Pooria,

Rerun your FEATools run, but select the "FEA" option.

The B31J option uses the empirical equations published in the ASME B31J Standard. Empirical equations are approximate, FEA will get you closer to reality. FEPIPE and NozzlePRO employ FEA methods, therefore depending on the parameters of your model, B31J may or may not agree.