Hydrocarbon Processing - September 2021 - 14

Reliability
A third rule of thumb is also worth
FIG. 4. Pressure-balanced constant-level
lubricator. Source: TRICO Manufacturing Co.
to one every 5.5 yr. Instead of an imputed
$3,000/yr, we now only spend $3,000 ÷
1.4 = $2,150/yr. We can be certain that a
$600 set of two advanced bearing protector
seals will last 6 yr = $100/yr. The payback
ratio is $2,150 ÷ 100, or about 20:1.
One-twentieth of 1 yr equals about 3 wk.
A second rule of thumb uses an exponential
approach. It assumes that if a
fully upgraded machine has a reliability
of 1.0, then a missed upgrade will lower
the machine's reliability (or life) to 90% of
1.0 = 0.9; two missed upgrades lower reliability
to 90% of 0.9 = 0.81; three missed
upgrades to 90% of 0.81 = 0.73; four
missed upgrades to 90% of 0.73, equaling
only 0.66, and so forth. We consider
this elementary rule of thumb rather optimistic;
reliability or operating life expectancy
with four deficiencies is probably
less than 50% of what would be achieved
with better bearings, better mechanical
seals, better couplings or whatever other
upgrades are available today.
Suppose, for example, that we had
requested the purchase of a $600 set of
advanced bearing protector seals after
hearing that a neighboring " Refinery X "
is routinely doing this for a critical pump.
We know that our critical pump has a
mean time between repairs (MTBR)
of 3 yr, and assume that Refinery X's
MTBR reaches 3 ÷ 0.9 = 3.3 yr. They, too,
spend money on pump repairs. We spend
$12,000 ÷ 3 = $4,000/yr, and " Refinery
X " spends $12,000 ÷ 3.3 = $3,600/yr.
Over a 6-yr period, we spend $24,000;
they spend $21,600. Their $600 upgrade
returns $2,400. Their mindset puts " Refinery
X " on the track to routinely do
these and similar upgrades. They either
are, or likely will soon become, a best-inclass
performer. Their market valuation
probably tells the story of doing things
smart and with forethought.
14 SEPTEMBER 2021 | HydrocarbonProcessing.com
sharing. Again, reasonable assumptions
are made; a probable 20% improvement
in failure avoidance, repair cost reduction
or life extension is thought to result
from each upgrade. In such upgrade examinations,
the first such initiative will
move equipment reliability from 1.0 to
1.2, a second (different) upgrade would
capture 1.2^2=1.44; further upgrades
yield 1.2^3 = 1.73, and 1.2^4 = 2.07. The
implementation of four proven upgrade
measures would cause the MTBR to be
extended two-fold. Yearly repair expenditures
would be 50% of what they were
before; employees previously involved in
repairs would spend time on repair avoidance
tasks. Safety would go up and community
goodwill would be given a boost,
as would worker morale.
Using pressure-balanced constantlevel
lubricators. In this example, we
opt for routine upgrades by (a) using
sets of advanced bearing protector seals
($600), (b) switching to extended-life
synthetic lubricants (incremental cost
of $200 per charge), (c) installing pressure-balanced
constant level lubricators
(FIG. 4) (incremental cost of $100) and
(d) purpose-designed stress-relieved (annealed
before final machining) brass or
bronze oil rings ($200). It would be reasonable
to assume that the four upgrades
totaling $1,000 will shift the asset's operating
life from 3 yr to 3 × 2.07 = 6.2 yr.
Suppose that our records showed it
costs $18,000 to repair the process pump
in this example, and repairs would be
made every 3 yr. Distributing $18,000
over 3 yr equals $18,000 ÷ 3 = $ 6,000/
yr. A one-time expenditure of $1,100
results in spending only $18,000 ÷ 6.2
= 2,900/yr. Prorated savings are about
$3,100 during each of the next 6 yr.
Near-term payback time will be $1,100 ÷
$2,900, which is less than 5 mos.
Where contaminants originate. Let us
return to our bearing protector seals and
an examination of where contaminants
originate. Moisture and dust often enter
bearing housings through old-style, ineffective
labyrinth seals or worn lip seals.
Moisture is airborne water vapor; it could
also be a stream of water from hose-down
operations. Contaminants frequently
enter through a breather vent, or from
the widely used non-pressure-balanced
constant-level lubricators depicted in just
about every pump text in print today.1,2
These references describe how abraded
oil ring material becomes an often-overlooked
source of oil contamination.
How to stop the contamination.
There should be no communication or
connection between the housing interior
and the surrounding ambient air. Breather
vents normally supplied at the top of bearing
housings should be discarded and the
threaded port fitted with the connector
shown in FIG. 4. Note that the traditional
open-to-surrounding-air constant-level
lubricator has been upgraded to the balanced
lubricator shown in this image.
Surprisingly, even the pressure-balanced
lubricator in FIG. 4 suffers from a
seldom-recognized water intrusion path:
the caulking that bonds the oil-filled glass
bulb to its support casting. Sooner or
later, caulking will develop tiny fissures
or cracks, allowing water to enter through
capillary action. This makes a compelling
case in favor of oil mist.
The use of a face seal, along with
recommendations such as deleting the
breather vent and using balanced constant-level
lubricators or upgrading to
oil mist2
will prevent the entry of virtually
all external contamination into the
housing. However, none of these measures
will avoid contamination from inadequate
oil rings and potential defects
introduced by an old-style bearing housing
protector seal.
LITERATURE CITED
1
Bloch, H. P., Fluid Machinery: Life Extension of
Pumps, Gas Compressors and Drivers, DeGruyter,
Berlin, Germany, 2020.
2
Bloch, H. P., Optimized Equipment Lubrication:
Conventional Lube, Oil Mist Technology and Full
Standstill Protection, DeGruyter, Berlin, Germany,
To be published December 2021.
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
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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