Calculating Equivalent Number of Inspections

The Equivalent Number of Inspections field is available on the baseline datasheets for the following Criticality Degradation Mech Evaluation families:

Criticality Env. Crack. Deg. Mech. Eval.
Criticality Ext. Corr. Deg. Mech. Eval.
Criticality Int. Corr. Deg. Mech. Eval.

The value in this field is calculated automatically based on:

The number of Inspections that you assigned to the associated degradation mechanism
The values that exist in the Inspection Confidence fields in those Inspections
The confidence equivalence factor (EF) that applies to those inspection confidence values

EF is determined as follows:

Equivalent Number of Inspections = (Very High EF x # Inspections with Very High Confidence) + (High EF x # Inspections with High Confidence) + (Medium EF x # Inspections with Medium Confidence) + (Low EF x # Inspections with Low Confidence)

Example

Suppose a Criticality Degradation Mech Evaluation is linked to six Inspections, where:

Two of those records contain the value Very High in the Inspection Confidence field
Four of those records contain the value Medium in the Inspection Confidence field

Tip: The Inspection Confidence field is not shown on the baseline Inspection datasheets. You can see the value by adding the field to the datasheet or creating a query that includes it.

Using the example with six Inspections (two Very High and four Medium), the equation would look like this:

Equivalent Number of Inspections = (Very High EF x 2) + (High EF x 0) + (Medium EF x 4) + (Low EF x 0)

Because two of the parenthetical components have a multiplication factor of zero (0), we can eliminate those from the equation, since the result would be zero (0). So, a simpler version of the equation would look like this:

Equivalent Number of Inspections = (Very High EF x 2) + (Medium EF x 4)

You can see from the equation that the number of inspections with Very High and Medium confidence (2 and 4) must be multiplied by the Very High and Medium equivalency factors. The following matrix is used to determine which equivalency factors to use.

	Very High Confidence	High Confidence	Medium Confidence	Low Confidence
Very High EF	1	N/A	N/A	N/A
High EF	0.333	1	N/A	N/A
Medium EF	0.111	0.333	1	N/A
Low EF	0.037	0.111	0.333	1

First, GE Digital APM determines the highest confidence among the Inspections that are included in the equation. In our example, since two of the Inspections have a Very High confidence and four have a Medium confidence, Very High is the highest confidence among those records. So, in the matrix, GE Digital APM finds the column containing the confidence level Very High. In the table below, this column is highlighted.

	Very High Confidence	High Confidence	Medium Confidence	Low Confidence
Very High EF	1	N/A	N/A	N/A
High EF	0.333	1	N/A	N/A
Medium EF	0.111	0.333	1	N/A
Low EF	0.037	0.111	0.333	1

The numbers in this column are then used to determine the equivalency factors to plug into the equation. So far, the equation looks like this:

Equivalent Number of Inspections = (Very High EF x 2) + (Medium EF x 4)

...where:

Very High EF is the value at the intersection of the Very High EF row and the Very High Confidence column.
Medium EF is the value at the intersection of the Medium EF row and the Very High Confidence column.

In this case:

Very High EF = 1

Medium EF = .111

You can see these numbers highlighted in the following table. Note that because their values are not used in the equation, the remaining columns have been removed from the table to simplify the example.

	Very High Confidence
Very High EF	1
High EF	0.333
Medium EF	0.111
Low EF	0.037

Understanding now how the Very High EF and Medium EF values are derived, we can now look at the entire equation again.

Equivalent Number of Inspections = (Very High EF x # Inspections with Very High Confidence) + (Medium EF x # Inspections with Medium Confidence)

Equivalent Number of Inspections = (Very High EF x 2) + (Medium EF x 4)

Equivalent Number of Inspections = (1 x 2) + (.111 x 4)

Equivalent Number of Inspections = 2 + .444

Equivalent Number of Inspections = 2.444

Because the final number contains a decimal less than 0.5, it is rounded down. So, the final result is:

Equivalent Number of Inspections = 2