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Vapor Belt Design

Vapor Belt Design

Vapor Belt Design

When a Vapor Belt is used on the Shell of a Heat Exchanger over the main shell, the attachment weld between it and the main shell forms as a single fillet lap joint. Please see the attached figure.
1. Is the Vapor Belt to be designed as a Jacket to Appendix 9 of ASME Sec VIII Div1. But, I find that
the pressure limitation for jacket vessel is 100 Kpa where as the design pressure of shell will always be more than the limit and here it is 25 Kg/Cm^2

2) Also as per UW-12 table type 6, such lap joint welds are not permitted for Full / Spot radiography jobs.
I am not sure whether my understanding is in order.
In these circumstances how to treat the vapor Belt design and attachment.

RE: Vapor Belt Design

Why do you want to use a fillet weld?
Use a full penetration weld

Daniel Breyer
Inspection Engineer


RE: Vapor Belt Design

DK44, DBreyer is correct this should be a full penetration detail, not a lap joint, not a single fillet.

I have designed any number of these things, I have only rarely been completely happy with the results. The best details provide a full penetration butt-weld between the elements of the main shell and the distributor (vapor) belt. In my opinion the best detail is similar to your sketch. Shell-Cone-Lg cylinder-Cone-Shell. Full penetration butt welds at each round seam. Rather that the shell carrying thru the interior a liner is attached at one end only, at the cone small end & slotted as needed. Main seams are full penetration, double welded, fully radiographable if needed.

Probably next best is to substitute a flanged & flued head for each cone. Same results but F & F heads tend to be harder to buy. Sometimes a formed head (elliptical, torispherical or flanged only) can be used for the belt ends. This can give you a butt-weld at the large cylinder, but a corner joint at the main shell. Less desirable.

Least desirable, to me anyway, is a design with flat end plates. Corner joints at ID and OD. Large welds usually per UW-13.2(e). No RT possible. Because of space requirements this tends to be the most common detail.

I have not found Apx 9 to be especially useful for vapor belts. They are main elements of the pressure boundary, and should be designed mostly per UG / UW rules. Some Apx 9 details might be used for closing members in some cases.

I'd say if you have space for two cones, you are very lucky. Butt weld 'em :)



The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Vapor Belt Design

DBreyer & SnTman.
1. Vpor Belt Transition is conical, the weld joint between the Cone and Main Shell is an outward Lap joint of Single fillet type. FPW cannot be achieved by construction.
2. Client wants Main Shell to be continuous and hence Conical Transition to Shell attachment weld is Lap Joint (of out side single fillet type)
3. Suitable slot openings are provided in the Main Shell under the Vapor Belt region.
4. Separate inner shell design is not acceptable to Client.
5.The Questions.
5.1 Are lap joints with outside single fillet, acceptable for pressure retaining parts forming a
352 If Vapor Belt is treated as a Jacket, is it limited by Pressure of 100 KPA by code App.9.

All views are welcome.

RE: Vapor Belt Design

DK44, I think your identification of the weld detail is mistaken.



The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Vapor Belt Design

You are very confused
1)This is not a jacket, not included in App 9 because external pressure is not possible in this design.
2)In your drawing the weld in cone-cylinder is not a butt weld.

This is a wrong design.


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