Life Cycle Cost & Reliability For Process Equipment Page 8
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22productive work output versus the work input such as (Actual Output)/(Name Plate Output). Utilization
is the ratio of time spent on productive efforts to the total time consumed such as (Actual Hours
Used)/(Maximum Hours Potential).
System effectiveness equations are helpful for understanding benchmarks, past, present, and future as
shown in Figure 4. This provides an understanding for trade-off information.
A
B
C
Best
Last
Last
New
Plant
Best
Plant
Parameter
Plant
Plant
Plant
New
B
Plant
*
?
Worst
*
Availability
0.95
0.95
0.98
C
0.3
0.4
Trade-off
Reliability
0.6
LCC
Area
Maintainability
0.7
0.7
0.7
Capability
0.7
0.8
0.6
Last
Best
?
Plant
Effectiveness
0.14
0.22
0.25
*
A
LCC
80
100
95
Effectiveness
Figure 4: Benchmark Data Shown In Trade-Off Format
Point A is preferred for cost compared to point B and point C. However, point C may be worth more
than point A, and if this is true, then point C is more desirable than point A or point B. Point B is
undesirable compared to point C and may not be worth the extra cost of point A.
ENGINEERING FACTS
LCC requires facts which are driven by data. Most engineers are of the opinion they lack data. In fact,
data is widely available as a starting point for LCC (Bloch 1994 and 1995). Often data resides in local
computer files but it has not been analyzed or put to effective use. Analysis can start with arithmetic and
grow to more complicated statistical details (Barringer 1995).
Follow the guidelines for each step listed in Figure 1, for working-out a typical engineering problem
shown below (remember, a single right or wrong method/solution does not exist--many methods and
routes can be used to find LCC). Substitute your own values determined by local operating conditions,
local costs, and local grades of equipment for your specific case.
Step 1: Define the problem.
An API pump will operating without an online spare at 100
horsepower, 1750 RPM, 250 psi, 500 gpm, 70% hydraulic efficiency, while pumping fluid with a
specific gravity of 1. At pump failure, the process shuts down and financial losses are incurred as each
hour of down time results in a gross margin loss of US$10,000/hour of outage.
Find an effective LCC alternative for maintenance strategies as the plant has an estimated 10 years life
and the plant will be sold-out during this interval. Find the most cost effective maintenance strategy from
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