FEA analysis on Hemispherical head
FEA analysis on Hemispherical head
(OP)
Anybody can help me to figure out Pressure vessel head calculation? I run with ANSYS for pressure 8.25Bar. Head thickness is 7mm , min 8mm -1mm corrosion. But Von-mises stress is 202Mpa that is higher than allowable stress 137Mpa. Can I comparable vonmises stress and allowable stress? So that head design is fail? I dont understand how can i compare vonmises stress for failure? But If i calculated with PV Elite , actual stress is 110 Mpa only at thickness 7mm.Is it applicable to calculate vonmises stress in pressure vessel? Highly appreciate if any professional help me. Thank in advance.





RE: FEA analysis on Hemispherical head
RE: FEA analysis on Hemispherical head
I think there is something wrong with your model or calculation. What is the radius of the head? The stress can be calculated with a simple formula as a function of R, t and P.
prex
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RE: FEA analysis on Hemispherical head
RE: FEA analysis on Hemispherical head
RE: FEA analysis on Hemispherical head
I attached sketch
RE: FEA analysis on Hemispherical head
There is no reference to von Mises or Tresca stress in Div.1, you must go to Div.2 to interpret the results of a stress analysis.
And of course von Mises or Tresca stress would be compared to the allowable stress.
prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads
RE: FEA analysis on Hemispherical head
although you have S1 S2 and S3 to get von mises or tresca, since it is purely by pressure, FEA results shall be very close to hand calcualtion by code formula or theoritical formula from text book.
You may have put wrong constraints on the model. Add a long shell section to it and constraint at the bottom of the shell not head.
Check the stress at the middle layer, not top or bottom layer. Pressure creates primary stress. Middle layer represents the primary stress.
RE: FEA analysis on Hemispherical head
1) If you are designing a vessel to ASME Section VIII, Division 1, if there are rules provided (which there are for heads, and head-to-shell joints), you MUST follow the rules. See U-2(g). Why are you even doing an FEA?
2) If, for some gawd-only-knows reason, you choose to perform an FEA, go to ASME Section VIII, Division 2, Part 5 to interpret the results.
My guess is that you are reading the maximum membrane-plus-bending von Mises stress from your FEA. That's fine, but it has a different "allowable" compared to S.
Here's my free two cents - you are unqualified to be performing an FEA to the ASME Boiler and Pressure Codes. Leave that type of work to the experts - you're likely to do more harm than good. Find someone who is qualified and have them teach you - based on my experience of training engineers in this field, you are looking at about a year of on the job training.
RE: FEA analysis on Hemispherical head
But TGS4 is right, you shall just go by code rules. To interpret FEA and correlated to Div 2 is not an easy task. Some times, garbage in garbage out. I saw a lot of FEA reports that the person does not know what he is doing. But don't give up, one day you will be the FEA expert. . Keep exploring and asking questions, llaren.
RE: FEA analysis on Hemispherical head
llaren - please review Part 5 of ASME Section VIII, Division 2 and come back here with any questions that you have.
RE: FEA analysis on Hemispherical head