Identification of Material Condition Measurements

DOESTD107393

measurements may be taken specifically for this purpose. Failure modes and effects analyses

(FMEAs) performed to support safe operation of the facility may be useful in identifying the failure

modes that have the most safety significance. In addition, the selection of ongoing maintenance tasks

for the component may have been based on actual experience and similar evaluations of the ways in

which significant failures could occur.

4.2.3.3 Identification of Material Condition Measurements

Practical measurements should be identified to monitor significant aging effects. As shown in Figure

45, the first step is to identify the physical characteristics associated with each significant failure mode

and corresponding aging mechanism. The emphasis should be on the physical characteristics

associated with stressors and aging mechanisms that have the most significant influence on a failure

mode (i.e., component or material properties most affected by the aging mechanism). Material

characteristics (e.g., hardness or dimensions) and electrical characteristics (e.g., electrical insulation

integrity) are examples of critical physical characteristics.

The next step is to identify the actual parameters to be measured or monitored for detecting the

presence and rate of degradation in a critical physical characteristic. To the extent possible, these

parameters should be direct measurements or observations of the previously identified critical physical

characteristics. A direct measurement is one that measures the actual critical physical characteristic,

such as material hardness when material hardness is the critical characteristic. Because some

physical characteristics are difficult to measure directly, validated indirect measurements may be

necessary. These indirect measurements should encompass characteristics that are as close as

possible to the critical physical characteristics. For example, vibration may be an indirect measurement

of wear; elasticity, as measured by an elongation test, may be an indication of electrical insulation

integrity. Visual observations, such as discoloration caused by heat and corrosion, may also be valid

indicators of physical degradation. The observable parameter should have been validated as an

accurate indication of the progress of a component or subcomponent to its point of failure. One or

more observable parameters should be chosen to monitor each critical physical characteristic.

Finally, the measurable and observable parameters for each component are brought together into a list

of practical measurements that can be performed to monitor significant aging effects. This list of

practical measurements provides the basis for obtaining baseline MCA measurements of component

material condition.

4.2.3.4 Baseline Measurements of Component Material Condition

Measurements should be made of significant aging effects to determine the current material condition

of life-limiting components to establish a baseline for determining the remaining lifetimes. These

measurements also form the basis for recommendations regarding periodic material condition

monitoring and trending to anticipate the end of lifetime that might be implemented during the ongoing

MCA phase.

4.2.4 DETERMINATION OF FACILITY REMAINING LIFETIME

The process for determining facility remaining lifetime is shown in Figure 46. The first task is to

determine the current condition of the component or subcomponents as indicated by the baseline

measurements plus the following historical considerations: time in service; usage or operational history;

stressor history or, if unavailable, a conservative approximation that bounds expected extremes and

maintenance and surveillance history.

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