Page 316 - Improving Machinery Reliability

286 Improving Machinery Reliability

failure rate that is the reciprocal of MTBF) for exponential failure modes. Also
reliability may be the product of many different terms such as

R = Rutilities * Rfeed plant * Rprocessing * Rpackaging * Rshipping

and similar configurations. To the user of a product, reliability is measured by
problem-free operation (resulting in increased productive capability while requir-
ing fewer spare parts and less manpower for maintenance activities, which results
in lower costs). To the supplier of a product, reliability is measured by completing
a failure-free warranty period under specified operating conditions. Improving reli-
ability occurs at an increased capital cost but brings with it the expectation for
improving availability, decreasing downtime and associated maintenance costs,
improved secondary failure costs, and results in a better chance for making money
because the equipment is free from failures for longer periods of time.
Maintainability deals with duration of maintenance outages or how lung it takes to
achieve the maintenance actions compared to a datum. The key figure of merit is
often the mean time to repair (MTTR), which measures the ease of maintenance
upon failure. On a qualitative basis, it refers to the ease with which hardware or
software is restored to a functioning state. On a quantitative basis, it has probabili-
ties as described for availability and is measured based on the total downtime that
includes all diagnosis, troubleshooting, teardown, removal/replacement, active
repair time, verification that the repair is adequate, time delays for logistic move-
ments, and administrative maintenance delays. Maintainability is different than
repairability which is the probability a failed item is restored to operable condition
within a specified active repair time.
Capability deals with productive output compared to inherent productive output,
which is a measure of how well the production activity is performed compared to
the datum. This index measures the systems capability to perform the intended
function on a system basis. Often the term is synonymous with productivity, which
is the product of efficiency times utilization. Efficiency measures the productive
work output versus the work input; whereas, utilization is the ratio of time spent on
productive efforts to the total time consumed.
Dependability is the product of reliability and maintainability. It measures how lung
things perform. Related issues about nonoperational influences are not included..

System effectiveness equations are helpful for understanding benchmarks, past, pre-
sent, and future status as shown in Figure 5-10 for understanding trade-off information.
The lower right-hand corner of Figure 5-10 brings much joy and happiness often
described as “bang for the buck.” The upper left-hand corner brings much grief. The
remaining two corners raise questions about worth and value. The system effective-
ness equation is useful for trade-off studies as shown in the attached outcomes in
Figure 5-1 1.
System effectiveness equations have great impact on the LCC because so many
decisions made in the early periods of a project carve the value of LCC into stone.
About two thirds of the total LCC are fixed during project conception even though