Frangible Roof Requirements

See figures 7 and 8.

Frangible roof requirements.

The roof plates must not be welded to the tank roof structure which normally rules out externally stiffened tank roofs from being considered as being frangible. 4 2 2 2 when a frangible roof to shell joint is required evaluate for items impacting compliance with requirements under api 650 section 5 10 2 6. Changes you probably missed. The reasoning behind present api design formulas is reviewed.

A roof to shell joint designed according to api 650 rules is considered to be frangible and in case of excessive internal pressure intended to fail before failure occurs in the tank shell or shell to bottom joint. The roof plate to curb angle fillet weld must be greater than 5mm. Emergency relief venting for asts. Siting and design recommendations for swimming pools in coastal areas.

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. The roof slope must not be greater than 1 5 for bsen 14015 and 1 6 for api 650 tanks. No further reproduction or distribution permitted. This paper presents the results of an investigation into the frangible joint behavior of tanks designed to api 650 rules.

Examples of some items to evaluate include tank bottom to shell joint corrosion or copyrighted material licensed to saipem. Frangible roof joints by zhi lu b s tianjin university 1982 m s tianjin university 1984 a dissertation submitted in partial fulfillment of the requirements for the degree doctor of philosophy department of mechanical engineering college of engineering kansas state university manhattan kansas 66506 1994 approved by. Moreover the api frangible roof design standard has been further limited to tanks having a conical roof where the ratio of rise to run of the roof does not exceed two inches 51mm in twelve. Frangible roof designs are typically not adequate on tanks under 50 diameter therefore alternate solutions are required.

That is of course if the tanks are built according to the rules for frangible roofs. If nfpa thought it worthwhile to make the code change retroactive so should api and sti in the evaluation of existing tanks.