Lug anchorage - Thermal Anchorage Movement

[huangdf118]

I am working on the support lug for a vertical vessel (DI: 84in, Operating Temperature 1200F; Pressure 63 psi).

The thermal expanison in radial direction is a big concern. The lug bolt holes will be deisgned as slots rather than circule hole allowing radial movement caused by theraml expansion. Due to other restricts, I am thinking to fully anchor one of the lugs (total 4 lugs) allowing rest of the 3 lugs moving. But I've never done it in the past, and not quite sure wheather or not it is feasible.

If the professionals here have the experiences on thermal anchaorage movement? Please advice on what need to be considered to evaluate thermal anchorage movement?


Thanks

 

[TGS4]

Generally a bad idea. You would be better to put all 4 on low friction slide pads and let the entire thing "float", kept centered by the attached nozzles.

 

[huangdf118]

Thanks TGS4. Could you let me know the disadvantage for "fix on lug" option. The rest of 3 lugs allow low friction float. So, the fixed one will not carry more stress. I may overlook some other sections. Thanks again

 

[TGS4]

It's not a technical rationale, but a practical one. If you specify that only 1 of 4 connections is to be tight, what do you think the likelihood that the initial construction will do it correctly? And what do you think is the likelihood that, during operation, someone won't just look at the three loose ones and tighten them, thinking they're doing a favour?

It's Murphy's Law. Something will go wrong. Leo them all loose (and the same) and you're more likely to keep things that way.

 

[KevinNZ]

Make the tight bolt a differently size and detail so it stands out as not the same as the other three.

 

[TGS4]

KevinNZ - unfortunately, I can guarantee to you that someone will figure out a way to bugger that up. Any time we try to make something idiot-proof, they just keep making better idiots.

 

[r6155]

Why not a skirt support?

Regards
r6155

 

[JGard1985]

I agree maybe a skirt support with a center bolt to locate the vessel.



Jeff
Pipe Stress Analysis
Finite Element Analysis

http://www.xceed-eng.com

 

[huangdf118]

The thermal expansion in vertical direction is large (vessel body + skirt), there are some important nozzles that could not handle large vertical thermal displacement. Another thing is that skirt design has the temperature limitation to 800F. The operating temperature of the vessel is about 1200F.

 

[marty007]

If I understand your question correctly, you have four bolt holes in a radial pattern?

If so, then it is important to not anchor any of the lugs.

Think about how the thermal expansion would play itself out with four radial holes.

Lets say you have lugs at 0°, 90°, 180°, and 270°, and you define a y-axis along the 0-180° orientation. Now, if you anchor the lug at 0°, what happens to the lug at 90° when the vessel gets hot? Because the lug at 0° is anchored, the vessel will want to move down the y-axis, and laterally along the x-axis. I highly doubt your lugs at 90° and 270 would have been slotted to account for this y-axis movement, but instead would have designed for only radial movement.

Having radial slots is inherently self-centering, so your vessel should not move.

 

[r6155]

I agree with TGS4 “You need to get expert help” in

https://www.eng-tips.com/viewthread.cfm?qid=449398

Regards
r6155