Shell & Tube exchanger pressure rule

[picasa]

Is there any requirement per TEMA code on the maximum difference or ratio between the shell side and tube side design pressure? Can the shell side pressure be very high as compared to the tube side pressure? and vice verca? What is the 2/3 rule? I heard of it, but could not find it in TEMA code.

If you think about it, if the shell side pressure is very high as compared to the tube side pressure, the tubes will need to be designed for the high external pressure in the respective load case. If the shell side pressure is too high, will it make tubes too thick?

 

[pve5]

picasa ( mechanical )

Standard practice is keep high pressure on tube side and not shell side. I have never seen exchanger designed with very high pressure on shell side. Keeping high pressure on shell side would be very uneconomical.

 

[SnTMan]

picasa- I don't know where you would find it written, but the "2/3 rule" dates from when hydrotest pressure was 1.5x (or 3/2x)and is based on the fact that at operating pressures if a tube rupture ocurred that the low pressure side would be exposed to stresses no higher than it was hydrotesed at. Example: operating pressures 150 / 100 psi,
100 X 1.5 = 150, 150 x 2/3 = 100.

Of course it should now be the "10/13" rule since hydrotest is 1.3x.

As for extrnal pressure on tubes, you absolutely have to watch this as cases can occur where the shell side pressure and temp exceed the allowable for the tube, for example, thinwall stainless at high temps. Sometimes the party specifying the exchanger does not do this calculation. You can then go to a thicker tubewall, derate the tube design temp, or do a diff pressure design. Don't get me started about u-bends.

Hope you find this useful.

Mike

 

[codeeng]

You've asked this question before.

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