Be very careful with this one. The API-650 Appendix P Nozzle Flexibility computation is for <em>low tank nozzles</em>, i.e. nozzles on the lower part of the shell.

The references for Appendix P discuss the instrumentation and full scale testing (with subsequent FE verification) of two large tanks, with diameters over 100 ft. The nozzles were located on the shell.

I do not believe you can apply Appendix P to your roof nozzles. I think you're going to have to build / analyze FE models to determine your flexibilities. Once you have these, yes you can input them into CAESAR II to model flexible anchors.

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Regards,
Richard Ay (COADE, Inc.)