[TheForge] OT - BLEVE?

[K Mayer]

>Date: Fri, 9 Jan 2015 13:14:27 -0500
>From: "Bruce ." <freemab222 at gmail.com>
>
>I have an idea and I want to do a reality check on it.  ?
>I'm looking for folks with practical and/or theoretical ?
>knowledge of storage of flammable gases and of
>?the causes and prevention of ?
>BLEVE -- boiling liquid expanding vapor explosions.

A BLEVE occurs when the liquid in a container is above its atmospheric pressure boiling temperature when the container ruptures.  The ambient pressure on the liquid drops to atmospheric, and the liquid flashes into vapor.  The container could be a boiler or a storage container (e.g. an LPG cylinder).  

A boiler will BLEVE if the pressure relief valve is stuck shut.  I do forensic engineering and have investigated a number of these cases.  Every one was due to the service company not manually opening the relief valve during the service calls.  All were sealed shut with mineral deposits, and the burner controls failed in the "on" mode.  The pressure relief valves on boilers and water heaters need to be exercised at least annually.  Be sure to have a new part on hand in case it doesn't reseat.

An LPG cylinder BLEVE involves flame impingement onto the metal.  So long as there is liquid against the inside surface where the flame is impinging, the liquid will boil and vent through the pressure relief valve.  The boiling liquid cools the metal.  Once the liquid boils away, the metal will heat and weaken.  Once it is weakened to the point that it can no longer withstand the stress of the contained pressure, it will rupture.  The liquid will then flash into vapor and create a large fireball.  In my collection of exemplar artifacts I have the lower 2/3 of a 20 pound propane cylinder; it flew a half block from the explosion.  The upper 1/3 was not recovered.  Note that fiberglass LPG cylinders will also BLEVE, but not as dramatically.  A propane cylinder pressure relief valve opens at 325 PSIG; this translates into the contained liquid being at ~160F.

Ken
:-)