Hydrocarbon Processing - December 2022 - 64

Valves, Pumps and
Turbomachinery
K. BRASHLER, Y. ALSHAHRANI and M. SABBAN,
Saudi Aramco, Dhahran, Saudi Arabia
Hot oil pump warm-up system best practices
and failure case study
Many industries utilize pumps in hot
applications, including oil and gas facilities.
Pump manufacturers and end users
consider the pump warm-up system
configuration to be an essential consideration
during pump design, manufacturing
and commissioning stages. The
scope of this article focuses on typical
guidelines and best practices for hot applications
where warm-up systems are required
for proper startup and reliability
of the pump. These warm-up systems are
designed to bring the pump up to a uniform
temperature in a controlled manner
before it is started, and to maintain the
standby pump at uniform process temperatures
to allow for auto-start.
However, there is a different train
of thought per recent guidelines from
API RP 682, which is that pumps handling
fluids with operating temperatures
greater than 150°C, or those handling
high-pour-point fluids, should utilize a
warm-up system to obtain and maintain
the appropriate pump operating temperature.
Pump manufacturers typically
provide specific recommendations for
warm-up system requirements, based on
different pump configurations. The following
outlines four primary considerations
to monitor during a pump warmup
process to prevent damage to the
machine and/or the mechanical seal(s).
Heating rate. A controlled heating rate
is required to minimize temperature gradients
that can produce non-uniform
thermal expansion,
resulting in compromised
internal clearances and subsequent
pump damage and/or seizure of
the rotating element. The original equipment
manufacturer (OEM) will provide
a recommended heating rate based on
the type and size of the pump. In the absence
of guidelines from the manufacturer,
a typical rule of thumb for the heating
rate is as follows:
* Maximum heating rate of 50°C/hr
(122°F/hr) up to 260°C (500°F)
* Maximum heating rate of 25°C/hr
(77°F/hr) above 260°C (500°F).
Thermal shock. Another important
consideration for a pump's warm-up procedure
is to avoid thermally shocking the
pump and associated components by
rapidly introducing hot fluid to it. Thermally
shocking the pump may result in
significant damage or failure, including
the mechanical seal faces. Typically, startup
procedures mandate a commissioning
of the mechanical seal support system
prior to initiating the warm-up process.
Thermal stratification. Another imFIG.
1. Thermal signature showing an uneven
temperature distribution.
64 DECEMBER 2022 | HydrocarbonProcessing.com
portant consideration is thermal stratification,
which can occur when pumps are
not warmed up properly. Fluid density
differences due to changes in fluid temperature
can result in a thermo-siphoning
effect, with the hotter fluid at the top of
the pump casing and cooler fluid migrating
to the bottom of the casing. The
uneven thermal expansion of the casing
and the rotating element can result
in galling of the rotating and stationary
components and/or complete seizure of
the rotor. Higher vibration amplitudes
can also be expected due to the internal
misalignment created by this condition.
FIG. 1 shows an infrared thermal signature
of a pump casing with this uneven temperature
profile across the pump casing.
Notice the top-top suction and discharge
nozzles-this condition can occur when
there are no warm-up lines located at the
bottom of the pump casing.
Pump startup temperature. A final
consideration for a successful pump
warm-up and startup is related to startup
temperature. The startup of a pump prior
to reaching the required startup temperature
can result in damage to internal
running clearances and/or mechanical
seals. The pump should be ready to start
when a pre-specified temperature margin
is established relative to the product
or operating temperature. This specified
temperature margin will vary with
the pump design and the nature of the
pumped fluid, and these guidelines are
typically provided by the pump designer.
This can be particularly important for
fluids with a high pour-point temperature
or for fluids that solidify at temperatures
below normal operating temperature. In
the absence of any guidelines or specific
requirements from the pump's OEM, the
recommended guideline is that pump
startup should not occur until the cas
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