Frangible Roof Weld

The reasoning behind present api design formulas is reviewed.

Frangible roof weld.

This failure is intended to vent the tank and contain any remaining fluid. Frangible is a word that means easily broken. The api 650. 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 paper presents the results of an investigation into the frangible joint behavior of tanks designed to api 650 rules. A small diameter tank which comprises a shell having a rim at its upper edge a roof and a frangible roof joint the roof joint including annular link means sealingly secured at or adjacent a. 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. One of the safety measures that can be employed for emergency venting is so called frangible roof to shell joint.

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. Api 650 gives rules for the design of frangible roof joints in fluid storage tanks. 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. 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.

The concept of frangible roof only applies to flat bottom cone roof tanks with limited roof apex angle. This video documents the research and testing on frangible joint storage tanks performed at kansas state university and thunderhead engineering.