# Radius of a pressure vessel?

1. Oct 26, 2015

### minoroctave

1. The problem statement, all variables and given/known data
The problem is to calculate the required thickness of the shell of a pressure vessel, given that the design pressure P is 400 psi, the strength S is 15800 psi, the corrosion allowance CA is 1/8"and $R_{design}$ is to be found by iteration.

2. Relevant equations

$t_{req}=\frac{P(R_{design} + CA)}{S-(0.6P)}$

To account for corrosion, CA is added to $t_{req}$
$t_{CA} = t_{req} + CA$

Using $t_{CA}$ , a standard size is selected, denoted $t_a$

3. The attempt at a solution
Guessing $R_{design}$, I solved for $t_a$

Re-arranging the equation to solve for P,

$P=\frac{tS}{(R_{design}+CA)+0.6t}$

and using the guessed $R_{design}$ value with the $t_{req}$ value found above, I should check if P>400psi?

2. Oct 26, 2015

### SteamKing

Staff Emeritus
It takes more than a radius to define the geometry of a pressure vessel. For instance, what is the capacity of this vessel? One liter, a thousand liters, what?

3. Oct 26, 2015

### Nidum

I'm sorry but you can't just guess your way through this sort of problem . You either need to learn the necessary engineering skills or get help from a professional .

4. Oct 26, 2015

### minoroctave

the capacity is 5000 US gal. I attached the full question

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5. Oct 26, 2015

### Nidum

Now finally we know what you are trying to do perhaps we can be a bit more helpful .

Draw a pressure vessel of credible shape and with required capacity . Decide for yourself what R should be to give a well proportioned design .

When you have your value of R the shell thickness calculation should be straightforward .

Last edited: Oct 26, 2015
6. Oct 26, 2015

### minoroctave

is this the same as solving the total capacity equation for $R_{design}?$
but wouldn't I need to know the length of the shell? that's not given either

7. Oct 26, 2015

### SteamKing

Staff Emeritus
That's what design is all about. You've got to take the capacity of the pressure vessel, along with the other specifications, and figure out the dimensions consistent with what service the pressure vessel must perform.

This is not a problem from a textbook where you plug numbers into a formula and crank out an answer.

I fear, given the deadline for this assignment, you will not be able to do all the necessary design calculations and make a drawing for your proposal.

8. Oct 26, 2015

### Nidum

You decide for yourself what the length of the shell is . You literally have to design the pressure vessel from very basic information .

9. Oct 26, 2015

### minoroctave

thanks everyone, I get it now

its ok, the deadline was extended

10. Oct 26, 2015

### Nidum

Pick a value of R which is at least in the ball park . Draw a pressure vessel with shell length L = 1.5 to 2 R . Put a semi elliptic shell each end (ratio 2:1)

Does it look OK ?? Adjust proportions if it doesn't . Calculate volume . Scale up or down to get correct volume . You now have a pressure vessel shell and a value for R .

11. Oct 26, 2015

### SteamKing

Staff Emeritus
12. Feb 20, 2016

### billy_boy

can the thickness of the head be different from the thickness of the shell