Vessel shell / dome mismatch

[07071975]

Recently we came across a big problem.Fabricated dome and shell dia got mismatched.

Fabricated Ellipsoidal dome id 3476 mm
Fabricated Shell id 3400 mm


Kindly help me with possible solution.

 

[weldtek]

Which one is correct? What's the material type & thickness? Is the head a 2:1? Is this for an ASME Sec VIII vessel?

 

[arto]

Whoops! I hate when that happens! ;-)
How about slit the shell lengthwise & add a 238mm[9-3/8"] strip & re-roll?

 

[waskillywabbit]

Whoops!

Head ID: 3476 mm = 136.85"
Shell ID: 3400 mm = 133.85"

You are only 3" off. Seems like a conical reducer at the intersection would be about as simple a fix as any.

Good luck...measure twice and cut once!


Brian
Pressure Vessels and Autoclave Systems

http://www.mcabeeconstruction.com

The above comments/opinions are solely my own and not those of McAbee Construction.

 

[JStephen]

The conical reducer sounds like an obvious option. But whatever you do, you're either going to have to do some re-engineering to make everything fit (and possibly reduce allowable pressure as well) or else bite the bullet and buy/fabricate the right item. If you put that conical reducer in, everyone that sees the thing for the next 50 years will wonder why it was built that way.

In the event that the thickness was considerably larger than the the offset, you might have other options. If the design pressure were actually very low, you'd have some other options.

 

[weldtek]

Depending on the mat'l type & thickness, a good fix may be to have the head fabricator re shape the head.

 

[unclesyd]

As weldtek suggest come back with more information.

In addition to his request you might add whether the vessel was PWHT'ed and the length.

PS:
I would get someone to fab the reducer if you go that way. The insulation guys are going to love you.

 

[bmoorthy]

You may convert the head to crown and petal type and still maintain the shape with in the permissible tolerances of UG 80/81 of ASME Sec VIII Div 1.

To reduce the amount of welding you may have only 3 petals and a small central crown. A good fabricator can easily maintain the shape with in limits.

 

[rzrbk]

Unless your company is fabricating this drum for it's own use, I would be hard pressed to believe that a purchaser would accept an extra cone section in their vessel.

Without the material/thickness/etc. information requested by weldtek, I would have to guess that in general, a new formed head may be less than or equal to the cost of the intensive cutting and welding required to resize the existing head.

 

[JoeTank]

Let me guess... you cut and rolled the shell BEFORE you strapped the head OD. Depending on design requirements and thickness, could you use a lap welded joint between shell and head?

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[07071975]

Dear all,


Thank you all for your valuable suggestions.


Shell / dome Mateial of construction as under

Dome : Thickness 25 mm 516 GR-70
: Ellipsoidal ratio 2:1

Shell : Thickness 14 mm 516 GR-70

Dear WELDTEK, could you suggest little more?

 

[weldtek]

You didn't say which diameter was correct, however, if the larger diameter is the one you want, or if not, but the owner could live with it, I would suggest cutting several feet out of the shell can(s) and splicing in a piece large enough to yield the correct diameter. Cutting back and adding a larger piece will enable you to avoid having two long seams just inches apart.
If you need the smaller diameter, the first thing I would do is contact the head fabricator to discuss the possibility of having him reshape the head(s). If you feel that none of these ideas will work, let us know, because there's obviously lot of talented people participating in this forum.

 

[deanc]

I agree with Stevebraune as the best solution.

Have you spoken with your AI? The Jusrisdiction?

I would require a NCR,new calcs.,NDE and maybe PWHT. It would be painful,but doable.

 

[waskillywabbit]

Just for curiosity's sake I'd like to know more of the specs of the vessel...length, orientation, supports, service...and particularly why the heads (~1") are twice as thick as the shell (~1/2")?

I can't see any customer accepting anything other than a "normal" shell correctly sized and attached to a correctly sized "normal" head, i.e. you fix the mistake so the vessel won't look like a "Frankenstein". While some of the suggestions are certainly "viable" options and structurally/code acceptable, I just can't seem to see some of them as anything other than "booty fab"...and I feel a customer would see them as the same, i.e. a cheap attempt to remedy a major mistake.

Best of luck.

Brian
Pressure Vessels and Autoclave Systems

http://www.mcabeeconstruction.com

The above comments/opinions are solely my own and not those of McAbee Construction.

 

[weldtek]

Just for info I ran the idea of re shaping the head past one of our local (Texas) head fabricators, and as I suspected, it's done all the time.

 

[abmech]

Check with your dished end manufacturer and get this re-pressed again to 3400mm diameter. Other option of making to shell ID to 3476 will call for approval from client/process, etc. I suppose 3400mm is correct diameter.

What are the design conditions which are causing disned end of 25mm thickness and shell of 14mm?

 

[GenB]

hey! I see no fixes here, you will have to change the shell or heads and use it in another job.
you have to accept and eat the mistake.

If you have a machine to expand the shell ends, disregard the above and calc for the thinning and enlarged OD
ER