Misalignment Fit up Head to Shell in a boiler 1

[Dudesa]

Hi All,

I have an issue on a fit up of a flat head (tubesheet) with the shell.
head & shell th 45mm
ID 2000mm
in order to keep final lenght due to an error on nozzle fit up the head have been reduced in hight (smaller diameter) and i have now a misalignment of about 15 mm all around.

What will be the maximum misalignment allowed according to ASME VIII div 1,

Yhank in advance

 

[gr2vessels]

Dude,
I'm having trouble understanding your expression "misalignment". The ASME VIII Div 1, UG-34 would give you all the "fit-up" requirements for the flat head (tubesheet). Please note that misalignment means offset of two centerlines, which cannot be measured in terms of 15 mm all around. Also remember, a picture tells more than 1000 words, try post/send a sketch of your misalignment as an attachment and we'll try to help you.
Cheers,
gr2vessels

 

[Dudesa]

gr2vessels,

thank for this quick answer, you are right I mixed up with alignment it is mmore an offset.

I attached a sketch of it.

 

[GoofyatEEE]

Looks like a pretty big "woops" to me. I would suggest that now is the time to get your friendly local ASME code guru in to assist. Only a detailed review of the calcs and design will lead you to the best answer on this one.

 

[CodeRef]

The VIII-1 governing paragraph for alignment of butt welded joints is UW-33. In your case, for section thicknesses between 38 to 51 mm, the maximum misalignment is 3mm.

 

[unclesyd]

What are your design conditions?

Is the weld prep as drawn?

Has the weld prep been completed?

 

[Dudesa]

The welding will take place next week with a "transition weld" on the inside and then outside part by SAW.

For shell part
the design pressure about 800psi and Temperature 550F.

thanks

 

[JoeTank]

I seriously doubt your AI is going to be happy at all with that mess. i suggest you get the AI on board about this ASAP. Better to find out the bad news now rather than after it's welded.

Joe Tank

 

[doct9960]

Dudesa,

I agree with Joe. Keep us informed of the outcome.

 

[gr2vessels]

Hi dudesa, I'm back.
It looks a bit dodgy for a cookbook type of vessel design, but it's not hopeless. The code is recommending a few "standard shapes" for those dished ends, but does not preclude the use of other shapes, if you can produce a calculation (or even a FEA) to show the head is OK. Try to create the shape of a semi or tory head using the available thickness of material, then run the calcs for the given maximum thickness you can squize out of the fit-up sketch. It could herald some bad news, like de-rating of your vessel, but you may also be lucky to salvage the vessel rating, who knows. At least you know where you are, when the AI will tell you to scrap the dished end.
cheers,
gr2vessels

 

[BillBirch]

Could you swage it down somehow?

 

[Dudesa]

Thanks for your support,

For your info
A transition weld will be done by SAW on the inside and outside.

regards

 

[gr2vessels]

Well done;- ditch that sily cookbook called ASME...
cheers,
gr2vessels

 

[MJCronin]

Dudesa..

Could you psot pictures or cross-sectional sketches of the repair for us that are "pictorally challenged" ?

Thanks...

-MJC