Hydrocarbon Processing - August 2021 - 12

Reliability
HEINZ P. BLOCH, RELIABILITY/EQUIPMENT EDITOR
Heinz.Bloch@HydrocarbonProcessing.com
ARC spring dampers eliminate compressor instability
A recent book1
describes novel approaches
in applied process gas compressor
technology. Among its many
topics, the book1
where compressor rotor instabilities can
originate, but also how permanent fixes
can be designed in from the start and/or
retrofitted after a failure event.
Prior art often includes squeeze film
damper bearings (SFDs); their underlying
principles resemble the well-known
shock absorbers in motor vehicles. Although
SFD bearings will often prove
successful, reliability-related concerns
may exist for the elastomeric O-rings installed
in most SFDs. Static O-rings will
degrade over time due to the loads imposed
by the weight of a rotor assembly.
It follows that most forms of degradation
reduce the effectiveness of the SFD; all
too often, such degradation forces an unforeseen
shutdown. This brings us to the
analogy of shock absorbers plus springs,
as used in motor vehicles.
highlights not only
In large compressors, O-ring degradation
effects are mitigated by designs that
incorporate an ARC spring damper inside
each bearing. An ARC spring damper
serves to support and center the SFD,
although the now lightly loaded O-rings
remain in place. FIG. 1A-FIG. 1D show the
sequence in which an ARC spring was
installed to become part of the overall
SFD bearing assembly.
In many recent applications of ARC
spring technology, the novel add-on
damper supports were designed and
manufactured by the compressor manufacturer-in
this instance, DresserRand,
a Siemens company located in
Olean, New York. In several other compressor
applications, BRG Machinery
Consulting LLC assisted in advancing
the ARC spring damper design by using
analytical methods and participating in
validation tests.
Once installed as shown in FIG. 1, ARC
springs eliminated virtually all the rotor
and bearing loads on the O-rings, thereby
greatly improving the overall reliability
of the system. Wired for instrumentation
(FIG. 1C and FIG. 1D), a series of rigorous
tests provided proof that all three design
objectives had been reached by adding
well-engineered ARC spring technology
to the traditional SFD geometry:2
* The basic SFD oil film design
should be kept the same
* The ARC spring damper should
be designed soft enough to allow
motion, yet strong enough to center
the bearing cage shown in FIG. 1
* The ARC spring should be
sufficiently robust to avoid
fatigue failure.
Combining the subject ARC spring
with squeeze film dampers in modern
compressor bearing systems was demonstrated
to be a complete success. It
constitutes a permanent remedy to previously
encountered instabilities that had
led to severe compressor failures.
LITERATURE CITED
1
Elliott, H. G. and H. P. Bloch, Compressor
Technology Advances-2020 and Beyond, DeGruyter
Publishing, Berlin, Germany, 2021.
2
Kuzdzal, M. J. and J.F. Hustak, " Squeeze film
damper bearing experimental vs. analytical results
for various damper configurations, " Proceedings
of Texas A&M University Turbomachinery
Symposium, 1996.
HEINZ P. BLOCH resides in
Montgomery, Texas. His
professional career commenced
in 1962 and included long-term
assignments as Exxon Chemical's
Regional Machinery Specialist
for the U.S. He has authored or
FIG. 1. Installation of an ARC spring damper.
12 AUGUST 2021 | HydrocarbonProcessing.com
co-written more than 780 publications, among them
23 comprehensive books on practical machinery
management, failure analysis, failure avoidance,
compressors, steam turbines, pumps, oil mist
lubrication and optimized lubrication for industry.
Mr. Bloch holds BS and MS degrees (cum laude)
in mechanical engineering from Newark College
of Engineering (NCE). He is an ASME Life Fellow and
was awarded lifetime registration as a Professional
Engineer in New Jersey. He is one of 10 inaugural
inductees into NCE's Hall of Fame, which honors
its most distinguished alumni.
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