Page 346 - Handbook of Materials Failure Analysis

12 Oil Degradation Particles 343

100µm 200µm
(a) (b)
FIGURE 13.48
The evidence of the formation of friction polymer fiber from the bearing oil samples: (a) the
molten friction polymer bead and the fiber formation (200 ); (b) the molten friction polymer
bead and the fiber formation (50 ).

shining feature resembles to the metal wear particles. However, at 200 magnifica-
tion (Figure 13.57b), the particle’s surface indicates the typical attributes of varnish
particles. Figure 13.58 displays other two similar pseudo-metal wear particles.
Figure 13.59 demonstrates other examples of pseudo-metal wear particles. These
two particles were from wind turbine gearbox oils samples. The first particle
(Figure 13.59a) resembles to a fatigue wear particle with partial dark oxide, whereas
the second particle (Figure 13.59b) resembles to a severe sliding wear particle with
partial dark oxide surface. Through ESEM/EDS analyses, both examples were con-
firmed to be varnish particles.
Figure 13.60a shows the secondary electronic image of one of the first particle.
In situ EDS analysis results (Figure 13.60b) confirms the varnish compositions.
Figure 13.61a displays the detailed features of the second particle. The deep striations
on the particle surface indicate that the particle had been subjected to sliding wear.
However, in situ EDS analysis results (Figure 13.61b) reveal its varnish compositions.

12.5 CASE STUDY 6: THE VARNISH DEPOSIT AND THE ONSET
DAMAGE ON THE BEARING PADS OF A 55 MW GAS TURBINE LOAD
GEARBOX
A load gearbox in a 55 Mw gas turbine experienced the varnish deposit issue. The
gearbox was a one-stage reducing load gearbox which transmitted the power from
3
the turbine to the generator. An oil tank (6.5 m ) supplied the lubricant to all the bab-
bit bearings of the turbine, generator, and the gearbox. The comprehensive turbine oil
analysis program did not detect the abnormality, but filtergram analysis detected the
varnish particles and the wear particles for some time. Figure 13.62 shows the typical
varnish particles.
The varnish deposit on the bearing pads had inflicted damage to the bearing.
Figure 13.63 shows the typical wear particles found in the oil samples. After the prob-
lems had been detected through the filtergram technique, the gearbox was overhauled