Tube average thickness in design of heat echanger 1

[mechengineer]

Hi all,
Whether we need to consider using the minimum thickness = the average thickness - under tolerance as the tube thickness input in heat exchanger design if the average thickness gieven in the MDS/PDS?
Regards

 

[EdStainless]

If your min wall is greater than the nominal (average) - under tolerance, then you could either order the average wall or you could specify the actual minimum wall.
For design work, if it is mechanical then you should use the min.
If you are doing thermal design work, you should use Average wall thickness.
Though if the wall tolerance makes a difference to your thermal design, you have bigger problems.

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P.E. Metallurgy, consulting work welcomed

 

[mechengineer]

@Edstailess,
Thanks for sharing your thoughts.
That means the manufacturer tolerance shall be considered in mechanical design. However, code and UHX does not has such requirement. Most of vendors just use the tube thickness what indicated in PDS/MDS as mechanical design input whatever it’s the average or the minimum. For example, tube thickness 19.05(average) or tube thickness 19.05
UG-16 also say that it is safe and acceptable if the plate and pipe thickness within the tolerance. May the average or minimum only affect thermal HTRI design?

 

[EdStainless]

Strength, pressure rating, and vibration should all be based on the minimum wall.
So either 19.05mm (if ordering min wall) or 0.9*19.05=17.15mm if ordering avg wall.
We used to get tube orders with all sorts of odd minimum wall requirements.
Just remember that if you order min wall you can get up to 20% heavier.

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P.E. Metallurgy, consulting work welcomed

 

[SnTMan]

Second Ed's posts. Might add if tubeside pressure drop is of interest, plus tolerance might warrant a look

Regards

Mike

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

 

[mechengineer]

@Edstailess,
Yes,now understood. 19.05 mm of thickness as the minimum thickness of the tubes is incorrect. All tubes thickness from the market is the nominal or average thickness.

 

[EdStainless]

No not all of them, it depends on how they were ordered.

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P.E. Metallurgy, consulting work welcomed

 

[mechengineer]

Hi,
The tube material is not required CA as per TEMA RCB-1.517. The nomial thickness used in ASME VIII-1 UHX. The under tolerance of the tubes is much less that the CA. Thus, I thick that it shall not be considered.
HTRI design margin 10% will allow to block 10% of tubes if the tubes leak till the heat transfer area is lower than design required. in that case, it may replace the bundle if the tubes failed. that may consider the reason why it does not consider the CA and under tolerance for the tubes in the heat exchanger mechanical design.

It is only the tolerance different if you purchse the tubes with the niminal thickness and the minimum thickness. We may just use the nominal or minimum of the thickness in the mechanical design without consider the tolerance.

Regqrds,

 

[MJCronin]

These might be helpful for this particular topic ...

https://www.eng-tips.com/viewthread.cfm?qid=485735

https://www.cheresources.com/invisi...-determine-tube-thickness-in-heat-exchangers/

https://www.youtube.com/watch?v=gd61XHFqpr0

MJCronin
Sr. Process Engineer