Hydrocarbon Processing - August 2021 - 20

Valves, Pumps and Turbomachinery
FIG. 5. Temporary port to allow seal cavity
draining.
It was also recommended to install
FIG. 3. Cut on primary seal O-ring.
it was discovered that there was only one
common flowmeter and one common
recycle line. For such a parallel operation
system, the individual controlling system
(flow monitoring and recycling) provides
more reliable operation and prevents such
extreme off-design running.
FIG. 4. Extremely small orifice bore size of the
seal leak detection line.
with a rated capacity of 63 gal/min
(which is also the BEP for these pumps).
This far exceeded the allowable operating
range, which should be 22 gal/min-
75 gal/min. This indicates how severely
the pumps were operated. The data also
showed that this off-design operation
was for an extended period of time, and
that this kind of operation was for more
than 10% of the extracted data duration.
It is known that operating outside the
allowable operating window results in reliability
issues, an increase of vibration levels
and consequently frequent seal failures,
which are what these pumps were experiencing.
This is an indication of a poor controlling
system. Therefore, the controlling
system of these pumps was evaluated, and
20 AUGUST 2021 | HydrocarbonProcessing.com
Recommendations. From the above, it
was clear that some modifications were
required to improve how the pumps are
operated and controlled considering the
actual site condition. The pump vendor
was consulted to increase the orifice
bore size of the flush line from 1 mm
to 2 mm, considering that the existing
suction strainer size will prevent larger
particles from blocking the orifice. This
was accepted considering the differential
pressure and required flow across the
orifice during pump operation at higher
flowrates. For the seal leak detection system,
it was recommended to change Plan
76 to Plan 75 to prevent liquid from accumulating
inside the seal cavity. Since
changing the seal leak detection plan
was a major work and would take time
to implement, a short-term solution was
provided. It was recommended to install
a temporary drain for the seal cavity to allow
plant operators to empty any liquid
accumulation, as shown in FIG. 5.
differential pressure transmitters across
the pump suction strainers. Considering
the strainers' opening size and the
amount of particles carried out with the
process, it is always recommended to
monitor the strainer condition to prevent
severe blockage and net positive suction
head (NPSH)-related issues.
It was also important to address the
controlling system deficiencies of these
pumps. As mentioned above, this is a
parallel operation mode controlled by a
common flowmeter and a common recycle
line. It was recommended to reconfigure
the controllers' settings for low-/
high-flow and recycle line control valve
action to consider the number of pumps
in operation. For example, the minimum
flow setpoint should be different if one
pump or two pumps are running.
Takeaway. It is true that low specific speed
pump designs are relatively more sensitive
than other designs and require more
diligence in operation and controlling. It
is important for end users to thoroughly
evaluate the process needs and specifications
before procuring these pumps and
their auxiliary systems. Investing in a good
controlling system can easily achieve a
payback when considering equipment reliability
and availability aspects.
MOHAMMED BADUGHAISH is a
Mechanical Engineer with 12 yr of
experience in rotating equipment
within the oil and gas industry.
His work experience has focused on
hydraulic pumps, troubleshooting
and maintenance. He works as a
pump engineer in Saudi Aramco's Consulting Services
Department. He obtained his BS degree from King
Fahd University of Petroleum and Minerals (KFUPM)
and an MS degree in mechanical engineering from
the University of Central Florida.
http://www.HydrocarbonProcessing.com
Hydrocarbon Processing - August 2021

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