Hoop & Radial Stress correlation of pressure vessel with FEA using ANSYS

This video explains hoop stress and radial stress calculation for thick cylinder and its validation through FEA. It also explains the FEA model creation, internal pressure application and results extraction using ansys workbench
Note: In present video, the pressure vessel is assumed to be thick vessel category and hence the lames equation is used for hoop stress calculations. Small difference is observed for hoop stress calculation for thick and thin vessel.
For thin vessel, Hoop stress is (Pi * d)/(2 * t)
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[@NTC]

thank you, this video is very helpful!

[@graspengineering9249]

You're very welcome!

[@saraelbahji4524]

Please when you applied pression on the nozzle , is the Ansys gave the value 3017.9psi to have equilibrium or it was you which do it ? If Ansys can do it can you show me how ? I know my questions are annoying thank you for your patience

[@graspengineering9249]

Pressure applied on nozzle is competing pressure which we calculate analytical by comparing areas at the opening. ANSYS does not calculate it.

[@adamkennedy3800]

@Grasp Engineering Hi, I was wondering why there was not a compensating pressure applied to the header/run/vessel portion? There will be axial forces in the vessel due pressure thrust.

[@graspengineering9249]

Hello Adam, If you check video both the sides of the vessel are fixed and hence no need to apply compensating pressure. Fixed support does not allow it to deform at both ends.

[@amvali]

Hi there, I have a question about fix support, why did you use fix supports at the ends? why not cylindrical support and let the radial free? I the pressure vessel has elliptical ends, how would you constraint end without actually modeling the ends?

[@graspengineering9249]

Hello, Greetings! You can use radial constraint also. Radial constraint are more accurate as it will not show localised stresses at constrain ends. I had used fixed supports becuase our area of interest is junction only. If both ends have head, you can use boundary condition at saddle supports.

[@NTC]

can we use the shell elements instead of solid ones? I understand that with solid elements you can get the normal stresses at any node, but it seems impossible to get the normal stress in the local z-axis of a shell element

[@graspengineering9249]

You can use shell element too. You should get normal stress too. Just check shell top/middle or bottom options while extracting stresses.

[@raviphanindra9454]

Thank you for the video. What is the procedure for application of compensating pressure if analysis is done using Shell elements? where should I apply compensating pressure for nozell if shell elements are used for analysis?

[@graspengineering9249]

Good Question ! You can apply compensating force in that case on outer edges of the vessel.

[@raviphanindra9454]

@@graspengineering9249 Thank you

[@satyabarua]

You did the calculations assuming the cylinder to be a thick cylinder; however the internal radius/ thickness ratio is 24:1 ( more than 10), does it still qualifies as a thick cylinder? did I miss something here?

[@graspengineering9249]

Hello Sanz, Please kindly check the description note. thanks !

[@smithavivek8998]

Very well explained. Sir you have evaluated the normal stresses at the nodes. I am using ansys 14.2 and not showing the option to evaluate nodal stresses. I tried in the vertex points but its showing some error .Please guide me..

[@graspengineering9249]

You can probe nearby node, it may have same stresses. You can also create path across thickness and check the stress values for nodes across the path.

[@zohrajoutei2500]

Thank you !! Please why the Y axis présents the hoop stress ? in other video of you you did a cylindrical coordonate system and so Y axis represented the hoop stress, is there any difference please ? do I have to choose this or the other ?

[@graspengineering9249]

Thank you for the detail view. Hoop stress is normal stress in tangential direction, so you need see how you cut the cylinder and which is normal or tangential direction. You can easily compare with global so no need of cylindrical coordinate.

[@arunsiddharth8307]

Sir, should we consider nozzle loads and moments while validating for hoop stresses ? Or after the validation is done the nozzle loads are being applied?

[@graspengineering9249]

We are validating internal pressure loads with hoop stress. For nozzle force & moments loads, you can validate through the output reactions.

[@dhaivatthakar2082]

Hello Sir...Can we use principal stress distribution of stress tensor distribution across thickness to find hoop stress ?what is the difference between normal stress and principal stress values across thickness ?

[@graspengineering9249]

Hello, yes you can see principal stresses to find hoop stress. Normal stress calculated at an angle when shear stress is considered as zero, the max value of normal stress is major principal while minimum value is minor principal stresses. You can cross check values across thickness by doing exercise shown in video.

[@abdulharissiregar3118]

please answer my question, why you take so much normal stress solution ? i need to know cause i my task about pipe stress analysis to find torsional, bending and thermal stress in pipe bend, i really want to know please answer sir

[@graspengineering9249]

Hello Abdul, We took normal stress to validate hook stress calculations. Hoop stress is tangential stress and is compared with normal stress only. Generally we should see the von mises stresses for stress computation. In order to see thermal stress, you can check von mises/equivalent stress.

