Page 57 - Root Cause Failure Analysis

48 Root Cause Failure Analysis
actual net positive suction head (NPSHA), lowering suction liquid temperature, or
increasing suction pressure. Depending on the type of cavitation, one or any combina-
tion of these corrective actions will eliminate the problem.
Once the short list has been generated, however, cost must be considered. Each poten-
tial corrective action should be carefully scrutinized to determine if it actually will
correct the problem. This is important because the normal tendency in less fonnal
evaluations is tofix the symptoms ofproblems rather than the true root cause. There-
fore, this phase of the evaluation should evaluate each potential corrective action to
ensure that it eliminates the real problem.

Howevel; on some occasions, correcting the symptoms or implementing a temporary
solution is the only$nancially justifiable course of action. In these instances, the rec-
ommendation should clearly define the approach that should be taken. It should out-
line the rationale for the decision and describe the limitations or restrictions that the
partial correction will have on plant performance, equipment reliability, and other fac-
tors of plant operation and maintenance.

Although the number of temporary fixes should be limited as much as possible, they
often are unavoidable. Every effort should be made to implement permanent correc-
tive actions, and the goal is to eliminate all negative factors associated with the event
or incident. While there generally is a corrective action that meets this goal, the chal-
lenge is to find the best acceptable action that also is cost effective.

COST-BENEFIT ANALYSIS
A full cost-benefit analysis is the final step before recommending a course of action. It
is needed to compare costs with the benefits derived from the corrective action(s)
being considered. For example, many machine failures are the direct result of misap-
plication. In these instances, the “best” solution would be to replace the machine with
one that was properly designed for the application. However, this solution usually is
very expensive and may require a major modification of the installed system.

A cost-benefit analysis is simply a direct comparison of the actual total costs associ-
ated with an activity (e.g.. replacing a pump or modifying a production line) with the
benejts to be derived from the change. The amount of historical data available deter-
mines the level of detail possible with such an analysis. If sufficient information is
available, the analysis should include all costs associated with the area, machine, or
system being investigated.

While this may sound straightforward, developing an accurate cost-benefit analysis
sometimes is very difficult. In part, this is due to the lack of factual, detailed historical
data for many of the machines and production systems within the plant. As a result,
much of the cost data, such as power consumption, repair costs, and repair intervals,
are not available to the investigator. Without this information, it is almost impossible
to fully define the current or historical cost of a production system or area.