Machinery Lubrication India Jan Feb 14 10 | Page 16

increases. Then, when the unit is
returned to service, the newly formed
corrosion (rust) on any exposed piping
or surfaces often is shaken loose or
washed away with the restarted oil flow.
Furthermore, where there are pockets in
which stagnant oil may have settled, a
slug of particulate and coagulating oil
can easily form. When the oil flow is
restarted, this particulate matter is
easily pulled into the lubrication flow
streams and circulated throughout the
lubrication system.
One substantial area of concern is the
control system. Because of the system’s
complexity and low-flow velocity within
the control piping, the system acts as a
collection point for particulate.

Biological Growth
When a lubrication system is secured
for prolonged periods of time,
biological growth can occur. Low-flow
areas can collect a tremendous amount
of sludge over the years. With this
amount of growth, a sudden change in

Biological growth, particulate and separated lubricant additives have collected on this
pump (above left). The lube oil cooler on the right has biological growth and adhered
lubricant additives.

established for normal operating
conditions. One of the parameters
typically monitored is particulate levels.
The International Organization for
Standardization (ISO) has developed a
method (ISO 4406) for quantifying the
level of particle contamination. The
values gathered in a particle count test
identify the number of particles in a
given volume of fluid that are above a
specific size range, which is generally set
at 4 microns, 6 microns and 14 microns.
The data is normally presented in a
format such as 17/15/13, which
provides a numeric range value
representing the measured quantity of
particles greater than 4 microns, 6
microns and 14 microns, respectively.

Case Studies

This orifice plug from a boiler feed pump
turbine control has deposits covering the
orifice holes.

the lubricating system’s temperature,
such as that which occurs when
returning the system to service, can
result in the biological growth dying off
and the remains being pushed through
the system.

Cleanliness Codes

Most plants have equipment monitoring
programs that define lubricant property
limits. These limits are usually

In a recent turbine outage, the
lubrication system was placed into
operation, and the main turbine was
placed on turning gear. While the
system was operating, an auxiliary
filtration skid was connected to the
main turbine reservoir to run in parallel
with the normal filtration system. The
skid had dual 7-micron filters and
processed the main turbine reservoir
four times per hour. An oil sample
recorder pulled samples at 20-minute
increments from the center of the
turbine oil reservoir and then
documented 31 hours of results from
the mesh blockage particle counter.

14| January-February 2014 | www.machinerylubricationindia.com

As
Figure
1
indicates,
after
approximately 12 hours in operation, a
large slug of contaminants must have
released into the system, causing the
need to change filters. At that point, a
decision was made to reduce the filter
size and continue. Once the turbine was
rolled, the auxiliary filtration unit was
secured. Inspection of the last set of
filters revealed a significant collection
of particulate captured within the
filters.
In another example, a filtration skid
with a particle counter was tied into a
turbine reservoir during the plant’s
startup. This power plant normally only
operates during peak summer months
in the southern part of the United
States, leaving it shut down for at least
six months out of the year. The particle
counter recorded main turbine reservoir
contaminant levels above 4, 6 and