Design pressure of atmospheric lines

[sandypiping]

Is there any guideline of specifying the design pressure of piping which is vented to atmosphere. I understand that it will be 150# rating; however, there is an argument that it should be specified as 345 Kpag as per ASME B31.3. I couldnt find any relevant clause for this. Any help will be appreciated.

 

[KevinNZ]

The maximum pressure an open ended vent line can see is depends on the pressure drop along the line when fully open. At the start it will be upstream line pressure and dropping to the end. There could be critical flow right at the end still be quite a high pressure.

 

[georgeverghese]

Also take into account the possiblity of a deflagration event at a release point if the pipe is in flammable fluid service. For most hydrocarbon systems, a min design pressure of 700kpag is preferred to withstand the generated deflagration pressure in the event of loss of purge concident with accidental ignition at the release point resulting in flashback.
345kpag is legacy design pressure for LP vent lines, and is generally recognised to be inadequate to handle deflagration events.