Relief for Ignition/Explosion Credible Scenario?

[BenThayer]

We are being requested by corporate to review sizing rupture discs for the event of air/solvent vapor explosions in our tanks.

We have quite sophisticated nitrogen purging and procedures to prevent this event and have never had a problem. We typically use Layer Of Protection Analysis to address things but only if considered to be a credible scenario.

I have never seen this scenario listed as a sizing case in sources such as API 520, etc.

Is anybody doing this for solvent storage tanks and 500 to 5000 gallon agitated reactors?

Thanks, Ben

 

[sshep]

Hey BenThayer,

Good luck with that- whatever ruture siscs you have now (unless the whole roof is a rupture disk) can probably only be shown to be too small for a tank due to the speed of a deflagration. I have been asked to do the same thing many years ago. What is the pressure rating of your tank?

The reason that this scenario is not covered well in the standards is that it is impractical. For example, in a frangible roof API 650 tank, it is better to just let the roof go than to try and contain and direct such an event. Layers of protection to avoid a flamable mix and prevent sources of ignition are the only way to go.

best wishes, sshep

P.S. Someone created a relief systems forum not too long ago- an activity which I have tried support. Hopefully we can get a pool of relief expertise started because there are many questions along these lines. I would like to encourage further participation by getting people to add that forum to their existing lists.

 

[JoeTank]

API commissioned a study on the frangibility of small diameter tanks. The results were based in part on studying the effect of an internal deflagration, not an explosion. The PVRC publish a couple of bulletins on the work. It seems that these documents could be of use to yopu in your work.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[SeanB]

Seeing as frangible roofs were mentioned above I thought that I should mention that API has demonstrated that frangible roofs do not work on tanks with less than a 50 ft diameter. I recently had to design a small chemical storage tank. The chemical itself is very volatile at elevated temperatures. Without being able to take credit for a frangible roof my only option was to add multiple PV valves on the tank roof.