Part UHX 14 - Your Opinions Please

[SnTMan]

Hello All, I am running my some of my first tubesheet calculations under Part UHX, using CodeCalc. This particular unit is a pipe-size externally sealed floating head unit, (TEMA AEW) and is a replacement rather than a "new" design

1) Stationary tubesheet - 5/8" thk, floating tubesheet 2" thk. Permitted under Part UHX? If not, why not?

2) CodeCalc is calculating certain quantites for the stationary tubesheet, but not for the floating tubesheet, such as: tubesheet shear stress, stress and force in outermost tube, allowable tube-tubesheet joint load. Any ideas why, other than "Not Required"?

3) Do you think tubesheet calculations could be performed using TEMA formulas under U-2(g)?

I can't help thinking Part UHX was a solution in search of a problem.

Thanks for your input.

Mike

 

[PVGuy]

SnTMan,

1. This is not permitted under UHX; I am not quite clear about the derivation that requires this. However, both tubesheets are required to have the same thickness but may have different edge conditions.
2. It is not that UHX does not require them; I believe it is becaue they are redundant or identical to the stationary values.
3. The forward to ASME BPV books basically says that the book is not the end all/have all. It is a set of minimum requirements and ultimately the responsibility fall to the designer/engineer/fabricator. It also says that it is not intended to prevent other configurations that are not included here. That being said, make sure that those approving this design understand this as well.

Good Luck

 

[SnTMan]

PVGuy, thanks for your response.

I am trying to gain some confidence in applying UHX. Not really looking forward to that first fixed tubesheet run.

Re your answer to 2), you may be right. However, CodeCalc seems to require each tubesheet to be run separately with all applicable data entered by the user, and the quantities I mentioned are not calculated for the floating end.

3) You're right about needing buy-in from the AI, customer, etc.

And 1) I find it curious that design practices that have been used successfully for many years are suddenly not permitted, as in my example. Another example:

Clad CS stationary tubesheet, SS floating head and tubesheet. Very common construction. Now not permitted.

What do we do with replacement bundles designed under TEMA? Part UHX requires a great deal of information to make the calculation that may not be available for replacement work, the work may or may not be within UHX scope, and the design may or may not meet UHX requirements.

The best solution may just be to not Code stamp it if the customer will permit.

Maybe not the best situation, but there it is.

Mike

 

[PVGuy]

SnTMan,

The code is great; but unfortunately many treat it like gospel. This can be good and bad. For instance, most people do not pay attention to all of the points in the code that state "minimum" for the requirements listed here. On the other side, many designers, inspectors, and end users believe that all designs have to be pushed into the tiny range that the code allows. This is not the intent of the code nor the wish of the code writers. Basically, if the design falls within the scope of UHX, then you dont have to worry; but if you need to be more flexible then that, as long as good engineering practice is used, you are ok for U-2(g). If you need more ammunition, read the interpretations and code cases involving UHX. They are full of language like, "..if the design...is it ok to use U-2(g)..". Many of these have the reply of Yes. Also you may check with your insurance company. I know some of them have some code experts on staff.

 

[SnTMan]

PVGuy, unfortunately I have not had a chance to read up on the interpretations, I'll bet it's interesting. Prior to a period of underemployment, I had been using TEMA under the Code Case (I think) that allowed delaying the implementation of pert UHX, and after this period, I became involved in a shell and tube project featuring rectangular tubesheets. I am now having my first real experience with UHX and am now discovering some of its peculiarities.

Thanks for your input. I would really value hearing others' experiences as well.

Mike