Doing an EVA

Doing the EVA.

You are ready to start the Extreme Value Analysis when:

• EVA is activated;
• The CMLs have measurements;
• The Nominal WT and Renewal thickness are filled in for all the CMLs with measurements; and
• The Equipment has a start date.

(See Preparing for an EVA.)

Open the EVA Page

To open the EVA page:

• Click on the EVA button.
  EVA button.
   
• You are directed to the EVA page.

Define Stratification(s)

Note: It is recommended to use 20-30 tubes per Stratum. More than this can lead to non-conservative estimates.

To define the Stratifications:

• First, create a Default Stratum for all CMLs:
  • Select the CMLs in the CML grid or hold <Ctrl> and select the CMLs directly from the HX Overview.
  • Click the Stratification button on the CML toolbar (small EVA icon) & fill in the New stratum name. 
  • Click Confirm.
    Stratification button.
    
    Stratification window.
     
• Look at the Histogram below the CMLs (and change the Step Value if desired). This gives an indication of the measurement spread. 

• If required, create more Stratums:
  • Select desired CMLs.
  • Click the Stratification button to define / redefine a Strat.
• Review the Histograms (per Strat) again.

Histogram with homogeneous data. You can change the Step value.

 

Run the EVA Calculations

To run the EVA calculations:

• Press the Calculate button at the top of the EVA page.

EVA Calculate button.

 

• IMS will fit a Gumbel distribution for every Strat and do an extrapolation in space.
• When the calculation is done, the EVA Calculation Charts grid will be populated - one row for each Strat, showing CR, etc.

Review the Results

Now it is time to review the results.