hi,

I just want to know, Do I need to subject the vessel connected to the pipe for seismic analysis OR just the pipe only?

for seismic study I think you need to subject it to the whole system (pipe & equipment) as long as it is above ground.

Also, Do I have to evaluate the nozzle loads of vessel with seismic loadcase?

In my understanding No, in fact the nozzle evaluated for the operating load case, because you want to study the loads at the connected equipment for the long run (operating case) not for an occasional moment (seismic)

hopefully it's useful to you.

Regarding the second question (nozzle load evaluation with seismic loads), I think it depends on your project specifications. For example for the project I'm currently working for, it's mentioned in the relevant specs that occasional loads should also be considered for load evaluating. I suggest you to check your project requirements at first, afterwards you can decide whether not to consider the occasional loads for nozzle limit check.

P.S: Personally I think not considering the seismic loads for nozzle loads is not impeccable!

In this country we must consider seismic design for vessels, including the loads from attached piping. Wind is the same.

I have seen a lot of rework required when this is done correctly, for example not transferring the EQ loads from the piping down to the vessel base.