Chemical Engineering July 2013 - 42

Feature Report
discover failure
and remove
from service
Teardown
FIGURE 6. Downtime represents one of
the most significant and costly issues
for many processes
waste material have to be disposed
of, but piping, insulation and flooring
may have to be decontaminated
or treated as hazardous waste.
Other costs of decommissioning
include dismantling of equipment,
waste disposal of chemicals (unused
chemicals,
water-treatment and
cleaning chemicals, as well as those
in above- and below-ground tanks,
evaporation ponds and contaminated
pipes).
Costs of downtime
Process downtime is one of the most
significant and costly issues for many
processes. To properly take into account
the costs of downtime over the
life of the process, engineers must
estimate how much cost is accrued if
the process fails, either in whole or in
part. Further, once it fails, the question
becomes how long will it take to
restore operation?
In terms of equipment selection and
design, which equipment and design
features will be less likely to cause
downtime? Which will be most easily
maintained? How quickly can an
expected failure be repaired so the
equipment can be put back in service?
The risks and costs of process downtime
can be considered in a semiquantitative
form by examining the
likelihood of an event occurring in a
given time period and the cost per unit
time of that failure.
Downtime Cost = frequency of
failure/year
x downtime/days
x $ losses/day
Downtime starts with the failure of
the equipment and stops when it is
put back in service. Better maintenance
training can reduce the diagnosis
and repair time significantly. The
basic sequence is the discovery of a
failure, followed by teardown, diagnosis,
obtaining parts, repair, restart and
monitoriing (Figure 6).
$100
$1,000
$10,000
Cost of event
FIGURE 7. A matrix can help quantify the costs of downtime in a process
One factor with a great impact on reducing
downtime is the availability of
parts. The parts may be common, such
as O-rings or gaskets, seals or bearings,
or they may be less common, such as
pump housings or drive shafts.
If a complete shutdown costs
$100,000 per day, the expected frequency
of a catastrophic shutdown
three times per year is a total of
$300,000. For a non-critical failure
that reduces productivity, but does
not shut down the process entirely,
an event cost of $50,000, with a frequency
of five times per year would
total $250,000 (Figure 7).
The following examples (Figure 8
and Table 1) emphasize maintenance
training and parts availability in the
prevention of downtime. Suppose the
additional cost of training and parts
is $80,000. With downtime cost at
$20,000 per day, the investment of
$80,000 saved $86,000 compared to
without the training and parts after
just one outage event.
In a second example, a $70,000 design
feature reduces downtime by making a
routine and expected part replacement
faster, from three days to one day. Over
40 CHEMICAL ENGINEERING WWW.CHE.COM JULY 2013
the 10-year life of the process, the saving
is $890,000.
Those examples represent the costs
of just one critical unit operation and
one design feature. When considering
similar analyses across an entire
plant, the cost savings can be substantial.
The conclusion of the above
is that a relatively small upfront investment
may save considerable cost
in the long run.
NEW, USED, REFURBISHED?
There is a saying that all process
plants run on used equipment, and
that is true. The LCC analysis is not
prejudiced with regard to used or refurbished
equipment - LCC considers
the balance of downtime prevention
and investment in equipment and preventative
maintenance. If you know
your process requirements and have
the resources to keep used equipment
functioning as reliably as necessary,
then used or refurbished equipment
is the right choice. There are several
LCC issues to consider when deciding
between new, refurbished and used
equipment.
Not all buyers are in a position to
$100,000
$1,000,000
5
4
3
2
1
$500
$400
$300
$200
$100
$5,000
$4,000
$3,000
$2,000
$1,000
$50,000
$40,000
$30,000
$20,000
$10,000
$500,000
$400,000
$300,000
$200,000
$100,000
$5,000,000
$4,000,000
$3,000,000
$2,000,000
$1,000,000
Dagnosis
Obtain
parts
Repair
Restart
Monitor
Events per year
http://WWW.CHE.COM
Chemical Engineering July 2013

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