Pressure vessels, wall thickness

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Discussion Overview

The discussion revolves around the calculation of wall thickness for a cylindrical pressure vessel intended to store gas at a specified pressure and volume. Participants explore whether the vessel should be treated as a thin or thick cylinder and the implications of their calculations on determining the required wall thickness.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculated the inner radius and hoop stress, concluding that the vessel should be treated as a thick-walled cylinder with a minimum wall thickness of 0.231 m.
  • Another participant expressed confusion about how to determine whether to use thin or thick cylinder equations, noting a "chicken and egg" problem regarding the radius.
  • A different approach was presented, where a participant calculated the internal volume based on the given pressure and volume, leading to a different inner radius and wall thickness, suggesting the vessel is a thin-walled cylinder.
  • Some participants discussed the need to recalculate using thick-walled equations after initially using thin-walled equations, indicating potential inaccuracies in the first approach.
  • There was a reiteration of the importance of the problem statement indicating that the compressed volume of gas is 20 m³, which some participants found confusing in relation to their calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the vessel should be treated as thin or thick-walled, with multiple competing views and approaches presented. The discussion remains unresolved regarding the correct method and resulting calculations.

Contextual Notes

Participants noted potential inaccuracies in calculations based on the choice of equations and the assumptions made about the vessel's dimensions. There are unresolved mathematical steps and dependencies on definitions of thin and thick-walled cylinders.

  • #31
0.74 was an error in my maths!
I had the assignment back and got the question right.
Persevere with the thick walled equations and you'll get there.
Use the examples in the workbook to guide you.
 
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  • #32
Rubear I found it to be thick walled and a minimum thickness off 231mm would this be correct??
 
  • #33
Yes but that's using the thin walled equation isn't it? You need to redo using the thick walled equation for greater accuracy I think.
 
  • #34
no not cracked it yet. I am stuck trying to apply thick walled equations...
 
  • #35
I got the thick walled equation to = 6.71
And the thin walled equation to =7.71...
 
  • #36
which equations are they Big Jock? do you mean thickness ratio?
 
  • #37
yeah thickness ratio equations got those answers and from everything else I have read on this question I believe all the answers are in this thread. I just re worked them all to confirm the answers I got and to make sure I was 100% correct with what I had come up with
 
  • #38
im totally confused. so far i have done the following...

calculate the radius r = √(20 / 2∏) = 1.784mcalculate the hoop stress σ = 96526602.1 / 5 = 19.3x106 (2800psi)

calculate wall thickness t = (1.784 x 362.6) / 2800 = 0.231mthickness ratio = 1.784 / 0.231 = 7.72im totally confused as to what i need to do next...
 
  • #39
Radius minus wall thickness = inside radius...
 
  • #40
ok so Ri = 1.553m and Ro= 1.784m

what am i looking to find out with these figures?
 
  • #41
Subtract outer radius from inner radius you get you wall thickness also put Ri and Ro into your wall thickness equations, see if that helps
 
  • #42
Big Jock said:
Subtract outer radius from inner radius you get you wall thickness also put Ri and Ro into your wall thickness equations, see if that helps

yes but that's just based on thin walled. Subtracting wall thickness from radius is based on the same figures as when taking ri from ro
 
  • #43
I had another look at this. Do I need to use thick wall equations with thin wall values, to get a more accurate value for Hoop Stress σh, and then use this new value of σh to re-calculate the wall thickness?
 
  • #44
so using known values in thick walled equations...

when r = ri = 1553mm

Axial Stress = 7.82MPa
Hoop Stress = 18.1MPa
Radial Stress = -2.5MPa


when r = ro = 1784mm

Axial Stress = 7.82MPa
Hoop Stress = 15.6MPa
Radial Strss = 0MPa





do i now need to recalculate wall thickness?
 
  • #45
can anyone help?
 
  • #46
oxon88 said:
I had another look at this. Do I need to use thick wall equations with thin wall values, to get a more accurate value for Hoop Stress σh, and then use this new value of σh to re-calculate the wall thickness?


Hi Oxon.

Long time ago I did this but, yes, calculate as per the textbook for approximation of wall thickness. Then take that value and repeat with appropriate equation for the approximated thickness to get true thickness.

Hope that helps?
 

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