[@saraelbahji4524]

Please when you delete contacts , is it equivalent to "bonded contact" ? Please if in the reality there is welds can we model it as bonded or model one part on the vessel? Please is the analysis give the same results if we slice or not the geometry ( when mesh and BC are the same) ?

[@graspengineering9249]

If you don't want to create welds, we can use bonded contact to replicate welds. If you need to create weld for example we might create weld to do weld fatigue, then we need to model actual weld. In this case all parts of vessel are integral and no need to create contacts. Creating weld or bonded contact will not affect much overall global stress. Bonded contact will be the worst case scenario.

[@jakub1908]

Hello, can someone tell me, what is physical interpretation of compensating pressure, which is P/((Do/Di)^2-1) ? Where it comes from??

[@graspengineering9249]

Hi, We haven't modelled complete structure and pressure loads are applied internaly, hence there is effect of pressure loads at openings, to compensate this effect, compensating pressure is applied at the openings in which two areas at opening are equated and compensating pressure is calculated as mentioned in formula.

[@konderuanil]

Can you please elaborate about compassionate pressure. In which direction we need apply on the ends and when we decide to apply that.

[@graspengineering9249]

To compensate the effect of thrust due to inside internal pressure at the openings & in order to keep system in equilibrium, we need to apply compensating pressure. It should be applied in negative direction at the openings.

[@jayvaghela49]

Sir how to make this nozzle shell junction

[@graspengineering9249]

Please refer our cad modeling playlist, you will find similar cad modeling vidoes.

[@arunsiddharth8307]

sir how did you create the partition around the nozzle shell junction for refined mesh ?

[@graspengineering9249]

Hi Arun ! You can do slicing in design modeler near by nozzle-shell junction by plane or by surface.

[@arunsiddharth8307]

thank you sir......but that's not the exact doubt I had.....can I have your mail id? so that I can explain you clearly the doubts I'm having

[@graspengineering9249]

[e-mail]

[@shaliniverma8709]

Sir, kindly upload a video for internal pressure in a battery box....

[@graspengineering9249]

Please mention your problem statement

[@kadiresunitha3697]

Can you give reference book on FEA to find stress in thin cylinders?

[@graspengineering9249]

You will find in strength of material book how to find stresses in cylinder. We will try to add it on on blogpost. www.graspengineering.com/category/fea_article/fea_advance/

[@luoluojack6282]

why, two side both are FIXED，i think THRER is displacement in X,Y direction free, Z direct 0 mm.

[@graspengineering9249]

It is most conservative approach. The best way to simulate this apply radial constraint at one end (which reduces stress concentration) and compensating pressure at other end. Please refer other pressure vessel videos from our channel for more information. thanks.

[@saraelbahji4524]

Last question please , why we compare analytical stress with Minimum stress and not maximum ?

[@graspengineering9249]

We compare with maximum stress . Where we compare with minimum stress?

[@HOLA666666HOLA]

for example in 19:02 we have maximum normal stress is -1019.9psi and minimum is -1039.9 and we compare this last value with analytical value -1000 psi and the same for hoop stress in 19:29 we took the minimum 25155psi and compare with analytical 24510.2psi

[@saraelbahji4524]

thank you very much Manal

[@saraelbahji4524]

yes in reality we are many which need trainings but we can t afford it so we take advantage of your interesting videos and your precious help to succeed our researchs

[@graspengineering9249]

Dont worry, We will reply for your concerns.

[@arunsiddharth8307]

why haven't the compensating pressure for shell has not been defined?

[@graspengineering9249]

As constrained is defined for both ends of the cylinder, hence no need to consider the compensating pressure at ends. If you want to consider then, constrained one end of cylinder & apply CP at other end.

[@arunsiddharth8307]

thank you sir. I'm having another clarification.... I have used cylindrical support at one end with radial free and constrained at the other directions, however I experiencing rigid body motion. is it a good engineering practice to ignore that warning?

[@rakeshpatil3723]

@@arunsiddharth8307 Welcome. You can ignore warnings, but should not ignore errors. Kindly check the proper constrained & connections so that you will not experience any rigid body motion.

[@abdulharissiregar3118]

sir can you explain to me how to make analytical calculation the von mises stress ?

[@graspengineering9249]

You can use von mises equation based on principal stress with user defined function in ANSYS and compare it with linearizaed equivalent or von mises stresses, both should match.

[@abdulharissiregar3118]

@@graspengineering9249 thank you sir

[@ayaz4731]

Can anyone give me reference for compensate pressure calculation? As shown in video

[@graspengineering9249]

As mentioned in the video, it is used to compensate the pressure, which we will get after equating two areas at opening. It is calculated with simple analytical formula (Hollow and solid cylinder area), you can google for references.

[@쟉이-w3r]

Where can I download this modeling file?

[@graspengineering9249]

Please check below link, we are uploading cad models here: www.graspengineering.com/category/design/fea-cad-geometry/

[@anggasteven1746]

Can I make FEA with PV elite ?

[@graspengineering9249]

PV elite is design software's not useful for FEA.