Torispherical Head Calculation / Inside Crown radius value

[joeseeker16]

Hi ,

This is regarding the torispherical head thickness calculation , in UG-32(e) , it has been clearly mentioned that the inner crown radius (L) equals the outside diameter of the skirt (OD) , the same has been rightly mentioned in (CASTI Guidebook ASME Sec. VIII Div. 1 page.137 ) and (Pressure Vessel Handbook - E. Megyesy - 10th Ed) and many other sources..

But in ASME SEC.VIII-DIV.1Example Problem Manual PTB-4-13 page 29 ( example E4.3.4) , the inner crown radius L has been considered the same as the INSIDE DIAMETER of the vessel , the example is attached for reference

Now which case I`ve to considered during the solution if the given is the vessel inner diameter(Di) ? :

1- Considering L = Di + 2 vessel thickness ( which equals the skirt OD and conforms ASME in both UG-32 and appendix 1-4 ) (which equals in this case 72+2 *0.625 = 73.25 inch.
2- considering L = Di + head thickness + corrosion allowance = 72+ 0.625+0.125 = 72.75 inch.

None of these options is matching the solution shown in the example above , appreciate anyone who can clear this confusion.

Regards,

 

[JStephen]

The formulas in UG-32 are for certain heads with standard dimensions. The head in the example is not one of those, it uses non-standard dimensions, so they evaluate it using the appendix as noted.

 

[joeseeker16]

@Jstephen ,

Thanks for replying , so you mean to say the following :

-The inside crown radius (L) as a value differs accordingly with the head wither it was standard or non-standard :

In other words if the torispherical head is standard , so the knuckle radius is 6% of the inside crown radius L , and L as a value shall equal the skirt OD , but if it is non-standard torispherical head , L in this case = K1D , where D here is the skirt ID as per appendix 1-4 symbols in ASME code , is it what you mean to say ? and this is fine , so who is deciding wither the head will be a standard or non-standard ?

I believe also all the dimensions here shall be considered corroded as per UG-16(e) of the code ,right ? i mean in case of non-standard head , D/2h values in table UG-37 from where you`ll get K1 and substitute in the equation shown above to obtain L should be in the corroded condition ( DIcorr = Di + C.A ( corrosion allowance)

Appreciate if you or anyone has a calculated example for both cases ( standard / non-standard torispherical head.

Regards.

 

[r6155]

Formula in UG-32 is an example only (reduced formula and not a head with standard dimension): “For the case in which the knuckle radius is 6% of the inside crown radius and the inside crown radius equals the outside diameter of the skirt “.

See Appendix 1.4(d) for general formula.
Regards
r6155

 

[joeseeker16]

r6155 ,

so when you want to calculate the value of inside crown radius , you consider it = skirt OD or the same internal diameter of vessel (D)? , unfortunatly the answers still didn’t clear my point .

 

[r6155]

joeseeker16
Please, read slowly several times UG-32 and 1.4(d). Try to understand, it is very simple
Regards
r6155

 

[JStephen]

ASME isn't telling you what shape that head should be (other than certain limits on it) but rather what the thickness will be for the geometry you use. Usually, it'll be 100%/6% or 2:1 elliptical or 80/10, but can be otherwise if you choose. I think I've also seen some minor variations in how head geometry is standardized with the head companies.

 

[marty007]

Just to throw one detail in here regarding torispherical heads. Take a look at the following interpretation: VIII-1-86-175

This may be the reason that the code does not use the standard inside crown radius (ICR = OD) in the example.

If you use ICR = OD, then add corrosion allowance, then the inside crown radius in the corroded condition would equal ICR(corroded) = OD+CA > OD. This violates the code as is clarified in the interpretation.

So long story short, per the rules of ASME VIII-1, a standard torispherical head violates VIII-1 if your vessel has any corrosion allowance.

Cheers,
Marty

 

[joeseeker16]

@marty007

Thanks for replying , focusing in the last sentence of your comment above which i found it logical and matching the requirments of UG-32 where the ICR should not exceed the outer diameter of the skirt,kindly refer the attachment i found in one of the PV references ( CASTI guide book ASME Sec VIII ) , where the example was for standard torispherical head with a corrosion allowance 0.125 inch and it clearly considered UG-32 not appendix 1-4.

for the attached example , if we adjust for corrosion allowance , we shall find the following :
L)corr = OD + C.A = (120+2x0.88)+0.125 = 121.9
OD (in corroded condition) = Di + 2C.A+ 2xThk = 120+ 2x0.125+2x0.88 = 122.01
from the results, Lcorr < OD)corroded condition , where UG-32 condition has been safely applied without any violation right ? correct me if something above was wrong please.

kindly note that the confusion am still falling in is facing sometimes references using L = ID while applying Appendix 1-4 Whereas some other references ( in the same attachment (CASTI guidebook)in the second case of non-standard torispherical head ) considering L = OD.

Thanks.