here i am attaching the pipe support. I do not know how can i introduce for my exhaust pipe. it is having Pipe Shoes.


Please Help me to resolve the problem.

Hi priyan
consider simple rest+guide support.
For large diameter pipe you can model zero rigid from centre of pipe to periphery of pipe then put (rest +guide)at that point for very critical system. It will change moment of nearby nozzle ( accuracy is high).

Do not try to model detailing of pipe support in caesar. Caesar don't do local analysis it do only overall system analysis.

You take load from caesar then compare it with support standard acceptable load or do a finite element analysis in case load at that point is unacceptably high.

HI shr
consider simple rest+guide support.
For large diameter pipe you can model zero rigid from centre of pipe to periphery of pipe then put (rest +guide)at that point for very critical system. It will change moment of nearby nozzle ( accuracy is high).
you mean "at that point ",it isn't the periphery of pipe ,it should be the bottom the support?

Hi zzw
You can go for that.
You may not required to make the system to much complex.

Okay i understand SHR. then How can we solve those types of support.

Hi SHR,

Can you explain it what exactly you need you have to restraint in ceaser or u have model any 3d software.What i understood your question just Use y restraint in ceaser model and z&x depending upon pipe direction add z or x restraint and provide gap 0.125 .Thats all the system will work.

Binoi.S

Hi Binoi
I haven't deny that caesar will work fine with just Y, Z or X support in conventional way.
Cross check with large diameter pipe with proposed detail support model specially closer to sensitive nozzle, you will find considerably difference in nozzle load specially moment. By slight additional work you are making a caesar model, more closer to actual piping configuration.

That detailing may not required for all supports within the system.

Dear Shr,

"You take load from caesar then compare it with support standard acceptable load or do a finite element analysis in case load at that point is unacceptably high"

Your first part of sentence make sense and seems ok.The continuing part of your sentence which says we go for FEM analysis of support in case load at support location exeeds support laod taking capability

Are you trying to say you do FEM analysis for simple supports like shoe as in this case.

I will appreciate your reply.

Regards,
Aslam

Dear Priyan,

As per your attached sketch,you are required to define a +Y Restraint and a Guide with a gap of +/-25 mm in your caesar piping model at node where you plan to support your pipe.

You do not have to worry about insulation at your support location.You have taken care of it by defining insulation thickness and its density in your model.

Regards,
Aslam

Dear Aslam,

since you guys are discussing about support, can i ask you how do you treat a dummy or trunion (sliding or sloted bolt) support in ceasarII if we have different tempearture of ambient and instillation in relating to real world situation.

Regards,
junmar

Hi Aslam
For example say in case of rest + axial stop support, if axial load is quite high, Caesar is not the right tool to check whether there will be any local stress failure at pipe shoe.
In that case we may go for finite element analysis method or any other calculation.
I do not suggest it for simple cases since there is a cost implication.
For large diameter pipe I was suggesting for slight detail modelling for very different reason.

Regards
Habib

Dear Habib,

As far as restraint load is concerned(irrespective of direction of action)

1)If restraint load falls within support load taking capability and stresses in the pipe are in complaince with the design code there will not be any local or gross failure in the pipe concerned.

2)Suppose if restraint load exeeds support allowable loads then what benifit you will achieve by doing stress analysis of that support.I think either you will try to reduce load at that support or provide a stonger support for the same load.

3)Could you please explaine how you will do local stress analysis and which tool is appropriate for doing that and which code you will follow?

4)Could you please explaine different reason to go for detail modelling.



Regards,
Aslam

Hi Aslam

1) Caesar do overall piping system analysis not local analysis. You put two axial stop in a line, caesar will not show any stress failure only show heavy support load but we can not accept it. If you do local stress checking with that load on pipe ( By FEM) it will show stress failure.
2) If support load exceed we can check with saddle or stiffener to make it more stronger it take care of more load.
3) Local stress check to be done by mechanical stress failure theory of material same as any mechanical item design ( I personally have not done FEM analysis)
4)For normal support modelling caesar consider support at centre line of pipe, but physically we place support at the bottom of pipe, so in caesar model also if we place support at bottom of pipe, output result will be more closer to reality . ( not recommended for small bore line).

Regards

Habib

Hello Friends,

I was doing the exhaust gas supporting for two to three projects. I was reading this today and I completed agree what Shr says. It will definatly affects the nozzle movements. If we model the rigid element and then the support the results will be different than what we have when we place the support for small bore pipes.

Dear Habib,

1)Difficult to grasp your point number one.

3)Their is no such thing as "mechanical stress failure theory of material same as any mechanical item design" for local stress analysis. I would say its entirely a different world.
Please find some time to read ASME sec VIII div-2(Design by analysis) and try to understand concept of plastic hinge,racheting and shakedown,stress categorisation and their limits.

3)The concept behind modelling rigid from the center to bottom of the pipe comes from the basic theory on which caesar works .Replacemet of pipe element between these two points by a rigid element transfers variables values to a point where your pipe element actually begins.

If you do not do that then this element will contribute to global element stiffness matrix and results will be with some finite error.The ammount of error will depent on the size of the pipe.Bigger the pipe higher wiil be error.

Regards,
Aslam

Confirm this issue with client at project specification preparation time.Input agreed value in caesar configuration file for calculation.

Regards,
Aslam

Dears,

My approach to this support problem would be the following:

1. I would always use Caesar II or other piping program with the required restraints for the analysis. If you can do it by hand you're welcome.

2. I would check/design the restraint (the shoe) to take the support loads appropriately (by considering the thermal gradient if available). This can be done either by hand calculation or by a FEA (such as FE-Pipe or Nozzle-Pro).

3. In case there is a SIF need to be introduced due to the shoe I would add in to the analysis model and re-run it to see if there is an effect on the stress analysis. This stage can be added in to the first stage if I can guess what the SIF would be.

Regards,

Ibrahim Demir

Thanks Ibrahim
For providing more clear explanation on the issue which I probably could not explain well even though I was trying to point out same thing.
Regarding zero rigid modelling I like to refer "COADE pipe stress seminar notes" clause 3.2 modelling techniques, simplest method / more accurate / most accurate method, page no 3-10 to 3-12.
Some good company I have worked with give clear instruction to use more accurate method ( zero rigid model from centre of pipe to bottom of pipe)above particular size of pipe.

Regards

Habib

Providing stepped rigid ( one from the centre of the pipe to the surface of the pipe with pipe temperature and another one from the pipe surface to bottom surface of the shoe with a proper temperature gradient ) is going to give better prediction on the displacement of the pipe at the support in case the shoe hight is large enough.

By doing this you may see the swing of the pipe around the lateral support location under the large lateral support loads.

However, if you have not decided what type of support you are going to use there is no need to do that at the preliminary analyses. If you have definite support type which is given by the project to comply modeling with rigids would be better however time consuming.

Regards,

Ibrahim Demir

Hi Ibrahim
I totally agree with you.
However we generally ignore shoe. Model upto surface of pipe with zero rigid with pipe temperature as you mention & place support there.

Regards

Habib