Hello, This is my first time here and please be patient about my English grammar.
Now i'm using Caesar II version 4.30 and now i have found that program not calculate axial force due to pressure in pipe. For example when i have model an elbow with ancor at two end points ,apply pressure like 16 bar then run analysis. The result in case sus (W+P1) shown that only force due to weight acting at ancor.
Is this program assume this elbow as pressure vassel or i miss something?
I really appreciate if you could help

Regards;
TCK

Hi, there!

The default Caesar settings don't take into account the so called "pressure elongation effect". Caesar manuals recommend to consider this effect only for FRP systems.

However, for large bore high pressure steel pipes, the pressure axial effect cannot be ignored.
So, you have to change the default settings from Configuration File: COMPUTATIONAL CONTROL/Bourdon Pressure/"Transl Only".

Inside the stress (*._a) file, you have also to change the default settings of Special Execution Parameters:
a) "Activate Bourdon Effects"/"Translation only";
b) "Stress Stiffening due to Pressure"/"Use Pressure #1" or "Use Pressure #2".

This changes will "tell" to Caesar to modify the stiffness matrices of the straight pipe elements in order to "catch" the pressure axial effect.

You'll see after the above settings that the displacements, element forces and axial stress distribution will be significantly changed.

However, you must be aware that the restraint summary will display only the STRUCTURAL FORCES (excluding the pressure axial forces). For the equipment nozzles or axial stop supports, you have to add yourself the pressure effect contribution.

Regards,

Dorin Popescu

Senior Pipe Stress Engineer
Washington Group - Romania - Ploiesti Office

Thanks a lot for your reply.

But could you please explain more about
1. Do I have to input thrust force directly by myself and how much force to be input (F=P*A?)
2. Does the force on item 1 effect axial stress and hoop stress?

Regards;
TCK

1) The axial pressure thrust force ( F = p*A indeed) should be added "by hand" only for pipe support design or pressure vessel nozzle checking (WRC 107 module). A good reference is "Modelling of internal Pressure and Thrust Load on nozzles using WRC368" in Coade Mechanical Engineering News from July 2001 (you can download it from this site, Newsletter section).

2) The pressure stresses are computed correctly, taking into account the pressure elongation effect, so that you'll obtain the actual values. Only for axial forces it is necessary to operate the above correction.

Regards,

Dorin

Hi Dorin Daniel:


LC Peng, president of PENG ENGINEERING, is a leading authority in the field of pipe stress analysis and piping engineering.

LC Peng has authored, co-authored and presented many technical papers on these subjects

http://www.pipestress.com/Pages/PEpapers.html:

Local Stresses in Vessels - Notes on the Application of WRC-107 and WRC-297

Also:

The Art of Checking Pipe Stress Computer Programs

Treatment of Support Friction in Pipe Stress Analysis
:rolleyes:

Leonard@thill.biz
www.thill.biz