3 replies to this topic

[Pankajtr]

Hi, Im a final year student of mechanical engineering and I have a few doubts about my final year project, Im designing a vessel for process industry. In which I have to deal with internal vacuum.Which can go upto 0.001MPa.
Problem I am facing now is, For calculation of thickness of vessel for internal or external pressure,we can find by conventional formula of hoop stress or by codes.

But for vacuum,these formulaes , I found contradictory, as Pressure is total reverse in nature for vacuum.

So, please suggest me some, idea so that I can move forward. any suggestions will be great for me.

[Absolute Zero]

Refer to ASME Pressure Vessel Code BPVC Sec VIII Rules for Construction of Pressure Vessels, Div 1,2,3.

[Pankajtr]

Thanks for refereing, codes.

1) I've gone through the Sec.III Div 1, UG-27,28. In which they are norms for Wall thickness calculation.

But the problem remains the same,

Here also, in Stress equations, Thickness decreases as Pressure decreases.

But Thickness should increase as Vacuum increases (or Pressure decreases).

OR
May there may be any considerations for vacuum conditions,that I am not aware of.


I am trying to find such cases,hope will find that.

Anyways, guide me for this problem and thanks for suggestions.


Regards,
Pankaj

[kkala]

Cylindrical vessels in vacuum can fail because of buckling and relevant calculations are based on this concept (lobes, etc). A simple and rather clear presentation can be found in J. Coulson & J Richardson Chemical Engineering Volume 6, An introduction to Chemical Engineering Design, Pergamon Press; 1st edition 1983, a lot of editions up to date. Chapter 13 is devoted to mechanical design of process equipment, in which 5 pages refer to Design of vessels subject to external pressure. I believe this could help clarify your queries. The whole Chapter 13 is quite useful as an introduction to mechanical design.
The book is widely known, I do not think you will find difficulty in finding it in the library or among students of Chemical Engineering.