*i RE12L to failure. Higher Ti concentrations (>2 ppm) were detected
after failure.
3. Ferrographic analysis indicated that most of the Ti was contained in
spherical metallic debris after the failure. Some Ti debris was present before.
the failure.
REFERENCES
1. Beerbower, A.: Spectrometry and Other Analysis Tools for Failure
Prognosis. Lubr. Eng., vol. 32, no. 6, June 1976, pp. 285-293.
2. Seifert, W. W; and Westcott, V. C.: A Method for the Study of Wear
Particles in Lubricating Oil. Wear, vol. 21, 1972, pp. 27-42.
3. Westcott, V. C; and Seifert, W. W.: Investigation of Iron Content of
Lubricating Oil Using a F-irograph and an Emission Spectrometer. Wear,
vol. 23, 1973, pp. 239-249.
4. Scott, D.; Seifert, W. W.; and Westcott, V. C.: Ferrog ► aphy - An Advanced
Design Aid for the 80's. Wear, vol. 3^ 1975, pp. 251-260.
5. Ward, Arthur F.: Inductively Coupled Argon Plasma Spectroscopy, Develop-
ment, Technique, and Applications. Am. Lab., vol. 10, no. 11, Nov.
1978, pp. 79-87.
5
OWNAL PA G'-1- 1:3
OF POOR QUALITY
TABLE I. - ELEMENTAL ANALYSTS OF OIL SAMP_ES USING ORDINARY
SOAP PROCEDURE AND A PLASMA SPECTROMETER
Sample Elements, ppm
Fe Ag Al Cr Cu Mg Ni Si Ti
1 0 0 0 2 0 c 5 05/27/76	 Soapa
Before
	
(plasma
failure	 spect.)b (0.5)
1
(0.1)
0
(0.5)
0
(0.1)
0
(1.1)
2
(0.2)
0
(0.1)
c
(2.2)
4
(0.2)
09/10/76 Soap
Before
failure (plasma) (0.5)
5
(0)
0
(0.3)
4
(0.1)
2
(0.6)
3
(0.1)
0
(0)
c
(0.8)
0
(0.3)
29/14/76 Soap
After
failure (plasma) (2.5)
3
(0)
0
(1.6)
3
(0.9)
0
(0.6)
3
(0)
0
(0.9)
c
(10.6)
5
(2.2)
2Oil Cooler Soap
after
failure (plasma) -
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Oil Filter Soap
after
failure (plasma) 1	 (4.1) (0) 1	 (2.6) (1.0) 1	 (1.6) 1 (0.5) (1.2) (49.3) (3.1)
aArmy Oil Analysis Lab, Ft. Campbell, KY
bAir Force Materials Lab, WPAFB, OH 45433
cN ,,t determined
TABLE II. - ANALYSIS OF OIL SAMPLES FOR TITANIUM
USING PARTICLE SIZE INDEPENDENT ATOMIC
ABSORPTION SPECTROPHOTOMETRYc
Sample Titanium concentration,
ppm
From engine:
5/21176 0.4	 a(0.2)
9/10/76 0.5	 a(0.3)
9114116 3.1	 a(2.2)
Oil	 Filter b11.5
	 a(3.1)
*Plasma data From table 1.
bSample contained large particles which settled
to bottom of bottle.
cReference 6.
ORIGINAL PAGE" IS
OF POOR QUALITY
(al Electron micrw raph of wear debris.
Ti Mn FeTi Cr Fe Ni
161 EDX analysis of particle A.
Figure 1. - Wear debris from oil sample CUM ibefore failures.
ORIGINAL PAGE
BLACK A'•D WHITE PHOTOGRAPH
a^ Electron r1tcroyrapr of sphe, ical particles.
Au	 Fe Fe	 Au	 S1 Au K	 Ti	 Zn Au
io , Energy dispersive X-ray analvsis Q E X 1 01 sphere
	 Background EDX of ferrogram.
f inure 2.
	
Spherical panccl s from oil sample 9110A ihetore failure'.
a
ibi X-ray distribution of Fe.	 W X-ray distribuh^n of Ti.
ORIGI NAL PAu -	 kAi'kf
g^ACK A
ND v40ITE PHOTOG
jai [leciro n nicrnnraph of spherical particles and debris
id, X - ra, nwlrihution of Cu.
	 iei X-ray distribution of Si.
Figure 3. Spherica l particles and debris from od sample Qil(VlbVWtore failure" andacco+,pa(wn q elemental
X-rav -^aps.
`,.. - 
I ^l AL f AG
BACK AND WHITE
d. Oph.al	 rape or %phenwl particle% and dehrn tror n nd in oil
luter salter tadurr .
Figure 5 • Debris from oil sample from oil filter i.rfrer failure)
'mmAaDrtmuE,aNOE0NkoumLL
Z
ci
LL
L
^
c
c
L
_
 
Ui=
ndAn0NN21ACAx0wA„nrFaNadv`otnA600u_E9buuwA
B
L
A
C
K
	
.
-OGRAPH
Vlt^;^	 r .. .
BLACK AND 'WINITE PriD l l^ r^^l^'I
la1flectron m r rograp! • of debris. Ibl X • rav drstrIbulion of 11.fi
' I . l o rd. L!IsIr11Ji , 1 _.I 1e, >	 rd/ dI%If IIj J!,,^1 nl %I.
t o x rah distriflutlon of 1 r. Jr X ray dWrlbution of Sr.
I pure 7.	 Debris from oil sample 0114116 latter fadurel and ar(ompaovrrsq elel rrrnlal X ray Flaps.
NUr
OC
v
}
w
i
ORIGINAL Q
OF POOR QUA'--iN
6390
Mean	 5127176	 9110176	 9114176 Oil coder Oil filter
six	 before	 before	 after	 after	 after
samples
	
failure
	
failure	 failure	 failure	 failure
1974
i"	 Engine oil samples
F l9ureS. - Wear severity index lisl for various oil samples.


Ferrographic and spectrometer oil analysis from a failed gas turbine engine

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