API 650 roof design 1

[anousone]

Hi,
the use of a frangible joint for the roof to shell junction is recommended by API 650. That is to say that the roof will act like a venting surface in case of an explosion in the tank. What is the main reason for this? Isn't it possible to optimize the venting surfaces (according to NFPA 68 for example)on the roof, without having to consider the whole roof as a venting section? Does anyone have information regarding this subject?
Thanks.

 

[JoeTank]

You are reading way too much into API-650 on this issue. The frangible roof calculations concept is intended to protect the tank in the event of a pool fire, not an internal explosion. There are no concepts of "vent surface" involved. It's just the plain old idea that the roof-to-shell junction will fail before the tank shell-to-bottom joint is uplifted. The resulting failure of the joint is assumed to be sucfficient to vent the tank.

API-650 does not recommend the frangible roof concept. It is neutral on that issue. It requires that the tank be protected from overpressure for the emergency condition of a pool fire. The designer MAY count on frangible roof behavior (if verified by calculations) or an emergency venting system may be provided.

Again, API-650 has no provisions for venting an explosive event.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com