Calculating minimum blank thickness B13.3 ASME 1

[ghensky]

Ok after sufficient time waste here I am. This is my first time to calculate minimum thickness of a blind flange. I can read the Chart (attached) and find the blind thickness, but at the same time trying to work out the equation but with no success. Here are the specs,

Mild Carbon Steel A105
Gasket diameter, dg = 24"
Design Temperature = 80 Deg Cel
Maximum Allowable Stress at design temperature, S = ? (Do not know how to read Table A-1 of B31.3)
Internal gauge pressure, P = 110 PSI
Weld Joint Quality Factor, E = 1 (That's what I understood, since there is no weld on the flange)
Weld Joint Strength Reduction Factor, W = 1 (Again, that's my understanding, use 1 since there is no weld on the flange)
Corrosion Allowance, c = 0.02" (Flat surface)

Minimum thickness, tm = dg*SQRT(3P/16SEW)+c = 24*SQRT(3*110/(16*16500*1*1))+0.02 = 0.87"

1. Where is the value of S for Mild Carbon Steel A105 in Table A-1)
2. Is my chart value correct? (attached)
3. In the equation I made a guess for the S value to bring it to 0.87"

When I use the chart, I get the minimum thickness of 0.877" corresponding to 125 PSIG. But when I plug all the values and calculate using the formula, the minimum thickness is no where close to any sensible thickness. Could someone point my mistakes pls? Thanks!

 

[TGS4]

In the 2012 Edition of B31.3, A105 has an allowable stress of 23.3ksi at 100°F and 22.0ksi at 200°F. Your 80°C is 176°F, so to the nearest 0.1ksi, your allowable stress would be 22.3ksi.

Per 304.5.2, you should be using the equation in VIII-1, UG-34. In UG-34, Figure UG-34 shows you that sketch (j) is appropriate for your configuration. UG-34(c)(2) tells you that you should be using equation (2)for the calculation. Equation 2 is a little more complicated than your equation.

So, your chart method (not sure where that came from) appears to be incorrect - use the formulae as indicated in B31.3 and VIII-1.

 

[ghensky]

Thanks TGS4 now I can read A-1 with confidence after your comment! But how did you calculate 22.3 ksi for 176 deg F? (Did you interpolate?)

Also, I just learned the difference between a blank and a blind flange. I needed the calculation for the blank, not for the blind flange. So I think I used the right equation by chance, hehe! I wish I could modify the title of the post.

So for anyone reading this post without any prior experience about blank vs blind flange, my problem is to calculate the blank and the answer is,

Minimum thickness, tm = dg*SQRT(3P/16SEW)+c = 24*SQRT(3*110/(16*22300*1*1))+0.02 = 0.75" (Equation obtained from ASME B31.3-2014 304.5.3(b)).

 

[TGS4]

Linear interpolation is permitted for intermediate values in the Table.

If you want to change the title of the thread, just "red flag" your original post and ask the site owners to change it for you.

For calculating the thickness of a blank, that is indeed the correct calculation. When I perform the calculation, I get 0.75in.

 

[ghensky]

Oops, I also got 0.75" but forgot to change in the post.
Thanks for pointing that out and your great cooperation!