Tapered Transition

[humbubble]

I have a 42" od x 5/8" thk. elliptical head that is going to be welded to a 42" od X 1" thk. rolled cylinder. From the weld joint down 2" the id is machined to 40-1/2" id. from the weld joint we machined a 3:1 taper to the 40-1/2" id. We are left with a jog 2" down now though. Is this still per code? See pdf for a visual.

 

[vesselfab]

What is the minimum thickness for the shell?

 

[SnTMan]

Why did you not do it in one bevel, 3/8" x 1 1/8"?

If you are proposing no taper from 40 ID to 40 1/2 ID, bad idea.

Regards,

Mike

 

[Duwe6]

Leafing that square-shouldered 1/4" step is "illegal" - specifically disallowed by Code. Just bevel it back at the same 3:1 taper you are using at the weld prep.

Better than that, why not counterbore the 1" internally down to 3/8", back about 1½ - 2", and then transition to the i" using a 3:1 taper. Counterbores are what is traditionally used for thicker-to-thinner transitions. The 1½ - 2" is necessary to get the counterbore well away from the weld area, to make it easier to x-ray or UT the butt weld.

 

[humbubble]

vesselfab - minimum thickness for pressure is 1/16", the extra thickness is for external loads. We can go down as far as 3-1/2" before getting into the effective area.

SnTMan - We had to send this out to be machined because our large LTL has not been hooked up. Our design was to have the taper run all the way, but the shop where we sent it, gave us this. We are short on time and trying to make due with what we got.

Duwe6 - I felt the same way, but our AI accepted it. The tapered transition per UW-9 specifies per the weld joint. Our AI is considering this outside the weld joint. Is there anything more specific you can cite from code that does not allow a step in the middle of the vessel. We are not capable of machining this piece at out shop. We would have to send it back.

 

[SnTMan]

humbubble, I think it is very odd that your AI thinks this is OK.

Another option is to build up the square corner with weld metal, again to a 3:1 taper.

You have my sympathies regarding your vendor.

Regards,

Mike

 

[Duwe6]

I fully agree with SnTman.

Can you send that AI to me? I have some existing vessels fabricated by folks that couldn't spell ASME, and they used a lot of 'hillbilly' engineering and fabrication techniques. I'll bet I could generate U-1's for them.

 

[SnTMan]

Duwe6, I could maybe send you an AI, but be warned it would solve my problems, not yours