Sect. VIII UHX 1

[BigTank]

This is a general question regarding the subject...

Where does the thickness h end, and the flanged extension thickness hr begin, affording the code's definitions of these thicknesses?

Often times it seems that, for a fixed tubesheet exchanger for example, beyond the shell side pressure boundry diameter there is a slight extension that is thicker than hr, and exposed to only the tube-side pressure and the moment resulting from the bolt loading. This thickness always falls between that of the flanged extension and the portion of the tubesheet exposed to both tube-side and shell-side pressures, but seems to have no basis for calculation under the code.

Am I missing something?

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Fitter, happier, more productive

 

[gr2vessels]

BigTank,
The hr extension doesn't need any additional thickness past the shell OD. It is common practice to leave the hr same thickness as the tubesheet, to minimize the unecessary machining. On the same principle, if you see any 'additional' thickness on the flange extension, is for saving a buck on machining costs.
Cheers,
gr2vessels

 

[BigTank]

I think you may have misunderstood my question, gr2. I also think that this is a case of the picture being worth 1000 words. Let's see if this works:

From what I've encountered, typically the tubesheets of a fixed-tubesheet exchanger will have a large bolting flange diameter (O.D.), then a 'boss' on either side of that diameter to which is attached the shell on one side, and a bolting flange on the end of the channel to the other. These bosses seem to typically be of different diameters. Ref. figure UHX 13.1(b) for an illustration of a similar configuration without the bosses.

The attachement of the shell-side boss to the shell would be done as in fig. UW13.2(i). The shell-side boss is pictured here.

Now imagine on the tube-side a confined-face flange bolting to the tubesheet, causing the need for the 'boss' on that side as well for gasket seating. The diameter of this 'boss' is the second largest (with the bolting flange extension being largest), and the shell-side attachment 'boss' being the smallest. You can see how this would result if you imagine a confined-face joint in fig. UHX-13.1(b).

The result of this as I see it are 3 thicknesses: the thickest portion being through the shell side boss to the tube-side face 'h', the second thickest being between that shell side boss diameter and the tube-side boss diameter, and the thinnest being the flanged extension 'hr'.

It's this middle thickness that I'm questioning. It appears that this thickness could be calculated as that required by UHX, but calculated with the shell-side pressure being zero.

I hope that makes sense.

Thoughts on this interpretation?

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Fitter, happier, more productive

 

[SnTMan]

BigTank, you do not normally need to calculate this intermediate thickness. It is usual practice that hr<h(intermediate)<h. Therefore, only h and hr are calculated.

These "bosses" to use your term, are often called "turns" in the shell & tube world. The diameter of the shellside turn is less that the shell ID by some clearance, 1/4" is common. It is also commonly 1/4" deep, or some other depth as per company practice, etc.

The tubeside turn diamater is generally, if used in a confined joint, 1/8" less that the gasket ID, and is usually 1/4" deep as well.

Sometimes in small diameter or low pressure exchangers the thickness reductions from the turns can make hr thinner than required, or than desired. In this case a "tongue and groove" style gasket facing can be useful, similar to Fig UG-34(k), except only one side has the groove. See TEMA F-3.

Hope this helps

Mike

 

[BigTank]

Right on, Mike. Very nice explanation. My apologies for my makeshift terminology. That's exactly the explanation I was hoping for. Star, my friend.

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Fitter, happier, more productive

 

[SnTMan]

BigTank, no apologies necessary, glad to help, that's what this forum is all about.

Mike

 

[Suffer]

Mike, for confined face fixed tubeshet, what thickness (h or hr) to be used for bending stress analysis?

Also, i did not see hr in UHX section.

thanks

 

[SnTMan]

Suffer, see Part UHX 9.3 & 11.3 for nomenclature, see Figs UHX-9 and 11.1.

Depends on the HX configuration, bending stress is calculated in, for example, UHX-12.5.8 for U-tube, based on h.

hr is calculted in UHX 9.5

Regards,

Mike

 

[Suffer]

Thanks Mike, very useful information

 

[Suffer]

Mike, you have any information for o-ring design and groove demension? I am working on BEW type cooler.

Thanks,

 

[SnTMan]

Suffer, there is O-ring design info all over the net, suggest a Parker or other maker handbook.

Regards,

Mike