Frangible Roof Weld

Hi henry you can refer to 3 10 2 5 addendum march 2000 which states roof plates shall be attached to the top angle of the tank with a continuous fillet weld on the top side only you may want to review the tank design if this connection ask for frangible joint not exceeding 5mm continuous weld.

Frangible roof weld.

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. 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. The concept of frangible roof only applies to flat bottom cone roof tanks with limited roof apex angle. The api 650.

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. Such joint is practically sacrificial weld which has to collapse in event of excessive internal pressure while shell to bottom joint has to be undamaged to provide structural and safe integrity of tank. This failure is intended to vent the tank and contain any remaining fluid. 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.

The reasoning behind present api design formulas is reviewed. One of the safety measures that can be employed for emergency venting is so called frangible roof to shell joint. The securement of the annular link mechanism to the rim and the roof is such as to permit articulation of the annular link mechanism relative to the rim and roof to a point of failure of the joint. Api 650 gives rules for the design of frangible roof joints in fluid storage tanks.

Frangible is a word that means easily broken. This paper presents the results of an investigation into the frangible joint behavior of tanks designed to api 650 rules.