Dear Naderi,

Your observation is correct. The program assumes that a X-direction force (axial) for a horizontal vessel is a non-operating force such as a heat exchanger bundle pullout force or transportation force. Chances of the worst wind/earthquake occurring at the same time are very rare. As typically done in the these calculations maximum of these conditions is taken.

But, if you have a large loads acting on a nozzle located on the head of a horizontal vessel. Then this operating force should be added to Wind/Seismic. In this case you can use the workaround suggested by Mahesh.

We will try to address this in the software. One thought is to use check boxes on the Loads Dialog that indicate if a particular load needs to be combined with Wind/Seismic.

Btw, what is source of the X-forces that you are applying to the vessel?