Dry Gas Seal Failure due to Axial Sub-synchronous Vibration
on a Hydrogen Recycle Gas Compressor.
Robert C. Eisenmann, Jr. - BP Machinery Advisor
Luis Santos-Gutierrez – Rotating Equipment
Engineering Superintendent
Bio: Robert C. Eisenmann, Jr.
Currently the BP Refining Machinery Advisor and Downstream
Segment Engineering Technical Authority (SETA) with Refining
Technology and Engineering based in Houston, Texas. He provides
technical advice to the BP global refining portfolio to support
business delivery, company strategy, industry direction, and
technical assurance to support business decisions. He also promotes
technology solutions and development and implementation of best
practices across the BP refineries. He is currently the API 618
Chairman, API 692 Chairman, serves as a SME for BP’s Engineering
Technical Practices and has been a member of the Texas A&M
Turbomachinery Advisory Committee since 2012. Bob has over 25
years of experience in the industry. Bob graduated from Texas A&M
University at Galveston in 1992 with a B.S. in Marine Engineering.
Bio: Luis Santos-Gutierrez
Currently the BP Rotating Equipment Engineering
Superintendent at the BP Whiting Refinery in Whiting, IN. He
leads the rotating equipment engineering team and acting
subject matter expert for process rotating equipment at the
site. Luis is responsible for the Life Cycle Management of the
refinery’s rotating equipment fleet and delivery of the
rotating equipment strategy .
Luis has over 18 years of experience in the industry in various
machinery engineering and project commissioning
roles. He is a graduate from the University of Puerto Rico at
Mayagüez with a B.S. in Mechanical Engineering.
Abstract
Approximately 6 months after commissioning a new hydrotreater
hydrogen recycle gas compressor the site experienced a dry
gas seal failure. The investigation revealed wear of the primary
seal dynamic sealing element due to movement thought to be
caused by design and installation issues. The onset of a second
failure indicated the root cause had not been identified. Further
investigation discovered the compressor was experiencing high
axial vibration during operation ultimately causing the seal
failures.
This case study will present the data from each failure,
monitoring methods used, analysis conducted, options
evaluated and the corrective action taken to resolve the
problem.
Hydrogen Recycle Compressor
• Commissioned in November 2013
• Motor/Gearbox/Compressor Train
• 12,500 hp (9.325 MW) 4 pole synchronous motor (1800
rpm)
• Speed increaser gearbox with 12,733 rpm output
speed
Hydrogen Recycle Compressor
• Motor /Gearbox/Compressor Train
• Commissioned in November 2013
• 12,500 hp (9.325 MW) 4 pole synchronous
motor (1800 rpm)
• Speed increaser gearbox with 12,733 rpm
output speed
• 7 stage straight through centrifugal barrel
compressor
– Gas MW range from 2 MW to 5.3 MW
– ~ 1840 psi (127 bar) suction pressure
– ~ 2200 psi (152 bar) discharge pressure
Tandem Dry Gas Seal with Intermediate Labyrinth
• Flow control
• Gas Conditioning Secondary Seal
Unit (GCU) Primary Vent Gas Supply Secondary Vent
• Fully
instrumented
system Seal Gas
• Secondary seal
gas
• Primary vent
backpressure
Intermediate Cavity
controlled
The First Outboard Dry Gas Seal Failure
• Initial failure was detected 4 months after initial
commissioning.
• Vent flow and control valve position changed over
time indicating a degrading seal.
• Outage occurred in July of 2014 (~6 months of
operation).
• Seals were replaced, failure investigated.
Increasing Vent Flow
• 1st Noticed
Failed “J” Ring and spring holder
10
Leak Path after J ring damage
Conclusion of 1st failure investigation…
• PTFE J-ring failed due to fretting and
accelerated by:
– Contamination/debris
• Amplifier did not function during a
previous unit shutdown
– Swash (axial movement)
• Indication of incorrect contact on nut
assembly
Actions taken from 1 st failure
• Perform lapping and contact checks on the seal
sleeve to locking nut to ensure perpendicularity and
avoid potential for “swash”
– Bluing showed 85-90% contact
• Perform run-out check on thrust collar to ensure that
no axial run-out
– Run-out found to be <0.0005”
• Seal gas booster was replaced
– PM established to test functionality of seal gas booster
The Second Outboard Dry Gas Seal Failure
• Machine ran for 7 months with no issue.
• At 7 months noticed that vent flows and control
valve position of outboard seals started changing
indicating a degrading seal.
• RCA was re-initiated.
• Outage occurred in Fall of 2016 (~27 months of
operation) to implement solution and address
degrading seal.
• Same failure mode as first failure
Primary seal vent trends for 2nd run
2nd Failure Investigation
• June 2015 axial probes
were configured to
collect vibration
• Discovered sub-
synchronous axial
vibration around half
running speed (110Hz-
125Hz ) with peaks up to
2.5 mils (0.0635 mm/sec)
• This finding shows that
axial shuttling is
happening under normal
operation causing
accelerated wear on
PTFE J ring.
Solution Option
• Texas A&M paper by Scan DiCamillo; Kingsbury
discussed axial vibration due to lightly loaded thrust
bearings
• Test was conducted in order to manipulate
– Increased and decreased oil pressure
– Increased and decreased oil temperature,
– Temporarily shut off coupling cooling oil spray
• Testing had minor influence on axial vibration
frequency and amplitude
– Largest response was when coupling cooling oil spray
was shut off
Defect Elimination: H2 Recycle Compressor @GOHT
• Installed new pre-loaded
thrust bearing in 2016
(Bearing with o-ring
dampner)
• Axial vibration was reduced
over 75% during normal
operation.
• After 1 year of operation axial
vibration has not increased
from startup condition.
Current Spectrum – Minor Low Frequency Noise
Lessons Learned / Follow up actions
• Ensure H2 recycle compressors thrust bearing load is
adequate to full range of conditions
• Axial vibration should be monitored at OEM FAT to
determine if the issue is present
– Company specification was modified to require monitoring axial
vibration during acceptance tests with acceptance criteria.
• Axial vibration should be checked/monitored in the field
