Inclusion of piping in fire relief liability

[gleng]

Does API 521 indirectly require one to include inlet/outlet piping when sizing for fire relief of a code vessel in it's guidelines for assumed fire coverage of 2500ft2? I'm sizing a valve for a small piece of equipment where the inlet/outlet piping has a relatively significant surface area.

 

[MortenA]

If it is of any significanse then include it. Its about safety - not meeting some code. The code shall ensure this but your case may require special considerations.

Anyway - the smalles API 526 valve (size D) is usuallu much too large when compared to the relief rate from fire cases for small vessels - so it most likely wouldnt lead to a diffrent valve. The flare/vent calculation migt change sligtly.

Best regards

 

[unclesyd]

We have an area where we have ten 100,000 gal interconnected reactors where we do a partial oxidation of cyclohexane with air. All ancillary piping for each reactor is considered in both PSV's and fire safety. The differentiation between each reactor was originally one isolation valve, but has been recently changed to 3. This was changed to minimize the inrush of reactants from the piping in the event of a vessel failure where the original single valve prevented the reactor from dumping. The deluge system is sized for the total volumetric loss of all fluids, vessels and lines.

I've been trying to find out which code or standard was used this area of our plant.
The big argument for several years was essentially the same question that you posted. It was resolved by the top man of the corporation who said account for every drop of Cyclohexane at all times.

 

[johngerhart]

There is no rule that says you have to relieve the pipe and vessle with one relief . If I size the relief for the piping and vessel and mount on the vessel, it may not work at protecting the piping . Set up multiple relief devices and stagger the relieving pressure set point . The pipe is probably going to have a much higher pressure rating so you could relieve it separately at a slightly higher rate than the vessel . API expects you to protect all the effected volume , it does not require you do it with one valve .

 

[CHD01]

Include the piping area; because you need to size the vent device for the tank including the entire affected volume, which must therfore include the piping in determining the area exposed to fire which is required to determine the total vent rate per API 2000 for atmospheric and low pressure tanks.

The more you learn, the less you are certain of.