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#75319 - 01/12/21 10:11 AM Tied Expansion joint with gap
Ahmed_Kamal Offline
Member

Registered: 01/13/17
Posts: 90
Loc: Egypt
Hello,

I am working with system connected to equipment which its vendor provided an expansion joint before nozzle connection. In expansion joint data sheet the movement provided as below:

1: Axial movement : 30 mm

2- Lateral movement : 4mm

My question is: if the X axis is axial direction I will provide restrain at tie rod in axial direction with 30 mm gap connected by c node with expansion joint, in the two lateral direction How can I simulate the 4 mm gap in lateral direction (shall I simulate Ry & Rz with 4 degree gap, I find that not the right way)?

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#75320 - 01/13/21 05:23 AM Re: Tied Expansion joint with gap [Re: Ahmed_Kamal]
Lido (TCS) Offline
Member

Registered: 03/23/05
Posts: 50
Loc: livorno - italy
Ahmed, I haven't ever seen tied expansion joints (I think you means lateral expansion joints with tie rods for pressure thrust containment) with gap on tie rods: It could be a very special expansion joint (?)
Perhaps the tie rods are only installed for transportation issues and they have to be removed before use? In this case it could be not a tied expansion joint, but a simple axial expansion joint, and the values indicated for axial and lateral displacements could represent admissible values.
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TCS Eng.

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#75322 - 01/13/21 06:23 AM Re: Tied Expansion joint with gap [Re: Ahmed_Kamal]
danb Offline
Member

Registered: 04/22/05
Posts: 1335
Loc: ...
Ahmed,
The information you mention in the data sheet refer to the EJ capabilities. You need to find in the DS specified the EJ type if is tied or untied.

You also have to see the EJ drawing for more details.
There are EJ with tie rods that allow for compression and are only as safety device (do not allow for expansion due to pressure thrust).

Most likely you have an untied EJ for which you have to check that the maximum movements stay within the values specified by the vendor.
It would be beneficial if you can ask the rotating engineer to have a call with the vendor. He would be able to discuss with you about the EJ features.
Regards
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Dan

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#75323 - 01/13/21 04:59 PM Re: Tied Expansion joint with gap [Re: Ahmed_Kamal]
Ahmed_Kamal Offline
Member

Registered: 01/13/17
Posts: 90
Loc: Egypt
Please find drawing of expansion joint as attached. I think I can only give axial gap and check lateral displacement however lateral displacement will allow some rotation. So what do you think is better?


Attachments
Flexible Joint Pos. 90.pdf (18 downloads)


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#75324 - 01/14/21 01:07 AM Re: Tied Expansion joint with gap [Re: Ahmed_Kamal]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 918
Loc: Louisiana, US
Assume rotational stiffness is for the expansion joint without tie rods. Assume tie-rods halt expansion joint rotation - seems to be manufacturer intent.

Expansion joint = nodes 10-20, 30 mm long, stiffnesses as listed.
Effective diameter = (46.53 / pi)^0.5*2

Tie rod = 0 weight rigid node 10-21. Axial restraint with 30mm gap on node 21, cnode 20.
Vertical and lateral restraint with 4mm gap on node 21, cnode 20.
RX/Y/Z no gap, node 21, cnode 20.

You're "supposed to" install an anchor on the pipe near the expansion joint, preferably inline.

CAESAR will estimate the stiffness of the tie-rods to be that of the same diameter pipe and thickness, but thickness x 10. Not great, not bad, but likely "close enough."

Run the analysis. Provide a cursory review of vertical, lateral, and rotational loads. Do they seem reasonably able to be absorbed by the tie-rods?

Depending on the equipment, you're going to find that the pressure thrust alone overloads the equipment. In this case, you should close the gap on the far end of the expansion joint. I.E. instead of x with 30 mm gap, it's a +x with gap, -x without gap.

Also depending on the nozzle sensitivity, you might have to make that 0 weight rigid weigh 97.5 kg, and pick the better orientation, and have them swap the flow orientation of the expansion joint as needed.

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#75328 - 01/15/21 09:40 AM Re: Tied Expansion joint with gap [Re: Ahmed_Kamal]
Ahmed_Kamal Offline
Member

Registered: 01/13/17
Posts: 90
Loc: Egypt
Thank you Michael. But I think that as well as there is a lateral displacement then a rotation in lateral direction shall be exit, so RY & RZ shall have some gap.

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#75329 - 01/15/21 10:30 PM Re: Tied Expansion joint with gap [Re: Ahmed_Kamal]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 918
Loc: Louisiana, US
Ahmed,

I don't disagree - but that gap is going to be a function of the following:

1. Tie rod bolt circle radius
2. Tie rod flange hole diameter
3. Tie rod diameter
4. Flange thickness

Let's assume the drawing is to scale.

The bolt circle diameter would be 980 mm.
The rod diameter would be 20mm.
The bolt hole diameter would be 25 mm.
The flange thickness is also 20mm.

The angular gap is approximately 7 degrees, which is admittedly surprisingly large.

Seeing that it's using M20 nuts, which are for M20 rods, which are 20mm, it might stand to reason that the drawing is accurate and to scale.

But that's an assumption you should take up with the manufacturer.


Edited by Michael_Fletcher (01/15/21 10:39 PM)
Edit Reason: Corrected gap.

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#75344 - 01/21/21 05:24 AM Re: Tied Expansion joint with gap [Re: Ahmed_Kamal]
Lido (TCS) Offline
Member

Registered: 03/23/05
Posts: 50
Loc: livorno - italy
Ahmed,
effectively it seems a non-standard lateral expansion joint with expansion and angular possibilities.
strange...

first of all, have you checked the pressure thrust? I read 46.53kN/bar, therefore for 0.85bar the piping arrangement and supports (limit stop or full anchor supports , i suppose)and/or connected equipment must are designed for about 4000kg of thust force deriving from this expansion joint.
uncontrolled pressure thrust could be very very dangerous, expecially when the designer does not expect fot it...

then, for my point of view, you can model as a normal tied lateral expansion joint, making a complete model with tie rods, and leaving +-30mm gap on one side.


Edited by Lido (TCS) (01/21/21 05:29 AM)
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TCS Eng.

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