Head to Shell welding detail (taper transition)

[Paulettea]

Dear All
In table 4.2.5 of ASME BPVC Sec.VIII-2 the detail for welding of a head to shell joint is illustrated. Detail number 4 & 5 are the cases when head is thinner than the shell. In these two cases there is a criterion which says:
a>=3b
I think that this needs a little clarification. The question is that can I taper the head from both sides with the ratio of 1/3 or if I want to taper from both sides the sum of the ratios has to be 1/3.
Suppose that I have a shell which is 10 mm thicker than the head. If my taper is from just one side, then it is clear that the taper length has to be at least 30 mm. Now if I want to taper from both sides can I give each side a chamfer of 5mm x 15mm and say that both tapers have the ratio of 1/3?
Warm Regards

 

[saplanti]

I do not have the code with me, so I will write from my experience.

You do not mention about the type of the head. I assume that the heads are hemispherical. The transition is going to be part of the hemispherical head in calculation (the transition portion will be physically on shell side), (otherwise you cannot have 10 mm less thickness for the head) and you need to satisfy the head internal/external surface will flash with cylindrical portion, or the spherical head internal and external radius will stay within the thickness border of cylindrical shell portion. Therefore you need to go drawing board/ AUTOCAD etc.. to verify your case and adjust the head diameter for the transition. I assume the head and shell materials are the same for this approach, different materials can make the problem slightly difficult.

The transition in your case is NOT cylindrical shell to cylindrical shell, so your approach is not easy to be used.

Hope this helps.

 

[saplanti]

Depending on the internal radius of the head that you come up for the transition, the head thickness may change slightly. If you are writing the minimum thickness on the head drawing, the change in the radius may change the minimum thickness.