10/4/2014 CR4 - Thread: Pressure Vessel Shell to Elliptical Weld Head Joint

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wijeeshAssociate

Join Date: Apr 2008Location: IndiaPosts: 27

Pressure Vessel Shell to Elliptical Weld Head Joint10/19/2011 1:30 AM

Dear All

In ASME pressure vessels,

A Shell of (40mm thk) & a head of (20mm thk) (2:1 elliptical) can be joined as per Fig UW 13.1 by adding additional weldmaterial in heads???

Code - ASME Sec VIII Div 1

A difference in thickness of 20mm is acceptable or not? is there any limitations?

Please advise

Regards

Vgsh

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#4 "Re: Pressure Vessel Shell to Elliptical Weld Head Joint" by blackpanic73 on 10/19/2011 1:10 PM (score 1)

TornadoGuru

Join Date: May 2009Location: Ketchikan, AK,USAPosts: 14940Good Answers: 564

Re: Pressure vessel Shell to Elliptical weld head joint10/19/2011 1:50 AM

That sounds virtually impossible. Please review the shell and head calculations.

I'm not sure, but as I recall, the allowable thickness difference is much less than that. (1/16" or 1.5mm?)

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AnonymousPoster #1

Re: Pressure Vessel Shell to Elliptical Weld Head Joint10/19/2011 7:45 AM

Wajeeb,

In ASME VII, where two components of unequal thicknesses are joined, there is usually a taper machined into thethicker component. Then a standard full penetration weld is made to join the two components

In the USA, elliptical heads are usually ordered with a "straight flange" (SF) to facilitate the weld(www.brightontrueedge.com) to the shell.

With a proper ASME Code sizing of components, most pressure vessels have equal thicknesses of elliptical heads andshells.(i.e. this problem will not exist) I do not understand why you are trying some kind of bizarre third-world solutionon an issue that should not exist.

Please explain....Is your shell too thick for the design pressure expected or have you miscalculated the head thickness ?

Is this the first vessel you have ever designed ?

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10/4/2014 CR4 - Thread: Pressure Vessel Shell to Elliptical Weld Head Joint

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brkmechCommentator

Join Date: May 2009Location: UAEPosts: 82Good Answers: 3

Re: Pressure Vessel Shell to Elliptical Weld Head Joint10/19/2011 10:50 AM

Acceptable if your calculations are right, which is not probable in case of ellipsoidal heads.

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blackpanic73Commentator

Join Date: Sep 2011Location: neighbor of thebest country in the worldPosts: 60Good Answers: 2

Re: Pressure Vessel Shell to Elliptical Weld Head Joint10/19/2011 1:10 PM

Dear wijeesh

Greeting to you

The maximum allowable change in thicknesses between shell and head is one-fourth of the thickness of the thinnersection - head thickness - in this case .

In Your Case the change in thicknesses exceed this limit, so it is not allowable to weld thickness 40 mm to thickness 20mm.

Note: the thickness of the head must equal to the thickness of head at the same design pressure if you used ellipsoidalhead (2:1). But if you used semi - spherical head the thickness of semi spherical head in this case will equal to 1/2thickness of the shell from the thickness calculations, then you must increase the head thickness to achieve theallowable limit of change of thickness to weld it to gather by using tapered transition.

Remember that :

- FIG. UW-13.1 a,b,c,d & e used for end heads when the thickness of the shell section of the vessel does not exceed5⁄8 in. (16 mm).

- FIG. UW-13.1 f,g & h are examples of attachment methods which are not permissible.

- FIG. UW-13.1 j & k shall be provided at joints between formed heads and shells that differ in thickness by more thanone-fourth the thickness of the thinner section or by more than 1⁄8 in. (3 mm), whichever is less.

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asd23789Commentator

Join Date: Jun 2011Posts: 65

Re: Pressure Vessel Shell to Elliptical Weld Head Joint10/20/2011 12:12 AM

Dear blackpanic73 sir,

In your reply it is mentioned : "The maximum allowable change in thicknesses between shell and head is one-fourth ofthe thickness of the thinner section - head thickness - in this case ."

I am not able to understand why you say " the maximum allowable" ?

the purpose of the code in providing taper is to have uniform fusion along the width of weld and to have less amountof discontinuity stresses.

also the statement in Code : " A tapered transition having a length not less than three times the offset between theadjacent surfaces of abutting sections as shown in Fig. UW-13.1 sketches (j) and (k) shall be provided at jointsbetween formed heads and shells that differ in thickness by more than one-fourth the thickness of the thinner sectionor by more than 1⁄8 in. (3 mm), whichever is less."

when code mentions whichever is less, it tries to have taper at the min possible difference between 2 joining parts.

Please correct.

Thanks & Regards

ASD23789

__________________The light of blindness of knowledge is yet to reach me, forget being clever.

asd23789Commentator

Re: Pressure Vessel Shell to Elliptical Weld Head Joint10/21/2011 11:56 PM

Dear blackpanic73 sir,

I request you to please elaborate on your post.

Sorry for any rudeness in my earlier comment.

Regards

ASD23789.

10/4/2014 CR4 - Thread: Pressure Vessel Shell to Elliptical Weld Head Joint

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asd23789Commentator

Join Date: Jun 2011Posts: 65

Re: Pressure Vessel Shell to Elliptical Weld Head Joint10/22/2011 12:00 AM

Dear blackpanic73 sir,

Please help regarding your comment.

Sorry for any rudeness.

Regards

ASD23789

__________________The light of blindness of knowledge is yet to reach me, forget being clever.

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#4 "Re: Pressure Vessel Shell to Elliptical Weld Head Joint" by blackpanic73 on 10/19/2011 1:10 PM (score 1)

Users who posted comments:

Anonymous Poster (1); asd23789 (3); blackpanic73 (1); brkmech (1); Tornado (1)

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