Hi!.
I have a steam main line, For limit the displacement in axial direction aplied LIM support with 50 mm of gap, The piping flexibility analys does not have overloads in expansion therm case , but the restrain report presents load near to 1 MN in this LIM support. Is posible limit this displacement?, Is necesary get especial piping supports for this values of load.

Similar questions have been asked on this forum many times. General principles:

1. Restraints can be used to limit loads on terminal points, usually by an increase in pipe stresses and, as you have just discovered, the creation of large structural loads elsewhere.

2. Expansion loops can be used to limit loads on terminal points by adding pipe and elbows to the system. Usually, the elbows in the expansion loops will be among the more highly stressed elements in the piping system. They may produce moments about an axis perpendicular to the plane of the expansion loop that causes a problem with terminal point loadings. They may also produce excessive movements of the pipe in proximity to the expansion loop. These moments and movements can usually be controlled by guiding the run pipe on both sides of the loop.

A balance of restraints and loops can usually come up with a solution that is acceptable from all perspectives. Sometimes it can be difficult to find this "Goldilocks" (not too big, not too little, but just right) solution.

To answer your original question, I seriously doubt that you can buy any commercial pipe support hardware rated for 1 MN, and I want no part of signing my own name to a design for an engineered support of this magnitude. If you have sufficient faith in yourself that you would be able to sleep at night after having designed such a support, then you are welcome to do just that.

I agree with you CraigB, getting this sort of load out of a pipe wall would be a nightmare, and probably a short term failure.

I wonder what the axial stress in the pipe is ...and for that matter, how about the Euler buckling load between guides ? Neither would be flagged as a Code problem, and are probably gross.

Time for a decent bit of guides and loops design.

Cheers
MoverZ
... or was it Z over M ?

Hi, Ivan!

From your initial data, I believe that you have restrained a straight pipe along the axial direction at the both end points/sections.

Since ASME B 31.3 does not take into account the axial force for the actual thermal stress range (SE) computation purpose, on the one hand, and Caesar II does not perform any buckling calculation, on the other hand, no pipe failure has been identified.

Probably, if you change the "Add F/A in Stresses" option in Caesar Configuration File / "Sif's and Stresses" section, from "default" to "yes", you'll get the actual high axial stress value and the corresponding failure result.

So, check again the supporting approach of your system and delete the additional axial restraint to allow the axial thermal movement of the pipe in one direction.


Regards,

If at the node so huge load is coming , then y CAESAR II is not showing the system is failed ?????????
i too faced the same problem , wen i kept lateral restraint support...huge forces were there in lateral directions , but stress was passing...

Dorin says it right. Purely axial load does not, by default, create B31.3 expansion stress (range) in CAESAR II but you can throw a few switches to get it to appear.

B31.3 Equation (17) tells us how to calculate SE and no axial load appears there. Paragraph 319.2.3(c) explains why. That paragraph goes on to list "special cases" where axial stress should be included. The Code does not mention your specific situation.

Stress alone should not be your only measure of adequate design. Those high loads also flag a concern.

Buried piplines may have a thrust block (anchor) near the soil exit point to limit displacement of above ground piping. According to CAESAR II output, these anchors carry tremendous loads. Every once in a while a user comments that they have to pour enough concrete to fill a house to hold that position. But is that what really happens? My guess is there is some tolerance (slop) in installation that gives a little wiggle room. Perhaps this concrete must move a little to properly re-engage with the surrounding soil. That little movement can cause a great reduction in the original axial load.

Try this with your system - change your gap from 50mm to 60mm. How much does that load drop? How certain are you of that 50mm?

Look back at your (original) calc's: How much strain (actual movement that would have to be restrained) would be required to get that big of a predicted load 1MN in that pipe? That's one place to look for the difference.

Second part of the same related question: Could that much movement actually take place at that position? Is the net straight run of the pipe long enough, and is the pipe hot enough (expanding from cold position to hot position) to actually (try to) move that far?

Gentlemen,

Im having a query in doing underground piping. It would be grateful if any of you could guide me. I have filled the Soil model and the spreed sheet by giving the K values. After the programe is run it doesnt link with the main input. In the animation it doesnt show the underground portion nor is it taking those inputs. What shall be done for this.

Regards

Sameer

Sameer,

You should start a new topic with this.

hi.