HI

Can anybody elaborate the role of Pressure in the equipment modeling? as we are modeling equipment as rigid the how the pressure is effecting?
recently one of my stress system is rejected by the client ,the reason saying that pressure and thickness of the equipment is not modeled correctly and and it will effect the nozzle load.(I used Line pressure as equipment pressure)

i have tried the same model with different pressure and thicknesses,but the nozzle load is same for all

Your client is incorrect. Pressure has no influence on a rigid body.

Thickness does however have an influence. Maybe that's what he had in mind. Stifness is also a factor to be recognised. As I recall it, Caesar II models a rigid body by multiplying the wall thickness by 10. This is a good approximation since nothing is infinitely rigid, and it serves well for valves, pump bodies etc. That said, a small diameter and thin wall 'rigid' body may notable lack rigidity.

As far as I know, below is the logic of rigid element weight.

Rigid elements stiffness will be determined by the adjusted wall thickness.(10 times of inputted wall thickness), and the total weight of rigid element will be sum of inputted rigid weight and fluid weight, 1.75*insulation weight, refractory weight.
However if the weight is '0', it will be zero regardless of any input data.

Wonder if I used weightless rigid to determine thermal displacement at the nozzle by modelling equipment and the nozzle, thickness affects the result. Since stiffness will be decided by the thickness. Nozzle loads shall be differ.

Thickness will not affect axial thermal growth. You are correct, the thickness affects the stiffness. However, we're after relative stiffness here, by that I mean the stiffness of the rigid should be much larger than the pipes connected by the rigid.

Remember, we really have no idea what the cross section of the rigid body is. The concept of the "10 * thickness" means that a 6" rigid is stiffer than a 4" rigid, but not as stiff as an 8" rigid - all of which would be stiffer than pipe elements.

In the case I use '0' weight rigid to calculate the nozzle displacement, nozzle loads are only reaction forces of displacement at the nozzle and the rigid thickness won't have any effect on nozzle loads. Unless I give specific stiffness at the anchor restraint.

I had had a test, changing thickness of weightless rigid, but the result(in this case, nozzle loads) was same.

Also, I do understand concept of 10times of thickness. Maybe that's the reason stress result of rigid and pipe connection is 0. Since we cannot know the exact 'I(or Z)'.

Hope I understand correctly.

In the case I use '0' weight rigid to calculate the nozzle displacement, nozzle loads are only reaction forces of displacement at the nozzle and the rigid thickness won't have any effect on nozzle loads. Unless I give specific stiffness at the anchor restraint.

I had had a test, changing thickness of weightless rigid, but the result(in this case, nozzle loads) was same.

Also, I do understand concept of 10times of thickness. Maybe that's the reason stress result of rigid and pipe connection is 0. Since we cannot know the exact 'I(or Z)'.

Hope I understand correctly.

Correct, stresses on rigid elements are set to zero purposely, since the cross section is unknown.