Hydrocarbon Processing - October 2021 - GP-34

MAINTENANCE AND RELIABILITY
Oxidation vs. oil hours
30
20
10
Limit
SENTRON LD8000, 40
500
1,000
1,500
2,000
2,500
Oil service
FIG. 2. Oxidation increases with oil service.
TAN-E vs. oil hours
5
4
3
2
1
Limit
500
1,000
1,500
2,000
2,500
Oil service
FIG. 3. TAN increases with oil service as a result of fluid oxidation.
values typically start off lower and then gradually increase over
the life of the fill as oxidation and nitration occur (FIG. 3). The
initial pH (ipH) of a fluid complements TAN measurements and
can identify the formation and level of strong acids even earlier,
which is particularly important in landfill and biogas applications.
Total base number (TBN) measures the fluid's reserve alkalinity.
Over-based detergent additives contribute to this alkalinity,
and the fluid's TBN value decreases as these detergents
neutralize harmful acids. This test is most relevant to diesel engine
oils, which have higher amounts of detergents but can, and
should, be used in stationary gas engine oils as required by the
manufacturer for extended oil drain intervals.
Focusing on proper sampling. Used oil analysis is conducted
by most gas engine operators, but some aspects may
be overlooked that prevent an operator from realizing the full
value of the analysis. For example, a program can be compromised
if proper oil sampling techniques are not followed. Several
steps should be used to take a representative sample:
* Samples should be taken from the same location
and at the same interval.
* The sample valve should be installed after the
engine oil pump but before the oil filters.
* Samples should be taken while the engine has been
running at normal operating temperatures and load
for at least 1 hr.
* The sample valve and related tubing/piping should be
purged before filling the oil sample container. The sample
container must be kept clean prior to taking samples.
34 SEPTEMBER/OCTOBER 2021 | GasProcessingNews.com
3,000
3,500
SENTRON LD8000, 40
4,000
4,500
5,000
FIG. 4. Large gas engines should be sample monthly at minimum or
sooner, depending on the OEM requirement.
* All relevant engine and oil information should be included
during sample registration, including the brand name of the
oil in use, total engine hours, oil service hours and whether
or not the fluid was changed after the sample was taken.
* The sample should be sent to the lab as soon as possible.
After these steps have been taken and the used oil has been
sampled, operators should focus on reviewing and trending the
data. A new oil reference sample must be listed on the analysis
report to compare the properties of the used fluid with those of
the new fluid.
The rate at which an engine consumes oil is also an important
factor to consider, as higher consumption rates (and
subsequent higher fresh oil makeup rates) have a sweetening
effect on the fluid's health, whereas an engine with minimal
consumption may degrade the oil sooner.
Large gas engines should typically be sampled monthly, but
this can vary depending on the manufacturer, so it is important
to adhere to the engine OEM sampling frequency (FIG. 4).
When analysis results indicate the development of an abnormal
condition, it is also prudent to re-sample more frequently to
closely monitor increased wear rates and fluid degradation.
Realizing the full value. While almost all operators conduct
some form of used oil analysis, some use it strictly as a tool to
identify mechanical failure. Operations focused on efficiency
and best practices also monitor the fluid's physical properties
and chemical degradation, contaminants and equipment health
in stationary gas engine oils. Gas engines are of significant value,
so the investment in monitoring the aforementioned items
is simply good business.
By doing this, operators can gain a clearer picture of the oil's
condition and overall engine health and realize the true value
of used oil analysis. For example, water is a catalyst for oxidation,
and the presence of water in an engine increases the rate
of corrosive wear and can contribute to hydrolysis. The presence
of water in the oil can be screened by the crackle test, but
the Karl Fischer test method can more accurately identify how
much water is present. Excess water contamination can actually
increase the oil's viscosity, but it also reduces the load-carrying
capability of the fluid film as it forms an emulsion.
Elemental analysis is also standard testing and uses a method
3,000
3,500
4,000
4,500
5,000
TAN-E, mg/g
Oxidation, A/cm
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Hydrocarbon Processing - October 2021

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