Frangible Tank Roof Design

A frangible roof joint forming a flexible gastight connection between a tank shell and a roof comprising an annular link mechanism sealingly secured at or adjacent a first edge thereof to a rim of the tank and sealingly secured at or adjacent a second edge thereof to the periphery of the roof.

Frangible tank roof design.

In such tanks the roof to shell joint is intended to fail in the event of overpressurization venting the tank and containing any remaining fluid. This video documents the research and testing on frangible joint storage tanks performed at kansas state university and thunderhead engineering. Api 650 gives rules for the design of frangible roof joints in fluid storage tanks. See figures 7 and 8.

This failure is intended to vent the tank and contain any remaining fluid. This paper presents the results of an investigation into the frangible joint behavior of tanks designed to api 650 rules. A frangible roof is a roof to shell joint or junction that is weaker than the rest of the tank and will preferentially fail if the tank is over pressurised. The reasoning behind present api design formulas is reviewed.

Failure of the roof to shell junction can be expected to occur when the stress in the compression ring area reaches the yield point says f 6 calculated failure pressure. That is of course if the tanks are built according to the rules for frangible roofs. The concept of frangible roof only applies to flat bottom cone roof tanks with limited roof apex angle. In the event of over pressurization the frangible roof to shell joint is designed to fail before the tank shell or the shell to bottom joint.

In fact the frangible roof design fulfills the venting requirements due to deflagrations inside tanks for most tank sizes greater than about 35 feet in diameter.