The minimum wall thickness check is simply that, a "check". The value computed according to equations 3 and/or 4 has no effect on any other computation performed by CAESAR II.
For Table 104.1.2, if you're using one of the basic generic materials (1 through 17), then CAESAR II knows which row of the table to refer to. If you're using the material database (materials 100 and up), the "type" of material is unknown. In this case, CAESAR II defaults to the "ferric" row of the table.
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Regards,
Richard Ay - Consultant