Hydrocarbon Processing - November 2021 - 83

Valves, Pumps and Turbomachinery
FIG. 7 shows a line-shaft bearing/bushing.
The bearing shows evidence of high temperature
from lack of lubrication, and the
carbon bushing was fractured.
The shaft speed of vertical pumps with
sulfur-lubricated sleeve bearings is critical
in terms of increased friction/temperature,
which can result in damage from
sulfur solidification. Low-flow conditions
will also add to this temperature rise in
the bearings. Based on these factors, it is
recommended to restrict shaft speed to
a maximum of 1,800 rpm. FIG. 8 shows a
couple of cases where shafts have failed
due to lubrication issues and high heat
generation at the sleeve bearing. This is
based on reducing the radial loads/forces
and to reduce the risk of temperature increase
in the sleeve bearings.
Corrosion issues. Pump material selection
is an important design consideration
to ensure adequate corrosion resistance.
The following case example demonstrates
that there can be other corrosion
mechanisms to consider, which can have
a direct influence on pump reliability.
The presence of water and sulfur containing
H2
S can result in wet H2
S corrosion
in the vapor space, which can lead to deterioration
of the sulfur pit.
FIG. 9 shows significant concrete desiccation
at the pump soffit location and
other areas of the sulfur pit walls. Severe
corrosion of the cover plate was also
present. These conditions resulted in
both corrosion and introduction of foreign
material to the pit. It is imperative
to mitigate water intrusion from washdown,
steam-leak and environmental issues.
This corrosion mechanism can also
result in corrosion of the pump baseplate
and foundation, resulting in reduced
stiffness and subsequent vibration and
alignment issues.
Takeaways. There are a few takeaways
to highlight; however, none of them are
more important than the initial design review
to ensure that the sulfur properties
and other design aspects have been considered.
Choosing the right application
will be critical to maintain acceptable reliability.
The following actions highlight
a few of the key considerations to ensure
trouble-free operation:
* Ensure proper installation
to minimize the external
loads on the pump.
* Always perform precommissioning
checks prior to startup.
* Ensure that temperature and
level controls are working for
proper pump function.
* Mitigate any steam leaks or
other sources of water to
avoid wet H2
S corrosion.
* Conduct sulfur pit inspections
periodically to identify any sulfur
pit deterioration and subsequent
accumulation of foreign material
in the pump suction boot area.
The following is a list of proven maintenance
and reliability tips for improving
molten sulfur pump reliability and reducing
maintenance costs:
* Utilize flexible steam hoses to
maintain steam to jacketing during
pump removal. This will allow
for proper draining of the pump,
as well as for maintaining
temperature on the pump
during the free draining of the
pump when lifted from the
pit. Residual sulfur left in the
pump requires significantly
more time and effort to perform
maintenance and parts can be
damaged during disassembly,
resulting in higher maintenance
costs. It is often difficult to
distinguish between damage due
to disassembly or from operation
during the troubleshooting.
* Before applying steam to the
pump jackets and starting the
pump, ensure that the pump has
reached equilibrium temperature.
The pump should be held in
the pit for several hours to
allow all the parts to reach
uniform temperature. If steam is
applied prematurely, the pump
components will grow at different
rates and cause possible damage.
* Operation procedures should
include a monthly pump rotation
to ensure that foreign material
does not accumulate around
a long-term standby pump.
* All water sources, including
wash water, should be avoided
on or around the sulfur
pit. Utilize water stops to
prevent ingress of water.
* Always baseline the pump
performance variables following
commissioning, which can be
FIG. 8. Failed line shaft and sleeve bearing
location.
FIG. 9. Soffit and cover plate damage due to
wet H2
S corrosion.
used for future troubleshooting
purposes. These key variables
include discharge pressure,
motor amperage, and top
anti-friction bearing housing
skin temperature.
ACKNOWLEDGMENT
The authors would like to provide a special thanks
to Dr. Emad Abu-Aisheh at Saudi Aramco for his valuable
troubleshooting contributions and for providing
inspection photos for this article.
KEITH BRASHLER is a Pump Specialist with
Saudi Aramco. He has 32 yr of rotating equipment
experience in oil and gas, power generation, nuclear,
and pulp and paper, with an emphasis on pump
and system troubleshooting. Mr. Brashler is a
vibration analyst (ISO Category 4), and a certified
maintenance and reliability professional. He earned
a BS degree in mechanical engineering from
Washington State University.
WESAM KAHALF Allah is a Pump Engineer at
Saudi Aramco. He has 8 yr of experience with the
company. He earned a BS degree in mechanical
engineering from Purdue University and an MS
degree in engineering from Texas A&M University.
Hydrocarbon Processing | NOVEMBER 2021 83
Hydrocarbon Processing - November 2021

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