Machinery Lubrication India Jan Feb 14 10 | Page 17

To control particulate matter, it is
better to use filter element sizes than
ISO charts, since ISO charts allow a few
large particles, which can lead to
journal bearing failure.

Figure 1. The results from a mesh blockage particle counter revealed that a large
amount of contaminants were released into the lubrication system after 12 hours of
operation.

high for more than two hours. Added

30-inch diameters. However, when the

filtration was able to bring the particle

turbine is on turning gear, this oil film

levels down to acceptable limits, but

thickness is only a few microns thick at

when the turbine speed was increased

best.

to synchronize the generator to the
power grid, another spike occurred.

As the speed increases, so does the film
thickness between the rotor and

Plants generally do not monitor particle

bearings. If a large mass of particulate

levels as equipment is placed back into

gets into a journal bearing when the

service. When a turbine is at normal

particulate matter can scar or damage

thickness between the turbine rotor and

the journal and/or bearing profile,

the bearing surfaces is in the order of

which in turn affects the fluid dynamics

0.002 inches for journal diameters from

within the bearing. This often leads to

8 to 16 inches. The minimum film

overheated bearings and possibly to

thickness increases to 0.010 inches for

bearing failure.

There are many ways to reduce risks
when bringing large equipment back
into service. A review of vibration data
and other parameters can tell a lot
about how the equipment performs
when going from cold to normal
operating conditions. It also will inform
you of what is needed to extend the
health of the equipment or increase the
operating efficiency.

film thickness is only microns thick, the

operating speed, the minimum oil film

Understanding what is occurring
provides the best way to identify and
assess risk. Once a risk is identified,
actions can be taken, consequences
evaluated,
mitigations
and
contingencies developed, and an
implementation plan pursued.

the largest journal bearings with

Figure 2. This graph illustrates the changes in oil particulate during the startup of a
turbine. The dash lines provide the lSO 4406 “alert” level for specific particle sizes.

Perhaps the most versatile and costeffective method to help reduce the risk
to equipment is to have a kidney-loop
filtration system available. This type of
system can be connected to a tank or
reservoir to support bringing the
equipment back into service.
The filtration unit should be sized to
process the contents of the tank or
reservoir several times per hour. In
addition, the unit can be equipped with
a cooler for summer months when
thermal loads on the plant limit
equipment operation. Along with
filtering and cooling, a kidney-loop
system can include a dehydrator, which
provides an excellent way to extract
water from the oil before placing the
equipment on turning gear. This will
reduce the amount of water that gets
pushed
through
high-pressure
differential regions of the oil film in the
journal bearing and reduce the risk or

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