Appendix 13 question 1

[MikeG7]

For a rectangular pressure vessel, let's say the outside dimensions are 1 x 1 x 4 "units" long.
One cross section is 1 x 1 and the required thickness calculations would be very different from the 1 x 4 cross section analysis. What is the correct way?

 

[EnergyMix]

Are you confusing the thickness with the length of the unit? Why did the thickness of the material change between the sides?

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[chicopee]

The best thing is to present a sketch or drawing because your description is very confusing as pointed out by the above responder.

 

[MikeG7]

Sorry to confuse you the sketch will help. In the sketch attached "t" is the thickness and the proportions of the cube are 1 x 1 x 4. What I'm asking is what is the correct cross section for the Appendix 13 calculations.

 

[gr2vessels]

Look up at 13-7 paragraph. Also, look at the examples at 13-17 paragraph. They are quite self explanatory.
Cheers,
gr2vessels

 

[MikeG7]

gr2, I have followed the examples of 13-17 and in general I understand the concept, but what I am still not sure of is that all these equations terminology is of short side and long side plates and the end plate. There is a particular cross section of the cube that is taken into consideration. But if the cube is sectioned in another plane, the answers are different. To explain, per my sketch, if the cross section is taken in one direction the short and long plates are both 1 unit long. But by my logic the cross section could just have easily been decided to be taken on the 1 x 4 side. The results would be different.

 

[innovation2]

I think you need to establish which direction you would like to run your pitch for reinforcement. If it was me, I would remove the end caps and focus on the "long" axis of your cube. The end caps can be considered seperately as braced stay or flat plate.

 

[MikeG7]

Thanks Innovation2
I don't have reinforcement, Appendix 13 caters for both reinforced and un-reinforced cases. Still I think your point is relevant. But now, by choosing the "long" axis, haven't you then chosen to only perform the analysis on the "easy" section and it would be possible to pass the calculation in this direction, but fail in the other direction if you were checking to see if a certain thickness is sufficient?

 

[innovation2]

In App 13-7 it states that he equations in these paragraphs, the moments and moments of interia are calculated on a per-unit-width basis. In your example you would negate the dimension 4 and work on this cross section. Use 13-4(f) to review the end plates.

Example 13-17(a) is just about spot on for your example. I would consider the longest dimenison to be the centerline and adjust the equations to accomodate the per-unit-width as in example 13-17(a). I think you have some valid points but ASME has made some assumptions that are not perfectly clear regarding the design as it is difficult to determine the "end/head" in your case.

 

[MikeG7]

Well, if everything was clear I guess we wouldn't be asking questions or be having debates...thanks, I'll follow your advice as it is at least moving me forward on this.