Hydrocarbon Processing - January 2021 - 24

Pump failed

Pump failed, after O/H
started with VG46 oil

09-05-20

09-04-20

09-03-20

09-02-20

09-01-20

09-12-19

09-11-19

09-10-19

09-09-19

09-08-19

09-07-19

09-06-19

09-05-19

09-04-19

09-03-19

09-02-19

09-01-19

PDE Acc
09-12-18

14
12
10
8
6
4
2
0
09-11-18

HP DTA pump acceleration trend

Valves, Pumps and Turbomachinery

FIG. 2. Trends of acceleration enveloping before and after lube oil change.

INSIDE
INTELLIGENCE

flushing/oil replenishment was done as
and when required, but no substantial results were achieved.

for the
Downstream Industry

Action taken.

24 JANUARY 2021 | HydrocarbonProcessing.com

* It was decided to ensure that the
lube oil used for the bearings was
the correct lubricant. The viscosity
required to lubricate the bearings
used in the pump was calculated.
* The calculation of viscosity is a
stepwise procedure that includes
the calculation of rated viscosity
initially, for which bearing mean
diameter (dm) is required.
* The dm is the sum of the bearing
bore (d) and its outer diameter
(OD) divided by 2. For 7,311,
the mean diameter is 87.5 mm
[OD = 120, d = 55, dm = 0.5
(OD + d)].
* Referring to the standard chart
between the rated viscosity and
dm for the above calculated value
and 3,000 rpm, the rated viscosity
for the pump bearings was
calculated to be 10 mm2/sec.
* After determining the rated
viscosity, the ISO viscosity
grade was calculated to be
27 mm2/sec using the standard
chart between operating
temperature and viscosity.
* Considering the kappa value
to be > 1, the required lube oil
viscosity as per ISO 3448 (with an
operating temperature of 70°C)
was ISO VG 32. This means that
the required lube oil viscosity to
effectively lubricate the bearings
of this pump is ISO VG 32.
* It was decided to move one step
down from the presently used
VG 68 to VG 46 to get closer to
the calculated value. After this
overhaul, the pump was operated.

FIG. 2 shows the trend of vibration data
showing the pump behavior before and
after changing the lube oil. It is clearly evident that a significant reduction in pump
vibration values occurred, and the pump,
which always started with higher values
after overhauling, is running with low values even after 5 mos of operation.

Takeaway. The higher-viscosity grade

synthetic oil being used was not lubricating the bearings properly. High-viscosity
oils and lubricants will prevent metal-tometal contact, but will generate unnecessary heat and loss of power as the rolling
elements are forced to work through the
oil film. The oil used was almost double
the rated viscosity for the bearings and had
a high-viscosity index, which also effects
the thickness of the hydrodynamic film.
In hydrodynamic lubrication, the coefficient of friction increases with higher
viscosity of the lube oil due to internal
lubricant friction, which can affect the
lubricating film when the load and rpm
are constant. A common myth is that if
the bearings are failing and the operating temperature is high, a higher-viscosity
oil must be used. Sometimes, this may
provide a positive result, but changing
lube oil without a thorough investigation
should never be done, as it can become a
cause of the failure. The rated viscosity
plays a vital role and can be easily calculated using bearing mean diameter, operating temperature and rpm.

AKHIL JEET SINGH RATHORE
works as a Mechanical Engineer
for Indorama Eleme Petrochemicals
& fertilizers Ltd. in Nigeria. He has
more than 12 yr of vibration
analysis experience in the cement,
automobile, petrochemicals,
refining and fertilizer industries. Mr. Rathore
previously worked with SKF India for 5 yr as a
reliability engineer. He holds Mobius Vibration
Analysis CAT-II, BINDT CAT-I, SKF India VA Level-II,
SKF Nigeria MCSA CAT-I, ASNT UT-II certificates.

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Hydrocarbon Processing - January 2021

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