Tube rupture - what to about the water?

[MortenA]

For a gas heater HX (T&S): If the gas pressure is higher than the shell design pressure i assume that e.g. a bursting disc is required for protection in case of a tube rupture.

My question is then: What to do with the water? I believe that it will be pushed out by the gas - is it safe just to let it flow through the vent header to the KO drum (assuring that this vessel is large enough to accomodate the water inside the HX?

Will those doing piping design have to do anything special considering that there now is multiphase water/gas flow in this header instead of just gas?

Best regards

Morten

 

[MJCronin]

MortenA...

Your question only leads the reader into a detailed analysis of relief valves and emergency venting systems.

Of course the cooling water will be pushed along the gas escape path.....with the attendant dynamic affects on the relief/vent piping system. Was the system designed for these affects

Your very reasonable and well thought-out question is why the regulatory agencies want to see detailed DIERS type calculations for every installation.

Good luck

-MJC

 

[MortenA]

Maybe this is why i have had less than average response so far ;-)

Best regards

Morten

 

[gr2vessels]

Morten,
The exchanger design was suppose to incorporate some details related to your case/question. The shell side design pressure should not be less than 10/13 of the tubeside design pressure.
The shell side inlet nozzle, assuming bottom inlet, should be your forced drain path under the gas pressure of the burst tube(s). That is, the pressure transducer located in the outlet pipe, just above the shell side outlet nozzle, should close the outlet isolation valve. Also, depending on the gas pressure, flow, temperature, you should have a relief valve on the shell side inlet piping, to compensate for the water back-flow to a place of your selection (drain, KO Drum, etc..). I assume that you will attempt to shut-down the gas line due to the tube burst, sensed by the shell side excessive pressure increase....This way you should deal only with a shell side full of water, at worst scenario. Normally, you only empty the shell side after complete depressurizing of the shell and tubeside. And yes, the pipers should check the pipe rating for the over-pressure limited by the shell side pressure relief valve.
Also, I remember this topic was debated a not long while ago in this forum, have a check...
cheers,
gr2vessels

 

[MortenA]

gr2vessels

Well all i can say to that is that i have seen many HX where the pressure difference between shell and tubes are higher than 10/13.

Best regards

Morten