Before you do the above, make SURE you equivalence your model in PATRAN. (Elements...equivalence..) This should solve your problem or reduce the number of failed ratios.
If your matrix/diagonal ratio is around the order of E+08 or E+09 then you can set that as a maximum which will allow your model to run and still get good results. NASTRAN has a smaller default ratio which wont allow it to run. Right now, your model is "soft" as we here like to call it... Add...
You can prevent the corossion by preventing chromium carbide formation. How? Add another element which is a stronger carbide former than chromium. I believe Mo is one of them. if you have any other questions or comments, let me know (manousa1@msu.edu).
The rust at the welds is a result of Chromium depletion on the weld boundaries. When heated (welded), chromium and carbon forms chromium carbide. Therefor, there is a depletion of chromium and chromium is a great corrosion retardant.
