ASME VIII Div1.Cone/cylinder intersections

[johnnymist2003]

Hi all,

I have a kettle type heat exhanger-TEMA AKL.The tubesheets are both fixed tubesheets.The tubesheets are welded directly to the conical part of the shell, using a hub of minimum dimensions(lets say 25 mm).Per ASME VIII, Div.1, Appendix 1, the small end of the cone (at the cone/tubesheet junction) needs to be reinforced.Assume that the limiting distance of reinforcement [sqrt(Rsts)] is GREATER than 25 mm.May I take into consideration the area available in the tubesheet hub in order to reinforce the junction (obviously also reducing the length available to 25 mm) OR should I ignore this area in the hub? The obvious answer is to ignore the area available in the hub as this would be the more conservative approach, however, the reason for asking the question is that ignoring the area in the hub necessitates a substantial increase in cone section thickness to reinforce the junction.The exchanger is stainless steel, so obviously there are also price implications involved.I'd appreciate any thoughts (based on Code/TEMA considerations).Please do not refer to ASME new Appendix UHX (the exchanger was designed to an earlier Code edition).
Thanks.
John

 

[prex]

In my opinion you can use the metal in the hub (of course only above the minimum required for a shell with the same diameter): this position comes from the fact that the hub is not required to resist any stress other than the stresses in a shell. The hub is provided only to insure a smoother transistion to the tubesheet and hence for fatigue resistance reasons.

prex

http://www.xcalcs.com

Online tools for structural design

 

[JoeTank]

I wish I had an ASME Code handy at this moment, but if I did, I believe that I would find that the rules for a cone-cylinder intersection are for the intersection of a cone and a cylinder only. A 25mm stub on a tubesheet is hardly a cylinder. I wonder if you are trying to apply the right ASME rule here. A fixed cone-tubesheet connect would seem to be equivalent to a cylinder-tubesheet connection with an added twist. An additional outward force would be applied to the perimeter of the tube sheet, the magnitude of which would be determined by the cone slope, diameter and pressure.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[johnnymist2003]

Hi Steve,

you are quite correct, the reinforcement rules do indeed apply to the intersection of the cone / cylinder.However,
in my opinion, the "hub" would be considered a cylinder because at the junction,it would be subject to stress due to the internal pressure [no mention is made of a "minimum" cylinder length - except where the minimum reinforcement length is calculated as sqrt(Rs ts)] . Thus, I think that the Code Appendix 1 rules for reinforcement of the junction would apply.Comments please.
John