FAQ for Corrosion Analyzer EVS
Frequently Asked Questions about OLI Corrosion Analyzer EVS
Question: I have a question about the input data for EVS. The second input is Area (sq-cm). What is this measurement? Is it the total area of pits on a given surface, is it the average surface area of a single pit, is it the fraction of surface covered by pits?
Answer: This is simply the area of the metal that is exposed to pitting. For example, if a coupon is exposed to an aggressive environment, then this is the area of the coupon. In a practical application, we may want to calibrate EVS using coupons with a relatively small area and then make predictions for larger exposed areas.
We do not include the area of pits in the analysis. The parameter that characterizes the pit is its depth.
Question: How then are the number of pits on that area (the surface density) accounted? Is it expected that ALL the pits identified in that defined area be entered into the grid, and not just a selection? I’ll ask Tracey Jackson or some other client-colleague to provide us with some example scans to see if what they measure is readily entered into the existing format.
Answer: If we would like to apply Extreme Value Statistic (EVS) we have not to know the “the number of pits on that area (the surface density)”. For each coupon we have to know only the depth of the DEEPEST pit measured at a given observation time. For example, If we have a coupon with the area A = 2 cm X 3 cm = 6 cm2. The only one thing that we have to know is the depth of the deepest pit on this coupon, let say Lmax = 100 μm at, let say, at t = 10 day. These are the only numbers that must be input into the OLI code.
The task to measure the number of pits (and their area) on some particular area is much more complicated
