Frangible Roof Tanks

This paper presents the results of an investigation into the frangible joint behavior of tanks designed to api 650 rules.

Frangible roof tanks.

This failure is intended to vent the tank and contain any remaining fluid. By way of example for a tank having a diameter of 20 feet 6 lm a shell of 3 16 in. Api 650 gives rules for the design of frangible roof joints in fluid storage tanks. 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.

However in the context of tanks the word has a specific meaning and is defined in the main tank construction standards bsen 14015 and api650. Frangible roof joints for fixed equipment and effective frangible shell roof roof storage tanks materials user connections association eemua 183 guide for the prevention of 1999 the engineering uk current guidance on the causes of bottom bottom leakage from vertical equipment and leakage inspection and leak. 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.

Frangible roof tanks are also vulnerable to damage if overfilled. Even when using a frangible roof however some owners still. The reasoning behind present api design formulas is reviewed. Such relatively weak roof to shell joints are known as frangible.

Thus appropriate measures wellknown to tank designers are required to insure that the liquid level in the tank does not rise above the top straight side of the tank. For reasons discussed above many tank owners prefer to satisfy emergency venting requirements with a frangible roof particularly for tanks without a floating roof because of the frangible roof s potential to vent deflagrations without substantial damage to the shell or bottom. 4 8mm thick plate a. Frangible is a word that means easily broken.

Frangible roof tanks are also vulnerable to damage if overfilled. 4 8mm thick plate a.