MACHINERY LUBRICATION- INDIA SEPTEMBER-OCTOBER 2019 | Page 33

B y B ryan J ohnson , P alo V erde N uclear G enerating S tation
OIL ANALYSIS
How
Light Affects
Oil
Analysis
Results for Varnish Potential
As oil or oil additives degrade,
they develop varnish and begin
to accumulate this material
within the oil. The amount of varnish
carried by or within the oil will
progressively increase as the oil
continues its service. The oil’s carrying
capacity for varnish will also fluctuate
based on temperature. As the oil
becomes saturated, this material can
settle from the oil and form harmful
deposits. Fortunately, varnish can be
extracted from oil and measured in a
laboratory by its change in color.
The ASTM D7843 standard provides
requirements for performing membrane
patch colorimetry (MPC) testing.
However, this test has been found to be
biased by exposure to ultraviolet (UV)
light. A recent experiment demonstrated
that overhead lighting, such as
fluorescent lights, can have a similar
effect. Therefore, caution is needed to
avoid contact with all but incidental
light when handling oil samples that will
require an MPC test.
Increases in MPC measurements of 50
to 100 percent have been demonstrated
following several days of exposure to
indoor lighting only. As such, seemingly
benign sources like fluorescent overhead
lighting can dramatically alter MPC
varnish test data. For example, one oil
sample increased from a measurement
of 21 to 41 in a 16-day period due to
exposure to fluorescent lighting.
Case Study
For a comparative study, a single oil
sample drawn from a large turbine oil
reservoir was processed for an MPC
measurement. The sample was split
and placed into light-blocking and
translucent sample bottles at the time
of sampling. All the bottles were made
of high-density polyethylene (HDPE).
A series of tests was designed to
determine the impact of time and
Caution is needed
to avoid contact with
all but incidental
light when handling
oil samples that will
require an MPC test.
temperature with the sample limited to
light exposure within the laboratory.
Duplicate oil samples were drawn on
the same day by the same personnel.
One sample was placed into the
standard semi-translucent sample
bottle. The second sample was drawn
into a light-blocking brown bottle.
TRANSLUCENT
CONTAINER MPC LIGHT-BLOCKING
CONTAINER MPC
39 26
3 days after heating 38 22
7 days after heating 40 24
14 days after heating 41 26
40 27
OIL SAMPLES
As found, after 16 days (pre-heating)
Heated for 24 Hours at 60°C and Stored
in a Dark Location
Reheated Samples
7 days after second heating
MPC test data and test conditions
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