Page 92 - Improving Machinery Reliability

64 Improving Machinery Reliability

Sneak analysis identifies the proper and improper operation of a system’s hard-
ware and software. The analysis provides a systematic, consistent, and thorough
review of the system’s current and logic paths, down to the individual statement and
component level. Sneak analysis is not restricted to critical functions (as are many
other analyses) but analyzes the complete system, function by function. The analysis
will identify the cause and recommend a solution to a sneak condition, design con-
cern, or document error before the problem occurs. If left undetected, sneak condi-
tions occurring during testing usually result in program delays to the project.
The sneak analysis process generates detailed functionally oriented patterns,
called network trees, of the circuitry and software that can be reviewed individually
or in groups to understand the system. These network trees not only make sneak
analysis possible, but are a powerful tool in reducing the cost and improving the
quality of other reliability and safety analyses, such as Failure Mode and Effects
Analysis, Hazard Analysis, Fault Tree Analysis, Common Cause Failure Analysis, or
Mean-Time-Between-Failure Analysis, which may be specified on a project.
The major benefits derived from the performance of sneak analysis are:

1. Savings of overall project dollars.
2. Increased confidence in system safety, reliability, and operability through inde-
pendent design verification.
3. Fewer system development delays.

Identification of sneak conditions early in the project life cycle can provide cost
savings as a result of changing a circuit or logic path on paper-rather than changing
actual hardware or software. Empirical data obtained after performing a sneak analy-
sis demonstrates that increased reliability and operability of the system occur when
corrections for identified sneak conditions are made.

Selecting a Pump Vendor

The broad principles governing the selection of major machinery vendors were
stated earlier in the chapter. How these principles can be applied most advantageous-
ly is again best illustrated in a typical example. Take pumps, for instance.
An up-to-date edition of Thomas Register of American Manufacturers will list
dozens of pages of pump manufacturers. Their detailed product listing contains
another 100 or so pages ranging from “Pumps, Acid,” to “Pumps, Wine.” Even after
reducing the potential bidder’s list to manufacturers of refinery-type centrifugal
pumps, there remain some 20-30 vendors who could be invited to bid on a given
project or for a given pumping service. Were all of them to be considered, much
time and money would be spent on preparing bid specifications, providing the neces-
sary vendor liaison, and finally evaluating the profusion of bids received. I
The need to limit bidding to a few capable vendors is quite evident. But what con-
stitutes capable vendors? What criteria should be applied to narrow down the selec-
tion to manageable size? How many bids are manageable? This segment of our text