Shell & Tube HE - Tubes under External Pressure

[anubis512]

Hi,

I'm working on a project where the shell side is rated 350/-15 psig while the tube side is rated 200/-15 psig. In my mind, the tubes could theoretically experience 350 psig external pressure, which is not what it's rated for. I can't seem to find very much literature on a HE where the shell side is at a higher pressure than the tubes. I'm specifically analyzing a tube rupture case where the shell ruptures the tubes, pressurizing them beyond it's MAWP. Can anyone provide some guidance on how to approach this?

Thanks!

 

[MJCronin]

If there is a possibility of extreme pressure on one side, protect the tubes of the HX by installation on a relief valve or rupture disc.

This is also a matter of economics.

Significant savings can be gained if the cost of the HX can be decreased by decreasing the system design pressure through use of a relief device.

MJCronin
Sr. Process Engineer

 

[SnTMan]

anubis512, umless differential pressure design is used each common element must be designed for the max pressure to which it is exposed, so the tubes, tubesheet, etc. must be designed for full shell pressure with tubeside at full vac. So far so good.

Now as to overpressure protection in the event of tube rupture, one approach is to a install a relief device as per MJCronin. Another commonly used is to set the low side design pressure such that in the event of a tube rupture, the low side is exposed to maximum stresses corresponding to its stresses at hydrotest.

So, for your example the tubeside pressure would be set at 1/1.3 * (350+15), or 281 psig.

In the old days this was known as the "two-thirds" rule (1/1.5), now I guess its the "ten-thirteenths" rule

Regards,

Mike

 

[LCeballos]

anubis12. See in ASME VIII div 1. Part UG (Paragraph UG-28).

Regards,

Luis C.