Hydrocarbon Processing - December 2021 - 80

Valves, Pumps and Turbomachinery
ther BB3 or BB5 type pumps with 10-12
stages of opposed impellers to help hydraulically
balance the thrust force. The
proposed pump (with the proposed suction
and discharge nozzles size and the
double-suction, first-stage impeller) is
Pumps with hydrodynamic bearAsk
a competent inspector (preferably API-SIRE certified)
with pump knowledge for shop inspection activities of the
pumps. Competent means having necessary, valid and
relevant training, knowledge and experience. There is
a big difference between watching/seeing and inspection.
internal crossover passage of opposed
impeller design is long and has potential
for acoustic vibrations. Increased vibrations
at the vane pass frequencies of 5X
and 7X at the reduced flow between the
minimum continuous stable flow and the
midpoint are probable; therefore, a critical
evaluation for acoustic resonance is
recommended at the early design stage.
The measurement record for noise
levels will be helpful to see if a correlation
exists with cases of increased vibrations.
Acoustic phenomena triggered by the
vane pass may manifest with an increase
in rattling sound.
Test stand. The configuration, layout
and support of the temporary test piping
is important. The test motor health, alignment
and length of the torque meter may
influence the pump vibration. During the
bidding stage, it is important to verify the
vendor's test facility. Sometimes, due to
limited space and access at the test area,
the test setup may have a flow regulation
valve close to the pump discharge flange.
Considering high discharge pressure, significant
turbulence is expected close to
the discharge flange due to throttling for
reduced capacity. Turbulence will induce
higher vibrations in the pipe and pump
casing, thereby increasing vibrations on
the bearing housing.
The site configuration will eliminate
such a force response if the suction
and discharge piping system is carefully
designed and installed. The risk
for resonance on the test stand should
be determined and analyzed. The rigid
foundation of the test stand should have
a suitable dampening effect compared to
the actual foundation.
Nozzles size and location. Suction
and discharge nozzle sizes should be
checked carefully. The vendor should
use the product's hydraulic range chart to
demonstrate that the duty points for the
80 DECEMBER 2021 | HydrocarbonProcessing.com
at the BEP. Locations of the suction and
discharge nozzles are also important to
mitigate the risk of vibration at the bearing
housing. The discharge nozzle of BB3
or BB5 is normally at the middle of the
casing with enough distance and symmetry
to both inboard (IB) and outboard
(OB) bearing housings. However, the
suction nozzles normally located near
the IB bearing housing have an effect on
the vibration of the IB bearing housing.
Operating deflection shape (ODS)
analysis. ODS analysis is the simplest
way to check and validate how a pump
and structure react during operation
condition. These shapes are used to determine
the effects on a structure of internal
and external excitation forces. ODS
analysis provides an animated view of a
pump and structure's motion at specified
frequencies. Data for the model are taken
for the structure under typical operating
conditions. ODS analysis for similar jobs
may provide good supporting documentation
at the bidding stage to confirm that
the proposed model has a proven design,
in terms of vibration.
Balance drum location. The location
of the balancing drum is important.
The rotor has additional damping due
to the balance drum. Other things being
equal, lower vibrations can be expected
on the bearing housing close to the balance
drum. Normally, the balance drum
is recommended to be located close to
the OB. Shaft vibration readings and
bearing housing vibration data for pumps
with a balance drum near the OB results
in IB vibration being greater than OB vibration,
for all operating points.
Recommendations. Practical mitigation
actions to minimize the risk of vibration
of BFW pumps during shop performance
or mechanical running tests
were reviewed.
ings and proximity probes (e.g., BFW
pumps) should have a vibration value
at the bearing housing and
shaft displacement probes
measuring within the allowable
limit of API 610 at all
points on the performance
curve during the factory test.
Shaft displacement probes
data should not be used as
the only basis for acceptance
or rejection of the pump during
the shop performance test.
An engineer should also ask the vendor
for a test experience list and vibration
data for the quoted model during the bidding
stage. The previous experience of
the vendor must be carefully reviewed,
validated and witnessed (when necessary),
and the engineer should check that
both bearing housing vibration and shaft
displacement probes data of the previous,
similar model were within API 610
allowable vibration limits.
ACKNOWLEDGMENTS
The author is very grateful to practitioners, field
and factory workers for sharing their experience.
Special thanks is also given to Mr. Mehrshad Rahimi
for the drafting figures.
LITERATURE CITED
1
American Petroleum Institute, API 670, " Machinery
protection systems, " 5th Ed., November 2014.
2 American Petroleum Institute, API 610,
" Centrifugal pumps for petroleum, petrochemical
and natural gas industries, " 11th Ed., September
2010, Errata, July 2011.
3
4
International Organization for Standardization,
ISO 10816-7, 1st Ed., February 2009.
Nelson, W. E., Pump Vibration Analysis for the
Amateur, Turbomachinery
Laboratories,
Department of Mechanical Engineering, Texas
A&M University, Texas, U.S., 1987.
5
Hydraulic Institute, ANSI/HI 9.6.4, " Rotodynamic
pumps for vibration measurement and allowable
values, " 2016.
SHAHAB ZARDYNEZHAD is a
registered Senior Mechanical/
Pipeline Engineer in Alberta
and British Columbia with more
than 29 yr of experience working
in the world's largest oil, gas and
petrochemical projects. He has
experience in engineering, procurement services,
manufacturing, shop/field inspection, installation,
commissioning, startup, reliability, maintenance
and operation of pumps, compressors and turbines.
He holds a BS degree in mechanical engineering
from the University of Petroleum of Iran, an MS
degree in industrial engineering from IUST Iran
and an MS degrees in mechanical engineering
and project management from the University of
Calgary in Canada. He is also a certified API
inspector for rotating equipment.
http://www.HydrocarbonProcessing.com
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