i have a long vertical line giong to top of a very high vessel.

at bottom line there is a rest (see attached file, node 2622) having operative load -9495N

in node 2715 there is a constant spring used to unload node 2622 (9000N costant).

the problem is the Hydro scase:
the spring is seen as rigid and is like a vertical stop. So the 2622 node is high loaded (-91180N) while in spring node i have the opposite load (+85958N).

I can tell "during hydro don't istall the spring".

but how can i implement it in caesar model?

i can't set "hanger stiffness" to "ignore" bacause i would false all the other spings (in the model there other springs, in attached file i deleted the other connected pipes). and i don't want to make a second model only for hydro test analysis.

how can i solve it?

Add a displacement of 0.0001 at that location, just for that load case, perhaps.

you mean: add the 0.0001 displacement in the hanger point?
maybe i have to set a displacement 0.386mm because if i delete the hanger , the point where was the hanger in hydro moves vertically 0.386 mm.

what do you think?

maybe you can deactivate Bourdon

I'm not sure Caesar will let you displace anywhere you have a restraint and possibly a spring, so I'd put it nearby... say one of the welds on the elbow if it's on a bend... or a node that's a convenient distance above or below it.

I think a displacement of any value is fine so long as you have a good reason for it.

0.001 assumes you're throwing in a temporary support.

If you find you don't need the support, then it sounds like if you put in a displacement of 0.386 to represent sag, you still have 2 different models - you're just choosing to "delete" the one you calculated the 0.386 value.

A question. In hydro spring are seen as rigid and this us the problem origin. In real world also if in hydro you spine the spring, the spring rod, long about 1500mm, will bend the 0.386mm and the spring will raise, not acting as a limit stop. So maybe the forced displacement near spring in hydro case can simulate this thing. And is real and right. What do you think?

Ultimately, that's a question for the spring manufacturer, but I'd be inclined to say no.

I would expect the pin to be in shear, not bending.

The shear modulus for typical carbon steel is around 82 GPa.

Assuming a 20 mm diameter rod, one shear location (though I expect you'd have 2 shear points on the rod), you'd need around 1e7 N to shear 0.386mm.

But if you can find the distance from the outer casing to the inner column, you might get a better answer.

And I'm uncertain of this point, but it's not clear to me right now that you *must* have the springs locked during a hydrotest. I would check procedures to verify if it's permissible to do release them.

I've just never had an issue with hydrotest failures with rigid springs before.

the 0.386mm were caused by bourdon effect. i disabled bourdon and now spring hanger load in correct.

BUT....

what if for some reason bourdon effct shold remain activated?

the problem is that caesar change springs in rigid supports during hydro test.

maybe it would be interesting to have a setting in spring "let it working during hydro instead of making it rigid", so to choose spring per spring what you like more.

so I was right
or "told you so"
it really depend on what pressure you have. There are some good posts regarding the subjects.
Also the term Bourdon effect is not really related to the translation.
I would rather say pressure elongation. The Bourdon effect is about the rotation due to oval section.
There are the pressure gauges that use this effect.
Regards,

I don't think I've heard it described this way before, but that makes sense.

I think of it as the tendency of any shape containing pressure attempting to resolve into a sphere of outward expansion.

It's possible to have pressure contraction, too. Consider the case of a rubber expansion joint bulging outwards faster and then drawing the ends inwards. But I doubt we'll see too many balloons installed as piping components, so it probably doesn't make a presence in this line of work.

Actually I am a mechatronic robotics engineer that fate gave me stress assignments not having so much robots to design . So in my time in university I have learned about Bourdon effect as being what I said. That a circular shape of an oval section tube will tend to open when subject of pressure. But this was because an oval section tend to become a round section under the pressure effect. In order to have this Bourdon effect you need to have a heavy out of round section, otherwise the effect is not important. Now if you read also the Coade explanations it will tell you the same that this effect is not really obvious unless if you have a "very" oval section or you have a very big pressure. The thing is that people tend to apply just to be on their opinion on the safe side. Who am I to disagree. I can only say my 2c.

"Actually I am a mechatronic robotics engineer that fate gave me stress assignments not having so much robots to design "

ehm... i am your twin