Ellipsoidal Head Thickness Calculation Inquiry

[joeseeker16]

Hi ,

This is regarding the design of ellipsoidal heads in pressure vessels, where I have a case here for a vessel of internal Dia = 2400 mm , and design pressure of P= 6barg, the design was done with the aid of PV-ELITE software.

while reviewing the final calculation report generated by one , i noticed in the elliptical head calculations part that the program directly considered Mandatory appendix-1 (SUPPLEMENTARY DESIGN FORMULAS) paragraph 1-4(c) instead of considering UG-32(d) , where the calculations have shown the factor "K " (a factor in the equations for ellipsoidal heads depending on the head proportion D/2h as per appendix 1-4 description ) , an snap shot of the report is shown below for reference :

"Elliptical Head From 30 To 40 SA-516 70 , UCS-66 Crv. B at 80 °C

Material UNS Number: K02700

Required Thickness due to Internal Pressure [tr]:

= (P*D*Kcor)/(2*S*E-0.2*P) Appendix 1-4(c)

= (6.059*2406.0000*0.997)/(2*137892.00*1.00-0.2*6.059)

= 5.2711 + 3.0000 = 8.2711 mm."

Any idea why the program considered appendix1-4(c) not UG-32 ? any clarification when we can use each ? as far as I know that we use this equation in case the elliptical head ratio is not 2:1 but this was not our case here as the vessel suppose to be ellipsoidal 2:1 head , was it something wrong during the input?

Appreciate your clarifications..

Regards,

 

[r6155]

UG-32 is only for D/2h = 2
With 3 mm corrosion D/2h= 1,995 and K= 0,997, hence app 1-4 (c) is used.
Regards
r6155

 

[joeseeker16]

@ r6155

but i think D/2h = 2 Already in this case as D = 2406 and h = D /4 = 601.5 , 2h = 1203 unless i am missing something , therefore : D / 2h = 2 , how did you get it 1995 ?
Regards,

 

[TomBarsh]

Your ellipsoidal head has 2:1 ratio in the new condition. It's 2400 ID and the height inside is (2400/2) / 2 = 600.

In corroded condition (3 mm corrosion) the head has a diameter of 2406 ID and the height inside is 603.

D / 2h in the corroded condition is: 2406 / (2 * 603) = 2406 / 1206 = 1.995. Which is not 'precisely' 2:1

Use the formula given in Appendix 1-4(c) where K = 1/6*(2 + (D/2h)^2) = 1 / 6 * (2 + (2406 / (2 * 603)) ^ 2) = 0.997

Oddly enough, Table 1-4.1 states that "interpolation is unnecessary", but software typically use the formula exactly.

 

[r6155]

Look at your formula, it´s used for D = inside diameter = 2400 hence h= 600
D corroded = 2400 + 2*3 = 2406
h corroded = 600 +3 = 603
D / 2h = 2406 / 2*603 = 1,995
Kcorroded = 0,997

See sketch

Regards
r6155

 

[r6155]

Now the sketch

r6155

 

[joeseeker16]

@ tombarsh , r6155

so you have to calculate it always in the corroded condition to obtain the factor K ?

 

[joeseeker16]

@r6155

sorry man , you attachment is not working , i tried to downloaded it but i failed ...

 

[r6155]

I made a mistake, sorry

Regards
r6155

 

[r6155]

I dont know what happens with the web
I try again and upload the file

r6155

 

[r6155]

@ joeseeker16

D / 2h = ratio of the major to the minor axis of ellipsoidal heads, which equals the inside diameter of
the skirt of the head divided by twice the inside height of the head, and is used in Table 1-4.1, hence corrosion shall be added to calculate factor K.

Regards
r6155

 

[joeseeker16]

@r6155

thanks for the sketch , now it`s working ..

Regards,