Developing the LA matrix in detail starts with identifying the locations. This starts with "Environmental Definition" and "Material Definition" from the CBDA. The objective here is to define specific locations on the subcomponent where the material-environment combination is the most severe or the most likely to sustain early or extensive corrosion. Such locations occur at crevices, welds (and their associated structure including heat affected zones and highly stressed regions), under deposits, at flow variations, locations of high residual stresses associated with bends and deformations, high heat transfer (output side) or high heat transfer resistance (input side), and other locations of potentially high reactivity.
Identifying these LAi is best undertaken by an interdisciplinary team including those familiar with fabrication, corrosion, metallurgy, stress, and fluid flow.
In the beginning it is easier to identify more sites since they can be eliminated later as the evaluation process starts. However, some nominally innocuous conditions may be more reactive than first thought or may be more important to one discipline than another.
After the LAi are developed, the array of modes based on the "Mode Definition" step of the CBDA is identified to head the columns. Again, these may be more extensive initially partly because the different LAi may require different modes to be considered and partly because there may be questions initially that are better left open than reaching closure prematurely.
Lifetime Prediction, Roger W. Staehle, Adjunct Professor, Department of Chemical Engineering and Materials Science, University of Minnesota, Staehle Consulting Co.