Pressure vessels, wall thickness

[RuBear]

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.

 

[Big Jock]

Rubear I found it to be thick walled and a minimum thickness off 231mm would this be correct??

 

[RuBear]

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.

 

[oxon88]

no not cracked it yet. I am stuck trying to apply thick walled equations...

 

[Big Jock]

I got the thick walled equation to = 6.71
And the thin walled equation to =7.71...

 

[oxon88]

which equations are they Big Jock? do you mean thickness ratio?

 

[Big Jock]

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

 

[oxon88]

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...

 

[Big Jock]

Radius minus wall thickness = inside radius...

 

[oxon88]

ok so R_i = 1.553m and R_o= 1.784m

what am i looking to find out with these figures?

 

[Big Jock]

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

 

[oxon88]

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 r_i from r_o

 

[oxon88]

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 σ_h, and then use this new value of σ_h to re-calculate the wall thickness?

 

[oxon88]

so using known values in thick walled equations...

when r = r_i = 1553mm

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


when r = r_o = 1784mm

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





do i now need to recalculate wall thickness?

 

[oxon88]

can anyone help?

 

[LDC1972]

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 σ_h, and then use this new value of σ_h 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?