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)

Important

At least one Stratum is required to do an EVA calculation.

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.

Important

For each Stratum one should aim for a homogenous spread, i.e., only CMLs or tubes subject to the same Degradation Mechanisms and thus corrosion behavior.

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.