Hi experts,

Just want to know how do i model untied universal with slotted hinge arrangement in CAESAR II?

I can neglect the pantograph modeling at this moment during preliminary design.

I doubt there's a one-size-fits-all description to cover all scenarios. I'd suggest posting documentation what yours looks like, with permissive/restritive loads or movements with stiffnesses defined.

With that said, such an expansion joint would generally be modeled like any other expansion joint, except perhaps:

1. You might model the end connected by a restraint-cnode to pipe that features x, y, z, rx, ry, rz,
2. You may have limits on dx, dy, dz, drx, dry, drz OR fx, fy, dz, mx, my, mz OR both, which may be anisotropic in nature.
3. Slots may mean you also have anisotropic gaps in your x, y, z, rx, ry, rz restraints.

Thanks Michael for your response.

Can you/other experts please confirm that the bellow model with cnodes are correct or not considering untied universal with slotted hinge.

Pantograph effect is ignored at the moment.

Thanks

Node 10-20 is length "L," the length of the expansion joint.

Node 10 has restraints x with gap, y, z, rx, ry, and rz. They are all CNODEd to node 11. Rz may potentially be removed. Verify with manufacturer if the pantograph is permitted to be rotated along the 2 bolts on the end and in the center at the gimbal. All others, except x with gap, may have a manufacturer stiffness. Check with manufacturer. x with gap does not have a stiffness - or rather, it has unlimited stiffness, because it's assumed once the slots run out to their ends, then they shouldn't allow further extension/contraction.

Node 20 is the same except for CNODEd to 19.

Node 11-19 is rigid element also with length "L." There may be additional design considerations at play. It might be considered frictionless or intentionally friction-acting. Seek clarification from the manufacturer.

But I'm going to assume frictionless, and thus suggest there are no further actions to be had.

Thanks Michael for your response.

I just want to know that

1. You mentioned that Check with manufacturer. x with gap does not have a stiffness - or rather, it has unlimited stiffness........
I think that the bellow stiffness in axial direction will take care.Right?

2. pressure thrust effect at the centre of the expansion joint and simulation of the weight of the centre spool at pantograph gimbal location...Whether i need to consider any axial restraint with cnode at the centre also.

1. Applying a stiffness to the axial direction - x - with a gap will instruct caesar to ignore all stiffness until the gap condition is met, after which the stiffness is what you specify. After the gap condition is met, the stiffness now acts like a spring, but specifically not like friction. It'll spring back.

My interpretation of the design is if you blinded off either end and pressurized it, the expansion joint would provide almost no resistance to the pressure thrust up until the slot condition is met. Depressuring it will do nothing until it pulls a vacuum, after which it'll provide almost no resistance to contracting.

I would expect that from an expansion joint loading perspective, using unlimited stiffness after the slot condition is met is conservative.
I would expect from a nozzle loading perspective, using unlimited stiffness is non-conservative, but reasonably accurate.

2. Unless I misunderstood something and the gimbal is somehow a fixed point in space, I don't see it needing special consideration. My understanding of the mechanism is the gimbal is fixed to the center of the expansion joint, but that doesn't factor into the expansion joint simulation in CAESAR.

If the gimbal IS a fixed point in space (and not just a fixed point relative to the inner cylinder), please advise and we'll work from there.

In CAESAR, and expansion joint has forces that come out either end, which expands/contracts the expansion joint according to its axial stiffness, minus the amount that gets subtracted out the ends due to the stiffness of elements beyond nodes 10 and 20. Since we're assuming there is no axial stiffness to the expansion joint, it'll be up to the pipe to decide if P*A will move it and the slot conditions are met.

Thanks for your response.

However, i found that since my configuration is somewhat matching with the attached EJMA configuration I checked with including the 2 pairs of hinge expansion joint to get rid of pressure thrust & slotted hinge gaps etc.

Whats your/other experts experience say using 1 hinge joints pair for regenerated catalyst standpipe & riser & 2nd hinge joint pair on spent catalyst stand pipe with Jbend connected to regenerator.

I agree that the EJMA diagram proposed will eliminate pressure thrust amongst most EJs, provided the EJs are identical and there's no pressure isolation device in between.

I don't envision running into problems unless you're altering an existing failing design, and you're forced to make things "better," instead of "per new design rules."

I'll also point out that the expansion joints will probably be activated while the expansion joints are depressurized. You can expect to see fatigue to set in more readily in the EJs in this configuration if it's not reasonably designed.

I'm not going to jump to conclusions as to what you think a given application *should* be, so instead I'll just genericize.

Let's talk about some configurations.
1) Straight line with 2 EJs.

You'll end up with double the pressure thrust, but the effective stiffness will be halved compared to a single expansion joint.

The benefit is that you practically eliminate forces being transmitted laterally through the pipe, perpendicular to the hinge pin. This is compared to a single expansion joint which permits free rotation through the pin, but the pin still transmits load.

The detriment is that you have a rotating section of pipe between 2 EJs. If there's significant rotation, the two outermost flange connections of the two expansion joints get pulled closer to each other.

I don't think CAESAR understands that, but I don't have a way to test it at the moment. So, buyer beware.

2) 2 EJs that are separated by one 90 degree turn.

So I don't think there are many pros to this configuration, and a lot of cons.

The pressure thrusts are mutually reduced. That's about the only pro I can offer.

However:
If your pipe is installed in the horizontal, and your hinge pins in the vertical, you're now supporting the weight of your pipe on those two hinges. Your EJ manufacturer will thank you for your repeat purchase if you don't adequately support this. And by virtue of supporting it, you're reducing the effectiveness of the EJs.

If, for some unknown reason that you install the pins in the horizontal, your expansion joints will activate based on weight alone, and the elbow simply falls and creates a pocket. Same deal - support needed, and the support reduces EJ effectiveness.

Thus you have vertical configurations. Hinges should probably be parallel to the ground, but the weight of the pipe is likely going to extend the expansion joint in the vertical, thus creating a low point. This may or may not be tolerable.

3) 2 EJs with 2 90s in between.
There's not much to say about this that hasn't been discussed before. Take a look at your own diagram and note the substantially large displacement

4) Combination - 1 + 2
This is a configuration that's prescribed for hypan ball joints in systems with large axial displacements. This allows the pipe to act more like a mechanism than a pipe. Note that CAESAR might not give you an accurate answer, here.

5) Combination - 1 + 3
Take what your image says - note the deflection of the vertical run of pipe. That has a set amount of overhead loading associated with that displacement. The second expansion joint below the one on the riser helps take some of that out.

6) Combination 2 + 3
I can't really imagine a need for this, and nothing but headaches. Don't do this is my only advice.

Strictly talking about the EJ model, I think that you should model the hinges with rigid without weight elements going outde of pipe.
I went on the internet and I see that this was used on some FCCU on the vertical position. most probably no pressure in the line (almost atm) as the thrust will be quite high.
Regards