Displacement

while i was doing a stress analysis for large dia pipe..
i faced the below problem...

I have provided a loop ( before and after the loop i have
provided a guide with gap of 10 mm)

The bend centre node and To node displacements in the
beginning of loop are unreasonable..there is thermal
displacement of around 30 mm in a centre node and To node of
bend..

The stress levels in the bend is safe...but i am little
bit worried about the unjustified displacements in the bend element.

What would be the reason??? can anybody help me.

If you have doubts, you can confirm by manual calculations. So, besides thermal disp, you have an axial disp due to pressure because you have a large thin wall pipe... this shouldn't be difficult...

Goodluck!

Hi Moorthy

Depending on the dia of your pipeline, the temperatures involved and the location of anchors (or linestops) upstream and downstream off your loops, 30mm does not sound an excessive displacement.

We often see axial displacements going into loops much greater than this. You just need to make sure that your loop is sized appropriately for the expansion and that you check your pipe shoe to make sure that your shoe is long enough to make sue that it will not fall off the pipe support as it moves axially.

Thanxs for your replies.

It is not an axial displacement..

See. I have provided a Guide with 10 mm before and after the loop.

So the pipe can move laterally 10 mm. The bend starts at 5500mm from the Guide. Where i am getting around 17mm lateral displacement in the centre node of bend and 39mm lateral displacement in the To node of bend.

The bend is pulling off by the loop. Is it reality?

Hi Moorthi,

I am curious of problem but I don’t understand the situation… can you attach the picture of your system… and if possible include your displacement result… thanks

Regards!

Are you looking at the EXPansion case results?

I am still confused about your situation , but on my own understanding... your pipe route is from a guide, then 5.5m is the first elbow of your loop? then the bend displaced 17mm laterally, of course this is possible... take note that you have 10mm gap at the guides (5.5m away from the elbow), the pipe is not that rigid to have a max disp of 10mm to the 5.5m distance (plus this is a loop location)... then, the "to node" of the bend should be displacing more due to thermal/pressure, which is probably because the bend direction is the same direction of the displacements. (show/attach a simple sketch to have clarity on your inquiry)


Goodluck!

Exp loop is used to compensate the axial growth not lateral movement. Axial growth = Lo*Alpha*dT. Please calculate this value between distance both anchor (Lo). Please don't forget that EXP load case not used to observe the displacement instead of Stresses. The real displacement is still in NATIVE OPE load cases. Every load cases Lxx = Lyy(-)or(+) Lzz is a combination load cases which not give real values for moments and displacement.

Pls. find the attached file.

Richard: It is during operating case.

Dear Moorthy,

With reference to your attachment, i want you to concern or check the force at the guide instead of more concerning on Stress level as mentioned as 50% which is less.

That is, check whether the force at the guide is within the allowable load or not.

Hope so this may clear your doubt.

With reference to the guide in question. Is there a second guide to the left of the referenced guide?

A second guide would provide a straight(er) line of thrust into the expansion joint.

If you do not have a second guide to the left of the referenced guide, depending on the piping configuration to the left of the guide, the actual dimension involved, perhaps the piping could be rotating at the referenced guide and producing the x-displacement noted at the TO end of the elbow.

Yes Mr. Ken, I have provided a second guide too.

The load on the guide is about 6T..for huge diameter pipe it may be OK.

People should not be narrow-minded, just because it is an expansion loop... doesn't mean it will move only in axial direction!

The sketch you've provided is only around the loop area, piping before this location is also significant to you entire piping displacement. For example, if your piping before the first guide is going to (-x) direction (including thermal disp) making the first guide causing a seesaw event (teeter-totter reaction), that is why your getting (+x) displacement on your bends? If this is so, your bend "to node" should add-up displacements to (+x) direction depending on the lenght of your bend...

Cheers!

My question is the displacement is abnormal than the actual..
How the displacement can be 17, 33 & 51 in the from, centre & to nodes of the bend. This may not be possible in Practicle.

Did you said you have a large dia pipe? how large? what is the ftf of the bend? you have to sktech the entire system in order for someone to explain to you one by one.

I have mentioned in my first post itself, its a large dia pipe (80")

The problem is only in the loop area..hence i have given the sketch that area alone.

I hope, the sketch is may be enough to understand the problem i m facing.

Moorthi,

If you are concerned about your lateral movements in the loop, I think it is advisable to check the piping before and after the loop. Like ichigo have said, these movements may have been caused by the downstream or upstream piping of the loop.

How hot is your pipng, and I would say that the bend lenght is 2032mm.

Everthing is OK before and after the loop (only a max. lateral displacement of 10mm)..i m facing the problem only in the loop...It is 270 Deg.C, the bend is 1.5D(Mitre)..3000mm.

In this context,how the pipe can expand from 17mm to 51mm in the bend itself.

Pls. give me a valuable suggestion.

Come on, think a little. What you have is an expansion loop. This is an offset portion of the piping that is parallel to the main run.

1. The offset (as well as the perpendicular legs) expands as temperature increases, too.

2. The expansion of the two legs of the main run expands and forces the inner elbows on the two perpendicular legs toward each other.

3. The expansion of the portion of the expansion loop that is parallel to the main run expands and forces the two outer elbows on the perpendicular legs away from each other.

4. There is a stiffness associated with each elbow, and with all of the 5 legs of straight pipe.

WHAT DO YOU THINK THE RESULT OF ALL THIS IS?

A: The expansion loop produces bending moments in all associated components. (How do you think the bending stresses are generated? Did you think you could have bending STRESSES without bending STRAINS?) And the bending moments impose a radius of curvature on each straight leg of pipe. You can verify this for yourself if you compare the lateral deflections of the two outer elbows to the lateral displacement of the midpoint of the parallel leg of the expansion loop, if you have placed a midpoint node.

didnt you check the rotation of your ellbow? Remember you got almost 5000mm of arclenght. 34mm IS NOT POSIBLE TO ATTAIN WITH ITS ROTATION ALONE...
try to solve it by hand with the data stated in your attachment. A very simple geometric calculation....
Why are you so bathered with this anyway?

Regards!

I've never said that loop has no lateral movement. I only said please calculate axial GROWTH....go to simple loop sizing base on this parameter and the pipe diameter....

You should not take any words different that people wrote...I hope you've ever use that simple nomograph...

What is your pipe diameter ? or you can check on GA drawing weather this line will crash with others line when the displacement take place .