438 mm = 17.25 inches (looks like you're using 18 inch Schedule Std. pipe). TEMA defines the "nominal ID" as the shell ID rounded to the nearest inch, which in this case would be 17 inches so you need a 1/8 inch (3.2 mm) clearance between the shell ID and the baffle OD.

438 mm - 3.2 mm = 434.8 mm (17 1/8 inches).


-Christine

Watch out for a minor detail here.
The column is nominal size.
C74 is on the money with her interpretation of this.
Though I know of some people that would say that using 18" nominal for the shell size is also acceptable.
Then once that tells you that you need 3.2mm of diametral clearance you apply that to your actual shell design ID.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

Thanks for your responses.
However, can anyone share real example i.e. heat exchanger currently in operation.
Regards,
Ijaz

For example, a HX shell, nominally 58" OD x 2" wall, so nominal ID is 54".
So you would allow 1/4" total clearance.
When you look at the actual design you see that the OD is 58.5" and the wall is 1.875" so the design ID is 54.75".
So the baffle size is 54.75 - 0.25" = 54.5"

I have seen them go the other way also. Say 75" nominal OD x 2.5" wall giving a nominal ID of 70".
The clearance would be 0.375".
The detail design shows 74.5" OD x 2.625" wall giving a 69.25" design ID.
And a baffle diameter of 69.25-0.375" = 68.875"

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

For tube bundle replacements the usual practice is just to match the OD of the existing baffles. For TEMA heat exchangers, ~99% of the time the baffle-to-shell clearances match Table RCB-4.3 but tighter clearances are occasionally used in order to minimize "E" stream bypass.


-Christine

Also check with the thermal designers if they have used a clearance tighter than that you intend to apply for this TEMA R exchanger.

And if it is a long HX or has issues related to fouling people sometimes use looser clearances.
You need to ask what is intended.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed