Page 351 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

CORROSION DAMAGE, DEFECTS, AND FAILURES 329

5.3.7.1 Functional Failure A functional failure is the inability of a system to
perform and satisfy a specified performance standard. A total and complete loss of
function is clearly a functional failure. However, it also includes the inability of a
system to function at the level of performance that has been specified as satisfactory.
To define a functional failure of a component or a system, a clear and total under-
standing of the functions of the system is necessary. It is very important to determine
all the functions of every item in the system that are significant in a given operational
context, as a functional failure can be defined only in these terms.

5.3.7.2 Potential Failure When a particular function has been defined, it is pos-
sible to identify the indication that the particular failure is imminent. Under these
circumstances, it might be possible or advisable to remove the suspected component
or system from operational service as it is only in these terms that the functional fail-
ure mechanism can be identified followed by its elimination. The failure that occurs
under these conditions is termed as potential failure.
A potential failure is a definite identifiable condition that indicates when functional
failure is imminent. The fact that potential failures can be identified is an impor-
tant facet of modern maintenance theory, as it permits maximum use of each system
without the consequences associated with functional failures. The units or parts are
replaced or repaired at the potential failure stage, so that potential failures preempt
functional failures.
In some cases, the identifiable condition that indicates imminent failure is directly
related to the performance criterion that defines the functional failure. The following
three factors help to identify either a functional or a potential failure.

1. Clear definitions of the functions of a component or a system as they relate to
the equipment or operating context in which the item is to be used.
2. A clear definition of the conditions that constitute a functional failure.
3. A clear definition of the conditions that indicate the imminence of the failure.

Thus it is not only important to define the failure but also necessary to probe the
exact evidence by which it can be identified.

5.3.7.3 Consequences of Failures There are many consequences of corrosion-
based failures ranging from minor failures of equipment, loss of productivity, minor
injuries to personnel, and as serious as loss of lives. Failure analysis is the conven-
tional method of relating a failure to its consequences as well as the lessons learned
from the failure along with the necessary steps and precautions to be taken to avoid the
future occurrence of similar failure. Failures may range from modest cost of replacing
a failed component to the possible destruction of a piece of equipment and fatalities.
The consequences of a failure determine the priorities of the maintenance or improve-
ments in design to prevent future failures of a similar nature and degree.
The more complex the design of the equipment, the more ways by which the equip-
ment is likely to fail. The four groups of corrosion-based failure consequences are the
following: