EVA - Overview

Methodology Overview

EVA (Extreme Value Analysis) is a statistical method to calculate the maximum Wall Loss, from a smaller representative sample, e.g. for a HX (Heat Exchanger). It involves:

• Taking Wall Thickness readings from a representative sample (e.g. selection of HX tubes)
• Fitting a distribution (IMS fits Gumbel) on the data;
• Extrapolating the max Wall Loss in space (determine max Wall Loss for the whole HX); and
• This enables the user to Extrapolate the max Wall Loss in time (use IMS to predict the Wall Loss over time and determine the NID (Next Inspection Date)).

The EVA methodology and calculations are explained further in Appendix: The EVA Methodology.

Note: The software is aligned and can be used together with the Shell Recommended Practice: Shell | Asset Management System MEC – Inspection of Heat Exchangers Recommended Practice (Version MEC_RP_04-04.20_v1). 

Software Overview

This online manual explains how the above methodology can be implemented in the IMS software. 

When performing an EVA on a HX, you can refer to the following high-level workflow and flow chart. This outlines the flow in IMS. Take note that some preparation is required before one can start doing an EVA.

High-level workflow in IMS.

 

After EVA has been enabled for a Circuit and the CMLs created, this flow applies.

EVA Tutorial Video